Research On Regulating System Model Of Hydropower Station And Stability Characteristics By Full Characteristic Curve Of Hydraulic Turbine

With the increase of installed capacity and proportion of hydropower units in power grid and the further expansion of renewable energy application scale,the dynamic characteristics of hydropower units in power grid have more stringent requirements.For conventional power plants,it is necessary to ensure safe and stable operation,and for pumped storage units,it is necessary to have good peak load regulation and valley filling capacity for power grid.According to the requirement of coordinated development of "source-network-load" in the 13 th Five-Year Plan,it is more difficult to accurately plan and rationally layout hydropower stations.The number of long diversion pipeline,high head and large discharge of hydropower station is increasing.During the operation of hydropower units,the coupling effect of water,machinery and electricity is more obvious,and the operation conditions are more complex.The stability of operation and the quality of regulation are attracting more and more attention from relevant departments and scholars.When the stability of hydropower units involved in power network is analyzed theoretically,the corresponding mathematical models are usually established.Because of many conditions,such as the coupling effect of water,machinery and electricity;the characteristics of time-varying,non-linear,non-minimum phase regulation system;the existence of redundant and changeable boundary conditions,the mathematical model of hydropower units have to be simplified accordingly.However,it may lead to the mismatch between the stability in actual operation and theoretical analysis.So a certain stability margin needs to be guaranteed.At present,most of the studies on ultra-low frequency oscillation and stability of hydropower system only focus on the stable critical condition.Then it is necessary to make a deeper study on how to ensure the stability margin and oscillation attenuation characteristics of the system in engineering practice.In this paper,based on the previous research results,the stability and stability of the regulation system of hydropower units are studied in depth,and a case study is provided for the application of the research content in combination with the engineering practice.The main contents are as follows:(1)Generally,due to the lack of data in the small flow area and the small speed area in the general hydro-turbine model comprehensive characteristic curve,the simulation of hydro-generating units in the small flow or small speed area seriously affects the calculation accuracy and model stability of the transition process.In view of the above difficulties,thispaper deduces the zero-flow and zero-speed operating point theoretically according to the geometric size parameters of the turbine itself.Through the extension of the data of the comprehensive characteristic curve of the turbine,the flow and moment characteristic curves of the turbine combined with the internal and external characteristics are obtained.This method further improves the simulation accuracy of the mathematical model of hydropower units.What’s more,it provides a basis for calculating the transfer coefficients of hydraulic turbines at various operating points in non-working areas in the transition process calculation.(2)Considering that a part of the torque will change with the speed of the generator when it is loaded,the speed of the generator is not output unilaterally,so the first-order generator model is improved.By analyzing the relationship between load disturbance and unit speed,based on different pipe water hammer equations and governor regulation modes of hydroelectric unit regulation system,six mathematical models of transfer function of regulation system are deduced.In addition,the differences of different models are compared,and the physical essence of different models is explored.The accuracy of the model is verified by comparing the results with those of Topsys,a professional software for transition process calculation.Furthermore,the stability regions of different models are compared and analyzed,and the effects of different water hammer models on the stability regions are discussed.(3)For ensuring the region of stability margin of the system and quantitatively analyzing the oscillation attenuation characteristics,The concept of region of stability margin is introduced to evaluate the stability of the regulation system of the hydropower station.Firstly,from the point of view of theoretical analysis,the relationship between the region of stability margin and the damping ratio,frequency and attenuation coefficient is deduced,and the theoretical calculation method of stability margin region is introduced.Then the time-domain numerical simulation model corresponding to the theoretical analysis model is built,and the applicability of the model to the analysis of system dynamic characteristics in time-domain is verified.Then the critical stability region and stability margin region of a hydropower station under real parameters are drawn,and the ultra-low frequency oscillation of the regulating system in the same margin region is simulated,and the corresponding stability degree of the system is analyzed.The attenuation characteristics of ultra-low frequency oscillation represented by the region of stability margin are obtained.Finally,the influence of different operating conditions on the stability of hydropower units is summarized,which provides a reference for engineering practice.