Research On Control Strategy Of Microgrids With Parallel Synchronous Generators And Virtual Synchronous Generators

In recent years,the permeability of distributed energy has been increasing and the installed proportion of traditional synchronous generators has been gradually reduced,which leads the rotating reserve capacity and the moment of inertia in the microgrid have been relatively reduced and the trend of high power electronization has gradually emerged.Due to the inertia and damping of the mechanical rotor,the synchronous generator has the capability of voltage,frequency support and regulation,which provides enough inertia for the microgrid.Based on that,the virtual synchronous generator technology combines the flexibility of power electronic equipment and the operation mechanism of synchronous generator,effectively solves the problem of low inertia of the system,and plays an important role in promoting the stability of microgrid.However,due to the differences in mechanical inertia characteristics,speed regulation characteristics and energy storage capacity between SG and VSG,the operation response characteristics of SG and VSG are different.Therefore,the research on the parallel operation stability control of micro-sources is increasingly extensive and in-depth in the world.Now,the study for parallel VSGs has been relatively mature,while the SG and the VSG parallel problems more complexity.It is easy to cause larger power oscillation of VSG during load mutation or micro-source closing,which may affect the stable operation of important loads in the grid and reduce the ability of the power distribution system.Therefore,parallel SG and VSG model are studied,the steady-state performance and transient response characteristics of the system are researched,and the factors affecting the transient performance of the paralleling system are deeply analyzed from the aspects of pre-synchronization and inertia matching respectively in this dissertation.The main contents are as follows:Firstly,a parallel VSG topology is established according to the VSG mathematical model,based on which the generation mechanism of system circulation and steady-state power distribution inequality in the parallel system is analyzed,the circulation is suppressed by virtual impedance and voltage and current double-loop modulation,and the design method of VSG parameters based on power distribution by capacity is unified.Secondly,aiming at the problem of phase angle difference jumping caused by traditional VSG pre-synchronization,the influence of phase Angle difference input signal on the transient response performance of parallel SG and VSG system is analyzed,and a new phase regulator based on triangle constructor is proposed to make the frequency compensation signal smooth and continuous,and the networking performance of VSG is optimized.Then,based on SG and VSG parallel model,the inertia and damping parameters of VSG are summarized,and the small signal model of active power loop of parallel system is derived.From the perspective of the inertia difference,the causes affecting the transient response performance of the system are analyzed in depth.A new active power given algorithm of VSG is proposed,and the power-frequency oscillation during the power transition of the microgrid is suppressed successfully.Finally,this dissertation builds an experimental platform based on VSG algorithm to verify the VSG algorithm and the pre-synchronization algorithm,and preliminarily proves the feasibility and practicability of VSG and related algorithms.