Fundamental and carrier frequency-dependence on electric field and power dissipation for Inverter-fed High Voltage Rotating Machine

In this study, transient analysis of Stress Grading(SG) system under PWM waveform is conducted to reveal the effects of fundamental frequency on potential distribution and power density. Risetime, level and jump voltage of PWM waveform used in an analysis is 1 mu s, 3 and 5 kV, respectively. Fundamental and carrier frequencies are changed in the range from 50-500 Hz and 0.5-6 kHz, respectively. For comparison, analyses under sinusoidal and square voltages which correspond to fundamental and carrier frequencies are conducted. Analytical results show that maximum surface field on SG system under PWM waveform is 1.1 times higher than that under square voltage regardless of fundamental and carrier frequencies. Power density under PWM waveform increases than that under square voltage. The value of power density under PWM waveform is estimated by the sum of power density under sinusoidal voltage which corresponds to fundamental frequency and square voltage which corresponds to carrier frequency. The error of this estimated value is in the range from 8-15 %. This shows that estimated value is accurate enough to estimate temperature rise under PWM waveform.