Analysis of the voltage harmonics of PWM voltage fed inverters using high switching frequencies and different modulation functions

This paper presents different methods to determine the harmonics of pulse width modulated patterns by means of a minimum on mathematical equations. The first solution is based on a FFT algorithm and allows detailed investigations for a low frequency ratio of the PWM. The second solution consists of a single expression by which any harmonic based on a high switching frequency can be determined. It can, however, also be applied at low frequency ratios above z 15 and takes different modulation schemes into account. Starting from the pure sinusoidal PWM a third harmonic can be injected, the space vector modulation can be applied or the flat top modulation can be considered. The third approach calculates the most important harmonics of the PWM by a simple equation which can be solved without numerical help. The results of the paper are suitable for three phase PWM transistor inverters in electrical drives or in line converters.