Question

The output voltage waveform of a three-phase square wave inverter contains

Answer 1

The output voltage waveform of a three-phase square wave inverter contains only odd harmonics.

when the output of a square wave inverter is decomposed into it's fourier transform it contains only odd harmonics and probably a DC component. All the even harmonics are cancelled out.

The generated harmonics in the inverter output mainly depends on the switching frequency of the PWM. Inverter produces a symmetric waveform that falls somewhere in the range of triangle wave, sine wave, and square wave. These waveform contains significant odd harmonics and insignificant even harmonics.