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ISA Transactions (00190578) 164pp. 1-13
Data-driven control methods in the frequency domain commonly require the determination of controller structure. Relaxing such restriction in the proposed algorithm, the controller design is transformed into an optimization problem, based on the υ-gap Metric criterion. By defining a desired stability margin and the desired frequency response of the controller, a criterion is determined to characterize a family of controllers. Therefore, a model free procedure is proposed to determine a family of controllers, by taking the plant frequency response and the desired stability margin. On the other hand, by adopting a new index, presented in this paper, the designer can determine the optimal controller, based on the implementation conditions. Another advantage of the proposed method is its applicability to uncertain Multi-Input Multi-Output (MIMO) systems. The loop performance in the presented algorithm can be also enhanced by appropriate selection of weighting matrices in a loop shaping procedure. Two examples are also presented to demonstrate the effectiveness of the method for multi-variable non-square uncertain systems, including a practical example of a purely delayed system. © 2025 ISA
Journal of Process Control (09591524) 139
Surge is a form of dynamic instability created as an unstable pattern in the flow of fluid and can severely affect centrifugal compressor performance by causing fluctuations in flow and pressure parameters. Due to the heavy and costly damage that the surge may cause in various industrial processes such as petrochemical plants, it is necessary to design an appropriate control system to reduce the effect of this phenomenon. The problem of active surge control of a centrifugal compressor using the throttle control valve (TCV) in the presence of compressor parametric uncertainties as well as large demands on upstream and downstream loads is investigated in this work. The control objective was to design a robust control system that can stabilize the compressor over a wide operating range without knowing the upper bound for the uncertainties and load demand. The controller should also react quickly by generating a smooth control signal without saturating the control input. These objectives are achieved by designing a sliding mode controller along with a nonlinear disturbance observer. The performance of the proposed disturbance observer-based controller is evaluated under various operational and load conditions and the results are compared against fuzzy type 1, conventional sliding mode, and wavelet-based neural network robust adaptive controllers. The results show that the proposed method can tolerate large disturbances without any knowledge on the upper bound of the incident disturbance, both on the downstream pressure and upstream mass flow which is highly desirable in practice. The comparative study proves the efficacy of the proposed method using various performance measures. The study also confirms the superior robust performance and stability of the proposed method in front of matched and mismatched disturbances as well as model uncertainties especially close to the instability boundary. Although choosing a TCV actuator has made the control system design easier, the sensitivity of the control valve to flow coefficient and zero calibration under different operating ranges of the compression system is studied carefully and some recommendations for the users are provided. © 2024 The Authors
IEEE Transactions on Transportation Electrification (23327782) 10(2)pp. 3482-3491
An innovative control method for reducing the torque ripple of non-sinusoidal brushless dc motors in field weakening regions based on direct power control is proposed here. Torque ripple, due to the disproportionate stator current and its non-sinusoidal back EMF voltage, is one of the known drawbacks of brushless dc motor drives. Upon motor speed acceleration, the waveform of the stator current becomes distorted, which in turn intensifies the torque ripple. This proposed method is able to control the motor speed from zero to values higher than the base speed range. The realization of the proposed method in the stationary reference-frame makes the method implementation simple and robust. In addition to controlling motor speed, by applying a three-phase conducting method instead of the conventional two-phase conducting method and control of instantaneous input power into the rotor in the proposed method, the torque ripple is also reduced, simultaneously. The torque ripple reduction and robustness of the proposed method are compared with the phase advance angle (PAA) method through simulation and experimental. The results indicate the superiority of the proposed method in both the steady- and transient-states. Moreover, the implementation of the proposed method on a prototype brushless direct current (BLDC) drive is successfully evaluated. © 2015 IEEE.
Ghotb, H. ,
Ataei, M. ,
Siahi, M. ,
Moarefianpour, A. Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering (09596518) 238(2)pp. 327-343
This article deals with the problem of distributed observer design containing time delays for uncertain nonlinear distributed generators systems in alternating current–islanded micro grids. In contrast with the centralized observer with the ability to accumulate full output of the plant, we design a set of distributed observers, each having access to partial output of the plant through a distributed observer network. Each observer obtains partial plant output and communicates with its neighboring observers through consensus network. The design method is based on the Lipschitz condition of uncertain nonlinear terms while having time-delay system in view. Suitable selection of Lyapunov functions is made, and the Jensen inequality is considered in delayed uncertain nonlinear micro grids in an undirected network. Furthermore, via design algorithm, the necessary and sufficient conditions for the design of parameters are determined so as to stabilize the error dynamics. Finally, numerical simulations are provided to consider the effectiveness of the proposed method. © IMechE 2023.
Electrical Engineering (14320487) 106(1)pp. 93-109
One of the most prevalent and destructive types of cyber-attacks on power systems is the false data injection (FDI) attack. In a false data injection attack, the attacker inflicts large damages on the network by manipulating the measurements. The pivotal solution to opposing this type of cyber-attack is to use phasor measurement units (PMUs). In this paper, a new method is presented to confront the FDI attack by using the optimal placement of PMU instruments. In the proposed algorithm at the beginning, all PMUs placements that achieve network observability are determined using the tabu search (TS) algorithm. Then, from the observable placement vectors, the placements that minimize the possibility of a cyber-attack on the network is identified. For this purpose, a new attack criterion is presented, which is obtained from the adversary strategy in the attack scheme. Since the measurements obtained from the PMUs must be transferred to a phasor data concentrator (PDC) center, the PDC placement also must be determined. In this paper, the optimal placement of PDC is presented by considering the cost of communication infrastructure, because the cost of communication infrastructure between PMUs and PDC is significant. For this purpose, we have used the Kruskal algorithm. The simulations performed on the IEEE 30-bus and 118-bus test system confirm the effectiveness of the proposed method for opposing cyber-attacks and reducing the cost of communication infrastructure. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023.
International Journal of Systems Science (00207721) 55(13)pp. 2741-2758
Designing a full-state observer for nonlinear systems has always been accompanied by challenges and restrictive constraints. Mainly, applying a state observer in nonlinear systems with non-minimum phase characteristics is more challenging when the limiting constraints are not satisfied due to diverging internal dynamics. In this paper, a robust sliding-mode observer approach has been successfully employed to estimate the states of nonlinear systems with unbounded and diverging dynamics. The design principles of this observer are based on applying a classifying algorithm in single-input single-output and multiple-input multiple-output nonlinear systems. It is noteworthy that this observer is highly robust against disturbance, uncertainty and measurement noise, and its conditions are less conservative compared to previous nonlinear sliding-mode observers. One novel feature of the proposed observer is that while the system's state gets unbounded and diverged in fault-occurring scenarios or critical circumstances, this observer retains accuracy. The efficiency of the proposed observer is verified in the simulation results for two nonlinear industrial systems, including a hydro-turbine power generation plant and a continuous stirred tank reactor. © 2024 Informa UK Limited, trading as Taylor & Francis Group.
IET Cyber-Physical Systems: Theory and Applications (23983396) 9(4)pp. 463-476
Zero-dynamics attack (ZDA) is a destructive stealthy cyberattack that threatens cyber-physical systems (CPS). The authors have warned about the risk of a cyberattack by introducing a new general ZDA that can be effective and robust in non-linear multiple-input multiple-output CPS. In this proposed attack policy, the adversary extracts the sensor and actuator online data on the network platform. Then, by utilising a state observer and considering specific delay times, the attacker injects a ZDA signal into the actuator channels of the cyber-physical system. As a result, the internal dynamics will diverge from the nominal working region of the controlled cyber-physical system, while the outputs remain close to the actual outputs of the attack-free system. Therefore, this cyberattack can remain stealthy, and it can also be robust against revealing signals. The efficiency of this new attack policy is demonstrated in the simulation results for a continuous stirred tank reactor regarded as a cyber-physical system. © 2024 The Author(s). IET Cyber-Physical Systems: Theory & Applications published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.
Journal of the Franklin Institute (00160032) 360(14)pp. 10728-10744
This paper deals with state estimation for a class of Lipschitz nonlinear systems under a time-varying disconnected communication network. A distributed observer consists of some local observers that are connected to each other through a communication network. We consider a situation where a communication network does not remain connected all the time, and the network may be caused by intermittent communication link failure. Moreover, each local observer has access to a local measurement, which may be insufficient to ensure the system's observability, but the collection of all measurements in the network ensures observability. In this condition, the purpose is to design a distributed observer where the estimated state vectors of all local observers converge to the state vector of the system asymptotically, while local observers exchange estimated state vectors through a communication network and use their local measurements. According to theoretical analysis, a nonlinear and a robust nonlinear distributed observer exist when in addition to the union of all communication topologies being strongly connected during a time interval, the component of each communication graph is also strongly connected during each subinterval. The existence conditions of the distributed observers are derived in terms of a set of linear matrix inequalities (LMIs). Finally, the effectiveness of the presented method is numerically verified using some simulation examples. © 2023 The Franklin Institute
Ghotb, H. ,
Ataei, M. ,
Siahi, M. ,
Moarefianpour, A. Transactions of the Institute of Measurement and Control (01423312) 45(11)pp. 2149-2167
This paper considers a distributed observer design for a class of nonlinear systems with time delays in a network. Specifically, each distributed observer has access to partial output as it communicates with its neighboring observers through consensus protocols defined on the network. The network includes N local observers where adjacent observers transmit and receive information through a delayed telecommunication graph network. The design method is based on Lipschitz condition of nonlinear terms while having time-delay cases in view. Appropriate selection of Lyapunov functions is made and the Jensen inequality applied in delayed nonlinear systems in undirected, strongly connected, and directed networks containing spanning trees. Also, via the design algorithm, the necessary and sufficient conditions for the design of parameters are defined so as to stabilize the error dynamics. Finally, numerical simulations are provided to verify the effectiveness of the proposed method. © The Author(s) 2023.
Asian Journal of Control (19346093) 25(1)pp. 262-270
A nonlinear disturbance observer based on a super twisting controller is designed and implemented on the uncertain spacecraft attitude control subsystem simulator. The reaction wheels' angular momentum and their rate saturation are concerned in the controller design. The super twisting algorithm (STA) is devised in a way to make the reaction wheels into rest at the end of the maneuver. A nonlinear-disturbance-observer (NDO) is applied in estimating the external disturbances, unmodeled inertia moment, the eccentricity of rotation and mass center of simulator, and the reaction wheel saturation constraint. The finite-time stability of the closed-loop system is established according to the Lyapunov theory. The simulation and experimental results of this newly designed controller-observer on the spacecraft attitude simulator are compared in uncertain conditions. © 2022 Chinese Automatic Control Society and John Wiley & Sons Australia, Ltd.
