A novel direct digital SPWM method for multilevel voltage source inverters

A novel direct digital Sine Pulse Width Modulation (SPWM) method based on equal-area theorem for multilevel inverters is proposed in this paper. The principle of the proposed modulation schemes is elaborated, and the best scheme with the lowest THD is identified. The THD and fundamental voltage produced by the proposed method with modulation index M from zero to its maximum value are calculated and compared with carrier-based SPWM method. It is demonstrated that the proposed direct digital SPWM method can provide far lower THD while its fundamental voltages are on par with the carrier-based SPWM method. Other advantages of the proposed modulation scheme include simplicity, digital oriented, and generalized for multilevel inverter with any levels and any topologies. Simulations and experiments are carried out. The experimental results agree well with simulations, which prove the validity of the proposed digital SPWM method.