System for determining battery impedance
A method for real-time characterization of a battery includes providing electric power to one or more electrical power loads, charging and discharging the battery based on power needs of the one or more electrical power loads, and monitoring for a circumstance where charging and discharging of the battery results in terminal voltage of the battery substantially equaling open-circuit voltage of the battery and recording the measured terminal voltage as a first measured voltage. The method may also include monitoring for a subsequent circumstance subsequent when charging and discharging the battery results in battery current larger than a predetermined value and recording an existing terminal voltage as a second measured voltage. The method may also include using the first and second measured voltages to determine a measured internal impedance of the battery. These actions may be performed between startup and shutdown of the power system.
1. A method for real-time characterization of a battery in a power system, the method comprising:
between startup and shutdown of the power system, operating the power system by:
providing electric power to one or more electrical power loads of the power system,
charging and discharging the battery based on power needs of the one or more electrical power loads,
with at least one information-processing device, monitoring for a circumstance where the charging and discharging of the battery based on the power needs of the one or more electrical power loads results in a measured terminal voltage of the battery substantially equaling an open-circuit voltage of the battery and recording the measured terminal voltage as a first measured voltage,
with the at least one information-processing device, monitoring for a circumstance subsequent to the measured terminal voltage substantially equaling the open-circuit voltage when charging and discharging the battery based on the power needs of the electrical power loads results in a battery current larger than a predetermined value and recording an existing terminal voltage as a second measured voltage, and
with the at least one information-processing device, using the battery current larger than a predetermined value, the first measured voltage and the second measured voltage to determine an internal impedance of the battery, wherein the internal impedance of the battery is equal to the difference between the first measured voltage and the second measured voltage divided by the battery current larger than a predetermined value.
2. The method of claim 1 , wherein monitoring for a circumstance where the charging and discharging of the battery based on the power needs of the one or more electrical power loads results in a measured terminal voltage of the battery substantially equaling an open-circuit voltage of the battery and recording the measured terminal voltage as the first measured voltage includes:
with the at least one information-processing device, monitoring for a circumstance where battery current has remained smaller than a reference value for a reference period; and
when battery current has remained smaller than the reference value for the reference period, recording with the at least one information-processing device the measured terminal voltage of the battery as the first measured voltage.
3. The method of claim 2 , further comprising using the internal impedance of the battery to estimate with the at least one information-processing device a value indicative of a state of health of the battery.
4. The method of claim 3 , further comprising, subsequent to estimating the value indicative of the state of health of the battery, repeatedly reestimating with the at least one information-processing device the internal impedance of the battery based on the estimated value indicative of the state of health of the battery and at least one of a measured temperature of the battery, a measured terminal voltage of the battery, or a measured battery current magnitude.
5. The method of claim 4 , further comprising determining with the at least one information-processing device a limit for a magnitude of battery current based on voltage limits for the battery and the estimated internal impedance.
6. The method of claim 1 , further comprising using the internal impedance of the battery to estimate with the at least one information-processing device a value indicative of a state of health of the battery.
7. The method of claim 6 , further comprising, subsequent to estimating the value indicative of the state of health of the battery, repeatedly reestimating with the at least one information-processing device the internal impedance of the battery based on the estimated value indicative of the state of health of the battery and at least one of a measured temperature of the battery, a measured terminal voltage of the battery, or a measured battery current magnitude.
8. The method of claim 7 , further comprising determining with the at least one information-processing device a limit for a magnitude of battery current based on voltage limits for the battery and the estimated internal impedance.
9. The method of claim 6 , further comprising using the value indicative of the state of health of the battery to determine with the at least one information-processing device whether the battery has reached an end of its useful life.
10. The method of claim 6 , further comprising using the value indicative of the state of health of the battery to estimate with the at least one information-processing device how much remaining life the battery has.