Patent Description:
Battery packs in electric vehicles (EV) or hybrid electric vehicles (HEV) can be connected in series or parallel. When battery packs are connected in parallel, significant differences in battery pack voltages can lead to high voltage equalizing currents, and high equalizing currents may result in a difficult and/or time-consuming process to connect a battery pack to the configuration. Moreover, the voltage equalizing current may exceed the maximum battery current limits causing pack shutdown or damage. <CIT> discloses a power storage device including a plurality of modules each including secondary batteries, a charging switch that controls charging to the secondary batteries, a discharging switch that controls discharging of the secondary batteries, a voltage measuring unit that measures a voltage of the module, and a switch control unit that controls one or both of the charging switch and the discharging switch. The modules are connected in parallel. The switch control unit maintains an on state of the discharging switch for at least one of the modules for a predetermined period, and controls the charging switch of the module in which a maximum module charging current estimated based on the voltage of the module is a predetermined value or less, to be in an on state. <CIT> discloses a storage battery system including a plurality of battery units having a plurality of battery cells and a power adjustment device connected to the battery units via respective contactors and connected to a main circuit. A storage battery management device includes a minimum value determination unit and a controller. The minimum value determination unit, from the battery units in which a difference between a maximum cell voltage and a minimum cell voltage of the battery cells forming each of the battery units is equal to or less than a certain value, determines a minimum value of the minimum cell voltage. The controller controls a cell balance process of the battery unit managed by itself, by using the minimum value of the minimum cell voltage determined by the minimum value determination unit as a cell balance target voltage. According to one aspect of the present invention there is provided a method of charging or discharging a plurality of battery packs as defined in claim <NUM>. According to another aspect of the invention there is provided a battery pack system as defined in claim <NUM>. Preferred features of the invention are recited in the dependent claims.

Referring first to <FIG>, a battery pack system <NUM> showing a battery pack configuration 100A is provided. The battery pack configuration 100A includes battery packs 102A, 102B, 102C, and 102D with corresponding contactors 104A, 104B, 104C, and 104D in the open position where the battery circuits are open and inactive (i.e., current cannot flow to or from the battery packs within the circuit). The contactors 104A-D function to switch an electrical power circuit between a closed circuit and an open circuit for the corresponding battery packs 102A-D. The battery pack configuration 100A shows an initial condition of the battery pack system <NUM> where the battery pack 102D has a state of charge (SOC) that is substantially equal to the minimum SOC as indicated in <FIG> while the states of charge (SOCs) of the battery packs 102A-C are between the shown minimum SOC and the maximum SOC of <FIG> and are substantially equal to each other. As also shown in <FIG>, the battery pack configuration 100A transitions to the battery pack configuration 100B via a charging method disclosed further herein. The battery pack configuration 100B includes the battery packs 102A-D each having the maximum SOC (as indicated in <FIG>) and the contactors 104A-D in the closed position.

Referring now to <FIG>, and <FIG>, a graphical representation of the charging method further described herein is shown. As shown in <FIG>, a battery voltage curve <NUM> in terms of battery SOC is provided where a battery pack (as denoted by an asterisk) is provided at region A. The battery pack has a substantially lower SOC and battery voltage as compared to the voltages and SOCs of the battery packs at region B. According to the method described herein in further detail, when charging the batteries, the battery pack at region A is charged first. As the battery pack is charged, the SOC and the voltage of the battery pack increase and move along a curve <NUM> towards the battery packs at region B. Once the battery pack's SOC and voltage are within a predetermined range of or substantially equal to the batteries at region B, the battery packs at region B may be connected to the previously charging pack with an acceptable equalizing current, and all packs begin to charge until the battery packs reach the maximum voltage and SOC at region C along the curve <NUM>.

<FIG> shows an alternate configuration of battery packs where multiple battery packs at region B have a substantially lower battery pack voltage and SOC than the battery pack at region A. In this instance, the multiple battery packs at region B are charged first until their respective SOCs and voltages are within a predetermined range of or substantially equal to the battery pack at region A. At which point, all the battery packs are charged until the battery packs reach the maximum voltage and SOC at region C along the curve <NUM>.

<FIG> illustrates a charging profile <NUM> and also illustrates a charging method (discussed further herein) of an embodiment of the battery system <NUM>. As shown at time zero, a battery pack #<NUM> has a voltage associated with position I and has the lowest voltage. As the battery pack #<NUM> is charged, the voltage of the battery pack #<NUM> increases along the charging profile <NUM> toward battery packs #<NUM>, #<NUM>, #<NUM>, #<NUM>, #<NUM>, and #<NUM>. When the voltage of the battery pack #<NUM> is within a predetermined range of or substantially equal to the voltage of the battery pack #<NUM>, the two packs are connected and the battery pack #<NUM> begins to charge in addition to the battery pack #<NUM>. A similar pattern follows for battery packs #<NUM>, #<NUM>, #<NUM>, #<NUM>, and #<NUM> as these battery packs are brought online to charge at various later times or simultaneously with the other battery packs depending on the predetermined voltage range as denoted in region II.

As charging continues through region III, the battery packs #<NUM> and #<NUM>-#<NUM> continue to charge. When the voltage of the battery packs #<NUM> and #<NUM>-#<NUM> are within a predetermined range or substantially equal to the voltage of the battery pack #<NUM>, the battery pack #<NUM> is brought online and begins to charge in conjunction with the battery packs #<NUM>, #<NUM>-<NUM> through region IV until charging of the battery packs is complete as indicated. Because the number of battery packs being charged at any one time may vary, the electrical power and/or current between battery packs may not be constant, and therefore voltage may not climb at a constant rate as illustrated. The current and/or electrical power between battery packs will increase at a roughly proportional rate with the number of battery packs that are online, while charging at a constant current will see voltage increasing at a decreasing rate as additional battery packs are brought online.

