Articles
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.
