document: Parallel operation of capacity-limited three-phase four-wire active power filters Three-phase four-wire active power filters -LRB- APFs -RRB- are presented that can be paralleled to enlarge the system capacity and reliability . The APF employs the PWM four-leg voltage-source inverter . A decoupling control approach for the leg connected to the neutral line is proposed such that the switching of all legs has no interaction . 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 , co-operating with the cascaded load current sensing scheme . Multiple APFs can be paralleled to share the load power without requiring any control interconnection . In addition to providing the theoretic bases and detailed design of the APFs , two 6 kVA APFs are implemented . The effectiveness of the proposed method is validated with experimental results
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