Spectral calculation of the output voltage of an inverter with unipolar pulse width modulation

Inverters with pulse width modulation are used for connecting DC and AC networks, e.g. in uninterrupted power supply systems, AC electromotor drives, for powering induction furnaces, in audio technique. The output voltage spectrum of inverters with unipolar pulse width modulation in the case of triangular carrier signal contains a harmonic with frequency equal to the frequency of the modulating signal. It also contains harmonics with frequencies equal to the sum of frequency of the modulating signal and a multiple of double the frequency of the carrier signal. Analysis of the inverter´s output voltage harmonics was performed in time domain via development of the inverter´s output voltage waveform into a sum of periodical waveforms and by calculating spectrums of each individual part. The dependency of the amplitudes and frequency spectra on the wave forms of the carrier signal and modulating signal was demonstrated.