Topic: Power Electronics
A single-phase inverter using bipolar PWM produces an output voltage waveform with a switching frequency much higher than the fundamental frequency. If the modulation index Ma is increased from 0.8 to 1.2, how does the amplitude of the fundamental output voltage change?
- A. It increases linearly with Ma even beyond 1
- B. It increases with Ma even beyond 1 and then saturates
- C. It saturates and remains constant beyond $Ma=1$
- D. It decreases beyond $Ma=1$
Answer: B. It increases with Ma even beyond 1 and then saturates
Explanation: In sinusoidal PWM, when the amplitude modulation index $M_a \le 1$ (linear region), the fundamental output voltage amplitude is linearly proportional to $M_a$. When $M_a$ is increased beyond 1 (overmodulation, e.g., to 1.2), the output voltage continues to increase but non-linearly. It eventually saturates to the fundamental amplitude of a pure square wave ($\frac{4}{\pi} V_d$) as $M_a$ becomes very large.