Research Of Single-phase Grid-connected Photovoltaic Power Generation System

With the exhaustion of traditional energy and the increasingly serious environmental pollution,the society urgently needs to develop new energy to adjust the energy structure and achieve sustainable development.Solar energy is an inexhaustible renewable energy with the advantages of clean,safe and sufficient energy.It plays an important role in the long-term energy strategy.As we all know,photovoltaic grid-connected power generation has been gradually promoted at home and abroad.Although its control technology is becoming more and more mature,its stability,reliability and power quality have attracted more and more attention from domestic and foreign experts,scholars and governments as the structure of power grid access end changes.In this paper,two-stage single-phase grid-connected photovoltaic power generation system is taken as the research object.Theoretical analysis,simulation and experimental verification are carried out on the photovoltaic cell model,maximum power point tracking technology,grid-connected inverter and its filter topology and overall control scheme.Firstly,MPPT technology of photovoltaic cells is analyzed and studied.Traditional MPPT control method is analyzed,and an improved MPPT method based on variable step length is adopted.Simulation analysis shows that the conversion efficiency of grid-connected photovoltaic power generation system is improved.Then the grid-connected filter in photovoltaic grid-connected power generation system is analyzed emphatically.The working principle and resonant damping technology of LCL filter are analyzed,and its parameter design is studied.high frequency harmonic component damage caused by grid inverter in the power system equipment,increase the power loss and other issues,on the basis of analyzing the working principle of the LCL filter,the two improved LLCL filter and LCLCL filter in-depth theoretical analysis,with the parameters of the LCL filter design,resonance damping technology as reference object,calculated the LLCL,LCLCL filter parameters,and its damping technology was analyzed.Adopting the compound control strategy of current double closed-loop + grid voltage feedforward,and the simulation analysis of the control strategy shows that the THD value of the grid-connected current of LCL type,LLCL type and LCLCL type filter is 1.36%,1.13% and 1.02%,respectively.The results prove that LCLCL filter can effectively filter high frequency harmonics.In addition,because in the photovoltaic power generation system,the input and output instantaneous power imbalance,there is two times the power frequency dc bus voltage ripple,fever can cause busbar capacitance so as to reduce its operating life,at the same time can also lead to grid current harmonic,there are three influence grid current power quality,based onthis,this paper adopts improved cycle integral control,can effectively restrain dc bus two times the ripple effect on the grid current,power frequency single-phase photovoltaic grid power system simulation analysis shows that by adopting cycle integral control technology can effectively reduce the THD value.After using periodic integral control,the grid-connected current THD can be reduced from 3.41% to 1.07%.Finally,through parameter design,device selection,software debugging,etc.,an experimental platform with rated power of 5KW grid-connected inverter was built to verify the feasibility of grid-connected inverter system.When grid-connected inverter is at half-load rated power,the effective value of grid-connected current is 22.5a,and the harmonic content is 1.57%.When the grid-connected inverter is at full load rated power,the effective value of grid-connected current is 11.4a and the harmonic content is 3.65%,and all of them can achieve the unit power factor effect and meet the requirements of grid-connected power quality.