A New Control Strategy for Multilevel Inverter to Reduce THD

The paper deals with a new control strategy for single-phase multilevel inverter with asymmetrical input dc sources to reduce total harmonics distortion (THD) of output voltages. Multilevel inverter circuits have been designed and simulated using PSIM software to generate 3 to 9-level output voltages. The switching angles at different voltage levels has been changed in accordance with the value of sinusoidal wave. Unequal independent dc sources have been connected to each Hbridge unit. The driving signals at the gate of MOSFETs of the H-bridge units have been applied using gating blocks with proper switching angles. The THD of output voltage was estimated without any filter circuit at the output. This study shows that THD of the output voltage of proposed inverter has been decreased significantly when the number of voltage steps at the output of inverter with changing of switching angle in sinusoidal steps compared to THD obtained in case of switching angle changed in equal steps.