Battery cell balancing based on wireless charging

Abstract

A system (11) of a cell stack (12) and a charger device (13) for charging a cell stack (12) by active balancing of cells (3), the cell stack (12) comprising: a series of cells (3) having at least a first cell and a second cell connected in series by cell contacts (14) between a positive cell stack contact (15) and a negative cell stack contact (16), the charger device (13) is connectable to a power source and comprises: a charger module (18) connected to the stack positive contact (15) by a charger positive contact (19) and to the stack negative contact (16) by a charger negative contact (20) and configured to charge the series of battery cells (3) based on a charger program when the charger device (13) is connected to the power source, the system (11) comprises: a balancer module (21) providing, for each cell (3) of the cell stack (12), a balancer stage (22) configured to transfer energy from an already fully charged cell (2) to a cell (3) having a lower state of charge, wherein each balancer stage (22) of the balancer module (21) is connected in parallel only to one individual cell (3) of the cells (3) of the cell stack (12), and wherein each balancer stage (22) of the balancer module (21) comprises an RFID antenna (24), wherein at least a first RFID antenna connected in parallel to the first balancer stage of the first battery cell and a second RFID antenna connected in parallel to the second balancer stage of the second battery cell are arranged within an RFID communication distance to exchange energy and / or information via a common first magnetic field (25), wherein the first balancer stage (22) uses more or less all the energy provided by the charger module (18) at the battery cell contacts (14) of the fully charged battery cell (3) to generate the magnetic field (25) and bypasses the charging current of the fully charged battery cell (3) in this way.

Description

Technical Field

[0001] The present invention relates to a system of a battery stack and a charger device for charging the battery stack by active balancing of battery cells, the battery stack comprising: a series of battery cells having at least a first battery cell and a second battery cell connected in series between a positive battery stack contact and a negative battery stack contact through battery cell contacts, and the charger device being connectable to a power source and comprising: a charger module connected to the positive battery stack contact through a charger positive contact and to the negative battery stack contact through a charger negative contact and configured to charge the series of battery cells based on a charger program when the charger device is connected to the power source, the system comprising: a balancer module providing a balancer stage for each battery cell of the battery stack, the balancer stage being configured to transfer energy from a fully charged battery cell to a battery cell having a lower state of charge, wherein each balancer stage of the balancer module is connected in parallel only with a single one of the battery cells of the battery stack.

[0002] The present invention also relates to a battery stack having a series of battery cells having at least a first battery cell and a second battery cell connected in series between a positive battery stack contact and a negative battery stack contact through battery cell contacts. Background Art

[0003] Many portable devices are powered by a battery stack comprising a plurality (at least two) of battery cells connected in series between a positive battery stack contact and a negative battery stack contact. This increases the available capacity and voltage of the battery stack. In such a system, the individual battery cells must be continuously monitored to ensure that they operate within a controlled range. Otherwise, the capacity and lifespan of the battery may be affected. Linear Technology provides the LTC680x series of integrated circuits for charger devices to charge such a battery stack and monitor each individual cell in the battery stack. The LTC680x monitors the cell parameters of each individual cell in the battery stack and transmits this information to a central processing unit via a proprietary serial bus. When a battery cell begins to reach its fully charged upper limit, a command is issued to the LTC680x to turn on the passive shunt of that cell, bypassing the charging current around that cell and allowing the current to continue flowing to other battery cells. Using such a passive shunt is inefficient and the shunt current generates a significant amount of heat at a relatively high charging current.

[0004] Linear Technology also provides the integrated circuit LT8584, which is capable of actively redirecting the charging current back to the power source used to charge the battery stack. The energy is not lost as heat but is instead reused to charge the remaining batteries in the battery stack. Figure 1Figure 1 shows such a prior art system 1, which includes a battery stack 2 having 12 battery cells 3 connected in series and a charger device 4 for charging the battery stack 2. The charger device 4 includes 12 balancer stages 6, each balancer stage being connected to a battery stack monitor 5 and including an LT8584 integrated circuit 7 and a wound transformer 8. Each LT8584 integrated circuit 7 measures the actual state of charge of the battery cell 3 to which it is connected and provides these cell parameters to the battery stack monitor 5 via a proprietary serial bus. The battery stack monitor 5 is the master controller that monitors all these cell parameters of all the battery cells 3 in the battery stack 2 and sends commands to the respective LT8584 integrated circuits 7 to release current through the primary coil of the wound transformer 8 in the case where the battery cell 3 has reached a fully charged state. The secondary coil of the wound transformer 8 is connected to a battery stack positive contact 9 and a battery stack negative contact 10 and feeds back this discharge current for re - use in charging the battery stack 2.

