| Electro-hydraulic servo control system is widely used in power,aviation,aerospace and military industries for its advantages of high control accuracy,fast response,and high output power and so on.Turbine regulation system is one of its main applications.In steam turbine control system,control signal processing finally needs to be achieved by adjusting valve opening.Electro-hydraulic servo system,as the final actuator of valve opening adjustment in turbine regulating system,is one of the core components of entire control system.Electro-hydraulic servo system is a nonlinear system with multiple time-varying parameters and external load disturbances,its structure and working environment are complex.Therefore,it is important to analyze its performance,design a suitable controller and improve its control performance,which is of great significance to improve the tuning quality of steam turbines.This research is based on an actual project of thermoelectric power conditioning system in a paper mill in Henan Province,under the support of Shaanxi Provincial Science and Technology Research and Development Project“Study of Small-scale Steam Turbine DCS and Digital Electro-hydraulic Control System”,The theoretical analysis and research on establishment of non-linear mathematical model of turbine electro-hydraulic servo system and design and application of servo controller are carried out.mainly including the following aspects:(1)Analysis of working principle and controlling difficulties of electro-hydraulic servo systemThe composition and working principle of the electro-hydraulic servo system are analyzed,and control difficulties in the system are found out:Electro-hydraulic servo valve and the oil motive have problems such as strong non-linearity,high-order unmodeled dynamics,time-varying parameters,and external load disturbances,which results in a decrease in the followingperformance and anti-interference performance of the system.(2)Establishment of nonlinear mathematical model of electro-hydraulic servo systemBased on the principle of force balance and flow continuity,a nonlinear mathematical model of electro-hydraulic servo system is established.Stability,controllability and time-varying parameters of the system are analyzed based on the small deviation linearization of the system.The influence of time-varying parameters are further verified in the MATLAB simulation platform.The results prove that time-varying parameters of the system such as the oil supply pressure and volumetric elastic modulus of oil have significant influence on performance of electro-hydraulic servo system.(3)Design of electro-hydraulic servo system controllerAiming at the problems of nonlinearity,time-varying parameters and external load disturbance in electro-hydraulic servo system,sliding mode variable structure controlling with strong robustness is selected as the servo controller.For problems of chattering and slow operation in sliding mode control based on exponential rate,PID control law is combined with the exponential reaching law to improve it.In order to further verify performance of improved control algorithm,a fuzzy PID controller and a traditional PID controller are designed for comparative experiments.(4)Application of electro-hydraulic servo system in DEH regulation system of single extraction steam turbineFirstly,according to the principles of energy conservation and gas continuity,combining with the practical situation,mathematical model of each part of the single extraction steam turbine are deduced.Then the designed servo controller based on improved sliding mode control is applied to DEH regulation system of6 MW single extraction steam turbine,and its control performance is studied through a large number of simulations.(5)Realization of DEH regulation system for single extraction steam turbineS7-300 PLC is used as the hardware development platform,and industrial control configuration software Wincc and Step7 are used to design the system’s human-machine interface and control program.The communication between thefield management layer and the main station is realized through the industrial Ethernet,and then the control system of the turbine unit is realized.The system has been tested in the control of 2# unit in a thermal power system of a paper mill in Henan province.During this period,the system runs smoothly,and there is no system failure due to overspeed or other reasons.The results show that the servo controller based on improved sliding mode control has good dynamic characteristics and high control accuracy,which is beneficial to the improvement of the safety and stability of the steam turbine unit. |
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