Hybrid AC-DC systems integrate ac bus and various dc buses as well as multiple power electronic converters, and such systems are consequently vulnerable to instability issues. In order to investigate the stabilities of hybrid AC-DC systems with multiple dc buses and identify which converters are mainly responsible for instability, this article proposes a stage-by-stage stability analysis method. The small-signal models of AC-DC and DC-DC converters are established, based upon which the whole system is separated into multiple stages according to its structure, and checked stage-by-stage. Make sure that equivalent input admittance (or impedance) of stage $k(k=2, 3, \ldots)$ has no right-half-plane poles so that it is self-stable, then consider the equivalent input admittance (or impedance) of stage $k$ as the equivalent load admittance (or impedance) of stage $k-1$ , and check the stability of stage $k-1$ ; and repeat the process until the whole system has been checked. All stage being stable can ensure the stability of overall system. The converters that are mainly responsible for instability can be clearly identified by this stage-by-stage method, and it could be beneficial for stability enhancement of the system. The effectiveness of the proposed method is verified by simulations in PSCAD/EMTDC and experiments of the control hardware in the loop (CHIL).

中文翻译：

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多路直流母线混合交流－直流系统的小信号稳定性分析方法

混合AC-DC系统集成了AC总线和各种DC总线以及多个电力电子转换器，因此此类系统易受不稳定问题的影响。为了研究具有多个直流母线的混合AC-DC系统的稳定性，并确定哪个转换器是造成不稳定的主要原因，本文提出了一种逐级稳定性分析方法。建立了AC-DC和DC-DC转换器的小信号模型，在此模型的基础上，整个系统根据其结构分为多个阶段，并逐级检查。确保阶段的等效输入导纳（或阻抗） $ k（k = 2，3，\ ldots）$ 没有右半平面的极点，因此它是自稳定的，然后考虑级的等效输入导纳（或阻抗） $ k $ 作为级的等效负载导纳（或阻抗） $ k-1 $ ，并检查舞台的稳定性 $ k-1 $ ; 并重复该过程，直到检查完整个系统为止。所有阶段的稳定可以确保整个系统的稳定性。通过这种逐步方法可以清楚地识别出主要负责不稳定的转换器，这对于提高系统的稳定性可能是有益的。通过PSCAD / EMTDC中的仿真以及回路中的控制硬件（CHIL）的实验，验证了该方法的有效性。