[0005] This known system 1 for active balancing of the battery cells 3 of the battery stack 2 has the following disadvantages, namely that a large amount of energy is lost in the wound transformers 8 of those battery cells 3 that are already fully charged. The charging current flowing from the battery stack positive contact 9 through this series of battery cells 3 to the battery stack negative contact 10, as long as all these battery cells 3 are charged, is discharged or bypassed through the primary coil of the wound transformer 8 for the balancer stages 6 of those battery cells 3 that are already fully charged, which results in high energy losses in those wound transformers 8 until the end of the charging process.

[0006] In addition, each balancer stage 6 must be connected to one of the battery cells 3 using a balancer cable. This additional cable between the battery stack 2 and the charger device 4 increases complexity and cost.

[0007] US11495994 B2 discloses a battery stack for active balancing of battery cells based on a decentralized system. Each battery cell is connected to a balancer unit via a dissipative element. The dissipative element is implemented as a MOSFET and is used to short - circuit the already fully charged battery cells at the end of charging.

[0008] US2019 / 0089022 A1 discloses a battery stack having battery cells, each battery cell being connected to a transmission module to communicate with a receiving module of a centralized battery management unit. The battery management unit monitors the remaining capacity and state of charge of the battery cells and detects battery cells with operating anomalies for replacement. All the transmission modules and receiving modules are arranged on a magnetic core to enable data communication based on RFID (NFC). Summary of the Invention

[0009] The object of the present invention is to provide a system for a battery stack and a charger device to charge the battery stack by active balancing of battery cells, and to provide a battery stack that can improve energy efficiency and can charge the battery stack more flexibly and faster.

[0010] This object is achieved in a system according to claim 1 and a battery stack according to claim 9.

[0011] In the system of the present invention, each balancer stage of the balancer module includes an RFID antenna and is configured to perform decentralized communication with one or two or all other balancer stages without the participation of a master controller to exchange information and energy between the battery cells of these balancer stages. This means that at least the first RFID antenna of the first balancer stage connected in parallel to the first battery cell and the second RFID antenna of the second balancer stage connected in parallel to the second battery cell are arranged or positioned such that they are within the RFID communication distance of each other to exchange energy and / or information through a common first magnetic field. This direct energy transfer from a fully charged battery cell to an uncharged battery cell is much more efficient than the power system of the prior art system that feeds the discharge current back into the battery stack positive contact and the battery stack negative contact to charge the battery stack. The electrical isolation of the battery cells and the balancer stages using RFID antennas enables the great advantage of active balancing of the battery cells.

[0012] The balancer module of the present invention with its respective self - sufficient balancer stages can be part of the physical housing of the charger device or, in another embodiment of the present invention, can be part of the battery stack. This simplifies the charger device to a charger integrated circuit that processes a charger program to charge, for example, a lithium - ion battery stack that needs to be charged by the charger device at different charging currents and charging voltages at different time periods. Since in this embodiment the balancer module is part of the battery stack, there is no need for balancer cables to connect each balancer stage to the associated battery cell, which reduces the technical complexity and cost and improves ease of use. A further advantage achieved is that after charging the battery stack while the battery stack powers a portable device, the balancer module can be used to transfer energy from battery cells with a higher state of charge to battery cells with a lower state of charge compared to this higher state of charge. This helps to avoid deep discharge of the battery cells while the other battery cells of the battery stack are still in an acceptably higher state of charge. This balancing of the battery stack while it powers a portable device can extend the life of the battery stack.

