Space vector based pulse density modulation scheme for multilevel inverter control with zero voltage switching

Space vector based pulse density modulation scheme is a control method proposed for multilevel inverter producing octadecogonal space vector. A multilevel inverter is constructed by connecting two level inverter at right end and three level inverter at left end of a three phase transformer winding whose secondary is star connected. This inverter is fed with three different DC voltages possible of generating 18 sided polygon whose vectors are displaced by 20°. Space vector pulse density modulation technique is achieved by comparing the sector and region in which original voltage reference and error voltage resides respectively. As a result of this comparison, optimized switching vector is selected to be applied to multilevel inverter. Output voltage control is achieved by adding zero vectors to the inverter. The proposed scheme results in elimination of lower order harmonics and complicated timing calculations as compared to space vector pulse width modulation. Simulink model and simulation results of the proposed scheme are also discussed.