基于混合储能的交直流混联微电网功率分级协调控制策略

Hierarchical Coordinated Power Control Strategy for AC-DC Hybrid Microgrid with Hybrid Energy Storage

针对交直流混联微电网孤岛运行时,仅靠互联变流器协调网间功率无法有效缓解系统频率与电压波动,且单一蓄电池储能难以适用多场景功率需求的问题,提出利用超级电容和蓄电池混合储能的交直流混联微电网功率协调控制策略。将混合储能作为储能子网连接在直流母线上,优先采用超级电容平抑交直流子网内功率波动,提出以储能荷电状态来划分五种工作模式的改进混合储能控制策略。兼顾超级电容快速响应特性和减少互联变流器的频繁起动,根据直流子网电压和交流子网频率波动程度,提出功率自治和功率互济工况的两级分层协调控制策略。通过设计混合储能处于不同工作模式的网间功率互济场景,仿真证明了所提混合储能和互联变流器协调控制策略能够平抑各子网负荷功率波动。

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.