(285e) Actuator Placement for Fault Tolerant Control of Transport Reaction Processes

When considering the control problem for transport reaction processes, an important issue is the actuator placement so that the system exhibits desired properties, such as enhanced controllability. A complexity in this endeavor lies in the spatial dependence of the concepts of controllability and observability which prompted a number of researchers to address the important topic of actuator and sensor placement. The current approach to actuator placement is to select the actuator locations based on open-loop considerations to ensure that the necessary controllability and reachability or power factor requirements are satisfied [1]. Actuator and sensor failures are a different issue that has often plagued chemical industries, as they may lead to deteriorating product quality or potentially dangerous process operation, such as runaway conditions. Motivated by the importance of the aforementioned failures, the issue of fault tolerant and fault accommodating controller design has been an active research topic in the chemical engineering community. However, while there has been extensive research from the control community on fault detection and diagnosis of finite dimensional systems using model-based robust and adaptive control techniques, the issue of fault tolerant control for distributed processes has been investigated only recently [2,3].

To address the issue of fault tolerance specifically for distributed processes, we consider a radically different problem than previously [1]. The actuator optimization metric is not defined in terms of enhanced controllability, improved performance or enhanced robustness with respect to disturbances or unmodeled dynamics, but with respect to fault tolerability. Taking advantage of the spatial variability that transport-reaction processes naturally benefit from, we explore an entirely new concept of identifying actuator locations by identifying groups of actuators that, while being physically apart, have the same authority on the process states. This new system is only applicable to distributed parameter systems wherein two or more different locations within the spatial domain of definition can provide the same level of controllability and at the same time the same feedback gain can be applicable to all such locations. The identification of such actuator groups has the potential to greatly facilitate the design of fault accommodating control structures, such that the profound simplicity of the controller design will significantly reduce the costs associated with process supervision and be accompanied by obvious performance advantages.

[1] A. Armaou and M. A. Demetriou, “Optimal Actuator/Sensor Placement for Linear Parabolic PDEs Using Spatial H2 Norm,” Chem. Eng. Sci., 61, 7351-7367, 2006.

[2] M. A. Demetriou, “Utilization of LMI methods for fault tolerant control of a flexible cable with faulty actuators,” Proceedings of the 2001 40th IEEE Conference on Decision and Control, pp. 1885-1890, vol. 2, Orlando, Florida, December 4-7, 2001.

[3] A. Armaou and M. A. Demetriou, “Robust Detection and Accommodation of Incipient Component and Actuator Faults in Nonlinear Distributed Processes,” AIChE J., in press, 2008.