Studies On The Dynamic Phasors Model And Interharmonics Of PV Interconnected Grid With Inverter

In recent years,with the development of power electronics technology,photovoltaics(PVs)are applied more and more widely.The high percentage of renewable energy represented by PVs has become the trend of the future Internetof Energy.However,the PVs are interconnected with grid by inverters,and it's random output will bring complicated power quality problems.Interharmonics is the most important one of them.The establishment of a model that can accurately describe the dynamic and static characteristics of PV inverter is the basis of related research.Therefore,this thesis focuses on the PV inverters' dynamic phasor model and thier interharmonic problem.First,the analytical model of harmonic analysis for PV grid-connected system under the disturbance of MPPT control is derived,whose correctness is verified by simulation.Based on this model,the generation mechanism and related characteristics of interharmonic can be derived.It is found that in the vicinity of the maximum power point,MPPT output disturbed voltage control command,which can introduce interharmonic components of current to the grid through the inverter's internal control link.MPPT control parameters,PI parameters and external environmental factors will affect interharmonic emission level.Secondly,according to the dynamic phasor and the symmetrical component,the dynamic phasor sequence compoment harmonic model of PV inverter is established,which is successfully applied to the asymmetrical short circuit analysis of PV inverter.The simulation results verify the correctness of the model.Thirdly,by reducing the fundamental frequency of the dynamic phasor analysis,the dynamic phasor sequence compoment interharmonic model of PV inverter is deduced.Simulation and experiments verify the correctness of the model.Based on this model,the transfer law of interharmonic on the AC and DC sides can be analyzed.Finally,according to the mathematical definition of dynamic phasor,the concept of dynamic phasor perturbation is proposed.The dynamic phasor perturbation model of PV inverters which considering detailed control strategy is deduced.Compared with the simulation results,the result shows that the model's order is low and can effectively improve the solution speed of the interharmonic.It also can accurately reflect the interharmonics caused by the PV output fluctuations,voltage background interharmonic and perturbation of the MPPT.Based on this model,the effect of the control parameters on the interharmonics emission characteristics is analysed.This thesis establishs the interharmonic model of PV inverter and analysis its related characteristics,which can provide theoretical basis and research methods for the PVs' interharmonics,providing theoretical support for the prevention and control of interharmonics.