Research On Stability And Transient Process Control Optimization Of Hydro-turbine Governing System

Hydro-turbine generating units(HTGU)are widely installed in power grid,which play an important role in energy supply,peak modulation and emergency standby.The safe operation of HTGU is of great importance to improve power quality and maintain the stability of power system.With the development of hydropower generation in China,the capacity of hydropower stations is continuously increasing.Recent years,several superhuge HTGU like the 850 MW HTGU in Wudongde hydropower station,the 1000 MW HTGU in Baihetan hydropower station,and the 375 MW pumped-storage units(PSU)in Xianju pumped-storage hydropower station have been put into operation successively,which indicates that the capacity of HTGU and PSU is constantly growing,and the structure of HTGS is also becoming more and more sophisticated.Under such circumstances,the hydraulic and mechanical inertia of HTGU and the complexity of the oil,gas and mechanical structures of the control unit are constantly increasing.Moreover,when the HTGU is connected to the power grid,the influence of hydraulic,mechanical and electromagnetic coupling on the hydro-turbine governing system(HTGS)is prominent,which leads to highly nonlinear characteristics of the operation of the unit.Hydraulic and mechanical inertias of HTGS also lead to high difficulty in the water diversion system design,therefore,“ one tube-multiple units” and asymmetric layout form is becoming more and more common.The hydraulic interference between units makes the operation characteristics of the governing system of HTGS even more complicated,which have brought a series of engineering problems to be solved.In order to achieve the stable operation and efficient control of large-capacity HTGS,it is urgent to study the stability and transition process control optimization of large-capacity HTGS.With the purpose of revealing the stability and transient characteristics of largecapacity HTGS under grid-connected operation and the condition of the complex water diversion system layout,along with enhancing the HTGS control performance under transition process,three aspects are studied in this paper: i)the stability and transient characteristics of grid-connected HTGS;ii)the stability and transient characteristics of the HTGS with asymmetric water diversion system;iii)control optimization of guide vane closing law under load rejection and successive load rejection.The contributions of this paper are as follows:1)The mathematical description methods of the subsystems of HTGS are studied in depth.The nonlinear mathematical model of “one pipe-one turbine” water diversion system and the nonlinear mathematical model of “one pipe-double turbine” water diversion system considering the nonlinear head loss in pipes are proposed.On that basis,the mathematical models of the subsystems are integrated to construct the linear,nonlinear and refined numerical simulation models,thus providing model basis for further research.2)The stability and dynamic characteristics of grid-connected HTGS are studied,the multi-time scale oscillation phenomena are revealed.In order to investigate the stability and transient characteristics of grid-connected HTGS under the coupling effect of hydromechanical-electromagnetics,the Hopf bifurcation theory is introduced to analyze the stability and transient characteristics of HTGS under load disturbance.The multi-scale oscillation phenomenon and its generation mechanism is revealed.Moreover,the effect of system parameters on the stability and the transient characteristics of the coupling system is also studied.In addition,the sensitivity of the coupling system to internal and ambient disturbances is investigated.3)The multiple stability characteristics asymmetric-HTGS(AHTGS)and their generation mechanisms are revealed,the effect of topological structure on system stability is studied.Based on the nonlinear mathematical model of the HTGS with “one pipe-double units” water diversion system,the bifurcation analysis of the AHTGS is carried out to analyze the stability and transient response of the system.The multiple stability characteristics of the AHTGS are revealed,and the influence of the system parameters,such as flow inertia time constant,head loss and turbine inertia time constant,on the multiple stability domains of the system are investigated.In addition,the influence of the topological structure of diversion system and the ratio of the control parameters of the two HTGUs on the system stability is studied.Based on the research results,some tuning suggestions for AHTGS parameters,topological structure and control parameters are given.4)A novel GVCL optimization strategy is proposed for PSU.In order to avoid the hydraulic and mechanical instability under load rejection,the characteristics of guide vane closing laws(GVCLs)and their influence on the hydraulic and mechanical characteristics of the PSU are investigated in the first place.A novel improved three-phase GVCL is proposed.Then,based on the refined numerical simulation model,multiple nonlinear constraints are introduced,the speed oscillation numbers are innovatively integrated into the optimization objectives.Thereafter,the multi-objective optimization model are established considering speed rise,speed oscillation numbers,water pressure at volute and draft tube.Moreover,a novel artificial sheep algorithm is proposed to optimize the GVCLs.The optimized GVCL improves the increase of rotational speed and volute pressure by 34.4%and 1.09%,respectively.5)The effect of working condition parameters on the transient process of successive load rejections are studied,a novel GVCL optimization strategy for double PSUs are proposed.Firstly,the influences of the interval time,the water head and the GVCL on the key indexes of the transition process of successive load rejection are analyzed.Secondly,the objectives and constraints are extended to two PSUs,and a high working condition adaptability GVCL optimization strategy for successive load rejection is proposed.The optimized GVCL can reduce the maximum rotational speed of the two units by 0.54% and5.89%,reduce the speed oscillation by 1 time.In addition,the volute pressure and draft tube pressure are more balanced than the original GVCL,which has validated the effectiveness and application potential of the proposed strategy.