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| Evaluation of Distributed Large Signal Stability Strength and Feedback Control Design for DC Microgrid Clusters |
| Liu Sucheng1,2, Luan Li1,2, Li Long1,2, Hong Tao1,2, Liu Xiaodong1,2 |
1. School of Electrical and Information Engineering Anhui University of Technology Maanshan 243000 China;
2. Key Lab of Power Electronics & Motion Control Anhui University of Technology Maanshan 243000 China |
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Abstract A DC microgrid cluster (DCMGC) is an interconnected network by multiple small DC microgrids to improve flexibility, reliability and economic benefits of the power supply system. However, the high penetration and intermittence of distributed energy resources, the wide adoption of power electronic devices and equipment, and the flexible working characteristics of the system make the DCMGC facing significant large-signal stability challenges. On one hand, most existing analysis methods of large signal stability focus on establishing the large signal reduction or simplified model of the system, and using nonlinear theoretical tools to judge the stability. Thus, the centralized methods always require the information of the overall system, which will inevitably result in the problem of high computation complexity with more subgrids are interconnected into although the reduced models are utilized, and lack of scalability with the stability analysis subject to topological changes. On the other hand, the research works on large signal stability analysis of DCMGCs usually neglect the impact of coupling dynamics between subgrids. To address the challenges with the existing works, this paper proposes a distributed large-signal stability strength evaluation and feedback control design method for DCMGCs. The proposed method is based on the distributed modeling and vector Lyapunov function, and the introduction of the stability strength and the connectivity strength to reveal the impact of coupling dynamics on the large signal stability of the system.
Firstly, the distributed large-signal model of the DCMGC is established, where every DC microgrid in isolated mode and its coupling dynamics are explicitly expressed. Secondly, the large-signal stability criterion of the established model is derived based on vector Lyapunov function. The concepts of stability strength, connectivity strength, and coupling ratio are introduced to facilitate evaluating the impact of the coupling dynamics on system stability, providing the basis for feedback control design of power flow control and large signal stabilization. Thirdly, numerical analyses are performed on a specific DCMGC model. Fourthly, the advantages of the proposed method are further clarified through comparative analysis with the other well-known method, i.e., the scalar Lyapunov function, for large-scale interconnected dynamic systems. Finally, the effectiveness of the proposed method is verified based on the hardware-in-the-loop experimental results.
The following conclusions can be drawn through the theoretical analyses and the experimental verification: (1) The proposed method is based on distributed modeling, which overcomes the limitations of centralized modeling methods in scalability and computational complexity. It helps to identify the stability strength of every subgrid in the DCMGC. (2) The introduction of the stability strength and the connectivity strength has uncovered the impact of the coupling dynamics on the large signal stability of the DCMGC, specifically, the increase of tie-line parameters leads to the stability enhancement, so does the increase of local feedback control coefficient, but the increase of the feedback coefficient deteriorates the system stability. (3) Compared with the scalar Lyapunov function, the vector Lyapunov function of the proposed method has lower conservatism in the stability evaluation.
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Received: 21 August 2024
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2025, Vol. 40 