JVC/Journal of Vibration and Control (10775463) 29(1-2)pp. 346-361
This paper aims to design an attitude controller for a flexible spacecraft under external disturbance and uncertainty. The spacecraft’s attitude is controlled by a super twisting controller based on a disturbance observer. This paper’s spacecraft system is non-minimum phase since mode-shapes are included in the output; thus, the following four methods are designed to compensate for the constraint: (1) The output redefinition method, where outputs are redefined as a combination of mode-shapes and quaternions. (2) The flexible spacecraft is controlled without measuring the mode-shapes, and only the quaternion parameters are selected as the output. (3) An advanced sliding surface is proposed, in which the mode-shapes are considered in the sliding surface. (4) The difference between flexible and rigid spacecraft dynamics is considered as disturbance, and its effect on the system is compensated. The finite-time stability of the closed-loop system is proved by leveraging the Lyapunov theory. The numerical simulation illustrates the closed-loop system’s effectiveness in terms of robustness compared to the existing controller and the four mentioned methods. © The Author(s) 2021.
IEEE Transactions on Automatic Control (00189286) 68(8)pp. 4970-4976
This note argues over the existence of invariantly differentiable functionals for globally exponentially stable time-delay systems. We show that the existence of invariantly differentiable, Lipschitz on bounded sets Lyapunov-Krasovskii functional is a necessary and sufficient condition for the global exponential stability of time-invariant nonlinear systems described by retarded functional differential equations with discrete type delay. The presented converse results are in terms of the invariant derivative definition. To prove converse results, both pointwise and historywise dissipation conditions are provided. The validity of the results is illustrated by an example. © 1963-2012 IEEE.
IEEE Transactions on Transportation Electrification (23327782) 9(3)pp. 3769-3779
In this article, a second-order sliding mode control (SMC), based on super-twisting algorithm, is proposed for direct power control (DPC) of the brushless dc (BLDC) motor. The proposed controller uses a super-twisting scheme that requires only sliding surface information and can handle system uncertainties and external disturbances, well. This scheme can improve the BLDC motor torque ripple by solving the disadvantages of the conventional SMC method, such as the chattering effect and high-frequency switching control. This method is simple and robust for the BLDC motor's biggest challenge, torque ripple, which does not require any voltage and current control loops or complex reference frame transformations. The simulation results of the proposed method are compared with the DPC and model predictive control (MPC) methods, which indicate the superiority of the proposed method in both the steady and transient states. Moreover, the motor parameters variation in the tracking of active and reactive power are discussed. In addition, the practical results of the proposed method in both cases of speed and load variation show the effectiveness of this method in reducing power (torque) ripple and current total harmonic distortion (THD) and increasing the system's efficiency compared to other methods. © 2015 IEEE.
In the present research, a synchronization control approach together with a novel disturbance observer for nonlinear passive bilateral teleoperation systems is proposed. All if the unknown dynamic terms such as external disturbances, modeling uncertainties and friction forces are lumped into one disturbance signal. Afterwards, the DOB technique is designed to obtain the estimated lump disturbance signal for both the master and the slave manipulators. The exponential convergence of lump disturbance estimation error to zero is verified. Also, based on the proposed control law, the positions of the master-slave system synchronize and the position errors are globally exponentially stable despite communication delay. Finally, the efficacy of the suggested scheme on a bilateral tele-rehabilitation system is shown by simulation results. © 2022 IEEE.
IET Control Theory and Applications (17518644) 15(8)pp. 1115-1125
This paper presents the computation of the non-parametric uncertainty model for multi input multi output (MIMO) systems, which is described by normalized coprime factors (NCF) using the frequency response data of the system. This computation is accomplished by minimizing a υ-gap metric criterion. For this purpose, the problem is formulated to a convex optimization context, such that a semidefinite programming (SDP) can be implemented. Minimization constraints and the normality constraints of coprime factors are converted to linear matrix inequalities (LMI). Thus, by convex optimization algorithms, the semidefinite programming will be optimized. The proposed method can also be used for non-square multi input multi output systems in a conservative assumption. So, through the first process of optimization, the frequency responses of the normalized coprime factors are derived. Finally, to evaluate the performance of the proposed method in the computation of the normalized coprime factors of a system, the simulated results of this method are compared with those obtained by the other methods for two types of systems. © 2021 The Authors. IET Control Theory & Applications published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology
European Journal of Control (09473580) 56pp. 132-141
This paper presents an observer for a class of nonlinear systems, suitably affine in the input and the delayed terms, with constant, known, and arbitrarily large time-delays in both internal and output variables. It is assumed that the system at hand is globally drift-observable and that the function describing the dynamics is globally Lipschitz. Moreover, it is assumed that the system at hand admits full uniform observation relative degree. A differential geometry-based approach is followed. The well-known chain procedure is employed in order to deal with arbitrarily large output delay. It is proved that, for any given delays at states and output, there exist a suitable gain matrix and a Hurwitz matrix, involved in the observer algorithm, such that, when a sufficiently large number of chain elements are employed, the observation error converges asymptotically to zero. The effectiveness of the proposed method is illustrated by numerical examples. © 2020 European Control Association
Ataei, M. ,
Salarieh, H. ,
Pishkenari, H.N. ,
Jalili, H. Acta Astronautica (00945765) 173pp. 22-30
Attitude and vibration control of a general form of flexible satellites is addressed in this paper. Partial differential dynamic equations are derived considering new details such as multi sectioned solar panels and elastic connections between main hub and solar panels. Boundary control approach is adopted to eliminate simplification errors of discrete models, using just one actuator in the hub. Asymptotic stability of attitude dynamics is proved for a group of boundary controllers and necessary conditions for asymptotic stability of vibrations are discussed. Being independent of modeling accuracy and using easily measurable feedbacks are among advantages of the proposed class of controllers. Through simulations using FEM technique and a controller with the least number of boundary feedback parameters, good performance of the introduced method is illustrated. © 2020 IAA
Journal Of Medical Signals And Sensors (22287477) 10(1)pp. 53-59
Obstructive sleep apnea (OSA) is a common disorder which can cause periodic fluctuations in heart rate. To diagnose sleep apnea, some studies analyze electrocardiogram (ECG) signals by adopting chaos-based analysis. This research is going to specifically focus on whether it is possible to use chaos-based analysis of heart rate variability (HRV) signals rather than using chaotic analysis of ECG signals to diagnose OSA. While conventional studies mostly use chaos-based analysis of ECG signals to detect OSA, here, we apply correlation dimension (CD) as a chaotic index to analyze HRV data in OSA patients. For this purpose, 17 patients with OSA and 9 healthy individuals referred to a sleep clinic in Isfahan/Iran are studied, and their HRV time series were extracted from 1-h ECG signals recorded overnight. The preliminary step to calculate CD is phase-space reconstruction of the system based on HRV time series. Corresponding parameters, including embedding dimension and lag time, are estimated optimally using enhanced related methods, and then CD is calculated using Grassberger-Procaccia algorithm. Moreover, to evaluate our results, detrended fluctuation analysis (DFA), one of the well-known nonlinear methods in HRV analysis to detect OSA, is also applied to our data and the result is compared with those obtained from CD analysis of HRV. CD index with P < 0.005 indicates a significant difference in nonlinear dynamics of HRV signals detected from OSA patients and healthy individuals. © 2020 Isfahan University of Medical Sciences(IUMS). All rights reserved.
International Journal on Electrical Engineering and Informatics (20856830) 12(1)pp. 33-43
This paper aims to present the stabilization a two-axis gimbal system. The coupling effects and instances of mass unbalance have been considered in the proposed gimbal model; and a direct self-tuning regulator (STR) is utilized to improve the system performance. For this purpose, the parameters of controller polynomials have been calculated through the application of a recursive least square approach. Alternatively, a specific control signal is generated for both elevation and azimuth axes and applied to the gimbal system. The stabilization results of the targeted two-axis gimbal system confirm the effectiveness of the proposed controller for both elevation and azimuth axes. Moreover, an experimental study is implemented on the dynamics modeling and control of a two-DOF gimbal system. The controller algorithm is implemented through Arduino Uno because of its easy compatibility and portability. © 2020, School of Electrical Engineering and Informatics. All rights reserved.
ISA Transactions (00190578) 91pp. 125-134
Asymptotic stabilization of a class of nonlinear systems with known constant long input delay is addressed in the presence of external disturbance by applying sliding mode control method. Modified prediction variable scheme is employed to compensate long delays in the input, where conventional prediction variable approaches cannot be employed. This is mainly due to the fact that the external disturbance appears in the prediction variable, which renders the controller dependent on the external disturbance. In order to tackle this problem, the nonlinear disturbance observer based predictor is used. A suitable disturbance observer is designed to estimate the external disturbance that appears in the prediction variable. Respected to some existing results, the prediction-based control for more general class of the nonlinear systems in the presence of external disturbance is the main contribution of this paper. Actuator and sensor delays exist in the most common dynamic systems. So, the proposed control scheme can be employed in many conventional systems. The simulation results indicate the robustness and efficiency of the proposed controller. © 2019 ISA
In this paper, a finite time control method for an uncertain nonlinear system is proposed. An adaptive sliding mode disturbance observer is designed to estimate the disturbance in finite time. The assumptions on the disturbance are relaxed in the sense that, its first derivative upper bound is considered to be unknown and only the order of its second derivative upper bound is known. Based on the output of proposed disturbance observer, a terminal sliding mode control scheme for the uncertain nonlinear system is presented. The designed control law is continuous and nonsingular. Furthermore, compared with some existing sliding mode controllers, the conditions on the controller parameters bounds are relaxed. It is proved that the disturbance observer error as well as the system states converges to the origin in finite time. Finally, the effectiveness of the proposed method is shown by numerical simulations. © 2019 Elsevier Ltd
IET Control Theory and Applications (17518644) 13(13)pp. 2047-2055
In this study, stabilisation of input-delay non-linear systems in the presence of disturbance based on prediction variable is studied. For both disturbance estimation and delay compensation, an extended prediction variable as well as adaptive sliding mode controller are proposed in which the open-loop system is not required to be stable. In the proposed prediction variable one needs to estimate disturbance in the future. In order to solve this problem a new non-linear disturbance observer (NDOB) is proposed. Considering the NDOB in the closed-loop system, the stability analysis of error dynamic is performed. And the asymptotic stability of non-linear system with input delay is guaranteed for some class of disturbance. Simulation results finally validate the good performance and robustness of the proposed controller based on disturbance observer. © The Institution of Engineering and Technology 2019.
