The calculation of subharmonics in an asynchronous PWM induction motor drive

An asynchronous PWM (pulse width modulation) scheme developed for a traction application is described. This method for determining nonintegral harmonics involves an application of Fourier analysis to the output waveform. Results are presented, including pulse quantization in the controller. The subharmonic content is shown graphically as a function of the modulating frequency ratio to establish the ratio at which subharmonic may be neglected. There is no significant subharmonic production for the three types of modulation technique analyzed. For practical frequency ratios, quantization effects are more significant than differences in modulation technique.<>