基于驱动脉冲自校准的全桥电路共模抑制技术

Reduction of Common Mode EMI in a Full-bridge Converter through Automatic-tuning of Gating Signals

基于全桥变换器共模噪声电流产生机理的分析,指出双极性PWM调制下两桥臂具有共模噪声互补效应,但实际装置中由于驱动脉冲传输延时的不一致使这一优势不能完全体现出来。据此提出一种基于驱动脉冲沿自动校准的全桥电路共模抑制技术。该方法利用DSP实时检测共模噪声并计算其能量,然后采用智能搜索算法对居于对角线位置的功率开关的驱动脉冲沿进行自动校准,以降低共模噪声水平。实验证实该方法能在500kHz到5MHz频段有效降低共模噪声电流,降低幅度可达10dB。该方法主要依赖软件实现,硬件开销很小。由于共模噪声能量的计算相对其FFT简单得多,且控制过程对实时性要求不高,因而控制软件可以与变换器控制系统合用同一片DSP,具有较高的性价比。

Based on an analysis of the mechanisms of common mode electromagnetic interference （EMI） associated with a full-bridge converter, it is pointed out that although theoretically bipolar switching should produce very low common mode noise because the two phase legs can compensate for each other, in practice this mechanism is often disrupted by different transmission delays of the gating signals. In this paper, a method to compensate those differences in transmission delays 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 an intelligent search algorithm is employed to tune the pulse edges of the gating signals for the diagonal switch pairs in order to minimize the CM noise. Experimental results show that about 10dB reduction of the CM current can be obtained from 500kHz to 5MHz. Implementation of the this method requires little hardware expense. The calculation burden on the DSP is also mild since calculation of the CM noise energy is very simple compared with its FFT, and also there is no stringent requirement on the speed. Therefore this method can be implemented on the same DSP that carries out the control task of the converter, making it more cost-effective.