Lab testing of Ni-MH battery packs on four different hybrid control strategies to evaluate life and performance

A project was undertaken to evaluate the effects of four different hybrid control strategies on nickel metal hydride (Ni-MH) batteries in series-strings. The goal of the project was to compare the resulting cycle life, capacity fade, power fade, and energy throughput (simulated miles). Project results were inconclusive related to the state-of-charge (SOC) excursion and how it relates to differences in capacity fade, but did produce evident differences with regard to increased resistance/power fade. The project results also indicated that excessive overcharging for equalizing purposes are a contributing factor to reduced performance. This paper describes the test methodology and summarizes the project results