Study On Stand-alone Photovoltaic System And Energy Management

In the21st century, problems caused by energy shortage and environment pollu-tion become more serious. New energy sources, represented by wind and solar energy,have draw worldwide attention, because of their clean and sustainable features. Thestand-alone photovoltaic system can supply the residents who live in remote or farfrom utility grid area with power. This paper focuses on the designment and optimi-zation of the stand-alone photovoltaic system. The main contents are listed as follows:1)The power–voltage (P-V) characteristic of photovoltaic arrays operating underpartial shading condition exhibits multiple peaks. Conventional maximum powerpoint tracking (MPPT) methods can be trapped at local maximas, which lead to powerloss. By analyzing the current–voltage (I–V) curve of PV arrays which are partialshaded, a new strategy to search the global maximum power point (GMPP) is pro-posed. Auxiliary line, current control and perturb and observe (P&O) are combinedtogether to fulfill the goal.2)This paper introduces a design of600w rated output power PV inverter whichhas a wide input range and high conversion efficiency. The front stage is based onpush-pull circuit and designed by PWM adjustor of SG3525. TL431incooperationwith L817A forms type II compensator and the procedure of compensator design hasbeen explained. Full-bridge inverter circuit is used in the back stage. The SPWM andthe average value closed loop control technology are conducted by using a MicroController Unit (STM32F103VC).3)The photovoltaic energy management strategy has been proposed. Lead acidbatteries are charged in three stages, which are constant current charge, constantvoltage charge and float charge.The open-circuit voltage method and the ampere hourintegral method are combined together to estimate the battery SOC. A set of optimi-zation of lead-acid battery discharging strategy is presented.The photovoltaic sys-tem’s overall block diagram and control strategy have be illustrated.At last, simulations and experiments are presented to assess the performance ofthe proposed maximum power point tracking strategy which proved strong and relia-ble. Experiments show that the inveter gets little harmonic in its output voltage andhas up to88percent conversion efficiency. The energy management system is alsoproved works well by the charging and discharging test.