Journal of Optimization Theory and Applications (00223239) 180(3)pp. 1036-1064
Many real-world dynamics can be modeled as nonlinear time-delay systems. In order to capture a more realistic model for system dynamics, the exact values of time-delay should be taken into account. For nonlinear time-delay systems, the estimation of delays in both state and output equations is discussed. A cost function is defined based on least-square error between actual and estimated values of the output measurement. The value of time-delays in the nonlinear system are then derived using a gradient-based optimization method. Because of the implicit description of the cost function with respect to the delay value, its gradients cannot be obtained by standard analytical differentiation rules. In this case, the optimal computational methods are utilized to derive two formulas for computing the gradient. An optimization scheme is then formulated to estimate both state and output delays. The effectiveness of the proposed estimation method is finally demonstrated using the simulation results on a benchmark chemical process. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.
Sadeghi, R. ,
Madani, S.M. ,
Lipo, T.A. ,
Agha kashkooli m.r., M.R.A. ,
Ataei, M. ,
Ademi, S. IEEE Transactions on Industrial Electronics (02780046) 66(10)pp. 7510-7519
This paper presents the performance analysis of brushless doubly fed induction generator (BDFIG) during symmetrical voltage dips. The equivalent circuit consists of resistances and dependent voltage sources in its rotor loop; thus, its voltage-dip analysis becomes more challenging. To overcome such difficulty, a reduced full-order model of the BDFIG into a new T-model is presented. A detailed mathematical analysis is performed subject to voltage-dip conditions. The time variation for the machines fluxes, electromotive forces, voltages, currents, and active and reactive powers are analyzed and their analytical approaches are derived. The current/voltage stress of power converter during voltage dip is discussed. The accuracy of the proposed T-model and the theoretical voltage dip is confirmed via experimental tests on a 3-kW BDFIG, and simulation results of a 2-MW BDFIG. © 1982-2012 IEEE.
IEEE Transactions on Sustainable Energy (19493029) 9(1)pp. 371-380
The Brushless Doubly-Fed induction Generator (BDFG) has a commercial potential forwind power generation, due to its low maintenance cost. For simplicity, the Cascaded Brushless Doubly Fed induction Generator (CBDFG) topology is usually applied as a model for BDFG. The BDFG-based wind turbines must be synchronized and connected to the grid, without inrush current. This paper purposes an improved Direct Torque Control (DTC) method for smooth synchronization of BDFG. Since BDFG has a complicated model, due to the resistance and voltage source in its rotor loop, finding proper references for smooth synchronization is difficult. To overcome this difficulty, a new model for BDFG is proposed. Appropriate flux and torque references for the DTC scheme are proposed based on this model, in order to achieve grid synchronization without inrush current. A 2-MW BDFG is simulated to show the efficiency and accuracy of this proposed method. The experimental results of a 3-kW laboratory scaleBDFGconfirm the efficiency of this proposed method. © 2017 IEEE.
Khodadadi, H. ,
Khaki-sedigh, A. ,
Ataei, M. ,
Jahed-motlagh, M.R. Multidimensional Systems And Signal Processing (09236082) 29(1)pp. 19-33
Recently, there has been a great interest in the application of Lyapunov exponents for calculation of chaos levels in dynamical systems. Accordingly, this study aims at presenting two new methods for utilizing Lyapunov exponents to evaluate the spatiotemporal chaos in various images. Further, early detection of cancerous tumors could be obtained by measuring the chaotic indices in biomedical images. Unlike the available systems described by partial differential equations, the proposed method employs a number of interactive dynamic variables for image modeling. Since the Lyapunov exponents cannot be applied to such systems, the image model should be modified. The mean Lyapunov exponent is defined as a chaotic index for measuring the contour borders irregularities in images to detect benign or malignant tumors. Moreover, a two-dimensional mean Lyapunov exponent is incorporated to identify irregularities existing in each axis of the targeted images. Experiments on a set of region of interest in breast mammogram images yielded a sensitivity of 95 % and a specificity of 97.3 % and verified the remarkable precision of the proposed methods in classifying of breast lesions obtained from breast mammogram images. © 2016, Springer Science+Business Media New York.
International Journal of Systems Science (00207721) 49(12)pp. 2558-2570
This paper proposes a cascade high-gain observer for a class of triangular nonlinear systems with large and diverse time delays at states and output equation. Compared with some existing results in the literature, the main contribution is to consider the simultaneous and diverse delays in both states and output and further, to propose a cascade observer in dealing with arbitrarily large delayed measurements. By choosing a suitable Lyapunov-Krasovskii functional, the sufficient condition is presented that guarantees the exponential convergence of observation error to the origin. Simulation results on a numerical example and a practical case study involving inverted pendulum are finally given to illustrate the effectiveness of the proposed approach. © 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.
IET Electric Power Applications (17518660) 12(6)pp. 757-766
Here, a reduced-order model for stand-alone cascaded doubly fed induction generator (CDFG) is presented for aircraft application, which is capable of operating in both starting and generating modes. This generator has lower maintenance cost and higher reliability, in comparison with traditional variable speed constant frequency system, based on a doubly fed induction generator (DFIG). These features make the CDFG appropriate for embedded aircraft applications. The main drawback of this generator is its inherent complexity; therefore, its analysis and control design is difficult. This complexity is due to the existence of resistances and voltage sources in the rotor loop of the full-order model. To overcome this difficulty, this study proposes a reduced-order model for the CDFG, which is similar to that of the DFIG in the synchronous reference frame. To demonstrate the efficiency of the proposed model, a field-oriented controller for CDFG is designed based on this model and compared to the full-order model. The performance and accuracy of the proposed model is validated through simulation and experimental results subject to balanced and unbalanced load change, and rotor speed variations test scenarios. © The Institution of Engineering and Technology 2018.
In this paper, a sliding mode observer for the class of Lipschitz nonlinear systems with uncertainty is proposed. The uncertainty is assumed to be bounded and the matching condition is first taken into account. The generalized Lipschitz condition is employed to consider some structural knowledge of Lipschitz nonlinearity. This yields less conservative results in stability analysis of proposed observer dynamics. The results are then extended to the unmatched uncertainty. Moreover, a synthesis method in terms of some linear matrix inequalities is established to achieve the proposed sliding mode observer. The simulation results on manipulator with revolute joints actuator are finally given to exhibit the effectiveness of the proposed observer and related synthesis method. © 2018 IEEE.
Transactions of the Institute of Measurement and Control (14770369) 40(3)pp. 712-718
The stability problem of nonlinear time-delay systems is addressed. A quadratic constraint is employed to exploit the structure of nonlinearity in dynamical systems via a set of multiplier matrices. This yields less conservative results concerning stability analysis. By employing a Wirtinger-based inequality, a delay-dependent stability criterion is derived in terms of linear matrix inequalities for the nominal and uncertain systems. A numerical example is used to demonstrate the effectiveness of the proposed stability conditions in dealing with some larger class of nonlinearities. © 2018, © The Author(s) 2018.
IEEE Transactions on Industrial Electronics (02780046) 65(11)pp. 9147-9156
This paper proposes and implements a super-twisting sliding mode direct power control (SSM-DPC) strategy for a brushless doubly fed induction generator (BDFIG). DPC has fast and robust response under transient conditions; however, it suffers from active and reactive power ripples and current distortions, which degrades the quality of the output power. In contrast, vector control has good steady-state current harmonic spectra; however, it is not robust to machine parameters variations, and thus needs a phase-locked loop for synchronous coordinate transformations. The SSM-DPC strategy controls active and reactive power directly without the need of the phase-locked loop. Moreover, its transient performance is similar to DPC and its steady-state performance is the same as vector control. The proposed controller is robust to uncertainties toward parameter variations and achieves constant converter switching frequency by using space vector modulation. Simulation and experimental results of a 2 MW and 3 kW laboratory-scale BDFIG are provided and compared with those of integral sliding mode and DPC to validate the effectiveness, correctness, and the robustness of the proposed strategy. © 1982-2012 IEEE.
Turkish Journal Of Electrical Engineering And Computer Sciences (13000632) 25(1)pp. 172-183
The distribution static compensator (DSTATCOM) is used for various purposes such as load balancing, harmonic rejection, and power factor correction (PFC) in power distribution networks. In unbalanced and polluted power systems, the classic definition of power factor cannot be used for PFC due to the existence of harmonics and negative sequence components in voltage and current waveforms. In this paper, PFC is performed using the IEEE power factor definition for harmonic and unbalanced environments. Moreover, the application of a proportional-resonant (PR) controller is proposed as an effective controller in the stationary frame for DSTATCOM performance improvement. The PR controller is used in the abc-frame for load balancing and is then compared theoretically and by simulation with the conventional PI controller, which has the main drawback of steady-state error when used in the stationary frame. To improve the DSTATCOM structure, an LCL harmonic filter is used as it is advantageous over the L/LC filter in terms of the size of the filter. The proposed DSTATCOM compensates for the disturbances in the source current imposed by nonlinear, unbalanced, and low power factor loads. Simulation results show the capability of the DSTATCOM including the proposed PR controller in improving the power quality of distribution systems. © 2017 TÜBITAK.
IET Radar, Sonar and Navigation (17518784) 11(2)pp. 330-340
In this study, the use of a family of Chebyshev chaotic maps for pulse compression in multiple input-multiple output (MIMO) radars is studied. It is shown that, these one-dimensional chaotic maps, which are amongst the simplest chaotic systems, can produce arbitrary number of sequences with arbitrary length, low peak-to-average power ratio (PAPR), high merit factor (MF) or equivalently low integrated side-lobe ratio (ISLR), very low peak side-lobe ratio and low cross-correlation levels. The complexity of algorithm for generating sequences in this method is linear. Besides, because of the flat spectrum of the generated sequences, high spectral efficiency can be achieved utilising these sequences. Moreover, simplicity of the map results in cheap building blocks of MIMO radars. Additionally, a simple method to improve the autocorrelation side-lobe is given. By lowering the autocorrelation side-lobes, ISLR or equivalently MF is enhanced. Nevertheless, in comparison with well-designed unimodular sequences, the produced sequences show higher PAPRs. By utilising a PAPR reduction mechanism, this shortcoming is alleviated. © The Institution of Engineering and Technology.