Referring now to <FIG>, a method <NUM> of charging the battery pack system <NUM> is shown. The method <NUM> begins at block <NUM> where a battery pack with the lowest voltage is determined and selected. This can be done by an electronic control module (ECM) in one embodiment. Then, at block <NUM>, the contactor of the selected pack is closed. The method <NUM> then proceeds to block <NUM> where the battery pack system <NUM> iteratively sequences through and checks the voltages of the other battery packs as discussed further herein and is shown at blocks <NUM> and <NUM>.

To check the voltages of the remaining battery packs (at block <NUM>), one of the remaining battery packs is selected and the voltage of the selected battery pack is measured. Then, at block <NUM>, the absolute value of the difference in voltages is calculated and compared to a predetermined dVmax value, wherein the dVmax value is the maximum acceptable voltage differential to safely connect the battery packs. The dVmax value is selected with consideration to the continuous charging current capability of the battery packs, as well as the internal resistance of the battery packs. The voltages of the respective battery packs are measured at no load and with no compensation for battery internal resistance voltage drop.

As shown in block <NUM>, if the absolute voltage difference is less than or equal to the dVmax value, then the method <NUM> proceeds to block <NUM> where the contactor of the selected pack is closed. The method <NUM> then proceeds back to block <NUM>, where another battery pack is selected and compared with the voltage threshold as outlined above. Conversely, if the absolute voltage difference between the lowest voltage battery pack and the selected battery packs is greater than the dVmax value, then method <NUM> does not close the contactor of the selected battery pack and returns to block <NUM>, where another battery pack is selected and compared with the dVmax value as outlined above. It is contemplated that in alternate embodiments, the dVmax value may vary depending on the vehicle operating parameters or engine configuration. The sequencing process iteratively cycles through the remaining battery packs as outlined in blocks <NUM>, <NUM>, and <NUM> until all the battery packs in the battery pack system <NUM> are checked.

The method <NUM> then proceeds to block <NUM> where the battery packs (selected from the process of blocks <NUM>, <NUM>, and <NUM>) with closed contactors begin to charge. After a predetermined period of time allotted for charging the selected battery packs at block <NUM>, the battery pack system <NUM> then sequences through the remaining battery packs via blocks <NUM>, <NUM>, and <NUM> in a similar iterative process as outlined above with respect to blocks <NUM>, <NUM>, and <NUM>.

To check the voltages of the remaining battery packs at block <NUM>, one of the remaining packs is selected and the voltage is measured. Then, at block <NUM>, the absolute value of the difference in voltage between the selected battery pack and the voltage of the charging battery pack(s) from block <NUM> is calculated. The absolute voltage difference is then compared with the dVmax value. As shown in block <NUM>, if the voltage difference is less or equal to than the dVmax value, then the method <NUM> proceeds to block <NUM> where the contactor of the selected pack is closed. The method <NUM> then proceeds back to block <NUM>, where another battery pack of the remaining battery packs is selected and compared with the dVmax value as outlined above. Conversely, if the voltage difference between the charging battery pack(s) and the selected battery packs is greater than the dVmax value, then the method <NUM> does not close the contactor of the selected battery pack and returns to block <NUM> where another battery pack is selected and compared with the dVmax value as outlined above. It is contemplated that in alternate embodiments, the dVmax value may vary depending on the vehicle operating parameters or engine configuration. The sequencing process iteratively cycles through the remaining battery packs as outlined in blocks <NUM>, <NUM>, and <NUM> until all the battery packs in the battery pack system <NUM> are checked.

The method <NUM> then proceeds to block <NUM> where the selected packs and the previously charging packs are charged. After a predetermined time period of charging, the method <NUM> proceeds to block <NUM> where the battery pack system <NUM> determines whether charging is complete. In one embodiment, charging is complete when all of the battery packs of the battery pack system <NUM> are at the pre-established maximum SOC setting and the pre-established maximum voltage setting. If charging is complete, then the method <NUM> moves to block <NUM> where the method <NUM> is stopped. If charging is not complete; however, the method <NUM> returns to block <NUM> to iteratively check the remaining battery packs as outlined above.

Referring now to <FIG>, an alternative charging method <NUM> is shown. Method <NUM> is similar to the method <NUM> discussed above, where the difference between the methods is described further herein.

After a predetermined amount of time of charging for the selected battery pack (selected from blocks <NUM>-<NUM>) at block <NUM>, the battery pack system <NUM> cycles through and checks the voltages of the remaining battery packs and selects the battery pack having the lowest voltage. Once the lowest voltage battery pack is selected, the method <NUM> then proceeds to block <NUM> where, similar to block <NUM>, the absolute voltage difference of the selected battery pack is and the charging battery pack(s) is calculated and compared to a predetermined dVmax value. If the voltage difference is less than or equal to the dVmax value, then the contactor of the selected pack is closed at block <NUM>, and the method <NUM> returns to block <NUM> where the battery pack with the next lowest voltage is selected, if applicable. Conversely, if the absolute voltage difference between the selected battery pack and the voltage of the charging battery pack(s) is greater than the dVmax value, then the method <NUM> does not close the contactor of the selected battery pack and returns to block <NUM> where the battery pack with the next lowest voltage of the remaining battery packs is selected, and the absolute voltage difference is calculated and compared with the dVmax value as outlined above. The sequencing process iteratively cycles through the remaining battery packs as outlined in blocks <NUM>, <NUM>, and <NUM> until all the battery packs in the battery pack system <NUM> are checked.

The method <NUM> then proceeds to block <NUM> where the selected packs and the previously charging packs are charged. After a predetermined period of time allotted for charging the batteries, the method <NUM> proceeds to block <NUM> where the battery pack system <NUM> determines whether charging is complete. As mentioned previously, charging is complete when all the battery packs of the battery pack system <NUM> are at the pre-established maximum SOC setting and the pre-established maximum voltage setting. If the condition at block <NUM> is met, then the method <NUM> moves to block <NUM> where the method <NUM> is stopped. If the condition at block <NUM> is not met, however, the method <NUM> returns to block <NUM> to check the voltages of the remaining battery packs as outlined above.

