Research On Modeling And Control Of Flexible Loop Network Controller

With the continuous development and change of power electronics technology,the application of power electronic technology in urban distribution system has become increasingly widespread.The demand for power quality is increasing and new challenges to the distribution are posed constantly.The distribution network needs to be changed to high efficiency,high reliability and low energy consumption.In order to meet the new demand for the development of urban power supply,the AC/DC hybrid distribution network based on flexible loop network controller(FLNC)is a new solution.The FLNC is the application of voltage source converter equipment to interconnect multiple distribution networks with each other and form a ring network.Compared with the traditional contact switch,FLNC can change the distribution network closed-loop design and open-loop operation,to avoid security risks caused by the impact current during traditional switch transposition,to reduce the operational risk and the maintenance cost of system,to improve the flexibility of distribution network topology.First,a power model and boundary conditions of three-terminal FLNC for power dispatch of distribution network are presented in this paper.According to two different situations of three-terminal FLNC,the power allocation results which can meet the different conditions are propose,the power control method used in FLNC is given,and the simulation results verify the effectiveness of the power dispatch model and the boundary condition.In view of the four-terminal FLNC and above,the idea of a new power range reduction method is proposed.Based on the operation principle of MMC,the detailed switch model and switching cycle average model of MMC based on NLM are deduced respectively.Then,the expression of modulated wave base wave voltage is obtained by Fourier decomposition.Four different kinds of rectangular wave are formed.On this basis,an average model based on fundamental voltage source combination is obtained.A power grid with three-terminal MMC-FLNC and the rated capacity of 50MVA is taken as an example,the simulation speed and accuracy under different models are tested by simulation,and the power balance of the models are verified.Finally,the carrier phase-shifting PWM(CPS-PWM)is introduced,the detailed switch model and the average model in the ABC coordinate system of MMC based on CPS-PWM are simulated respectively.The average model and small signal model of MMC in DQ coordinate system are proposed.In the light of three closed loop control models,small signal analysis is carried out.A power grid with three-terminal MMC-FLNC and the rated capacity of 50MVA is taken as an example,the power balance of the models at different time scales are verified by simulation,and the simulation speed and precision are compared.