Effect of Common-Mode Interference on Communication Performance of a Motor Drive System

With the advent and development of power semiconductor switches like IGBT or MOSFET, high-speed switching devices have sprung up and sped up dynastic response of converters. However, these devices in operation will produce very large dv/dt and di/dt, which result in sever electromagnetic interference(EMI). In a variable-frequency drive(VFD) system, due to the coupling common-mode(CM) noise, communication between programmable logic controller(PLC) and VFD will be affected by CM current at the motor side if communication cables get too close to the motor ones. This paper emphatically analyzes the effect of common-mode interference on communication performance of a motor drive system. It introduces the generation mechanism of CM voltage and current at the motor side in a VFD system first and briefly illustrates how it couples to the communication cables. At the same time, some certain influence factors of CM current in communication system are respectively explained. Then it elaborates the detailed mechanism how CM current on communication cables affects the error rate which is employed to evaluate the communication quality. Besides, the numerical relationship between CM current on communication cables and the error rate is also discussed and confirmed by series of experiments. Finally, some software or hardware solutions are put forward to achieve the aim of interference suppression and decreasing the error rate when CM current on communication cables is constant.