High-Frequency Harmonic Loss Location Verification Using Temperature Rise

The additional high-frequency harmonic losses in the stator of an electrical machine are a consequence of pulse-width modulation (PWM). These losses are mainly due to the added harmonics from the PWM supply, which increases the eddy current and hysteresis losses in the iron sheets. In this paper, high-frequency harmonic losses are studied using a specially constructed 5-kW, four-pole squirrel cage induction machine equipped with 18 Pt-100 sensors. To enable observation of differences in local temperature rise, the same operating points of the motor are measured for generator supply providing a sinusoidal voltage and for converter supply. These findings are further supported by a complementary simulation in which the same motor is modeled using the finite element method (FEM) for both power supply configurations. The differences in temperature rise can be directly used to indicate the location of the increased losses due to PWM supply. In addition, the harmonic power of the supply waveforms recorded in the experimental tests with different switching frequencies are extracted and compared with the temperature rises to verify the loss increase. It is found that the losses behave similarly to the increase in temperature, thus confirming their correctness.