Voltage drops effects in bipolar transistor PWM inverters

Pulse width modulation (PWM) control applied to bipolar junction transistor (BJT) voltage source inverter (VSI) is the most used solution for adjustable speed drives in the power range up to 100 kW. Open loop control to make the V/f rated constant is generally used. However, the inverter output voltage is not purely sinusoidal and the distortion is due to a bunch of power devices features: lock-out time, power transistors and diodes forward voltage drop, transistor storage time and BJTs and diodes differential resistances. The authors present a complete inverter model and the inverter output voltage is calculated keeping into account the power devices nonidealities mentioned above. Simulation results for different carrier frequencies, inverter output frequencies, load characteristics and modulation index are presented. Finally, some experimental results for validating the method proposed are shown