Research on a new three phase series hybrid active power filter

In order to reduce inverter capacity and enhance system reliability, a new three phase series hybrid active power filter with small self-inductance series transformer (ST) is presented. Different from conventional scheme, the self-inductance of the ST in this filtering system is very small about 0.01∼0.10 in per unit, and the series active filter is controlled as a harmonic current source instead of a harmonic voltage source or a fundamental current source. In this scheme, both the inverter and the secondary of the ST needn’t endure the source fundamental current but only endures a certain times of the filtered source harmonic current, and no LC fundamental tuned circuit is needed, so the cost and dissipation of the whole filtering system can be cut down a lot. When series active filter is switched off by reason of malfunction, the power supply on load will not be affected or interrupted, and the filtering effect of passive filters is also improved to a certain extent due to the existence of the ST with its secondary on open-circuit state.