A VSFPWM Method of Three-Phase CSI for EMI Mitigation based on DC Current Ripple Prediction

Pulse-width-modulation (PWM) is one of the main reasons of electromagnetic interference (EMI) in switching power converter. The level jump, high di/dt and dv/dt of output square-wave voltages or currents caused by the switching process of active components like IGBT or MOSFET lead to the increase in harmonics near switching frequency, its multiples and even higher. And frequency variation is an effective method to mitigate EMI. A variable switching frequency pulsewidthmodulation (VSFPWM) method for three-phase current source inverter (CSI) is introduced in this paper. Based on the ripple prediction of DC current, switching frequency is designed to be updated in DSP in every interruption period to keep the ripple current of DC inductor constant. Both simulation and experiment results show that the application of VSFPWM in CSI can significantly reduce switching losses and suppress differential mode (DM) EMI noises.