Study On Dynamic Characteristics Of Regulating System Based On Hydro-turbine Compound Model Tocombinedinternal Model And External Model

With the increase of the single hydro-unit capacity and new energy permeability in the power grid,the requirements of hydro-unit dynamic characteristics for power grid are higher and higher.At the same time,with the increase of the number of long distance water transfer system and long distance transmission system,the coupling effect of hydraulic,mechanical and electrical systems become more important.As a result,the stability and the quality of the hydropower units are getting more and more attention.Based on previous research results and the new problems in engineering,the hydraulic turbine composite mathematical model is proposed by combining the internal characteristics model and the external characteristics model.The convergence criterion of hydraulic turbine model is obtained.These results are using in a general simulation platform including hydraulic,mechanical and electrical systems that basis on PSCAD(PSCAD-HME).Using this platform,the problem that hydraulic turbine regulation system stability is reduced with the load disturbance amplitude increased is solved.The analysis regulating quality theory using in the system with surge is improved.The following results have been achieved.(1)The energy balance equation for hydraulic turbine is built by analyzing the energy loss form in each hydraulic turbine flow component.The hydraulic flow characteristic equation and torque characteristic equation are obtained by combining the hydraulic turbine energy balance equation and flow regulation equation.The hydraulic turbine internal characteristic model is improved.A parameter identification method that combining the least squares method and the genetic algorithm is designed for obtaining the relevant parameters of internal model by using the measured data of external characteristics of hydraulic turbine.And then,the hydraulic turbine compound mathematical model is obtained and the model precision has been increased by combining the internal model and external model.(2)In order to solve the poor convergence of hydraulic turbine model in engineering simulation,a hydraulic turbine model single point iterative solution process with unit speed as iteration variable is proposed.The iterative theorem is adopted to obtain the iterative convergence criterion.This criterion is applied to the calculation of fixed step length and variable step length,and the computational efficiency is improved.(3)The commonly used power grid simulation software PDCAD in engineering has relatively independent user defined modules,but the calculation of hydraulic system initial working condition requires all the hydraulic systems parameters used in one equation.In view of this problem,a virtual management calculation module is created for the accomplishment of the hydraulic system parameters colletion,the hydraulic system constant flow calculation and the calculation results distribution.And then,the simulation platform PSCAD-HME was constructed.(4)With the increase of load disturbance amplitude,the regulation stability of hydraulic turbine reduces.In order to find out the mechanism of this problem,a simulation is analyzed by PSCAD-HME and the cause of this problem is the governor speed saturation.Furthermore,the influence of the proportional items,.integral items and differential items on the speed saturation is analyzed.An anti-speed saturation of PID governor control strategy is proposed and the effect of load disturbance amplitude on the stability is eliminated.(5)In order to solve the problem of the error in regulating quality analysis when the inertia time constant of pressure pipe with the excessive surge,it is analyzed that the influence of the flow inertia time constant of the pressure pipeline on the turbine flow and turbine torque.The system model is simplified for considering the main function of the inertia time constant of the pressure pipeline.The analytic expressions of the main wave,the tail wave and the regulating quality indexes are obtained.It is verify that the analytic expressions of the regulating quality indexes have higher accuracy by used the PSCAD-HME platform.The influence law and value suggestions of the surge correlation parameters on the regulating quality are obtained.