A novel online controller for tuning shunt active power filters based upon switched-capacitors

This paper presents a novel online controller for tuning shunt active power filters (APF). The idea of the proposed controller is based upon using a low rating switched-capacitor circuit as online estimator to extract the fundamental reactive component of the nonlinear load current. This reactive component is shifted in appropriate phase using two phase-shifters to obtain a 3phi signal. The line current is sensed and compared instantaneously with this 3phi signal using three comparators. The outputs of the comparators represent each moment the profile of the harmonic current. This harmonic current is taken as a reference signal to drive a simple closed-loop P-I controller in order to produce the necessary modulating signals for the triggering module of the APF. In the case of balanced load, which is the case under investigation in this paper, one switched-capacitor circuit is needed. In spite of being simple and straightforward, the proposed controller will be able to solve the problems arising with the p-q algorithm based controllers.