Computing Optimal Schedules of Battery Usage in Embedded Systems

Abstract

The use of mobile devices is often limited by the battery lifetime. Some devices have the option to connect an extra battery, or to use smart battery-packs with multiple cells to extend the lifetime. In these cases, scheduling the batteries or battery cells over the load to exploit the recovery properties of the batteries helps to extend the overall systems lifetime. Straightforward scheduling schemes, like round robin or choosing the best battery available, already provide a big improvement compared to a sequential discharge of the batteries. In this paper we compare these scheduling schemes with the optimal scheduling scheme produced with two different modeling approaches: an approach based on a priced-timed automaton model (implemented and evaluated in Uppaal Cora), as well as an analytical approach (partly formulated as non-linear optimization problem) for a slightly adapted scheduling problem. We show that in some cases the results of the simple scheduling schemes (round robin, and best-first) are close to optimal. However, the optimal schedules, computed according to both methods, also clearly show that in a variety of scenarios, the simple schedules are far from optimal.

Lifetime Improvement by Battery Scheduling

“…In [5] it is shown that, according to the KiBaM model, in theory the best way to discharge the batteries in a multiple battery system is by using them in parallel. For a system with N identical batteries discharged with a continuous current I the lifetime is then given by:…”

“…The batteries that have been used in this computation are similar to those used in [5], i.e., c = 0.166 and k = 2.815·10 −4 s −1 . However, here the capacity is increased to a realistic value, C = 2400 As, instead of the much smaller capacity of 330 As used in [5]. This type of battery is used in the Itsy pocket computer, which was also simulated by Rakhmatov et al in [14,15].…”

“…Three of these schedulers were also used in [5] in the setting of priced timed automata: sequential, load-round-robin and best-of-two. These schedulers are used here to see what the effect is of the bigger battery capacity on the lifetime gain.…”

“…The off periods last 1 minute, and the on periods are uniformly distributed over the interval minute. This load has also been used in [5], but there the modelled batteries had a capacity that was approximately 8 times smaller than the real capacity, which is used here.…”

Model-based energy analysis of battery powered systems

“…- • Chapters 5 and 6 are extensions of [40] and [36]. The analytical approach to the scheduling problem presented in Chapter 6 was worked on in collaboration with Alexandru Mereacre.…”