Large-format battery management system with state of charge balancing
A battery system with a large-format Li-ion battery powers attached equipment by discharging battery cells distributed among a plurality of battery packs. The discharging of the battery cells is controlled in an efficient manner while preserving the expected life of the Li-ion battery cells. Each battery pack internally supports a battery management system and may have identical components, thus supporting an architecture that easily scales to higher power/energy. Battery packs may be added or removed without intervention with a user, where one of battery packs serves as a master battery pack and the remaining battery packs serve as slave battery packs. When the master battery pack is removed, one of the slave battery packs becomes the master battery pack. Charging and discharging of the battery cells is coordinated by the master battery pack with the slave battery packs over a communication channel such as a controller area network (CAN) bus.
1. A method of powering an end device by a battery system, the battery system comprising a plurality of battery packs, the method comprising:
gathering, by a master battery pack of the battery system, battery status information from each battery pack of the plurality of battery packs, wherein the plurality of battery packs comprises the master battery pack and one or more slave battery packs and wherein the battery status information from each battery pack includes state of charge (SoC) data;
determining, by the master battery pack and based the battery status information, whether a first subset of the plurality of battery packs have different SoC data;
selecting, by the master battery pack, a first type of balancing from a plurality of balancing types appropriate for the first subset of the plurality of battery packs; and
performing, by the master battery pack, the selected first type of balancing via a power bus until desired SoC values are obtained for the first subset of the plurality of battery packs.
2. The method of claim 1 , wherein the plurality of balancing types comprises a converter balancing technique, a direct balancing technique, and a staggered balancing technique.
3. The method of claim 2 , further comprising:
identifying, by the master battery pack, a first battery pack having a high SoC value from the gathered battery status information; and
comparing, by the master battery pack, the high SoC value with SoC values of all remaining battery packs.
4. The method of claim 3 , further comprising:
in response to the comparing, when a first SoC difference between the first battery pack and a second battery pack is greater than a first predetermined amount, initiating, by the master battery pack, the converter balancing technique for the first and second battery packs.
5. The method of claim 4 , further comprising:
sending, by the master battery pack, to the first battery pack a first enable message over a communication channel, wherein the first enable message instructs the first battery pack to discharge over the power bus; and
sending, by the master battery pack, to the second battery pack a second enable message over the communication channel, wherein the second enable message instructs the second battery pack to enable a converter of the second battery pack and to charge from the power bus.
6. The method of claim 4 , further comprising:
in response to the comparing, when a second SoC difference between the first battery pack and a third battery pack is greater than the first predetermined amount, initiating, by the master battery pack, the converter balancing technique for the first, second, and third battery packs.
7. The method of claim 6 , wherein one of the first, second, and third battery packs serves as the master battery pack of the battery system.
8. The method of claim 3 , further comprising:
in response to the comparing, when a third SoC difference between the first battery pack and a fourth battery pack is less than a second predetermined amount, initiating, by the master battery pack, the direct balancing technique for the first battery pack and the fourth battery pack.
9. The method of claim 8 , further comprising:
sending, by the master battery pack, to the first battery pack a third enable message over a communication channel, wherein the third enable message instructs the first battery pack to discharge over the power bus; and
sending, by the master battery pack, to the fourth battery pack a fourth enable message over the communication channel, wherein the fourth enable message instructs the fourth battery pack to charge from the power bus.
10. The method of claim 8 , wherein one of the first and fourth battery packs serves as the master battery pack.
11. The method of claim 3 , further comprising:
in response to the comparing, when a fourth SoC difference between the first battery pack and a fifth battery pack is less than a third predetermined amount, a fifth SoC difference between the first battery pack and a sixth battery pack is greater than a fourth predetermined amount, and a sixth SoC difference between the first battery pack and a seventh battery pack is greater than the fourth predetermined amount, initiating the staggered balancing technique to the first battery pack, the fifth battery pack, and the sixth battery pack.