IEEE Transactions on Signal Processing (19410476) 65(3)pp. 690-704
Controlling peak side-lobe level (PSL) is of great importance in high-resolution applications of multiple input multiple output (MIMO) radars. In this paper, designing sequences with good autocorrelation properties are studied. The PSL of the autocorrelation is regarded as the main merit and is optimized through newly introduced cyclic algorithms, namely, PSL minimization quadratic approach, PSL minimization algorithm where the smallest rectangular, and PSL optimization cyclic algorithm. It is revealed that minimizing PSL results in better sequences in terms of autocorrelation side lobes when compared with traditional integrated side-lobe level minimization. In order to improve the performance of these algorithms, fast-randomized singular value decomposition is utilized. To achieve waveform design for MIMO radars, this algorithm is applied to the waveform generated from a modified Bernoulli chaotic system. The numerical experiments confirm the superiority of the newly developed algorithms compared to high-performance algorithms in monostatic and MIMO radars. © 2016 IEEE.
This paper proposes an observer for the class of triangular nonlinear systems including the model uncertainty, with constant delays in the state and input equations. It is assumed that the nonlinear perturbations satisfy the Lipschitz condition and the uncertain part is bounded. The main idea is based on the designing a high-gain observer in combination with the sliding mode observer which leads to a robust high-gain observer that has not been sufficiently studied previously. A compensation term is included in the observer dynamics that is designed based on the solution of a Lyapunov inequality. For stability analysis, if the matching condition is satisfied, by using a suitable Lyapunov-Krasovski functional, simple sufficient conditions are provided that guarantees the observation error converges to the origin asymptotically. The simulation results for a nonlinear system in triangular form illustrate the effectiveness of the proposed approach. © 2017 IEEE.
Khodadadi, H. ,
Khaki-sedigh, A. ,
Ataei, M. ,
Jahed-motlagh, M.R. ,
Hekmatnia, A. Journal of Medical and Biological Engineering (16090985) 37(3)pp. 409-419
Measuring the contour boundary irregularities of skin lesion is an important factor in early detection of malignant melanoma. On the other hand, cancer is usually recognized as a chaotic growth of cells. It is generally assumed that boundary irregularity associated with biomedical images may be due to the chaotic behavior of its originated system. Thus, chaotic indices can serve as some criteria for classifying dermoscopy images. In this paper, a new approach is presented for extraction of Lyapunov exponent and Kolmogorov–Sinai entropy in the skin lesion images. This method is based on chaotic time series analysis. Converting the region of interest of skin lesion to a time series, reconstruction of system phase space, estimation of the Lyapunov exponents and calculation of Kolmogorov–Sinai entropy are the steps of the proposed approach. The combination of the largest Lyapunov exponent and Kolmogorov–Sinai entropy is selected as a criterion for distinction between melanoma and mole categories. Experiments on a set of dermoscopy images yielded a sensitivity of 100% and a specificity of 92.5% providing superior diagnosis accuracy compared to other related similar works. © 2017, Taiwanese Society of Biomedical Engineering.
Renewable and Sustainable Energy Reviews (13640321) 72pp. 1167-1176
High performance grid-tied inverters have stringent control requirements both under steady-state and under transient conditions. Many different control systems have been applied to grid-tied inverters. However, there are few publications reviewing the literature on these control systems and their classification, particularly with regard to recent developments in this area. In this paper, a review of solutions for the control of grid-tied inverters is carried out. These control systems are compared and classified as implementation platform, reference frame, output filter of inverter, control strategy, modulation method, and controller. The major advantages and disadvantages of these parameters are highlighted and compared. Then, the most important characteristics of these parameters have been presented in a table to show which parameters can be used in various control systems for grid-tied inverters. © 2016 Elsevier Ltd
Journal of Electrical Engineering and Technology (19750102) 12(4)pp. 1357-1368
The lack of controllability over the wind causes fluctuations in the output power of the wind generators (WGs) located at the wind farms. Distribution Static Compensator (DSTATCOM) equipped with Battery Energy Storage System (BESS) can significantly smooth these fluctuations by injecting or absorbing appropriate amount of active power, thus, controlling the power flow of WGs. But because of the component aging and thermal drift, its harmonic filter parameters vary, resulting in performance degradation. In this paper, Quantitative Feedback Theory (QFT) is used as a robust control scheme in order to deactivate the effects of filter parameters variations on the wind power generation power smoothing performance. The proposed robust control strategy of the DSTATCOM is successfully applied to a microgrid, including WGs. The simulation results obviously show that the proposed control technique can effectively smooth the fluctuations in the wind turbines' (WT) output power caused by wind speed variations; taking into account the filter parameters variations (structural parameter uncertainties). © The Korean Institute of Electrical Engineers.
IEEE Access (21693536) 5pp. 14490-14501
The quantitative feedback theory is adopted as a robust control scheme for the distribution-static-compensator (DSTATCOM) in order to deactivate the effects of variations in its harmonic filter parameters on the fault ride through the capability of wind turbines (WTs). These variations may be due to factors like component aging and thermal drift. The DSTATCOM is applied in parallel with the wind generation (WG) together with a bridge-type-fault-current-limiter in series, to improve FRT capability of the WT. This proposed robust control strategy of the DSTATCOM is applied to a microgrid, including WG. The performance of this proposed scheme is simulated in PSCAD/EMTDC environment and the results indicate its efficiency. © 2013 IEEE.
Nonlinear Dynamics (0924090X) 89(4)pp. 2879-2887
A robust nonlinear observer for a class of nonlinear time-delay systems is introduced. The generalized sector constraint is employed to deal with many commonly encountered nonlinearity in dynamic equation. It is assumed that time-varying delay exists in both state and output equations, and further it directly appears in nonlinear function. By utilizing two correction terms in nonlinear observer related to the dynamic equation as well as system’s nonlinearity, the stability analysis of observer error dynamic is presented. For uncertain systems, a synthesis method to obtain robust nonlinear observer is then given in terms of some LMI’s. The effectiveness of proposed observer and related synthesis method are finally demonstrated through simulation examples. © 2017, Springer Science+Business Media B.V.
In this paper, the stability analysis of networked control systems, as important class of time delay systems is presented. The analysis method utilizes a new Lyapunov-Krasovskii functional to provide less conservative results with respect to the existing methods in literature. The delay dependent stability criteria based on improved version of Wirtinger inequality and reciprocally convex combination inequality are derived in terms of linear matrix inequalities. A numerical example is finally given to show the effectiveness and benefits of the proposed analysis methods compared with some recent results. © 2017 IEEE.
Journal of Theoretical and Applied Mechanics (14292955) 54(3)pp. 987-1000
In this paper, adaptive control for a class of uncertain nonlinear systems with input constraints is addressed. The main goal is to achieve a self-regulator PID controller whose coefficients are adjusted by using some adaptive fuzzy rules. The constraints on the control signal are taken into account as a saturation operator. The stability of the closed-loop system is analytically proved by using the Lyapunov stability theorem. The proposed method is then applied to a surface vessel with uncertain dynamic equations. The simulation results show the effectiveness of the proposed control strategy.
Nonlinear Dynamics (0924090X) 83(1-2)pp. 361-374
This article investigates chaotic attitude maneuvers in a satellite for a range of parameters via Lyapunov exponents (LEs) and designs an appropriate robust nonlinear controller to ensure chaos suppression and achieve desired performance. Since the dynamic equations of satellite are described as a nonlinear non-autonomous system, an improved technique for calculating the LEs of such systems as a measure of chaos phenomenon is presented. Using the proposed algorithm, the chaotic behavior of satellite is proved within a range of its parameters. Then, by converting dynamic equations to canonical form, a robust nonlinear control is proposed using back-stepping sliding mode method. The stability of closed-loop system and its robustness against disturbances and uncertainties are guaranteed by proving a theorem. Moreover, by converting the system description into a compatible form with the conditions of the Melnikov theorem, an analytical approach is presented to ensure chaos suppression in the controlled system. Finally, the simulation results for different operational conditions of a three-axis stabilized satellite are provided to show the effectiveness of the proposed analyses and syntheses. © 2015, Springer Science+Business Media Dordrecht.
Journal Of Engineering Science And Technology (18234690) 11(11)pp. 1528-1542
In this paper, the design of command to line-of-sight (CLOS) missile guidance law is addressed. Taking a three dimensional guidance model, the tracking control problem is formulated. To solve the target tracking problem, the feedback linearization controller is first designed. Although such control scheme possesses the simplicity property, but it presents the acceptable performance only in the absence of perturbations. In order to ensure the robustness properties against model uncertainties, a fuzzy adaptive algorithm is proposed with two parts including a fuzzy (Mamdani) system, whose rules are constructed based on missile guidance, and a so-called rule modifier to compensate the fuzzy rules, using the negative gradient method. Compared with some previous works, such control strategy provides a faster time response without large control efforts. The performance of feedback linearization controller is also compared with that of fuzzy adaptive strategy via various simulations. © School of Engineering, Taylor’s University.
Transactions of the Institute of Measurement and Control (14770369) 38(3)pp. 364-369
A new method is proposed in this article in order to determine a guaranteed interval of time delay in input signal for a class of non-linear control systems with state feedback. This method is based on the stability sufficient condition of a non-linear control system using the Lyapunov direct approach. For this purpose, the dynamic equations of the non-linear input-delayed system are reformulated as a non-linear system without delay, but with delay-dependent coefficients in the state-space description. The control strategy is considered a linear state feedback. Then, by introducing an appropriately related Lyapunov candidate, the stability sufficient condition of the closed-loop system is satisfied, leading to a guaranteed interval of delay according to the state feedback gain. The main results are gathered and proved as a lemma. The effectiveness of this proposed method is investigated by simulating the state feedback control of a non-linear synchronous generator with a delay in input. © SAGE Publications.
International Journal of Biomedical Engineering and Technology (17526418) 22(4)pp. 349-369
This paper investigated the effect of Electroencephalogram signals on diagnosis of the possible brain dysfunctions. It is the most common non-offensive way to analyse brain healthiness on the basis of chaotic theory. Normal person's EEG signals are different from the people who suffer from epilepsy, schizophrenia, post-traumatic stress disorder and Alzheimer's diseases in many respects, namely amplitude, frequency, statistical features and in general dynamic behaviour. The findings indicate EEG signals are non-linear and chaotic. EEG signal was considered as chaotic time series in the research. Diagnosis of diseases was conducted using analysis of chaotic parameters. They include Lyapunov exponent and correlation dimension. For this end, appropriate algorithms were rendered to extract necessity parameters for reconstructing phase space and calculated chaotic indices with relative consideration. The findings showed patients are recognised from healthy persons. It was also possible to distinguish two types of epilepsy, namely grand mal and temporal lobe. The results showed acceptable way of predicating epilepsy. Visual diagnosis of disorders by EEG is a big challenge for neurologist as complexity of the brain dysfunctions. This research can be useful for physicians to diagnose and predict diseases. © 2016 Inderscience Enterprises Ltd.
