Analysis and improvements of the filtering characteristic of the series hybrid APF based on fundamental magnetic flux compensation

In the series hybrid active power filter (SHAPF) based on fundamental magnetic flux compensation (FMFC), the PWM inverter acts as a controlled fundamental current source, but its control characteristic is not ideal, moreover, the secondary terminal of the series transformer exhibits an interferential harmonic voltage, which has a great influence on the filtering effect. In this paper, the mathematical model of the whole filtering system is established firstly. Then, the filtering characteristic of the filter is analyzed in detail. Two novel improving measures, including an in-phase harmonic injection method and a novel PI controller with voltage feed-forward, are investigated. The validity of the proposed improvements is verified by the well experimental results.