A Hybrid Modulation Method With the Maximum Controllable Range of the Neutral-Point Current for Three-Level NPC

In order to analyze the maximum neutral-point (NP) voltage controllability of the three-level NPC under carrier-based pulsewidth modulation, this article deduces the accurate relationship between the three degrees of freedom under carrier-based pulsewidth modulation (zero-sequence voltage, zero-level disassembly phase, and the extent of zero-level disassembled) and the NP current. Meanwhile, a hybrid method is proposed to obtain the suitable values of the three degrees of freedom that can achieve the maximum controllable range of the NP current directly. Therefore, the proposed hybrid method avoids the huge computational burden caused by the cyclic traversal method. Compared with the traditional method of injecting zero-sequence voltage or disassembling the zero level, the proposed method can realize the maximum controllability of the NP voltage under the full range of the power factor and the modulation index with a lower switching frequency. The proposed method is verified by experiments.