Research On Compound Control Strategy Of Photovoltaic Grid-connected Inverter

Photovoltaic generation technology is one of the ways to effectively deal with the energy and environment problem.In photovoltaic generation technology,photovoltaic grid-connected invertersis an p ivotal interface between photovoltaic cells and power grid,which get more and more attention.However,there are more control strategies in the research of photovoltaic grid-connected inverters,with the extensive use of some large-scale electromechanical equipment and non-linear loads,etc.,which may decline the ability of communication equipment and power electronic sensitivity,affect the control process of the inverter.So,affecting the inverter control process,the harmonic content of the grid-connected current increases,and the grid-connected result is not ideal.So,it is very important to study a new composite control strategy for photovoltaic grid-connected inverters.First,establish the LC and LCL topology of the PV grid-connected inverters to compare the performance and structure of them.Low-cost LCL photovoltaic grid-connected inverter is choiced.At the same time,based on the constraints of the optimal design of the LCL grid-connected filter,the LCL filter is designed.Then,aiming at the problems of photovoltaic inverters,the three-phase asymmetry of the grid-connected current and the harmonic content of the photovoltaic inverter for the traditional control strategy are greatly increased,the output current will fluctuate,the PIR control strategy of the existing photovoltaic inverter is improved,and a PIR compound control strategy of the LCL photovoltaic inverter is proposed.This compound control strategy take advantages of PI and PR controller to track the DC signals and AC signals,and the PIR controller is also improved and the main four performance parameters of the PIR controller are simulated and selected.At the same time,the current reference value in current loop control is also obtained to compare with feedback current of grid-connect,and the feasibility of the strategy is verified by simulation analysis,which reduces THD of grid-connected current.Finally,in view of the complex coordinate transformation and decoupling calculation problems of the traditional PI control scheme under the synchronous rotating coordinate system,and the inadequacy of the control ability of the grid-connected current,an compound control strategy using the PI+repeated control in the stationary coordinate system.This control strategy introduces a repeated control scheme based on the PI control scheme and organically combines the two schemes.The weighting coefficient is added to the PI control branch and the repeated control branch,respectively,to optimize the system control design,and through simulation analysis verify the correctness of the control strategy.What’s more,the system can also keep a good stability and fast dynamic response capabilities.