Multiloop control strategy for four-wire current source active power filter

Despite the fact that three-wire active power filters have been implemented using both voltage source and current source technology, the research of four-wire current source active power filters has been truly minimal. Only a few topologies have been presented over the years. This paper proposes a four-wire current source active power filter topology for improving the quality of supply in four-wire systems. The proposed topology is controlled using a multiloop control strategy suitable for a single-chip microcontroller implementation. The control strategy combines the load current feedforward connection and the cascaded closed-loop control of the supply currents and the capacitor voltages of the LC-type supply filter. By using the cascaded closed-loop control, the stability of the system can be achieved without the need to overdimension the supply filter. The performance of the proposed system is verified experimentally using a microcontroller controlled four-wire current source active power filter prototype rated for a 5 kVA load.