Extraction of Maximum Power from Battery connected PV system under Partial Shading Condition

Today, due to depleting conventional energy resources and rising global pollution most countries are increasingly shifting their dependence on conventional energy sources especially solar energy due to its abundant availability and ecofriendly nature. In this project a standalone PV system, coupled with a energy storage device, which functions as a backup has been analyzed and designed. Standalone PV system is most suitable for remote and rural areas which are difficult to integrate with the existing national grid. Due to rotation of earth, the amount of solar irradiation is not constant and hence the PV power extracted is variable during 24 hours span of a day. Also as the load changes according to the consumer requirement, the output power from a PV system may not sufficient to meet the load demand. Or it may happen that load demand is less than the PV output power. Hence a Li-On battery is used as a energy storage device because of its high energy density and fast dynamic response. To properly analyze and control the PV system, the single diode model of the PV cell is studied. The dynamic characteristic of Li-On battery is modelled using a RC equivalent circuit. To obtain maximum efficiency of power conversion from the PV system, it should be operated at its Maximum Power Point. The PV modules are often subjected to non-uniform radiation or partial shading condition, which modifies the Power Vs Voltage curve of the PV modules to introduce multiple local minima and one global maxima. Global maxima detecting MPPT algorithms: Particle Swarm Optimization technique and Grey Wolf Optimization technique are employed to track the global maxima in order to achieve highest power efficiency possible. The Li-On battery is connected to the PV system through a bi-directional DC-DC converter to control the charging and discharging process while maintaining a constant dc link voltage. The DC output power has to be inverted into AC power since most loads are AC in nature. Three independent control loops are designed to properly operate the PV system. The MPPT control loop is responsible for forcing the operating point of the PV system to the MPP under any irradiation condition. The battery charge /discharge control generates proper PWM pulse for the switches of the Bi-directional DC -DC converter to store excess energy from the PV modules and supply deficit energy to the load. The battery charge/ discharge control loop has additional task of maintaining the DC link voltage at a constant value. The inverter control loop is employed to regulate the near sinusoid AC output voltage under load variations. The system is simulated in MATLAB/SIMULINK and obtained simulation results are found to be satisfactory