A novel series hybrid single-phase active power filter

In the paper, a novel practical series hybrid active power filter based on the fundamental magnetic flux compensation of the series transformer is proposed. The power filter adopts the combined structure of a shunt passive filter and a series active filter by placing a series transformer´s primary winding between power utility and harmonic-producing loads. The secondary winding of the transformer is connected with a voltage-source PWM converter, and the PWM converter is employed to produce a fundamental current in specific proportional to the fundamental current component of the power systems. By analyzing in detail the series transformer´s equivalent circuit, when the injected fundamental current and the fundamental component of the power utility satisfy the fundamental magnetic flux compensation condition, the series transformer can really exhibit very low impedance at the fundamental frequency and magnetizing impedance to harmonics. The harmonic currents are forced to flow into the passive filter branches. The validity of the theory and excellent compensation characteristics are verified by the experimental results