Modified Synchronous Reference Frame Method for Active Power Filter under Asymmetric and Distorted Supply Voltages Condition

In this paper, a modified harmonic and reactive current detection method based on synchronous reference frame (SRF) theory for three-phase four-wire shunt active power filter (SAPF) is proposed under distorted supply voltages condition. The main objective of the method is to extract the fundamental positive-sequence active currents, which can compensate the fundamental positive sequence reactive components, the unbalanced components and harmonics of the load currents. A model of three-phase four-leg SAPF with LCL-filter based on the proposed SRF method has been designed and simulated on MATLAB/simulink. Simulation results indicate that not only the current total harmonic distortion (THDi) values for each phase of the supply currents are reduced from 21.71%, 22.37% and 20.82% to 4.56%, 4.67% and 4.58%, but also the supply currents are balanced and sinusoidal after compensation.