Modeling And Dynamic Analysis Of A Hydroelectric Generation System In Large Fluctuation Process

A hydroelectric generation system is a complex nonlinear system,which is composed of the synchronous generator,the hydro-turbine,the pipe system and the governor.The dynamic quality of the hydroelectric generation system is directly related to the safety,stability and economical operation of a hydropower station.In recent years,with the development of modern hydroelectric power industry,a large number of hydropower stations with high water-head and large single unit have been built in China,which leads to the instability problem of hydroelectric generation systems.Therefore,for the safe and stable operation of hydropower stations,the study of the complex nonlinear dynamic behavior of hydroelectric generation systems has important theoretical significance and practical value.This paper aims to propose nonlinear dynamic models of the hydroelectric generation system targeting some typical large fluctuation transient processes(e.g.load rejection transient,sudden load increase transient and sudden load decrease transient).From the perspective of the transmission and dissipation of energy,the hydroelectric generation system has been incorporated into the theory frame of generalized Hamiltonian system.The contents and conclusions of this paper include:(1)Dynamic modelling of the hydroelectric generation system.Considering the hydraulic-mechanical-electrical coupling characteristics of the hydroelectric generation system during different large fluctuation transient processes,we establish a novel dynamic model of hydroelectric generation system whose pipe layout is one pipe with one unit.Moreover,we select the hydroelectric generation system with multiple units as a research object.The dynamic model of multi-unit hydroelectric generation system is successfully proposed taking into account the hydraulic coupling effect in common penstock.(2)Investigation of the dynamic stability.Combining nonlinear dynamics theory with actual engineering,the dynamic operating property of the proposed hydroelectric generation system for the large fluctuation transient process is analyzed.Form the point of view of system science,the dynamic characteristic of system instability(e.g.chaos and bifurcation)is described.Based on numerical experiments,dynamic evolution laws of the critical influence indices such as the turbine head,torque,flow and speed are obtained.(3)Hamiltonian modeling and analysis.The generalized Hamiltonian system,as a general open mathematical system,provides significant advantages for describing the energy dissipation and exchange with the external environment.This task aims to put the hydroelectric generation system to the theory frame of generalized Hamiltonian system.From the energy transmission and dissipation of the system,we establish a transient Hamiltonian model of the hydroelectric generation system utilizing the method of orthogonal decomposition.The Hamiltonian energy function is also obtained.A numerical application is carried out to investigate the effectiveness of the proposed approach and the dynamic characteristics of the system.These methods and results implemented in this work provide theoretical tools to guarantee the stable operation of hydropower stations.