A Maintenance-optimal Swapping Policy - For a Fleet of Electric or Hybrid-electric Vehicles

Motivated by high oil prices, several large fleet companies initiated future plans to hybridize their fleets to establish immunity for their optimized business models against severe oil price fluctuations, and adhere to increasing awareness of environmentally-friendly solutions. The hybridization projects increased maintenance costs especially for highly costly and degradable components such as Li-ion batteries. This paper introduces a degradation-based resource allocation policy to optimally utilize batteries on fleet level. The policy, denoted as Degradation-based Optimal Swapping Policy, incorporates optimal implementation of swapping and substitution actions throughout a plan of finite time horizon to minimize projected maintenance costs. The swapping action refers to the inter-change in the placement of two batteries within a fleet. The substitution action refers to the replacement of degraded batteries with new ones. The policy takes advantage of the different degradation rates in the batteries health states; due to different loading conditions; achieving optimal placement at different time intervals throughout the plan horizon. A mathematical model for the policy is provided. The optimization of the generated model is studied through several algorithms. Numerical results for sample problems are shown to illustrate the capability of the proposed policy in establishing substantial savings in the projected maintenance costs compared to other policies.