12. The method of claim 11 , further comprising:
sending, by the master battery pack, to the first battery pack a fifth enable message over a communication channel, wherein the fifth enable message instructs the first battery pack to discharge over the power bus;
sending, by the master battery pack, to the fifth battery pack a sixth enable message over the communication channel, wherein the sixth enable message instructs the fifth battery pack to charge from the power bus, wherein the direct balancing technique is applied for the first battery pack and the fifth battery pack; and
sending, by the master battery pack, to the sixth battery pack a seventh enable message over the communication channel, wherein the seventh enable message instructs the sixth battery pack to enable its converter and to charge from the power bus, wherein the converter balancing technique is applied for the first battery pack and the sixth battery pack.
13. The method of claim 12 , further comprising:
obtaining current SoC values for the fifth and sixth battery packs; and
in response to the obtaining, when an eighth difference between a first current SoC value of the fifth battery pack and a second current SoC value of the sixth battery pack is greater than a fifth predetermined value, switching the direct balancing technique to the first battery pack and the seventh battery pack from the first battery pack and the sixth battery pack.
14. The method of claim 13 , further comprising:
sending, by the master battery pack, to the fifth battery pack an eighth enable message over the communication channel, wherein the eighth enable message instructs the fifth battery pack to enable a converter of the fifth battery pack and charge from the power bus, wherein the converter balancing technique is applied for the first battery pack and the fifth battery pack; and
sending, by the master battery pack, to the sixth battery pack a ninth enable message over the communication channel, wherein the ninth enable message instructs the sixth battery pack to disable a converter of the sixth battery pack and to charge from the power bus, wherein the direct balancing technique is applied for the first battery pack and the sixth battery pack.
15. The method of claim 11 , wherein one of the first, fifth, and sixth battery packs serves as the master battery pack of the battery system.
16. The method of claim 1 , further comprising:
obtaining, by the master battery pack, current SoC values from the plurality of battery packs;
determining, by the master battery pack and based the current SoC values, whether a second subset of the plurality of battery packs needs to be balanced in charge;
selecting, by the master battery pack, a second type of balancing from the plurality of balancing types appropriate for the second subset of the plurality of battery packs, wherein the first type and the second type of balancing are different; and
applying, by the master battery pack, the selected second type of balancing for the second subset of the plurality of battery packs.
17. The method of claim 16 , wherein the applying comprises:
obtaining a safety interlock indicator and a wake indicator; and
only when the safety interlock indicator is indicative of being on and the wake indicator is indicative of being off, enabling the applying.
18. A first battery pack configured for installation in a battery system for electrically powering an end device, wherein all installed battery packs installed in the battery system have identical electrical and electronic components, the first battery pack comprising:
a communication interface circuit configured to interface to a communication channel;
a power bus interface circuit configured to interface with a power bus and to provide electrical power to the end device;
a controller comprising at least one processor; and
a memory storing controller instructions that, when executed by the at least one processor, cause the controller to:
when the first battery pack serves as a master battery pack of the battery system:
gather battery status information from each of the installed battery packs, wherein the installed battery packs comprise the master battery pack and one or more all slave battery packs and wherein the battery status information from each battery pack includes testate of charge (SoC) data;
determine, based the battery status information, whether a first subset of the installed battery packs have different SoC data;
select a first type of balancing from a plurality of balancing types appropriate for the first subset of the installed battery packs; and
perform the selected first type of balancing until desired SoC values are obtained for the first subset of the installed battery packs.
19. The first battery pack of claim 18 , wherein the memory storing controller instructions that, when executed by the at least one processor, further cause the controller to:
identify a second battery pack having a high SoC value from the gathered battery status information; and
compare the high SoC value with SoC values of all remaining battery packs.
20. The first battery pack of claim 19 , wherein the memory storing controller instructions that, when executed by the at least one processor, further cause the controller to:
in response to a result of the comparison, when a first SoC difference between the first battery pack and a second battery pack is greater than a first predetermined amount, initiate, by the master battery pack, a converter balancing technique for the first and second battery packs.