A new concept in regulation of dc sources in cascaded multi-level inverters to improve output voltage total harmonic distortion

In cascaded multi-level inverters, it is usually assumed that the dc sources have the same constant voltage and output harmonics minimization is accomplished by applying proper switching angles. Employing different dc voltages with proper ratios can result in further reduction of the harmonics. This paper introduces a new concept in selecting the values of the input dc source voltages in cascaded multi-level inverters in order to improve the output voltage total harmonic distortion (THD). After formulation of the system, i.e., describing the inverter’s output voltage components in terms of the switching angles and unequal dc source voltages, a rule is applied to obtain the step heights of the staircase output waveform (dc source voltages), so that the output waveform becomes as close to the required fundamental sine wave as possible. Substituting the obtained dc source voltages into the harmonics elimination equations results in a set of equations, which are functions of switching angles only. Solving the...

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