Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
  • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
  • G01R31/396—Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or discharging batteries or for supplying loads from batteries
  • H02J7/50—Circuit arrangements for charging or discharging batteries or for supplying loads from batteries acting upon multiple batteries simultaneously or sequentially
  • H02J7/52—Circuit arrangements for charging or discharging batteries or for supplying loads from batteries acting upon multiple batteries simultaneously or sequentially for charge balancing, e.g. equalisation of charge between batteries
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or discharging batteries or for supplying loads from batteries
  • H02J7/80—Circuit arrangements for charging or discharging batteries or for supplying loads from batteries including monitoring or indicating arrangements
  • H02J7/82—Control of state of charge [SOC]

Definitions

• This invention relates generally to voltage measuring devices and methods, and more specifically to devices and methods monitoring battery cells in a battery stack.
• each cell of a battery stack is monitored because the voltage for each cell may drift too high or too low for a particular application or a particular cell may stop working, affecting the overall performance of the battery stack.
• Circuits that monitor the battery cells in the battery pack monitor the voltage across each cell and the voltage for the entire series.
• a mechanical tab electrically connects each battery cell to the monitoring circuit.
• the mechanical tab over time may become disconnected due to physical conditions such as dropping the battery pack.
• the circuit loses the ability to monitor individual cells.
• a battery cell tab monitoring apparatus includes a conductive element electrically connected between two battery cells.
• the conductive element is connected to a sensing circuit.
• the sensing circuit includes a pull-down current source connected to pull current from the conductive element and/or a pull-up current source connected to drive current into the conductive element.
• a voltage measuring circuit is connected to sense voltages during operation of the pull-down current source and the pull-up current source. The measured voltage may be used to determine the status of the conductive element. For instance, absolute voltages or voltage variations beyond certain thresholds can indicate that the conductive element such as a battery cell tab is flexing or cracking, which can be a precursor to the breaking of the battery cell tab.
• Absolute voltages or voltage variations beyond other thresholds can indicate that the conductive element is fully disconnected from the battery cells.
• One approach to sensing the different absolute voltages and voltage variations is to push and pull different currents to and from the conductive element. Alternating the pushing and pulling reduces battery cell imbalance caused by the voltage checks and provides an opportunity to make additional voltage readings.
• the current sources used to push and pull the sensing currents may also be used to bring the battery cells into balance when an imbalance is detected.
• FIG. 1 is a circuit diagram of an example battery cell tab monitor configured in accordance with various embodiments of the invention
• FIG. 2 is a circuit diagram of an example battery cell tab monitor configured in accordance with various embodiments of the invention.
• FIG. 3 is a flow diagram of the operation of an example battery cell tab monitor detecting a fixed voltage threshold as configured in accordance with various embodiments of the invention.
• FIGS. 4-6 are sample waveforms that may be observed in the system when configured in accordance with various embodiments of the invention.
• FIG. 7 is a flow diagram of the operation of an example battery cell tab monitor detecting a voltage shift as configured in accordance with various embodiments of the invention.
• FIGS. 8-10 are sample waveforms that may be observed in the system when configured in accordance with various embodiments of the invention.
• FIG. 1 illustrates an example embodiment circuit 100.
• the circuit 100 includes a conductive element 105 electrically connected to a first battery cell 110 and a second battery cell 115.
• the conductive element 105 is electrically connected to a sensing circuit 120.
• the sensing circuit 120 includes a pull-down current source 125 connected to pull current from the conductive element 105.
• the sensing circuit 120 also includes a pull-up current source 130 connected to drive current into the conductive element 105.
• the pull-down current source 125 and the pull-up current source 130 can each operate with just one current source, in a different approach each may include multiple, independently controllable current sources.
• the pull-down current source 125 includes a first pull-down current source 127 and a second pull-down current source 129.
• the pull-up current source 130 includes a first pull-up current source 132 and a second pull-up current source 135.
• the sensing circuit 120 contains a first control circuit 140 and a second control circuit 145.
• the first pull-down current source 127 provides about 1 milliamp of current and is controlled by the first control circuit 140.
• the second pull-down current source 129 provides about 10 microamps of current and is controlled by the second control circuit 145.
