Design Of The Stand-Alone Photovoltaic System Based On The Maximum Power Point Tracting

With the increasing depletion of global fossil energy, the renewable energy of solar gaining the more attention of Governments and a series of policies were issued to support, so photovoltaic has been rapid development. The stand-alone photovoltaic power generation as one of the branches has become a key investment target to various countries, because it can give power supply in remote areas, and has some advantages of a short construction period, an easy maintaining, an unattended operation, a random size, etc.This paper presents a stand-alone photovoltaic power generation system with maximum power point tracking (MPPT) and intelligent charging and discharging. This paper first describes the current development of photovoltaic industry at home and abroad. Then it introduces this system involved in principle and characteristics of photovoltaic cells, principle and common algorithms of maximum power point tracking, principle of SEPIC chopper circuit, physical and chemical principles and common charging methods of lead-acid batteries. Finally, the system hardware and software solutions are described in detail, and gave the corresponding experimental results. The system uses Infineon’s XC866microcontroller as the master chip, selects SEPIC chopper circuit to form the DC-DC module, uses the analog-digital conversion module from microcontroller to measure the output voltage, output current of Photovoltaic cells. Then the system uses maximum power point tracking algorithm with a combination of constant voltage tracking and perturbation and observation to automatically adjust the DC-DC module working state, so that the output power of photovoltaic cells near the maximum power point. Meanwhile, the system according to the measured output voltage of a photovoltaic cell to determine the current of the light intensity, and then the system decides to charge the lead-acid battery, or power to the load, or neither charge nor power by the light intensity and remaining power of battery. During the charging process, the system knows the current need of power which used to charge lead-acid battery by measuring the terminal voltage of lead-acid battery, and determining the current charging method according to the voltage. The system uses segmented charging method, they include the maximum power point tracking charging method, constant current charging method, constant voltage charging method, floating charge method.We can prove the following by testing entity of the system. Maximum power point tracking algorithm can improve the power output of photovoltaic cells by about10%, and in combination with the charging strategies to improve the energy efficiency of the entire system about25%. The system can be long running stably and reliably.