Based on the transmission theory, the mechanism of the generation of the motor terminal over voltage caused by the long line transmission of PWM pulses in the PWM variable frequency driving system is studied. This paper focuses on the effects of the variant length and characteristic impedance of cables on the over voltage by large numbers of experiment results. In terms of the impedance matching method, a network fixed at motor terminal is designed to reduce the over voltage. The utility of this network is testified by the experiments.
