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Safe Parking of Nonlinear Process Systems

Traditionally, most of the research in fault-tolerant control has been concerned with preserving nominal process operation in the presence of faults. This has been addressed within the so-called reliable control approaches (which essentially treats the faults as disturbances and designs fault-tolerant controllers) and reconfiguration-based control approaches that assume the existence of a backup control configuration. Yet, there are numerous examples in the chemical process industries where the process economics do not permit deployment of redundant control configurations. In such scenarios, the only recourse is the swift recovery of the failed component. During the fault-recovery period, however, the absence of an established framework to handle such situations, and the use of ad-hoc approaches could lead to the onset of hazardous situations or the inability to resume nominal operation upon fault-recovery. Motivated by these considerations we have developed, utilizing the nonlinear predictive controllers described in the previous section, a safe-parking framework to handle process operation during failure conditions (Gandhi and Mhaskar, 2008).

To this end, first Lyapunov-based model predictive controllers, that allow for an explicit characterization of the stability region subject to constraints on the manipulated input, are designed. The stability region characterization is utilized in selecting `safe-park' points from the safe-park candidates (equilibrium points subject to failed actuators). Specifically, a candidate parking point is termed a safe-park point if 1) the process state at the time of failure resides in the stability region of the safe-park candidate (subject to depleted control action), and 2) the safe-park candidate resides within the stability region of the nominal control configuration. Performance considerations, such as ease of transition from and to the safe-park point and cost of running the process at the safe-park point, are then quantified and utilized in choosing the optimal safe-park point. Subsequently, we have addressed the implementation of the safe-park framework handling uncertainty and limited availability of measurements (Mahmood, Gandhi, and Mhaskar, 2008), subject to recycles and other kinds of networks, as well as considered the problem of fault-diagnosis (estimating the size of the fault) and fault isolation. More recently, we have focussed on sensor fault detection and isolation as well.

Dr. Prashant Mhaskar
Professor and Canada Research Chair (Tier II)
Brian MacDonald
MaSC Candidate
Hadi Shahnazari
Ph.D. Candidate
Maaz Mahmood
Part-time Ph.D. student
Simultaneous actuator and sensor fault isolation of nonlinear systems subject to uncertainty
2016 American Control Conference (ACC) , 6857-6862 (2016)  -  [ Publisher Version ]
Fault detection and isolation analysis and design for solution copolymerization of MMA and VAc process
AIChE J, 62 1054-1064 (2016)  -  [ Publisher Version | Open Access Version (free) ]
Detecting and Isolating Sensor and Actuator Faults in Solution Copolymerization of MMA and VAc Process
2015 American Control Conference, 1617-1622 (2015)  -  [ Publisher Version ]
Safe-Parking of a Hydrogen Production Unit
Du, M.Mhaskar, P., Zhu, Yu, Flores-Cerrillo, Jesus
Industrial and Engineering Chemistry Research (2014)  -  [ Publisher Version ]
Active fault isolation of nonlinear process systems
AIChE J, 59 (7) 2435-2453 (2013)  -  [ Publisher Version ]
An Integrated Fault Diagnosis and Safe-Parking Framework for Fault-Tolerant Control of Nonlinear Systems
Int. J. Rob. & Non. Contr., 22 105-122 (2012)  -  [ Publisher Version ]
Isolation and handling of sensor faults in nonlinear systems
Proc American Control Conf, 6667-6672 (2012)  -  [ Publisher Version ]
Active Fault Isolation of Nonlinear Systems
Proc American Control Conf, 6667-6672 (2012)  -  [ Publisher Version ]
An integrated fault detection and isolation and safe-parking framework for networked process systems
Du, M., Gandhi, R., Mhaskar, P.
Industrial and Engineering Chemistry Research, 50 5667-5679 (2011)  -  [ Publisher Version ]
A safe-parking and safe-switching framework for fault-tolerant control of switched nonlinear systems
International Journal of Control, 84 9-23 (2011)  -  [ Publisher Version ]