LC-filter Resonance Cancellation with DPWM Inverters in Adjustable Speed Drives

Discontinuous PWM methods cannot easily be used in LC-filtered inverters for adjustable speed drives, as it causes resonances in the filter. This paper present a new method to cancel the resonance and compares this method to previously proposed methods. Wide band gap devices are entering the market offering high switching frequencies and low switching loss due to fast turn on and turn off. The fast turn on and turn off generates high dV/dt, which must be filtered e.g. to protect motors from bearing stress and avoid EMC issues. Discontinuous PWM methods can be reduced to reduce the losses in the inverter and filter. Instead of abruptly clamp in one of the inverter legs and cause resonance in the filter. This method will charge or discharge the filter capacitor before clamping, this way the capacitor current is zero, and the capacitor voltage is equal to the average inverter voltage. Thereby, no resonance will be generated in the filter. Simulations show that the proposed method effectively reduces the resonance in the filter.