A three-level T-type inverter has higher efficiency and lower output voltage harmonics compared with the traditional two-level inverter. However, neutral-point voltage fluctuation and common-mode voltage (CMV) can negatively affect the performance of the three-level T-type inverter. This study proposes a novel hybrid variable virtual space vector (HV2SV) strategy to mitigate this problem. Based on the virtual space vector scheme, new variable virtual small and medium vectors are reconstructed with the principle that the change of neutral-point charge of each virtual vector in a switching period is zero, and the adjustment factor is further added to the virtual vector to achieve the balance of the neutral-point voltage. At the same time, the vectors with a large CMV are eliminated to ensure that the CMV is minimised. Therefore, the HV2SV has excellent neutral-point voltage balance control capability and common-voltage suppression at both high- and low-modulation ratios. Theoretical analysis, simulations, and experimental results demonstrate the effectiveness and feasibility of the proposed strategy for full modulation ratios.

中文翻译：

---

基于混合变量虚拟空间矢量的三电平T型逆变器中性点电压平衡控制

与传统的两电平逆变器相比，三电平T型逆变器具有更高的效率和更低的输出电压谐波。但是，中性点电压波动和共模电压（CMV）会对三电平T型逆变器的性能产生负面影响。这项研究提出了一种新颖的混合变量虚拟空间向量（HV2SV）策略来缓解此问题。基于虚拟空间矢量方案，以每个虚拟矢量的中性点电荷在切换周期内的变化为零的原理重构新的可变虚拟中小矢量，并在虚拟矢量上进一步增加调整因子达到中性点电压的平衡。同时，消除具有大CMV的向量，以确保CMV最小化。因此，HV2SV具有出色的中性点电压平衡控制能力，并且在高和低调制比下均具有共电压抑制功能。理论分析，仿真和实验结果证明了所提出的全调制比策略的有效性和可行性。