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IEEE Access (21693536) 12pp. 84374-84386
Maximum power point tracking (MPPT) techniques are regarded as an important component of photovoltaic systems (PVSs) to extract the output power of a photovoltaic array. Algorithms based on perturbation suffer from the tradeoff between steady-state oscillations around (MPP) and the tracking speed. In this article, a fuzzy logic controller (FLC)-based Adaptive P&O MPPT algorithm for PVSs with fast tracking and low oscillations under rapidly irradiance change conditions are developed. When the operation point reaches a steady state, the proposed method can halt any artificial perturbation. Consequently, no oscillations around the MPP, and energy loss is reduced compared with conventional perturbation-based algorithms. The proposed algorithm can detect any change in irradiance without using additional sensors by employing a technique called drift avoidance. In addition, the FLC creates variable step sizes adaptively to accomplish speedy, accurate convergence to the MPP under normal and changeable weather circumstances. In a MATLAB program environment, the suggested method is simulated. DSP TMS320F28335 is used to validate that the proposed algorithm can monitor MPP with a low settling time, low steady-state oscillations, and a high convergence rate at the operational point. © 2013 IEEE.
Haghighat, M. ,
Niroomand, M. ,
Tafti, H.D. ,
Townsend, C.D. ,
Fernando, T. Journal of Modern Power Systems and Clean Energy (21965420) 12(1)pp. 1-21
To maximize conversion efficiency, photovoltaic (PV) systems generally operate in the maximum power point tracking (MPPT) mode. However, due to the increasing penetration level of PV systems, there is a need for more developed control functions in terms of frequency support services and voltage control to maintain the reliability and stability of the power grid. Therefore, flexible active power control is a mandatory task for grid-connected PV systems to meet part of the grid requirements. Hence, a significant number of flexible power point tracking (FPPT) algorithms have been introduced in the existing literature. The purpose of such algorithms is to realize a cost-effective method to provide grid support functionalities while minimizing the reliance on energy storage systems. This paper provides a comprehensive overview of grid support functionalities that can be obtained with the FPPT control of PV systems such as frequency support and volt-var control. Each of these grid support functionalities necessitates PV systems to operate under one of the three control strategies, which can be provided with FPPT algorithms. The three control strategies are classified as: constant power generation control (CPGC), power reserve control (PRC), and power ramp rate control (PRRC). A detailed discussion on available FPPT algorithms for each control strategy is also provided. This paper can serve as a comprehensive review of the state-of-the-art FPPT algorithms that can equip PV systems with various grid support functionalities. © 2013 State Grid Electric Power Research Institute.
PCIM Europe Conference Proceedings (21913358) 2024pp. 74-83
Power cycling is typically performed by periodically self-heating a power device using a DC current. This paper demonstrates a technique to boost the heating power to shorten the heating phase, by the addition of switching loss. This power cycling technique is demonstrated on 190 mΩ, 600 V Gallium Nitride (GaN) discrete devices, where it achieves 240,000 thermal cycles per week with a junction temperature swing ∆TJ of 100°C, and where the device remains integrated in a switching converter. The device under test is heated rapidly from 30°C to 130°C in 0.5 s, by hard-switching at 1 MHz, at rated current and 400 V. An optimized thermal path cools the junction back to 30°C in 2 s. The junction temperature is closed-loop controlled to maintain an approximately constant temperature swing. This requires junction temperature sensing with low ms-scale latency, implemented here using peak turn-on di/dt as the junction temperature indicator. The inferred temperature is fed into a control system that governs the heating and cooling durations. The resulting closed-loop-controlled heating time is shown to be a sensitive real-time indicator of device change. The paper discusses the practicality of temperature calibration methods, in light of temperature-sensitive electrical parameters’ known drift and sensitivity to bias temperature instability, and the problem of self-heating during calibration. Experimental results show one GaN device surviving 400,000 cycles with a ∆TJ of 102°C with no apparent thermal degradation, and another GaN device cycling at a ∆TJ of 136°C, whose heating duration reduces from 500 to 10 ms over the course of 30,000 cycles, indicating an apparent degradation of the device’s thermal properties. © VDE VERLAG GMBH · Berlin · Offenbach.
IECON Proceedings (Industrial Electronics Conference) (25771647)
Impedance mismatching is a prevalent issue in wireless power transfer (WPT) systems across various power levels and operating frequencies. In scenarios where coils are closely coupled, the maximum power transfer does not occur at the natural resonant frequency of the coupled coils due to impedance mismatching between the internal impedance of the power source and the WPT system’s input impedance. This results in the frequency splitting phenomenon. This paper first examines the frequency splitting phenomenon using the maximum power transfer theorem. Subsequently, a Perturbation and Observation (P&O)-based method with a variable step size is proposed to enhance power transfer efficiency over a range of coil-to-coil distances. Unlike conventional, time-consuming search-and-find impedance matching (IM) methods, this approach achieves optimal IM network parameters in a single step. A scaled-down 20-watt prototype is fabricated to validate the effectiveness of the proposed method in terms of input current, active and reactive input powers, as well as power factor correction (PFC). © 2024 IEEE.
Haghighat, M. ,
Tafti, H.D. ,
Gholipour shahraki, M. ,
Niroomand, M. ,
Townsend, C.D. ,
Barajas, N.V. ,
Liang, G. ,
Konstantinou, G. ,
Pou, J. IEEE Access (21693536) 12pp. 168568-168580
Grid-connected photovoltaic (PV) systems enhance grid stability during frequency fluctuations by adopting power reserve control (PRC) and contributing to frequency regulation. The cascaded H-bridge (CHB) converter is a suitable choice for large-scale photovoltaic systems. This paper introduces a distributed PRC strategy designed for CHB-based PV systems, necessitating minimal inter-module communication and thus simplifying implementation. Each submodule (SM) within the CHB converter periodically engages in maximum power point tracking to assess the system’s total accessible PV power. Through coordinated control, the strategy evenly allocates the necessary power across sub-modules based on their PV power availability, offering a balanced power distribution while acknowledging operational constraints on power disparity among SMs. Simulation and experimental results confirm the efficiency of the proposed approach under various conditions, showcasing accurate PV power estimation, seamless transition between operating modes, fast dynamic response, and regulation of the dc-link voltages. © 2013 IEEE.
