Design Of Charging Controller For Independent Photovoltaic System

With the rapid energy consumption and the increasingly serious environmental problems,solar energy is attracting more and more attention due to the advantages of clean and renewable energy.Solar power has been developed rapidly as an effective way of solar energy utilization.Maximum Power Point Tracking(MPPT)technology can maximize the conversion of solar energy into electrical energy,improve the efficiency of photovoltaic power generation,which is widely used in photovoltaic power generation systems.The technology of MPPT has been applied on three main aspects: firstly,the MPPT technology is used directly for the load power supply;secondly,it is used for charging the battery;thirdly,in photovoltaic grid connected system,it is used to transfer power to power grid.This paper takes the independent photovoltaic system for lead-acid battery charging as the research object,some key technologies,such as the maximum power tracking for photovoltaic cells and battery charging methods,were studied.The paper presents an implementation scheme of independent photovoltaic power generation system,based on Freescale's MK02 microcontroller chip.Firstly,the working principle and output characteristics of the solar cell are introduced,and summarized the advantages and disadvantages of several classical maximum power tracking control algorithm.Then we use a method to obtain the maximum output current of DC/DC circuit to achieve the MPPT,which is more simple and can effectively reduce the cost of hardware.Besides,the charging method of lead-acid battery is deeply explored,in the traditional three stage charging method,combined with the special background of the maximum power of photovoltaic system,a three-stage photovoltaic charging method is proposed.The current limiting is added to the MPPT,prevent over-current charging to damage battery structure.Secondly,BUCK is selected as the main power circuit topology structure,and introduces the principle of adjusting the duty cycle to achieve the maximum power output ofphotovoltaic cells.The control circuit is designed,and the design of the flyback power supply based on UC3843 is introduced in detail.In addition,combined with the Freescale 's official software development tools,completed the maximum power tracking algorithm and charging algorithm software code,the paper gives the flow chart of the program.Finally,the system test platform is set up,and the MPPT and the three stage charging are verified by PV simulator and PV array.The test results show that the algorithm can track the maximum power accurately,the charging current can be controlled within a limited range,and can switch to the corresponding charging stage according to the voltage state of the battery,which verified the independent photovoltaic system Charging controller design is feasible.