Research On Modeling And Control Strategy Of Three-Phase Grid-Connected PV System Based On The Dynamic Phasor Method

With the large-scale development and utilization of grid-connected PV systems in recent years,the dynamic research of grid-connected PV systems has become a common concern in the power industry and the photovoltaic industry.The power generation characteristics of PV systems are different from traditional energy sources,so the establishment of a model that can quickly respond and accurately describe the operating characteristics of grid-connected PV systems is the basis of related research work.The relevant research lacks the dynamic phasor model for the overall simulation of large-scale PV system and the corresponding control strategy at present.Therefor,this paper focus on the research on the dynamic phasor model and control strategy of the two-stage three-phase grid-connected PV system.There is the main content of this paper.(1)The electromagnetic transient model of the three-phase grid-connected PV system is established,and the principle and implementation method of MPPT are introduced in detail.The dual-loop control strategy is introduced for the control part of the inverter,and the effectiveness of MPPT and dual-loop control is verified under different environmental conditions by simulation.(2)According to the dynamic phasor method,the dynamic phasor model of gridconnected PV system is established.The modeling of the inverter includes the dynamic phasor model in the three-phase static coordinate system and the rotating coordinate system.For the voltage and current dual-loop control part,a dynamic phasor model of the dual-loop control under the rotating coordinate system is also established.By comparing simulation results of150 MW PV station,it is verified that the dynamic phasor model of the PV system can accurately reflect the dynamic characteristics of the electrical quantities in the PV system,and the simulation speed is improved.(3)Harmonic analysis is performed when an asymmetric fault occurs in the power grid,combined with the symmetrical component method,and an asymmetric control strategy with separation of positive and negative sequences is added.A dynamic phasor model of the control system based on the rotating coordinate system is derived as well.By comparing simulation results of 150 MW PV station,it is verified that the asymmetry control is effective for balancing the three-phase current.The dynamic phasor model of asymmetry control has the ability to analyze the dynamic characteristics of the PV system when it is asymmetry and significantly reduces the simulation time.(4)In the case of grid voltage dips,the LVRT control strategy is introduced.A LVRT control strategy based on reactive power support was added to the system,and its dynamic phasor model was established for the first time.Through simulation analysis,it is verified that the control strategy meets the requirements of LVRT,and the dynamic phasor model of LVRT control can accurately reflect the dynamic characteristics of the PV system during the voltage dips.