This article introduces a hybrid nine-level inverter topology with extended dc-bus utilization for operation at over modulation range without the presence of lower order harmonics (predominantly fifth and seventh) when compared to conventional two-level and multilevel inverter with hexagonal voltage space vector structure. The proposed inverter is a cascade of a five-level T-type unit and an H-bridge (HB) unit. An increase in the dc-bus utilization is possible by increasing the pole voltage levels to $\pm (V_{\text{dc}}/2+V_{\text{dc}}/8)$ using the HB capacitor voltage and also the capacitor voltages are balanced by adding a offset to sine reference. The aforementioned pulsewidth modulation strategy allows us to increase the peak phase fundamental voltage from $0.577V_{\text{dc}}$ to $0.625V_{\text{dc}}$ in case of unity power factor (p.f) load and to $0.637V_{\text{dc}}$ for 0.82 p.f load with the proposed nine-level inverter. The limiting factor on increasing the dc bus utilization such as p.f, HB capacitor balancing are analysed broadly in this article. The proposed inverter scheme and its claim of increasing the peak phase fundamental voltage is experimentally validated in a laboratory prototype.

中文翻译：

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具有 T 型和 H 桥的级联九电平逆变器拓扑结构，可提高直流总线利用率

本文介绍了一种混合 9 电平逆变器拓扑，与具有六边形电压空间矢量的传统两电平和多电平逆变器相比，该拓扑具有扩展的直流总线利用率，可在不存在低阶谐波（主要是五次和七次谐波）的情况下在超调制范围内运行结构体。建议的逆变器是一个五电平 T 型单元和一个 H 桥 (HB) 单元的级联。通过将极电压电平增加到 dc 总线利用率可以增加$\pm (V_{\text{dc}}/2+V_{\text{dc}}/8)$使用 HB 电容器电压以及通过向正弦参考添加偏移来平衡电容器电压。上述脉宽调制策略允许我们将峰值相位基波电压从$0.577V_{\text{dc}}$ 至 $0.625V_{\text{dc}}$ 在单位功率因数 (pf) 负载的情况下 $0.637V_{\text{dc}}$对于 0.82 pf 负载和建议的九电平逆变器。本文广泛分析了提高直流总线利用率的限制因素，例如 pf、HB 电容器平衡。所提出的逆变器方案及其增加峰值相位基波电压的主张在实验室原型中得到了实验验证。