Research On The Inverter And MPPT Algorithm Of Grid-connected PV System

With the increasing environmental pollution and the growing global demand for energy,fossil fuels will be slowly abandoned,replaced by solar energy of the new clean energy.In order to improve the control performance of PV grid-connected inverter and improve the efficiency of power generation,PV grid-connected inverter control technology and new type of maximum power point tracking(MPPT)technology are the research hotspots.In this paper,three-phase two-level inverter system with the Boost booster is selected as the research object,and the former MPPT control algorithm and the grid-connected inverter control strategy are studied.Firstly,the mathematical model of three-phase grid-connected inverter is designed,and the parameters of double closed-loop controller are designed.In order to solve the problem of the DC bus voltage disturbance and the grid voltage disturbance and the impact of the grid current on the power grid,the voltage feedforward is added to the inner loop to improve the dynamic performance of the grid-connected inverter.For the grid current total distortion rate(THD)is high only when using PI regulator,the grid strategy with PI control and repetitive control is studied.At the same time,the disturbance of the power grid and the harmonics are well restrained,and the steady state precision is improved.Anti-jamming capability is enhanced.For the grid voltage imbalance,the three-phase software phase-locked loop based on symmetrical component method is adopted to improve the anti-jamming capability of the system.Through the simulation analysis of the double closed-loop grid-connected inverter,it is proved that the control strategy has good dynamic and stability in the case of grid voltage mutation,frequency change and harmonic condition.Secondly,the engineering and modeling of the PV array are analyzed.Based on the basic principle of MPPT,the MPPT device of PV cell is designed,and several traditional MPPT control algorithms are studied and improved.The advantages and disadvantages of the MPPT are compared and analyzed.Finally,a variable step perturbation Observation method with hysteresis loop comparison,this method can eliminate the power fluctuation in the process of stabilization,and solve the misjudgment problem of the optimization process.The simulation results prove the effectiveness of the control method.Thirdly,the model of the PV array under local shadow conditions is built.In order to solve the problem of tracking failure in the multi-peak case,the method of selecting the reference voltage for two peaks is analyzed.Based on the principle of fireworks explosion optimization algorithm,a new MPPT algorithm is proposed for three or more peaks,which avoids the local maximum power point and has the advantages of fast and accurate tracking.Then,the feasibility of the method is verified by simulation.Meet the tracking requirements.Finally,the 1.8kW grid-connected experimental platform is set up.The parameter design,selection and hardware circuit design are carried out.Through the DSP software programming,the PV grid strategy and the MPPT algorithm are experimentally studied,and the experimental results are analyzed to verify the feasibility and effectiveness.