Observer Design for the Series Interconnection of Li-Ion Battery Cells Subject to Reduced Voltage Information

Abstract

This work studies the estimation of internal states and voltages in a battery pack composed by lithium-ion cells subject to limited voltage and temperature measurements. A reduced-order electrochemical model for each cell is used. The considered cells are heterogeneous. They are electrically interconnected in series and thermally coupled. The resulting model is linearized and reformulated as a descriptor system. Such a model provides a unified modeling framework accounting for both battery cell dynamics and algebraic states arising from standard Kirchhoff’s laws. An observability study is exploited to design an observable descriptor system that requires the measurement of the surface temperature of one cell together with the total voltage. We resort to Lyapunov theory and the algebraic relationship between the descriptor system states and the measurements to derive a state observer that meets the following conditions. The error system is input-to-state stable and the effect of cell-to-cell variations on a specified performance variable is minimized. The state observer is obtained by solving a set of LMIs. The proposed scheme is able to estimate the state of each individual cell, including state of charge and inner temperature, as well as the unmeasured voltages. The effectiveness of the approach is tested in simulation.

Cell-Level State of Charge Estimation for Battery Packs Under Minimal Sensing

“…is Lipschitz continuous with respect to x, in which Φ = [Φ s Φ u ] was defined in the vicinity of (19). That is,…”

“…To date, the cell-level SOC estimation problem in a battery pack under reduced sensing has not been sufficiently explored. Series cell SOC estimation using only the total voltage measurement has been studied previously in [5,19,20], whereas the estimation for parallel (and parallel-series) configuration has been overlooked for multiple reasons. First, the cells in parallel are widely considered to behave as one single cell.…”