Comparison between harmonic reduction procedures for 5-level inverters

This paper presents two selective harmonic elimination (SHE) and a mixed SHE-selective harmonic mitigation (SHM) procedures applied to 5-level inverter. The first one is a graphical procedure to control harmonic spectrum of a given voltage and/or current waveform. A fundamental frequency technique using a reference sinusoidal signal (RSS) to modulate the output voltage waveform v(0) is applied, considering unequal dc voltage sources. The switching angles are identified. It is shown that they allow to delete all harmonics except those having order 10 k +/- 1, k = 1, 2, .... The second one is an analytical procedure that eliminates the third and fifth harmonics and their multiple. The third one is a mixed analytical-graphical procedure that eliminates the third and its multiple and reduces the fifth and seventh harmonics. The obtained results are compared and the Total Harmonic Distortion (THD) in all cases is computed.