Hierarchical Coordinated Power Control Strategy for AC-DC Hybrid Microgrid with Hybrid Energy Storage
Wang Li1, Hu Jiacheng1, Zeng Xiangjun1, Zhao Bin1, Zhang Zhiguo2
1. School of Electrical and Information Engineering Changsha University of Science and Technology Changsha 410004 China; 2. Tibet East China Hydropower Equipment Co. Ltd Lhasa 851414 China
Abstract In the AC-DC hybrid microgrid, the AC and DC subgrids are interconnected through converters, providing the hybrid microgrid with the advantages of both AC and DC microgrids. However, this interconnection can cause power fluctuations in subgrids and affect each other, leading to system frequency and voltage fluctuations. Relying on interlinking converters to coordinate intergrid power cannot effectively alleviate these fluctuations, and a single battery energy storage cannot meet power requirements in multiple scenarios. Therefore, this paper proposes a coordinated power control strategy using a hybrid energy storage system (HESS) with the coordination of supercapacitors, batteries, and interlinking converters. The hybrid energy storage is connected as a separate subgrid to the common DC bus, and droop control is used to stabilize the voltage of the common DC bus. The utilization of supercapacitor energy storage capacity needs to be improved, and battery charging and discharging times in traditional hybrid energy storage control are ineffective. Thus, an improved hybrid energy storage control strategy is proposed by dividing the state of charge into five working modes. The operating modes of AC-DC hybrid microgrids are divided based on the fluctuation value of fpu and Udc.pu to reduce the charging and discharging frequency of HESS, extend the service life, and avoid unnecessary power flow caused by the frequent start-up of bidirectional AC-DC converters. Two levels of hierarchical coordinated control (power autonomy and mutual power support) are proposed, and the mutual power support mode is divided into three types based on different surplus and loss states of the AC and DC subnets. Finally, fifteen operating conditions are obtained with the five operating modes of HESS and three mutual power support modes of AC-DC subgrids. Seven operating conditions are summarized by analyzing the similar power flow between networks under operating conditions. A simulation model is built to analyze the power flow between AC and DC microgrids under five operating modes of HESS. The effectiveness of the proposed control strategy is verified. Through simulation analysis, the following conclusions can be drawn. (1) The improved HESS control strategy fully utilizes the advantages of high-power density and fast response speed of supercapacitors. Batteries can be used to charge and discharge supercapacitors to avoid overcharging or discharging. (2) The mutual power support mode is achieved by coordinating the energy storage subgrid and interlinking converter. HESS participates in intergrid mutual power support, and operating mode adaptive switching is achieved by controlling Pscref and Pbatref. (3) Typical operating conditions of HESS in five different modes are simulated. The output power of various distributed power sources and intergrid support power is obtained based on the hierarchical coordinated control strategy for AC-DC hybrid microgrids. The stability of grid voltage and frequency is maintained during power fluctuations in load, wind, and photovoltaic output, ensuring the power supply reliability of hybrid microgrids.
Wang Li,Hu Jiacheng,Zeng Xiangjun等. Hierarchical Coordinated Power Control Strategy for AC-DC Hybrid Microgrid with Hybrid Energy Storage[J]. Transactions of China Electrotechnical Society, 2024, 39(8): 2311-2324.
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2024, Vol. 39 
