This paper presents an improved pulsewidth modulation strategy in conjunction with an optimal compensator for fast capacitor voltage balancing in three-level neutral-point-clamped (NPC) inverter. The voltage balancing compensator is designed in such a way that it produces optimal unbalance compensation coefficient according to the inherent limitations related to the variability range of modulating signals. It generates maximum compensating neutral current for the full modulation depth extending into overmodulation region and throughout the entire range of load power factor angles, and thus improves the unbalance compensation ability for all the operating conditions of the inverter. The optimal compensation offset signal corresponding to each operating point is determined from the boundary limit of the auxiliary modulating signals. Particle swarm optimization is applied for such purpose. The performance of the proposed optimal compensator for different combinations of modulation index and load power factors are evaluated through extensive simulation study using Matlab/Simulink and validated in experimentation using a three-level NPC inverter prototype with induction motor load. Finally, the voltage balancing performances of the proposed compensator are compared with that available in literature to confirm the usefulness of the proposed concept.

中文翻译：

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三电平NPC逆变器快速电容电压平衡的改进调制策略


本文提出了一种改进的脉宽调制策略，结合最佳补偿器，可在三电平中性点钳位 (NPC) 逆变器中实现快速电容器电压平衡。电压平衡补偿器的设计方式是根据与调制信号的变化范围相关的固有限制来产生最佳的不平衡补偿系数。它在延伸到过调制区域和整个负载功率因数角范围的全调制深度内产生最大补偿中性点电流，从而提高了逆变器所有运行条件下的不平衡补偿能力。每个工作点对应的最佳补偿偏移信号由辅助调制信号的边界限制确定。粒子群优化就是为此目的而应用的。通过使用 Matlab/Simulink 进行广泛的仿真研究，评估了所提出的针对不同调制指数和负载功率因数组合的最佳补偿器的性能，并在使用带有感应电机负载的三电平 NPC 逆变器原型的实验中进行了验证。最后，将所提出的补偿器的电压平衡性能与文献中的电压平衡性能进行比较，以确认所提出的概念的有用性。