[0013] Communication between the first balancer stage and the second balancer stage and all other balancer stages of a balancer module can comply with the standard ISO 18.092 known as Near Field Communication. Any other similar RFID standard can also be used. As an example, Near Field Communication enables an RFID communication distance of approximately 10 centimeters. Thus, a company developing a charger device or a battery stack with balancer stages (each balancer stage including its own RFID antenna) can decide which of these RFID antennas will be within or outside the RFID communication distance of other RFID antennas or other balancer stages. Based on this physical arrangement of the RFID antennas, some balancer stages can communicate with each other and their battery cells can exchange energy with each other, while others cannot, which enables many different embodiments to have advantages according to specific different applications.

[0014] In another embodiment of the present invention, two or more battery stacks can be placed together at a distance closer than the RFID communication distance. Since each balancer stage is constructed to communicate with other balancer stages to determine which battery cells are in greater need of receiving energy, this communication is not limited to the balancer stages of one balancer module and does not require a master controller as in prior art systems. Thus, two battery stacks placed close together will charge those battery cells that are most in need of energy without involving any charger device.

[0015] These and other aspects of the present invention will become apparent and be elucidated with reference to the embodiments described hereinafter. Those skilled in the art will understand that various embodiments can be combined. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Shows a system according to the prior art, which includes a battery stack having 12 battery cells connected in series and a charger device for charging the battery stack.

[0017] Figure 2 Shows a system according to the present invention, which includes a balancer module, wherein each balancer stage includes its own RFID antenna to independently communicate with other balancer stages regarding energy transfer. DETAILED DESCRIPTION

[0018] Figure 2A first embodiment of the present invention is shown, in which the system 11 consists of a battery stack 12 and a charger device 13 that charges the battery stack 12 through an active balancing of lithium-ion battery cells 3. The battery stack 12 includes a series of three battery cells 3, which at least have a first battery cell and a second battery cell connected in series between a battery stack positive contact 15 and a battery stack negative contact 16 through battery cell contacts 14. The charger device 13 can be connected to the mains through contacts 17 and a cable to supply power to the charger device 13 as a power source. The charger device 13 includes a charger integrated circuit 18, which is connected to the battery stack positive contact 15 through a charger positive contact 19 and to the battery stack negative contact 16 through a charger negative contact 20. The charger integrated circuit 18 is configured to charge the series of battery cells 3 based on a charger program when the charger device 13 is connected to a power source to charge the lithium-ion battery cells 3. The charger program charges the battery cells 3 with different charging currents and charging voltages during different time periods, as described, for example, in EP 4 040 637 A1.

[0019] In Figure 2 the embodiment of the present invention shown, the battery stack 12 of the system 11 includes a balancer module 21 implemented on a printed circuit board, which provides a balancer stage 22 for each battery cell 3 of the battery stack 12. Each balancer stage 22 is configured to transfer energy from a battery cell 3 that has been fully charged to a battery cell 3 with a lower state of charge, where each balancer stage 22 of the balancer module 21 is only connected in parallel to a single battery cell 3 in the battery stack 12. Each balancer stage 22 includes an RFID chip 23 connected to an RFID antenna 24. The RFID chip 23 in this embodiment of the present invention is implemented to comply with the standard ISO 18.092 known as near field communication and processes a program that enables it to handle anti-collision and RFID communication with other RFID chips 23 of the balancer module 21. The RFID chip 23 or Figure 2 another integrated circuit of the balancer stage 22 not shown in

