Research On Model Predictive Control Of Photovoltaic System Based On Single-phase Heric Grid-connected Inverter

In recent years,with the rapid development of renewable energy and distributed power generation technology,its core technology,grid-connected control technology,has also received widespread attention.For grid-connected inverters using traditional control methods such as PI and PWM,reactive power transmission between the inverter and the DC side may occur,resulting in low output efficiency of the inverter.Sunways' s Heric(Highly Efficient and Reliable Inverter Concept)topology,because it adds a bypass structure to the full-bridge inverter topology to avoid the problem of low inverter power factor,so in photovoltaic power generation systems Heric inverters are also used more and more widely.This dissertation mainly focuses on the control strategy of single-phase photovoltaic gridconnected inverter system,so as meet the photovoltaic grid-connected system can improve the output voltage waveform of the inverter and reduce the harmonic content of the grid-connected current while maintaining the maximum power output.Aiming at the two main control problems of maximum power point tracking and grid-connected inverter in photovoltaic gridconnected systems,MPPT controllers based on photovoltaic maximum power point-tracking and predictive current controllers based on Heric grid-connected inverters were designed respectively.To this end,this dissertation focuses on the following two issues:Firstly,the topology and principle of single-phase photovoltaic grid-connected inverter system are introduced.As the core component,grid-connected inverter is analyzed,and the working principle and utilization advantages of Heric grid-connected inverter are analyzed.By analyzing the photovoltaic cell circuit,the mathematical model of the photovoltaic cell is established,and the working principles and advantages and disadvantages of several widely used MPPT control methods are analyzed.This dissertation selects the improved variable step conductance increment method as the control method of the photovoltaic system.The simulation verified the output voltage,current,and power output of the photovoltaic system with the incremental conductivity method when the light intensity was changed.The results show that the incremental conductivity method can control the photovoltaic system to output a stable DC voltage,and when external conditions change,Photovoltaic systems can also have fast dynamic response capabilities.The stable output of the photovoltaic system can lay the foundation for the model predictive current control of the subsequent inverter grid-connected part.Secondly,in view of the large voltage jump of the single-phase Heric inverter during the switching process,this dissertation consider combining the three basic voltages of the Heric inverter to form 8 virtual voltages,and design a model based on the virtual voltage to predict the current control.It can reduce the degree of inverter output voltage jump and improve the accuracy of grid-connected current prediction.The design idea of the controller is clear and the parameter adjustment is simple,which can well implement the control of the grid-connected inverter.Finally,the control strategy proposed in this dissertation is applied to the single-phase photovoltaic grid-connected inverter system,which realizes the photovoltaic maximum power point tracking and the control of the Heric grid-connected inverter,and designs simulation experiments under several other working conditions.The effectiveness and reliability of the controller are verified by comparing with the control strategy designed in this dissertation.