In this study, a review on high-frequency modelling in electric machines is conducted. Pulse-width modulation (PWM) creates common-mode-voltage (CMV) and common-mode-current (CMC) in electric drives with high-frequency impacts such as shaft voltage and bearing current which in turn cause bearing failures. To predict and reduce these failures in an electric machine, transitional modelling of high-frequency pulses is necessary. At the first step, several methods for high-frequency modelling in an electric drive are categorised. At the second step, several types of bearing currents discussed and CMV and CMC in electric drives are introduced. At the third step, CMV, CMC and bearing currents are simulated for six types of PWM methods and experimental verification is reported. Finally, root-mean-square value of a distorted parasitic current is introduced for comparing the electromagnetic effects of PWM methods.

In this study, the theory of pulse width modulation (PWM) is developed for both sine-wave PWM (SPWM) and chaotic sine-wave PWM (CSPWM). In SPWM, power spectra are analysed by an analytical method such as double Fourier series (DFS) technique, and the integral-series Fourier method is fully devised and analytically theorised for CSPWM. It is shown that the root-mean-square value of inverter's zero-sequence voltage does not rely on carrier and reference frequency in fixedfrequency SPWM, while in CSPWM, this depends on frequency modulating gain and chaotic sequence of numbers. Also, the computation time of purely numerical harmonic analysis can be much heavier than analytical ones. Furthermore, the DFS and integral-series Fourier methods are applied to SPWM and CSPWM with two different frame sizes of squirrel cage motors for the shaft voltage and the electromagnetic interference (EMI). The numerical and experimental results show that CSPWM can have positive effect on the shaft voltage while it definitely weakens the EMI problems.

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