This paper proposes a hybrid modulation strategy for a medium-voltage hybrid seven-level (7-L) converter, which consists of a three-phase silicon (Si) IGBT-based active-neutral-point-clamped (ANPC) stage and a cascaded silicon carbide (SiC) MOSFET-based H-bridge (HB) stage in each phase. Within the framework of the proposed modulation strategy, three floating HB converters are controlled using a high-frequency three-level (3-L) space-vector-modulation (SVM), while a low-frequency modulation is applied to the ANPC converter. To regulate the DC voltages across floating capacitors, a zero-sequence voltage (ZSV) injection method is adopted. The proposed method possesses three major advantages. First, it enables the simplification from a 7-L to a 3-L SVM, which significantly reduces the computational burden. Second, with all the high-frequency switching actions assigned to SiC devices in the HB stage, the power loss of the hybrid 7-L converter is reduced. Third, the hybrid modulation together with the ZSV injection enables a wider stable operating range compared to the existing 7-L SVM method. Finally, both simulation and experimental results performed on the scale-down and the full-scale 1 MVA prototype validate the effectiveness of the proposed hybrid modulation strategy.

中文翻译：

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Si/SiC 混合多电平转换器的有源混合调制策略


本文提出了一种中压混合七电平 (7-L) 转换器的混合调制策略，该策略由基于三相硅 (Si) IGBT 的有源中性点钳位 (ANPC) 级和一个每个相位中级联基于碳化硅 (SiC) MOSFET 的 H 桥 (HB) 级。在所提出的调制策略的框架内，使用高频三电平 (3-L) 空间矢量调制 (SVM) 控制三个浮动 HB 转换器，同时对 ANPC 转换器应用低频调制。为了调节浮动电容器上的直流电压，采用了零序电压（ZSV）注入方法。所提出的方法具有三个主要优点。首先，它可以将 7-L SVM 简化为 3-L SVM，从而显着减少计算负担。其次，通过将所有高频开关动作分配给 HB 级中的 SiC 器件，可以降低混合 7L 转换器的功率损耗。第三，与现有的 7-L SVM 方法相比，混合调制与 ZSV 注入能够实现更宽的稳定工作范围。最后，在缩小尺寸和全尺寸 1 MVA 原型上进行的仿真和实验结果验证了所提出的混合调制策略的有效性。