Optimal Charging Control for Lithium-Ion Battery Packs: A Distributed Average Tracking Approach

Effective lithium-ion battery pack charging is of extreme importance for accelerating electric vehicle development. This article derives an optimal charging control strategy with a leader-followers framework for battery packs. Specifically, an optimal average state-of-charge (SOC) trajectory based on cells' nominal model is first generated through a multiobjective optimization with consideration of both user demand and battery pack's energy loss. Then, a distributed charging strategy is proposed to make the cells' SOCs follow the prescheduled trajectory, which can effectively suppress the violation of the safety-related charging constraints through online battery model bias compensation. This article highlights the superiorities of the proposed leader-followers-based charging framework that combines the offline scheduling and online closed-loop regulation for battery pack charging, which brings benefits to significantly reduce the computational burden for the charger controller as well as improve the robustness to suppress the negative impact caused by the cell's model bias. Extensive illustrative results demonstrate the effectiveness of the proposed optimal charging control strategy.

I. Introduction

Lithium-ion (Li-ion) batteries have gained a large market share for electric vehicle (EV) applications, owing to their superiorities of high energy density and low self-discharge [1], [2]. However, several issues remain to be further solved for the performance enhancement of Li-ion batteries, such as the safety guarantee, cell equalization, and energy efficiency improvement [3], [4]. Among these issues, how to achieve reliable charging management for batteries is still a key but challenging problem [5]. In real applications, a well-designed charging strategy could not only prevent the battery from overcharging or overheat to further ensure its safety, but also provide an effective way to improve the battery performance and reduce energy loss. Therefore, it is vital to develop a suitable charging strategy for reliable management of Li-ion batteries.