Optimal Power Restoration Strategy for Multi-Terminal Flexible Interconnected Distribution Networks Based on Flexible Interconnection Device and Network Reconfiguration
Xu Yutao1, Feng Qihui1, Tan Zhukui1, Zhang Chao2, Yuan Xufeng2
1. Electric Power Research Institute Guizhou Power Grid Co. Ltd Guiyang 550025 China; 2. Electrical Engineering College Guizhou University Guiyang 550025 China
Abstract：With the developments of the "dual carbon" goal and accelerated energy transformation, a high proportion of new energy and large-scale new load integration, as well as the widespread application of flexible power electronic equipment, have put forward higher requirements for the morphology, structure, operation control, and power quality of the existing distribution network. Flexible interconnection device (FID) enables flexible interconnection between different feeders in the distribution network, enabling rapid restoration of power supply after faults. At present, the power recovery strategy for FID is to directly provide the control strategy for the corresponding scenario, operating status of the FID, and the final operating status of various switches. There is little research on the coordinated control of multi terminal FIDs, support for power supply recovery control strategies, dynamic process of power supply recovery in distribution networks based on FIDs, and collaborative cooperation between FIDs and various mechanical switches. To address these issues, this paper takes the four-terminal flexible interconnection distribution network with DC network as the case study, and proposes a two-stage power supply restoration strategy for multi-terminal flexible interconnection distribution network based on FID and network reconfiguration. Firstly, based on the operation principle of FID, the smoothing control structure for FID with fast power transfer under fault conditions, and the VSG control strategy considering the switching simultaneous grid connection control, are proposed to support the fast power supply restoration in the first stage after a fault. Then, a second-stage power restoration strategy combining FID and network reconfiguration is derived by building and solving a global optimization model considering contact switching and FID capacity limitation, which restores the lost loads to a larger extent. Finally, a 58-node four-terminal flexible distribution system with DC network is constructed by using PSCAD/MTDC simulation software for simulation verification. The results showed that through the proposed two-stage fault recovery strategy, the important load of the fault network was increased by 0.05% after optimization, and the general load was improved by 9.61% after optimization. The total recovery situation was improved by 7.07%. This fully demonstrates the effectiveness of the proposed method. The following conclusions can be obtained from this paper. (1) The proposed two-stage power restoration strategy combining FID and network reconfiguration can not only support seamless power transfer of lost loads, but also realize a wider range of lost loads restoration. (2) The proposed fault smooth switching control with mode switching can smoothly and quickly complete the power restoration after a fault occurs, and guarantee the non-stop transfer of some loads. (3) The proposed VSG control strategy considering synchronous grid connection of switches can effectively avoid the inrush current at the instant of switch closure when switching from off-grid to grid-connected operation after fault removal, and also avoid the inrush current generated by frequent switching of the contact switches under power during the optimization phase of network reconfiguration. The two-stage recovery strategy proposed in this paper can achieve a wider range of fault recovery, but the focus of this paper is on the recovery strategy and process, and it does not involve the study of how to make use of the active regulation capability of FID to achieve the detailed continuous state transfer and action sequence of near-zero-power switching of the contact switch, which will be studied in detail in our future work.
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2024, Vol. 39 
