Parallel Operation of One-Cycle Controlled Three-Phase Active Power Filter

Harmonic and reactive currents in the power line degrade the power quality, increase transmission losses, and impair generators. Shunt connected active power filters (APF) offers an effective solution by canceling the harmonic or reactive components from loads. For high power loads, paralleling several units of APFs may offer some advantages over the solution of using an individual APF with a larger power handling capacity. However, the safe operation of APFs and the compensation current sharing among the paralleled APFs could be potential problems. This paper studies the present parallel control methods, and then proposes a peak current limitation method for one-cycle controlled (OCC) APF. When the proposed method is integrated in OCC core, each APF contributes its compensation current up to a preset limit. When the load harmonic current is within the preset limit, the APF cancels all the harmonics. When the load harmonic current exceeds the up limit, the APF cancels part of the harmonics as much as it can and passes the remaining harmonics to the line, so that the APF is operated safely. Two parallel approaches, a cascade structure and a centralized structure, are proposed for OCC APFs with peak current limitation. Experiments have been conducted with two units of OCC APFs of 2.5kW each to verify the simplicity and the effectiveness of the control method