(439f) Fault-Detection and Isolation and Fault-Tolerant Control of Nonlinear Process Systems Using Asynchronous Measurements

McFall, C., University of California, Los Angeles
Davis, J. F., University of California - Los Angeles
Ohran, B., University of California, Los Angeles

Chemical process operation is relying extensively on automated control systems in order to deal with the stringent requirements of safety, environmental sustainability, and profitability. Automation, however, tends to increase the vulnerability of a chemical process to faults (e.g., failures in the actuators, sensors or in the controllers) potentially causing a host of safety, environmental and economic problems. Management of abnormal situations is a major challenge in the chemical and process industries since abnormal situations account annually for at least 10 billion USD in lost revenue in the US alone. An important consideration of many process measurements is that they are often asynchronous, subject to time-varying delays, and vulnerable to data losses. This can be due to the nature of the measurement it self (i.e., difficult concentration measurements) or due to the communication network (wired or wireless) that may introduce such dynamics.

This works addresses the problem of fault-detection and isolation and fault-tolerant control when several system measurements are not available synchronously. First, a fault-detection and isolation (FDI) scheme that employs model-based techniques is proposed that allows for the isolation of faults. This scheme employs model-based FDI filters similar to those found in [1] in addition to observers that estimate the fault free evolution of asynchronously measured states during times when they are unmeasured. Specifically, the proposed FDI scheme provides detection and isolation of faults that are relative degree one to the set of synchronously measured states, and grouping of faults that relative degree one to the set of asynchronously measured states. The detection occurs immediately after a fault takes place, and the isolation, limited by the arrival of asynchronous measurements, occurs as asynchronous measurements come in. Once the FDI methodology has provided the system supervisor with a fault diagnosis, the supervisor takes appropriate action to seamlessly reconfigure the system to an alternative control configuration that will enforce the desired operation. We will present applications of the proposed asynchronous FDI and FTC framework to a polyethylene reactor simulation.

1. Mhaskar, P., C. McFall, A. Gani, P. D. Christofides and J. F. Davis, ''Isolation and Handling of Actuator Faults in Nonlinear Systems,'' Automatica, 77: 83-62, 2008.