Design and Implementation of A Hybrid Output EMI Filter for High Frequency Common-Mode Voltage Compensation in PWM Inverters

This paper presents a hybrid output EMI filter for common-mode voltage compensation in PWM inverters. Its structure composes of a single-leg 4-level active filter and a passive LC filter which facilitates the suppression of common-mode voltage in high-frequency range. To avoid the saturation of common-mode transformer caused by low frequency components of common-mode voltage, the conventional single-leg 4-level active filter is modified by inserting a series capacitor into its output. Detection of PWM voltages is done at the inverter output to achieve better common-mode voltage compensation characteristic. The design guidelines for the hybrid filter are also given, to facilitate systematic design in real implementation of the filter. Experimental results with real motor drive system illustrate clearly a significant reduction of common-mode voltage.