A new PWM method to reduce beat phenomenon in large-capacity inverters with low switching frequency

In an asynchronous pulsewidth modulation (PWM) method, the ratio of the car rier frequency to the fundamental frequency must be at least 15-20 in order to suppress the beat phenomenon. However, it is impossible to achieve this condition for large-capacity inverters (e.g., gate-turn-off thyristor inve rters), when the fundamental frequency is high. Assuming that the beat phen omenon is caused by an error generated in the PWM process, we have introduc ed a compensator to reduce the error. As a result, beat phenomenon can be d ecreased for a low carrier frequency. Effectiveness of the proposed method is shown by experimental results.