Enhancement of Carrier-Based Modulation Strategies for Multilevel Converters

Carrier-based modulation strategies can be improved by inclusion of zero sequences in the modulation signals. In this paper, the modulation signals of a three-level neutral-point-clamped converter are modified to achieve maximum benefit of the DC-link voltage, and to help achieve voltage balance between the DC-link capacitors. The proposed strategy is obtained from the analysis of space-vector modulation patterns. Therefore, compared to standard sinusoidal PWM, 15% larger amplitudes of the output voltage fundamentals, better voltage-balancing performance, and lower switching frequencies in the devices can all be achieved. Furthermore, implementation of this modulation technique in a digital-signal processor is much easier than space-vector modulation, and also lowers processing time requirements. Efficiency of the modulation algorithm is verified by simulation and experiment