The reference active source current for active power filter in an unbalanced three-phase system via the method of instantaneous power theory

This paper presents a method to generate the reference active source current for active filter operating under unbalanced three-phase sinusoidal system using the instantaneous power theory. The conventional application of the instantaneous power theory is effective in a balanced three-phase sinusoidal system. However, in a practical system three-phase voltage unbalancing does generally exist. The proposed method uses the principle of geometrical similarity to process the zero-axis voltage and current into zero-sequence active current. From the theoretical formulations, the proposed method obtains the same result as the equal resistance synchronous detection method. The reference active source current is sinusoidal and in-phase to source voltage, and can be directly calculated without 0-d-q axis conversion. From computer simulations and circuit implementations, both results are satisfactory and have very good agreement