Control Strategies And Simulation Study On PV System Based On Supercapacitor-Battery Energy Storage

Nowadays,searching for new type of alternative energy becomes a key problem which nearly decides whether human being can enjoy a healthy and sustainable development in the future with the deepening of world's population pressure,the deterioration of environmental pollution,and the crisis of world energy resources.Solar energy power generation gets more attention by the home distributed power generation which is usually implemented by a home stand-alone photovoltaic system for its CO2 free,dust free,environmental friendliness and low cost.But in a cloudy day,its output power may suffer a great fluctuation with the passing by of a cloud which demands the storage element provides the system load with percussive power.A traditional stand-alone PV system normally takes lead-acid batteries as storage elements whose charge current and discharge current are usually strictly stipulated.Thus the polar plates of the batteries can be damaged little by little and the usage cost of the system can be increased in a disguised form.What's more,traditional MPPT methods are usually fixed step ones which results in a greater fluctuation of output power and accumulated damage to the batteries.In order to cope with the problems above,two improvements on traditional stand-alone PV system are presented in this paper.First of all,a kind of improved stand-alone photovoltaic system with a supercapacitor-battery hybrid energy storage is presented and designed in this paper.In this kind of PV system,supercapacitor cooperates with the batteries according to the energy level of the energy storage element.At the same time,the working principles of the system is designed to ensure that the energy storage element won't be damaged by a over-high or over-low voltage level.Secondly,variable step MPPT method replaces the traditional fixed step ones based on improvement on traditional fixed step ones.Thirdly,the simulink model of the presented and designed system is build and simulated on the simulink platform.The result of the simulation shows that the designed system not only smooths the wave of the output power well but also keeps the charging power of the batteries and the load power steady while the output power fluctuates.Thus the rationality of the design is proved.