Niroomand, M. ,
Kardehi moghaddam, R. ,
Modares, H. ,
Naghibi sistani, M. JVC/Journal of Vibration and Control (10775463)
This paper presents a fixed-time optimal control design approach using reinforcement learning (RL) that guarantees not only fixed-time convergence of the learning algorithm to an optimal controller but also fixed-time stability of the learned control solution. To ensure the former, zero-finding capabilities of the zeroing neural networks (ZNNs) are leveraged, and novel adaptive laws are presented accordingly. To ensure the latter, conditions on the cost function are provided for which its corresponding optimal controller assures the fixed-time stability of the closed-loop system. It is also shown that imposing a fixed-time stability constraint on the infinite-horizon optimal control solution actually solves the classical fixed-final-time (FFTM) finite-horizon optimal control problem. The Hamilton–Jacobi–Bellman (HJB) equation for the FFTM optimal control problem is time-varying, which makes it hard or even impossible to learn it directly online using RL. The presented approach bypasses this difficulty by developing an online solution for infinite-horizon optimal control problems under fixed-time stability constraints and with fixed-time convergent tuning laws. This approach makes learning and closed-loop system settling times predictable, tunable, and bounded. Simulation results for fixed-time optimal adaptive stabilization of a torsional pendulum system clarify this new design for nonlinear optimal control theory. © The Author(s) 2024.
Niroomand, M. ,
Kardehi moghaddam, R. ,
Modares, H. ,
Naghibi sistani, M. International Journal of Intelligent Systems (1098111X) 2024
This paper introduces an inclusive class of fixed-time stable continuous-time gradient flows (GFs). This class of GFs is then leveraged to learn optimal control solutions for nonlinear systems in fixed time. It is shown that the presented GF guarantees convergence within a fixed time from any initial condition to the exact minimum of functions that satisfy the Polyak-Łojasiewicz (PL) inequality. The presented fixed-time GF is then utilized to design fixed-time optimal adaptive control algorithms. To this end, a fixed-time reinforcement learning (RL) algorithm is developed on the basis of a single network adaptive critic (SNAC) to learn the solution to an infinite-horizon optimal control problem in a fixed-time convergent, online, adaptive, and forward-in-time manner. It is shown that the PL inequality in the presented RL algorithm amounts to a mild inequality condition on a few collected samples. This condition is much weaker than the standard persistence of excitation (PE) and finite duration PE that relies on a rank condition of a dataset. This is crucial for learning-enabled control systems as control systems can commit to learning an optimal controller from the beginning, in sharp contrast to existing results that rely on the PE and rank condition, and can only commit to learning after rich data samples are collected. Simulation results are provided to validate the performance and efficacy of the presented fixed-time RL algorithm. © 2024 Mahdi Niroomand et al.
IET Generation, Transmission and Distribution (17518687) 18(19)pp. 3097-3107
The increasing penetration of the distributed energy resources (DER) in the power grid, which, while having significant advantages, also pose significant challenges. The behaviors of DERs differ from those of synchronous generators, particularly in abnormal conditions. For this reason, the power grid enforces grid codes to ensure that DERs perform properly in different conditions. For instance, short circuit faults and unbalanced grid voltage are severe transient events that inverters need to be able to pass through without disconnecting from the grid. Furthermore, the inverters are required to support the grid voltage by regulating the active and reactive power injections. This article proposes a voltage support control scheme to support grid voltage during asymmetrical voltage drop by utilizing an optimization problem. In this optimization problem, the active and reactive powers injected into the grid will be obtained optimally by considering constraints such as instantaneous active and reactive power oscillation magnitudes and peak current limitation. To aid in this purpose, the corresponding mathematical formulations such as instantaneous active and reactive power oscillation magnitudes will be obtained by using the currents and voltages in stationary reference frame. The proposed scheme will be verified by simulating it in MATLAB/Simulink under three different scenarios and tested on a real-time experimental Opal-RT platform. © 2024 The Author(s). IET Generation, Transmission & Distribution published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.
This paper presents a quadratic high step-up DCDC converter incorporating a coupled inductor (CI), a passive clamp circuit and a voltage multiplier cell (VMC). This converter operates based on parallel charging of capacitors by CI and series discharging of this energy at the output. Moreover, the converter includes a diode-capacitor clamp circuit to decrease the voltage stress on the active switch and the output diode. As a result, this converter has high voltage gain (VG) and low voltage stress on switches, which is appropriate to increase the output voltage in photovoltaic panels. Since the proposed converter reduces voltage stress on the active switch, a switch with low resistance is utilized, which is improving power efficiency. The presented converter is analyzed in continuous conduction mode (CCM), discontinuous conduction mode (DCM) and steady-state. The experimental results relevant to the presented converter is verified with a 300V-90W prototype. © 2024 IEEE.
IET Generation, Transmission and Distribution (17518687) 17(13)pp. 3058-3069
This research proposes a cost-efficient microinverter. The proposed microinverter can eliminate the leakage current using common-ground configuration. It uses three switches and only one of them operates at high frequency. In addition, a passive lossless snubber is applied to limit voltage stress and provide soft-switching performance for the high-frequency switch. A pair of coupled inductors is used to provide higher voltage gain which makes it possible to keep the operating duty cycle in the normal range and makes the proposed inverter suitable for AC module application. The input current of the proposed microinverter is continuous which reduces the loss of the input capacitor by high-frequency current component reduction. The operating principle of the proposed inverter is described in both positive and negative current modes. In positive current mode, the proposed microinverter works similar to SEPIC converter and in negative current mode its performance is similar to CUK converter. The dynamic behavior of the proposed microinverter is analyzed through simulation and a simple PI controller is designed to accommodate the worst case. Theoretical loss analysis is applied and finally the results of this research are compared with other researches. The performance of the proposed inverter is justified by simulation and practical results of a 300-watts prototype. © 2023 The Authors. IET Generation, Transmission & Distribution published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.
International Journal of Energy Research (1099114X) 2023
This paper proposes a perturb and observe (P&O) maximum power point tracking (MPPT) algorithm for photovoltaic (PV) systems. P&O is a simple technique that comes with serious problems, steady-state oscillation, and deviation from the maximum power point (MPP). This algorithm uses variable step size to decrease the convergence time, and it uses the average value of the last three duty cycle to find MPP fast and accurately. In addition, the probability of deviation has been reduced using the direction of the current when the irradiance changes. The irradiance change identifier, steady-state determiner, duty cycle selector, step size alternator, and boundary condition imposer are the extramodules attached to the structure of the original P&O algorithm to change the step size. This algorithm has been tested along with different types of P&O and INC algorithms in MATLAB software and practical experiments using a boost switching converter. The irradiance pattern used in the simulation includes step and slop, increasing and decreasing patterns, and the proposed algorithm obtained an overall efficiency of 98.54%. © 2023 Ali Saberi et al.
