A low-loss motor terminal filter for overvoltage suppression

Inverter-fed motor drive systems are widely used because of their benefits for energy efficiency and for flexible control of machinery using maintenance-free induction motors. As the inverter produces fast-switching voltage pulses, the transmission-line effects of the motor cable and motor stator windings become significant, and may lead to a doubling of the supply voltage to the motor and to the cable, causing premature failure of the motor and cable insulation. A typical protective measure is to use a passive filter to reduce the surge voltage and alter the rise time of the voltage pulses at the motor terminals. However, the filters have the drawbacks of bulky size and lossy. Importantly, the filter parameters are dependent on the cable length and characteristics. This paper presents a low-loss motor terminal filter that can suppress overvoltage and modify the rise time of the voltage pulses at the motor terminal for cables of any length. A comparative study into the performance between the popularly-used RC and RLC filters, and the proposed filter will be conducted. The proposed structure is confirmed by studying the experimental results of a 1-hp motor drive system.