the main objective of static power converters is to produce an AC output waveform from a DC power supply. The output voltage waveform is not exactly a sinusoidal wave. Some ways should be found to improve the output voltage waveform. This paper introduces a method to minimize the total harmonic distortion (THD) of output voltage waveform in multilevel inverters. Steps amplitude of output voltage wave is so effective in total harmonic distortion. DC voltage sources of a cascade inverter determine the amplitude of steps. Capacitors, batteries, and renewable energy voltage sources can be used as the multiple DC voltage sources. Values of these DC sources could be set optimum to improve the THD. Parametrical Fourier analyzing of output signal would give an equation which helps us in this project. This equation presented in this paper.