Method and apparatus for measuring the state of charge of an electrochemical cell pulse producing a high discharge current
First Claim
1. A method of measuring the state of charge of an electrochemical storage unite having a pair of output terminals at which appears, in the absence of any load, a nominal voltage, said storage unit further having an internal impedance which varies in accordance both with the load across the output terminals and with the state of charge of the storage unit, said method comprising the steps:
- applying a stress pulse across said output terminals in the form of a voltage pulse having a limited duration and a predetermined non-zero fixed voltage sufficiently less than said nominal voltage so as to cause the storage unit to deliver an external discharge current having a monotonic relationship with said state of charge;
measuring said external discharge current across the output terminals during the application of the stress pulse; and
determining said state of charge directly from the measured external discharge current.
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Abstract
The state of charge of an electrochemical storage unit is measured by applying to the electrochemical storage unit (32), a voltage pulse which is less than its nominal voltage, so as to make the storage unit deliver a high discharge current for a short period of time. The level of the voltage pulse is chosen to cause a discharge current that varies monotonically and preferably approximately linearly as a function of the state of charge of the storage unit, so that the state of charge can be unambiguously estimated by measuring the discharge current.
13 Citations
9 Claims
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1. A method of measuring the state of charge of an electrochemical storage unite having a pair of output terminals at which appears, in the absence of any load, a nominal voltage, said storage unit further having an internal impedance which varies in accordance both with the load across the output terminals and with the state of charge of the storage unit, said method comprising the steps:
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applying a stress pulse across said output terminals in the form of a voltage pulse having a limited duration and a predetermined non-zero fixed voltage sufficiently less than said nominal voltage so as to cause the storage unit to deliver an external discharge current having a monotonic relationship with said state of charge; measuring said external discharge current across the output terminals during the application of the stress pulse; and determining said state of charge directly from the measured external discharge current. - View Dependent Claims (2, 3, 4, 5)
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6. Apparatus for measuring the state of charge of an electrochemical storage unit, comprising:
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means for imposing a stress pulse across the output terminals of said electrochemical storage unit in the form of a predetermined fixed non-zero voltage to thereby cause a discharge current to be drawn from said electrochemical storage unit for a limited time, said predetermined fixed voltage being sufficiently less than a nominal voltage of the storage unit that said discharge current provides an unambiguous measure of said state of charge for all possible states of charge of said electrochemical storage unit; means for measuring said discharge current; and means for determining the state of charge of said electrochemical storage directly from the measured discharge current. - View Dependent Claims (7, 8, 9)
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Specification