The Research Of Off-grid Photovoltaic Power System

With the rapid development of world economy, the traditional fossil energy sources suchas coal, oil, natural gas are used extensively, which causes serious energy shortages andenvironmental pollution. Nowadays, energy issues have brought more and more attention ofcountries around the world. Many countries have focused their attention to the new energy.Solar energy got extensive development and utilization for its "unlimited" reserves, universalexistence and cleanness. Currently, solar energy is mainly used in power system. Solar powersystem can be divided into grid photovoltaic power system and off-grid photovoltaic powersystem according to whether the solar power grid. Grid photovoltaic power system has thefeatures of grand scale, large investment and mainly concentrated in rich light regions. Whileoff-grid photovoltaic power system is widely distributed, low-cost and flexible. So off-gridphotovoltaic power system has its unique advantages in remote areas where the power supplyis difficult. Therefore, it is necessary to research the off-grid photovoltaic power system.Frist, this paper presents a kind of off-grid photovoltaic power system based on theexisting research of the system. It includes: Solar Cells, Solar Charger, Energy StorageDevices, Step-up Circuit and Inverter Circuit. Second, a deep analysis is made about eachmodule and designed their indicators. After comparing the existing topology, the topologycircuit is chosen which is the module required. Boost converter is used as the main circuit ofthe Solar Charger, Push-pull Forward convertor as the main circuit of the Step-up Module andFull-bridge inverter as the main circuit of the Inverter Module. Third, the control strategy ofeach circuit is designed according to the selected topologies. The Charger is adoptedthree-period control method which includes: Constant Current mode, MPPT mode, ConstantVoltage mode. In MPPT mode, a new control strategy of picking the output current of Chargeris put forward, which is combining with the battery charging, and through the perturbationmethod to achieve the maximum power tracking. In Push-pull Forward circuit, a Dead-timeTimer control strategy is introduced, which is applicable to double side converters. Voltage-tracking control is applied in the inverter circuit of SPWM control, which is easy toimplement.Finally, according to the selected topologies and the control strategies, the circuitparameters are designed. Then experimental circuits are built and debugged through softwareprogramming. Charger experimental results verified the feasibility of the proposed MPPTcontrol strategy. The Push-pull Forward circuit experiment verified the feasibility of theDead-time Timer control strategy. The whole system test results confirm the usability of thesystem.