IEEE Transactions on Circuits and Systems (15498328) 70(9)pp. 3806-3817
Wireless power transfer (WPT) systems' efficiency is significantly impacted by non-monotonic variations in the coupling coefficient. For very short distances or strong-coupling cases, the WPT efficiency is minimal at the natural resonant frequency, with two peaks around this frequency, known as the frequency splitting phenomenon. On the other hand, WPT capability decreases for long distances or weak coupling cases. Therefore, adaptive matching is required for WPT systems with varying distances, like wireless charging systems for electric vehicles (EVs). This paper first presents a detailed analysis of the frequency splitting phenomenon by studying the root locations of the WPT system's transfer function. Then, a real-time fixed-frequency adaptive impedance matching (IM) method is proposed, in which the amplitude and phase of the input impedance is estimated using the average active power, the average reactive power, and the amplitude of input voltage. Unlike traditional search-and-find techniques, the proposed method calculates the optimal IM network parameters only in a single iteration, which improves the convergent speed. A scaled-down 20-Watt prototype controlled by the TMSF2812 is fabricated and used to validate the effectiveness of the proposed method over a wide range of coil-to-coil distances. © 2004-2012 IEEE.
IEEE Journal of Photovoltaics (21563381) 12(2)pp. 557-564
Photovoltaic (PV) power fluctuations, caused by fast irradiance changes, because of passing clouds, may pose challenges to the stability and reliability of power systems with high penetration of PV inverters. In this regard, new standards impose power ramp rate control (PRRC) on grid-connected PV systems. Available solutions in the literature lack the capability of fast measurement for power ramp rate and fast dynamics under rapid irradiance changes. This article proposes an adaptive flexible power point tracking-based PRRC strategy to obtain fast dynamics. The proposed algorithm in this article performs an additional measurement in the middle of each computation step to detect rapid irradiance changes and subsequently to measure the power ramp rate quickly. Afterward, the voltage step undergoes adaptive calculations to constrain the power ramp rate to the predefined value. Comparison between simulations of the proposed strategy and conventional solutions reveals the superiority of the proposed algorithm for limiting the ramp rate under the influence of rapid irradiance changes. The results gained on experimental grounds on a 2.5-kW PV system are provided to validate the performance of the proposed PRRC algorithm under various operating conditions. © 2011-2012 IEEE.
Mathematical Problems In Engineering (1024123X) 2021
Selective harmonic elimination pulse-width modulation (SHEPWM) is a widely adopted method to eliminate harmonics in multilevel inverters, yet solving harmonic amplitude equations is both time consuming and not accurate. This method is applied here for a 7-level cascaded multilevel inverter (CMLI) with erroneous DC sources. To meet the seven harmonic amplitude equations, two notches are applied with the use of higher switching frequency than nominal. These notches can be placed in six different positions in the voltage wave, and each was assessed in a separate manner. In order to solve the equations, a hybrid algorithm composed of genetic algorithm (GA) and Newton-Raphson (N-R) algorithm is applied to achieve faster convergence and maintain the accuracy of stochastic methods. At each step of the modulation index (M), different positions for the notches are compared based on the distortion factor (DF2%) benchmark, and the position with lowest DF2% is selected to train an artificial neural fuzzy interface system (ANFIS). ANFIS will receive the DC sources' voltages together with required M and will produce one output; thus, eight ANFISs are applied to produce seven firing angles, and the remaining one is to determine which one of the notches' positions should be used. Software simulations and experimental results confirm the validity of this proposed method. The proposed method achieves THD 8.45% when M is equal to 0.8 and is capable of effectively eliminating all harmonics up to the 19th order. © 2021 Seyed Yahya Nikouei et al.
IET Renewable Power Generation (17521416) 15(13)pp. 2931-2943
This paper proposes a frequency-control scheme for Doubly Fed Induction Generator (DFIG)-based (Type-3) wind turbines to improve the primary-frequency-control when the grid power balance is disturbed. The increasing penetration level of renewable energy sources, like wind power plants, reduces the total available inertia of modern grids, which deteriorate the frequency response in case of sudden power-mismatches. The proposed closed-loop participation of wind power plant interacts with the thermal units to reduce the frequency nadir and frequency settling-time, during the inertial and primary stages. The designed disturbance observer decreases the uncertainties in the estimation of grid parameters, which results in robust PI performance in adjusting the ancillary power provided by wind turbines. Certain measures considered within the control loop to limit the rate-of-change-of-frequency within the permissive range to avoid the protective relays tripping. Comparative simulations studies on modified IEEE 9-bus and 68-bus test systems verify the effectiveness and advantages of the proposed method. © 2021 The Authors. IET Renewable Power Generation published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology
Photovoltaic (PV) systems have emerged as one of the most widely used source of renewable and clean energy and have the aptitude to provide a considerable contribution to electricity generation in the future. One major area of interest which has dominated the field for many years concerns controlling grid-connected PV systems, in which specific primary requirements such as maximum power point tracking (MPPT) under both uniform or non-uniform solar radiation figures and injecting high-quality currents in terms of a low total harmonic distortion (THD) must be met. From this perspective, the control system for grid-connected PV systems has two cascaded loops, including outer and inner loops. While the former is the power /voltage control loop and responsible for producing the current references for the inner loop, the latter is the current control loop and in charge of regulating the injected currents. Increasing the penetration of PV systems into the grid has caused adverse effects on the whole distribution network. These undesirable effects, which are actually led by the fluctuating nature of the power generated by the PV systems, undoubtedly further complicate the efficient performance of the electricity grid and have major implications on the accessibility, reliability, and quality of the distribution network to which the PV system is connected. One solution to rectify these problems and provide reliable and efficient power generation is to continuously upgrade grid integration guidelines corresponded to momentous customers’ demands, but it gives rise to more issues for the PV intermediate inverters. Afterwards, advisable for the majority of PV systems is to present multiple operations. Consequently, new generation of multi-purpose PV inverter systems involve more developed and smart control policies to meet enhanced controllability. In the matter, low voltage ride-through (LVRT) capability, compensating reactive power, improving power quality, frequency control using active power curtailment, flexible control of active power (e.g., the P restrictions), and reliability-focused thermal control are of ancillary and intelligent services deemed to provide the new generation of PV systems with a substantial degree of control flexibility. Meanwhile, controlling the PV interfaced inverters is the major part to which intelligent control functions for grid-connected PV systems are applied. Altogether, the chief to further reduce the total cost of an efficient and reliable PV system is of those control functions applied to the future PV inverters, giving rise to higher penetration level of cost-efficient PV systems into the electricity grid. Fundamental and up-to-date control functions implemented in the grid-tied PV systems have been discussed in this chapter. © 2021 by Nova Science Publishers, Inc.
