Detection method of battery cell degradation

This paper introduces a method, which precisely estimates deviations in the State-of-Charge and resistance values of the cells in a battery pack. The aim of the algorithm is to provide the required information a) for an early detection of cell failures and b) to decide, which cells must be charged or discharged by the charge equalization circuit. The problem is formulated as an inverse problem because the cell resistance values can not be estimated during operation modes of zero or constant battery current and a regularization term ensures that the estimation problem is stable. The paper will present test results from a battery pack, where the algorithm has been implemented in a Battery Control Unit.