Journal of Electrical Engineering and Technology (19750102) 11(5)pp. 1057-1062
In this paper, an advanced and modified MRAS technique is utilized for controller design in electric power systems. The weighting factors of the proposed MRAS are tuned by using PSO. This optimal-adaptive controller is also normalized by normalization techniques to guarantee the system stability. The proposed MRAS then is applied to design STATCOM stabilizer and UPFC power flow controller. STATCOM stabilizer is a regulatory controller, while the power flow controller of UPFC is a tracking one. Therefore, the ability of the proposed MRAS technique to design regulatory and tracking controllers is investigated. In order to indicate the effectiveness of the proposed method, it is evaluated against the conventional methods. Simulation results demonstrate the validity of the method, under uncertainties and different disturbances. © The Korean Institute of Electrical Engineers.
Aim of this paper is to estimate time delays in nonlinear dynamic systems with unknown time-delays, such that time-delays appear in both state and output equations. The problem of estimating unknown delays is formulated as a dynamic optimization problem in which the cost function is defined based on the least-squares error between predicted and actual system output. Using proposed estimation method derives unknown time-delays by evaluating the gradient of cost function. Since, the gradient cannot be obtained analytically by standard differentiation rules, a practical computational method is presented to compute gradient and related cost function. The effectiveness of proposed algorithm is finally demonstrated by applying it to a practical example. © 2016 IEEE.
Research Journal of Applied Sciences, Engineering and Technology (discontinued) (20407459) 10(9)pp. 997-1006
An adaptive robust variable structure speed controller is designed for wide range of desired velocity control of a Permanent Magnet Linear Synchronous Motor (PMLSM). This is performed for comprehensive nonlinear model of PMLSM including non-idealities such as detent force, parameter uncertainty, unpredicted disturbance and nonlinear friction. The proposed method is based on the robust Sliding Mode Control (SMC) in combination with an adaptive strategy for a wide range of velocity. The simulation results are provided for the above mentioned comprehensive model of PMLSM with a variable velocity profile. Moreover, as an evaluation criterion, a Proportional-Integral (PI) controller is designed whose parameters are optimally tuned by the Particle Swarm Optimization (PSO) algorithm for better comparison. © Maxwell Scientific Organization, 2015.
Scientia Iranica (10263098) 22(2)pp. 519-529
Exoskeleton is a well-known example of an unconstrained robot for which the desired path is not predefined. Regarding these two effective features, a formulation for impedance control algorithm is presented and its prominence is demonstrated both mathematically and through simulation. Moreover it is essential to control this robot by an adaptive method because at least dynamic characteristics of the load are unknown. Unfortunately the existing methods do not address aforementioned traits or become unstable as inertia matrix becomes singular. Here an adaptive algorithm is generated based on the logic of Least Squares identification method rather than the Lyapunov stability criterion to tackle those limitations. © 2015 Sharif University of Technology. All rights reserved.
Chaos, Solitons and Fractals (09600779) 81pp. 20-29
Nonlinear analysis of complex dynamics displayed by current mode dc-dc converter and idea of Lyapunov exponents assignment by ramp compensator in order to control chaotic behavior is proposed in this article. A discrete-time iterative nonlinear mapping model is derived. The occurrence of the complex behaviors of bifurcation and chaos generated by varying the circuit parameters are investigated through numerical analysis and software implementation of the circuit. Next, in order to control bifurcation and chaos in these converters, the ramp compensation method is used. By inserting the ramp compensation parameter in the dynamical equations of the system, these complex behaviors are examined theoretically and numerically as well. It is proved that through this method, the stable period-one operation of the converter can be extended. By evaluating the Lyapunov exponents (LEs) of the system, the impact of the slope on the location of LEs are determined analytically. This leads to a design methodology for control of chaos in this converter based on LEs assignment in desired values by proper selection of compensator slope. By developing an experimental set up, practical results are obtained to confirm the theoretical analysis and simulations. © 2015 Elsevier Ltd. All rights reserved.
AEU - International Journal of Electronics and Communications (16180399) 69(10)pp. 1445-1452
Abstract In this paper an importance sampling (IS)-based technique is proposed to achieve the blind equalizer and detector for chaotic communication systems. Chaotic signals are generated using nonlinear dynamical systems. These signals have wide applications in communication as a result of their appropriate properties such as pseudo-randomness, large bandwidth, and unpredictability for long time. Based on the different chaotic signal properties, different communication methods such as chaotic modulation, masking, and spread spectrum have been proposed before. In this paper, chaos masking is adopted for transmitting modulated message symbols over an unknown channel, in which the joint demodulation and equalization is a nonlinear problem. Several methods such as extended Kalman filter (EKF), particle filter (PF), minimum nonlinear prediction error (MNPE), have been previously presented for this problem. Here, a new approach, based on Monte Carlo sampling, is proposed to joint channel equalization and demodulation. At the receiver end, importance sampling is used to detect binary symbols according to maximum likelihood (ML) criterion. Simulation results show that the proposed method has better performance, compared to existing methods, especially at low SNR. © 2015 Elsevier GmbH.
International Review of Aerospace Engineering (19737459) 7(4)pp. 134-141
In this paper a comprehensive model of a tracker system including derive subsystem is presented. Since the main part of the under consideration system consists a two Degree-Of-Freedom (DOF) gimbal subsystem, at first, the model of a two-axis gimbal is considered. For this purpose, after introducing the coordinate systems and different transformation matrices, the related equations of pitch and yaw axes by considering the friction torques, mass unbalances and cable restraint torques are derived. Moreover, all disturbance terms and the methods for their reduction or elimination are investigated. Then, the derive system of the gimbal including a DC motor with a gear is modeled and governing overall equations of the whole system is obtained. In order to have a model with practical considerations, the model of rate gyro which is used for measuring the angular velocities is also included. Finally, the simulation results of the under consideration case study by using the derived comprehensive dynamical equations of this paper are provided. Analysis of these results are used to synthesis the behavior of the practical system and choosing the suitable control structure in order to achieve stabilization and tracking objectives. © 2014 Praise Worthy Prize S.r.l. All rights reserved.
ISA Transactions (00190578) 53(2)pp. 415-422
For the participation of the steam power plants in regulating the network frequency, boilers and turbines should be co-ordinately controlled in addition to the base load productions. Lack of coordinated control over boiler-turbine may lead to instability; oscillation in producing power and boiler parameters; reduction in the reliability of the unit; and inflicting thermodynamic tension on devices. This paper proposes a boiler-turbine coordinated multivariable control system based on improved sliding mode controller (ISMC). The system controls two main boiler-turbine parameters i.e., the turbine revolution and superheated steam pressure of the boiler output. For this purpose, a comprehensive model of the system including complete and exact description of the subsystems is extracted. The parameters of this model are determined according to our case study that is the 320 MW unit of Islam-Abad power plant in Isfahan/Iran. The ISMC method is simulated on the power plant and its performance is compared with the related real PI (proportional-integral) controllers which have been used in this unit. The simulation results show the capability of the proposed controller system in controlling local network frequency and superheated steam pressure in the presence of load variations and disturbances of boiler. © 2013 ISA.
Engineering Journal (01258281) 18(2)pp. 101-118
This paper presents the idea of vector control for permanent magnet synchronous motor (PMSM) based on chaos theorem, using chaos controller. PMSM will demonstrate chaotic phenomena when its parameters fall into a certain area. To achieve this aim, the sub-system of controller has been designed by considering block diagram structure of vector control for PMSM and by applying the setting of Lyapunov exponents method. Also, asymptotical stability of closed loop system with given controller is shown, using the direct Lyapunov method. The performance of designed controller in chaotic mode is compared with conventional vector control methods. Also, the normal mode for PMSM is considered and the performance of controller is compared. Simulation results indicate that not only does this controller eliminate the chaos in chaotic mode and have good performance but also is able to control the system in normal mode by using almost the smaller control signal effort.
The present article provides an analysis of complex dynamics displayed by Power-Factor-Correction Boost Converter under Peak Current-Mode Control. PFC Boost converter has been studied with nonlinear analysis and the discrete-Time modeling approach has been used. In order to increase stable period-1 operation range, new application of ramp compensation approach has been used, also slope of the compensating ramp that guarantees the stable operation of the PFC Boost converter is investigated. Finally, results are proven by simulation and theoretical analysis. © 2014 IEEE.
Biomedical Signal Processing and Control (17468108) 14pp. 291-296
The early detection of abnormal heart conditions is vital to identify heart problems and avoid sudden cardiac death. The people with similar heart conditions almost have similar electrocardiogram (ECG) signals. By analyzing the ECG signals' patterns one can predict arrhythmias. Since the conventional methods of arrhythmia detection rely on observing morphological features of the ECG signals which are tedious and very time consuming, the automatic detection of arrhythmia is more preferable. In order to automate detection of heart diseases an adequate algorithm is required which could classify the ECG signals with unknown features according to the similarities between them and the ECG signals with known features. If this classifier can find the similarities precisely, the probability of arrhythmia detection is increased and this algorithm can become a useful means in laboratories. In this article a new classification method is presented to classify ECG signals more precisely based on dynamical model of the ECG signal. In this proposed method a fuzzy classifier is constructed and its simulation results indicate that this classifier can segregate the ECGs with an accuracy of 93.34%. To further improve the performance of this classifier, genetic algorithm is applied where the accuracy in prediction is increased up to 98.67%. This proposed method increases the accuracy of the ECG classification regarding more precise arrhythmia detection. © 2014 Elsevier Ltd. All rights reserved.
The present article provides an analysis of complex dynamics displayed by current mode controlled switching dc-dc converter. Current-mode controlled boost converter has been studied with nonlinear analysis and the discrete-time modeling approach has been used. By changing circuit parameters, complex behaviors like chaos and bifurcation occur in the switching dc-dc converter. For increasing stable period-1 operation range, the ramp compensation approach has been used and by changing its slope, its effect in the converter will be shown. Finally, the largest average lyapunov exponent for different slopes is reviewed and simulated. © 2014 IEEE.