• the first pull-up current source 132 provides about 1 milliamp of current and is controlled by the first control circuit 140 and the second pull-up current source 135 provides about 10 microamps of current and is controlled by the second control circuit 145.
• the control circuits 140 and 145 may be hardware based controllers or firmware based controllers.
• the first control circuit 140 comprises a hardware based controller that can turn on and off the first pull-up current source 132 and the first pull-down current source 127.
• the second control circuit 145 comprises a firmware based controller that can turn on and off the second pull-up current source 135 and the second pull-down current source 129.
• a hardware based controller 240 includes comparators 220 and 222 connected to compare voltages from the conductive element 105 to different threshold voltages Vthl and Vth2 as described in more detail below.
• the signals from the comparators 220 and 222 are provided to a hardware logic element 224, such as those know to the skilled in the art, that in turn provides a push current control 228 signal to control the first pull-up current source 132 and a pull current control 226 signal to control the first pull-down current source 127.
• a firmware based controller 245 as shown in FIG. 2 includes a microcontroller
• the analog-to-digital converter 254 is connected to receive voltages from the conductive element 105 and convert those voltage signals to a digital signal for processing by the microcontroller 252.
• the microcontroller 252 is connected to control the operation of the analog-to-digital converter 254.
• the microcontroller 252 is also programmed and configured to create and send a push current control 258 signal to control the second pull-up current source 135 and a pull current control 256 signal to control the second pull-down current source 129 based upon the voltage digital signals provided by the analog-to-digital converter 254.
• Switches 262, 264, 266, and 268 control the sensing of voltages and the provision of current for the hardware based controller 240, and switches 272, 274, 276, and 278 control the sensing of voltages and the provision of current for the firmware based controller 245.
• the sensing circuit 100 includes a voltage measuring circuit 150 connected to sense voltages during operation of the pull-down current source 127 and the pull-up current source 132.
• the sensing circuit 100 contains a second voltage measuring circuit 155 connected to sense voltages during operation of the pull-down current source 129 and the pull-up current source 135.
• voltage measuring circuit 150 are connected to determine the status of the conductive element 105.
• voltage measuring circuit 150 can compare voltage measured during operation of the pull-down current source 127 to a first voltage threshold and the voltage measuring circuit 150 can compare the voltage measured during operation of the pull-up current source 132 to a second voltage threshold. Based on the comparisons of the measured voltages to either fixed thresholds or on the measured voltage variations, the control circuit 140 can determine the status of the conductive element 105.
• voltage measuring circuit 155 can compare voltage measured during operation of the pull-down current source 129 to a third voltage threshold and the voltage measuring circuit 155 can compare the voltage measured during operation of the pull-up current source 135 to a fourth voltage threshold. Based on the comparisons of the measured voltages to either fixed thresholds or on the measured voltage variations, the control circuit 145 can determine the status of the conductive element 105.
• the control circuit 140 controls the pull-up current source 132 and the pull-down current source 127 to alternate in operation to balance the load on the first battery cell 110 and the second battery cell 115.
• alternating between the pull-down current source 127 and the pull-up current source 132 allows the voltage measuring circuit 150 to compare voltage variations in both the positive and negative directions to confirm the accuracy of the measurements. For example, a measurement made during operation of the pull-down current source 127 can be compared to a measurement made during operation of the pull-up current source 132 to determine whether a given measurement lies within an expected range such that spurious measurements can be disregarded.
• the circuit 100 need not include both a pull-up current source
• the circuit 100 includes other known load balancing mechanisms, the need to use the pull-up current source 130 and pull-down current source 125 to reduce load imbalance is reduced, and one of the pull-up current source 130 or the pull-down current source 125 can be implemented to perform the voltage checks as described herein. In such an approach, the elements of the unused current source can be removed or left out of the circuit 100.
• control circuit 140 operates the first pull-down current source 127 and/or the first pull-up current source 132 periodically to determine whether the conductive element 105 electrical connection is intact.
• the control circuit 145 may operate the second pull-down current source 129 and/or the second pull-up current source 135 periodically to monitor quality of the conductive element 105 electrical connection.
