The detection of directive current is very important for APF. Because of the phase difference between a phase voltage and its positive sequence voltage in the three-phase asymmetry system, the directive current can not be detected accurately by traditional FBD method. An improved FBD detecting method was proposed, the improved FBD acquires the phase of the fundamental positive-sequence voltage by instantaneous symmetrical components, which reduces detection error caused by the three-phase voltage asymmetry, and introduces mean value theory to extract the linear part of equivalent conductance, so as to improve dynamic response capability of directive current detection. The simulation results verify that the APF based on the improved FBD can effectively detect and compensate harmonic and reactive current in the three-phase asymmetrical system.
