Design And Operation Control Strategy Of DC Micro-grid System In Photovoltaic Station

For the realization of photovoltaic power station localization and cleaning,the paper design a DC micro-grid system based on the project of Badaling solar energy comprehensive pilot engineering of station load.The DC micro-grid system is including distributed photovoltaic power,energy storage and station electric load.The system design and operation control strategy are studied.First of all,based on the analysis of the advantages and disadvantages of the basic topology of the common DC micro-grid,the double bus structure is chosen as the basic topology.DC bus voltage is selected as 750V.In the design of converter,the full bridge rectifier circuit,Boost circuit,non isolated bi-directional Buck-Boost circuit and full bridge inverter circuit are used as the grid,photovoltaic,energy storage and load converter topology.On the basis,the specific parameters of the converter are designed,and based on the K-means algorithm,the selection of PV and energy storage capacity in the DC micro-grid system is given.In the aspect of operation control,based on the realization of the control unit of the converter,6 basic operating modes and switching conditions are analyzed.The system control strategy based on the energy storage unit as the control core and the grid connected converter as the backup control unit is established.In order to achieve the maximum utilization of distributed power energy,two kinds of additional limit working states,such as short-time energy overdraft and short-time energy excess,are proposed.The criterion of limit operation mode is given by the load forecasting algorithm.The simulation model of DC micro-grid is established in PSCAD.Firstly,the change of load demand and the change of PV power output are simulated.The simulation results show that the response of each converter in the DC micro-grid is rapid,and the voltage of the bus voltage fluctuates slightly,and the system has a good dynamic response.Secondly,this paper makes a detailed simulation of the switching process of all the working modes of the micro-grid system.The simulation results show that the system can realize the automatic switching of different modes,and verify the effectiveness of the proposed control strategy and the soft start mode.The grounding mode has a direct impact on the fault characteristics of DC micro-grid and the design of protection system.The steady-state power quality,system transient characteristics,electrical safety and power supply continuity of DC microgrid are analyzed theoretically under cdifferent grounding modes.The final choice of IT(Isolation&Terre)approach for system grounding.The simulation results verify the rationality of the grounding mode selection.