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Growth Limiting Correction for Battery Capacity Estimation

IP.com Disclosure Number: IPCOM000130433D
Publication Date: 2005-Oct-28
Document File: 2 page(s) / 15K

Publishing Venue

The IP.com Prior Art Database

Abstract

The voltage across a battery's terminals reflects the capacity of a battery. However, the mapping from capacity to voltage is not the same from battery to battery (due to differences in the vendor, battery age, variance in manufacturing etc). This variation is exasperated during rapid charging or discharging of the battery. In a system that uses voltage to estimate a battery's capacity, variation in the voltage increases the difficulty in accurately estimating the true capacity.

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BATTERY

CAPACITY ESTIMATION

Growth Limiting Correction for

Battery

Capacity Estimation

Disclosed Anonymously

The voltage across a battery's terminals reflects the capacity of a battery.  However, the mapping from capacity to voltage is not the same from battery to battery (due to differences in the vendor, battery age, variance in manufacturing etc).  This variation is exasperated during rapid charging or discharging of the battery.  In a system that uses voltage to estimate a battery's capacity, variation in the voltage increases the difficulty in accurately estimating the true capacity.

This system leverages knowledge about a battery and it cannot change its capacity faster than a given rate (determined by the battery characteristics and the charging or discharging environment).

In the case of charging, when the unit is connected to the charging source, the software that monitors battery voltage to estimate the capacity will only 'allow' the estimated capacity to grow by a certain % per sampling period.  If the capacity is growing faster than allowed, software will clamp the growth down, and apply an offset to every voltage reading, figuring that the voltage read is higher than it should be for a given capacity.  For periods where the clamping is not used, the offset is reduced.

A similar process is used for the discharging case.

Figure 1:  Illustrates how this algorithm affects the estimated curves over time during a charge.  The green curve shows the estimate capa...