ANALYSIS OF PWM VOLTAGE SOURCE INVERTERS IN THE OVERMODULATION REGION

In this paper is analyzed PWM Voltage Source Inverter in the overmodulation region. The waveform symmetries and the proportionality between the reference magnitude and the fundamental voltage generated are also maintained in the overmodulation zone. In continuity will be shown that the relationship between the control variable and the fundamental voltage generated differs widely with the strategy and the pulse number used in low switching frequency PWM techniques unlike that at high switching frequencies. The shape of the output voltage waveform is only partially under control. The modulator effectively loses control of the output waveforms becomes progressively distorted and includes low-frequency harmonics of the fundamental component. As a result the boundaries between any two consecutive zones of modulation and the maximum modulation index also vary with the strategy and the pulse number used. The performance of the different strategies is evaluated. Simulations results are included to verify the derived expressions.