Microprocessor control of PWM inverter for sinusoidal output

The authors describe and analyze two PWM (pulse width modulation) control methods for UPS (uninterruptible power supply) systems. The first method is hysteresis control with a single measure value. The second method is microprocessor-based constant-frequency PWM with a dead-beat controller. Simulation results are presented for a single-phase UPS and a three-phase UPS with a DY transformer using the latter method. It is noted that UPS systems with hysteresis controllers, because of finite turn-on and turn-off times and finite hysteresis width, require a differentiator which is very difficult to implement. PWM with a dead-beat controller has a constant switch frequency; at a switch frequency of 2 kHz, better results were achieved using a smaller LC filter