A Universal Common Mode Voltage Suppression Algorithm for AC Motors With Odd-Phase Number

Abstract

Multiphase ac motors are widely used in wide-speed and high-power applications. However, under pulsewidth modulation (PWM), the system inevitably generates common mode voltage (CMV) and poses a threat to the system. Especially, odd-phase ac motors driven by two-level multiphase inverters cannot achieve the elimination of CMV in theory. This article proposes a universal suppression algorithm for CMV of odd-phase ac motors. By appropriately injecting zero-sequence voltage and pulse phase shifting, the amplitude reduction and constant amplitude control of CMV can be achieved at different maximum modulation ratios, respectively. The CMV amplitude reduction control suppresses the CMV amplitude to positive and negative minimum values, while the CMV constant amplitude control keeps the CMV amplitude constant to positive minimum or negative minimum values. This algorithm can effectively reduce the common mode (CM) electromagnetic interference (EMI) of the system. The algorithm can be simply implemented by carrier comparison PWM and requires little calculation time. Finally, simulation and experimental results demonstrate the effectiveness of the proposed algorithm in suppressing the CMV of odd-phase motors.