Parallel operation of three-phase four-wire active power filters without control interconnection

This paper presents the parallel operation of the three-phase four-wire active power filters (APFs). Functions of the proposed APF include compensation of reactive power, harmonic current, unbalanced power and zero-sequence current of the load. The objective is to achieve unity power factor, balanced line current and zero neutral-line current. Compensation of all components is capacity-limited, cooperating with the cascaded load current sensing scheme, multiple APFs can be paralleled to share the load power without requiring any control interconnection. Besides providing the theoretic bases and detailed design of the APFs, two 6 kVA APFs are implemented. The effectiveness of the proposed methods is validated with some experimental results.