Research On Control Strategy Of Photovoltaic Grid-connected Inverter Based On Virtual Synchronous Generator

Photovoltaic power generation needs to connect to the grid with power electronic equipment in any mode of operation,which has little contribution to grid inertia.Therefore,the gradual increase of photovoltaic power generation will inevitably affect the operation state of conventional power system.In this paper,the grid-connected structure with photovoltaic and hybrid energy storage based on virtual synchronous generator(VSG)control strategy is analyzed and designed.Firstly,the mathematical model of photovoltaic cells is established,and the output characteristics are verified by simulation analysis.In order to keep the battery at the maximum power point(MPP)at all times,the improved maximum power point tracking(MPPT)algorithm is used.The mathematical model of photovoltaic grid-connected inverter controller is established,and the LCL-type grid-connected filter is designed to improve the power quality at the interface of VSG.Most of the current research on VSG is aimed at the AC side of the controller,but neglects the energy control of the DC side and makes it ideal as a constant voltage source directly.In view of this problem,the DC side is analyzed in detail in this paper.In order to improve the stability and reliability of the DC side,the hybrid energy storage module is configured for the photovoltaic units in the DC side to realize the voltage stabilization of the DC side under the double closed loop control strategy.The control of inverter is introduced into the second order model of SG,and the VSG power frequency,excitation module and integral control strategy are designed.The simulation results show that the designed VSG control strategy is feasible and effective.Finally,the VSG grid-connected control strategy model with photovoltaic and hybrid energy storage modules is built in the simulation platform.In this paper,the output of VSG and its benign interaction with large power grid are designed when the load switching and the VSG instruction value are changed.The simulation resultsshow that the DC side can effectively reduce the impact of load sudden change on the power grid under the action of mixed energy storage,keep the DC side voltage constant,and make up the power difference effectively by charging and discharging.The AC side can realize the output characteristic similar to SG through VSG network connection.Through the comparative analysis of VSG and traditional control strategy,it is verified that VSG control strategy can participate in frequency modulation and voltage regulation independently,which is beneficial to improve the stability of the system with photovoltaic power supply and promote the further development of photovoltaic industry.