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Introduction. Recently, photovoltaic (PV) systems are increasingly favored for converting solar energy into electricity. PV power systems have successfully evolved from small, standalone installations to large-scale, grid-connected systems. When the nonlinear loads are connected to a grid-tied PV system, the power quality can deteriorate due to the active power supplied by the PV array, there’s a noticeable decline in the quality of power delivered to consumers. Its combination with the shunt active power filter (SAPF) enhances system efficiency. Consequently, this integrated system is adept at not only powering local loads but also at compensating for reactive power and filtering out harmonic currents from the main grid. The novelty of the work describes how an operation of a small scale PV system connected to the low voltage distribution system, and nonlinear load can be achieved, the investigation aims to analyze the system’s behavior and elucidate the advantages of employing various control algorithms. These proposed algorithms are designed to ensure a unity power factor for the utility grid while prioritizing high convergence speed and robustness against load power fluctuations across different levels of solar irradiation affecting the PV modules. The purpose of this work is to enhance the dynamic performance of the SAPF by cooperatively using a self-tuning filter (STF) based instantaneous active and reactive power method (PQ) with a novel predictive current control, enhance the system resilience, ensure optimal management of the total active power between the PV system, the electrical network and the non-linear load by integrating the functionalities of the SAPF under different levels of solar irradiation and maintain the DC-link capacitor voltage constant. Methods. A novel predictive current controller is designed to generate the switching signals piloted the three phase source voltage inverter, also a novel algorithm of instantaneous active and reactive power is developed, based on STF, to extract accurately the harmonic reference under non ideal grid voltage, also the perturb and observe algorithm is used to extract, under step change of solar irradiation, the maximum power point tracking of the PV module and the PI controller is used to maintain constant the DC-link capacitor voltage of the SAPF. Results. The efficacy of the proposed system is primarily centered on the grid side, and the performance evaluation of the control system is conducted using the STF based PQ algorithm and predictive current control. In addition, comprehensive testing encompasses all modes of operation, including scenarios involving distorted voltage sources, step changes in solar radiation, and variations in nonlinear loads. Results highlight superior performance in both transient and stable states, affirming the robustness and effectiveness of the proposed controllers. Practical value. The total harmonic distortion value of the grid current for all tests respects the IEEE Standard 519-1992. References 21, tables 7, figures 25.

Introduction. Recently, photovoltaic (PV) systems are increasingly favored for converting solar energy into electricity. PV power systems have successfully evolved from small, standalone installations to large-scale, grid-connected systems. When the nonlinear loads are connected to a grid-tied PV system, the power quality can deteriorate due to the active power supplied by the PV array, there’s a noticeable decline in the quality of power delivered to consumers. Its combination with the shunt active power filter (SAPF) enhances system efficiency. Consequently, this integrated system is adept at not only powering local loads but also at compensating for reactive power and filtering out harmonic currents from the main grid. The novelty of the work describes how an operation of a small scale PV system connected to the low voltage distribution system, and nonlinear load can be achieved, the investigation aims to analyze the system’s behavior and elucidate the advantages of employing various control algorithms. These proposed algorithms are designed to ensure a unity power factor for the utility grid while prioritizing high convergence speed and robustness against load power fluctuations across different levels of solar irradiation affecting the PV modules. The purpose of this work is to enhance the dynamic performance of the SAPF by cooperatively using a self-tuning filter (STF) based instantaneous active and reactive power method (PQ) with a novel predictive current control, enhance the system resilience, ensure optimal management of the total active power between the PV system, the electrical network and the non-linear load by integrating the functionalities of the SAPF under different levels of solar irradiation and maintain the DC-link capacitor voltage constant. Methods. A novel predictive current controller is designed to generate the switching signals piloted the three phase source voltage inverter, also a novel algorithm of instantaneous active and reactive power is developed, based on STF, to extract accurately the harmonic reference under non ideal grid voltage, also the perturb and observe algorithm is used to extract, under step change of solar irradiation, the maximum power point tracking of the PV module and the PI controller is used to maintain constant the DC-link capacitor voltage of the SAPF. Results. The efficacy of the proposed system is primarily centered on the grid side, and the performance evaluation of the control system is conducted using the STF based PQ algorithm and predictive current control. In addition, comprehensive testing encompasses all modes of operation, including scenarios involving distorted voltage sources, step changes in solar radiation, and variations in nonlinear loads. Results highlight superior performance in both transient and stable states, affirming the robustness and effectiveness of the proposed controllers. Practical value. The total harmonic distortion value of the grid current for all tests respects the IEEE Standard 519-1992. [ABSTRACT FROM AUTHOR]

