<p> This thesis considers the problem of control of nonlinear process systems subject to
input constraints and faults in the control actuators and process equipments. Faults
are considered that preclude the possibility of continued operating at the nominal
equilibrium point and a framework (which we call the safe-parking framework) is
developed to enable efficient resumption of nominal operation upon fault-recovery.
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).
This safe-park point is chosen as a temporary operating point where process is to
be operated during fault rectification. This ensures that process can be safely operated
during fault rectification and the nominal operation can be resumed upon fault
recovery. When multiple candidate safe-park points are available, 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 quantified and utilized in choosing the
optimal safe-park point. </p> <p> Next, we extend the safe-parking framework to handle practical issues such as plant-model mismatch, disturbances and unavailability of all process state measurements.
\i\Te first consider the presence of constraints and uncertainty and develop
a robust Lyapunov-based model predictive controller. This controller is utilized to
characterize robust stability region which, subsequently, is utilized to select 'safepark'
points. Then we consider the problem of availability of limited measurements.
An output feedback Lyapunov-based model predictive controller, with high-gain observer
to estimate unmeasured states, is formulated and its stability region explicitly
characterized. An algorithm is then presented that accounts for the estimation errors
in the implementation of the safe-parking framework. </p> <p> We then further extend the framework to handle faults in large scale chemical
plants where multiple process units are connected via material, energy and information
streams. In plant-wide setting, the safe-park point for the faulty unit is chosen
such that the safe-parking has no or minimum effect on downstream units, and hence,
the nominal operation in the downstream units can be continued. Next we consider
the scenario where no viable safe-park point for the faulty unit exists such that its
effect can be completely absorbed in the subsequent unit. A methodology is developed
that allows simultaneous safe-parking of the consecutive units. The efficacy of
the proposed framework is illustrated using a chemical reactor example, a styrene
polymerization process and two CSTRs in series example. </p> <p> Finally, we demonstrate the efficacy of proposed Lyapunov based Model Predictive
Controller and Safe-Parking framework on a polymerization reactor model to control
the polymerization reactor and to handle faults that dont allow continuation of the
nominal operation in the reactor. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/19020 |
| Date | 03 1900 |
| Creators | Gandhi, Rahul |
| Contributors | Mhaskar, Prashant, Chemical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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