This paper presents synchronization of two identical uncertain chaotic systems using combination of optimal theory and variable structure control. An adaptable variable structure control for compensating nonlinear parts and uncertainties of chaotic systems, and a quadratic optimal regulation for synchronizing linear part of chaotic systems are designed. Asymptotic stability of error dynamical system is proved using Lyapunov direct method. To show the effectiveness of the proposed controller, chaotic Lu system is considered as the case study. Simulation results are very promising. © 2013 IEEE.
Transactions of the Institute of Measurement and Control (14770369) 34(4)pp. 388-400
One of the main problems in small hydro-power plants that are locally used is their frequency control system. In this paper, a suggested control system based on the fuzzy sliding mode controller is presented for controlling the network frequency. Also, the proposed control strategy is compared with a PI controller and conventional sliding mode controller. In order to regulate the membership functions of fuzzy system more accurately, the particle swarm optimization algorithm is also applied. Moreover, because of unavailability of the control system variables, an estimator is suggested for estimating and identifying the system variables. This estimator will reduce the costs of implementing the control method. The simulation results show the ability of controller system in controlling the local network frequency in the presence of load and parameter's variations. © 2011, SAGE Publications. All rights reserved.
European Transactions on Electrical Power (15463109) 22(6)pp. 812-830
The load frequency control (LFC) is very important in power system operation and control for supplying sufficient, reliable, and high-quality electric power. The conventional LFC uses an integral controller. In this paper, a new control system based on the fuzzy sliding mode controller is proposed for controlling the load frequency of nonlinear model of a hydropower plant, and this control system is compared with the proportional-integral controller and the conventional sliding mode controller. To regulate the membership functions of fuzzy system more accurately, the particle swarm optimization algorithm is also applied. Moreover, because of the unavailability of the control system variables, a nonlinear estimator is suggested for estimating and identifying the system state variables. This estimator provides the physical realization of the method and will reduce the costs of implementation. The proposed control method is performed for the LFC of hydropower plant of Karoon-3 in Shahrekord, Iran. The simulation results show the capability of the controller system in controlling local network frequency. Copyright © 2011 John Wiley & Sons, Ltd. Copyright © 2011 John Wiley & Sons, Ltd.
Journal of Electrical Engineering (1339309X) 63(4)pp. 233-241
In this paper, a new method for robust PSS design based on the power system pole placement is presented. In this stabilizer, a feedback gain matrix is used as a controller. The controller design is proposed by formulating the problem of robust stability in a Linear Matrix Inequality (LMI) form. Then, the feedback gain matrix is designed based on the desired region of the closed loop system poles. This stabilizer shifts the poles of the power system in different operational points into the desired regions in s-plane, such that the response of the power system will have proper damping ratio in all the operational points. The uncertainties of the power system parameters are also considered in this robust technique. Finally, in order to show the advantages of the proposed method in comparison with conventional PSS, some simulation results are provided for a power system case study in different operational points. © 2012.
Journal of Power Electronics (15982092) 12(1)pp. 145-156
These days, the application of electronic power transformers (EPTs) is expanding in place of ordinary power transformers. These transformers can transmit power via three or four wire converters. Their dynamic performance is extremely important, due to their complex structure. In this paper, a new method is proposed for improving the dynamic performance of distribution electronic power transformers (DEPT) by using sliding mode control (SMC). Hence, to express the dynamic characteristics of a system, different factors such as the voltage unbalance, voltage sag, voltage harmonics and voltage flicker in the system primary side are considered. The four controlling aims of the improvement in dynamic performance include: 1) maintaining the input currents so that they are in sinusoidal form and in phase with the input voltages so they have a unity power factor, 2) keeping the dc-link voltage within the reference amount, 3) keeping the output voltages at a fixed amount and 4) keeping the output voltages in sinusoidal and symmetrical forms. Simulation results indicate the potential and capability of the proposed method in improving DEPT behavior.
Etahadtavakol, M. ,
Ng e.y.k., ,
Lucas, C. ,
Sadri s., ,
Ataei, M. Infrared Physics and Technology (13504495) 55(4)pp. 345-352
Breast diseases are one of the major issues in women's health today. Early detection of breast cancer plays a significant role in reducing the mortality rate. Breast thermography is a potential early detection method which is non-invasive, non-radiating, passive, fast, painless, low cost, risk free with no contact with the body. By identifying and removing malignant tumors in early stages before they metastasize and spread to neighboring regions, cancer threats can be minimized. Cancer is often characterized as a chaotic, poorly regulated growth. Cancerous cells, tumors, and vasculature defy have irregular shapes which have potential to be described by a nonlinear dynamical system. Chaotic time series can provide the tools necessary to generate the procedures to evaluate the nonlinear system. Computing Lyapunov exponents is thus a powerful means of quantifying the degree of the chaos. In this paper, we present a novel approach using nonlinear chaotic dynamical system theory for estimating Lyapunov exponents in establishing possible difference between malignant and benign patterns. In order to develop the algorithm, the first hottest regions of breast thermal images are identified first, and then one dimensional scalar time series is obtained in terms of the distance between each subsequent boundary contour points and the center of the mass of the first hottest region. In the next step, the embedding dimension is estimated, and by time delay embedding method, the phase space is reconstructed. In the last step, the Lyapunov exponents are computed to analyze normality or abnormality of the lesions. Positive Lyapunov exponents indicates abnormality while negative Lyapunov exponents represent normality. The normalized errors show the algorithm is satisfactorily, and provide a measure of chaos. It is shown that nonlinear analysis of breast thermograms using Lyapunov exponents may potentially capable of improving reliability of thermography in breast tumor detection as well as the possibility of differentiating between different classes of breast lesions. © 2012 Elsevier B.V. All rights reserved.
International Journal of Robotics and Automation (19257090) 27(2)pp. 163-176
One of the important problems in the design of an underwater robot is its intelligent navigation system. This system autonomously performs the task of the robot guidance and control. The intelligent control system of the fish robot guidance comprises different control sections such as control of motion trajectory angle, yaw angle, orientation control, speed control, depth control, intelligent control of error, etc. In this paper, the control of the yaw angle of a laboratory 4-link fish-like robot guiding it in the horizontal direction is studied. This is in fact part of the navigation control system which guides the robot at a given depth. In this regard, a desired dynamic model describing the under study laboratory 4-link fish-like robot motion with three joints is derived. The model validation is examined by comparing its response and the system response to an experimentally imposed torque. Then, a fuzzy controller is proposed to achieve suitable performance of the step response such as desired steady state error, reduction of the maximum overshoot, and decreasing of the settling time. The desired erformances are achieved by applying the complete rule base, data base and suitable membership functions in the fuzzy controller. The simulation results based on the practical considerations and the conventional experimental inputs show the motion trajectory improvement using the proposed control system.
IEEE Transactions on Power Delivery (19374208) 26(2)pp. 882-890
The dynamic voltage restorer (DVR) is one of the modern devices used in distribution systems to protect consumers against sudden changes in voltage amplitude. In this paper, emergency control in distribution systems is discussed by using the proposed multifunctional DVR control strategy. Also, the multiloop controller using the Posicast and P+Resonant controllers is proposed in order to improve the transient response and eliminate the steady-state error in DVR response, respectively. The proposed algorithm is applied to some disturbances in load voltage caused by induction motors starting, and a three-phase short circuit fault. Also, the capability of the proposed DVR has been tested to limit the downstream fault current. The current limitation will restore the point of common coupling (PCC) (the bus to which all feeders under study are connected) voltage and protect the DVR itself. The innovation here is that the DVR acts as a virtual impedance with the main aim of protecting the PCC voltage during downstream fault without any problem in real power injection into the DVR. Simulation results show the capability of the DVR to control the emergency conditions of the distribution systems. © 2011 IEEE.
International Journal of Innovative Computing, Information and Control (13494198) 7(5 A)pp. 2051-2062
In this paper, an adaptive method for chaos suppression and regulation in uncertain unified chaotic system is proposed. For this purpose, at the first step, an adaptive non-linear state feedback is designed to suppress the chaotic behavior of under consideration system. In this way, the Lyapunov's direct method is used to select the appropriate adaptive non-linear state feedback. The asymptotic stability guarantee of uncertain unified chaotic system using non-linear feedback controller, in a stochastic point on the general manifold of its equilibrium points, is proved in a lemma. At the second step, a combination of suggested adaptive non-linear state feedback and linear feedbacks, with constant and adaptive gains, is used to regulate the controlled system at the desired set-point placed on the general related equilibrium manifold. In this stage, the asymptotic stability of the controlled system on the desired set-point is proved in another lemma using the Lyapunov's indirect method. Finally, simulation results of applying the controllers to uncertain unified chaotic system for different cases are provided to show the well-acceptable performance of the proposed controllers. © 2011 ICIC INTERNATIONAL.
An adaptive fuzzy variable structure velocity controller of a permanent magnet linear synchronous motor (PMLSM) is designed for a command profile which has rapid change in a wide range. This is performed for comprehensive nonlinear model of PMLSM including non-idealities such as detent force, parameter uncertainty, unpredicted disturbance, and nonlinear friction. The proposed method is based on the adaptive sliding mode control (SMC) enhanced with a fuzzy inference to determine coefficients of the controller. The fuzzy block uses the desired and real velocity, and also its derivative as three inputs and a and C as outputs. A set of 343 rules come together to make a fuzzy rule base which brings a powerful controller with high resolution for different situations. As an evaluation criterion of the performance of the proposed method, a proportional-integral (PI) controller is designed whose parameters are optimally tuned by the particle Swarm Optimization (PSO) algorithm for better comparison. © 2011 IEEE.
This paper presents an improved method for eigenvalue assignment of the LTI multivariable systems by state feedback. In this method, vector companion form of the system representation is used. The proposed method, in addition to the controllable multivariable systems, can be applied to the stabilizable ones. Moreover, by this method, both types of numerical and parametric state feedback gain matrices can be achieved. The numerical state feedback gain matrix is unique; however, the parameters in the parametric one are determined in order to achieve a gain matrix with minimum Frobenius norm. The numerical examples show the performance and software implementation capability of the proposed technique. © 2011 AmirKabir Univ of Tech.
