Investigation of Additional Harmonic Losses in Induction Motors Driven by PWM Inverters: Variation with Slot Shapes and Load Conditions

The additional harmonic losses in induction motors driven by PWM inverters are investigated from both results of experiments and finite element methods. Both the experimental and calculated results show that the total additional motor loss decreases with an increase in switching frequency, whereas it does not depend on load conditions. On the other hand, the finite element methods reveal the variation in each loss component with switching frequency, load conditions, and rotor-slot shapes. It is clarified that the components of additional motor loss considerably varies with these factors. In the closed rotor slot motor, the harmonic core losses decrease whereas the harmonic secondary cage losses increase with load. On the other hand, in the semi-closed slot motor, the ratios of these components are not considerably changed with load. This difference is mainly caused by the variation in magnetic saturation and skin effect at the rotor bridges of closed slot motor.