A new controller based on a fractional-order synergetic controller (FOSC) is proposed for a three-level T-type inverter using a shunt active power filter (SAPF). The SAPF is designed to compensate for the reactive power and eliminate the current harmonics caused by non-linear loads, in cases of distorted or unbalanced source voltages. The proposed FOSC technique with the designed parameters and defined macro-variable is a robust control technique that operates well in both transient and steady-state scenarios, ensuring fast convergence and closed-loop system stability. The FOSC technique utilizes a phase-locked loop (PLL) technique on a self-tuning filter (STF) to enhance the SAPF's ability to compensate current harmonics and reactive power in all situations involving non-linear loads and source voltage variations according to IEEE Std. 519. The proposed control was implemented and verified using Matlab software, where the obtained results were compared with the results of the conventional control based on proportional-integral (PI) controllers in different operating conditions. The results indicate that the proposed FOSC technique outperformed the traditional control in terms of DC voltage tracking and the minimization of the total harmonic distortion of the current. [ABSTRACT FROM AUTHOR]

• An air-magnetic hybrid stiffness adjustable configuration is designed for large-scale instrument vibration isolation. • A novel feedforward active control strategy via an online self-tuning filter to minimize the model uncertainty loss. • The vertical and horizontal natural frequencies exhibit a remarkably ultra-low resonance of lower than 0.5 Hz. • Maximum vibration attenuation reaches 78 dB in the vertical and 70 dB in the horizontal with the proposed method. • Experiments verify the proposed vibration isolation system achieving superior transmissibility in the real world. This study aims to resolve the compromise between low suspension stiffness and high load-bearing capability in vibration isolation and enhance the suppression performance of ultra-low frequency vibration through advanced active feedforward control methods, featuring high-performance precision isolation for large-scale ultra-precision instruments. An air-magnetic hybrid parallel configuration of positive and negative stiffness is employed to achieve adjustable stiffness, endowing the vibration isolation system with quasi-zero stiffness characteristics. A novel self-tuning feedforward control strategy is proposed through a self-tuning filter to update the controller parameters online, minimizing the loss caused by model uncertainties. The vertical and horizontal natural frequencies of the system exhibit a remarkably low resonance frequency of lower than 0.5 Hz. With the self-tuning feedforward strategy, the maximum vibration attenuation reaches 78 dB in the vertical direction and 70 dB in the horizontal direction, reducing the cumulative power at 100 Hz by 61.4 % and 47.8 %, respectively. The above results showcase the proposed approach with excellent performance in isolating low-frequency vibrations. The ultra-low frequency active vibration isolation system designed in this paper achieves exceptionally low suspension stiffness. The implemented self-tuning feedforward controller isolates large precision machinery from broadband floor vibrations and significantly enhances the vibration isolation performance of the system. [ABSTRACT FROM AUTHOR]

