Design of common-mode and differential-mode voltage dv/dt filter at PWM inverter output terminals

When motor was directly connected with PWM inverter, the common-mode voltage with a high dv/dt value would be brought which was thought to have relations with the producing of bearing current, common-mode leakage current, and serious electromagnetic interfere (EMI) issues. Especially, when motor was connected with inverter through a long cable, because of the effects of distribution parameters existed in cable, voltage reflection would be occurred at motor terminals, hence resulting in the voltage at motor terminals be doubled and leading to the winding insulation failure. In this paper, an improved inverter side passive filter was proposed on the bases of analysis of common-mode and differential-mode voltage, and a detailed design procedure of parameters was given. Compared with the conventional filter, the proposed filter could mitigate dv/dt value of common-mode and differential-mode voltage simultaneously. Thus, the side-effects accompanied with them were reduced. The validity of proposed filter was supported by the experimental results.