Combination of Zero Common Mode and Spread Spectrum for Four-Module Motor Drive Systems

In parallel three-phase inverters, zero common-mode voltage can theoretically be achieved through zero common-mode modulation techniques. The advantage of spread spectrum PWM over constant switching frequency PWM is its ability to eliminate peaks of EMI. Therefore, this paper proposes a modulation method that combines zero common-mode and variable switching frequency to simultaneously reduce common-mode EMI and differential-mode EMI. Under the premise of using the zero common-mode vector, this method uniformly changes the switching period within a certain range, employing a four-module motor as the load for modulation. Simulation results show that this strategy not only achieves zero common-mode voltage but also reduces conducted EMI by more than 20 dB, confirming the effectiveness of the proposed method.