Four wire active power filter control circuit with phase locked loop phase angle determination

This paper presents a shunt active power filter control circuit for a four-wire three-phase supply network. The active power filter is implemented with a four-wire three-phase PWM voltage converter connected to the AC mains with neutral conductor. The neutral is connected to the middle point of two capacitors in series on the converter DC side. Its AC currents are controlled with a generalised space vector based hysteresis current controller in the αβ0 coordinate system. The active power filter compensates current harmonics of positive, negative and zero sequence so that the mains currents constitute a first harmonic positive sequence system. These current harmonics are determined in the Park's referential, whose transformation angle is calculated with a phase locked loop controller.