Compensation Control Methods For Stiction In The Control Valve

In the industrial process control system, pneumatic control valve is the most common terminal element, whose performance will be directly associated with the quality of control system. The pneumatic control valve always works with the controlled medium. So after a period of time, some nonlinear characteristics may appear, among them, stiction is the most common. The stiction in the valve will cause oscillation of control loops easily, and result in efficiency loss and even a standstill of the productive process. Therefore, after the detection of the stiction in the valve, it is necessary to introduce an appropriate compensation to overcome the stiction. Based on the related references, the thesis focuses on the compensation method for the stiction in the valve from theoretical and practical aspect. The main contents as follows:1、The selection basis of the Knocker compensator’s parameters is analyzed. It is found that the selection of pulse amplitude is relatively more difficult and usually relies on manual error experiment. Then an optimization algorithm of pulse amplitude self-tuning on-line is proposed based on golden section law. And a simulation study is introduced to demonstrate the proposed algorithm’s usefulness.2、The conventional implementation of the two-move compensation is analyzed, which may cost too much time, especially in the face of the process system with large delay characteristic. Then a new implementation of the two-move compensation without waiting for the process system to be stable is proposed, which can improve the efficiency of the application of the two-move compensation. And a simulation study is introduced to demonstrate the proposed implementation’s usefulness.3、Based on MPC compensation control for the single parameter model of stiction in the control valve, He model of double parameters is converted to the corresponding input constraints, and MIQP solver is applied to realize the MPC compensation control of stiction in the valve. And the compensation effect is compared to the conventional PID control by simulating, the effectiveness of the MPC compensation control is demonstrated.