• the first pull-down current source 127 is controlled to pull about 1 milliamp out of the conductive element 105 for about two milliseconds. Then, the first pull-up current source 132 is controlled to push about 1 milliamp into the conductive element 105 for about two milliseconds. In this example, this check is performed once every eight seconds. If the electrically conductive element 105 is disconnected from the first battery cell 110 and the second battery cell 115, the resulting voltage at the disconnect will be sensed by the voltage measuring circuit 150 both at a low threshold as occurs when the pull-down current source 127 operates and at a high threshold when the pull-up current source 132 operates. Upon meeting both these low and high thresholds on consecutive checks, the sensing circuit 120 will signal this to be a disconnected conductive element or tab such that the device enters a fault condition.
• the sensing circuit 120 applies or pulls a larger current such as about 1 milliamp to sense whether a voltage variation reaches a certain threshold from which it may be determined that the conductive element 105 has broken and is no longer in electrical contact with the first battery cell 110 and the second battery cell 115A.
• a smaller current, such as about 10 microamps may be pulled from or pushed into the conductive element 105 to sense voltage variations that indicate wear of the conductive element 105.
• the control circuit 145 can receive information regarding relative charge of the first battery cell 110 and the second battery cell 115.
• the control circuit 145 operates the pull-up current source 135 and the pulldown current source 129 to balance the relative charge of the first battery cell 110 and the second battery cell 115.
• sensing circuitry as known in the art can determine an imbalance of charge between the first battery cell 110 and the second battery cell 115.
• the sensing circuitry in various approaches may comprise a controller circuit separate from those shown in FIG. 1 or may be in communication with control circuit 140 and/or control circuit 145. Such imbalances between cells in a battery pack can lead to poor performance including perhaps failure of the battery pack.
• the sensing circuit 120 can correct the imbalance of charge between the first battery cell 110 and the second battery cell 115 by pushing current or pulling current via the conductive element 105 using any of the current sources. Selective pushing and pulling of current into and out of particular battery cells can work to rebalance the relative cell charges of the battery pack. Moreover, depending on the amount of imbalance, a larger current may be applied by the first pull-down current source 127 or a smaller current may be applied by the second pull-down current source 129, depending on the amount of imbalance in the cells to be corrected.
• the remainder of the example circuit 100 shown in FIG. 1 includes well known elements used for the operation of a sensing circuit 120 used in conjunction with battery cells.
• resistors 171, 172, and 173 work with capacitors 181 and 182 to filter voltage transients on the first battery cell 110, the second battery cell 115, and the combination of the battery cells 110 and 115.
• circuit node VC1_CTAB It is also possible to eliminate the circuit node VC1_CTAB and only use circuit node VCl for both pull-down current sources and both pull-up current sources, with consideration given to the effects of resistor 172 if the VC1_CTAB circuit node is eliminated. Additional elements could be added in other approaches.
• the method 300 includes at step 305 pulling current out of a conductive element 105 disposed between a first battery cell 110 and a second battery cell 115. At step 310 the method includes sensing a first voltage across the first battery cell 110 while pulling current out of the conductive element 105.
• the method includes pushing current into the conductive element 105 disposed between the first battery cell 110 and the second battery cell 115 and at step 320 sensing a second voltage across the first battery cell 110 while pushing current into the conductive element 105.
• the steps of pulling current 305 and pushing current 315 may be performed in either order.
• the step of pushing current 215 from the conductive element 105 may be performed before pulling current 305 through the conductive element 105.
• either steps 305 and 310 or steps 315 and 320 are skipped, such that current is either pulled into or pushed from the conductive element 105; such an approach may be accompanied by application of other known load balancing methods.
• the method includes determining a connection status of the conductive element 105 based at least in part the first voltage and the second voltage.
• the steps of pulling current 305 out of the conductive element 105 and pushing current 315 into the conductive element 105 can be alternated periodically.
• either the step of pulling current 305 out of the conductive element and/or pushing the current 315 into the conductive element may include pushing or pulling a first current at a first interval and pushing or pulling a second current and a second interval.
• the step of pulling the first current at the first interval may include pulling a current of about 1 milliamp to determine whether the conductive element 105 is connected to a sensing circuit 120.
• the step of pulling the second current at the second interval may include pulling a current of about 10 microamps to determine a degradation of the connection between the conductive element 105 and the sensing circuit 120.
