A New Switching Angle Calculation Method for a Symmetrical Multilevel Inverter

The quality of the multilevel inverter (MLI) output voltage depends on the instants of level shifting in a cycle of AC output waveform. These instances are called switching angles. In this paper, a new method for switching angle calculation is suggested for symmetric multilevel inverters. The proposed method is derived based on superposition of square and sinusoidal waveforms and is applicable to multilevel inverters with odd number of levels in output. In the proposed method the switching angles are expressed as a function of the level height, for unit amplitude output AC staircase waveform. It is found that for a fixed number of levels in output AC waveform, there are limits on the range of the level height. Further, it is observed that the values of total harmonic distortion, harmonic components, and fundamental voltage depend on the level height. The variation of each of the above parameters with the full range of the level height for three, five, and seven level output AC voltage is obtained numerically and presented here. These results are applicable for any number of odd levels in output AC voltage, and are useful in optimizing the output voltage quality of multilevel inverters.