Research On New Method And Control Strategy For High/Low Voltage Control At The End Of The Distribution Network

With the rapid development of China's power grid,a large number of distributed generations are connected.The distribution network has changed from a radial passive network to an active network with direct interconnection between power supply and users,which affects the voltage distribution of the distribution network and makes the terminal voltage problem of distribution network more and more obvious.China lacks effective guidance on terminal voltage management,and it is particularly important to explore effective,economic and reliable new technologies.Based on the national conditions of the power grid and the necessity of voltage management,this paper proposes a terminal voltage control scheme of distribution network based on the photovoltaic-energy-storage system.The main research work is as follows:(1)The domestic voltage fluctuations at the end of the medium and low voltage distribution network,including high voltage and low voltage are introduced.Examples are given to illustrate the corresponding measures taken by various regions to improve the voltage and the governance results,then we analyze the voltage problems of medium and low voltage distribution network,pointing out the shortcomings in China's management and technical levels.The research and work status of this subject at home and abroad is expounded,and the research significance of this topic is also pointed out.(2)The hazards of high and low voltage at the end of distribution network are expounded,and the mechanism of voltage fluctuation at the end of distribution network is analyzed,and the voltage at the end of distribution network is also analyzed from relevant parameters.The simulation model of MATLAB/Simulink is built to verify the generation of high and low voltage.The traditional control methods and their advantages and disadvantages are introduced.The principle and advantages of the new technology for voltage control of the photovoltaic-energy-storage system are briefly described.(3)The topological structure of the photovoltaic-energy-storage system is introduced,and the control strategy of the new scheme of controlling high and low voltage at the end of distribution network is elaborated.The maximum power of the photovoltaic output is tracked by the constant voltage control method,The charging and discharging control of the energy storage device closely matches the output of the photovoltaic cell,and the configuration of the capacity of the energy storage device is studied at an optimized angle to ensure economic,efficient and stable operation of the photovoltaic-energy-storage system.When the voltage fluctuates,by detecting and calculating the active and reactive power required by the distribution network,the power compensation to the distribution network is realized by the grid-connected technology using the terminal voltage outer loop control and the inverter current inner loop control.The parameter selection scheme of current inner-loop and voltage outer-loop control in the design of the controller,and the corresponding following and anti-disturbance performance are given.(4)According to the actual situation of typical stations,the appropriate parameters are selected,and the equivalent simplified circuit simulation model is built by using MATLAB/Simulink simulation software.The feasibility of maximum power tracking is verified by analyzing the simulation waveform of photovoltaic output.The reliability of battery charging and discharging control is verified by analyzing the simulation waveform of battery voltage and current,The DC bus voltage simulation waveform is analyzed to verify the stability of the photovoltaic-energy-storage system.The simulation waveforms of user terminal voltage and grid current are analyzed,and the effectiveness of the proposed method in dealing with the terminal voltage fluctuation of distribution network is verified from both high and low voltage aspects.The experimental waveforms are further simulated and analyzed based on star_sim simulation platform.The results verify the effectiveness and feasibility of the terminal voltage control technology.