Research On Microgrid Operation And Control Strategy Based On Virtual Synchronous Generator

With the increasing penetration of distributed generation in power grid,the development of HVDC and the extensive application of power electronic transformer,more and more converters are used in power grid,and the degree of power electronization in power system is getting higher and higher.Due to the intrinsic characteristics of power electronic devices,the lack of inertia and the decrease of damping in power system lead to the decrease of security margin.Virtual synchronous generator(VSG)can make the converter simulate the electromechanical transient characteristics of synchronous generator,and has unique technical advantage,such as virtual inertia,virtual damper,frequency and voltage regulation,seamless switching between grid-connected and islanding mode.In the traditional power system dominated by generator sets,the mass converters still need to track the power grid for a long time,so it is of great practical significance to study the virtual synchronous generator.Therefore,the control strategy of virtual synchronous generator in microgrid under different operation conditions is studied in this paper.Firstly,the basic principle of synchronous generator are summarized.On this basis,the control structure and realization principle of virtual synchronous generator are given.In order to enhance the effect of harmonic suppression and speed up the dynamic response,a virtual impedance design method is proposed by cascading a second-order generalized integrator with a third-order generalized integrator.Secondly,aiming at the unreasonable sharing of reactive power in multi-machine parallel system,a reactive power control method based on voltage compensation is proposed.In order to solve the problem of power oscillation caused by DC component,a double-loop control method based on quasi-resonant controller is presented.In order to ensure seamless switching between grid-connected and islanding mode,a presynchronization control strategy is presented.In order to improve the asymmetric operation capability of virtual synchronous generator,balanced control strategies under unbalanced load and unbalanced grid voltage are proposed respectively.In order to combine PV generation and storage energy compensation,a coordinated control strategy is established.Finally,based on the platform of MATLAB/Simulink,the above control methods are simulated and analyzed,and the results verify the correctness and effectiveness of the proposed strategy.