A Series-LC-Filtered Active Trap Filter for High Power Voltage Source Inverter

Passive trap filters are widely used in high power Voltage Source Inverters (VSI) for the switching harmonic attenuation. The usage of the passive trap filters requires clustered and fixed switching harmonic spectrum, which is not the case for low pulse-ratio or Variable Switching Frequency (VSF) Pulse Width Modulation (PWM). Switching harmonic compensating using auxiliary power converters has been proposed and investigated by researchers. Like the traditional Active Power Filers, the performance of the existing approaches depends on the extraction of the switching harmonics and the accurate current control of the auxiliary converter, which can be challenging considering that the switching harmonics have very high orders. In this paper, an Active Trap Filter (ATF) based on output impedance shaping is proposed. It is able to bypass the switching harmonics by providing nearly zero output impedance. A series-LC-filter is used to reduce the power rating and synthesize the desired output impedance of the ATF. Compared with the existing approaches, the compensated frequency range is greatly enlarged. Also, the current reference is simply set to zero, which reduces the complexity of the control system. Simulation and experimental results are provided to show the effectiveness of the proposed method.