A systematic approach to the design and reliability analysis of a fault-tolerant controller—II. Reliability analysis and assurance

Abstract

Abstract A reliability assurance process is devised as part of a systematic approach to the design and reliability analysis of fault tolerance controllers (FTC). Performing complexity analysis and reliability analysis on controller components logic is shown to provide means for design refinement to mitigate any potential failure whether by appropriate design of detecting flags, by introduction of redundancies to specific modules, or by adding safeguard measures to assure continuous and valid control actions. The reliability approach is applied to an FTC comprised of an adaptive direct digital controller (ADDC) and a redundant controller designed on the basis of fuzzy logic (FEC). The design logic of the FEC and the interface between both controllers is found to be simple to debug and maintain compared to the ADDC. Performing failure mode and effect analysis provides additional information for improving on the design of the controller and for verification of the adequacy of the acceptance tests employed in the interface system. The analysis led to adding a self-diagnosis algorithm to the ADDC and employing a self-organized routine for generation of the control rules in the FEC logic. To guarantee continuous and proper operation, a rule-based tie-breaker is introduced to arbitrate between the two controllers. Plans for verification and validation of operability and reliability of the FTC are discussed.