Abstract To reduce the number of power conversion stages and achieve the direct connection to medium-voltage (MV) grid without line-frequency transformer integration, a three-terminal hybrid AC/DC microgrid with one AC port and two DC ports has attracted great interests. It is composed of a cascaded H-bridge (CHB) converter based AC grid port and two dual active bridge (DAB) converters based DC microgrid ports. The large number of power modules increases the probability of module failure, which may cause unbalanced capacitor voltages of CHB converter and unstable DC microgrid voltages. This paper proposes an improved power regulation method with a combination of zero-sequence voltage (ZSV) and negative-sequence current (NSC) injection. When module failure occurs, first, ZSV is injected to adjust the modulation margin in the faulty phase; then, based on three-phase power analysis, NSC injection is activated to realize DC voltage balancing control in three clusters. In addition, the constraints ofZSV and NSC injection are respectively investigated, and the selection of injected ZSV and the derived NSC are analyzed. In a three-terminal hybrid AC/DC microgrid, the simulation waveforms validate the effectiveness of the proposed fault-tolerant operation scheme with the stable DC microgrid voltages and balanced DC capacitor voltages. Experimental results on a CHB converter also verify the effectiveness of the proposed scheme.

中文翻译：

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一种改进的三端交直流混合微电网模块故障时的功率调节方法

摘要 为减少功率变换级数，实现中压电网直接接入，无需工频变压器集成，一个交流端口和两个直流端口的三端交直流混合微电网引起了人们的极大兴趣。 . 它由一个基于级联 H 桥 (CHB) 转换器的交流电网端口和两个基于双有源桥 (DAB) 转换器的直流微电网端口组成。功率模块数量多，增加了模块故障的概率，可能导致CHB变流器电容电压不平衡，直流微网电压不稳定。本文提出了一种结合零序电压 (ZSV) 和负序电流 (NSC) 注入的改进功率调节方法。当模块发生故障时，首先注入ZSV调整故障相的调制余量；然后，基于三相功率分析，激活NSC注入，实现三组直流电压均衡控制。此外，分别考察了ZSV和NSC注入的约束条件，分析了注入ZSV和衍生NSC的选择。在三端混合 AC/DC 微电网中，仿真波形验证了所提出的容错运行方案的有效性，具有稳定的直流微电网电压和平衡的直流电容器电压。CHB 转换器的实验结果也验证了所提出方案的有效性。在三端混合 AC/DC 微电网中，仿真波形验证了所提出的容错运行方案的有效性，具有稳定的直流微电网电压和平衡的直流电容器电压。CHB 转换器的实验结果也验证了所提出方案的有效性。在三端混合 AC/DC 微电网中，仿真波形验证了所提出的容错运行方案的有效性，具有稳定的直流微电网电压和平衡的直流电容器电压。CHB 转换器的实验结果也验证了所提出方案的有效性。