Referring again briefly to <FIG>, if a new battery pack 102d is installed with a large SOC disparity from the pre-existing packs 102a-102c, the charging method disclosed herein will automatically accommodate such new battery pack 102d by charging the new pack 102d without any manual intervention. Similarly, if any individual battery pack <NUM> fails, or an anomaly during use of a battery pack <NUM> causes the corresponding contactor <NUM> to open so that the battery pack <NUM> is not used for the remainder of the vehicle mission, the charging method disclosed herein will automatically bring all battery packs <NUM> to the same SOC without any manual intervention.

Referring to <FIG>, in some embodiments, the voltage of the batteries is measured according to a bus voltage rather than an open circuit voltage of the individual battery. In such embodiments, battery voltage may vary depending on the amount of current being charged to or discharged from the battery, and the open circuit voltage cannot be easily and accurately calculated due to a significant amount of current inflow. In such a case, when a subsequent battery pack is brought online, it will likely not be at equilibrium with a previous pack or packs which have already undergone charging, i.e. will likely have a much higher open circuit voltage that is substantially equal to the bus voltage of the previous pack or packs. Therefore, when charging resumes, the new pack will already be at a higher potential than the previous packs, causing the new pack to receive a disproportionately low amount of a charging current and the previous packs receiving a disproportionately high amount of the charging current. The higher current may cause damage to the previous packs.

A charging profile <NUM> is illustrated in <FIG>, including a charging method (discussed further herein) of an embodiment of the battery system <NUM> to avoid disproportionate allocation of a charging current. The charging profile <NUM> includes a measured bus voltage line <NUM> and an open circuit voltage line <NUM>. As shown at time zero, a battery pack #4a has an open circuit voltage associated with position I, which is the lowest voltage among the battery packs shown. The battery pack #4a therefore receives the charging current to begin charging. A bus voltage is generated according to the line <NUM>, which creates a significant disparity between the measured bus voltage and the actual open circuit voltage according to line <NUM>. As the battery pack #4a is charged, the voltages of the battery pack #4a increase along the charging profile <NUM> toward battery packs #6a, #1a, #5a, #3a, #7a, and #8a.

As the measured bus voltage of the battery pack #4a approaches the voltage of the battery pack #6a, the charging current is reduced, lowering the measured bus voltage of the battery pack #4a. As the charging current approaches zero, the bus voltage approaches the open circuit voltage of battery pack #4a. When the charging current is low and the bus voltage of the battery pack #4a is within a predetermined range of or substantially equal to the voltage of the battery pack #6a, the two packs are connected and the battery pack #6a begins to charge in addition to the battery pack #4a. A similar pattern follows for battery packs #1a, #5a, #3a, #7a, and #8a as these battery packs are brought online to charge at various later times or simultaneously with the other battery packs depending on the predetermined voltage range as denoted in region II.

As charging continues through region III, the battery packs #1a and #3a-#8a continue to charge. As described above, when the measured bus voltage of the battery packs #1a and #3a-#8a are within a predetermined range or substantially equal to the voltage of the battery pack #2a, the battery pack #2a is brought online and begins to charge in conjunction with the battery packs #1a and #<NUM>-#<NUM> through region IV until charging of the battery packs is complete as indicated.

For example, now referring to <FIG>, the charging method of a battery pack system <NUM> is shown. The battery pack system <NUM> includes four battery packs 132A-D with corresponding contactors 134A-D in an open position where the battery circuits are open and inactive (i.e., current cannot flow to or from the battery packs within the circuit) and in a closed position where the battery circuits are closed. The contactors 134A-D function to switch an electrical power circuit between a closed circuit and an open circuit for the corresponding battery packs 132A-D. <FIG> shows an initial condition of the battery pack system <NUM> where the battery packs 132A, 132B, and 132C have a state of charge (SOC) of approximately <NUM>%; the contactors 134A-C of the corresponding battery packs 132A-C are closed so that the battery packs 132A-C are charging with a maximum charge current value allowed as determined by the battery pack system <NUM>. The battery pack 132D has an SOC of approximately <NUM>% and an open contactor 134D, so that the battery pack 132D is not charging.

As the voltages of the battery packs 132A-C approach and slightly exceed the voltage of the battery pack 132D as shown in <FIG>, the charge current is reduced in steps until the charge current reaches a low voltage. The charging process then continues at a low charge current until the desired target voltage is reached in each of the battery packs 132A-C. As shown in <FIG>, the contactor 134D of the battery pack 132D is then closed, and the charging process continues with the battery packs 132A-D.

Referring now to <FIG>, an alternative method <NUM> of charging the battery pack system <NUM> is shown. Method <NUM> is similar to the method <NUM> discussed above, where the difference between the methods is described further herein.

As the battery pack or battery packs selected from blocks <NUM> and <NUM>-<NUM> begin to charge at block <NUM>, the charging process begins by slowly or methodically increasing the voltage value of the charge current to avoid overshooting any remaining packs that may have slightly higher voltages, until the charge current is at a predetermined maximum charge current value allowed by the system. After a predetermined period of time allotted for charging the selected battery pack(s) at block <NUM>, the battery pack system <NUM> selects one of the remaining battery packs at block <NUM> and measures the voltage of the selected battery pack. In another embodiment, similar to the method <NUM> discussed above, the battery pack system <NUM> may identify and select the remaining battery pack with the lowest voltage. The absolute voltage difference between the selected battery pack and the charging battery pack(s) is calculated. The difference is then compared with a predetermined dVmax value. As shown in block <NUM>, if the absolute voltage difference is greater than the dVmax value, the method <NUM> returns to block <NUM> to select another battery pack, if applicable. If the absolute voltage difference is less than or equal to the dVmax value, then the method <NUM> proceeds to block <NUM>, where it is determined whether the system voltage, or the average measured voltage of the charging battery packs, is greater than the voltage of the selected pack. If the system voltage is greater, then the charge current is reduced at block <NUM> until the charge current inflow is below a predetermined inflow value. The contactors on the selected pack are then closed at block <NUM>, and the process begins again at block <NUM>. If the system voltage is not greater, then the contactor on the selected pack is closed at block <NUM> and the process begins again at block <NUM>. The sequencing process iteratively cycles through the remaining battery packs as outlined in blocks <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> until all the remaining battery packs in the battery pack system <NUM> are checked.