In order to minimize losses in the distribution network, integrating non-conventional energy sources such as wind, tidal, solar, and so on, into the grid has been proposed in many papers as a viable solution. Using electronic power equipment to control nonlinear loads impacts the quality of power. The unified power quality conditioner (UPQC) is a FACTS device with back-to-back converters that are coupled together with a DC-link capacitor. Conventional training algorithms used by ANNs, such as the Back Propagation and Levenberg–Marquardt algorithms, can become trapped in local optima, which motivates the use of ANNs trained by evolutionary algorithms. This work presents a hybrid controller, based on the soccer league algorithm, and trained by an artificial neural network controller (S-ANNC), for use in the shunt active power filter. This work also presents a fuzzy logic controller for use in the series active power filter of the UPQC that is associated with the solar photovoltaic system and battery storage system. The synchronization of phases is created using a self-tuning filter (STF), in association with the unit vector generation method (UVGM), for the superior performance of UPQC during unbalanced/distorted supply voltage conditions; therefore, the necessity of the phase-locked-loop, low-pass filters, and high-pass filters are totally eliminated. The STF is used for separating harmonic and fundamental components, in addition to generating the synchronization phases of series and shunt filters. The prime objective of the suggested S-ANNC is to minimize mean square error in order to achieve a fast action that will retain the DC-link voltage's constant value during load/irradiation variations, suppress current harmonics and power–factor enhancement, mitigate sagging/swelling/disturbances in the supply voltage, and provide appropriate compensation for unbalanced supply voltages. The performance analysis of S-ANNC, using five test cases for several combinations of loads/supply voltages, demonstrates the supremacy of the suggested S-ANNC. Comparative analysis was carried out using the GA, PSO, and GWO training methods, in addition to other methods that exist in the literature. The S-ANNC showed an extra-ordinary performance in terms of diminishing total harmonic distortion (THD); thus PF was improved and voltage distortions were reduced. [ABSTRACT FROM AUTHOR]

The low harmonic distortion and reduced switching losses are the advantages of using the multilevel inverter. For this purpose, the three-level inverter is used in this paper as a three-phase four-leg shunt active power filter (SAPF). The SAPF is used to eliminate the harmonic current to compensate the reactive power current, and to balance the load currents under an unbalanced non-linear load. A fuzzy logic controller and self-tuning filters (STF) are used to control the active power filter (APF) and generate the reference current. To demonstrate the validity of the proposed control strategy, we compared it with a conventional p − q theory, under distortion voltage conditions and unbalanced non-linear load. The Matlab-Simulink toolbox is used to implement the algorithm of Fuzzy logic control. The performance of the SAPF controller is found very effective and adequate as compared with the p − q theory.

This paper presents a seven levels inverter (MLI) used as 3Φ Modified Shunt Active Line Conditioner (MSALC) providing features of low harmonic distortion (low THD) and low Harmonic Current Ratio Factor (HCRF), reduced switching losses, suppressing harmonic currents, compensation of reactive power, enhancement of power factor, balancing load current under unbalanced non-linear load and distorted voltage conditions. It employs Self Tuning Filters (STF) for ideal (reference) current generation. Fuzzy Rule-Based (FRB) current controller generates switching patterns or sequence for Electrical potential source inverter. MATLAB fuzzy logic trainer toolbox is used for stimulating the proposed system. The effectiveness of the presented MSALC is desirable to suppress harmonics which is proved from the simulation results validated by experimental prototype hardware using the THD and HCRF values obtained which is not yet reported in other Shunt Active Line Conditioner (SALC) for various types of loads under both steady state and dynamic load conditions. [ABSTRACT FROM AUTHOR]

In this paper, a new approach is proposed for voltage and current harmonics compensation in grid-connected microgrids (MGs). If sensitive loads are connected to the point of common coupling (PCC), compensation is carried out in order to reduce PCC voltage harmonics. In absence of sensitive loads at PCC, current harmonics compensation scenario is selected in order to avoid excessive injection of harmonics by the main grid. In both scenarios, compensation is performed by the interface converters of distributed generation (DG) units. Also, to decrease the asymmetry among phase impedances of MG, a novel structure is proposed to generate virtual impedance. At fundamental frequency, the proposed structure for the virtual impedance improves the control of the fundamental component of power, and at harmonic frequencies, it acts to adaptively improve nonlinear load sharing among DG units. In the structures of the proposed harmonics compensator and the proposed virtual impedance, a self-tuning filter (STF) is used for separating the fundamental component from the harmonic components. This STF decreases the number of phase locked loops (PLLs). Simulation results in MATLAB/SIMULINK environment show the efficiency of the proposed approach in improving load sharing and decreasing voltage and current harmonics.

