대용량 전력변환장치의 멀티레벨 펄스폭 변조기법

The three level circuit systems are able to reduce harmonic currents without requiring high frequency switching to the devices, and are suitable for high voltage, large capacity systems. However the three level circuit system has a problem that the mid point potential varies when the current flows into or out of the mid point. the variation causes voltage deviation in the DC waveforms as well as unbalanced voltage stress to the switching devices therefore the variation should be suppressed. In this paper we have proposed a new kind of PWM method for three level circuit system based on the change of phase PWM reference value with the ability to suppress the mid point voltage variation. The new method is easily implemented without complicated calculation and it's performance is similar to space vector modulation. The validity of the proposed method is verified by computer simulation