Fault diagnosis of external soft-short circuit for series connected lithium-ion battery pack based on modified dual extended Kalman filter

Abstract

Battery fault diagnosis is intractable to guarantee the safety and reliability in an advanced battery management system, especially the diagnosis of external soft-short circuit is still an open and challenging issue. Herein, a novel dual-Kalman filter diagnostic method is developed through deeply analyze the characteristics of the external soft-short circuit fault in the series-connected lithium-ion battery pack. First, a modified extended Kalman filter is applied to obtain the open-circuit voltage online, where the relationship between the curve and state of charge is constructed previously that time-saving not to update the relationship in real-time. Second, the SOC difference between the “median cell” and “minimum cell” is obtained by interpolation. Then, the external soft-short circuit current and resistance are calculated by linearly fitting the difference curve before the inflection point. Where after the point, the SOC difference does not always increase with time even if the short-circuit resistance is fixed owing to the nonlinear characteristics of the battery. The experiments are performed that on one hand is to clarify the fault characteristics and on the other is to validate the effectiveness of the diagnostic algorithm. The proposed diagnostic method gives an excellent performance for detecting the fault of the external soft-short circuit.