The dynamic voltage restorer (DVR) is mainly used in a utility grid to protect sensitive loads from power quality problems, such as voltage sags and swells. However, the effectiveness of the DVR can wane under unbalanced grid voltage conditions. Recently, DVR control algorithms have been developed that enable the elimination of voltage harmonics in weak and distorted utility networks. This paper presents a modified control method for the DVR, which can (1) compensate the voltage swell and (2) eliminate the voltage harmonics in a combined utility condition consisting of voltage unbalance and harmonic distortion. A self-tuning filter (STF) is used along with the pq control method to increase the control performance of the DVR. One of the advantages of STF is that it eliminates the need to have multiple filters as part of the control method, and thus reduces the controller complexity. Analysis of the fault ride-through capability of the new DVR revealed an improvement in the voltage stability offered to distributed generation-integrated weak utility networks. The proposed DVR control method is modeled in MATLAB/Simulink and tested in both off-line and real-time environments using the OPAL RT real-time platform. Results are then presented as a verification of the proposed system. [ABSTRACT FROM AUTHOR]

In this paper, a proton exchange membrane PEM fuel cell power plant is used to improve the filtering performance of the conventional active power filter, as well as simultaneously contribute with the electric grid to supply the power to the load. The five-level inverter is used as a shunt active power filter, taking advantages of the multilevel inverter such as low harmonic distortion and reduced switching losses. It is capable of compensating power factor, current harmonics and can also make the interface between renewable energy sources and the electric grid, injecting the energy generated by PEM fuel cell to the load. The active power filter control strategy is based on the use of self tuning filters for reference current generation and a fuzzy logic current controller. The MATLAB Fuzzy Logic Toolbox is used for implementing the fuzzy logic control algorithm. The obtained results show that the PEM fuel cell contributes successfully to supply simultaneously the load with the electric grid and produced a sinusoidal supply current with low harmonic distortion and in phase with the line voltage. [ABSTRACT FROM AUTHOR]

This paper proposes backstepping technique for the direct-current bus voltage control in three-phase four-wire shunt active filter. The identification of reference currents is made by synchronous referential frame theory with self-tuning filter. The three-phase four-wire shunt active filter is implemented with DSPACE 1104 system to compensate harmonics generated by unbalanced system of non-linear loads. Four-leg topology is used for the inverter of shunt active filter and the switching patterns of the inverter are generated by analogue hysteresis card. The experimental results verify the good performance of the proposed shunt active filter in term of harmonic currents reduction and improvement of power quality. A comparison between backstepping controller and the conventional proportional-integral controller is illustrated, in steady state, the two controllers fixe direct-current bus voltage at its reference value, however, a clear advantage of the backstepping control in dynamic state can be observed. [ABSTRACT FROM AUTHOR]

If sensitive loads are connected to the point of common coupling (PCC), compensation should be carried out in order to reduce PCC voltage harmonics. In this case, compensation is performed by the interface converters of distributed generation (DG) units. In this paper, a novel method is proposed for voltage harmonics compensation in islanded microgrids. The proposed method is capable of adjusting compensation percentage in proportion to the existing level of distortion at PCC. Also, this controller provides a proper sharing of compensation workload, considering the nominal capacity of DGs, which will improve the sharing of nonlinear load. Also, to decrease the asymmetry among phase impedances of microgrid, a novel structure is proposed to generate virtual impedance. At fundamental frequency, the proposed structure for the virtual impedance improves the control of the fundamental component of the power, and at harmonic frequencies, it acts to adaptively improve nonlinear load sharing among DG units. In the structures of the proposed harmonics compensator and the proposed virtual impedance, a self-tuning filter is used for separating the fundamental component from the harmonic components. This self-tuning filter decreases the number of the phase-locked loops. The simulation results in MATLAB/SIMULINK environment show the efficiency of the proposed approach in improving load sharing and decreasing voltage harmonics. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In the case of undistorted and balanced grid voltages, low ratio shunt active power filters (APFs) can give unity power factors and achieve current harmonic cancellation. However, this is not possible when source voltages are distorted and unbalanced. In this study, the cost-effective hybrid active power filter (HAPF) topology for satisfying the requirements of harmonic current suppression and non-active power compensation for industry is presented. An effective strategy is developed to observe the effect of the placement of power capacitors and LC filters with the shunt APF. A new method for alleviating the negative effects of a nonideal grid voltage is proposed that uses a self-tuning filter algorithm with instantaneous reactive power theory. The real-time control of the studied system was achieved with a field-programmable gate array (FPGA) architecture, which was developed using the OPAL-RT system. The performance result of the proposed HAPF system is tested and presented under nonideal supply voltage conditions. [ABSTRACT FROM AUTHOR]

