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Furukawa Review No.44

Battery State Sensor
~Curve Fitting of Lead-acid Battery's Voltage Relaxation with Expanded Kalman-filter~

Noriyasu Iwane


Stable open circuit voltage (OCV) prediction in a short time is required to detect the state of the lead-acid battery for automobile. We have found in our past development that the voltage relaxation behavior of the lead-acid battery could be expressed in higher-order exponential function of 5 or higher order, and the trial result to detect OCV in a short time was reported in Furukawa Denkou Jihou No.120 (Sept. 2007, in Japanese). In actual usage of the function, the optimum coefficients of the function shall be obtained according to the actual voltage behavior. This time, the calculation method is changed from the general leastsquares method which requires high computational effort, to the expanded Kalman-filter calculation which is known as the less computational effort method, and the trial calculation was performed to assess the benefit.

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