Research On Switching Capacitor Single-Phase Grid-Connected Photovoltaic Inverter

Energy is very important to the development of human societ.Renewable energy such as solar energy has obvious ecological advantages compared with traditional fossil fuel energy,and has broad development potential.Nowadays,on account of the problems of environmental pollution and exhaustion of energy resources becoming worse and worse,exploring and using of new energy becomes more and more important.Solar energy is one of the most clean,practical and large-scale renewable energy resources.The whole world focuses on the use of photovoltaic(PV).The PV gridconnected system will be the main utilization of solar energy,so it will develop rapidly.The inverter is the last or the only one power converter stage of grid-connected PV station,whose efficiency and reliability will influence the performance of the whole system.According to different standards,the structuce of the grid-connected photovoltaic inverter is divided into many kinds.This article mainly studies nonisolated single-phase grid-connected photovoltaic inverter.This paper first summarizes the development situation of grid-connected photovoltaic system and analyses the influence of the current international financial crisis on photovoltaic industry.Secondly,in order to further improve the efficiency of the system and complete boost and inverter at the same time,this paper proposes a switching capacitor inverter topology.This paper analyzes the working principle,output characteristics,capacitive voltage stability factors,efficiency and economicy of switched-capacitor inverter.Aiming at the adverse effect of the ripple capacitance voltage fluctuation on the output current,the two optimization solutions are studied.First,the algorithm of step wave and EPWM chopping control is used to reduce the time interval of switching capacitor charging,thus reducing the switching capacitor voltage drop level,improving the current quality and achieving the duty cycle voltage regulator;Second,through predictive control,in which the switching capacitor voltage is dropped into the prediction model,so the drop of switching capacitor voltage does not affect the accuracy of the output currents tracking the given ones,a similar way also eliminates the negative impacts of semiconductor switching device conduction voltage drop on the output currents.The experimental results show that the modulation control algorithm and the switched capacitor inverter topology are correct and feasible,and exert certern superiority.