Charge redistribution method for cell arrays

Inactive Publication Date: 2012-10-04
SENDYNE
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0033]The goal of the charge re-distribution method is to “boost” proactively the cell with the lowest EMF, highest impedance combination in order to prevent it from triggering an array shutdown condition, as well as achieve optimum power output for the cell array under the specific load conditions.

Problems solved by technology

The challenge of balancing individual cells connected in series is a well-known issue in the battery industry.
As a result specific cells may not reach their optimum State of Charge (SOC) and the battery will not perform at its maximum potential.
Published Japanese patent application 09-084275 “Method and Apparatus for Controlling Charging of Assembly Battery Pack” introduces a bypass mechanism combined with current reduction at the end of charge in order to avoid overheating cells, with the drawback of prolonged charge time.
Assuming the battery has been charged optimally, the next and probably most important performance issue is its ability to deliver the stored energy to the active load.
So practically in order to prolong battery life cell charge should be actively unbalanced.

Method used

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  • Charge redistribution method for cell arrays
  • Charge redistribution method for cell arrays
  • Charge redistribution method for cell arrays

Examples

Experimental program
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Effect test

Embodiment Construction

[0042]A first insight is to choose to model each cell not merely with an effective internal resistance but with an effective internal impedance.

[0043]If a series array of cells were driving a DC load (for example an incandescent bulb or an array of LEDs) then there is no reason to pay any attention to the imaginary component (if any) of cell impedance.

[0044]Impedance, in distinction to a pure ohmic resistance, is dependent among other things on the load frequency. In battery cells, impedance increases significantly in low frequencies. In the case of a cell stack operating under a given load current, cells with the higher impedance will exhibit lower terminal voltage and subsequently lower power output. The same cells will also reach earlier the cutoff voltage, causing the whole battery to cease operation.

[0045]A second insight is to appreciate that some loads have a substantial non-DC component. This happens for example in electric and hybrid cars.

[0046]A third insight is to appreci...

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Abstract

Cell balancing aims to prolong the battery operating life by equalizing the Electro Motive Force (or Open Circuit Voltage) of the participating cells. Even perfectly balanced cells though will exhibit different output voltages because of differences in their internal impedances. The difference in voltage will depend on the load current frequency and intensity. A method is described for re-distributing charge in such a way so when the worst (from the point of view of voltage spread) possible load conditions occur, cells will have similar outputs and none will cross the under-voltage threshold causing a premature shut down of the battery.

Description

[0001]This application claims the benefit of U.S. application Ser. No. 61 / 408,505 filed Oct. 29, 2010, which application is incorporated herein by reference for all purposes.BACKGROUND[0002]The challenge of balancing individual cells connected in series is a well-known issue in the battery industry. Cells connected in series to form a battery system, even if they were “ideally” manufactured and identically characterized, over time will exhibit deviating electrochemical behavior. These behavioral differences are due, among other reasons, to manufacturing tolerances that get accented over time, but also due to differences in the environment within which each individual cell operates.[0003]There are two major concerns regarding cell imbalance. The first one regards maximizing the charge a battery system can accept. The goal is to achieve 100% SOC for the whole battery system. The second concern regards the ability of the battery to provide the maximum amount of stored charge to the use...

Claims

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Application Information

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IPC IPC(8): H02J7/00
CPCH01M10/441H02J7/007H02J7/0021H02J7/0014Y02E60/10H02J7/0016H02J7/0019H02J7/0048
InventorMILIOS, IOANNIS
OwnerSENDYNE