Over the past decade, photovoltaic (PV) sources have experienced an average annual growth of 60%, and electricity generation using PV sources outstrips one-third of those by the entire installed wind-generation capacity, and has incremented by a factor of 483, within a period of less than 30 years, from 1.2 GW in 1992 to 580 GW in 2019. Rooftops-mounted solar PV systems as well as PV farms alongside the roads in the suburbs are from objective evidence of the increase in the installed PV capacity. Indeed, descending and ascending trends in cost and efficiency of PV panels, respectively are the driving force that turn PV energy into the primary source of energy worldwide. In addition, raising environmental consciousness, seeking fossil fuels free energy supply, and popular political rules or regulations issued by local governments such as increasing funding for renewable energy sources by creating feed-in tariffs, are among other factors affecting the installed PV capacity. To achieve cost-effective PV systems with the highest possible power conversion efficiency, maximum power density as well as system reliability, conventional single-stage grid-connected DC-AC power converters are replaced by advanced and therefore further complicated power converter topologies. A comprehensive review on present PV energy conversion systems, including the system structure of various types of PV plants as well as circuit configuration of PV converter topologies applicable for gridtied PV systems is presented in this chapter. © 2021 by Nova Science Publishers, Inc.
IET Renewable Power Generation (17521416) 15(7)pp. 1469-1482
The new generation of photovoltaic (PV) systems represents higher sustainability during grid faults thanks to increased ancillary services, such as low voltage ride-through (LVRT) capability used when the PV system is subjected to voltage sag. Unlike previously presented strategies that just dealt with voltage sag problem under uniform radiation conditions, in this study, a new control strategy implementing LVRT capability during low-voltage faults under partial shading conditions is proposed. First, radiation levels are estimated by using the least-squares curve fitting (LSCF) algorithm. Second, the voltage/current of maximum power points (MPPs) and minimum power points are calculated. Also, the corresponding algebraic function for the (Power - Voltage) P-V curve is extracted using only PV voltage and power vectors. Finally, under partial shading conditions, the moving operating point to the right side of MPP is well-achieved through a power proportional-integral controller. To validate the effectiveness of the proposed control strategy, simulations and experiments are conducted on PV systems. The simulation and experimental results and the comparison made between this algorithm's performance and other methods confirm that the proposed algorithm outperforms other methods in terms of high accuracy, fast dynamic and low oscillations in different partial shading conditions and with different radiations. © 2021 The Authors. IET Renewable Power Generation published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology
Journal of Modern Power Systems and Clean Energy (21965420) 9(2)pp. 225-236
To obtain efficient photovoltaic (PV) systems, optimum maximum power point tracking (MPPT) algorithms are inevitable. The efficiency of MPPT algorithms depends on two MPPT parameters, i. e., perturbation amplitude and perturbation period. The optimization of MPPT algorithms affect both the tracking speed and steady-state oscillation. In this paper, optimization methods of MPPT parameters are reviewed and classified into fixed and variable methods. The fixed MPPT parameters are constant during MPPT performance, and a trade-off should be made between the tracking speed and steady-state oscillation. However, the variable MPPT parameters will be changed to improve both the tracking speed and the steady-state oscillations. Moreover, some of them are simulated, compared, and discussed to evaluate the real contributions of the optimization methods to the MPPT efficiency. Furthermore, significant features of the optimization methods, i.e., noise immunity, robustness, and computation effort, are investigated. © 2013 State Grid Electric Power Research Institute.
International Journal Of Photoenergy (1110662X) 2021
Under partial shading conditions, photovoltaic (PV) arrays are subjected to different irradiance levels caused by nonuniform shading. As a result, a mismatch between the modules, a reduction in the power generated, and the hotspot phenomenon will be observed. One method to reduce mismatch losses is to reconfigure the total-cross-tied (TCT) array in dynamic and static forms, where improved performance can be achieved through more efficient shading distribution thanks to increased dimensions. However, the increase in dimensions leads to the complexity of wiring and installation in static reconfiguration and the large number of switches and sensors required in dynamic reconfiguration. To rectify these problems, a two-step method is proposed in this paper. In the first step, the modules inside the PV array are divided into subarrays with wiring in static reconfiguration, rather than being wired as large-scale PV arrays. In the second step, an algorithm is developed for dynamic reconfiguration. The introduced algorithm searches for all possible connections and finally identifies the most optimal solution. As an advantage, this algorithm employs only the short-circuit current values of the subarray rows, which reduces the number of switches and sensors required in comparison to dynamic reconfiguration. Under 8 different partial shading patterns, simulations are conducted and results confirm that the proposed method outperforms the TCT array and statically modified TCT array in terms of power and mismatch losses. Among these, the highest power improvement is obtained with regard to the TCT array and statically modified TCT array under the fourth and eighth shading patterns, respectively. © 2021 Mohamad Hossien Nahidan et al.
Mathematical Problems In Engineering (1024123X) 2020
Photovoltaic systems have a nonlinear characteristic in which there is one optimum operating point called Maximum Power Point (MPP). However, when PV panels are partially shaded by surrounding objects, there are several MPPs, of which one of them is Global MPP (GMPP). Therefore, conventional Maximum Power Point Tracking (MPPT) algorithms get trapped into local MPPs. As a result, a multitude of Global MPPT (GMPPT) algorithms have been proposed. An outstanding GMPPT algorithm as well as the fast-tracking speed should find GMPP in complicated shading patterns where not only there are lots of MPPs, but also the peaks are close together. Therefore, in this paper, a novel GMPPT based on firework algorithm is proposed which is able to find GMPP in complicated shading patterns with fast tracking speed. Moreover, the firework is combined with Perturb-and-Observe (P&O) algorithm to reduce the computational effort in a way that the firework is only used to recognize GMPP; afterwards, P&O algorithm completes the tracking. Furthermore, the variable sampling time technique, based on the system settling time, speeds up the tracking process considerably. Finally, the proposed method is compared with previous works, simulated, and implemented on an experimental setup to prove its superiority. © 2020 N. Khalessi et al.
IEEE Journal of Emerging and Selected Topics in Power Electronics (21686785) 8(2)pp. 1584-1592
In this paper, a new topology to achieve ultrahigh step-up voltage conversion ratio and very low input current ripple is introduced for nonisolated high-power applications by using interleaved structure combined with coupled inductors (CIs) and switched capacitors. Using voltage lift capacitors in this topology not only recycles the energy related to leakage inductance of CIs and alleviates the voltage spike across the power switches but also increases the voltage gain of the converter. Moreover, utilizing CI structure provides zero-current switching (ZCS) turn-on condition for power switches and reducing the diodes reverses recovery losses and also improves the voltage gain of the converter. Using the interleaved structure in the low-voltage side noticeably decreases the input current ripple and current stress through magnetic elements. In addition, utilizing the voltage multiplier cell structure in the high-voltage side provides a high-voltage gain. The voltage stress across the power switches is considerably lower than the output voltage. Hence, the low-voltage-rated switches can be employed. Based on the mentioned advantages, the efficiency of this implementation is improved significantly. Finally, to validate the performance of the proposed converter, a 600-W, 24-V/520-V prototype circuit is implemented. © 2013 IEEE.
