Optimum control strategy for shunt active filter under disturbed AC voltage and unbalanced load conditions in 4-wire power system

Nonlinear loads draw non-sinusoidal current from utility that leads to harmonic voltage drops across the impedance between the grid and the loads connected. Moreover, in real distribution power systems, asymmetrical single-phase nonlinear loads lead to unbalance in 3-phase non-sinusoidal line current. As a result, not only does appear a nonsinusoidal voltage at the point of common coupling, but also we expect to have neutral current due to asymmetry of the 3-phase current in a four wire system. On the other hand, under non-sinusoidal three-phase voltage condition, sinusoidal source current and proper power factor cannot be achieved at the same time. In this paper, an optimum control strategy for shunt active filter is designed to get an appropriate compromise between the power factor and current total harmonic distortion under unbalanced nonlinear load and non-sinusoidal voltage condition in four-wire system. This control strategy not only balances the source current, but also optimizes the performance of the system by minimizing the apparent power drawn from the line within the defined current THD limit. Also a neutral current compensation strategy is used to reduce losses, and improve the overall efficiency of the power system. To verify the effectiveness of the proposed control scheme, the Simulink/Matlab simulation results are provided for several unbalanced nonlinear loads.