Study On Direct Drive Electro-hydraulic Actuator Of Control Valve

As one of the most common control unit in the industrial process control, control valve is widely used in chemical engineering, metallurgy, nuclear power, thermal power and some other industrial sectors. With technological development and social progress, systematization and intellectualization of the industrial control are continuously improved. Energy saving and pollutant reduction are gradually concerned. Therefore, there is higher and higher requirement on technical properties of control valve. As a key component of control valve, the actuator plays a decisive impact on the property of control valve. However, because of its slow response speed, high energy consumption and weak resistance to load disturbance, the classical actuator hinders the improvement of control valve's performance. So it is necessary to develop a new kind of actuator to improve the dynamic and static performance of control valve. Operation principles and characteristics of actuator are completely analyzed in this thesis. Research on developing new control valve actuator is carried out aiming at stronger resistance to load disturbance, bigger output thrust and higher response speed.Firstly, through study on the operation principle, merits and drawbacks of control valve electro-hydraulic actuator, the DDVC electro-hydraulic servo system is applied to control valve electro-hydraulic actuator and a new electro-hydraulic actuator—DDVC electro-hydraulic actuator—is obtained. The operation principle of DDVC electro-hydraulic actuator is expounded and its advantage over the classical is analyzed. Simultaneously, the actuator is systematically designed and components are selected. Then, the integrated design is preliminarily realized.Secondly, based on the operation principle of gear pump, theoretical study on the reversible gear pump is carried out. The bidirectional work is achieved by integrating two check valves inside the pump. The automatic compensation of axial and radial clearance is achieved by respectively imported the high pressure oil from the contracting cavity and the low pressure oil from the expanding cavity into the corresponding compensating cavities. Thus, the leakage is reduced, the volumetric efficiency is increased, and the working pressure is improved.Thirdly, according to the operation principle, the mechanism model of the DDVC electro-hydraulic actuator is established. Through analyzing the voltage-speed characteristic of servo motor speed control system and the flow characteristics and force equilibrium equation of the pump-cylinder system, the dynamic mathematical model of the actuator is established. Then, by employing the MATLAB software, the stability is researched. The result indicates that the stability margin is satisfactory.Finally, the control strategies of the DDVC electro-hydraulic actuator are simulated by means of MATLAB/Simulink. And the system performance indexes respectively utilizing PID control and PID-corrected compound control combining optimal state feedback control with observer-estimated load disturbance feed-forward control are comparatively analyzed. The simulation results indicate that PID control algorithm could limit the overshoot and the steady-state error to small values, while the rapidity, the resistance to load disturbance and the static characteristic are not satisfying. However, after using PID-corrected compound control, the response speed and the resistance to load disturbance are improved obviously, and the dynamic and static characteristics are both increased. Compared with similar product from abroad, overall properties of the proposed actuator are up to their level, and some properties are even better. The DDVC electro-hydraulic actuator could meet the operating requirement of high-performance control valves.