Reset Control Strategy Of A Kind Of Liquid Level Control Systems

Liquid level systems are difficult to control with many existing control methods due to time-delay, nonlinearity and large inertia. The requirement of fast response often conflicts with the overshoot specifications. In this thesis, the technique of the reset control is applied to solve the contradiction between settling time and overshoot. A conclusion that the reset control can improve the transient performance of a kind of liquid level systems is drawn on the experimental basis.First, the reset PID is introduced into the second-order liquid level system and the results show that it can obtain a much better control performance than the classic PID control. In addition, reset control and fuzzy control are analyzed and it has shown that the reset PID improves the transient response performance, such as speeding up the response and reducing the overshoot. Particularly, the advanced reset PID further reduces or even removes the overshoot.Second, for the sake of eliminating the rising edge overshoot, the state of the integrator is temporarily reset to a value which is slightly smaller than the steady-state during the transition. By this way, the integrator’s overmuch energy can be released upon the time of rising edge. It has shown that the proposed technique removes the overshoot and maintains the stability of this system.Finally, the steady-state of the integrator has something to do with the Mathematical model. But the identified model does not accurately describe the characteristics of the system. In order to obtain the precise steady-state of the integrator, the method of combining experiments and theoretical calculation is used to get the linear relationship of set-point and the steady-state of the integrator.The main contribution of this thesis is that the reset control is introduced into the liquid level system for the first time. In addition, the improved reset control based on the advanced reset is designed and achieves good performance.