Research On Micro-grid Control Strategy Based On Virtual Synchronous Generator

Because the traditional microgrid inverter interface control strategy lacks the inherent frequency and voltage regulation capabilities of traditional synchr onous generator sets,and has no inertia and damping characteristics,it will a ffect the stability of the voltage,frequency and power angle of the grid when it is integrated into the grid on a large scale.In this regard,scholars at home and abroad have proposed a virtual synchronous generator(Virtual Synchronous Generator,VSG)technology which realizes the characteristics of active frequency regulation and reactive voltage regulation by simulating the ontology model of synchronous generators.This paper studies the control strategy of virtual synchronous generator in microgrid.Firstly,the basic principles of VSG will be introduced,the active-frequen cycontrol and reactive-voltage controller of VSG will be established and the overall control strategy of VSG will be formed on the basis of the above.Aiming at the problem of VSG isolation / grid switching,this paper adds an integral link on the basis of VSG primary frequency regulation and voltage regulation control,so that VSG has secondary frequency regulation and voltage regulation control to achieve pre-synchronization of the frequency and voltage of the power grid and VSG.Phase angle pre-synchronization uses an improved pre-synchronization control method that does not require a phase-locked loop.This method controls the grid voltage q-axis component to 0 to achieve phase synchronization between the power grid and the VSG,thereby achieving smooth switching between the VSG and the grid The above methodw as simulated and verified.Based on the characteristics of flexible and adjustable VSG parameters,this paper further studies the parameter control of virtual moment of inertia J and damping coefficient D,proposes an exponential type of coordinated adaptive control strategy of moment of inertia and damping coefficient,and gives a parameter selection method using Trajectory method for stability analysis.This strategy can adjust the virtual inertia and damping coefficient online when the VSG angular velocity change rate and deviation are large.It can reduce the system overshoot ?% during the transient process,shorten the adjustment time,and optimize the dynamic adjustment of VSG inertia and damping.characteristic.Finally,this paper conducts specific analysis and modeling on the DC side,combined with the above AC side control methods,to establish a complete photovoltaic-hybrid energy storage VSG grid-connected power generation structure.First,the photovoltaic cell is modeled according to the mathematical model of the photovoltaic cell,and the MPPT control is completed;the storage battery and the super capacitor are connected in parallel to the DC side through their respective dual DC / DC converters.Analyze the influence of power loop parameters on energy storage control accuracy,design an energy management strategy with low-pass filtering,and limit management of supercapacitors.Finally,different working conditions are set for simulation to verify the feasibility and effectiveness of the above strategy.