Common-mode voltage and vibration mitigation of a five-phase three-level NPC inverter-fed induction motor drive system

Abstract

Common-mode (CM) voltage is one of the main reasons for the flow of bearing currents in induction motors (IM) that ultimately leads to the bearing failure and causes severe vibrations. For three-phase IM drives, many works have been reported either on the reduction or on the elimination of CM voltages that are generated due to pulse width modulation (PWM) action of the feeding power converters. However, for five-phase IM drives, very few studies are available with the perspective of the CM voltage elimination. Also, the effect of CM voltage on the mechanical vibrations of a five-phase IM has not been reported in the literature. Hence, in this paper, firstly, the modeling of CM current generated in the five-phase IM is done and its expression based on admittance transfer function is derived. Then the CM voltage is eliminated from a five-phase three-level neutral point clamped (NPC) voltage source inverter. The space vector pulse width modulation (SVPWM) technique is developed for the elimination of CM voltages. Only those switching states are selected which give zero CM voltage. The same selected switching states also give the balanced dc link capacitor voltages. Its effect is observed on the mechanical vibration of the motor and it is correlated with the CM current. The mechanical vibration is observed for both, with and without CM voltage elimination. Both the simulation and experimental results are given to validate the concept proposed.