Large Signal Stability Analysis For DC Microgrid Clusters

With the increasing utilization of distributed renewable energy power generation,microgrids have gradually become a research hotspot as the high-efficiency way to integrate and utilize distributed renewable energy power generation.Compared with AC microgrids(ACMGs),DC microgrids(DCMGs)have attracted more and more attention due to its advantages of high efficiency,low cost,simple control design,flexible and convenient construction,etc.In order to further exploit the advantages of the DC-based distributed power generation system,geographically adjacent multiple DCMGs can be interconnected to form a DCMG cluster to realize regional energy sharing and optimal utilization through flexible power flow control.However,small-scale DCMGs are weak grids of low inertia and high impedance.The weak-weak interconnection will reduce damping of DCMG clusters,while the system is always subject to a variety of large disturbances such as sudden changes in renewable energy output,constant power load(CPL)step,unit input and excision,short-circuit fault,etc.,endangering the stable operation of the system,resulting in severe consequences like system oscillation or collapse.Therefore,this thesis focuses on the analysis and verification of the large-signal stability(LSS)of DCMG clusters.Firstly,a system-level equivalent large-signal model is established for the DCMG cluster considering CPL.And a LSS analysis method based on Brayton-Moser mixed potential theory is proposed,which creates the mixed potential function for the LSS criterion.The influences of key circuit parameters,topology,and other factors on the LSS of the DCMG cluster are analyzed.The correctness and feasibility of the analysis are verified by real-time simulations.Then,a more general load model is considered based on the established equivalent large-signal model.And a LSS analysis method based on Takagi-Sugeno(T-S)fuzzy model is proposed.The regions of asymptotic stability(RASs)and the corresponding Lyapunov functions of the system are solved,which indicates the range of the disturbance that the system can tolerate.And the effects of key circuit parameters,power flow,topology,and other factors on the LSS of the DCMG cluster are analyzed based on RASs.The correctness and feasibility of the analysis are verified by Matlab/Simulink simulations and experiments.Finally,false data injection attacks(FDIAs)are highlighted for the cyber security of DCMG cluster.The models of FDIA,hierarchical control loop,and main circuit are established for the DCMG cluster.And a LSS analysis method based on T-S fuzzy model is proposed.The effects of FDIAs,hierarchical control loop,and main circuit parameters on the LSS of the DCMG cluster are investigated.The correctness and feasibility of the analysis are verified by controller hardware-in-the-loop(CHIL)experiments.