Shaft Modeling And Oscillation Analysis Of Compressed Air Energy Storage System

The compressed air energy storage(CAES)is gradually becoming a large-scale energy storage technology actively developed by countries around the world.It has the technical advantages of large energy storage capacity,long life cycle,fast dynamic response,and low pollution to the environment.The development of CAES is showing three major trends: larger capacity,multi-stage and higher speed,which brings great challenges to the safe and stable operation of the shaft system.Therefore,it is of great significance to establish the shaft model of CAES system and analyze its oscillation characteristics during the electromechanical coupling process.The main contents of this thesis are as follows:(1)For a typical four-stage expansion CAES system,the motion mathematical model of each rotating part of the shaft system is obtained by its equivalently processing,which focuses on the centralized equivalent of the multi-stage gears in the multi-coupling gearbox.Therefore the model of the segmented concentrated mass spring model of the shaft system is established.Compared with the turbo-generator set,the CAES system has a parallel distributed shaft structure.The output torque of each expander stage distributed on the shaft sections with different rated speed is transmitted to the multi-coupling gearbox in parallel to drive the synchronous generator.Based on the parameters of a specific four-stage expansion CAES system,the analysis of the inherent oscillation characteristics and parameter sensitivity of its shaft model reveals the oscillation characteristics and torque distribution of the shaft,which provides guidance for the design and optimization of shaft parameters.(2)The mechanical and electrical coupling transient model of the multi-stage expansion CAES system is established,which mainly includes the mathematical model of the shaft model,expanders,synchronous generator,excitation system,speed regulation system,etc.In order to reflect the volume effect of the high-pressure gas passage of the multi-stage expansion CAES system,a dynamic model of the inlet air pressure of each expander controlled by the valve is established.The electromechanical coupling model is simulated in MATLAB/Simulink for the inherent characteristic simulation of the shaft system,quasi-simultaneous grid-connection simulation,variable-operating condition simulation and short-circuit fault simulation.The simulation results verify the inherent oscillation characteristics of the shaft system and reveal the dynamic characteristics of key parameters in the system operation.(3)Based on the electromechanical coupling simulation model of the multi-stage expansion CAES system,the oscillation excitation sources on the expander side and the electrical side of the system are verified respectively,including the mechanical imbalance,faulty electromagnetic torque shock,synchronous generator load dump,sub-synchronous oscillation,and grid harmonics.The simulation results reveal the shaft oscillation characteristics and excitation principle of each oscillation excitation source,and the corresponding oscillation suppression strategy is proposed.