• the step 330 of determining the connection status of the conductive element 105 is based at least in part on the voltage measured at step 310, comparing the first voltage to a first voltage threshold at step 340 and at step 350 comparing the second voltage measured at step 320 to a second voltage threshold at step 350.
• an indication of the connection status of the connective element 105 is provided according to a function of the first voltage as compared to the first voltage threshold and the second voltage as compared to the second threshold.
• the specific voltage thresholds may vary according to a specific application.
• FIG. 4 shows the current and voltage waveforms expected when a 1 milliamp current is applied when the conductive element 105 is connected and has a low resistance.
• the indicators VC1 and VC1_CTAB indicate the nodes on the example circuit of FIG. 1 where the represented currents and voltages are applied and measured.
• a 1 milliamp current is pulled out of the VC1_CTAB node
• the voltage at the VC1 node does not change appreciably and does not cross the fixed low threshold Ti.
• the conductive element 105 is declared to be connected.
• FIG. 5 shows the current and voltage waveforms expected when the conductive element 105 is disconnected or has a very high resistance.
• the voltage measured at VC1 crosses the fixed low threshold Ti when the pull-down current source 127 is active and crosses the fixed high threshold T 2 when the pull-up current source 132 is active. This condition indicates the conductive element 105 is disconnected and open.
• FIG. 6 shows the current and voltage waveforms expected when the conductive element 105 is connected and has a moderate resistance.
• the voltage measured at VC1 varies but does not cross the fixed low threshold when the pull-down current source 127 is active or the fixed high threshold when the pull-up current source 132 is active. Because the fixed thresholds were not exceed, the system declares the conductive element 105 to be connected.
• the method 700 includes at step 702 a measurement of the initial voltage across the first battery cell 110. Subsequent voltage measurements are compared to this initial voltage to determine the state of the conductive element 105.
• the method includes pulling current out of a conductive element 105 disposed between a first battery cell 110 and a second battery cell 115.
• the method includes sensing a voltage drop across the first battery cell 110 caused by pulling current out of the conductive element 105.
• the method includes pushing current into the conductive element 105 disposed between the first battery cell 110 and the second battery cell 115 and at step 720 sensing a voltage rise across the first battery cell 110 caused by pushing current into the conductive element 105.
• the steps of pulling current 705 and pushing current 715 may be performed in either order.
• the step of pushing current 715 into the conductive element 105 may be performed before pulling current 705 through the conductive element 105.
• either steps 705 and 710 or steps 715 and 720 are skipped, such that current is either pulled into or pushed from the conductive element 105; such an approach may be accompanied by application of other known load balancing methods.
• the method includes determining a connection status of the conductive element 105 based at least in part on the voltage drop and the voltage rise sensed at steps 710 and 720.
• determining the connection status includes comparing a difference between the first voltage and an initial voltage to a first threshold to make a first comparison at step 740 and comparing a difference between the second voltage and the initial voltage to a second voltage threshold to make a second comparison at step 750.
• the first threshold and the second threshold are determined based on the last measured voltage such that the thresholds are measuring the total voltage change during a particular operation of one of the current sources.
• the method includes providing an indication of the connection status of the conductive element according to the first comparison and the second comparison.
• a firmware based control circuit 145 can command a 10 microampere current to be pulled out of the center tab or conductive element 105 for about 8 milliseconds.
• the control circuit 145 then turns off the pull-down current source 129 for 10 milliseconds, followed by the control circuit 145 controlling the second pull-up current source 135 to provide 10 microamperes of current to the conductive element 105 for about 8 milliseconds. If the conductive element 105 is partially disconnected, the control circuit 145 is able to detect voltage at the conductive element 105 moving due to the 10 microampere current being pulled from or pushed into the conductive element 105. This moving voltage is an indication of wear on the conductive element 105 or center tab disposed between the first battery cell 110 and the second battery cell 115.
• FIG. 8 shows the current and voltage waveforms expected when a ten microampere current is applied when the conductive element 105 is connected and has a low resistance.
• the indicators VC1 and VC1_CTAB indicate the nodes on the example circuit of FIG. 1 where the represented currents and voltages are applied and measured.
• the voltage at the VC1 node does not change appreciably from the initial voltage and does not cross the variable low threshold T 3 .
