In this thesis, a dual redundant control system which performs the task of tracking the command signal even in the case of controller failure is studied. At first, the failure detection scheme based on fuzzy logic is introduced. This kind of detection represents the controller failure as degree of failure rather than binary states of safe or fail. This method requires neither precise mathematical process model nor the complete analysis of controller failure characteristics.
Using this detection method, two kinds of redundant management schemes are investigated; one is an active type and the other is a repeatedly switching method with variable time weight. Monitoring the trends of the output. the active type control scheme changes the controller to a stand-by controller if the controller failure is detected. For the case of time weighted control scheme, the time weight of the suspected one as failed is reduced to maintain its required control performance but finally the time weight goes to zero if the controller really fails. The varying time weight method rather than complete switch over to backup controller can have a robust fault-tolerance capability in ill-defined environments or transient failures.