The method <NUM> then proceeds to block <NUM>, where the selected packs and the previously charging pack(s) begin charging by slowly or methodically increasing the voltage value of the charge current to avoid overshooting any remaining packs that may have slightly higher voltages, until the charge current is at the maximum charge current value allowed by the system. After a predetermined time period of charging, the method <NUM> proceeds to block <NUM>, where the battery pack system <NUM> determines whether charging is complete. In one embodiment, charging is complete when all of the battery packs of the battery pack system <NUM> are at the pre-established maximum SOC setting and the pre-established maximum voltage setting. If charging is complete, then the method <NUM> moves to block <NUM> where the method is stopped. If charging is not complete, however, the method <NUM> returns to block <NUM> to iteratively check the remaining battery packs as outlined above.

Generally, when discharging battery packs (e.g., during a drive cycle of a vehicle), battery pack(s) with the largest voltage(s) have closed contactors within the battery pack system <NUM> and are used first in the operation of the vehicle. As the voltage(s) of the battery pack(s) decrease during use, the voltage of the other disconnected battery pack(s), if any, are monitored to determine if the voltage of the disconnected battery pack(s) are within a voltage threshold of the discharging battery packs. Once the voltage(s) of the disconnected battery pack(s) is within a predetermined range of or substantially equal to the discharging battery pack(s), the contactors of the disconnected battery pack(s) are closed and the battery packs are used in conjunction with the prior discharging battery pack(s).

Referring to <FIG>, the battery pack system <NUM> in battery pack configurations 150A and 150B is provided. Similar to the battery pack configuration 100A, the battery pack configurations 150A and 150B include battery packs 102A-D with corresponding contactors 104A-D in the open position where the battery circuits are open and inactive (i.e., current cannot flow to or from the battery packs within the circuit). The contactors 104A-D function to switch an electrical power circuit between a closed circuit and an open circuit for the corresponding battery packs 102A-D. The battery pack configuration 150A shows an initial condition of the battery pack system <NUM> where the battery pack 102D has a state of charge (SOC) that is between the shown minimum SOC and the maximum SOC, while the states of charge (SOCs) of the battery packs 102A-C are substantially equal to the maximum SOC. The battery pack configuration 150A transitions to the battery pack configuration 150B when the vehicle is driven via a method disclosed further herein. The battery pack configuration 150B includes the battery packs 102A-D each having the minimum shown SOC and the contactors 104A-D in the closed position.

<FIG> illustrates a discharging profile <NUM> of a general discharging method (as discussed in greater detail herein) of an embodiment of the battery pack system <NUM>. As shown, at time zero, battery packs #<NUM>, #<NUM>, #<NUM>, #<NUM>, #<NUM>, #<NUM>, and #<NUM> have substantially the same voltage and are substantially greater than the voltage of battery pack #<NUM>. As such, the contactors for battery packs #<NUM>, #<NUM>, #<NUM>, #<NUM>, #<NUM>, #<NUM>, and #<NUM> are closed and these battery packs are used during operation of the vehicle throughout region IA of <FIG>. During use, the voltages of the battery packs diminish, and at a time denoted by IIIA, the voltage difference between battery packs #<NUM>, #<NUM>, #<NUM>, #<NUM>, #<NUM>, #<NUM>, and #<NUM> and battery pack #<NUM> is within a pre-determined voltage range of or substantially equal to battery packs #<NUM>, #<NUM>, #<NUM>, #<NUM>, #<NUM>, #<NUM>, and #<NUM>. The contactor for battery pack #<NUM> is then closed thereby bringing battery pack #<NUM> online for use during operation of the vehicle. After time IIIA, all the battery packs are used during operation of the vehicle until the drive cycle is completed.

Because the number of battery packs being discharged at any one time may vary, the electrical power and/or current between battery packs may not be constant, and therefore voltage may not fall at a constant rate as illustrated. The current and/or electrical power between battery packs will decrease at a roughly proportional rate with the number of battery packs that are online, while discharging at a constant current will see voltage decreasing at an increasing rate as additional battery packs are brought online.

Referring now to <FIG>, a method <NUM> of discharging a battery pack system <NUM> is shown. The method <NUM> begins at block <NUM> where a battery pack with the highest voltage is determined and selected. Then, at block <NUM>, a contactor of the selected pack is closed bringing the selected pack online. The method <NUM> then proceeds to block <NUM> where the battery pack system <NUM> iteratively checks the voltages of the other battery packs as discussed further herein.

In checking the voltages of the remaining battery packs at block <NUM>, one of the remaining packs is selected and the voltage is measured. Then, at block <NUM>, the voltage of the selected battery pack is compared with the voltage of the lowest battery pack selected at block <NUM>, and the absolute difference in voltage between the packs is measured and compared to the predetermined dVmax value, wherein the dVmax value is the maximum acceptable voltage differential to safely connect the battery packs. The dVmax is selected with consideration to the continuous charging current capability of the battery packs, as well as the internal resistance of the battery packs. The voltages of the respective battery packs are measured at no load and with no compensation for battery internal resistance voltage drop.

