Research On Operation Control Of DC Microgrid With Photovoltaic And Energy Storage System

In recent years,with the continuous penetration of distributed generation,it has a certain impact on the security and stable operation of traditional AC grids,and the microgrid is considered to be one of the effective ways to solve this problem.In the microgrid,with the emergence of more and more DC micro-sources and DC loads,the application of DC microgrid can not only reduce the intermediate links of energy change,but also improve the utilization rate of energy.At the same time,the DC microgrid has the characteristics of good controlled and high power quality.Therefore,this subject has carried out in-depth and detailed research on the operation control of DC microgrid,and the specific research content is as follows:Firstly,the basic structure of the DC microgrid with photovoltaic and energy storage system was established.On this basis,the energy flow between each unit of the system under off-grid and grid-connected conditions is emphatically studied and analyzed,and the corresponding power balance expression is derived.Secondly,the photovoltaic cell,lead-acid battery and single-phase PWM rectifier were modeled and analyzed.The topological structure of photovoltaic power generation unit,energy storage unit and grid-connected converter unit in the system is described,and the basic control strategy of each unit is studied.The focus is on the constant voltage control method and the single-phase phase-locked loop technology based on the second-order generalized integrator.Simulations have verified the correctness of each mathematical model and the effectiveness of the control strategy.Then,according to the DC bus voltage signal,the operation control strategy of the whole system is proposed.Based on the bus voltage signal,the system operation mode is divided into five types,and the system can coordinate the control mode of each unit of the system according to the automatic switching of these five modes,so as to maintain the stability of the DC bus voltage.By constructing a simulation model of the DC microgrid with photovoltaic and energy storage system,the simulation analysis of on-grid and grid-connected conditions is carried out,and the simulation results have verified the effectiveness of the proposed operation control strategy.Finally,based on the above research,the design of the system hardware,software and monitoring system are completed.The hardware design mainly includes the design of the main circuit,signal conditioning circuit and drive circuit;the software design mainly includes the modular programming of the main program,interrupt service routine and control subroutine;the monitoring system design mainly includes the development of MCGS project and the realization of communication process based on Modbus protocol.By building a corresponding experimental platform for experimental verification,the experimental results have basically verify the feasibility of the control strategy proposed in this paper.