This paper presents insights into the tradeoffs that exist when balancing charge and temperature within a lithium-ion battery pack. Both charge imbalance and temperature imbalance can harm battery pack performance - the former limits the charge/discharge capabilities of the pack, and the latter is known to accelerate battery pack aging. The literature proposes the manipulation of balancing current, normally reserved for charge or voltage balancing, to additionally reduce temperature heterogeneity. The goal is to limit both charge and temperature imbalance simultaneously, as balancing one may increase imbalance of the other. A noticeable gap in the literature, one this paper seeks to address, is the lack of a more formal understanding of the tradeoffs between charge and temperature imbalance. This paper uses a formal framework to obtain insights regarding the cases of balancing neither charge nor temperature, balancing charge, and balancing temperature. This allows for the determination of different factors that describe how balancing one state impacts the other, as well as the discovery that temperature balancing can be improved through the control of the average pack current. A model predictive control scheme is used to determine balancing current and validate these insights for a variety of scenarios.
- Feedback control
- lithium-ion batteries
- model predictive control (MPC)
- state heterogeneity
- time-varying systems