As shown in block <NUM>, if the voltage difference is less or equal to than the dVmax value, then the method <NUM> proceeds to block <NUM> where the contactor of the selected pack is closed. The method <NUM> then proceeds back to block <NUM>, where another battery pack is selected and compared with the lowest voltage battery pack as outlined above. Conversely, if the absolute voltage difference between the lowest voltage battery pack and the selected battery packs is greater than the dVmax value, then the method <NUM> returns to block <NUM>, and another battery pack is selected and compared with the lowest voltage battery pack as outlined above. It is contemplated that in alternate embodiments, the dVmax value may vary depending on the vehicle operating parameters or engine configuration. The sequencing process cycles through the remaining battery packs as outlined in blocks <NUM>, <NUM>, and <NUM> iteratively until all the battery packs in the battery pack system <NUM> are checked.

The method <NUM> then proceeds to block <NUM> where the drive cycle of the vehicle begins and, correspondingly, the battery packs begin to discharge. After a predetermined period of time, to allow the selected batteries to charge at block <NUM>, the battery pack system <NUM> then sequences through the remaining battery packs via blocks <NUM>, <NUM>, and <NUM> in a similar iterative process as outlined above with respect to blocks <NUM>, <NUM>, and <NUM>.

To check the voltages of the remaining battery packs at block <NUM>, one of the remaining packs is selected, the voltage of the selected battery pack is compared with the voltage of the discharging battery pack(s) from block <NUM> at block <NUM>, and then the absolute voltage difference between the packs is calculated and compared to the predetermined dVmax value. As shown in block <NUM>, if the absolute voltage difference is less or equal to than the dVmax value, then the method <NUM> proceeds to block <NUM> where the contactor of the selected pack is closed. The method <NUM> then returns to block <NUM>, where another battery pack is selected and compared with the voltage of the discharging battery pack(s) as outlined above. Conversely, if the absolute voltage difference between the discharging battery pack(s) and the selected battery packs is greater than the dVmax value, then the method <NUM> returns to block <NUM>, and another battery pack is selected and compared with the voltage of the discharging battery pack as outlined above. It is contemplated that in alternate embodiments, the dVmax value may vary depending on the vehicle operating parameters or engine configuration. The sequencing process cycles through the remaining battery packs as outlined in blocks <NUM>, <NUM>, and <NUM> iteratively until all the battery packs in the battery pack system <NUM> are checked.

The method <NUM> then proceeds to block <NUM> where the selected packs in combination with the previously discharging packs are discharging or continued to discharge during the drive cycle of the vehicle. After a predetermined time period of discharging, the method <NUM> proceeds to block <NUM> where the battery pack system <NUM> determines whether the drive cycle of the vehicle is complete. In one embodiment, the drive cycle is complete when the drive cycle of the vehicle ends (e.g., when the mission of the vehicle is complete) or when all the battery packs of the battery pack system <NUM> are at the pre-established minimum SOC setting and the pre-established minimum voltage setting and are no longer capable of powering the vehicle. If the drive cycle is complete, then the method <NUM> moves to block <NUM> where the method <NUM> is stopped. If the drive cycle is not complete; however, the method <NUM> returns to block <NUM> to iteratively check the remaining battery packs as outlined above.

Referring now to <FIG>, an alternative discharging method <NUM> is shown. The method <NUM> is similar to the method <NUM> discussed above. The difference between the methods is described further herein.

After a predetermined amount of discharging time from when the selected batteries from blocks <NUM>-<NUM> begin discharging at block <NUM>, the battery pack system <NUM> checks the remaining battery packs (i.e., those with open contactors) and determines the battery pack having the highest voltage. Once this is completed, the method <NUM> then proceeds to block <NUM>, where similar to block <NUM>, the voltage of the selected battery pack is compared with the voltage of the charging battery pack(s), and the absolute voltage difference is calculated. The absolute voltage difference is then compared to a predetermined dVmax value. If the absolute voltage difference is less than or equal to the dVmax value, then the contactor of the selected pack is closed at block <NUM>, and the method <NUM> returns to block <NUM> where the battery pack with the next highest voltage is selected, if applicable. Conversely, if the absolute voltage difference between the selected battery pack and the voltage of the discharging battery pack(s) is greater than the dVmax value, then the method <NUM> does not close the contactor of the selected battery pack and returns to block <NUM> where the battery pack with the next highest voltage of the remaining battery packs is selected, and the absolute voltage difference is calculated and compared with the dVmax value as outlined above. The sequencing process iteratively cycles through the remaining battery packs as outlined in blocks <NUM>, <NUM>, and <NUM> until all the battery packs in the battery pack system <NUM> are checked.

After a predetermined period of time, the method <NUM> proceeds to block <NUM> where the battery pack system <NUM> determines whether the drive cycle is complete. As mentioned previously, the drive cycle is complete when the drive cycle of the vehicle ends (e.g., when the mission is complete) or when all of the battery packs of the battery pack system <NUM> are at the pre-established minimum SOC setting and the pre-established minimum voltage setting and are no longer capable of powering the vehicle. If the drive cycle is complete, then the method <NUM> moves to block <NUM> where the method <NUM> is stopped. If the drive cycle is not complete; however, the method <NUM> returns to block <NUM> to check the remaining battery packs as outlined above.

As discussed above in reference to <FIG>, in some embodiments, the voltage of the batteries is measured according to a bus voltage rather than an open circuit voltage of the individual battery. In such embodiments, battery voltage may vary depending on the amount of current being discharged from the battery, and the open circuit voltage cannot be easily and accurately calculated due to a significant amount of current inflow. In such a case, when a subsequent battery pack is brought online, it will likely not be at equilibrium with a previous pack or packs which have already undergone charging, i.e. will likely have a much higher open circuit voltage that is substantially equal to the bus voltage of the previous pack or packs. Therefore, when discharging resumes, the new pack will already be at a higher potential than the previous packs, causing a disproportionate allocation of current, which may cause damage to the battery packs.

Referring to <FIG>, an alternative method <NUM> for discharging a battery pack system <NUM> is disclosed. The method <NUM> is similar to the method <NUM> described above. The difference between the methods is described further herein.

