US 2010/0138178 A1Published application

Battery capacity estimating method and apparatus

AssigneeTesla Motors, Inc.

InventorsAnil Paryani, Scott Ira Kohn, Brian Boggs, Andrew David Baglino, Craig Bruce Carison

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Abstract

A method for accurately estimating battery capacity based on a weighting function is provided. The disclosed system monitors battery current and uses the monitored battery current to calculate the state of charge (SOCbyAh) of the battery. The system also measures the open circuit voltage (OCV) of the battery when the system is at rest, rest being determined by achieving a current of less than a preset current value for a period of time greater than a preset time period. The state of charge of the battery is calculated from the OCV (SOCbyOCV). The weighting function is based on ΔSOCbyAh and ΔSOCbyOCV, where ΔSOCbyAh is equal to SOCbyAhFirst time minus SOCbyAhSecond time, and where ΔSOCbyOCV is equal to SOCbyOCVFirst time minus SOCbyOCVSecond time. The weighting function also takes into account the errors associated with determining SOCbyAh and SOCbyOCV.

Claims19

Dependent claims

A method for estimating battery capacity of a battery, the method comprising the steps of:

reading CACCurrent, wherein CACCurrent is the current computed amp-hour capacity of the battery;
determining SOCbyAhFirst time at a first time, wherein SOCbyAhFirst time is the state of charge of the battery calculated by amp-hours at said first time;
determining SOCbyOCVFirst time at said first time, wherein SOCbyOCVFirst time is the state of charge of the battery calculated from the battery open circuit voltage (OCV) at said first time;
determining SOCbyAhSecond time at a second time, wherein SOCbyAhSecond time is the state of charge of the battery calculated by amp-hours at said second time;
determining SOCbyOCVSecond time at said second time, wherein SOCbyOCVSecond time is the state of charge of the battery calculated from the battery OCV at said second time;
calculating ΔSOCbyAh, wherein
ΔSOCbyAh=SOCbyAhFirst time−SOCbyAhSecond time;
calculating ΔSOCbyOCV, wherein
ΔSOCbyOCV=SOCbyOCVFirst time−SOCbyOCVSecond time;
calculating a weighting function, W, defined as
W
=
100
-
(
k


1
*
100
*
SOCbyAhError
Δ


SOCbyAh
+
k


2
*
100
*
SOCbyOCVError
Δ


SOCbyOCV
+
k


3
*
SOCbyOCVErrorPrev
)
wherein SOCbyAhError is the error associated with determining SOCbyAh, SOCbyOCVError is the error associated with determining SOCbyOCV, SOCbyOCVErrorPrev is the previously determined error associated with SOCbyOCV, and k1, k2 and k3 are constants;
and
calculating CACModified, wherein said CACModified=(W)(CACCurrent).

48 more elements

A method for estimating battery capacity of a battery, the method comprising the steps of:

monitoring battery current;
calculating Ah_used from said battery current, wherein Ah_used corresponds to the amp-hours used;
calculating SOCbyAh from said Ah_used, wherein SOCbyAh is the state of charge of the battery calculated using said Ah_used;
comparing said battery current to a preset current value;
measuring the open circuit voltage (OCV) of the battery when said battery current is less than said preset current value for a period of time greater than a preset time period;
determining SOCbyOCV from said measured OCV, wherein SOCbyOCV is the state of charge of the battery calculated from the OCV;
calculating ΔSOCbyAh, wherein
ΔSOCbyAh=SOCbyAhFirst time−SOCbyAhSecond time, wherein said first time and said second time correspond to two separate times when said battery current was less than said preset current value for a period of time greater than said preset time period;
calculating ΔSOCbyOCV, wherein
ΔSOCbyOCV=SOCbyOCVFirst time−SOCbyOCVSecond time;
calculating a weighting function, W, defined as
W
=
100
-
(
k


1
*
100
*
SOCbyAhError
Δ


SOCbyAh
+
k


2
*
100
*
SOCbyOCVError
Δ


SOCbyOCV
+
k


3
*
SOCbyOCVErrorPrev
)
wherein SOCbyAhError is the error associated with determining SOCbyAh, SOCbyOCVError is the error associated with determining SOCbyOCV, SOCbyOCVErrorPrev is the previously determined error associated with SOCbyOCV, and k1, k2 and k3 are constants;
and
calculating a current computed amp-hour capacity, CACCurrent, from a previously calculated computed amp-hour capacity, CACPrior, wherein
CACCurrent=(W)(CACPrior).

50 more elements

Dependencies are inferred from the claim text.