Abstract
This study presents a new approach for active fault-tolerant controller (FTC) design for constrained nonlinear multi-variable systems. The proposed approach utilize the nonlinear model predictive controller (NMPC) and fault estimation method which is on basis of extended kalman filters (EKFs). The deficiency of actuators and sensors and also the plant states measurement errors are estimated by the suggested approach. A supervisor unit using the fault information and fault modeling per sampling time, corrects the predictor model of the controller and compensates actuator and sensor faults in control system. Furthermore, by the presented feedback compensation, the robustness of the designed method against plant faults and uncertainties is ensured. The important advantages of the proposed method are: (1) The suggested FTC scheme based on NMPC leads to calculate more accurate control action than MPC in nonlinear processes, (2) it is comprehensive in fault accommodation point of view because it is able to compensate all types of faults in control systems simultaneously, (3) it has low computational cost because of using NMPC by analytical solution, (4) it can handle control and states constraints to prevent of actuator saturations and unsafe situations, (5) the simplicity and effectiveness of the designed FTC scheme for real applications is more significant. Simulation results on continuous stirred tank reactor process verifies the superiority and capability of the designed approach.
Highlights
In recent decades, many efforts has been made to design fault-tolerant controller (FTC) systems to guarantee the desirable performance for the process in the presence of components malfunction and dynamic perturbations
When the fault occurs in plant, it can be modeled as model mismatch; by using feedback compensation (FC) in nonlinear model predictive controller (NMPC) formulation, the control system can accommodates the fault in plant
The fault description in control system components is introduced in subsection 3.1, and the proposed fault estimator and supervisory schemes are presented in subsection 3.2 and 3.3 respectively, and the architecture of proposed FTC scheme is shown in 3.4
Summary
Many efforts has been made to design FTC systems to guarantee the desirable performance for the process in the presence of components malfunction and dynamic perturbations. The MPC scheme has been known as a mature practical control technique for constrained multi-variable control system design problem In this control scheme, the optimization techniques and plant model are used to generate the suitable control signals based on the predicted information of plant state changes. The main core of this paper is based on [20], that presents an active FTC for compensation of all types of fault in linear systems; in this study, a similar architecture is used for nonlinear systems. An AFTC scheme based on combination the nonlinear MPC (NMPC) with fault estimation is presented to accommodate actuator and sensor faults of affine nonlinear systems with some constraints on control and states.
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