Analysis and design of different control strategies of hybrid active power filter based on the state model

A configuration consisting of a combination of a series active power filter (APF) and a parallel passive filter is shown to be an efficient system for non-linear load compensation. For this topology, different compensation strategies are proposed to control the series APF. The most effective strategies determine the APF compensation voltage in proportion to the source current harmonics. The proportionality constant 'k' in the control algorithm implementation is related to the APF gain and complete system dynamic. In this study, the system state model is obtained for three control strategies of series APF: compensation voltage proportional to source current harmonics, compensation voltage opposite to the load voltage harmonics and a hybrid strategy which combines both previous strategies. The analyses of the resulting models provide the information needed to establish design criteria with respect to harmonic filtering and system stability. The methodology proposed in this study eliminates the arbitrary choice of the proportionality constant. The three strategies were analysed in two different situations: sinusoidal supply voltages and distorted supply voltages. Finally, results of an experimental prototype developed for this purpose allowed the proposed analysis to be verified.