In this study, a control method is proposed to improve the harmonic suppression efficiency of the single-phase active power filter in a distorted power system to suppress current harmonics and reactive power. The proposed method uses the self-tuning filter (STF) algorithm to process single-phase grid voltage in order to provide a uniform reference grid current, which increases the efficiency of the system. The results of the simulation study are presented to verify the effectiveness of the proposed control technique in this study. [ABSTRACT FROM PUBLISHER]

The present paper proposes the use of an advanced algorithm based on the instantaneous powers theory for harmonics current compensation. A fast and exact computation of harmonic references is more than crucial for any active filter control strategy, especially during the transient time and frequency domains. The proposed method contains mainly two stages, the first one is based on a self-tuning filter (STF) to perform instantaneous synchronized sine and cosine fundamental waveforms. These two signals are used to calculate the instantaneous active and reactive powers using the well-known PQ theory. The second one is based on a new proposed method to accelerate the power ripple cancelation in the PQ active and reactive powers. An analytic study is conducted to show the effectiveness of these methods which is consolidated by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a continuous terminal sliding mode controller (CTSMC) for single-phase dynamic voltage restorers (DVRs). The presented controller can substantially eliminate the chattering compared to the first-order sliding mode counterpart while achieving faster convergence speed compared to the super twisting counterpart. Moreover, the continuous control signal enables the voltage source inverter to operate at constant switching frequency. As the reference compensation voltage generator, an enhanced single-phase self-tuning (SP-STF) filter is also proposed. The SP-STF has excellent band-pass filtering property, can completely attenuate DC offset and has fast dynamic response. The SP-STF has been made frequency-adaptive through unknown grid frequency estimation under a delayed-based linear regression framework. Comprehensive stability analysis of the controller and filter are presented. Experimental studies are performed to demonstrate the effectiveness of the proposed comprehensive control solution. Comparative simulation studies are also provided to highlight the advantages of the proposed approach. Results show that the proposed technique can quickly detect and compensate for any grid voltage fluctuations and helps to maintain constant voltage at the load side despite voltage sag/swell and distortions. [ABSTRACT FROM AUTHOR]

This paper presents a five-level inverter which is used as a three-phase four leg shunt active power filter, taking advantages of the multilevel inverter such as low harmonic distortion and reduced switching losses. It is used to suppress harmonic current, compensate reactive power and neutral line current and balance the load currents under unbalanced non-linear load and distorted voltage conditions. The active power filter control is essentially based on the use of self tuning filters for the reference current generation and a fuzzy logic current controller. This study is divided in two parts. The first one deals with the harmonic isolator which generates the harmonic reference currents. The second part focuses on the generation of the switching pattern of the inverter by using a fuzzy logic controller applied and extended to a four leg five level shunt active power filter. The MATLAB Fuzzy Logic Toolbox is used for implementing the fuzzy logic control algorithm. The performance of the proposed shunt active power filter controller is found considerably effective and adequate to compensate harmonics, reactive power and neutral current and balance load currents under distorted voltage conditions. [ABSTRACT FROM AUTHOR]

