| Flexible interconnection technology has superior power flow control ability and flexible control means,which can greatly improve the utilization efficiency of energy and equipment in power system,improve the operation state of the system and optimize resource allocation.For the complex power corridor at present,a DC system can be embedded between the power consumption areas,and flexible interconnection equipment can be used to connect the power consumption areas with DC lines,so that flexible interconnection can be formed between different areas.As the end of electric energy transmission in power system,distribution network is closely connected with the user side.By interconnecting the distribution networks at the ends of different feeders,a flexible interconnected distribution network is formed,which has high economic and practical value for resource allocation and load bearing.Therefore,this paper takes a Flexible Interconnected Distribution Network with Embedded DC System(FIDN-EDC)as the research object,constructs and verifies the overall small signal model of the system,and proposes an application strategy based on load balancing control,and establishes a stability model to analyze its stability.The specific work contents are as follows:Firstly,a four-port FIDN-EDC topology is proposed,and its characteristics and advantages are introduced.Taking Modular Multilevel Converter(MMC)as the core equipment of this flexible interconnection system,its working mechanism is stated,and the corresponding control link is designed.At the same time,the system simulation model is built in PSCAD software to verify the actual operation effect of the system.The simulation results show that FIDN-EDC has good load transfer and DG absorption ability.Secondly,the small-signal models of MMC and its control system,AC system,DC system,load and distributed generation(DG)are established respectively,and the small-signal global model of FIDN-EDC system is combined by data connection.At the same time,the numerical verification is carried out in MATLAB,and the correctness of the global model is verified by comparing the calculation results of MATLAB with the transient simulation graphics of PSCAD.Finally,considering the practical application scenario of FIDN-EDC,a regulation strategy based on feeder load rate balance is designed to achieve the purpose of reasonably distributing the output of each feeder power supply and alleviating the pressure of heavy-duty power supply.Considering all kinds of factors affecting the stability of the system,the port small signal admittance model is established to analyze the influence of load change on the system,and the influence of control parameter change on the overall stability is also studied by analyzing the movement trend of the characteristic root and root trajectory of the system.The load balancing strategy is verified by PSCAD transient simulation,and the simulation results show that the proposed strategy has good control ability. |
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