The impact of switching frequency on PWM AC drive efficiency

The number of ac drives present in the power systems of most industrial facilities has shown a significant increase in the past 3 decades, taking an important percentage of the total power demand. Two options to produce energy savings on these drives is the use of an optimized flux level, and the operation with reduced switching frequency. Paper reports the development of a complete loss model for vector controlled low-voltage ac drives, which includes all converter and motor loss components. Using this loss model, an algorithm is implemented to run detailed loss evaluations in the entire constant-torque zone. Four ac drives of 4 kW, 11 kW, 55 kW and 110 kW are evaluated considering switching frequencies of 1 kHz, 2 kHz, 4 kHz and 8 kHz. Results confirm that reducing the switching frequency from 8 kHz to 2 kHz produce interesting power savings, while keeping a low level of harmonic content and a safe operation of the ac drive.