IET Microwaves, Antennas and Propagation (17518725) 14(1)pp. 36-44
Wireless charging is widely considered as a safe and reliable way for powering biomedical implants, as it avoids problems like surgical infection. Wireless power transfer (WPT) systems are desired to work efficiently against variations in coil–coil distance or output load. On the other hand, to maintain the maximum overall efficiency of the WPT system, the high frequency (HF) power amplifier, used to feed WPT system, must operate at optimal zero-voltage switching (ZVS) condition. In this paper, an automated dual-objective control strategy adaptive to variations in coil–coil distance or output load is proposed which ensures both targets of tracking maximum power point and operating at optimal ZVS condition by adjusting operating frequency and duty-cycle of switching voltage of HF power amplifier, respectively; that is while there have been few studies which have addressed both the two targets. To evaluate the effectiveness of the proposed strategy, a PCB prototype, operating at 800 kHz, is fabricated. Experimental results, demonstrating the proposed strategy increases transferred power from 23 mW to about 45 mW, are in good agreement with theoretical predictions. Additionally, while implanting the receiver coil in a real biological tissue, experiments show only 2% of degradation in power transfer efficiency as well as no frequency shift. © The Institution of Engineering and Technology 2019.
IEEE Journal of Emerging and Selected Topics in Power Electronics (21686785) 8(3)pp. 2747-2758
In this paper, a new nonisolated interleaved boost topology with ultralarge step voltage ratio based on coupled inductors (CIs) and switched capacitors is proposed. CI applied in the low voltage side along with the interleaved structure and utilizing new topology provide ripple cancelation and considerably reduce the input current ripple and current stress through power switches and magnetic elements. In addition, utilizing CIs in the high voltage side provides a high-voltage gain with an appropriate duty ratio. Voltage lift capacitors used in this structure not only alleviate the voltage spikes across the power switches but also increase the voltage gain. Zero current switching (ZCS) turn-on condition for switches and ZCS turn-off condition for diodes are achieved by employing CIs without any auxiliary circuit. This feature degrades the reverse recovery losses and improves the efficiency of the converter. The voltage stress of the power switches is noticeably lower than the output voltage, especially at high output voltages. Therefore, the low-voltage rated switches can be adopted. This topology provides autocurrent sharing without any controller. Finally, a 600-W, 24-V/480-V laboratory prototype has been built to verify the performance. © 2013 IEEE.
IET Power Electronics (17554543) 12(6)pp. 1510-1520
In this study, a new non-isolated interleaved bidirectional DC–DC converter with a high step voltage ratio based on coupled inductors (CIs) is introduced. The CIs significantly increase the voltage conversion ratio and provide soft-switching conditions for the switches at turn-on instant. Also, employing an interleaved structure combined with the CI in the low-voltage side noticeably reduces the current ripple and this feature has a vital role in the high-power applications. Also, this topology provides auto-current sharing for the two phases of the interleaved structure. The CIs in the high-voltage side, supply a steep gain in both buck and boost modes with an appropriate duty cycle. The proposed method provides zero current switching (ZCS) turn-off condition for all diodes and ZCS turn-on condition for all switches without requiring any auxiliary circuit. So the undesirable reverse recovery effects of diodes are considerably reduced. The proposed converter has the minimum number of switches for two-phase bidirectional structures. Also, a simple passive clamp circuit is proposed for the converter to limit the voltage spikes of CIs. Finally, a 600 W, 30/300 V laboratory prototype is implemented to verify the performance. © The Institution of Engineering and Technology 2019.
IEEE Transactions on Sustainable Energy (19493029) 10(4)pp. 2114-2122
Maximum power point tracking (MPPT) algorithms continuously change duty cycle of a power converter to extract maximum power from photovoltaic panels. In all of MPPT methods, two parameters, i.e., perturbation period (T{p}) and amplitude Δ D, have a great effect on speed and accuracy of MPPT. Optimum value of the perturbation period is equal to the system settling time, which is the system model-dependent parameter. Since the system model varies according to the change of irradiance level and temperature, the value of Tp has to be determined online. In this paper, the parametric identification method is adopted to identify the online value of Tp. The proposed method is based on the dichotomous coordinate descent-recursive least squares algorithm and uses an infinite impulse response adaptive filter as the system model. Computation of this algorithm is based on an efficient, fixed-point, and iterative approach with no explicit division operations; these features are highly suitable for online applications. As a result, the proposed method compared to previous works leads to more accurate and faster identification of the system settling time. To test and validate the proposed method, it has been simulated and implemented to be further validated with experimental data. © 2010-2012 IEEE.
Journal of Power Electronics (15982092) 18(1)pp. 11-22
This paper presents a single switch, high step-up, non-isolated dc-dc converter suitable for renewable energy applications. The proposed converter is composed of a coupled inductor, a passive clamp circuit, a switched capacitor and voltage lift circuits. The passive clamp recovers the leakage inductance energy of the coupled inductor and limits the voltage spike on the switch. The configuration of the passive clamp and switched capacitor circuit increases the voltage gain. A wide continuous conduction mode (CCM) operation range, a low turn ratio for the coupled inductor, low voltage stress on the switch, switch turn on under almost zero current switching (ZCS), low voltage stress on the diodes, leakage inductance energy recovery, high efficiency and a high voltage gain without a large duty cycle are the benefits of this converter. The steady state operation of the converter in the continuous conduction mode (CCM) and discontinuous conduction mode (DCM) is discussed and analyzed. A 200W prototype converter with a 28V input and a 380V output voltage is implemented and tested to verify the theoretical analysis. © 2018 KIPE.
IEEE Journal of Photovoltaics (21563381) 8(3)pp. 825-833
With the increasing deployment of photovoltaic (PV) sources in the power grid and their contribution to power generation, it is imperative to obtain accurate models for the reliability and stability of these plants. In this paper, a novel method is proposed for reliability assessment for the different structures involved in the implementation of PV plants, in which the failure rate of system components is calculated using the FIDES Guide standard, taking into account environmental conditions such as radiation curves, temperature, and humidity. Failure rates of the insulated gate bipolar transistor and converter capacitor were found to be greater than other components. After precise calculation of failure and repair rates, the probability of functioning in three states of full generation, partial failure, and down was obtained through Monte Carlo simulations. Considering the effect of the system's structure on its stability, the reliability of the system can be increased by adding inverter paths to its structure. Several such structures are proposed, and the most economical design is identified by analyzing load duration curves to obtain the energy loss in each configuration. The proposed algorithm was implemented in Isfahan University's 20 kW PV power plant. Simulations demonstrate the efficiency of the proposed algorithm in design and evaluation of economic system structures. © 2011-2012 IEEE.
