Comparison between approximate and accurate line voltage THD, case II: Multilevel inverter with equal DC sources

Multilevel inverters have found wide applications in industry, especially in high-voltage and high power. Many researchers have attended to decrease the produced harmonic content of output voltage waveform. One of the criteria to determine the harmonic content, which is very popular, is Total Harmonic Distortion (THD). Therefore, determination of its actual amount is important. The voltage of three-phase multilevel inverter is divided to phase voltage and line to line voltage. In previous studies, the formula of phase THD has been calculated. In this paper, a new method is proposed which against the old approximate methods, takes all harmonics into account for the line to line THD of multilevel inverter with equal DC sources. To show difference between the proposed actual method and the approximate methods, a comparison is carried out for the 3, 5, 7 and 11 level inverters. For writing the codes and simulation, MATLAB software is used.