| With the large-scale access of renewable energy to the grid,the "double-high" characteristics of the power system are profoundly affecting the shape and operating characteristics of the grid,and the traditional grid dominated by synchronous machines is being transformed.Frequency stability is being severely tested.Battery energy storage has received widespread attention in smoothing power fluctuations in the grid and improving frequency stability due to its flexible configuration and fast response capability.In addition,the virtual synchronous machine control strategy can make the energy storage with traditional synchronous machine characteristics,providing virtual inertia and damping to maintain the frequency stability of the new electrical energy power system with a high penetration rate,which has important theoretical value and practical significance for building autonomous power system.Accordingly,this paper takes energy storage based on virtual synchronous machine control as the research object,focuses on its operation and control in large power grids,and analyzes the dynamic action and stability mechanism of virtual synchronous machine and power grids according to the rotor motion equation and unit synchronization mechanism guides the design and improvement of energy storage system controlled by virtual synchronous machine from the theoretical point of view,and further enhances the energy storage and virtual synchronous machine control in high percentage new energy power systems operational reliability,the main work accomplished is as follows.(1)A virtual synchronizer-controlled battery energy storage electromechanical transient model applied to large-scale power grids is constructed.Firstly,the virtual synchronous machine technology is studied and the structure and overall modeling process of the energy storage system are described.The model includes virtual synchronous machine control,energy storage limitation module,and model interface module,and the virtual synchronous machine stator-rotor equations and energy storage charging and discharging power,charge state,operating efficiency,dead band,and inverter limitation characteristics are considered.Through the power system analysis and synthesis program,a user-defined approach is used to model the active power and frequency control of the virtual synchronous machine,and the inertia,damping,and dispatchable characteristics of the synchronous machine are simulated.The frequency response characteristics of the synchronous machine are compared with those of the sag control and synchronous machine in the IEEE 4 machine 2 region and Henan power grid as an example to verify the model validity and the advantages of the virtual synchronous machine technology over other control strategies.(2)An adaptive virtual synchronizer control strategy considering the grid operation state is proposed.To address the problem that the virtual synchronous machine control is difficult to take into account the small overshoot and rapid dynamic regulation of the system,the mechanism of the influence of grid fluctuation on the output characteristics of the virtual synchronous machine is analyzed by using frequency domain and time domain analysis,and the changes of virtual inertia and sag coefficient on the dynamic regulation of the virtual synchronous machine are clarified.According to the results of mechanism analysis and energy storage configuration constraints,the action state of energy storage and the corresponding control mode are analyzed in the process of a grid disturbance,and the adaptive virtual synchronous machine control is proposed correspondingly to achieve a fast response in the steady-state of the system,sufficient inertia support and better storage charge state maintenance effect in case of fault.(3)The frequency response model of energy storage participation in a high percentage of new energy power systems based on virtual synchronous machine control is proposed.Firstly,based on the existing frequency response model,variables characterizing the frequency control capability and penetration rate of renewable energy are introduced to establish the frequency model of a high proportional new energy power system,analyze the effect of the increasing penetration rate of new energy on the frequency stability and steady-state deviation of the power grid,and provide the theoretical basis for the participation of virtual synchronous machine in the frequency response analysis of the power grid.Based on the linearization equation of the virtual synchronous machine and the approximation simplification rules of the system frequency response model,the frequency response model of the virtual synchronous machine participating in the new energy power system and the frequency response model of the regional interconnection system are established respectively,and the mechanism of the virtual synchronous machine’s effect on the high proportion of new energy grid is explained,and the causes of the synchronous generator-like frequency regulation of the virtual synchronous machine control are clarified and verified by comparing with the time-domain simulation results.The model validity is verified by comparing it with the time-domain simulation results. |
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