Research On The Key Technologies Of Solar Photovoltaic Power Generation And Grid Connection

Due to the depletion of traditional energy and the deteriorating environment,countries around the world have started to adjust their energy structure to meet the growth of energy demand.Solar energy has been given a lot of attention because of the resources,the clean environment and the renewable energy.In order to increase the efficiency of photovoltaic(PV)power,we need a proper control strategy for power tracking control,in photovoltaic power generation system,the grid inverter control performance directly determines whether a high quality of electrical energy can be available to the user.Based on this,this article focuses on the maximum power point tracking(MPPT)and grid-connected inverter control technology.First,mathematical modeling of PV cells is performed,and the output characteristics of PV modules in different environments are simulated and analyzed.Study on the partial shade conditions on the output characteristics of the photovoltaic module,the structure of the photovoltaic array,simulation and analysis of serial arrays connected in parallel arrays,respectively.The simulation results show that the power output characteristics of series array can be multimodal in local shadow condition,while the parallel array presents unimodal characteristics.Secondly,the basic principle of MPPT is analyzed,and Boost circuit is selected as DC/DC circuit to carry out power transformation.Studied several kinds of typical unimodal MPPT control algorithm and compared their respective advantages and disadvantages,According to the advantages and disadvantages of the perturbation observation method and the conductance increment method,an improved variable-step perturbation observation method and variable step length conductance increment method based on power prediction are proposed.In the end,the improved variable step perturbation and observation method is compared with the typical perturbation and observation method,and variable step length conductance increment method based on power prediction is compared with the typical conductance increment method.Two kinds of the improved method can effectively reduce the system steady-state power fluctuations and reduce the power loss,and variable step length conductance increment method based on power prediction can solve the problem of miscalculation in the process of optimization,the simulation results prove the validity of the two kinds of improved control method.Again,the output power characteristic curve of PV array is multi-peak under local shadow condition,while the traditional method can get into local optimum under multi-peak condition.Therefore,the array of four components is studied.Based on the basic principle of radial movement algorithm,this paper proposes an improved radial movement optimization algorithm,which can quickly track the maximum power point and effectively avoid getting into local optimum.The simulation results of two,three and four peaks are simulated and verified.It is found that the method has better tracking performance.Finally,study on the control method of three-level grid-connected inverter with diode clamp.LCL filter is chosen as the filter link,at the same time,based on the principle of sliding mode control,in view of the chattering of sliding mode control problems,respectively,to improve the switching surface and the reaching law,the mathematical model and the control algorithm of the inverter are established in the alpha beta coordinates system.In the alpha beta coordinate system,the phase locked loop can be reduced.Design the parameters of LCL,using Simulink to simulation of the improved control strategy,verified and found that the proposed control strategy can very good guarantee the grid current at a relatively low harmonic and high power factor of the grid.