[0020] The programs processed by all the RFID chips 23 enable them to send and receive (exchange) these cell parameters and other information via a common magnetic field 25. The magnetic field 25 can be generated by one of the balancer stages 22, and other balancer stages 22 with RFID antennas 24 within the RFID communication range of, for example, 10 centimeters can communicate with this balancer stage 22. There are different ways to implement this program logic, but as an example, the first balancer stage 22 connected to the battery cell 3 with a charge state of 98% can communicate with the second balancer stage 22 connected to the battery cell 3 with a charge state of 87%. During the charger device 13 processes its charger program and charges the battery cell 3, the first balancer stage 22 and the second balancer stage 22 exchange these cell parameters every, for example, one second or five seconds. Each of these balancer stages 22 is constructed to compare the cell parameters received from other balancer stages 22 with its own cell parameters, and as a result of this comparison, negotiate and agree on an energy transfer with one or more balancer stages 22 sharing the common magnetic field 25 to transfer energy from the first balancer stage 22 of the first battery cell 3 with a higher charge state to the second balancer stage 22 of the second battery cell 3 with a lower charge state compared to this higher charge state of the first battery cell 3. This negotiation and agreement can be achieved in such a way that each balancer stage 22 that needs to allocate energy or needs to receive energy for its parallely connected battery cells 3 freely asks other balancer stages 22, and then before starting, the two affected balancer stages 22 must agree on the energy transfer. In another implementation, the balancer stage 22 that needs to allocate energy will simply use more or less all the energy provided by the charger integrated circuit 18 at the battery cell contacts 14 of the already fully charged battery cell 3 to generate the magnetic field 25. The balancer stage 22 that needs to receive energy for its battery cell 3 will simply extract as much energy as possible from the magnetic field generated by another balancer stage 22. Other more intelligent implementations with specific protocols are also possible.

[0021] When the battery cell 3 connected to the first balancer stage 22 reaches a full charge state of 100% or less defined in the setting, the first balancer stage 23 notifies the second balancer stage 22, allowing and forcing the second balancer stage 22 to obtain energy from the magnetic field 25 generated by the first balancer stage 22. The RFID chip 23 of the first balancer stage 22 more or less uses all the energy provided by the charger integrated circuit 18 at the battery cell contact 14 of the already fully charged battery cell 3 to generate the magnetic field 25, and in this way bypasses the charging current of the fully charged battery cell 3. The energy collected by the second balancer stage 22 from the magnetic field 25 is used by the RFID chip 23 of the second balancer stage 22 to provide more energy at the battery cell contact 14 of the battery cell 3 that has not been fully charged. As a result, energy is transferred from the already fully charged battery cell 3 to the battery cell 3 with a lower charge state, on the one hand to protect the already fully charged battery cell 3 from overload, and on the other hand to accelerate the charging process of the battery cell 3 that has not been fully charged. This active balancing is achieved without any balancing cable connection from the charger device 13 to the battery stack 12, nor an existing master integrated circuit in the prior art to manage the balancer stages for achieving active balancing. In addition, the balancer stages 22 are only connected via the air interface of the magnetic field 25, which ensures complete electrical isolation.

[0022] In Figure 2 In the first embodiment of the present invention shown in, all the RFID antennas 24 of the three balancer stages 22 are arranged on a printed circuit board within the same RFID communication range to ensure that information, energy exchange, and active balancing can occur between all three balancer stages 22 and their battery cells 3. In other applications and battery stacks, other arrangements may be useful in cases where different subsets of the balancer stages defining the same balancer module are defined and only the balancer stages of each subset are arranged within the RFID communication distance for communication and energy exchange. In a further embodiment of the present invention, one or more RFID antennas 24 of the balancer stage 22 may be located in an external region outside the RFID communication distance, where the magnetic field 25 is no longer as strong as in the internal region of the RFID communication range. Through these different positions, the balancer stages 22 in the internal region will be in a better position to collect more energy than other balancer stages 22 in the external region that are at a distance from the balancer stage 22 generating the magnetic field 25 exceeding the RFID communication distance. Those skilled in the art will understand that these different positions of the RFID antennas 24 can be used for different applications, and these positions can enable, disable, or favor some balancer stages.

[0023] In Figure 2In another usage scenario of the battery stack 12 shown in the figure, the battery stack 12 has been charged by the charger device 13, is now disconnected from the charger device 13, and is connected to a portable device to supply power to the portable device. The portable device can be any device that requires power from the battery cells 3, such as a mobile phone, a radio, a model airplane, or other devices. During the use of the portable device, the charge state of the battery cells 3 decreases, but not at the same rate due to differences in the battery cells 3. As a result, as Figure 2 shown, each battery cell 3 can include a different charge state. The balancer stage 22 can start communicating and exchanging their cell parameters from time to time or based on the charge state of some or all of the battery cells 3. Based on the comparison of the cell parameters received from other balancer stages 22 with the cell parameters of its own battery cells 3, the balancer stage 22 can decide to exchange energy between their battery cells 3. This can avoid a situation where one of the battery cells 3 is deeply discharged and thus damages the entire battery stack 12, while the other battery cells 3 still have a high charge state.

