Use of Synchronous Modulation to Recover Energy Gained From Matching Long Cable in Inverter-Fed Motor Drives

As inverter-fed motor drives generate fast-switching voltage pulses, the transmission-line effects on long motor cable and motor stator windings lead to overvoltage on the cable and motor terminals, as well as inside motor stator windings, and also an increase in the common-mode current. Such phenomenon would cause premature failure of motor and cable insulation. A general protective measure is the use of a passive filter, such as RC and RLC filter, to reduce the voltage surges by matching the cable impedance and/or altering the rise time of the voltage pulses. However, passive filters are bulky and lossy. This paper presents an active motor terminal filter with energy recovery function that can achieve the same functions as the passive filters, but consumes much less power. The proposed filter recovers energy gained from suppressing motor terminal voltage surges and regenerating the recovered energy back to the whole system. An experimental filter has been built and evaluated on a 1-hp three-phase motor drive system. A comparative study into the performance among commonly used RC filter and RLC filter and the proposed filter will be given.