A novel modulation strategy of three level NPC converter

The problem of neutral-point potential balancing of three-level NPC converter has always been the focus in its research. In all modulation strategies of three-level NPC converter, double modulation wave carrier-based PWM (DMWPWM) is a kind of strategy which achieved the neutral-point potential balance in full-scale power factor. This paper firstly analyzes the basic principle of DMWPWM strategy, and then it proposes a new modulation strategy of three-level NPC converter based on DMWPWM strategy. This modulation strategy is characterized by two sets of modulated waves: three-phase sinusoidal wave is the first, and the second group of modulated waves is calculated in this paper. The two sets of modulating waves take turns to act on the three-level NPC converter in two switching cycles so that the three-level NPC converter achieves the neutral-point potential balance under the full modulation index and the full power factor. Compared to DWMPWM strategy, this modulation strategy is simpler and easier to implement, also the correctness of the theoretical analysis has been verified by the simulation results.