US 6,307,378 B1Granted

Method and apparatus for measurement of electrochemical cell and battery impedances

AssigneeThe Penn State Research Foundation

InventorJames D. Kozlowski

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Abstract

A battery's impedance is measured by a technique that normally uses a current divider network which is connected to the battery. The circuit used according to this technique has a current generator producing a regulated current signal and has one or more sensing impedances which are normally positioned electrically parallel, or in some alternate embodiments in series, with the battery. A DC-blocking capacitor prevents the battery voltage from draining into the one or more sensing impedances. A magnetic field sensor or comparable device measures the magnitude and/or phase of current passing through the sensing impedances. Substitution of a number of calibrated impedances into the circuit in place of the battery permits an initial mathematical computation of the battery's impedance utilizing this technique. Thereafter battery impedances can be computed with the current without using calibrated impendances.

Claims17

Dependent claims

An apparatus for measuring impedance in an electrochemical cell comprising:

a current generator for producing an input current signal Ii along a current signal path in a current divider network;
said current divider network having at least a sensing current path and a battery current path, said sensing and battery current paths being in parallel to each other, each of said sensing and battery current paths also being in series with said current signal path, said current signal, sensing, and battery paths interconnecting with each other at a current dividing connector and at a current converging connector;
said sensing current path having a measurable sensing impedance Zs located along said sensing current path, a connector-wire impedance Z1 between said current dividing connector and said sensing impedance Zs, and a connector-wire impedance Z3 between said sensing impedance Zs and said current converging connector, wherein a portion Is of current signal Ii flows through said sensing current path;
said battery current path having a battery impedance Zb located along said battery current path, a connector-wire impedance Z2 between said current dividing connector and said battery impedance Zb, and a connector-wire-capacitor impedance Z4 between said battery impedance Zb and said current converging connector, wherein a portion Ib of current signal Ii flows through said battery path;
a DC-blocking capacitor in series with said battery impedance Zb and located along said battery current path to prevent said battery from discharging current through said sensing impedance Zs;
said sensing current path also having a magnetic field sensor with a coupling attached thereto for measuring the magnitude and phase of Is, thereby permitting mathematical determination of the value of Zb.

3 more elements

An apparatus for measuring impedance in an electrochemical cell comprising:

a current generator for producing an input current signal Ii along a current signal path in a current divider network;
said current divider network having a sensing current path and a battery current path, said sensing and battery current paths being in parallel to each other, each of said sensing and battery current paths also being in series with said current signal path, said current signal, sensing, and battery paths interconnecting with each other at a current dividing connector and at a current converging connector;
said sensing current path having a measurable sensing impedance Zs located along said sensing current path, a connector-wire impedance Z1 between said current dividing connector and said sensing impedance Zs, and a connector-wire impedance Z3 between said sensing impedance Zs and said current converging connector, wherein a portion Is of current signal Ii flows through said sensing current path;
said battery current path having a battery impedance Zb located along said battery current path, a connector-wire impedance Z2 between said current dividing connector and said battery impedance Zb, and a connector-wire impedance Z4 between said battery impedance Zb and said current converging connector, wherein a portion Ib of current signal Ii flows through said battery path;
a DC-blocking capacitor in series with said battery impedance Zb and located along said battery current path to prevent said battery from discharging current through said sensing impedance Zs;
said sensing current path also having a magnetic field sensor attached with a coupling thereto for measuring the magnitude and phase of Is and for determining the value of Zb using the equation
Zb=I′(Zs+Z1+Z3)+(Z2+Z4)
where I ′ = I s I i - I s ,
so that:
Z b = I s I i - I s ⁢ ( Z s + Z 1 + Z 3 ) + ( Z 2 + Z 4 ) .

7 more elements

A method for measuring impedance in an electrochemical cell comprising:

producing an input current signal Ii with a current generator along a current signal path in a current divider network;
establishing a sensing current path and a battery current path along said current divider network so that said sensing current and battery current paths are electrically parallel to each other and so that said parallel sensing current and battery current paths are in series with said current generator;
locating a measurable sensing impedance Zs along said sensing current path, locating a connector-wire impedance Z1 between said current signal path and said sensing impedance Zs so that a portion of current signal Ii flows from said current signal path through said connector-wire impedance Z1 to said sensing impedance Zs, and locating a connector-wire impedance Z3 between said sensing impedance Zs and said current signal path so that current flows from said sensing impedance Zs through said connector-wire impedance Z3 to said current signal path;
locating a battery impedance Zb along said battery current path, locating a connector-wire impedance Z2 between said current signal path and said battery impedance Zb so that a portion of current signal Ii flows from said current signal path through said connector-wire impedance Z2 to said battery impedance Zb, and locating a connector-wire impedance Z4 between said battery impedance Zb and said current signal path so that current flows from said battery impedance Zb through said connector-wire impedance Z4 to said current signal path;
and
locating a DC-blocking capacitor in series with said battery impedance Zb and located along said battery current path to prevent said battery from discharging current through said sensing impedance Zs;
instrumentally measuring the magnitude and phase of Is with a magnetic field sensor and determining the value of Zb using the equation
Zb=I′(Zs+Z1+Z3)+(Z2+Z4)
where I ′ = I s I i - I s ,
so that Z b = I s I i - I s ⁢ ( Z s + Z 1 + Z 3 ) + ( Z 2 + Z 4 ) .

7 more elements

Dependencies are inferred from the claim text.