Application Of Gird Connected Composite Device Based On Virtual Synchronous Generator In Low Inertia System

With the increase of the proportion of photovoltaic,wind power and other new energy generation in the power grid,and the large amount of electric energy through DC transmission,the proportion of synchronous generators in the power grid is decreasing,and more and more regional power grids have gradually become low inertia power systems.Due to the lack of equivalent inertia,the grid connection,power regulation and disconnection of low inertia power system are more likely to cause stability problems than conventional system.In order to solve this problem,a new method of connecting low inertia power system to the main grid is proposed to speed up the speed of connecting low inertia power system to the grid and enhance the controllability of low inertia power system.This paper mainly includes the following aspects.This paper analyzes the problems existing in the current low inertia power system and the main grid connection,combined with the existing structure and function of the grid connection composite device,applies the grid connection composite device to the low inertia power system and the main grid connection,which provides a new idea for the grid connection of the low inertia power system and the main grid.Aiming at the stability problem caused by the lack of inertia and damping of low inertia power system in the process of grid connection,the virtual synchronous generator technology is introduced based on the converter control of the original grid connected composite device.By deriving the small signal model of the virtual synchronous machine control and combining with the power transmission characteristics of the grid connected complex device,the range of the parameters involved in the control strategy is obtained.Based on PSCAD/EMTDC simulation platform,the model of grid connected composite device is built.The simulation results under traditional control and virtual synchronous machine control are compared to verify the superiority of the control strategy.Aiming at the problem that the transient impact of low inertia power system is too large,the pre-synchronization control link is introduced to realize the smooth grid connection of low inertia power system.Combined with the mode switching process of grid connected composite device,the switching strategies of converter control in different modes are given.The simulation results show that the strategy is effective.Through the work of this paper,the feasibility and specific implementation strategy of grid connected composite device applied to low inertia power system and main grid are studied,the control stability problem of grid connected composite device applied to low inertia power system is solved,and the smooth grid connection of low inertia power system is realized,It provides a new idea for fast grid connection and power flow control of low inertia system and main network in the future.