Method for cell balancing for lithium battery systems
View Patent ↗A rechargeable multiple cell battery pack has an application associated therewith that draws power from the battery pack. While the battery pack is in operation, voltage, current, state-of-charge (SOC), and impedance data are collected on a per-cell basis and an algorithm is performed to determine a state-of-charge for each individual cell of the battery pack consistent with predetermined criteria. The individual cells are charged to the respective, determined state-of-charge (SOC) levels.
1. A method of controlling a rechargeable battery pack having a plurality of cells suitable for use in an application comprising the steps of:
determining a desired discharge delivery rate for said battery pack based upon at least one of (i) usage data collected during operation of the application and (ii) predetermined expected usage data;
determining a desired regenerative energy acceptance for said battery pack based upon at least one of (i) regeneration data collected during said operation of the application and (ii) predetermined, expected regeneration data;
determining a respective target state-of-charge (SOC) for each one of said plurality of individual cells based upon said determined, desired discharge delivery rate and regenerative energy acceptance; and
charging said individual cells of said battery to in accordance with said respective target SOCs.
2. The method of claim 1 wherein said step of determining said respective target SOCs includes the substep of:
determining respective weighting factors applied to said desired discharge delivery rate and said desired regenerative energy acceptance.
3. The method of claim 2 wherein said step of determining said respective target SOCs is further performed based upon at least one of either (i) an overall minimum state of charge or (ii) a minimum energy capacity desired for said battery pack.
4. The method of claim 1 wherein said determined, target state-of-charge for individual cells differs between cells.
5. The method of claim 1 wherein said step of determining the desired level of regenerative energy accept includes the substep of:
selecting said regeneration data so as to include individual cell internal impedance determinations.
6. The method of claim 1 wherein said step of determining the desired discharge delivery rate includes the substep of:
selecting said usage data so as to include measurements of electrical characteristics of power drawn from said individual cells as a function of time.
7. The method of claim 6 further including the step of determining a first load profile based on said electrical characteristic-measurements for use in determining said respective target states-of-charge for said cells.
8. The method of claim 7 further including the step of determining a second load profile.
9. The method of claim 8 wherein said step of determining said respective target state-of-charge (SOC) levels includes the substep balancing said first load profile and said second load profile.
10. The method of claim 1 wherein said application for said battery pack includes a dynamoelectric machine alternatively configured for propulsion and for production of regenerative energy.
11. A rechargeable battery pack suitable for use with an application, comprising:
a plurality of battery cells each configured to produce electrical power on a battery pack input/output terminal thereof;
means for determining a desired discharge delivery rate of said battery pack based upon at least one of usage data collected during operation of the application and predetermined, expected usage data;
means for determining a desired regenerative energy acceptance based upon at least one of regeneration data collected during operation of the application and predetermined, expected regeneration data;
means for calculating a respective target state-of-charge (SOC) for each one of said battery cells based on said usage data and said regeneration data; and
means for charging said battery cells in accordance with said respective target SOCs.
12. The battery pack of claim 11 wherein said data include impedance measurements of said cells.
13. The battery pack of claim 12 wherein said data includes measurements of electrical characteristics of power drawn from said cell or cells as a function of time.
14. The battery pack of claim 13 wherein said calculating means includes a central processing unit (CPU) configured to determine said desired state-of-charge for said battery cell or cells, using said impedance level measurements and said electrical characteristics measurements.
15. The battery pack of claim 11 wherein said means for calculating said respective target SOCs includes means for determining respective weighting factors applied to said desired discharge delivery rate and said desired regenerative energy acceptance.
16. The rechargeable battery pack of claim 15 wherein said means for determining said target state-of-charge for the individual cells is further responsive to at least one of (i) an overall minimum state of charge or (ii) a minimum energy capacity desired for said battery pack.
17. The rechargeable battery pack of claim 11 wherein said means for charging includes a unit that charges said battery cell or cells to state-of-charge levels that differ between cells.