Research And Application Of Predictive PI Control Algorithm

Time delay characteristics widely exist in industrial processes.Due to the existence of time delay,the changes of controlled variables cannot be fed back to the controller in time,which is easy to cause problems such as increase of overshoot,prolonging transient time and even oscillation divergence.Predictive PI algorithm is an advanced control algorithm to solve the problem of large time delay.The algorithm has the advantages of simple structure,intuitive design,few setting parameters and easy adjustment.However,it also has some defects,such as weak anti-interference ability when controlling large inertia process,and unsatisfactory control effect for integrator and time delay process.Based on the traditional predictive PI algorithm,this paper conducts research on the above-mentioned problems,proposes corresponding modified predictive PI algorithm.Firstly,to solve the problem that the traditional predictive PI controller has poor control effect on integrator and time delay process and cannot resist external disturbances,an modified predictive PI controller that introduces a proportional disturbance structure is proposed.The controller is composed of a traditional predictive PI controller and a proportional controller.The traditional predictive PI controller regulates the set value tracking ability of the controlled object,and the external disturbance is controlled by the proportional controller separately.The proposed controller is simulated and compared with two existing modified controllers for integrator and time delay process.The simulation results show the effectiveness of the proposed method.Secondly,the traditional predictive PI controller is improved in terms of response speed and anti-interference ability.Based on the principle of predictive PI and the idea of Smith prediction,the output estimation of predictive time domain is introduced into the system feedback.When the system input changes,the controller can observe worse state changes than the reality,and then generate a larger control amount to improve the response speed.Aiming at the weak anti-interference ability of traditional predictive PI control with large inertia lag object,a proportional anti-interference structure is introduced into the control system to resist external disturbance.The effectiveness of the modified controller is verified by simulation comparison with the traditional predictive PI.Finally,the traditional predictive PI algorithm and the modified predictive PI algorithm proposed in this paper are applied to the actual temperature control of SXF-4-10 electric heating furnace.Because this type of electric heating furnace has the characteristics of inertia time as the dominant,the anti-interference performance of the traditional predictive PI is not good,and the disturbance recovery speed is very slow.The modified predictive PI controller has good control effect,which proves the practicability of the improved method proposed in this paper.