Improved shunt active power filters

This paper describes a shunt active power filters (APF) with improved dynamic performance. When the value of load current changes rapidly, the APF transient response is too slow, the line current suffers from dynamic distortion. This distortion causes an increase of harmonic content in the line current, which is dependent on a time constant. The APF control current dynamics is dependent on the inverter output time constant consisting of APF output inductance and resultant impedance of load and mains. In the proposed circuit transient performance of APF is improved using non-causal predictive current compensation. In the second solution modified output inverter is used. According to this modification the APF dynamics are improved. The Matlab simulation results of the modified APF are also presented in the paper. As an example a control circuit for a three-phase 75 kVA parallel active power filter (APF) is used.