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Thesis for the Degree of Master of Science

 

Year 2006
Markus Kettunen

Fault tolerant MPC with an embedded FDI system


Fault Tolerant Control (FTC) is a branch of control engineering, which is aimed at improving the fault tolerance and the availability of industrial plants. The fault tolerance has traditionally been implemented by using fault accommodation, controller reconfiguration or by solving the supervisory problem of changing the objectives of the controller. To make such system functional, an effective fault detection and isolation (FDI) system is required along with an advanced and flexible controller to carry out the necessary control actions. Model predictive controllers (MPC) have proven to be efficient especially in chemical process industries.

The aim of the master’s thesis is to study and develop fault tolerant MPC-based control strategies and test the strategies in a simulated process environment.

In the literature part a wide variety of FDI methods and different MPC formulations are presented, the structure of a modern MPC is reported, the methods for achieving fault tolerance are discussed and the recent fault tolerant and fault tolerant MPC solutions are presented and discussed.

The aim of the experimental part is to develop a fault tolerant MPC with an embedded FDI system for controlling a simulated heavy oil fractionator process, the Shell Control Problem. Principal Component Analysis (PCA), Partial Least Squares (PLS) and Subspace Model Identification (SMI) methods are used to achieve fault tolerance. The validation of the selected control strategy is carried out by introducing step- and ramp-shaped process disturbances into the measurements and measuring the performance of the FTC system. The results of the experiments are compared with results acquired with standard MPC.

The FTC system was functioning efficiently in the simulated process environment. Without the fault tolerance, the MPC was unaware of most faults, which often led to process instability. The results are encouraging and suggested that a fault tolerant MPC with an embedded FDI system would be a suitable option for controlling most modern industrial processes.


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