Method and device for determining the state of function of an energy storage battery
View Patent ↗In a method for determining the state of function SOF of an energy storage battery, in particular a starter battery for a motor vehicle, as the capability to supply at least one load with an amount of energy, by determining a characteristic value for the state of charge SOC of the energy storage battery and a characteristic value for the state of health SOH when an electrical load is applied to the energy storage battery, with state of health (SOH) being the suitability of the energy storage battery to emit a specific amount of energy to the at least one load while maintaining a minimum voltage, a characteristic value for the state of function (SOF) is determined by linking the characteristic values for the state of charge (SOC) and for the state of health (SOH).
1. A method for determining the state of function of an energy storage battery, the method comprising:
determining a characteristic value for the state of charge of the energy storage battery;
determining a characteristic value for the state of heath when an electrical load is placed on the energy storage battery, the state of health being the suitability of the energy storage battery to emit a specific amount of energy to the at least one load while maintaining a minimum voltage; and
determining a characteristic value for the state of function by linking the characteristic values for the state of charge and for the state of health.
2. The method of claim 1 , wherein the characteristic value for the state of charge is determined from the ratio of the difference between the present charge and a predetermined critical charge and the difference between the maximum charge of the energy storage battery and the predetermined critical charge being given by the equation.
(
SOC
(
t
)
≈
Q
(
t
)
-
Q
crit
Q
max
-
Q
crit
)
.
3. The method of claim 1 , wherein the characteristic value for the state of charge is determined from a Nernst state of charge as the ratio of the difference between present no-load voltage and critical no-load voltage to the difference between maximum no-load voltage and the critical no-load voltage.
4. The method of claim 3 , wherein the characteristic value for the state of charge is determined from the Nernst state of charge minus a characteristic value for the change in the state of charge resulting from an age-dependent change to an active mass of the battery.
5. The method of claim 4 , wherein the characteristic value for the change in the state of charge is determined from a change in the state of charge resulting from any reduction in the active mass.
6. The method of claim 4 , further comprising determining a characteristic value relating to the active mass of the energy storage battery for the change in the state of charge by determining the internal resistance (R i ) of the energy storage battery.
7. The method of claim 1 , wherein the characteristic value for the state of health is determined from load-dependent drops in battery voltage.
8. The method of claim 1 , wherein the characteristic value for the state of health is given by the equation:
(
SOH
(
t
)
=
U
(
t
)
-
U
crit
x
SOC
crit
SOC
(
t
)
U
max
-
U
crit
x
SOC
crit
)
where U(t) is the present discharge voltage, U crit is the critical discharge voltage, SOC crit is the characteristic value for the state of charge, SOC(t) is the characteristic value for the present state of charge, and U max is the predetermined normal discharge voltage of a corresponding energy storage battery in a new state.
9. The method of claim 1 , wherein the characteristic value for the state of function is the product of the characteristic values for the state of charge and for the state of health.
10. The method of claim 1 , wherein the characteristic value for the state of function is equal to zero when the characteristic value for the state of charge is less than or equal to zero.
11. The method of claim 1 , wherein the characteristic value for the state of function is equal to zero when the characteristic value for the state of health is less than or equal to zero.
12. The method of claim 1 , wherein the characteristic value for the state of charge is determined from the amount of charge which can be drawn in normal conditions at a temperature in the range from 20° C. to 30° C. by measuring discharge current which occurs when discharging a fully charged energy storage battery in a new state for a time period of between 5 and 25 hours.
13. A device for determining the state of an energy storage battery comprising:
measurement means configured to detect at least one of battery voltage, a battery temperature, charging and discharge currents, and no-load current; and
processor-controlled evaluation means;
wherein the evaluation means are configured to determine a characteristic value for a state of health of an energy storage battery; and
wherein the evaluation means is also configured to determine a characteristic value for a state of charge of the energy storage battery, the characteristic value for the state of charge being determined from a Nernst state of charge as the ratio of the difference between present no-load voltage and critical no-load voltage to the difference between maximum no-load voltage and the critical no-load voltage.
14. The device of claim 13 , wherein the characteristic value for the state of charge is determined from the Nernst state of charge minus a characteristic value for the change in the state of charge resulting from an age-dependent change to an active mass of the battery.
15. The device of claim 14 , wherein the characteristic value for the change in the state of charge is determined from a change in the state of charge resulting from any reduction in the active mass and from the change in the state of charge resulting from sulfation of the active mass.
16. The device of claim 15 , wherein the evaluation means also determines a characteristic value relating to the active mass of the energy storage battery for the change in the state of charge by determining the internal resistance (R i ) of the energy storage battery.
17. The device of claim 13 , wherein the characteristic value for the state of health is determined from load-dependent drops in battery voltage.
18. The device of claim 13 , wherein the characteristic value for the state of health is given by the equation:
(
SOH
(
t
)
=
U
(
t
)
-
U
crit
x
SOC
crit
SOC
(
t
)
U
max
-
U
crit
x
SOC
crit
)
where U(t) is the present discharge voltage, U crit is the critical discharge voltage, SOC crit is the characteristic value for the state of charge, SOC(t) is the characteristic value for the present state of charge, and U max is the predetermined normal discharge voltage of a corresponding energy storage battery in a new state.
19. The device of claim 13 , wherein the device is configured to determine a state of function of the energy storage battery as the product of the characteristic values for the state of charge and for the state of health.
20. A device for determining the state of an energy storage battery comprising:
measurement means configured to detect at least one of battery voltage, a battery temperature, charging and discharge currents, and no-load current; and
processor-controlled evaluation means;
wherein the evaluation means are configured to carry out a method comprising:
determining a characteristic value for the state of charge of the energy storage battery;
determining a characteristic value for the state of heath of energy storage battery when an electrical load is placed on the energy storage battery, the state of health being suitability of the energy storage battery to emit a specific amount of energy to the at least one load while maintaining a minimum voltage; and
determining a characteristic value for the state of function by linking the characteristic values for the state of charge and for the state of health.