Nickel Metal Hydride Batteries' Voltage Depression Detection in Vehicle Application

The paper investigates the voltage depression phenomenon which occurs in Nickel Metal Hydride Batteries under certain load conditions. Even in battery system for Hybrid Electric Vehicles (HEV), which are characterized by quite narrow SOC (State of Charge) variability, the voltage depression takes place. The present work shows briefly the means for recreating the voltage depression battery state under controlled condition such as the laboratory one, and it gives an interpretation of these measurements. According to the data, the paper presents an NiMH battery modeling approach, based on the load history, for detecting and evaluating the voltage depression in HEV applications. In particular, it is described a method that is able to separate voltage depression from the other voltage modifications. Then it described a possible application of the proposed approach for improving the accuracy of the the ageing estimation.