Active motor terminal overvoltage mitigation method for parallel voltage source inverters

Motor terminal overvoltage, which is caused by a long motor cable, is a common issue in industrial drives. This oscillating overvoltage can be dealt with by reinforcing winding insulation, yet it will still be a source for electromagnetic interference. Also, the voltage transition rates at the motor terminals may cause other adverse effects, especially when they also contribute to the common-mode voltage waveform. This paper proposes a du/dt filtering method that is dedicated for parallel connected inverters. The proposed method uses an intercell transformer between the parallel phase outputs to limit the circulating current. The leakage inductances of the transformer windings are then used to form an LC low-pass filter, along with an output capacitor. The method uses an interleaved PWM pattern to actively damp the oscillation that would be generated by the switching behavior and the LC circuit. This paper demonstrates the operation of the proposed du/dt filtering method by simulations.