Reduction of common mode EMI in a full-bridge converter through automatic tuning of gating signals

Theoretically, a full-bridge converter under bipolar PWM should produce very little common mode noise because the two phase-legs can compensate for each other, but this feature is often disrupted by different transmission delays of the gating signals. In this paper, a method to address this problem through automatic tuning of the pulse edges of gating signals is proposed. Specifically, the CM noise current is sensed by a DSP and the noise energy is calculated, then a search algorithm is employed to tuning the pulse edges of the gating signals in order to minimize the CM noise. Experimental results show that up to 10dB reduction of the CM current can be obtained from 500kHz to 5MHz. Implementation of the this method requires little hardware expense, and the software can be synthesized into the main control DSP of the converter.