IET Power Electronics (17554543) 11(13)pp. 2151-2160
A new non-isolated high-voltage gain three-port converter for standalone photovoltaic systems is proposed. The magnetic element of this converter is only one coupled inductor. The primary winding of the coupled inductor is shared between battery charger circuit and main converter. Leakage inductance energy of the coupled inductor is either transferred to battery or is regenerated via the passive-clamp circuit. Using switched capacitor and voltage lift techniques, the voltage gain is significantly increased for both low-voltage ports. Single magnetic element, high-voltage gain with reasonable duty cycle, lowvoltage stress on the switches, low winding turn ratio of coupled inductor and high efficiency are the merits of this converter. The operation principles and the steady-state analysis are described for the three modes of: single-input single-output, single-input dual-output and dual-input single-output. To verify the theoretical analysis, a laboratory prototype with 28 V input, 48 V battery voltage and 380 V output voltage is implemented and tested. © The Institution of Engineering and Technology 2018.
In photovoltaic (PV) systems, maximum power point tracking (MPPT) techniques are used in order to extract the maximum power from PV panels. So far, different MPPT methods have been presented. In all of these methods, two MPPT parameters, perturbation amplitude (Delta mathbf{D}) and perturbation period (T-{p}), have a great effect on the MPPT efficiency. In this paper, first, the dynamic behavior of PV systems are assessed in both steady and transient states with the use of the small signal model and the simulation. The PV operating point has different behavior in the steady and transient states; therefore, in the proposed method, first, a state of the system is identified. Afterwards based on characteristics of each state which are assessed in the dynamic behavior of the PV system, the MPPT parameters are optimized. Delta mathbf{D} is variable and based on the slope of the P-V curve with two different scaling factors; furthermore, the linear and exponential functions are used to determine the variable T-{p} based on an operating state. In order to prove the superiority of the proposed method over the existing methods, the simulations are done in MATLAB/Simulink and PSIM software, and also comparison is conducted between the proposed method and the previous works. © 2018 IEEE.
Journal of Solar Energy Engineering (15288986) 139(5)
This paper proposes a new method based on a Markov model to calculate the reliability of grid-connected photovoltaic (PV) systems. This system is a grid-connected PV system consisting of PV modules, a multiphase DC-DC converter, an inverter, an inverter controller, and an maximum power point tracking (MPPT) controller at University of Isfahan. This system is considered repairable. Also, different levels of operation are considered for the system equipment. Reliability of the PV modules, the multiphase DC-DC converter, and the inverter has been calculated by the Markov model. Finally, the reliability of the entire PV system is calculated by the Markov model. The proposed algorithm is applied to the PV system positioned at University of Isfahan. Simulation results show the applicability of this method for calculating the reliability of grid-connected PV systems. Copyright © 2017 by ASME.
Electric Power Components and Systems (15325016) 45(1)pp. 22-33
In this paper, a high-performance control structure is designed, implemented, and applied to a three-phase series–parallel uninterruptible power supply (UPS). This kind of UPS system provides input power factor correction, output voltage conditioning, and high efficiency. The control strategy proposed in this paper is based on voltage control of the parallel converter and current control of the series converter. It is shown that this strategy improves the system operation, specifically resulting in a smoother and more seamless transition between UPS operating modes. The controller in the proposed strategy is based on combination of two control methods with different characteristics and is therefore called a hybrid structure. To enhance the steady-state performance of the UPS and reach fast error convergence, a repetitive controller is used. In addition, to reach a fast transient response required for control of output voltage, a fast deadbeat is used. The stability of this hybrid controller is discussed, and the design procedure for a typical converter is given. For validation and verification of the theoretical analysis, both experimental and simulation results are shown. © 2017, Copyright © Taylor & Francis Group, LLC.
IET Generation, Transmission and Distribution (17518687) 11(8)pp. 2138-2145
In this study, a high-performance controller is proposed for single-phase grid-tied energy storage systems (ESSs). To control power factor and current harmonics and manage time-shifting of energy, the ESS is required to have low steady-state error and fast transient response. It is well known that fast controllers often lack the required steady-state accuracy and trade-off is inevitable. A hybrid control system is therefore presented that combines a simple yet fast proportional derivative controller with a repetitive controller which is a type of learning controller with small steady-state error, suitable for applications with periodic grid current harmonic waveforms. This results in an improved system with distortion-free, high power factor grid current. The proposed controller model is developed and design parameters are presented. The stability analysis for the proposed system is provided and the theoretical analysis is verified through stability, transient and steady-state simulations. © The Institution of Engineering and Technology 2017.
In this paper, the frequency splitting phenomenon is precisely investigated based on the concept of the maximum power transfer theorem for a two-coil wireless power transfer (WPT) system. Here, unlike the previous studies, in which the analysis were performed by the reflected impedance, the scrutiny is conducted based on the thevenin equivalent impedance. First, the cause of the frequency splitting phenomenon is described using the frequency characteristics of the thevenin impedance and the load power. Second, the splitting equation is derived and the splitting frequencies are calculated through it. Eventually, some methods, that have been used so far to improve the power transfer capability, in the presence of the frequency splitting phenomenon, are mentioned. In addition, using simulation results by MATLAB software, these methods are compared together and the best method is obtained. © 2017 IEEE.
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 Applied Research and Technology (16656423) 14(4)pp. 259-267
In this paper, a rotary electromagnetic microgenerator is analyzed, designed and built. This microgenerator can convert human motions to electrical energy. The small size and use of a pendulum mechanism without gear are two main characteristics of the designed microgenerator. The generator can detect small vibrations and produce electrical energy. The performance of this microgenerator is evaluated by being installed peak-to-peak during normal walking. Also, the maximum harvested electrical energy during normal walking is around 416.6 μW. This power is sufficient for many applications. © 2016 Universidad Nacional Autónoma de México, Centro de Ciencias Aplicadas y Desarrollo Tecnológico
International Journal Of Renewable Energy Research (13090127) 6(4)pp. 1296-1306
The operation of an on-grid, 20 KW, PV, pilot plant is analysed. The instantaneous environmental variables and weather conditions including solar irradiance, temperature, wind speed, and clouds are recorded and analysed, simultaneously along with plant responses including PV module temperature, generated power, current, and voltage. The power decreases with increasing ambient temperature. Increasing solar irradiance increases the temperature difference between modules and ambient. Instantaneous energy and exergy efficiencies during three different days, representing sunny, partly cloudy, and cloudy days, are further calculated. The energy efficiency varies between 5.76% and 15.53%, while that of exergy varies between 4.84% and 15.73%. For cloudy days, the exergy efficiency is higher than that of energy, while for a sunny day it is in reverse. Another important parameter affecting the generated power is partial shading on PV modules, particularly during early mornings and late afternoons. The shading changes from 3% to 9%, because of small azimuth and elevation angles. It was found that partial shading of 4.73% on PV modules may result a significant power decrease of 52.3%. A new algorithm based on Fuzzy Logic is proposed to overcome these power decreases under partial shading.
