Novel Operating Modes for the Charging of Lithium-ion Batteries

Abstract

Conventional battery simulation tools offer current, voltage, and power operating modes. This article presents General Operating Modes (GOMs), which move beyond these standard modes and allow battery models of any scale to simulate novel operating modes such as constant temperature, constant lithium plating overpotential, and constant concentration. The governing equations of the battery model are solved alongside a single algebraic constraint that determines the current. The operating modes are simulated efficiently and deterministically inside a differential-algebraic equation (DAE) solver, and constraints are satisfied within solver tolerances. We propose a mixed-continuous discrete (aka hybrid) solution to the constrained charging problem, using the GOMs to satisfy charging constraints. This approach enables nonlinear model predictive control (NMPC) to be implementable in real-time while directly using sophisticated physics-based battery models. The approach is demonstrated for three models of various complexity: a thin-film nickel hydroxide electrode model, a Single-Particle (SP) model, and a Porous Electrode Theory (PET) model. The hybrid fast charging algorithm is shown to be slightly suboptimal for the thermal SP model in some cases, which is not of practical importance for NMPC.