Redundancy Allocation Problem for a Continuous-State Series-Parallel System With Degrading Components: Electric Vehicle Application

Abstract

System reliability is a critical factor in designing complex engineering systems. Redundancy allocation problem (RAP) has attracted more interest owing to its wide scope of industrial applications for system reliability optimization. RAPs for binary-state and multistate systems have been extensively studied. However, the redundancy allocation for continuous-state systems composed of degrading components has not yet been fully explored. This study attempts to build the RAP for the continuous-state parallel-series system consisting of identical, independent, and nonrepairable components under active and cold-standby redundancy strategies. The degradation of individual components in a system is continuous and modeled by the gamma process. The degradation at the system level is derived according to a deterministic structure function that relates the system degradation to the degradation of its components. Genetic algorithm and exhaustive search method are used to find the cost-optimal redundancy design while satisfying a system reliability requirement. Series-parallel lithium-ion battery pack systems for electric vehicles (EVs) are used as an illustrative example to validate the proposed RAP and optimization model.