公共阻抗突变及变流器本地负载接入下储能单元荷电状态均衡研究

Study on Balance of Charge State of Energy Storage Unit Under Common Impedance Mutation and Local Load Access of Converter

孤岛直流微电网常配备储能系统以消除分布式能源随机出力和负荷波动带来的不平衡功率。在线路阻抗不匹配场景下,公共负载阻抗的突变以及储能变流器本地负载的接入都会影响储能单元暂态均流精度,进而降低荷电状态(state of charge,SOC)均衡水平。该文通过关联储能单元输出电流与荷电状态信息,根据系统运行状态自适应分配二者在下垂系数中的权重。基于上述策略,储能单元在稳态运行与暂态突变期间,其下垂系数分别跟随荷电状态差值及电流差值,从而迅速调节自身外特性阻抗,保证均流效果及荷电状态均衡。同时,采用电压恢复策略消除下垂控制带来的电压偏移。考虑到下垂控制对系统的稳定性有影响,文中给出系统控制结构图和用于分析系统稳定性的特征方程,结合劳斯稳定判据验证了系统的稳定性。最后通过Matlab/simulink仿真对比验证所提策略的正确性和有效性。

Island DC microgrid is often equipped with energy storage system(ESS)to eliminate the random output of distributed energy and the unbalanced power caused by load fluctuation.Due to the difference of line impedance among ESS,the sudden change of common load and the access of local load of energy storage converter will affect the transient current equalization accuracy of energy storage units(ESU),and thus affects the effect of state of charge(SOC)balance.In this paper,by associating the output current of ESS with SOC,the weights of the two in droop coefficient are adaptively allocated according to the operating state of the system.Based on above scheme,the droop coefficient of ESU during steady operation and transient mutation follows the difference of SOC and current,respectively.Thus,the external characteristic impedance of ESU can be quickly adjusted to ensure the current sharing effect and SOC balance Meanwhile,and the voltage recovery strategy is adopted to eliminate voltage offset caused by droop control.Considering that droop control has an effect on the stability of the system,this paper presents the characteristic equation and the control block diagram of the system,and verifies the stability of the system by using the stable law criterion.Finally,the correctness and effectiveness of the proposed strategy are verified by Matlab/Simulink simulation comparison.