# Dynamic Preventive Maintenance Optimization of Subway Vehicle Traction System Considering Stages
## 1 Introduction
Then, component repair intervals and the system's next inspection times are determined  
At present, some subway companies with opened earlier and larger network scales have begun to study the reform of the operation and maintenance model. There are two main research directions for the subway electrical system. One is the shift from regular maintenance to condition-based maintenance. Another is the formulation of maintenance strategies throughout the life cycle [17; 18]. Condition-based maintenance can effectively utilize maintenance costs and ensure system reliability. Premature or late maintenance of components and systems is prevented [19]. Condition-based maintenance of subway traffic signals, traction motors, converters, and fans is studied [20; 21; 22; 23]. The research focus on the maintenance strategy in the whole life cycle is the optimization of the regular maintenance strategy [24; 25; 26; 27; 28] and the reliability-centered maintenance strategy [29; 30; 31; 32]. Reliability-centered maintenance is applied in electric power, aviation, marine, chemical, machinery, and other industries. There are also some studies on urban rail vehicles. During the entire life cycle of a component, the failure rate has different periods of development and change. A more accurate maintenance plan can be obtained by researching the preventive maintenance strategy centered on reliability for different failure rate stages. In summary, the single-component and multi-component group maintenance model is adopted to optimize the preventive maintenance strategy of subway vehicle traction system in different stages in this paper. Three maintenance methods are used: preventive maintenance, preventive update maintenance and non-preventive failure maintenance. The objective function is the minimum maintenance cost per unit time. A single-component irregular preventive maintenance model for the subway traction system, constrained by reliability, is established. System single-component maintenance strategy optimization is implemented. On the basis of the preventive maintenance interval time for a single component, the idea of opportunistic maintenance is introduced. The decision variable is the reliability threshold of component opportunistic maintenance. The optimization goal is the minimum total maintenance cost within a certain maintenance time. A multicomponent group maintenance model for the subway vehicle traction system is established to optimize the preventive maintenance strategy of the subway vehicle traction system. In this work, an optimization model of preventive maintenance strategy for subway vehicle traction system is proposed. Section 2 describes the idea of single-component and multi-component group maintenance, and makes assumptions according to the characteristics of the subway vehicle traction system. Section 3 establishes the single-component maintenance model. Section 4 studies the group preventive maintenance model. Section 5 takes a subway vehicle traction system as an example to illustrate the efficiency and economy of the single-component and multi-component group maintenance model. The preventive maintenance strategy optimization of the subway vehicle traction system is realized. A comparative analysis was made with the current scheduled maintenance method implemented by the existing operation scale of a subway company. Finally, Section 6 summarizes and concludes.