| Hydropower unit is the core of hydropower energy production,which contains many complex subsystems,among which the shafting and hydro-turbine governing system(HTGS)are the key to ensure stable supply of high-quality electric energy.The shafting converts water energy into electric energy,but it operates in the harsh and transient hydraulicmechanical-electrical coupling environment for a long time,subject to hydraulic,mechanical,electromagnetic and other multiple excitations,accompanied by complex and changeable violent vibration,which brings huge energy loss,increases the failure risk and shortens its life cycle.According to the load demand,the HTGS adjusts the power production to ensure the power quality and ensure the safety and stability of the power grid(PG).However,there are many theoretical and technical defects in vibration inducement,nonlinear dynamics characteristics,and vibration reduction control of shafting.Meanwhile,the shafting and HTGS are interrelated during the load regulation process of the hydropower unit,but the coupling relationship and nonlinear dynamic characteristics of the coupling system have not been explored,and the dynamic regulation control optimization theory method which takes into account the shafting and HTGS of the hydropower unit has not been proposed.In addition,the nonlinear dynamic characteristics of the shafting-HTGS coupling system of grid-connected hydropower units have not been revealed,especially the method for harmonizing the multi-index performance of primary frequency regulation(PFR)and ultra-low frequency oscillation(ULFO)of grid-connected hydropower units has not been proposed.The above series theoretical scientific and engineering problems that need to be solved,seriously reduce the safety,reliability and efficiency of hydropower operations,and restrain the pace of hydropower efficiency and economic development.Therefore,it is urgent to research nonlinear dynamics and control optimization of the shafting-HTGS coupling system of hydropower units,to lay theoretical foundation and technical support for the safe design and operation control optimal of hydropower units.Therefore,this research aims to explore the nonlinear dynamics characteristics of shafting vibration of hydropower units,analyze the coupling relationship between shafting and HTGS of hydropower units,and realize the operation optimal control of the shaftingHTGS coupling system of hydropower units.The systematic research focuses on the multidimensional vibration nonlinear dynamics characteristics and vibration reduction control of the shafting vibration excited by multiple vibration-sources of hydropower units,the nonlinear dynamics characteristics and dynamic regulation control optimization of shaftingHTGS coupling system of hydropower units,the nonlinear dynamics characteristics of the shafting-HTGS coupling system of grid-connected hydropower units and the coordinated control optimization of PFR.Some theoretical research results have been obtained,which lay a theoretical basis and technical support for the safety and stability design check,operation optimial control,and decision-making of hydropower units.The main research contents and innovative achievements are as follows:1)Based on the research on the arcuate whirl of rotor and the nonlinear dynamics of shafting bent-torsional coupling vibration for hydropower unit,the nonlinear dynamic model of shafting bent-torsional coupling vibration considering the arcuate whirl of the hydropower unit is established.The influence of the rotor arcuate whirl and shaft torsional vibration on the radial vibration of the shafting are verified.The nonlinear dynamics characteristics of arcuate whirl coupled bent-torsional vibration of shafting and the nonlinear dynamics evolution law of shafting vibration with parameter variation are described.2)The nonlinear dynamic equation of shafting vibration excited by multiple coupling vibration sources is established,and the holographic spectrum theory was introduced to obtain two-dimensional and three-dimensional holographic spectrum of shafting vibration simulation and measured signals.The nonlinear dynamic characteristics of shafting vibration simulation and measured signals excited by multiple coupling vibration sources are analyzed,and the effectiveness of the nonlinear dynamic equation of shafting vibration excited by multiple coupling vibration sources was verified.The influence of each excitation vibration source on the nonlinear dynamic characteristics of shafting vibration is explored.3)The nonlinear dynamics equation of shafting multi-dimensional vibration of hydropower unit is established,and the global sensitivity of the system parameters for shafting multi-dimensional vibration is investigated by using the Sobol method.Meanwhile,based on the Euler-Lagrange error equation and Lyapunov theory,a multi-dimensional vibration state feedback vibration reduction controller for hydropower unit shafting is designed,and the nonlinear dynamics evolution law of shafting multi-dimensional vibration with control parameter variation are described,the nonlinear dynamics characteristic of shafting multi-dimensional vibration with and without controller are described,and the vibration reduction effect of the controller is verified.4)The nonlinear dynamics model of the shafting-HTGS coupling system of hydropower units is established.Based on the HTGS equation,the three-dimensional bifurcation surface of PID control parameters and the PI parameter bifurcation curve of the governor are obtained by using the Hopf bifurcation theory,and its stable and unstable domains are revealed.Based on the nonlinear dynamic model of the shafting-HTGS coupling system,the influence of shafting vibration on the HTGS is explored,and the nonlinear dynamics evolution law of the coupling system with variable PID parameters are described.On this basis,a multi-objective control optimization strategy considering both the shafting vibration and the dynamic regulation quality of the HTGS is proposed.The PID control parameter optimization was realized by using the multi-objective evolutionary algorithm based on decomposition(MOEA/D).The nonlinear dynamics characteristics of shafting vibration and HTGS of the typical optimal control schemes are analyzed.After optimization,the dynamic regulation performance of the hydropower unit is significantly improved.5)The nonlinear dynamic model of the shafting-HTGS coupling system of gridconnected hydropower unit is established.The stability and bifurcation characteristics of HTGS under grid-connected are investigated by using Hopf bifurcation theory.The damping characteristics of the HTGS are analyzed.Meanwhile,the nonlinear dynamic evolution law of the coupled system with misalignment distance variation are described,and the influence of shafting vibration on the HTGS and PG are explored.On this basis,the coordinated control optimization strategy for PFR of grid-connected hydropower units considering unit frequency,grid frequency,surge tank water level,shafting vibration regulation performance and ULFO is proposed,and the non-dominant genetic optimization algorithm-II(NSGA-II)is used to achieve multi-objective coordinated control optimally,the nonlinear dynamic response characteristics of the coupling system of the typical optimization control schemes are revealed,and the satisfaction after optimization is increased by 72.2%. |
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