[0024] In another embodiment of the present invention, three RFID chips 23 are implemented on a single integrated circuit, and only their RFID antennas 24 are separate physical elements. In this case, the communication between the balancer stages can be implemented only within the integrated circuit, and only the energy transfer between the balancer stages is carried out through the RFID antennas 24.

[0025] In another embodiment of the present invention not shown in the figure, the charger device of the system includes a balancer module implemented on the printed circuit board of the charger device, which provides a balancer stage for each battery cell of the battery stack. In this less preferred embodiment, since a balancer cable from the charger device to the battery stack is still required, the energy transfer for the active balancing of the battery cells is still completed through the RFID antenna located within the charger device.

[0026] In other embodiments of the present invention, the RFID communication distance can be only 1 centimeter or up to 1 meter.

Claims

1. A system (11) of a battery stack (12) and a charger device (13) for charging the battery stack (12) by active balancing of battery cells (3), the battery stack (12) comprising: A series of battery cells (3) having at least a first battery cell and a second battery cell connected in series between a battery stack positive contact (15) and a battery stack negative contact (16) through battery cell contacts (14), and The charger device (13) is connectable to a power source and comprises: A charger module (18) connected to the battery stack positive contact (15) through a charger positive contact (19) and to the battery stack negative contact (16) through a charger negative contact (20), and configured to charge the series of battery cells (3) based on a charger program when the charger device (13) is connected to the power source, and the system (11) comprises: A balancer module (21) providing a balancer stage (22) for each battery cell (3) of the battery stack (12), the balancer stage (22) being configured to transfer energy from a fully charged battery cell (3) to a battery cell (3) having a lower state of charge, wherein each balancer stage (22) of the balancer module (21) is only connected in parallel to a single battery cell (3) among the battery cells (3) of the battery stack (12), characterized in that Each balancer stage (22) of the balancer module (21) comprises an RFID antenna (24), wherein at least a first RFID antenna of the first balancer stage connected in parallel to the first battery cell and a second RFID antenna of the second balancer stage connected in parallel to the second battery cell are arranged within an RFID communication distance to exchange energy and information through a common first magnetic field (25), Wherein the first balancer stage (22) more or less uses all the energy provided by the charger module (18) at the battery cell contact (14) of the fully charged battery cell (3) to generate the magnetic field (25) and thereby bypass the charging current of the fully charged battery cell (3).

2. The system (11) according to claim 1, wherein each balancer stage (22) is configured to measure the actual state of charge and / or temperature of the battery cell (3) connected in parallel and exchange these cell parameters with other balancer stages (22) of the balancer module (21) through the common first magnetic field.

3. The system (11) according to claim 2, wherein each balancer stage (22) is configured to compare the cell parameters from other balancer stages (23) with its own cell parameters, and as a result of this comparison, agree to an energy transfer with one or more balancer stages (22) sharing the common first magnetic field to transfer energy from the first balancer stage of the first battery cell having a higher state of charge to the second balancer stage of the second battery cell having a lower state of charge compared to the higher state of charge of the first battery cell.

4. The system (11) according to any one of claims 1 to 3, wherein a first subset of balancer stages of the balancer module (21) includes the first balancer stage and the second balancer stage that share the common first magnetic field to exchange energy and / or information, and a second subset of balancer stages of the balancer module includes a third balancer stage having a third RFID antenna and a fourth balancer stage having a fourth RFID antenna that share a common second magnetic field to exchange energy and / or information.

5. The system (11) according to claim 4, wherein the first antenna and the second antenna that share the common first magnetic field and the third antenna and the fourth antenna that share the common second magnetic field are arranged to be able to exchange energy and / or information between all four balancer stages.

