Research On Inertia And Damping Coordinated Control Strategy Of Virtual Synchronous Machine Integrated To AC Microgrid

In recent years,due to the rapid development of new energy and microgrids,the penetration rate of distributed power based on power electronic equipment in power systems has become higher and higher.However,traditional power electronic devices lack inertia damping characteristics,resulting in system stability being threatened.The emergence of virtual synchronous machine technology effectively eliminates the problem of low inertia and weak damping brought by the grid connection of distributed power supplies,and enhances the support capability of distributed power supplies to the frequency and voltage of the grid.Most of the existing control methods focus on the influence of inertia on the frequency stability of the system,while ignoring the exploration of damping on the system stability.In this paper,the research on the inertia damping characteristics and control methods of the virtual synchronous machine is carried out by using the flexible and adjustable characteristics of virtual synchronous machine parameters.The research content of this paper mainly includes:1)The working mechanism of the source load side virtual synchronous machine in the AC microgrid is analyzed,the corresponding mathematical model is established,and a control method using the DC side voltage to provide virtual inertia is proposed for the rectified load.2)The small-signal model of the virtual synchronous machine is constructed,and the transfer function between the output active power variation and the set active power variation is obtained based on the system step response characteristics,the coupling mechanism between the moment of inertia and the damping coefficient under different operating states is analyzed in detail,and the dynamic response performance of the system under different coupling mechanisms is compared.The influence of phase-locked loop and energy storage physical constraints on the inertia damping characteristics are analyzed,and the addition of phase-locked loop equivalently increases the moment of inertia and reduces the damping coefficient,the existence of energy storage physical constraints restricts the value of inertia damping.3)Taking advantage of the flexible and controllable parameters of the virtual synchronous machine,the inertia and damping are adaptively adjusted during the oscillation process of the system,which improves the frequency stability of the system.Combining with the coupling mechanism,a coordinated control method for inertia damping is proposed,through Change the operating state of the virtual synchronous machine during the disturbance process,the virtual synchronous machine runs at the optimal damping ratio at the beginning of the disturbance,and then switches to over damping operation after a period of time to reduce the overshoot before the system reaches the steady state.This control method optimizes the transient response of the output power while improving the frequency stability of the system.4)A virtual synchronous machine digital simulation model is established by using the PSCAD/EMTDC? platform,verifying the correctness of the theoretical analysis and control methods in each chapter.