International Journal of Control (13665820) 84(12)pp. 1956-1964
In this article, an improved method for eigenvalue assignment via state feedback in the linear time-invariant multivariable systems is proposed. This method is based on elementary similarity operations, and involves mainly utilisation of vector companion forms, and thus is very simple and easy to implement on a digital computer. In addition to the controllable systems, the proposed method can be applied for the stabilisable ones and also systems with linearly dependent inputs. Moreover, two types of state-feedback gain matrices can be achieved by this method: (1) the numerical one, which is unique, and (2) the parametric one, in which its parameters are determined in order to achieve a gain matrix with minimum Frobenius norm. The numerical examples are presented to demonstrate the advantages of the proposed method. © 2011 Copyright Taylor and Francis Group, LLC.
European Transactions on Electrical Power (15463109) 21(1)pp. 824-838
Electric arc furnaces (EAFs) produce voltage fluctuations and flicker because of the reactive power severe variations. Furthermore, these loads absorb a large amount of reactive power. The static VAr compensators (SVCs) have been widely used by the industrial customers with arc furnaces to compensate the reactive power due to the quick response of the power electronic devices. In this paper, reactive power compensation in the steel industrial plant with several EAFs by utilizing open-loop controlled thyristor controlled reactor/fixed capacitor (TCR/FC) compensator is performed. The TCR/FC compensator is usually applied in conventional steel making plants; one is in Mobarakeh/ Isfahan, Iran which is considered as the case study in this paper. Simulation results show that, although open-loop controlled TCR/FC is effective for compensating reactive power, it cannot efficiently compensate the fluctuations of the reactive power and reduce the flicker intensity. © 2010 John Wiley & Sons, Ltd.
Substation has a critical role in power network because it is a subsidiary station of an electricity generation, transmission and distribution system where voltage is transformed from high to low or the reverse with power transformers. All devices in substation are controlled, protected and monitored by substation automation system (SAS) that collects information from the power equipment (process) and performs actions on it. Communication network is a fundamental element in all automation system and network performances can have a critical impact on the control process. In the past decade, new communication standard have been designed and retrofitted into substations. IEC61850 is a new international standard for substation automation. In this paper, the authors describe some important feature of IEC 61850 as an international communication standard in substation automation system, that separate this standard from other communication standard in substation. © 2011 IEEE.
Physics Letters, Section A: General, Atomic and Solid State Physics (03759601) 374(41)pp. 4226-4230
Permanent Magnet Synchronous Motor (PMSM) experiences chaotic behavior for a certain range of its parameters. In this case, since the performance of the PMSM degrades, the chaos should be eliminated. In this Letter, the control of the undesirable chaos in PMSM using Lyapunov exponents (LEs) placement is proposed that is also improved by choosing optimal locations of the LEs in the sense of predefined cost function. Moreover, in order to provide the physical realization of the method, nonlinear parameter estimator for the system is suggested. Finally, to show the effectiveness of the proposed methodology, the simulation results for applying this control strategy are provided. © 2010 Elsevier B.V. All rights reserved.
Journal of Electrical Engineering and Technology (19750102) 5(1)pp. 116-128
Modeling of the three phase electric arc furnace and its voltage flicker mitigation are the purposes of this paper. For modeling of the electric arc furnace, at first, the arc is modeled by using current-voltage characteristic of a real arc. Then, the arc random characteristic has been taken into account by modulating the ac voltage via a band limited white noise. The electric arc furnace compensation with static VAr compensator, Thyristor Controlled Reactor combined with a Fixed Capacitor bank (TCR/FC), is discussed for closed loop control of the compensator. Instantaneous flicker sensation curves, before and after accomplishing compensation, are measured based on IEC standard. A new method for controlling TCR/FC compensator is proposed. This method is based on applying a predictive approach with closed loop control of the TCR/FC. In this method, by using the previous samples of the load reactive power, the future values of the load reactive power are predicted in order to consider the time delay in the compensator control. Also, in closed loop control, two different approaches are considered. The former is based on voltage regulation at the point of common coupling (PCC) and the later is based on enhancement of power factor at PCC. Finally, in order to show the effectiveness of the proposed methodology, the simulation results are provided.
COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering (03321649) 29(3)pp. 667-685
Purpose - The purpose of this paper is to present a 3D finite element model of the electromagnetic fields in an AC three-phase electric arc furnace (EAF). The model includes the electrodes, arcs, and molten bath. Design/methodology/ approach - The electromagnetic field in terms of time in AC arc is also modeled, utilizing a 3D finite element method (3D FEM). The arc is supposed to be an electro-thermal unit with electrical power as input and thermal power as output. The average Joule power, calculated during the transient electromagnetic analysis of the AC arc furnace, can be used as a thermal source for the thermal analysis of the inner part of furnace. Then, by attention to different mechanisms of heat transfer in the furnace (convection and radiation from arc to bath, radiation from arc to the inner part of furnace and radiation from the bath to the sidewall and roof panel of the furnace), the temperature distribution in different parts of the furnace is calculated. The thermal model consists of the roof and sidewall panels, electrodes, bath, refractory, and arc. The thermal problem is solved in the steady state for the furnace without slag and with different depths of slag. Findings - Current density, voltage and magnetic field intensity in the arcs, molten bath and electrodes are predicted as a result of applying the three-phaseACvoltages to theEAF. The temperature distribution in different parts of the furnace is also evaluated as a result of the electromagnetic field analysis. Research limitations/implications - This paper considers an ideal condition for the AC arc. Non-linearity of the arc during the melting, which leads to power quality disturbances, is not considered. In most prior researches on the electrical arc furnace, a non-linear circuit model is usually used for calculation of power quality phenomena distributions. In this paper, the FEM is used instead of non-linear circuits, and calculated voltage and current densities in the linear arc model. The FEM results directly depend on the physical properties considered for the arc. Originality/value - Steady-state arc shapes, based on the Bowman model, are used to calculate and evaluate the geometry of the arc in a real and practical three-phase AC arc furnace. A new approach to modeling AC arcs is developed, assuming that the instantaneous geometry of the AC arc at any time is constant and is similar to the geometry of a DC arc with the root mean square value of the current waveform of the AC arc. A time-stepping 3D FEM is utilized to calculate the electromagnetic field in the AC arc as a function of time. © Emerald Group Publishing Limited.
This paper presents a chaos synchronization method for a class of uncertain chaotic systems using the combination of an optimal control theory and an adaptive strategy. A quadratic optimal regulator and an adaptive control are used to represent the controller's structure. The asymptotic stability of the corresponding error dynamical system is guaranteed through Lyapunov stability analysis. The proposed controller is employed in two uncertain chaotic Lu systems, and their promising performances are illustrated. © 2010 American Institute of Physics.
Chaos, Solitons and Fractals (09600779) 42(3)pp. 1755-1765
In this paper, a chattering-free sliding mode controller design for uncertain chaotic systems is presented. Since the implementation of the sliding mode control may cause a significant problem of chattering, many modified methodologies have been developed to overcome this drawback. However, each of them has own problems such as lack of robustness against disturbance variations, steady-state error, large convergence time and effect on transient performance. This paper proposes an improved sliding mode control strategy in which a modified sliding condition in a continuous function in control signal is taken into account instead of discontinuous part and also it adds an auxiliary continuous control to the control input. Then, the stability of controlled system is proved by using Lyapunov's direct method. The usefulness of this proposed method for eliminating the chattering phenomenon in transient and steady states, in the face of uncertain chaotic systems with disturbances, is well appeared. For this purpose, the Lorenz system is studied and its simulation results are presented to demonstrate the effectiveness of the proposed control scheme. © 2009 Elsevier Ltd. All rights reserved.
Chaos, Solitons and Fractals (09600779) 40(4)pp. 1938-1945
In this paper, an adaptive control method for set-point tracking of the Lorenz chaotic system by using non-linear feedback is proposed. The design procedure of the proposed controller is accomplished in two steps. At the first step, using Lyapunov's direct method, a non-linear state feedback is selected so that without any need to apply identification techniques, in despite of the uncertain parameters existence in the system state equations, the asymptotic stability of the general Lorenz system is guaranteed in a stochastic point of the manifold containing general system equilibrium points. At the second step, a linear state feedback with adaptive gain is added to the prior controller to eliminate the tracking error. In order to guarantee the system asymptotic stability at desired set-point, the indirect Lyapunov's method is used. Finally, to show the effectiveness of the proposed methodology, the simulation results of different experiments including system parameters changes and set-point variation are provided. © 2007 Elsevier Ltd. All rights reserved.
Journal of Electrical Systems (11125209) 5(1)
The power system dynamic instability is occurred by loosing balance relation between electrical generation and a varying load demand that justifies the necessity of using Power System Stabilizer (PSS). Moreover, the PSS must have the capability of producing appropriate stabilizing signals with limited practical amplitude and it should be robust against a wide range of operating conditions and disturbances. For this purpose, a robust PSS design based on an auto-tuning fuzzy logic control under multi-operating conditions by using Real Coded Genetic Algorithm (RCGA) is proposed. This method includes two fuzzy controllers; internal fuzzy controller and supervisor fuzzy controller. The supervisor controller tunes the internal one by on-line applying of nonlinear scaling factors to inputs and outputs using extra signals. The RCGA-based method is used for off-line training of this supervisor controller by considering that the operating conditions for training be different from those are used for test simulations. Then, the proposed PSS is tested in three operational conditions; nominal load, heavy load, and in the case of fault occurrence in transmission line. The simulation results are provided to compare the proposed PSS with conventional fuzzy PSS and conventional PSS. It is shown that the performance and robustness of proposed PSS in different operating conditions is more acceptable. Copyright © 2009 JES.
AC electric arc furnaces (EAFs) highly reduce power quality of the network by generating disturbances such as flicker and harmonics. These disturbances are due to the nonlinear electromagnetic and thermal field behaviors of the AC arcs. Analysis of these nonlinear behaviors is required for improving power quality in the network. This paper presents a three-dimensional finite element modeling of the electromagnetic fields in an AC three-phase electric arc furnace. The model includes the electrodes, arcs and molten bath. Current density, voltage and magnetic field intensity in the arcs, molten bath and electrodes are predicted as a result of applying the three-phase AC voltages to the EAF. This model does not consider the instantaneous geometry of the arc, instead a constant geometry, which is adjacent to the geometry of a DC arc with a DC current equal to the RMS value of the current waveform, is considered. Electromagnetic field of the AC arc in the time-domain is also modeled using the three-dimensional finite element method. ©2009 IEEE.
