## Improved series active power filter with fundamental and harmonic magnetic flux hybrid compensation

The filtering performance of series hybrid active power filter (SHAPF) based on fundamental magnetic flux compensation positively correlates with the magnetising impedance of the transformer. However, excessive magnetising impedance will decrease reliability while increasing capacity and costs of the whole system. In order to reduce the magnetising impedance while ensuring the same filtering performance of SHAPF, an improved series active power filter (ISAPF) with fundamental and harmonics magnetic flux hybrid control is presented here. The equivalent impedances to fundamental and harmonics in ISAPF are firstly analysed to explain the principle of ‘harmonic isolation’. Then the range of compensation coefficients is investigated in detail based on the complete control block diagram and the open-loop function of ISAPF. Moreover, stability conditions of an overall system with non-linear loads are deduced. Finally, a set of single-phase prototype with two kinds of special transformer has been constructed; the related experiments results showed that ISAPF can ensure the filtering performance while applying a transformer with smaller capacity, thus resulting in the reduction in capacity and the costs while increasing the reliability.