Study on common mode voltage suppression based on three-phase four-leg inverter

In PWM inverter fed induction motor system, with the increase of the switching frequency, the negative effects on the motor and the electromagnetic compatibility problem to the peripheral equipment produced by the common-mode voltage have been focused. This paper presents a three-phase four-leg topology, and adopts NZPWM control strategy to suppress common-mode voltage, at the same time, this paper analyses the topology structure of the three-phase four-leg and the principle of suppressing the common-mode voltage by NZPWM control technology, and provides the control strategy of the fourth leg. Further more, based on Matlab simulation platform, this paper make the simulations with SVPWM and NZPWM control strategies on the traditional three-phase three-leg, and it also simulates the new three-phase four-leg with NZPWM control strategy. The simulation results show that three-phase four-leg topology combined with NZPWM control strategy can restrain common-mode voltage and common-mode current effectively.