Control of a three phase four wires shunt hybrid filter

This paper describes a new strategy to control a particular structure of three phase four wires LC coupled parallel hybrid power filters (APF) for harmonics cancellation. The main differential point of the studied structure 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+AC voltage at the coupling C allow the use of low voltage at the DC bus and provide the necessary symmetry of available voltage, in the current controller, during ton and toff. The paper includes a general discussion of the structure, comparing it with the classical L coupled shunt APFs and presents a control method to obtain the necessary voltage symmetry to allow lower DC bus voltages and lower values of coupling L. The paper presents a control method based on time domain techniques, which gives a fast response. Simulation and experimental results are given to show the behavior of the system, used for harmonics cancellation.