Fast Offline Battery Capacity Estimation Approach With Performance Bounds

Capacity of a battery is a measure of the amount of charge, in Ampere hours (Ah), stored in the battery. With the battery ageing processes, the capacity of the battery reduces. Consequently, it is essential to have an accurate knowledge of battery capacity in order to perform crucial battery management tasks. For example, in the field of battery reuse, the estimated residual capacity of batteries will help in determining a suitable secondary application for the retired battery pack. Existing literature on offline capacity estimation are often based on low-discharge or 1C rate discharge of the battery. This means that a minimum of one hour wait is required before an estimate of capacity is made. In this paper, a novel approach is proposed for fast offline estimation of battery capacity using the knowledge of the open-circuit voltage (OCV) - state of charge (SOC) curve of the battery. The proposed approach consists of a novel method to estimate the battery OCV by applying a current profile that is optimized to reduce the uncertainty in OCV estimation. For capacity estimation, a constant current pulse is applied for a short duration. The capacity estimation accuracy is theoretically derived as a function of this current duration. The proposed fast capacity estimation approach is shown to be able to estimate the battery capacity within as short as 1 minute duration with an estimation error standard deviation of 0.02 Ah.