Assessment of PWM-Related Harmonic Losses in Three-Phase Induction Motors of Different Efficiency Classes

In three-phase squirrel-cage induction motors (SCIMs) fed by variable-speed drives (VSDs), the no-load harmonic losses associated with the pulse-width modulated (PWM) voltage can have a significant impact on motor efficiency and temperature rise. Moreover, the PWM switching frequency selected in the VSD has a direct impact on SCIM PWM-related harmonic losses, VSD inverter losses, and power drive system (PDS) efficiency. In this chapter, the main results of an experimental assessment of PWM-related losses in a 7.5-kW PDS integrating a commercial VSD and a 4-pole SCIM of IE1, IE2, IE3, and IE4 efficiency classes are presented for 2-, 5-, 16-kHz switching frequency and 25- and 50-Hz fundamental frequency, at no-load and rated-torque operation. Based on experimental data, the coefficients of empirical equations to model VSD losses and SCIM PWM-related losses are found using an evolutionary solving method. These equations can be used to fairly predict the best switching frequency and expected efficiency of VSD, SCIM, and PDS for different operating conditions. Among all motors tested, the IE4-class SCIM showed the highest no-load loss percentage increase due to PWM-related harmonic losses.