Research Of Single-phase Photovoltaic Grid-connected System With DC Injection Suppression Ability

The rapid consumption of fossil fuels results in energy crisis and environmentalproblems which plague the world today. Solar energy is a kind of ideal energy sourcewith advantages such as inexhaustibility and cleanness. Photovoltaic (PV) generation isan important form of solar energy application, in which the market share of thegrid-connected PV systems is growing, and the limitation of direct current (DC)injection into the network is an important requirement for grid-connected PV systems.In this paper, the two stages single-phase LCL filter grid-connected PV system as theresearch object, the PV grid-connected system and the DC injection issue ingrid-connected current are discussed.Firstly, the cause and the adverse effects are expounded, and the relevant standardsof some countries are introduced in the paper. These descriptions indicate the importantpractical significance of DC injection study in the PV grid-connected system. The thesisdepth analyzes the existing DC injection solution, according to the difference ofimplication mode classified these methods, and summarize their advantages anddisadvantages, so that the contrast and selection between the methods, further study arecarried out expediently.Generally，the solution of DC injection is proposed and implemented in L filter grid-connectedPV system, LCL filter is better than L filter, so the solution of DC injection in LCL filtergrid-connected PV system is studied in the article. Analysis the causes of DC injection, wecan see, the DC injection problem which is caused by the inconsonant action of switch componentscan be suppressed by control method. In the DC injection case, grid-connected current canbe divided into two parts of the DC and AC. Depending on the different targets of the PIregulation and PR regulation, control the two components separately with the tworegulators. On this basis, a quasi-PR+PI double controller DC injection suppressionmethod is proposed in the paper. Through the analysis of the double controller property,combined with the impacts of various parameters on its performance of the controller,introduces the design method of the double controller. The system can achieve unityfactor and DC injection suppression when connects to the grid by using doublecontroller as the grid-connected current controller. The control mode is simple, and easyto meet the stability and steady state precision requirements.With the quasi-PR+PI controller as a current loop controller, designed a two stage LCL filter grid-connected PV system, and verified the system performance throughsimulation model which is established in Matlab/simulink. The simulation method ofDC injection is improved. DC injection exist verification experiment is carried out inthe purchased PV grid-connected experimental system. Through experiment on theRT-LAB experimental platform, verify the correctness of the designed system and theeffectiveness of the DC injection suppression method.