Method for measuring battery parameters under discharge or charge
Certain embodiments are described that provide a method for measuring battery parameters under discharge/charge. (a) A battery at rest is provided having an initial State of Charge (SoC). (b) A discharge/charge excitation is applied for a first period of time. (c) The battery is allowed to rest for a second period of time. (d) A discharge/charge is applied, having a higher current and shorter duration than the discharge/charge of step (b). (e) The battery is allowed to rest for a third period of time. (f) Steps (b)-(d) are repeated. Parameters of the battery are measured during a plurality of the steps.
1. A method for measuring battery parameters under discharge comprising:
(a) providing a battery at rest having an initial State of Charge (SoC);
(b) applying a discharge excitation for a first period of time;
(c) allowing the battery to rest for a second period of time;
(d) applying a discharge having a higher current, and shorter duration than the discharge of step (b);
(e) allowing the battery to rest for a third period of time;
(f) repeating steps (b)-(d) until the initial SoC is less than 1%; and
(g) measuring parameters of the battery during a plurality of the steps;
wherein:
(a) the initial State of Charge (SoC) is about 100%;
(b) applying the discharge excitation for the first period of time comprises applying a discharge excitation of 0.1/x C discharge for x hours, where C is the number of amperes needed to completely discharge the battery in x hours;
(c) allowing the battery to rest for the second period of time comprises allowing the battery to rest for y hours, which is greater than 0;
(d) applying the discharge having the higher current and shorter duration comprises applying a discharge >1 C; and
(e) allowing the battery to rest for the third period of time comprises allowing the battery to rest for y hours.
2. The method of claim 1 wherein a rate of discharge of step (d) is at least 10 times a rate of discharge of step (b).
3. The method of claim 1 wherein the initial SoC is greater than 75%.
4. The method of claim 1 wherein the second and third periods of time are the same, and are at least two hours.
5. The method of claim 1 wherein the battery is modeled with an Open Circuit Voltage (OCV) source in series with an internal resistance (Rs) and two RC circuits in series (R 1 , C 1 , R 2 , C 2 ) and further comprising measuring the OCV at a resting voltage from step c.
6. The method of claim 5 wherein measuring parameters of the battery comprises measuring Rs from the instantaneous voltage change due to the high current pulse during step (d).
7. The method of claim 5 wherein measuring parameters of the battery comprises measuring R 1 , C 1 , R 2 , and C 2 by multi-exponentially modeling a depolarization curve during step (c).
8. A non-transitory computer readable medium having computer readable code stored thereon which, when executed by a processor, causes the processor to control a test apparatus in measuring battery parameters under discharge by:
(a) providing a battery at rest having an initial State of Charge (SoC);
(b) applying a discharge excitation for a first period of time;
(c) allowing the battery to rest for a second period of time;
(d) applying a discharge having a higher current, and shorter duration than the discharge of step (b);
(e) allowing the battery to rest for a third period of time;
(f) repeating steps (b)-(d) until the initial SoC is less than 1%; and
(g) measuring parameters of the battery during a plurality of the steps;
wherein:
(a) the initial State of Charge (SoC) is about 100%;
(b) applying the discharge excitation for the first period of time comprises applying a discharge excitation of 0.1/x C discharge for x hours, where C is the number of amperes needed to completely discharge the battery in x hours;
(c) allowing the battery to rest for the second period of time comprises allowing the battery to rest for y hours, which is greater than 0;
(d) applying the discharge having the higher current and shorter duration comprises applying a discharge >1 C; and
(e) allowing the battery to rest for the third period of time comprises allowing the battery to rest for y hours.
9. The non-transitory computer readable medium of claim 8 wherein the battery is modeled with an Open Circuit Voltage (OCV) source in series with an internal resistance (Rs) and two RC circuits in series (R 1 , C 1 , R 2 , C 2 ), and wherein measuring parameters of the battery comprises: measuring OCV at a resting voltage from step (c), measuring Rs from the instantaneous voltage change due to the high current pulse during step (d); and measuring R 1 , C 1 , R 2 , and C 2 by multi-exponentially modeling a depolarization curve during step (c).