As the battery pack or battery packs selected from blocks <NUM> and <NUM>-<NUM> begin to discharge at block <NUM>, the drive cycle of the vehicle begins, and, correspondingly, the battery packs begin to discharge, by slowly or methodically increasing the voltage value of the discharge current to avoid overshooting any remaining packs that may have slightly higher voltages, until the discharge current is at a predetermined maximum discharge current value allowed by the system. After a predetermined period of time allotted for charging the selected battery pack(s) at block <NUM>, the battery pack system <NUM> selects one of the remaining battery packs at block <NUM> and measures the voltage of the selected battery pack. In another embodiment, similar to the method <NUM> discussed above, the battery pack system <NUM> may identify and select the remaining battery pack with the highest voltage. The absolute voltage difference between the selected battery pack and the charging battery pack(s) is calculated. The difference is then compared with a predetermined dVmax value. As shown in block <NUM>, if the absolute voltage difference is greater than the dVmax value, then the method returns to block <NUM> to repeat the process with a different battery pack. If the absolute voltage difference is less than the dVmax value, then the method <NUM> proceeds to block <NUM>, where it is determined whether the system voltage, or the average measured voltage of the discharging battery packs, is greater than the voltage of the selected pack. If the system voltage is greater, then the discharge current is reduced at block <NUM> until the discharge current inflow is below a predetermined inflow value. The contactors on the selected pack are then closed at block <NUM>, and the selection process begins again at block <NUM>. If the system voltage is not greater, then the contactor on the selected pack is closed at block <NUM> and the process begins again at block <NUM>. The sequencing process iteratively cycles through the remaining battery packs as outlined in blocks <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> until all the remaining battery packs in the battery pack system <NUM> are checked.

The method <NUM> then proceeds to block <NUM>, where the drive cycle of the vehicle begins, and, correspondingly, the selected packs and the previously discharging pack(s) begin discharging by slowly or methodically increasing the voltage value of the discharge current to avoid overshooting any remaining packs that may have slightly higher voltages, until the discharge current is at the maximum discharge current value allowed by the system. After a predetermined time period of discharging, the method <NUM> proceeds to block <NUM>, where the battery pack system <NUM> determines whether drive cycle of the vehicle is complete. In one embodiment, the drive cycle is complete when the drive cycle of the vehicle ends (e.g., when the mission of the vehicle is complete) or when all the battery packs of the battery pack system <NUM> are at the pre-established minimum SOC setting and the pre-established minimum voltage setting and are no longer capable of powering the vehicle. If the drive cycle is complete, then the method <NUM> moves to block <NUM> where the method <NUM> is stopped. If the drive cycle is not complete; however, the method <NUM> returns to block <NUM> to iteratively check the remaining battery packs as outlined above.

Referring now to <FIG>, an alternative parallel battery configuration <NUM> is shown. <FIG> shows two battery packs <NUM>, <NUM> connected in parallel. It is within the scope of the present disclosure that the configuration is applicable to multiple battery pack systems including more than two battery packs. For example, the configuration <NUM> may be applied to battery pack systems including four battery packs as shown in <FIG>, <FIG>, and <FIG>; eight battery packs as shown in <FIG>, <FIG>, <FIG>, and <FIG>; or battery pack systems including any number of battery packs operable.

The battery pack <NUM> includes a battery management system <NUM> and a solid state switch, or high current contactor <NUM>. The contactor <NUM> is operably connected to a resistor <NUM> and another solid state switch, or low current contactor <NUM>. In a high voltage system, the battery pack <NUM> may optionally further include a second high current contactor <NUM>. Similarly, the battery pack <NUM> includes a battery management system <NUM> and a solid state switch, or high current contactor <NUM>. The contactor <NUM> is operably connected to a resistor <NUM> and another solid state switch, or low current contactor <NUM>. In a high voltage system, the battery pack <NUM> may optionally further include a second high current contactor <NUM>.

The battery pack <NUM> further includes a first main battery system contactor <NUM> positioned on a positive terminal and a second main battery system contactor <NUM> positioned on a negative terminal that facilitate the operative coupling of the battery pack <NUM> with the battery pack <NUM> in a parallel configuration. The main battery system contactors <NUM>, <NUM> are operably coupled to the high current contactors <NUM>, <NUM>, <NUM>, and <NUM> and the low current contactors <NUM> and <NUM> of the battery packs <NUM>, <NUM>. That is, when the main battery system contactors <NUM>, <NUM> are closed, the high current contactors <NUM>, <NUM>, <NUM>, and <NUM> and the low current contactors <NUM> and <NUM> are correspondingly closed, operably coupling the battery pack <NUM> and the battery pack <NUM> to each other in parallel. The main battery system contactors <NUM>, <NUM> provide safety to the user by isolating high internal voltages from the external environment where such voltages could cause damage or injury. The main battery system contactors <NUM>, <NUM> also provide the means by which the batteries, wired in parallel, may be connected or disconnected to fulfill the procedures discussed herein.

Referring now to <FIG>, a method <NUM> to utilize battery packs without balanced voltages is disclosed. The method <NUM> illustratively describes a method for a system with two battery packs; however, it is within the scope of the present disclosure that the method <NUM> can be expanded to systems with greater than two battery packs. For example, the method <NUM> may be applied to battery pack systems including four battery packs as discussed above, eight battery packs as discussed above, or battery pack systems including any number of battery packs operable.

