An Active Low-Loss Motor Terminal Filter for Overvoltage Suppression and Common-Mode Current Reduction

Inverter-fed motor drive systems are widely used in industrial applications because of their energy efficiency and flexible control of machinery using maintenance-free induction motors. As switching inverters generate 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 cable, overvoltage inside the motor windings, and an increase in the common-mode current. Such phenomena cause premature failure of the motor and cable insulation. A typical protective measure is the use of a passive filter to reduce the voltage surges and alter the rise time of the voltage pulses at the motor terminals. However, most passive filters have the drawbacks of bulky size and high power loss. This paper presents an active terminal filter that can perform the same functions as the passive filters with low power dissipation. An experimental filter has been built and evaluated on a 1-hp three-phase motor drive system with different motor cable lengths. A comparative study into the performance among the commonly used RLC filter and RC filter, and the proposed filter is provided.