Design of an embedded hardware platform for cell-level diagnostics in commercial battery modules

Abstract

While battery aging is commonly studied at the cell-level, evaluating aging and performance within battery modules remains a critical challenge. Testing cells within fully assembled modules requires hardware solutions to access cell-level information without compromising module integrity. In this paper, we design and develop a hardware testing platform to monitor and control the internal cells of battery modules contained in the Audi e-tron battery pack. The testing is performed across all 36 modules of the pack. The platform integrates voltage sensors, balancing circuitry, and a micro-controller to enable safe, simultaneous cell screening without disassembling the modules. Using the proposed testing platform, cell voltage imbalances within each module are constrained to a defined reference value, and cell signals can be safely accessed, enabling accurate and non-invasive cell-level state-of-health assessments. On a broader scale, our solution allows for the quantification of internal heterogeneity within modules, providing valuable insights for both first- and second-life applications and supporting efficient battery pack maintenance and repurposing.

Figures (14)

• Figure 1: Schematic 4P3S topology; $v_1$, $v_2$, $v_3$ are the Cells terminal voltage; $I_m$ module current; $V_m$ module voltage.
• Figure 2: (a) Battery tester and thermal chamber with the module mounted inside; (b) detailed view of the module, including external connectors and thermocouple placement (three thermocouples attached to the module casing); (c) components of the M&BH: (A) analog electrical circuit, (B) ADC, (C) balancing switches, (D) microcontroller, and (E) CAN adapter for the cycler; (d) schematic of the overall setup, including the battery tester, the module (series-connected Cells), and the M&BH. The module-to-board connections are highlighted with different colors: G$-$ (black) is the module ground, C1$+$ (orange), C2$+$ (blue), and C3$+$ (brown) are the Cell positive terminals.
• Figure 3: Top: actuated module current profile $I_m$. Bottom: resulting module voltage $V_m$ (for module no.29). The description and the exit conditions of each portion are reported; diagnostic segments are highlighted in yellow. By convention, positive current means charging; negative discharging.
• Figure 4: Top: measured Cell voltages $v_1$, $v_2$, $v_3$, with zoomed-in views. Middle: maximum Cell voltage imbalance $\Delta v_{max}$ and balancing threshold $v_{th}$. Bottom: switch states $S_1$, $S_2$, $S_3$ determined by \ref{['eq:balancing_alg']}.
• Figure 5: Top: C/3 discharge capacities for all 108 Cells in the pack. Bottom: corresponding C/3 discharge energies. Right: capacity and energy distributions by Cell position within each module, with Gaussian fits.