Stability Of A Hydroelectric Generating Unit And Its Regulation Characteristic In Multi-energy Complementary System

The stability and regulation of a hydroelectric generating unit(HGU)is an important guarantee to promote the transformation of traditional power system to a system that can absorb a large amount of intermittent renewable energy.Under the condition of intermittent energy into grid,HGU is faced with more complex operation environment and more frequent condition conversions,which leads to increasingly prominent stability problems and poses greater challenges to the regulation performance of HGU.In view of this,this paper aims to reveal the evolution law of HGU evstability from the perspective of internal and external disturbances.From the perspective of dynamic stability,the influence of internal parameter disturbances on the stability of HGU is analyzed in depth.Meanwhile,a comprehensive evaluation index is constructed to quantify the operation characteristics of the system under the influence of external intermittent energy.Based on the stability analysis,the regulation flexibility of HGU in multi-energy complementary system is quantified.The main results are as follows.1.To overcome the problem that the single stability analysis method cannot fully describe the local stability evolution mechanism under the disturbance of operation parameter of unit,the bifurcation point is used as the breakthrough point,which runs through the two stability research fields of nonlinear dynamics bifurcation and time domain oscillation.The stability response law of parameter disturbed is described from two dimensions of structural stability and motion stability.(1)To better describe the local stability evolution characteristics of HGU under parameter disturbance,the hydroelectric generating power system model under different scenarios are established.Further,considering the uncertainty of parameter,equilibrium bifurcation under single parameter disturbance and codimension-2 bifurcation under multi parameter disturbance are analyzed using continuation pursuit algorithm,dynamic bifurcation theory and Lyapunov theory.Meanwhile,bifurcation type,equilibrium curve stability,bifurcation location and neighborhood stability of bifurcation point are given.The results show that the uncertainty of parameter leads to various bifurcation types,and power system stabilizer(PSS)has the ability to delay the occurring of bifurcation point.(2)To better describe the oscillation of HGU under parameter disturbance,the small disturbance integrated by the bifurcation point induced by parameter disturbance is taken as the breakthrough point.The eigenvalue analysis and column vector normalization are used to quantify the oscillation frequency,damping and participation factor in the neighborhood of the bifurcation point under different scenarios.Furthermore,the main oscillation mode are obtained using the energy level theory.Finally,the influence of PSS on the damping and oscillation mode is given.The results show that there is always water hammer oscillation mode within the reasonable range of the parameters.PSS with fixed parameters cannot always improve the system damping,even worsen the system damping.2.Focusing on the problem of system stability under the impact of intermittent wind power,aiming at the defect that the single index cannot systematically evaluate the system operation state,a solution is proposed to recombine the evaluation indexes according to the weight,and then build a comprehensive evaluation index.(1)Facing the uncertainty of wind power,the wind power system is coupled to the hydropower system to build a wind-hydro hybrid power system(WHHPS).The comparative analysis is used to verify the effectiveness and reliability of WHHPS.The information entropy theory is utilized to quantify power uncertainty of different time scales.The power fluctuation is fitted with probability density using parameter estimation and nonparametric estimation methods.The optimal fitting function is selected based on the root mean square error,average absolute error and correlation coefficient.The results show that power uncertainty increases with time scale increasing.The applicability of parametric estimation and nonparametric estimation is different in different time scales.(2)To overcome the problem that the single index evaluation result is difficult to reflect the overall operation characteristics of system,the index of mean wave momentum,RichardsBaker flashiness index,continuous average climbing rate and time average volatility are recombined using the entropy weight theory.Then a comprehensive evaluation index model is constructed,and its reliability and effectiveness are verified using a practical engineering case.The operation characteristics of subsystem and complementary system in different time scales are obtained using the comprehensive evaluation index.Finally,the complementary degree of the hybrid system is quantified using the fluctuation complementary rate and load tracking index.The results show that the comprehensive evaluation index has the ability to reflect the operation characteristic of system.The fluctuation degree of complementary system is smaller than that of wind power system,and both of them increase with time scale increasing.3.Aiming at the problem that multi factor interaction makes it difficult to evaluate the regulation flexibility of HGU,the probabilistic evaluation index is used to quantify the evolution rules of regulation flexibility under the variation of reserve capacity,reserve access ratio and ramp rate with multi-time scales.Furthermore,the sensitivity factor ranking of the regulation flexibility of HGU is obtained using the Sobol global sensitivity analysis method,where the effects of the influencing factors themselves and the interactions between the influencing factors are considered.The results show that the reserve capacity,reserve access ratio and ramp rate has the ability to improve the regulation flexibility of HGU to a certain extent,and the reserve access ratio is a highly sensitive factor affecting the regulation flexibility of HGU.