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

With the rapid development of society,the shortage of fossil energy and environmental pollution problems are increasingly exposed.Photovoltaic power generation instead of traditional thermal power generation has attracted a lot of attention because of its environmental friendliness.Photovoltaic power supply and battery energy storage system need to be connected to the grid through power interface converter.Grid connected inverter can not provide inertia and damping characteristics for the system under the traditional control strategy.With a large number of photovoltaic power into the network,it is bound to have an adverse impact on the stable operation of the power system.As a control strategy of grid connected inverter,virtual synchronous generator(VSG)can effectively provide inertial support for the system,which plays an important role in maintaining the stability of power system.Firstly,this paper analyzes the two-stage photovoltaic grid connected system,and introduces its components and corresponding control strategies in detail through mathematical modeling method.Among them,the first stage uses disturbance observation method to make photovoltaic cells work at the maximum power point,and the second stage uses two traditional control strategies(PQ control,droop control)to achieve grid connected inverter.Secondly,the VSG grid connected system is studied.In order to improve the stability of DC side voltage and ensure the energy balance between photovoltaic system and grid connected inverter,a hybrid energy storage module composed of battery and super capacitor is added to the photovoltaic system,and the corresponding control strategy is designed to give full play to its advantages;the inverter control adopts VSG control strategy,and its power frequency controller,excitation controller and inner loop control are designed The simulation results show that the hybrid energy storage module has good voltage stabilizing function,and can ensure the photovoltaic system and grid connected by charging and discharging Power balance between transformers.At the same time,VSG grid connected optical storage system shows good frequency regulation ability in response to various emergencies,and can maintain the stability of system frequency in different conditions.Finally,in order to optimize the control parameters of VSG,the small signal model of VSG is established to obtain the corresponding control parameters accurately and quickly;in order to make VSG adjust the inertia and damping coefficient online and optimize its power frequency response,an inertia damping adaptive control strategy is designed by analyzing the influence of inertia and damping on the system.The simulation results show that the strategy can not only make the VSG better cope with the power frequency variation,but also enhance the dynamic response stability of the VSG.