Sliding Carrier SPWM for Voltage Balancing in Multilevel Inverters

Abstract:
A new modulation method to realize equalized energy extraction from the cells in a multilevel inverter (MLI) is proposed in this paper. This method is based on changing the location of the carrier waveform corresponded to each cell within one cycle, to control the delivered energy value by the cell. In order to recognize time points in which the transitions will take place between carrier waveforms, an energy study is carried out. The procedure provides the scheme for the first quarter cycle and for the second quarter cycle a sophisticated swapping will be used to make energy extraction even more equal. Since the proposed method is based on energy study, it is more effective compared to the methods trying to bring equalization by time interval balancing. The sliding carrier method is particularly useful for the MLIs with higher number of levels. Simulation results prove approximately 98% reduction in the variance value for the delivered energy values of different cells.