Additional harmonic losses of induction motors by PWM inverters: Comparison between result of finite element method and IEC/TS 60034

Abstract

In this study, we investigate the additional harmonic losses of induction motors driven by PWM inverters from both results of experiments and calculations. In the experiments, the additional loss caused by the inverter carrier is obtained by subtracting the total input of the motor driven by a sinusoidal power supply from that of the motor driven by the inverter. In the calculation, a combined 2-D and 1-D finite element method is applied in order to take into account the skin effect in electrical steel sheets used for the core. Then, the components of the additional motor loss are individually calculated according to their origins. Both the experimental and calculated results show that the total additional loss caused by the inverter decreases with an increase in the switching frequency and that the total additional loss does not depend on load conditions. These tendencies are exactly the same as that described in IEC/TS 60034. On the other hand, the finite element method reveals the variation in each loss component with switching frequency and load conditions. It is concluded that the variation in the additional loss with the switching frequency is mainly attributed to the variation in the core loss. In addition, the ratio of harmonic copper and rotor cage losses increase whereas that of harmonic core loss decreases with load because of an increase in the magnetic saturation at the rotor surface.