Development of a magnet power supply with a common-mode cancellation method based on automatic calibration of driving pulses

Abstract

Based on conventional H-bridge topologies of magnet power supplies, a high-frequency common-mode equivalent model was established. It is pointed out that the two phase legs have complementary effect of common-mode noise under bipolar PWM modulation. Due to the phase difference of the driving pulses in the real product, however, the effect of common-mode cancellation is greatly disrupted. Based on the common-mode equivalent model, a frequency domain analysis was carried out to determine the theoretical relationship between the common-mode noise intensity and the phase difference, which can guide the adjustment of the driving pulses. It was also found that the increase of switching frequency will aggravate the common-mode noise caused by the phase difference. To reduce the common-mode noise, a method that automatic calibration of the driving pulses was evaluated by a simulation and experimentally. Finally, a prototype is built, and the results of the prototype show that the proposed method can effectively reduce the common-mode noise.