The increasingly extensive use of non-linear loads, mostly including static power converters, in large industry, commercial, and domestic applications, as well as the spread of renewable energy sources in distribution-generated units, make the use of the most efficient power quality improvement systems a current concern. The use of active power filters proved to be the most advanced solution with the best compensation performance for harmonics, reactive power, and load unbalance. Thus, issues related to improving the power quality through active power filters are very topical and addressed by many researchers. This paper presents a topical review on the shunt active power filters in three-phase, three-wire systems. The power circuit and configurations of shunt active filtering systems are considered, including the multilevel topologies and use of advanced power semiconductor devices with lower switching losses and higher switching frequencies. Several compensation strategies, reference current generation methods, current control techniques, and DC-voltage control are pointed out and discussed. The direct power control method is also discussed. New advanced control methods that have better performance than conventional ones and gained attention in the recent literature are highlighted. The current state of renewable energy sources integration with shunt active power filters is analyzed. Concerns regarding the optimum placement and sizing of the active power filters in a given power network to reduce the investment costs are also presented. Trends and future developments are discussed at the end of this paper. For a rigorous substantiation, more than 250 publications on this topic, most of them very recent, constitute the basis of bibliographic references and can assist readers who are interested to explore the subject in greater detail.

This paper presents the use of a three-phase four-wire shunt active power filter to improve the power quality in the Department of Industrial Electronics of a large enterprise from Romania. The specificity is given by the predominant existence of single-phase consumers (such as personal computers, printers, lighting and AC equipment). In order to identify the power quality indicators and ways to improve them, an A-class analyzer was used to record the electrical quantities and energy parameters in the point of common coupling (PCC) with the nonlinear loads for 27 h. The analysis shows that, in order to improve the power quality in PCC, three goals must be achieved: the compensation of the distortion power, the compensation of the reactive power and the compensation of the load unbalance. By using the conceived three-leg shunt active power filter, controlled through the indirect current control method in an original variant, the power quality at the supply side is very much improved. In the proposed control algorithm, the prescribed active current is obtained as a sum of the loss current provided by the DC voltage and the equivalent active current of the unbalanced load. The performance associated with each objective of the compensation is presented and analyzed. The results show that all the power quality indicators meet the specific standards and regulations and prove the validity of the proposed solution.

This paper is focused on an adaptive controller for the direct current (DC) voltage in three-phase three-wire shunt active power filters systems. Although the controller structure of the proportional-integral (PI) type is determined off-line and does not change, the prescribed DC voltage and the controller parameters are calculated in an adaptation block, depending on the non-active power to be compensated. The adaptive control is based on the design expressions for the DC circuit of the shunt active power filter found by the authors, based on the detailed analysis of its operation, during the active filtering. The performances of the proposed adaptive control and its advantages compared to the classical control (where the prescribed DC voltage and the controller parameters are constant) were first determined on the virtual model of a laboratory setup. Then, the adaptive control was implemented on the dSPACE 1103 control board, which allowed the experimental determinations that prove and support the results obtained on the virtual model.

This paper analyzes the current decomposition, in three-phase, three-wire systems, based on the Conservative Power Theory (CPT), and its application in the active filtering in non-sinusoidal and unbalanced conditions, by simulation as well as on an experimental workbench. The CPT current decomposition includes, beside the active, reactive and void components, an unbalanced component. This component makes possible for the active filter to compensate also the current unbalance, if desired. This is particularly interesting when the voltage is also unbalanced because of the load unbalance or not. In this case, the compensation will eliminate the voltage asymmetry due to the load current unbalance, but if the grid impedances are not equal on all the three phases, the compensated sinusoidal and balanced current will unavoidably produce asymmetric voltages in the PCC. Moreover, due to the CPT definition of the active current, the grid voltage asymmetry will produce a load current unbalance. The current decomposition based on the Conservative Power Theory was analyzed on various case studies, for a combination of typical nonlinear balanced and unbalanced industrial loads. First, the active filtering system was tested by simulation in the Matlab Simulink environment, and latter the validated system was further tested on an experimental workbench. Because of the Simulink model modular structure, the virtual filtering system was built equivalent to the experimental system.

- In this paper, the performance of a three-phase shunt active power filter (APF) using the instantaneous power theory (p-q theory) has been compared with that corresponding to the use of the synchronous reference frame (SRF) based method. It is clear that, under balanced and sinusoidal voltage conditions, these two methods gives similar results. The entire system has been modeled using MATLAB-SIMULINK software. The simulation results demonstrate the applicability of both methods for the APF control.