New Structure for Three-Phase, Four-Wires Shunt Active Filter

This paper presents a new structure and control method for three phase four wires LC coupled parallel active power filters (APF) for harmonics cancellation. The main differential point with regard to other structures used in the past consists of the connection of neutral wire to negative of DC bus in the inverter, thus avoiding the need of split capacitors at the DC bus. The LC coupling and a particular control of the DC voltage at the coupling capacitor allow the use of low voltage at the DC bus and provide a symmetry of available voltage, in the current controller, during t_on and t_off. The paper includes a general discussion of the new structure, comparing it with the classical L coupled shunt APFs and presents the control method to obtain the above mentioned voltage symmetry, which allows lower DC bus voltage and lower values of coupling L. Simulation and experimental results are given to show the behavior of the system, used for harmonics cancellation.