Fault Tolerant Control Of Networked Control Systems Based On MPC

With the improvement of computer and network technologies, Networked Control Systems (NCS) begin to draw the attention of academic researchers. Due to the complicated structure of the NCS, its performance can be deteriorated by the faults, even they are small ones. Therefore, with increasing requirements for stability and security, Fault Tolerant Control (FTC) becomes a key issue in the design of NCS. Model Predictive Control (MPC) provides a suitable'implementation architecture'for FTC, on the other hand, it is capable of maintaining acceptable performance in the event of faults because of the'receding horizon'property.When the actuator faults occur in an NCS with constant time delays which are smaller than one sample period, an FTC strategy based on MPC is proposed, according to the following three cases: (1) In order to match the predictive model with the plant, a new predictive model with faults is developed, by introducing the fault information. The fault information is provided by the the Fault Detection and Diagnosis (FDD) unit and then the information is incorporated into the previously developed predictive model with time delays. (2) The plant outputs are used to regulate the predicted outputs to reduce the effects of external disturbances. (3) For the purpose of maintaining the performance of system in the event of faults, different cost functions, one with a reference trajectory and another with so-called"zone regions", are chosen to compute the optimal control sequences, taking into account of the predictive outputs.In order to verify the performance of the FTC strategy proposed, the simulations of NCS are compared in Matlab/Simulink with different FTC strategies, such as (a) the normal NCS, (b) NCS with actuator faults without FTC, (c) NCS making use of a predictive model with fault information, (d) NCS with regulated predictive outputs, and (e) NCS with chosen cost functions. The simulation results demonstrate that the FTC strategy proposed in the papers can recover the performance of NCS from the actuator faults quickly.The simulation results in this thesis show that the FTC strategies proposed not only stabilize the system in the event of faults, but also maintain the acceptable performance of it.