To solve the issue of neutral-point (NP) balancing in the three-level NP-clamed inverter, a novel carrier-based pulsewidth modulation (CPWM) strategy of double modulation waveforms is proposed in this paper. By combining the injection of zero-sequence voltage with the decomposition of modulation waveform organically, NP balancing is achieved over full range of inverter output voltages and load angles for linear loads. Furthermore, the switching frequency of power devices is significantly reduced as an optimal selection method of zero-sequence voltage is applied for the proposed strategy, which is equal to that for the CPWM strategy of single modulation waveform. Effectiveness of the proposed strategy is validated by both theoretical derivation and experimental results.
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Wang et al. (2016) studied this question.