• the conductive element 105 is declared to be connected.
• FIG. 9 shows one possible set of current and voltage waveforms expected when the conductive element 105 is disconnected or has a very high resistance.
• the voltage measured at VC1 crosses the variable low threshold T 3 when the pull-down current source 129 is active and crosses the variable high threshold T 4 when the pull-up current source 132 is active.
• This condition indicates the conductive element 105 is disconnected and open.
• the low threshold T 3 and the high threshold T 4 measure a voltage delta or change during the application of current from the current sources.
• the high threshold T 4 is measured from the voltage at the start of the application of current from the pull-down current source 132.
• FIG. 10 shows one possible set of current and voltage waveforms expected when the conductive element 105 is connected and has a moderate resistance.
• the voltage measured at the VC1 node crosses the low threshold T 3 when the pull-down current source 129 is active and the high threshold T 4 when the pull-up current source 135 is active.
• the threshold may be variable to test various conditions. Accordingly, when a particular threshold is crossed, it is possible to determine the magnitude of the resistance, and thus the amount of wear, of the conductive element 105.
• a particular example circuit for performing this method would include a conductive element 105 electrically connected to a first battery cell 110 and a second battery cell 115 and electrically connected to a sensing circuit 120.
• the sensing circuit 120 includes a first pull-down current source 127 connected to periodically pull a first current from the conductive element 105 for a first amount of time and a first pull-up current source 132 connected to periodically push current approximately equal to the first current into the conductive element 105 for approximately the first amount of time.
• a second pull-down current source 129 is connected to periodically pull a second current from the conductive element 105 for a second amount of time, and a second pull-up current source 135 is connected to periodically drive current approximately equal to the second current into the conductive element 105 for approximately the second amount of time.
• the first current is about 1 milliamp and the second current is about 10 microamps.
• a first control circuit 140 is connected to control operation of the first pull-down current source 127, the first pull-up current source 132, and a second control circuit 145 is connected to control operation of the second pull-down current source 129, and the second pull- up current source 135.
• a first voltage measuring circuit 150 is connected to sense voltages during operation of the first pull-down current source 127, the first pull-up current source 132, and a second voltage measuring circuit 155 is connected to sense voltages during operation of the second pull-down current source 129, and the second pull-up current source 135.
• the control circuits 140 and 145 are connected to determine a status of the conductive element 105 based at least in part on the measured voltages such that the control circuits 140 and 145 compare voltages during operation of at least one of the first pull-down current source 127 and the first pull-up current source 132 to a first voltage threshold, and the control circuits 140 and 145 compare voltages during operation of at least one of the second pulldown current source 129 and the second pull-up current source 135 to a second voltage threshold.
• the first pull-down current source 127 and the first pull-up current source 132 are controlled by at least one hardware based control circuit 140
• the second pulldown current source 129 and the second pull-up current source 135 are controlled by at least one firmware based control circuit 145
• the control circuit 145 can also be configured to receive information regarding relative charge of the first battery cell 110 and the second battery cell 115 and wherein the controller circuit 145 operates the second pull-up current source 135 and the second pull-down current source 129 to balance the relative charge of the first battery cell 110 and the second battery cell 115.
• a battery cell tab monitoring circuit as described herein can determine when the connection tab between two battery cells is disconnected and when the battery cell tab is exhibiting signs of wear that can be a precursor to breaking of the battery cell tab. Versions of the circuit also enable selective pushing and pulling of current into and out of the battery cell tab to balance the charge of battery cells in a battery stack when the battery cell charges become imbalanced.

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Secondary Cells (AREA)
• Charge And Discharge Circuits For Batteries Or The Like (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (2)

Family

ID=44258046

Family Applications (1)

Country Status (4)

Cited By (2)

Families Citing this family (21)

Family Cites Families (15)

• 2010
  • 2010-01-14 US US12/687,173 patent/US8547064B2/en active Active
  • 2010-12-13 CN CN201080065473.XA patent/CN102834997B/zh active Active
  • 2010-12-13 WO PCT/US2010/060087 patent/WO2011087658A2/en not_active Ceased
  • 2010-12-13 JP JP2012548942A patent/JP5653454B2/ja active Active

Also Published As

Similar Documents

Legal Events