The method <NUM> begins at starting block <NUM> and moves to block <NUM> to assess whether a first battery pack (e.g., battery pack <NUM> of <FIG>) has failed. If the first battery pack has failed, the method <NUM> then determines whether the second battery pack (e.g., battery pack <NUM>) has failed at block <NUM>. If the second battery pack has also failed, the method <NUM> has detected a battery pack system failure and prompts a system shutdown at block <NUM> in which all contactors and/or switches are opened (for example, configuration 100A or 150A of <FIG> and <FIG>, respectively). If, at block <NUM>, the method <NUM> determines that the second battery pack has not failed, the system is prompted to utilize the second battery pack in a single pack operation at block <NUM>. For example, referring to <FIG>, the high current contactor <NUM> of the second battery pack <NUM> is closed for single pack operation, and low current contactor <NUM> of the first battery pack <NUM> is opened. The failure of the first battery pack is also reported at block <NUM>, after which the method returns to the starting block <NUM> to reassess the status of the first and second battery packs.

Returning to block <NUM>, if the method <NUM> determines that the first battery pack (e.g., battery pack <NUM> of <FIG>) has not failed, then the method <NUM> proceeds to block <NUM> to assess whether the second battery pack (e.g., battery pack <NUM> of <FIG>) has failed. If the second battery pack has failed, the system is prompted to utilize the first battery pack in a single pack operation at block <NUM>. For example, referring to <FIG>, the high current contactor <NUM> of the first battery pack <NUM> is closed for single pack operation, and the low current contactor <NUM> is opened. The method then returns to the starting block <NUM> to reassess the status of the first and second battery packs.

If, at block <NUM>, the second battery pack is found to be active (i.e., has not failed), then the method <NUM> moves to block <NUM>, where the voltage of the first battery pack (Vbatt1) is measured, the voltage of the second battery pack (Vbatt2) is measured, and the absolute value of the difference in voltages is calculated and compared to the predetermined dVmax value, wherein the dVmax value is the maximum acceptable voltage differential to safely connect the battery packs. The dVmax is selected with consideration to the continuous charging current capability of the battery packs, as well as the internal resistance of the battery packs. The voltages of the respective battery packs are measured at no load and with no compensation for battery internal resistance voltage drop.

If the measured absolute voltage difference is less than the predetermined dVmax value, then the method <NUM> moves to block <NUM> and all the contactors associated with the first battery pack and the second battery pack are closed and the vehicle operates under normal multi-pack operation according to at least one of the appropriate methods discussed above according to boxes 730A, 730B, 730C, 730D, 730E, or 730F.

However, if the measured absolute voltage difference is greater than the predetermined dVmax value, then the method <NUM> moves to block <NUM> to determine whether the voltage of the first battery pack is greater than the voltage of the second battery pack. If the voltage of the first battery pack is greater than the voltage of the second battery pack, then the method <NUM> moves to block <NUM> where the vehicles operates with the first battery pack as the single operational battery pack. For example, referring to <FIG>, the high current contactor <NUM> of the first battery pack <NUM> is closed for operation of the first battery pack <NUM>, and the low current contactor <NUM> of the second battery pack <NUM> is closed to close the charging circuit, enabling charging of the second battery pack <NUM> during operation of the first battery pack <NUM>. The first battery pack <NUM> charges the second battery pack <NUM> through the resistor <NUM> until the voltage differential between the first battery pack <NUM> and the second battery pack <NUM> is less than or equal to the predetermined dVmax value, after which the method <NUM> returns to starting block <NUM> to reassess the status of the first and second battery packs.

If the voltage of the first battery pack is not greater than the voltage of the second battery pack (i.e., the voltage of the second battery pack is greater), then the method <NUM> moves to block <NUM> where the vehicles operates with the second battery pack as the single operational battery pack. For example, referring to <FIG>, the high current contactor <NUM> of the second battery pack <NUM> is closed for operation of the second battery pack <NUM>, and the low current contactor <NUM> of the first battery pack <NUM> is closed to close the charging circuit, enabling charging of the first battery pack <NUM> during operation of the second battery pack <NUM>. The second battery pack <NUM> charges the first battery pack <NUM> through the resistor <NUM> until the voltage differential between the first battery pack <NUM> and the second battery pack <NUM> is less than or equal to the predetermined dVmax value, after which the method <NUM> returns to starting block <NUM> to reassess the status of the first and second battery packs.

The method <NUM> enhances the safety of the system by providing full redundancies such that batteries of great imbalance are not fully activated within the system. In general, when the difference in voltage between the batteries is large (greater than a predetermined voltage threshold), the lower voltage battery pack is inactive for operation of the vehicle but is actively charged until the difference in voltage is reduced below the predetermined voltage threshold. In this way, vehicles can continue their mission even when some battery packs in a multi-pack system are not online, as the offline battery pack is disconnected by static or solid switches and/or contactors.

Referring now to <FIG>, an alternate battery configuration <NUM> for connecting two battery packs <NUM>, <NUM> in parallel is shown; however, it is within the scope of the present disclosure that the configuration <NUM> can be expanded to systems with greater than two battery packs. For example, the configuration <NUM> may be applied to battery pack systems including four battery packs as discussed herein, eight battery packs as discussed herein, or battery pack systems including any number of battery packs operable.

The first battery pack <NUM> includes a battery management system <NUM> and a solid state switch, or contactor <NUM> installed on a positive terminal and operably coupled to a converter <NUM>. A second solid state switch, or contactor <NUM> is installed on a negative terminal. This configuration provides a safety measure in case one of the contactors fails while it is in the closed position, relative to the battery pack <NUM>. In such a case, a user can still isolate the battery by opening the other contactor, preventing completion of the circuit. The second battery pack <NUM> also includes a battery management system <NUM> and a solid state switch, or contactor <NUM> installed on a positive terminal and operably coupled to a converter <NUM>. A second solid state switch, or contactor <NUM> is installed on a negative terminal, providing the same safety measure discussed above.

