Research Of The Common Mode Conducted EMI And Its Suppression For PWM Inverter

As the main component of the power electronic devices, inverter plays an irreplaceable role in people’s living and production. Moreover, the output waveform of inverter has been greatly improved with the application of PWM technology, which makes the load end(AC motor) present smaller ripple current, less copper loss and less switch loss. However, the PWM inverter itself can produce high-frequency common-mode dv/dt, which can not only bring about leakage current, but also develop shaft voltage by the electromagnetic coupling between the motor stator and rotor. The leakage current not merely affects the proper functioning of the sensitive equipments, but it also induces EMI problems. The shaft voltage will lead to shaft current, further produce the electric erosion on bearing, accelerating the aging of motor bearing. When inverter and induction motor is connected by long cable, the voltage outputted by inverter will occur traveling wave reflection phenomenon on the cable, generating overvoltage at motor end, which may bring about the insulation performance decline of motor and cable, and even insulation breakdown. Common mode conducted EMI has already become a dominating factor jeopardizing the security, restricting the application of inverter. This paper is researched and accomplished in these contexts, combing the researching achievements of predecessors and our research group.The research frame of this paper is as follows: firstly analyses the characteristics of common mode conducted EMI for PWM inverter theoretically, and then models the common mode conducted EMI, finally puts forward methods to suppress the common mode conducted EMI. For the theoretical analysis of the common mode conducted EMI, this paper has carried out from three aspects, which are common-mode voltage, overvoltage and conducted EMI propagation paths. The modeling of common mode conducted EMI has proceed from inverter, induction motor and transmission cable, and the model simulation and experiment comparison has also been presented. The suppression of common mode conducted EMI has started with two methods: one method is to suppress the common mode conducted EMI by filter, where a feed-forward common mode active filter is designed; and the other is to reduce the common mode conducted EMI from control strategy, where a new PWM control strategy based on spread spectrum technology is put forward.The research contents of this paper are helpful for the comprehensive and systematic understanding of common mode conducted EMI, and some models giving in this paper also have certain guiding significance for the EMI analysis of inverter and other power electronic devices. What’s more, these two methods given in this paper also have certain practical value and economic benefits.