Journal of Renewable and Sustainable Energy (19417012) 7(5)
Due to the growing use of photovoltaic (PV) systems in recent years, the reliability of these systems as one of the most important issues regarding durability and correct performance is important. This paper presents a comprehensive assessment of the reliability of Residential PV System (RPVS) in various conditions based on the Markov model. The systems taken into considerations consist of PV modules, a DC-DC converter, an inverter, an inverter controller, and a maximum power point tracking (MPPT) controller. These systems are considered repairable. To evaluate the effect of the three-phase boost converter and the PV modules on reliability, these systems have been considered towards this specific perspective. Furthermore, the impact of various factors on the reliability of the system components and the entire system is evaluated. Simulation results demonstrate the capacity of the proposed method to assess and comparison of the reliability of different RPVS. Also, the results indicate the impact of various factors such as temperature on it. © 2015 AIP Publishing LLC.
Biomedical Research (India) (discontinued) (0970938X) 26(3)pp. 497-504
In this paper, a new wireless power transmission method is proposed to supply deep brain stimulators. By using a wireless charger, the surgery for replacing the stimulator’s batteries and all of its problems including infection, pain, and making patients uneasy, have been omitted. The Resonance inductive coupling (RIC) method is chosen among the different wireless power transmission methods and a resonance-based structure is designed. There are some simulations and practical experiments at the end of the paper which show this structure can generate 324 milliwatt power. Also, the efficiency of this system in 10mm distance is 41.62% © 2015 Scientific Publishers of India. 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.
Advances in Power Electronics (20901828) 2014
A hierarchical control structure is proposed for hybrid energy systems (HES) which consist of wind energy system (WES) and energy storage system (ESS). The proposed multilevel control structure consists of four blocks: reference generation and mode select, power balancing, control algorithms, and switching control blocks. A high performance power management strategy is used for the system. Also, the proposed system is analyzed as an active power filter (APF) with ability to control the voltage, to compensate the harmonics, and to deliver active power. The HES is designed with parallel DC coupled structure. Simulation results are shown for verification of the theoretical analysis. © 2014 Mehdi Niroomand and Dong-Jun Won.
Advances in Polymer Technology (07306679) 33(S1)
This paper addresses the preparation of polyaniline (PAni) and polypyrrole (PPy) nanostructures as humidity sensor elements. The semicrystalline microstructure and chemical structure of synthesized PAni and PPy were studied by X-ray diffraction and Fourier transform infrared spectroscopy, respectively. The morphology of these polymers was studied by scanning electron microscopy and transmission electron microscopy, indicating fibrillar and tubular nanostructures for PAni and PPy, respectively. The humidity sensing performances of sensors based on the prepared nanostructural PAni and PPy were investigated, and the sensing mechanisms of both systems have been discussed. The interesting reverse behaviors during humidity exposure of PAni- and PPy-based sensors in different water vapor concentrations have been comprehensively justified. The temperature dependency of the electrical conductivity for PAni and PPy samples was investigated. The UV-vis spectroscopy was used to study the effect of moisture on the electronic transport properties of PAni and PPy nanostructures. © 2014 Wiley Periodicals, Inc.
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.
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.
Journal of Electrical Engineering and Technology (19750102) 8(6)pp. 1487-1496
In this paper, a novel algorithm for PD localization in power transformers based on wavelet de-noising technique and energy criterion is proposed. Partial discharge is one of the main failures in power transformers. The localization of which could be very useful for maintenance systems. Acoustic signals due to a PD event are transient, irregular and non-repetitive. So wavelet transform is an efficient tool for this signal processing problem that gives a time-frequency demonstration. First, different wavelet based de-noising methods are analyzed. Then, a reasonable structure for threshold value determining and applying manner on signals is presented. Evaluated errors are good evidences for choices. Next, applying the elimination low energy frequency bands is discussed and developed as a de-noising method. Time differences between signals are used for PD localization. Different ways in time arrival detection are introduced and a novel approach in energy criterion method is presented. At the end, the quality of algorithm is verified through the different assays in lab.
This paper is concerned with the current control of grid connected inverters based on a simple frequency adaptive repetitive controller. A grid-tie inverter is desired to behave as a robust current source inverter with the high gain in order to improve both the reference current tracking and disturbance rejection capabilities. The variations of grid impedance and frequency in distribution networks are some important challenges in the design of grid interfaced converters. In this research, the performance of a frequency adaptive repetitive controller (RC), which is based on the internal model principle (IMP), is investigated for a single-phase grid connected inverter. © 2013 IEEE.
International Review on Modelling and Simulations (19749821) 5(3)pp. 1184-1188
A ZVS-ZCS PWM SEPIC for high step-Up applications is proposed in this paper. A couple of auxiliary switches work under soft switching conditions. By using this ZVS-ZCS converter topology, zero current turn-on and zero voltage turn-off of the main switch can be achieved. In addition, the auxiliary circuit enhances the energy density of the converter because of feeding the output and it can be matched easily to other kinds of converter & snubber circuits made by capacitor. The performance of the proposed converter is verified through computer-aided simulations and experimental results. © 2012 Praise Worthy Prize S.r.l.
Many conventional incremental conductance (INC) methods are used for maximum power point tracking (MPPT) of photovoltaic (PV) arrays. In these methods the step size determines the speed of MPPT. Fast tracking can be achieved with bigger increments but the system might not operate exactly at the MPP and may oscillate about it instead; so there is a tradeoff between the time needed to reach the MPP and the oscillation error. The main purpose of this paper is to present an adaptive step size in the INC to improve solar array performance. Conventional proportional integral (PI) controller is applied the MPP to the PV output voltage terminals; however, in this paper brain emotional learning based intelligent controller (BELBIC) is used as an adaptive step size in the INC. This controller decrease the oscillation error, so there will be a considerable increase in system accuracy. At the end, the effectiveness of the proposed method is verified by simulation results at different operating conditions and comparing them with simulation results of conventional method. © 2012 IEEE.
This paper presents design consideration and performance analysis of novel reduced parts on-line three-phase uninterruptible power supply (UPS) system. The proposed UPS system is based on reduced switch count dual bridge matrix converter. It employs only six power switches, results in reducing the cost of the system compared to conventional on-line UPS topologies, while achieving excellent performance. The performance of proposed system is evaluated through simulation in term of input/output waveforms quality and shows the viability of topology. © 2012 IEEE.
