Optimized bi-directional balancing method and system
First Claim
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1. A battery balancing system comprising:
- a plurality of cells connected in series, wherein the plurality of cells includes a Min Q cell and a Max Q cell;
a balancer for each cell;
a monitor configured to determine a state of charge (SOC) of each cell;
a microprocessor configured to;
iteratively calculate a SOC error for each cell, based on a theoretical balancing of the Min Q cell and the Max Q cell, until the SOC error for each cell is less than or equal to a predetermined first threshold;
while the SOC error is less than or equal to a predetermined first threshold, iteratively re-calculate the SOC error for each cell using a calculated net charge or discharge time for each balancer until the SOC error for each cell is less than or equal to a predetermined second threshold; and
when the SOC error is less than or equal to a predetermined second threshold, instruct each balancer to physically balance each respective cell based on the respective calculated net charge or discharge time by adding or removing charge to or from each respective cell.
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Abstract
A battery balancing method and system which includes a plurality of cells connected in series, a balancer for each cell, a monitor configured to determine a state of charge (SOC) of each cell, and a microprocessor. The microprocessor iteratively calculates a SOC error for each cell, based on a theoretical balancing of the Min Q cell and the Max Q cell, until the SOC error is less than or equal to a first threshold; and iteratively re-calculates SOC error based on a net charge or discharge time for each balancer until the SOC error is less than or equal to a second threshold; and when the SOC error is less than or equal to the second threshold, instructs each balancer to physically balance each respective cell based on the respective calculated net charge or discharge time when the second threshold is met.
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Citations
29 Claims
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1. A battery balancing system comprising:
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a plurality of cells connected in series, wherein the plurality of cells includes a Min Q cell and a Max Q cell; a balancer for each cell; a monitor configured to determine a state of charge (SOC) of each cell; a microprocessor configured to; iteratively calculate a SOC error for each cell, based on a theoretical balancing of the Min Q cell and the Max Q cell, until the SOC error for each cell is less than or equal to a predetermined first threshold; while the SOC error is less than or equal to a predetermined first threshold, iteratively re-calculate the SOC error for each cell using a calculated net charge or discharge time for each balancer until the SOC error for each cell is less than or equal to a predetermined second threshold; and when the SOC error is less than or equal to a predetermined second threshold, instruct each balancer to physically balance each respective cell based on the respective calculated net charge or discharge time by adding or removing charge to or from each respective cell. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of balancing a battery stack, the method comprising:
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performing first loop calculations by; determining a first state of charge (SOC) of each cell in the battery stack; calculating an average SOC for the battery stack; calculating a difference in charge (Δ
Q) between each cell and the average SOC for the battery stack;calculating a charge or discharge time for each cell in the battery stack such that each cell matches the average SOC for the battery stack; determining a Min Q cell and a Max Q cell based on the Δ
Q of each cell;calculating a charge distribution for each cell in the battery stack based on a calculated balancing of the Min Q cell and the Max Q cell for the battery stack; calculating a second SOC for each cell in the battery stack based on the calculated balancing of the Min Q cell and the Max Q cell; determining a SOC error for each cell in the battery stack by calculating a percentage difference between the second SOC of the cell and the average SOC; and if the magnitude of the SOC error is above a predetermined threshold, then going back to the step of calculating the Δ
Q of each cell in the battery stack;
otherwise,calculating cumulative charge and discharge times for each balancer; and performing second loop calculations while the magnitude of the calculated SOC is less than or equal to the predetermined first threshold, by; calculating a net charge or discharge time for each cell based on first loop calculations; computationally rebalancing each cell using net charge/discharge times for each cell based on first loop calculations and the determined first SOC of each cell; calculating a third theoretical SOC of each cell in the battery stack; if a magnitude of any cell of the battery stack is above a predetermined second threshold, then going back to the step of calculating an average SOC for the battery stack of the first loop calculations using the third theoretical SOC of each cell;
otherwise,physically balancing each cell by adding or removing charge to or from each cell based the net charge or discharge time for each cell respectively. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A method of balancing a battery stack, the method comprising:
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in a first calculation loop; determining a first state of charge (SOC) of each cell in the battery stack; calculating an average SOC for the battery stack; calculating a charge to add to or remove from each cell in the battery stack such that a resulting charge in each cell in the battery stack is closer to the average SOC of the battery stack; simulating a charge redistribution based on the calculated charge to add or remove from each cell in the battery stack; calculating a second SOC for each cell based on the simulated charge redistribution; iteratively repeating the first calculation loop by going back to the step of calculating an average SOC for the battery stack, until a SOC error of each cell is within a predetermined first threshold;
wherein in each iteration, a charge or discharge time for each cell is recorded;in a second calculation loop; reducing charge balancing time for each cell in the battery stack by computing a net charge or discharge time for each cell based on the recorded iterative charge or discharge time calculation for each cell from the first calculation loop; simulating a balancing of each cell based on the reduced charge balancing time and the first SOC for each cell; determining a new SOC error for each cell in the battery stack; and if the magnitude of the new SOC error is above a predetermined second threshold then repeating the first loop calculations by going back to the step of calculating the charge to add to or remove from each cell in the battery stack such that a resulting charge in each cell in the battery stack is closer to the average SOC of the battery stack; otherwise, balancing each cell in the battery stack based on the net charge or discharge time. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29)
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Specification
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Current AssigneeAnalog Devices International Unlimited Company (Analog Devices, Inc.)
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Original AssigneeLinear Technology Corporation (Analog Devices, Inc.)
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InventorsShaffer, Brian J., Nork, Samuel Hodson
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Primary Examiner(s)WILLIAMS, ARUN C
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Application NumberUS13/426,277Publication NumberTime in Patent Office832 DaysField of Search320/118US Class Current320/118CPC Class CodesB60L 58/22 Balancing the charge of bat...H01M 10/425 Structural combination with...H01M 2010/4271 Battery management systems ...H02J 7/0014 Circuits for equalisation o...H02J 7/0018 using separate charge circuitsY02E 60/10 Energy storage using batteriesY02T 10/70 Energy storage systems for ...
