TITEL

Maximizing system lifetime by battery scheduling

SPREKER

Marijn Jongerden, promovendus, Universiteit Twente

TAAL

Engels

ABSTRACT

Mobile devices usually rely on batteries for their power supply. The capacity of the batteries is finite, and the duration with which one can use the device is limited by the battery lifetime. Lifetime, here, is the time of one discharge period of the battery, from full to empty. While the battery lifetime depends mostly on its capacity and the level of the load applied to it, another important influence, which is the focus of our research, is how the battery is used, i.e., its usage pattern. When a battery is continuously discharged, a high current will cause it to provide less energy until the end of its lifetime than a lower current. This effect is termed the rate-capacity effect. On the other hand, during periods of low or no discharge current, the battery can recover to a certain extent. This is termed the recovery effect. Exploiting these two non-linear effects can help in extending the battery lifetime.

One approach to improve system lifetime is to connect one or more extra batteries, which are chosen following some schedule or scheduling policy. In most systems, the batteries are used sequentially, i.e., only when one battery is empty the other is used. However, by switching back and forth between the two batteries one can make use of the recovery effect of the batteries and extend the overall system lifetime. Some research on battery scheduling can be found in the literature, where several straightforward scheduling schemes, like round robin or choosing the best battery available, are compared. Although this research does show that system lifetime can be extended by using battery scheduling, it is still unclear what the maximum possible lifetime is.

In our research, we compare the straightforward scheduling schemes with the optimal scheduling scheme produced with a priced-timed automaton battery model (implemented and evaluated in Uppaal Cora). The generated optimal schedules show that in certain cases the round robin and best-battery scheduling policies come close to the maximal system lifetime, but are in some cases far from good.