Abstract
This paper shows the possible gain on time before the end of useful time brought by switches addition in a multicell battery. In a first time, it presents a battery electric model. A battery includes many identical electrical energy cells that electrically interact. From a behavioral standpoint, cell performance is measured by fundamental parameters: State of Charge (SoC) and State of Health (SoH). To simulate cell electrical behavior, the Thevenin model or the Nernst model are often used. However, these models do not take into account the cells aging or the possible interactions on aging. A cell ages mainly in two ways: cyclic and calendar. This aging impacts both the elements of the equivalent electrical model and the fundamental parameters (SoC and SoH). Thus, the conventional electric model of a cell does not accurately reflect the cell aging. In this paper, another formal model based on the fundamental curve that relates electrical and behavioral parameters is proposed. It integrates aging into the equivalent electric model estimation. In a second time, in order to validate this model, this cell model is used to simulate parallel-series association. To improve battery lifespan, in addition to the usual balancing techniques, it may be relevant to require some traditional reliability and operating safety solutions. This requires to add switches inside battery. The presented simulation shows adding switches solution is currently not deployed. This is justified in this paper by examining the impact provide on lifespan improvement on an example, which is pretty weak. But it also shows that however, by managing active cells in a different way, adding switches and spare cells can really reach this improvement.
Highlights
This paper shows the possible gain on time before the end of useful time brought by switches addition in a multicell battery
Other schemes are based on the battery internal chemistry [12]. Another model is often deployed, that of Nernst [13]. It is based on the characteristic curve connecting open circuit voltage source (OCV) to State of Charge (SoC), as shown in Fig. 3 for a LiFePO4 cell
The Nernst model given by equation (4) has a defect: it is based on logarithms and cannot model the boundary behavior of SoC
Summary
Batteries often combine a large number of cells [1]. A single cell provides a current Icell with a voltage Vcell, depending on electrode and electrolyte nature, but their values are often insufficient for a common use. The present dominant technology is the lithium-ion, whose voltage Vcell is less than 4.2V. A cell is characterized by its initial capacity Q o expressed in ampere hours (Ah)
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