PWM逆变器-感应电机驱动系统中接地电流EMI问题的分析

在IGBTPWM逆变器－感应电机驱动系统中，IGBT的高速开关动作产生很高的dv/dt|和|dt/dt|能够导致严重的电磁干扰（EMI）问题。研究表明不仅需要了解干扰的频谱。而且也必须知道它们的时域波形才能全面刻画干扰的本质。如何准确描述并分析这种问题是复杂而困难的，该文应用系统函数的方法来描述这种EI耦合通道的特征，并不需要对寄生电路进行复杂的参数提取，而且能准确预测了EMI的时域波形和频谱特性，接地电流脉冲峰值对应|dv/dt|的 峰值，导通时，|dv/dt|基本不随着负载电流的变化而变化，而关断时，负载电流越小，|dv/dt|越小，由于|dv/dt|在开通时的值要比关断时大得多，因此接地电流EMI问题主要由IGBT的开通决定。系统函数的幅度频谱呈现带通特性，尽管逆变器工作时其拓扑结构发生变化，但是对描述耦合通道的系统函数的影响很小，当三相桥臂的两个IGBT同时开通或同时关断时，接地电流加倍。

ANALYSIS OF EMI DUE TO GROUNDING CURRENT IN A PWM INVERTER-INDUCTION MOTOR DRIVE SYSTEM

In IGBT PWM inverter - induction motor system, the high |dv/dt| and |di/dt| due to the fast switching of IGBT could bring serious EMI issues. Research shows that, in order to characterize the EMI issue, it is important not only to know its waveform in time domain but also to investigate its spectra. This paper uses a novel approach adopting a linear system function to characterize the EMI generation and coupling avoiding complicated parameter extraction of the parasitic circuit. The highest grounding current pike appears when the |dv/dt| is the highest. There is hardly a variance of the |dv/dt| at turn-on over a wide load current range, however, the lower the load current, the lower the |dv/dt| at turn-off. The grounding current EMI issue is mainly dominated by the turn-on of IGBTs because the |dv/dt| at turn-on is much higher than that at turn-off. The amplitude-frequency characteristic of the system function of coupling path appears as band-pass, and with small deviation, the legs of a three-phase inverter could be considered as almost three equal contributors to grounding current noise. Although the inverter's topology construction alternates while it works, it hardly has affect to this system function. The current may double when two IGBTs of three legs turn on/off almost at the same time.