6. The system (11) according to claim 4, wherein the first antenna and the second antenna that share the common first magnetic field are arranged outside the RFID communication distance of the third antenna and the fourth antenna that share the common second magnetic field to prohibit the exchange of energy and / or information.

7. The system (11) according to any one of claims 3 to 6, wherein the balancer module (21) is configured to transfer energy from a balancer stage (22) of a battery cell (3) having a higher state of charge to a balancer stage (22) of another battery cell (3) having a lower state of charge even when the charger device (13) is disconnected from the battery stack (12).

8. The system (11) according to any one of claims 1 to 7, wherein the balancer stage (22) is configured to exchange energy and / or information through the common first magnetic field that is an NFC interface compliant with ISO18.092 standard.

9. A battery stack (12) having a series of battery cells (3), the series of battery cells (3) having at least a first battery cell and a second battery cell connected in series between a battery stack positive contact (15) and a battery stack negative contact (16) through battery cell contacts (14), characterized in that the battery stack (12) includes a balancer module (21), the balancer module (21) providing a balancer stage (22) for each battery cell (3) of the battery stack (12), the balancer stage (22) being configured to transfer energy from a battery cell (3) having a higher state of charge to a battery cell (3) having a lower state of charge compared to the higher state of charge, wherein each balancer stage (22) of the balancer module (21) is only connected in parallel to a single battery cell (3) among the battery cells (3) of the battery module (12), and each balancer stage (22) of the balancer module (21) includes an RFID antenna (24), wherein at least a first RFID antenna of the first balancer stage connected in parallel to the first battery cell and a second RFID antenna of the second balancer stage connected in parallel to the second battery cell are arranged within an RFID communication distance to exchange energy and information through a common first magnetic field (25). The first balancer stage (22) more or less uses all the energy provided by the charger module (18) at the cell contacts (14) of the already fully charged cell (3) to generate a magnetic field (25) and in this way bypass the charging current of the already fully charged cell (3).

10. The battery stack (12) according to claim 9, wherein each balancer stage (22) is configured to measure the actual state of charge and / or temperature of the cells (3) connected in parallel and exchange these cell parameters with other balancer stages (22) of the balancer module (21) via the common first magnetic field.

11. The battery stack (12) according to claim 10, wherein each balancer stage (22) is configured to compare the cell parameters from other balancer stages (22) with its own cell parameters and, as a result of this comparison, agree to an energy transfer with one or more balancer stages (22) sharing the common first magnetic field to transfer energy from the first balancer stage of the first cell with a higher state of charge to the second balancer stage of the second cell with a lower state of charge compared to the higher state of charge of the first cell.

12. The battery stack (12) according to any one of claims 9 to 11, wherein a first subset of the balancer stages of the balancer module (21) includes the first balancer stage and the second balancer stage sharing the common first magnetic field to exchange energy and / or information, and a second subset of the balancer stages of the balancer module includes a third balancer stage with a third RFID antenna and a fourth balancer stage with a fourth RFID antenna sharing a common second magnetic field to exchange energy and / or information.

13. The battery stack (12) according to claim 12, wherein the first antenna and the second antenna sharing the common first magnetic field and the third antenna and the fourth antenna sharing the common second magnetic field are arranged to enable the exchange of energy and / or information between all four balancer stages.

14. The battery stack (12) according to claim 12, wherein the first antenna and the second antenna sharing the common first magnetic field are arranged outside the RFID communication range of the third antenna and the fourth antenna sharing the common second magnetic field to prohibit the exchange of energy and / or information.

15. The battery stack (12) according to any one of claims 11 to 14, wherein the balancer module (21) is configured to transfer energy from the balancer stage (22) of one cell (3) with a higher state of charge to the balancer stage (22) of another cell (3) with a lower state of charge even when the charger device (13) is disconnected from the battery stack (12).

16. The battery stack (12) according to any one of claims 9 to 15, wherein the balancer stage (22) is configured to exchange energy and / or information via the common first magnetic field as an NFC interface compliant with ISO18.092 standard.

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