Research On Dispatch And Control Strategy Of DC Distribution Grid

With the increasing seriousness of the energy and environmental problems as well as the social development requirements to improve the power supply,AC distribution grid is facing unprecedented challenges in power quality,supply capacity,reliability and access to distributed generations.DC distribution grid has significant advantages in these areas and it provides a new way to solve the problems faced by AC distribution grid.Under the background of DC distribution grid,it’s dispatch and control strategies were studied.This thesis started from the DC distribution grid and distributed generation.Its topologies and DC bus structures were studied.Then discussed the voltage grades of DC distribution grid.The AC/DC converter,DC/DC converter and DC transformer in DC distribution grid were analyzed.The output characteristics of distributed generations,storage battery and the operation characteristics of DC distribution grid were described.Secondly,the thesis studied the working principle of DC distribution grid’s energy management system and short-term power prediction system.A multi-period optimal dispatch strategy based on short-term power prediction and a dispatch model with the aims of minimum economy cost,minimum pollution cost and multi-objective optimization were proposed.And adopted a algorithm based on satisfaction function and evaluation function to transform the multi-objective problem into a single objective problem,then solved it by the particle swarm optimization algorithm.For the control strategy of DC distribution grid,a three-layer control system based on optimal dispatch was established in this thesis,including system dispatch control,DC bus voltage control,local converters control.The functions and strategies of the post two control layers were deeply studied.The second layer control method is based on DC bus voltage variations.The third layer control would make converters operate in constant power control,maximum power point tracking control,voltage droop control,or load shedding control according to the power instructions and operation mode instructions.In order to verify the multi-period optimal dispatch strategy based on short-term power prediction,a example system of DC distribution network in residential area was established.The calculation results indicated the feasibility of the proposed dispatch strategy and multi-objective optimization model.Then built the simulation model of DC distribution grid in Matlab/Simulink and simulated respectively in normal grid-connected mode,power limited grid-connected mode,normal and abnormal voltage states of off-grid mode.The results indicated that the DC distribution grid can run stably in all states.And the effectiveness of the control system is proved.