Water-machine-electricity System Multi Units Coupling Characteristic Study In Hydropower Station

Conduit system,hydraulic system and electrical system are three important parts of hydropower system in station.Complicated nonlinear dynamic system,incorporating different physical features,is formed by internal variable coupling among the systems.The stability of hydropower system and the regulation quality of unit’s transient operation are directly influenced by internal coupling characteristics and dynamic responding mechanism,which is important to the operational safety of the system in terms of theory and practice.Funded by the key project of NSFC named as"Hydro-mechanical-electric coupling study in hydropower station"(No.50839003),this thesis has conducted systematic research on hydro-mechanical-electric coupling problems,such as theoretical description,modeling theory,computational method and control of stability.Some complete and innovative theoretical results are obtained as follows.(1)The theoretical description and dynamic characteristic model in complex conduit systems are studied based on rigid water hammer,elastic water hammer and coupled water hammer models.The governing equation of coupling complex conduit system,including dynamic state of tunnel,surge tank,penstock and water turbine,is established.The nonlinear water turbine model is put forward based on characteristic correlation in system.By analyzing on complex water system characteristic,introducing and extending system dynamic equations,and comparative analyzing on the validity of model,the dynamic model,which can describe mutual hydraulic interference in one pipe and multi units system with branch pipes,and hydraulic decoupling analysis method are developed.The theoretical modeling and transient analysis of multi units coupling in tunnel-surge tank-penstock(main pipe and branch pipe)-water turbine system.(2)The internal coupling correlation among conduit system of hydraulic station,hydro generator system and speed control system is studied.According to the unified framework of Hamiltonian theory,the Hamiltonian function of hydro-mechanical-electric system is constructed.The energy transport relation between different subsystems is characterized by Hamiltonian function.The theoretical model of hydro-mechanical-electric coupling in complex hydraulic system is developed.The constitutive relation of variables between systems and its dynamic characteristics are described by structure matrix and damping matrix representing the structural characteristics.The transient analysis method about internal parameters coupling among systems is put forward.The correlative mechanism between the transient process of hydropower system and the power load disturbance,as well as the transporting mechanism of dynamical effects among systems,are indicated.(3)The hydro-mechanical-electric coupling theory and the modeling method based on coupled water hammer model are studied.The hydro-mechanical-electric coupling model based on coupled water hammer model is developed.The coupling transient analysis method is put forward based on the characteristic curve of turbine comprehensive model.According to the variation characteristic of power load,the movable guide vane and speed control system in this model is based on the comprehensive characteristic curve of turbine,which can automatically trace the variation characteristic of power load.The transient responding process of the hydro-mechanical-electric system is ended by iterating,and the transient time-history process is obtained.The numerical example shows that the established theoretical model and the proposed computational method can well reflect the coupling dynamical effect among systems during the transient process of hydropower system,and can effectively predict the parameters variations and variation rules during the transient process of hydropower system.(4)The stability and control problems under the coupling effect of hydro-mechanical-electric system in hydropower station are studied.The systematic Lyapunov function is constructed based on Hamiltonian function,and the stabilizing controller under a given output condition is designed.The control theory and strategy on injection modification of structure matrix and damping matrix based on Hamiltonian hydro-mechanical-electric coupling model are put forward.The corresponding controller is designed,and the tracking control of power regulation and frequency regulation by the movable guide vane is implemented.The simulation result shows that the control theory and method proposed in this thesis can effectively stabilize the transient oscillation in the system.