Research On Distributed Grid Connected Photovoltaic Power Generation And Energy Management System

Firstly,the study backgrounds and the development status at home and abroad of distributed grid connected photovoltaic power generation and energy management system are introduced in this paper.The characteristics of the distributed photovoltaic power generation system are analyzed,and the necessity of the grid connection and the management of the energy flow is expressed.Secondly,the structure of distributed grid connected photovoltaic power generation and energy management system is introduced.By analyzing the functions of MPPT control unit,energy storage unit and inverter unit,the main circuit scheme is determined.According to the relationship between the energy flow and power generation system,battery charge and discharge power and load power,the operation of the system will be divided into two modes;according to the storage state of charge and discharge current unit determines whether the system exists current grid,each working mode is divided into two working state of the control mode of every unit of the system in different working conditions.Thirdly,a simulation model of photovoltaic panels is set up.According to the output characteristics,three commonly used maximum power point tracking algorithms are analyzed and compared.According to the analysis results,the algorithm adopted in this paper is determined,and the control circuit of the boost chopper circuit for the MPPT control unit is determined.The control method of the energy storage unit is designed.The method uses the DC bus voltage as the control target and combines the two stage method to control the charging process of the battery.The operation of the inverter unit is determined by the stability of the DC bus voltage and the charge and discharge of the battery energy storage unit.The circuit scheme of the inverter unit two level three-phase bridge inverter and the dual d-q axis phase locked loop and the SVPWM control scheme are determined.Fourthly,main power circuit and the control circuit of the MPPT control unit,the battery energy storage unit and the inverter unit are designed.According to the control demand of the system,the digital controller is selected for each unit.Combined with the design of the control strategy,the MPPT control unit timer interrupt program,ADC interrupt program,capture interrupt program,MPPT subroutine and storage procedures and the corresponding flow chart of program unit,inverter unit and DC voltage control unit of the timer interrupt are given.Finally,the experiment platform is constructed and the control strategy is validated.The experimental results show that the incremental conductance method is presented in this paper has faster tracking speed and higher tracking precision,can meet the requirements of photovoltaic panels time to work at the maximum power point;power balance control method can effectively guarantee the stability of the DC bus voltage;the storage unit control scheme in better maintenance of power system balance at the same time,to control the charging process of the battery,well protected batteries;double d-q axis PLL waveform control and inverter unit grid current waveform is given.