Analysis And Design Of Linear Active Disturbance Rejection Control

Active disturbance rejection control(ADRC),as a new technique of disturbance estimation suppression control method,has shown good control performance in a large number of applications.Nevertheless,there are many theretical problems to be solved for ADRC.This dissertation studies the analysis and tuning of linear ADRC(LADRC)and its application in time-delayed industrial processes.Main contents of the dissertation include:1.A method to analyze LADRC via internal model control(IMC)is proposed considering the structural characteristics of LADRC.It is proved that LADRC structure can be changed to a two-degree-offreedom(2DOF)IMC structure,thus analysis and design of LADRC can be done in the IMC framework.For the processes without time delay,it is shown that the widely adopted bandwidth-tuning method for the conventional LADRC is equivalent to tuning the two time constants of the setpoint filter and the disturbance-rejection filter in IMC.For the processes with time delay,it is shown that the modified LADRC has a defect in its structure,that is,the setpoint tracking and the disturbance rejection performance are not completely decoupled,and the control bandwidth is limited by the time delay,which restricts the tracking performance.2.Two tuning methods are proposed for LADRC.First,a method to tune LADRC with known plant information is proposed.The generalized ADRC method uses the same bandwidth tuning idea as the conventional LADRC,but incorporates extra plant information.It is shown that the available plant model information can improve the control performance.To make use of the existing controller information in the control system,a method to tune LADRC with existing controller is proposed.It provides a convenient method to tune the parameters of LADRC for those control engineers who are already familiar with other control design methods,thus has good application potential.3.A two-degree-of-freedom control structure is proposed for unstable time-delayed systems.Set-point tracking and disturbance rejection are separated in this structure and ADRC is solely responsible for disturbance rejection.In this case ADRC plays its role as its name suggests without having to consider the set-point tracking performance,which will overcome the limitation of one-degree-of-freedom(1DOF)ADRC structure for delayed processes.The LADRC parameters are tuned with known information of the processes,thus the disturbance rejection performance can be improved.Simulation examples show that the proposed method can get better robustness and load rejection performance than the previous methods.4.A decentralized load frequency control(LFC)for multi-area power systems with communication delays is discussed in this paper.LADRC is proposed to improve the control peroformance of the system.The tuning of LADRC is based on the internal model control method,and order reduction and approximation are used to obtain a low-order LADRC.Simulation studies show that the proposed method is effective in dealing with delays while maintaining good transient response and robustness.