Biobjective Maintenance Strategy Optimization for Complex Multistate Systems Based on PH Distribution

Complex multistate systems (MSSs) are composed of components with multiple levels of performance and complex internal component structure, and they are widely used in engineering modeling. Failure of complex MSSs can cause significant economic losses and even safety issues. Therefore, optimizing the maintenance strategy to ensure reliable operation is a crucial issue. This article investigates the problem of maintenance strategy optimization for complex MSSs. First, the phase-type distribution is introduced to construct the infinitesimal generator matrix of components with multiple level maintenance considered. Second, the universal generation function method is employed to build the performance function of the system. After that, the i-NSGA-Ⅱ-dc algorithm is proposed to solve the maintenance strategy optimization problem with the biobjective of minimizing expense ratio and maximizing expected performance. Finally, the fuzzy-logic-based approach is used to assist decision-makers in selecting preferred solutions. The door system of the intercity multiple units is taken as an example to illustrate the applicability of the approach, and the results show that the door system is excessively maintained currently. The simulation results indicate that the optimized maintenance strategy can extend the maintenance interval and reduce the frequency of maintenance, and lower the maintenance cost rate in the meantime.