Research On Inverter Control Strategy Based On Virtual Synchronous Generator

With the development of distributed power generation technology,the penetration rate of distributed energy sources continues to increase,resulting in the lack of inertia and damping characteristics of the power system,which has a serious impact on the stable operation of the power system.By simulating the static and dynamic characteristics of the synchronous generator,the virtual synchronous generator technology can make the distributed generation unit have inertia and damping characteristics,and provide certain support for the power system.For this reason,it is important for building a reliable power system.significance.This paper focuses on the problem that the single virtual synchronous generator can not take into account the dynamic adjustment performance of power and frequency,and the voltage imbalance,power distribution,and circulating current when multiple virtual synchronous generators are connected in parallel with an unbalanced load.Aiming at the problems that the output power of the virtual synchronous generator oscillates at a fixed inertia and the dynamic response time of the frequency is too long,the control strategy of the virtual synchronous generator based on adaptive inertia is studied.First,the internal characteristics of the synchronous generator are introduced on the basis of droop control,and the virtual synchronous generator control strategy is obtained.Then,the model is analyzed and the overall control strategy of the virtual synchronous generator is given.Secondly,by analyzing the influence of the fixed inertia in the virtual synchronous generator on the dynamic response process of its output power and frequency,a virtual synchronous generator control strategy based on adaptive rotor inertia is introduced.The design of key coefficients such as droop damping coefficient,initial rotor inertia and inertia compensation coefficient is given in the frame of virtual synchronous generator,real-time adjustment of rotor inertia is realized,and the dynamic response characteristics of virtual synchronous generator output frequency and active power are improved.Aiming at the problems of voltage balance,power sharing and circulating current suppression in parallel system with unbalanced load,the control strategy of virtual synchronous generator under unbalanced load is studied.The positive and negative sequence voltages can be obtained through the method of positive and negative sequence separation based on the second-order generalized integrator(SOGI),and the obtained positive sequence voltage and negative sequence voltage can be controlled in sequence.Under the positive sequence dq axis coordinates,the positive sequence voltage is a DC quantity,and the negative sequence voltage is an AC quantity at twice the fundamental frequency.The relevant parameters of the controller are designed to improve the capacity of the virtual synchronous generator with unbalanced load.By analyzing the parallel system when the line impedance is inconsistent,there are problems of reactive power distribution and positive and negative sequence circulation.The positive and negative sequence virtual complex impedances based on SOGI are added to the positive and negative sequence voltage loops respectively to improve the voltage and current loops,reduce the impact of line impedance differences on power distribution,and realize the decoupling of active and reactive power.The voltage feedback control at the load end is used to reduce the voltage difference caused by the difference in line impedance,further improving power distribution and circulating current suppression.Finally,by building a virtual synchronous generator simulation model on the Matlab/Simulink platform,the simulation results verify the validity and feasibility of related theories and control strategies.