Common-mode equivalent circuit of single-phase full-bridge inverters

A modified equivalent circuit for common-mode current of single-phase full-bridge inverters is proposed. The circuit allows application of superposition theorem, and it provides more insights into the propagation mechanism of the CM noise. Taking the needs of applying the theorem of superposition into account, simulations and experiments are conducted on an inverter test-setup to validate the proposed equivalent circuit. Three operation conditions are studied, which is with one of the two legs detached from the DC bus, with that leg installed back in place but not switching and with normal unipolar PWM switching of both the two legs. Based on the proposed equivalent circuit and measured parameters from the test-setup, simulations with Matlab software predicted the CM current both in time and frequency domains with reasonable precision.