Advances in Power Electronics (20901828) 2012
This paper presents design consideration and performance analysis of novel reduced parts online three-phase uninterruptible power supply (UPS) system. The proposed UPS system is based on reduced switch count dual bridge matrix converter. It employs only six power switches and results in reducing the cost of the system compared to conventional online UPS topologies, while achieving excellent performance. The performance of the proposed system is evaluated through simulation in terms of input/output waveforms quality and shows the viability of topology. © 2012 Bahram Ashrafi and Mehdi Niroomand.
This paper is concerned with the control of three-phase Uninterruptible Power Supply (UPS) systems based on a B-spline Network (BSN). A UPS must be able to maintain regulated output voltage in the face of all line/load disturbances. To achieve this, the control system of a UPS must have a fast transient response and a low steady-state error. Fast controllers cannot always maintain the required steady-state accuracy. Therefore, in this paper, a hybrid control solution is proposed. In the proposed method, a fast yet simple controller based on deadbeat (DB) control law is used to achieve the fast transient response required for UPS output voltage control. A B-spline based controller is added to the deadbeat controller to improve steady-state performance of the UPS system. This results in distortion-free output voltage along with a fast error convergence. The system modeling and controller design for the proposed structure are presented in this paper. Simulations results are shown for verification of the theoretical analysis. © 2011 IEEE.
IET Power Electronics (17554543) 4(7)pp. 799-807
This study is concerned with the control of three-phase uninterruptible power supply (UPS) systems based on a hybrid controller. A UPS must be able to maintain regulated output voltage in the face of all line/load disturbances. In order to achieve this, the control system of a UPS must have a fast transient response and a low steady-state error. Fast controllers cannot always maintain the required steady-state accuracy. Therefore in this study, a hybrid control solution is proposed. In the proposed method, a fast, yet simple, controller based on deadbeat (DB) control law is used to achieve the fast transient response required for UPS output voltage control. Noting that non-linear loads that tend to distort UPS output voltage in steady-state have periodic waveforms in nature, a type of learning controller known as a repetitive controller is added to the DB controller to improve steady-state performance of the UPS system. This results in distortion-free output voltage along with a fast error convergence. The system modelling and controller design for the proposed structure are presented in this study. A brief stability analysis is given. Both simulations and experimental results are shown for verification of the theoretical analysis. © 2011 The Institution of Engineering and Technology.
This paper describes design considerations and performance analysis of a novel on-line singlephase to three-phase uninterruptible power supply (UPS) with reduced number of switches. The proposed topology uses only 5 active switches reducing the cost of the system compared to the traditional 10-switch topologies. The proposed UPS consists of a single-phase rectifier/charger, a two-leg/three-phase inverter connected to load, battery bank, DC link capacitor and an AC inductor. Detailed circuit operation and analysis as well as simulation results are also presented to verify its feasibility. © 2011 IEEE.
High performance UPS inverters have stringent control requirements both under steady-state and under transient conditions. Many different control techniques have been applied to UPS inverters. However, there are few publications reviewing the literature on these control techniques and classifying the same, particularly with regard to the recent developments in this area. In this paper, a review of the most solutions for control of UPS inverters is carried out. These control techniques are classified as conventional or classical control, predictive control, learning control and nonlinear control. The major advantages and disadvantages of these methods are highlighted and compared. Then, five control methods were compared using simulation and a hybrid controller (Repetitive Controller plus Deadbeat Controller) is evaluated by using experiments. © 2010 IEEE.
INTELEC, International Telecommunications Energy Conference (Proceedings) (02750473)
Transformers are a major capital item and the cost of a failure is high both in direct costs and downtime. For this reason they are monitored using a variety of methods. Partial discharges in power transformers are often a predecessor of a serious fault for this reason. Partial discharge measurements are an important diagnostic tool to monitor the insulation condition of a transformer. For on-line measurements, a detection method based on the acoustic signals emitted by the discharging source is used and can be detected. Moreover, the acoustic technique offers the possibility to locate and identify the PD source. This paper covers general aspects of acoustic methods for PD detection and localization in time, frequency and time-frequency domain.
International Review of Electrical Engineering (25332244) 4(1)pp. 14-21
In this paper, two control strategies for three-phase Series-Parallel Uninterruptible Power Supplies (SP-UPS) are described and compared. An SP-UPS consists of a parallel and a series converter, and most of the power required by load is supplied directly from ac input line during standby mode. Therefore, the overall efficiency is increased as compared to conventional UPS's. The first control strategy proposed for SP-UPS was based on voltage control of series converter and current control of parallel converter. However, recently an opposite strategy has been proposed, i.e., voltage control of parallel converter and current control of series converter. This paper compares these two control strategies. The comparison is made based on different performance criteria like seamless transition between backup and standby modes, dynamic performance, reference generation and the size of filters. Copyright © 2009 Praise Worthy Prize S.r.l. - All rights reserved.
In this paper, two control strategies for three-phase series-parallel uninterruptible power supplies are compared. A series-parallel UPS consists of a parallel and a series converter. In this topology, most power required by load is supplied directly from ac line during standby mode. Therefore the overall efficiency is higher than that of a conventional UPS. Traditionally, the control strategy of these structures was based on voltage control of series converter and current control of parallel converter. However, recently an opposite strategy has been proposed, i.e., voltage control of parallel converter and current control of series converter. This paper compares these two control strategies. The comparison is made based on different performance criteria like seamless transition between backup and standby modes, dynamic performance, complexity of reference generation and size of filters in two strategies.
This paper is concerned with high performance control of three-phase UPS system. The basic requirements of a UPS control system are mentioned. Different control techniques are classified and their performance is briefly described. A hybrid learning-adaptive controller is proposed based on the performance of existing methods. For the learning part, a Repetitive Controller (RC) is used and a Model Reference Adaptive Controller (MRAC) is selected for the adaptive part. The design of proposed RC-MRAC controller is presented and its performance is evaluated by using simulation and experiments.
Uninterruptible Power Supplies (UPS) play an important role in supplying critical loads. The majority of UPS systems employ batteries as a mean of energy storage. Since typical loads are supplied by ac voltage, an inverter is an indispensable part of a UPS to convert dc voltage to ac. Conventional control methods for single phase inverters suffers from many drawbacks like slow dynamic/transient response, oscillatory no-load behavior and distorted waveform in presence of non-linear loads. This paper in concerned with the control loop design for a single-phase voltage source inverter when employed in UPS applications. The regulation of the output voltage is done based on reference tracking to ensure good steady-state and dynamic performance. The control loop is designed taking into consideration the low damping during light loads. Three control strategies are proposed. The first is based on modified PID controller which demonstrated moderate performance and is suitable for low cost applications. The second method is based on an additional current control loop which has the benefit of inherent inverter protection. The last method is based on the theory of "Internal Model Controller" which gives nearly ideal steady-state regulation. Key points in implementing controllers with digital controllers are addressed. An experimental system is built to verify the validity of theoretical results.
