Model-based structural isolation of concurrent electro-thermal faults for eVTOL battery systems

Battery fault diagnosis is a prerequisite for safety certification to electric vertical take-off and landing (eVTOL) aircraft. Unlike ground vehicles, eVTOL systems operate under a zero-failure tolerance regime, as even minor battery anomalies can compromise flight safety. However, existing diagnostic methods exhibit two fundamental limitations: their structural dependence on single-fault assumptions and the limited adaptability to high-rate electro-thermal coupling under aviation duty cycles. To address these challenges, this study proposes a structurally decoupled, model-based diagnostic framework for battery modules. A cell-level electro-thermal coupling model is established to capture dynamic electrical–thermal interactions under high discharge rates. Four minimal structurally over-constrained subsystems are constructed to generate analytically decoupled residuals. This design enables systematic isolation of seven fault categories, including short circuits, interconnection faults, and multiple sensor failures, while preserving diagnosability under concurrent fault conditions. Kalman filtering enhances state estimation robustness, and an adaptive threshold strategy accommodates varying operational regimes. Under single-fault scenarios, the proposed method achieves a detection rate of 93.88%, enabling isolation and parameter estimation of all seven fault types. More critically, under concurrent-fault scenarios in a 10S3P module with 4323 possible fault-pair combinations, the types of individual faults can be identified in 85.5% of cases, and in 98.3% of cases, the types can be narrowed down to fewer than three candidates.