In the case of balanced and undistorted supply voltages, shunt APFs can achieve current harmonic cancellation and give unity power factors. However, this is not possible when grid voltage is non-sinusoidal and unbalanced. In this paper, we first show that the harmonic suppression performance of the well-known p-q theory deteriorates in non-ideal grid voltage conditions. A technique for alleviating the detrimental effects of a distorted and unbalanced grid voltage is proposed that uses a self-tuning filter with p-q theory. The proposed control technique gives an adequate compensating current reference even for non ideal voltage condition. The results of simulation study are presented to verify the effectiveness of the proposed control technique in this study. [ABSTRACT FROM AUTHOR]

This article presents a simulation and experimental study of a sliding-mode controller of the DC bus voltage of a three-phase shunt active power filter. The sliding-mode controller is introduced to improve tracking performance characteristics, power quality, and minimized consumption of the reactive power. The algorithm used to identify the reference currents is based on the self-tuning filter. The firing pulses of the insulated-gate bipolar transistor inverter are generated using a hysteresis current controller, which is implemented on an analog card. Finally, this study, under steady-state and transient conditions, is illustrated with signal-flow graphs and corresponding analysis. This study was verified by both time-domain computer simulations and experimental tests on a hardware prototype based on dSPACE-1104 (dSPACE, Germany). The experimental results show the feasibility and the effectiveness of the designed active filter associated with a sliding-mode controller and its capability in meeting the IEEE 519-1992 recommended harmonic standard limits. [ABSTRACT FROM PUBLISHER]

For the linear discrete time-invariant stochastic system with correlated noises, and with unknown model parameters and noise statistics, substituting the online consistent estimators of the model parameters and noise statistics into the optimal time-varying Riccati equation, a self-tuning Riccati equation is presented. By the dynamic variance error system analysis (DVESA) method, it is rigorously proved that the self-tuning Riccati equation converges to the optimal time-varying Riccati equation. Based on this, by the dynamic error system analysis (DESA) method, it is proved that the corresponding self-tuning Kalman filter converges to the optimal time-varying Kalman filter in a realization, so that it has asymptotic optimality. As an application to adaptive signal processing, a self-tuning Kalman signal filter with the self-tuning Riccati equation is presented. A simulation example shows the effectiveness. [ABSTRACT FROM AUTHOR]

For linear discrete time-invariant stochastic system with correlated noises, and with unknown state transition matrix and unknown noise statistics, substituting the online consistent estimators of the state transition matrix and noise statistics into steady-state optimal Riccati equation, a new self-tuning Riccati equation is presented. A dynamic variance error system analysis (DVESA) method is presented, which transforms the convergence problem of self-tuning Riccati equation into the stability problem of a time-varying Lyapunov equation. Two decision criterions of the stability for the Lyapunov equation are presented. Using the DVESA method and Kalman filtering stability theory, it proves that with probability 1, the solution of self-tuning Riccati equation converges to the solution of the steady-state optimal Riccati equation or time-varying optimal Riccati equation. The proposed method can be applied to design a new selftuning information fusion Kalman filter and will provide the theoretical basis for solving the convergence problem of self-tuning filters. A numerical simulation example shows the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new reference current computation method suitable for shunt active power filter control under distorted voltage conditions is proposed. The active power filter control is based on the use of self-tuning filters (STF) for the reference current generation and on a modulated hysteresis current controller. This active filter is intended for harmonic compensation of a diode rectifier feeding a RL load under distorted voltage conditions. The study of the active filter control is divided in two parts. The first one deals with the harmonic isolator which generates the harmonic reference currents and is experimentally implemented in a DS1104 card of a DSPACE prototyping system. The second part focuses on the generation of the switching pattern of the inverter by using a modulated hysteresis current controller, implemented in an analogue card. The use of STF instead of classical extraction filters allows extracting directly the voltage and current fundamental components in the α–β axis without phase locked loop (PLL). The performances are good even under distorted voltage conditions. First, the effectiveness of the new proposed method is mathematically studied and verified by computer simulation. Then, experimental results are presented using a DSPACE system associated with the analogue current controller for a real shunt active power filter. [Copyright &y& Elsevier]