In the illustrated embodiment, each of the converters <NUM> and <NUM> comprise a buck boost converter; however, it is within the scope of the present disclosure that alternate converters may be used. Each of the converters <NUM> and <NUM> are configured to balance voltages between the first battery pack <NUM> and the second battery pack <NUM>. For example, when the positive terminal contactor <NUM> of the first battery pack <NUM> is open, the converter <NUM> operates in place of the resistor <NUM> discussed above in relation to the first battery pack <NUM> of <FIG>. The converter <NUM> may transfer a fraction of the total battery pack current to balance the first battery pack <NUM> and the second battery pack <NUM>. Similarly, when positive terminal connector <NUM> of the second battery pack <NUM> is open, the converter <NUM> operates in place of the resistor <NUM> discussed above in relation to the first battery pack <NUM> of <FIG>. The converter <NUM> may transfer a fraction of the total battery pack current to balance the first battery pack <NUM> and the second battery pack <NUM>.

The converter <NUM> of the first battery pack <NUM> may draw an input voltage from the first battery pack <NUM> and output a different voltage that is controlled to match the voltage of the second battery pack <NUM>. Similarly, the converter <NUM> of the second battery pack <NUM> may draw an input voltage from the second battery pack <NUM> and output a different voltage that is controlled to match the voltage of the first battery pack <NUM>. If the output voltage is greater than the input voltage, then the corresponding converter <NUM> or <NUM> is in a "boost" state. Conversely, if the output voltage is less than the input voltage, the corresponding converter <NUM> or <NUM> is in a "buck" state. The illustrative buck boost converters comprising converters <NUM> and <NUM> may output voltages that are greater than or less than the input voltage depending on the need of the vehicle. The converters <NUM> and <NUM> may also modulate current flow between the battery packs such that the battery packs are within operable operating limits.

Now referring to <FIG>, an embodiment of a buck-boost converter <NUM> is shown. It is within the scope of the present disclosure that <FIG> also discloses the components of the converter <NUM> (<FIG>). As shown in <FIG>, a four-switch topology is used with switches <NUM>, <NUM>, <NUM>, and <NUM>. In the illustrated embodiment, switches <NUM> and <NUM> make up a first pair <NUM> and switches <NUM> and <NUM> make up a second pair <NUM>. However, it is contemplated that in alternate embodiments, other topologies may be used. As further shown, batteries <NUM> and <NUM> are connected at opposite ends of the converter <NUM>. Each of the batteries <NUM> and <NUM> is connected to one of the pairs of power electronic switches <NUM>, <NUM> connected in series across the batteries <NUM>, <NUM>, respectively (otherwise known as half-bridges <NUM>, <NUM> as shown in <FIG>). Each of the pairs of switches <NUM>, <NUM> comprise a semiconductor transistor and an anti-parallel diode. The semiconductor transistor permits current flow from the top terminal of the switch to the bottom terminal of the switch when turned ON, and the anti-parallel diode permits current flow from the bottom terminal of the switch to the top terminal of the switch whenever the diode is forward biased. Further, the mid-points of half-bridges <NUM>, <NUM> are connected via an inductor <NUM>.

The operation of the switches <NUM>, <NUM>, <NUM>, and <NUM> is coordinated by a digital or analog controller to facilitate controlled energy flow from either battery <NUM>, <NUM> to the other, irrespective of whether the voltage difference is positive or not. The inductor <NUM> is utilized as an energy storage device, and the controller alternates the buck boost converter <NUM> between circuit operating modes where in a first mode, the inductor <NUM> is charged by one of the voltage sources/batteries <NUM>, <NUM> by turning on two switches positioned diagonally from each other (e.g., switches <NUM> and <NUM> or <NUM> and <NUM>) with the remaining two switches turned off, and discharges into the other voltage source/battery <NUM>, <NUM> to provide the desired direction of current or energy flow. In a second mode, the inductor <NUM> is charged by the other voltage source/battery <NUM>, <NUM> by turning on the other two switches positioned diagonally from each other (e.g., switches <NUM> and <NUM> or <NUM> and <NUM>) with the remaining two switches turned off and discharges into the other voltage source/battery to provide the desired direction of current or energy flow. Advantageously, the configurations shown in <FIG> and <FIG> reduce power losses during battery pack balancing or pre-charging.

Claim 1:
A method of charging or discharging a plurality of battery packs, each connectable in parallel to a bus by a respective contactor (<NUM>), the method comprising:
a. identifying a battery pack (<NUM>) having a lowest or highest voltage of the plurality of battery packs;
b. closing the contactor (<NUM>) of the lowest or highest voltage battery pack (<NUM>);
c. measuring a voltage of a battery pack (<NUM>) selected from the plurality of battery packs;
d. determining a difference between the voltage of the lowest or highest voltage battery pack (<NUM>) and the voltage of the selected battery pack (<NUM>);
e. comparing the difference to a predetermined maximum acceptable voltage differential value;
f. closing the contactor (<NUM>) of the selected battery pack (<NUM>) if the difference is less than or equal to the maximum acceptable voltage differential value;
g. repeating steps c. through f. until each of the battery packs has been compared to the lowest or highest voltage battery pack (<NUM>);
h. charging or discharging the battery packs (<NUM>) with closed contactors (<NUM>) by providing a charge or discharge current;
i. selecting a battery pack (<NUM>) with an open contactor from the plurality of battery packs;
j. determining a difference between a voltage of the selected battery pack (<NUM>) with an open contactor (<NUM>) and a voltage of a battery pack (<NUM>) that was charged or discharged in step h.;
k. comparing the difference to the predetermined maximum acceptable voltage differential value;
l. closing the contactor (<NUM>) of the selected battery pack (<NUM>) if the difference is less than or equal to the maximum acceptable voltage differential value;
m. repeating steps i. through <NUM>. until a voltage of each battery pack (<NUM>) with an open contactor (<NUM>) has been compared to the voltage of the battery pack (<NUM>) that was charged or discharged in step h.;
n. charging or discharging the battery packs (<NUM>) with closed contactors (<NUM>) by providing a charge or discharge current; and
o. stopping charging or discharging once all battery packs (<NUM>) in the plurality of battery packs (<NUM>) are completely charged or discharged.