| The large-scale integration of distributed generations and electric vehicles,and the diversification of consumer demand for electricity have made the distribution network’s complicated flow and unbalanced load more and more prominent.Flexible Multi-state Switch(FMS)is a new type of intelligent power distribution equipment that replaces the normal open point at several key nodes.By using power electronic technology,it can effectively control the active and reactive power flowing through the equipment to achieve the continuous and flexible regulation of distribution network flow.Therefore,it has the functions of promoting renewable energy accommodation,balancing feeder load,and improving power quality,which will enhance the reliability and flexibility of the intelligent distribution network.Due to the different performance of FMS in different topologies,it is suitable for different application scenarios.And the calculation process of relevant selection indexes is cumbersome and lacks effective auxiliary analysis and calculation methods,so this thesis focuses on combing analysis and type selection research on FMS topology used in medium and low voltage distribution network.Firstly,review the current status of FMS research,and sort out the topologies of different transformation types to study the feasibility of each topology in the distribution network feeder connection.Among them,the AC-DC-AC topology is more suitable for multi-feeder interconnection scenarios.Taking FMS based on modular multilevel converter(MMC)topology as an example,the basic working principle of FMS is studied and the mathematical model of MMC topology in dq synchronous rotating coordinate system is established,and the control strategy is designed based to pave the way for subsequent simulation verification.Secondly,the topology selection of the single-terminal FMS topology under the medium and low voltage distribution network is analyzed from the three aspects of core component,functional evaluation and engineering application,and the 7 kinds of quantitative indexes and 3 kinds of qualitative indexes for topology selection are selected.Taking the traditional two-level voltage source converter topology,tri-level neutral point clamped converter topology and MMC topology in single-terminal form as examples,the calculation formulas for each quantization index are given.Afterwards,according to the calculation formulas of each index,the FMS topology auxiliary selection software for medium and low voltage distribution network is designed,which can quickly and intuitively give the comparison of the indexes of different topologies,and assist the user to make the topology selection decision.According to the three calculation examples calculated by the software,reference suggestions for three kinds of single-terminal topologies’ applicable scenarios are given.At the same time,the main circuit parameters output by the software are simulated using MMC topology in MATLAB/Simulink to verify the validity of the data.Finally,the topology selection of the multi-terminal FMS topology is explored,and the MMC topology suitable for medium voltage distribution network and the nine-arm modular multilevel converter topology and the bifurcate modular multilevel converter topology with device/bridge arm multiplexing characteristics are selected for analysis.The core parameters,operating losses and operating ranges of each topology are calculated,and the comparison results of the construction cost,floor space,operating efficiency,and power flow regulation capabilities of each topology are obtained.The scenarios applicable to the three kinds of topologies are given to provide recommendations for the selection of multi-terminal FMS topology in medium voltage distribution network. |
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