Computer Systems Science and Engineering (discontinued) (02676192) 23(4)pp. 241-253
One of the most important methods in loss reduction and controlling the voltages of distribution systems is the utilization of the fixed and switched capacitors. To do this, real modeling of the system in large scale unbalanced or balanced for both radial and meshed configurations are required. In this paper, a new technique for finding the optimal values of the fixed and switched capacitors in the distribution networks based on the Real-Coded Genetic Algorithm (RCGA) is presented. In this method, the modeling of radial or loop feeders with unbalanced or balanced network loads are basically considered. Also, the modeling of the load at different levels is simulated which low voltage and medium voltage capacitors those are available in the market are used. Regarding the above factors in addition to the various parameters in optimization problem, the RCGA is used to find the best and real optimal network with the best rate for the capacitors. Finally, this methodology is tested on a region of the distribution network of the city of Ahvaz in Iran and satisfactory results are obtained. These results show that in addition to the decreasing of the network losses and improvement of the voltage profile, the benefit saving due to application of capacitors is increased. © 2008 CRL Publishing Ltd.
Journal of Applied Sciences (discontinued) (18125654) 8(8)pp. 1406-1415
In order to improve dynamic stability of the power systems, the use of Power System Stabilizer (PSS) has been recently increased. For this purpose, there are varieties of methods for determining the controller coefficients of the system stabilizers. If these coefficients are tuned in each operational point by an adaptive mechanism, the robust performance of the system is improved. In this study, a new method for determining the coefficients of a selt-tuning FM with lead-lag controller based on pole-assignment and pole-slutting techniques is presented. In the design procedure, the required identification in self-tuning regulator is performed by using active and reactive power values. Moreover, the properties of the proposed methodology are compared with self-tuning PID stabilizer whose coefficients are determined by using pole assigment technique. Then, the advantages of the proposed stabilizer in which parameter adaptation is accomplished based on the proposed self-tuning method by combining the pole-assignment and pole-shifting techniques, is expressed with respect to other stabilizers. Finally, in order to show the effectiveness of the proposed methodology, some simulation results on a power system with definite parameters and different operational points are provided and compared by using ITAE performance index which denotes the integral of time multiplied by absolute error. © 2008 Asian Network for Scientific Information.
In this paper, an adaptive controller is designed to control an Electric Arc Furnace (EAF) electrode. For this purpose, a nonlinear model for EAF is considered. Piecewise-linearization method is used and based on the Lyapunov's method an adaptive control rule is achieved. EAF different operating conditions are considered and in each condition the system response by using proposed adaptive controller is compared with its response with PI controller which is usual controller for EAF. At first minutes of melting process, scrap surface changes suddenly. When the scraps are melted, the distance between electrode tip and melted material surface is considered to change sinusoidal containing the white noise. Also the effect of noise in current measurements is investigated. In all conditions the controller should change the electrode position so that the effective value of arc current remains constant. Additionally several conditions that don't occur in actual EAF are simulated to compare the response of those nonlinear systems that have transfer functions similar to EAF, with adaptive and PI controller. © ICROS.
This paper examines transient finite element solutions of an 100 MVA three phase electric arc furnace (EAF). In practice, it was observed that there were a few high voltage arcs between upper side of high-carrying-current electrodes and the EAF roof. In order to specify the operation and performance of this EAF, a two dimensional time stepping finite element method (FEM) was developed and induced voltages between the roof and the electrodes at the worst conditions were predicted. In addition, there were some measurements of effective value of induced voltages between the roof, electrodes and water pipes by which the roof was cooled. At the end, accordingly, the FEM simulations proved that in unbalanced and asymmetrical operations of this EAF, the probability of high voltage arcing remained. © ICROS.
Journal of Electrical Engineering (1339309X) 58(4)pp. 189-199
One of the most important methods in loss reduction and controlling the voltages of distribution systems is the utilization of the fixed and switched capacitors. To do this, real modelling of the system in actual operational conditions including unbalanced or balanced loading and for actual feeder structure, i.e, radial/meshed configuration, are required. In this paper, a new technique for finding the optimal values of the fixed and switched capacitors in the distribution networks with above properties based on the real coded genetic algorithm (RCGA) is presented. For this purpose, the modelling of the loads at different load levels are simulated with low voltage and medium voltage capacitors that are available on the market. Regarding the above factors in addition to the various parameters in the optimization problem, RCGA is used to find the best and real optimal network with the best rate for the capacitors. Finally, this methodology is tested on a region of the distribution network of the city of Ahvaz in Iran and satisfactory results are obtained. These results show that in addition to the decreasing of the network losses and improvement of the voltage profile, the benefit saving due to application of capacitors is increased. © 2007 FEI STU.
Power supplies normally provide a constant output voltage. In most of the applications a DC-DC converter is controlled by a voltage mode or a current mode controller. The DC converters are employed to feed electric vehicles, telephone sets and civil invertors, or for induction motors and frequency control. In this regard, optimal exploitation of DC transforms by classical controllers has been a controversial issue in reputable journals. Due to their switching property included in their structure, DC-DC converters have a non-linear behavior and their controlling design is accompanied with complexities. But by employing the average method it is possible to approximate the system by linear system and exploiting linear control methods. In this paper, control methods to control Buck converters by Linear Quadratic Regulator (LQR) controllers as well as optimal locating of the poles by genetic algorithm have been employed. All the analysis and simulations to duplicate on the above converter by MATLAB software were performed. The simulation results show the improvement in voltage control response. ©ICROS.
In this paper, the control of a double mass and spring system as a physical model of a flexible arm robot is considered. The main goal of design is to use an appropriate control method that produces suitable external torques such that the whole system can be completely stabilized and controlled. For this purpose, mathematical model of the system is required which is achieved by Lagrange's equations in the first part of the paper. Since the controller design in this paper is based on state space description, these dynamical equations are re-written in the form of state-space equations and are linearized about an operating state. After examining the controllability of the system, a state feedback controller and also a Linear Quadratic Regulator (LQR) are designed. Moreover, since in these controllers the states of the system are required, a suitable full-order state estimator is developed as well. Finally, simulation results are provided to show the effectiveness of the proposed controllers. © ICROS.
In this paper, a double- mass and spring system Is considered as a benchmark for future studies on flexible arm robots. By using an appropriate control method and applying suitable external torques, the system can be completely stabilized and controlled. This requires the exact mathematical model of system. To achieve mathematical description, the system behavior is described by Lagrange's equations. Then these dynamical equations are written In the form of state-space equations. Finally, simulation results are presented to show the effectiveness of derived mathematical model for further analysis and synthesis. © 2007 IEEE.
WSEAS Transactions on Computers (discontinued) (11092750) 5(3)pp. 469-476
Computations in a feature based stereo matching which is basically used for depth extraction are generally very high. These computations essentially include feature extraction and matching which feature matching is usually higher. For a feature-based stereo matching, we accurately tune the search space based on some stereo imaging parameters like the focal length with pixels scale, the displacement of features points and maximum disparity. We show that results of previous matches can be used to narrow down the search space to find current match. We use directional derivative of disparity as a temporary concept to tune the search space accurately. Then we develop a fast feature based stereo matching algorithm based on the proposed search space tuning and non-horizontal thinned edge points as features. For reducing the error in the matching stage, we use left-right consistency checking technique for a small number of feature points. Usually this technique doubles the execution time of matching, but we will show that increasing of execution time in the proposed algorithm is negligible respect to the other similar methods as well as the invalid matching is also highly reduced. Comparing to the other similar methods, experimental results for three tested images show that not only the execution time of the matching stage of the proposed algorithm is decreased to 42%, but also the error in the matching is decreased to 90%.
Ataei, M. ,
Lohmann b., ,
Khaki-sedigh, A. ,
Lucas, C. Chaos, Solitons and Fractals (09600779) 19(5)pp. 1131-1139
In this paper, a method for estimating an attractor embedding dimension based on polynomial models and its application in investigating the dimension of Bremen climatic dynamics are presented. The attractor embedding dimension provides the primary knowledge for analyzing the invariant characteristics of the attractor and determines the number of necessary variables to model the dynamics. Therefore, the optimality of this dimension has an important role in computational efforts, analysis of the Lyapunov exponents, and efficiency of modeling and prediction. The smoothness property of the reconstructed map implies that, there is no self-intersection in the reconstructed attractor. The method of this paper relies on testing this property by locally fitting a general polynomial autoregressive model to the given data and evaluating the normalized one step ahead prediction error. The corresponding algorithms are developed in uni/multivariate form and some probable advantages of using information from other time series are discussed. The effectiveness of the proposed method is shown by simulation results of its application to some well-known chaotic benchmark systems. Finally, the proposed methodology is applied to two major dynamic components of the climate data of the Bremen city to estimate the related minimum attractor embedding dimension. © 2003 Elsevier Ltd. All rights reserved.
IFAC Proceedings Volumes (IFAC-PapersOnline) (14746670) 36(16)pp. 169-174
The problem of Lyapunov Exponents (LEs) estimation from chaotic data based on Jacobian approach by polynomial models is considered. The optimum embedding dimension of reconstructed attractor is interpreted as suitable order of model. Therefore, based on global polynomial mode ling of system, a novel criterion for selecting the embedding dimension is presented. By considering this dimension as the model order, the best nonlinearity degree of polynomial is estimated. The selected structure is used for local estimating of Jacobians to calculate the LEs. This suitable structure of polynomial model leads to better results and avoids of sporious LEs. Simulation results show the effectiveness of proposed methodology. © 2003 International Federation of Automatic Control.
Etahadtavakol, M. ,
Ng e.y.k., ,
Lucas, C. ,
Ataei, M. pp. 255-274
Ataei, M. ,
Khaki-sedigh, A. ,
Lohmann b., ,
Lucas, C. pp. 3106-3111
In this paper, the problem of Lyapunov Exponents (LEs) computation from chaotic time series based on Jacobian approach by using polynomial modelling is considered. The embedding dimension which is an important reconstruction parameter, is interpreted as the most suitable order of model. Based on a global polynomial model fitting to the given data, a novel criterion for selecting the suitable embedding dimension is presented. By considering this dimension as the model order, by evaluating the prediction error of different models, the best nonlinearity degree of polynomial model is estimated. This selected structure is used in each point of the reconstructed state space to model the system dynamics locally and calculate the Jacobian matrices which are used in QR factorization method in the LEs estimation. This procedure is also applied to multivariate time series to include information from other time series and resolve probable shortcoming of the univariate case. Finally, simulation results are presented for some well-known chaotic systems to show the effectiveness of the proposed methodology. © 2003 EUCA.
