Proactive fault‐tolerant model predictive control

Abstract

in Wiley Online Library (wileyonlinelibrary.com) Fault-tolerant control methods have been extensively researched over the last 10 years in the context of chemical process control applications, and provide a natural framework for integrating process monitoring and control aspects in a way that not only fault detection and isolation but also control system reconfiguration is achieved in the event of a process or actuator fault. But almost all the efforts are focused on the reactive fault-tolerant control. As another way for fault-tolerant control, proactive fault-tolerant control has been a popular topic in the communication systems and aerospace control systems communities for the last 10 years. At this point, no work has been done on proactive fault-tolerant control within the context of chemical process control. Motivated by this, a proactive fault-tolerant Lyapunov-based model predictive controller (LMPC) that can effectively deal with an incipient control actuator fault is proposed. This approach to proactive fault-tolerant control combines the unique stability and robustness properties of LMPC as well as explicitly accounting for incipient control actuator faults in the formulation of the MPC. Our theoretical results are applied to a chemical process example, and different scenaria were simulated to demonstrate that the proposed proactive fault-tolerant model predictive control method can achieve practical stability and efficiently deal with a control actuator fault.

An exact penalty-function approach to proactive fault-tolerant economic MPC

“…The soft-constraint formulation (6) is equivalent with optimizing the nonsmooth penalty function min ∑ N−1 k=0 l(x k , u k ) + µ ∑ ||max(0, c I (x))|| 1 subject to the remaining constraints in (6), where c I (x) is a vector-function representation of the constraints G j x k − f j ≤ 0 in (5) for all k ∈ I [0,N−1] . A penalty function F(x, µ) is termed exact if, for a parameter choice µ >μ, whereμ is a nonnegative threshold value, the local minimizer of an unconstrained problem min x F(x, µ) is either a KKT point of the original constrained problem, or an infeasible stationary point [9].…”

“…Reconfigurable (active) FTC methods can broadly be classified as reactive or proactive [6]. Reactive approaches basically rely on controller reconfiguration after a fault occurs, while, in comparison, a proactive scheme seeks to utilize information about an incipient fault in the system, indicated by slowly developing performance degradation, to proactively manipulate the inputs and thereby minimize negative impact of a possible future fault.…”

“…To prevent possible loss of controllability and system destabilization, a proactive FTMPC scheme seeks to steer the system inside a safety region upon receiving warning about an incipient actuator fault. In [6], this is obtained by using Lyapunov-based tracking MPC, assuming that predesigned stabilizing Lyapunov-based controllers exist. Their approach, however, does not provide guarantees on the convergence rate to the safety region, as this depends on tuning of the predesigned controllers.…”

Dynamic Safety Constraints by Scenario Based Economic Model Predictive Control

“…Kovâcshâzy et al (2001) investigates responses due to reconfiguration of the controller. For faults which can be predicted, Lao et al (2013) have suggested to use MPC to make a smooth accommodation of the fault. Blanke et al (2006) suggest to use back calculation and a progressive accommodation scheme to achieve new LQR-gains during reconfiguration.…”

On integration of feedback control and safety systems: Analyzing two chemical process applications

“…For example, thresholds on a recently developed state-based Safeness Index [5] may be incorporated as triggers for safety system activation that allow the safety system to be aware of system-level safety considerations; the same metric, with different thresholds, can be utilized in MPC design to provide some coordination between the designs. Control designs [6,8,18,19,27,29,31,41] have been developed that can handle safety in the sense of faults [11,16,37]; however, these methods do not address safety system actions in control. Therefore, the development of systematic methods for coordinating control and safety systems poses fundamental challenges; for example, control/safety system logic should be developed to directly account for the impact of discrete safety system Integration of safety and control systems:…”