Influence of inverter output filter on the selection of PWM technique

This paper deals with the suitability of various pulse-width modulation techniques for a variable-speed AC drive equipped with a sinusoidal differential-mode and common-mode filter at the inverter output. Simulations and experiments are used for the investigation. If the average common-mode voltage is changed abruptly, the filter resonance may be excited, and the common-mode voltage at the motor terminals may rise to values higher than those obtained without the filter. This phenomenon may cause difficulties when the modulation is started, and it also creates a fundamental problem when a two-phase modulation method is used. The resonance problem can be avoided by selecting a modulation technique that does not cause sudden changes in the average common-mode voltage. A starting algorithm is proposed, enabling a trouble-free start of the drive equipped with a sinusoidal common-mode filter.