Reciprocity-transposition-based sinusoidal pulsewidth modulation for diode-clamped multilevel converters

Modulation strategies for multilevel inverters have typically focused on synthesizing a desired set of three phase sinusoidal voltage waveforms using a fixed number of DC voltage levels. This results in the average current injection and hence the net power drawn from the multiple DC bus terminals to be unmatched and time varying. Subsequently, the DC-bus voltages are unregulated, requiring corrective control action to incorporated. In this paper, the principle of reciprocity transposition in introduced as a means for modeling the DC-bus current injection simultaneously as the modulation strategy is formulated. Furthermore, a new sinusoidal pulsewidth-modulation strategy that features constant and controllable current injection at the DC-bus terminals while maintaining output voltage waveform quality is introduced. The proposed strategy is general enough to be applied to converters with an even number of levels and an odd number of levels. Analytical results comparing the performance of the proposed modulator with a conventional multiple carrier modulator are presented for example multilevel converters with four and five levels. Computer simulation results verifying the analytical results are presented for a four-level converter.