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Grid-Constrained Smart Charging of Large EV Fleets: Comparative Study of Sequential DP and a Full Fleet Solver

Ipek Kuvvetli, Christofer Sundström, Sogol Kharrazi, Erik Frisk

Abstract

This paper presents a comparative optimization framework for smart charging of electrified vehicle fleets. Using heuristic sequential dynamic programming (SeqDP), the framework minimizes electricity costs while adhering to constraints related to the power grid, charging infrastructure, vehicle availability, and simple considerations of battery aging. Based on real-world operational data, the model incorporates discrete energy states, time-varying tariffs, and state-of-charge (SoC) targets to deliver a scalable and cost-effective solution. Classical DP approach suffers from exponential computational complexity as the problem size increases. This becomes particularly problematic when conducting monthly-scale analyses aimed at minimizing peak power demand across all vehicles. The extended time horizon, coupled with multi-state decision-making, renders exact optimization impractical at larger scales. To address this, a heuristic method is employed to enable systematic aggregation and tractable computation for the Non-Linear Programming (NLP) problem. Rather than seeking a globally optimal solution, this study focuses on a time-efficient smart charging strategy that aims to minimize energy cost while flattening the overall power profile. In this context, a sequential heuristic DP approach is proposed. Its performance is evaluated against a full-fleet solver using Gurobi, a widely used commercial solver in both academia and industry. The proposed algorithm achieves a reduction of the overall cost and peak power by more than 90% compared to uncontrolled schedules. Its relative cost remains within 9\% of the optimal values obtained from the full-fleet solver, and its relative peak-power deviation stays below 15% for larger fleets.

Grid-Constrained Smart Charging of Large EV Fleets: Comparative Study of Sequential DP and a Full Fleet Solver

Abstract

This paper presents a comparative optimization framework for smart charging of electrified vehicle fleets. Using heuristic sequential dynamic programming (SeqDP), the framework minimizes electricity costs while adhering to constraints related to the power grid, charging infrastructure, vehicle availability, and simple considerations of battery aging. Based on real-world operational data, the model incorporates discrete energy states, time-varying tariffs, and state-of-charge (SoC) targets to deliver a scalable and cost-effective solution. Classical DP approach suffers from exponential computational complexity as the problem size increases. This becomes particularly problematic when conducting monthly-scale analyses aimed at minimizing peak power demand across all vehicles. The extended time horizon, coupled with multi-state decision-making, renders exact optimization impractical at larger scales. To address this, a heuristic method is employed to enable systematic aggregation and tractable computation for the Non-Linear Programming (NLP) problem. Rather than seeking a globally optimal solution, this study focuses on a time-efficient smart charging strategy that aims to minimize energy cost while flattening the overall power profile. In this context, a sequential heuristic DP approach is proposed. Its performance is evaluated against a full-fleet solver using Gurobi, a widely used commercial solver in both academia and industry. The proposed algorithm achieves a reduction of the overall cost and peak power by more than 90% compared to uncontrolled schedules. Its relative cost remains within 9\% of the optimal values obtained from the full-fleet solver, and its relative peak-power deviation stays below 15% for larger fleets.
Paper Structure (15 sections, 11 equations, 10 figures, 1 algorithm)

This paper contains 15 sections, 11 equations, 10 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. Problem Formulation
  3. Outline
  4. Related Works
  5. Sequential Heuristic DP Optimization Methodology
  6. Cost Function and Constraints
  7. Sequential Heuristic DP Algorithm Design
  8. Full Fleet Solver
  9. Case Study
  10. Small-scale Fleet Description and Constraints
  11. Large-scale Fleet Description and Constraints
  12. Results
  13. Small-scale Fleet Experiment
  14. Large-scale Fleet Experiment
  15. Conclusion

Figures (10)

  • Figure 1: Electric shuttles scheduled for intelligent charging.
  • Figure 2: Proposed smart charging general configuration.
  • Figure 3: Detection of uncontrolled charging sessions from the difference of the previous operation's terminal SoC (red) and the following operation's initial SoC value (blue).
  • Figure 4: Distribution of SoC gain and initial SoC across charging sessions between 2020 and 2023.
  • Figure 5: Smart vs uncontrolled charging comparison for 3 shuttles.
  • ...and 5 more figures