Formulation of phase voltage and calculation of its total harmonic distortion in multilevel Z-source inverter

Multilevel inverters have recently been received more attention in the power industry. Two traditional types of multilevel inverters are multilevel voltage-source inverter and multilevel current-source inverter. Despite this widespread use, multilevel Z-source inverter (ML-ZSI) has not been regarded enough, because a unique approach to voltage control of ML-ZSI has not yet been presented. Besides, the phase voltage and its total harmonic distortion (THD) have not been calculated for ML-ZSI so far. This study proposes two new methods for the formulation of phase voltage in ML-ZSI. The first method is based on Fourier series analysis of the phase-voltage waveform, and the second utilises the staircase waveform of the phase voltage. In addition, two new methods are introduced for computing the phase-voltage THD in ML-ZSI: approximate method and waveform-integration method. Although the waveform-integration method leads to the accurate answer, using this method is more difficult than an approximate method. The detailed description of suggested methods and comparison with each other are presented in this study. Simulation and experimental results are also given to demonstrate the new features of the proposed methods.