Fuel gauging for all: Page 5 of 7

August 19, 2016 // By Bakul Damle
Fuel gauging for all
As the pace of improvements in traditional consumer electronics such as smartphones and tablets is starting to plateau, many creative design engineers are focusing their attention on inventing the next big thing.

The ModelGauge m5 algorithm combines the short-term accuracy and linearity of a coulomb counter with the long-term stability of a voltage-based fuel gauge. The core of the algorithm combines the OCV state estimation with the coulomb counter. The OCV value of Li+ cell correlates to the SOC% and this relationship persists largely independent of the age of the cell (see figure 6).

Figure 6: SOC% vs OCV of a battery does not change with age.

As the cell cycles during the application, this process of traversing up and down through this curve largely desensitizes any local errors resulting from any model to cell mismatch. At the start, when the cell is first connected to the fuel gauge IC, the OCV state estimation is weighted heavily compared to the coulomb count output. As the cell is cycled in the application, coulomb counter accuracy improves and the mixing algorithm alters the weighting so that the coulomb counter result is dominant. From this point forward, the IC switches to servo mixing.

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