Research On Modeling And Simulation Of Distribution Network With Distributed Generation

With the rapid development of social economy and the depletion of global fossil energy,the traditional power generation and distribution methods have gradually revealed their disadvantages.Clean energy power generation represented by photovoltaic(PV)power generation and new power distribution methods represented by DC power distribution are becoming important directions for future power development.In order to simulate and analyze the dynamic characteristics of grid-connected photovoltaic power plants and solve the problems of large workload and low simulation efficiency when modeling large-scale PV power plants,this paper simplifies the system modeling process by clustering equivalent methods.Firstly,according to the typical structure of PV power generation system,the mathematical simulation model is established.Through the analysis of the system control strategy and operating characteristics,the parameters for clustering different PV power generation units that are directly related to the dynamic characteristics of the system are derived.Before the cluster analysis,the Canopy algorithm is used to preprocess the data to obtain the initial cluster center and the number of clusters.On this basis,the analysis is combined with the traditional FCM clustering algorithm to obtain the clustering result.Afterwards,the "homogeneous equivalence method" is used to perform equivalent modeling on the PV power generation units that are grouped together.Finally,through simulation examples,the dynamic characteristics of the equivalent model and the detailed model under different fault conditions are compared to verify the correctness of the equivalent modeling method of the large-scale PV power plant adopted in this paper.The scale of the whole electromagnetic transient simulation system for grid connected distributed power generation is too large and full electromechanical transient simulation can not accurately simulate the dynamic characteristics of high-frequency power electronic devices.To solve this problem,this paper established a hybrid electromagnetic-electromechanical transient simulation platform for PV grid-connected system.The whole electromagnetic transient simulation model of PV power generation system is built in PSCAD / EMTDC,and the electromechanical transient simulation model of conventional AC power grid is built in MATLAB / SIMULINK.The key technologies and solutions of interface processing,simulation timing and equivalent circuit selection in hybrid simulation are described.The effectiveness of the hybrid simulation platform is verified by the comparison between the simulation results of a specific example and the full electromagnetic transient model.In the aspect of DC distribution network simulation with distributed generation,the advantages and disadvantages of three typical topologies of flexible DC distribution system are compared and analyzed,the radial and two terminal DC distribution networks with distributed generation are modeled.The modeling methods and control strategies of key equipment such as voltage source converters(VSC)and DC transformers in the distribution network are introduced.The countermeasures of the two-end power supply distribution network in the case of single-end withdrawal from operation are proposed.In the PSCAD simulation platform,the accuracy of the built model and the effectiveness of the system control strategy are verified by specific calculation examples.