| Interconnecting multiple micrgrirds(MG)to form a networked microgrid(NMG)system is an effective way to improve the system reliability.When the NMG system operates autonomously,due to the lack of support from the main grid,a good operation and control system is required to ensure its efficient and reliable operation.However,the control of NMG system exhibits the characteristics of(?)abundant control objects,(?)diverse control objectives,(?)flexible topology,and(?)complex control strategies,which poses severe challenges to the design of control system.The hierarchical control architecture and distributed control method are effective solutions to the above problems.Besides,by considering the load-side resources,to construct the coordinated control method based on source-load interaction is of great significance for the stable operation of the NMG system.Therefore,this dissertation mainly focuses on the above problems and the main work is summarized as follows(1)A hierarchical and distributed control method for the NMG system is proposed.Firstly,a control objective system considering requirements of both system level and MG level is presented.Then,a two-level four-layer control architecture which can adapt to the multi-elements,multi-regional and flexible topology characteristics of NMG system is proposed,which can realize the decomposition and coordination of control objectives and functions.Finally,based on this control architecture,a distributed control method based on consensus theory is proposed.On the one hand,this method achieves multiple control objectives at both of the microgrid/system level,on the other hand,it improves the flexibility of the system.(2)A small-signal dynamic modeling method for NMG systems with two-level four-layer distributed control method is proposed.Firstly,a small-signal dynamic model considering the electrical/control system coupling is constructed.Based on this model,the detailed small disturbance stability analysis of the system to reveal the dynamic interaction mechanism is given.Then,through eigenvalue analysis,it is concluded that the interconnected operation of MG and the distributed control method will introduce less-damped oscillation modes.After that,the stability analysis of the less-damped modes including the participation factor analysis,coupling degree analysis and parameter sensitivity analysis is carried out.(3)Taking the air conditioning loads which have fast response and wide distribution at the end of power system as an example,a method of them participating in frequency control in NMG system is proposed.Firstly,the idea of integrating the cluster of air conditioners as a virtual distributed generator(DG)unit with droop characteristics is proposed,which can achieve coordination with conventional DGs.Then,the control architecture for the cluster of air conditioners is given.Based on this architecture,the control method for the cluster of air conditioners is designed according to the idea of"centralized coordination and decentralized self-discipline".By this control method,the virtual droop characteristics of clusters can be realized.(4)Based on the above research of stability analysis and load control,the hierarchical and distributed control method of NMG system is optimized from two aspects of dynamic performance improvement and source-load interaction control.Firstly,based on the stability analysis,the optimization model of key control parameters is designed to improve the dynamic performance.Then,the virtual DG formed by air conditioning cluster is integrated into the hierarchical and distributed control method.The coordination with conventional DGs is achieved by droop curve,which can effectively improve the frequency control performance.In summary,in order to overcome challenges of NMG system in(?)control architecture and method,(?)small-signal stability modeling and analysis,and(?)source-load interactive control,this dissertation proposed a hierarchical and distributed control method for autonomous NMG system.Relevant research results can provide theoretical and technical support for NMG system operation and control. |
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