Stability And Regulation Quality Of Hydro-turbine Governing System Considering Power Grid

In modern power system,hydropower plant due to its flexible operation characteristics undertakes the primary task of peak and frequency modulation.In the hydropower system,the turbine regulating system is the core component of load frequency control(LFC).The hydro-turbine generating unit can operate in an isolated grid mode or in a grid-connected mode.The former is an accidental and temporary operation mode while the latter is the main operation mode.For the hydropower plant with surge tank,there have a lot of researches on its stability and regulation quality of the regulation system of the hydropower station with surge tank.However,for the hydraulic-turbine regulating system with surge tank operated in isolated grid,there are few studies on the saturation characteristics of stable region and its mechanism.For the hydraulic-turbine regulating system operated in power-grid,in some research,the grid model is too simplified to take the action of grid regulation parameters into account and there are few studies on the effect of power grid on the stability and regulation quality of hydraulic-turbine governing system and its mechanism;meanwhile,most of the research methods for the influence of power grid are numerical simulation with less theoretical analysis.To make up all of the shortage listed above,this paper carries on the following three aspects:1 The saturation characteristics of stable region of hydraulic-turbine governing system with surge tank operated in the isolated gridThis part established a complete mathematical model of hydraulic-turbine governing system,derived the transfer function,by which obtained the higher order linear constant coefficient homogeneous differential equation describing the dynamic characteristics of the system.According to the characteristic equation of differential equation,combined with Hurwitz criterion,this paper obtained the analytic expression of stable region of the system operated in an isolated grid,analyzed the saturation characteristics of the stability region of a hydropower station with surge tank operated in the isolated grid and revealed its mechanism.This paper also put forward a concept of the saturated section of the surge tank,gave an effective method to calculate the saturation area of the surge tank and analyzed the influencing factors of the saturated section of the surge tank.Based on the prediction of the saturated section of the surge tank,this paper obtained an approximate analytical expression of stability region of the system operated in the isolated grid and.got some relevant conclusions.2 The reduced order processing of hydraulic turbine governing system connectedwith power gridThis part established a complete mathematical model considered the action of power grid,based on which deduced the transfer function of hydraulic turbine governing system connected with power grid.Thus the transfer function's order is too high(above fifth order)to be solved analytically.To solve this problem,this paper proposed two reduction methods,retaining main wave and tail wave respectively,to reduce the transfer function's order to be solvable;then obtained the Laplace transform of the unit speed signal from the reduced order transfer function;and then ascertained the time domain response equation of unit speed.Furthermore,this paper classified the power grid according to the different characteristics of speed fluctuation of system connected with different power grid,and put forward the classification criterion of grid type.3 Study on stability and regulation quality of hydro-turbine governing system connected with power grid based on reduced order modelOn the basis of the reduced order model,this part analytically solved stable region and analyzed the influence of grid parameters on stable region.Moreover,this paper derived the formula for the critical stable area of the surge tank considered characteristics of power grid according to thr reduced order transfer function,by which the effect and mechanism of power grid on regulating quality were expounded in this paper.Furthermore,this paper obtained the expression of the characteristic parameters to measure system's regulation quality based on speed fluctuation equation,in which way described the internal mechanism of the interaction between the three subsystems of water,mechanical,electricity in marhematical language and analyzed and compared the effects of hydraulic parameters,mechanical parameters and grid parameters on the speed fluctuation characteristic parameters.In addition,this paper discussed the influence of governor regulation mode,load disturbance type and grid frequency disturbance type on frequency response of the system and got some valuable conclusions.