Pre-charging battery electrical system from discrete battery strings

Abstract

A battery system includes: a load bus for connection to a DC link; a single pre-charge circuit connected to the load bus; a plurality of battery packs; and a control circuit. Each battery pack includes a plurality of battery strings, the plurality of battery strings including: battery cells connected in series; a positive contactor for connecting the battery string to a load bus; and a pre-charge contactor for connecting the battery string to the pre-charge circuit. The control circuit selects the battery string to pre-charge the DC link, closes the pre-charge contactor of the battery string to connect the selected battery string to the pre-charge circuit, and opens the pre-charge contactor of the selected battery string to disconnect the battery string from the pre-charge circuit when the DC link is pre-charged, and closing the positive contactor of the selected battery string to connect the battery string to the load bus.

Description

Technical Field

[0001] This document relates to rechargeable battery technology, and more specifically to a technique for activating multiple battery packs in parallel to power large mobile work machines. Background Technology

[0002] Powering large mobile work machines (e.g., wheel loaders) with electric motors requires a large mobile electrical energy source capable of providing tens to hundreds of amperes of current. Multiple high-capacity battery cells connected in series and parallel can provide the continuous power needed by large electric mobile work machines. However, when multiple batteries are connected in series and parallel, it is necessary to avoid directly connecting individual battery cells to a direct current (DC) link and their capacitors. Doing so can generate high inrush currents, which could potentially damage the batteries and components of the work machine. Summary of the Invention

[0003] Large, electrically powered mobile machinery uses high-capacity battery systems. These high-capacity battery systems should be kept safely online.

[0004] An example battery system includes: a load bus for connection to a DC link; a single precharge circuit connected to the load bus; multiple battery packs; and control circuitry. Each battery pack includes multiple battery strings, each battery string including: multiple individual battery cells connected in series; a positive contactor for connecting the battery string to the load bus; and a precharge contactor for connecting the battery string to the precharge circuit. The control circuitry is configured to: select a battery string for precharging the DC link; close the precharge contactor of the battery string to connect the selected battery string to the precharge circuit; and, when the DC link is being precharged, open the precharge contactor of the selected battery string to disconnect the battery string from the precharge circuit, and close the positive contactor of the selected battery string to connect the battery string to the load bus. Attached Figure Description

[0005] Figure 1 It is a front view depicting an example operating machine according to this disclosure.

[0006] Figure 2 This is a block diagram of a modular battery system for operating machinery according to the present disclosure.

[0007] Figure 3 This is a circuit diagram of an example battery pack of a modular battery system according to this disclosure.

[0008] Figure 4This is a flowchart illustrating an example of a method for precharging a DC link when connected to a modular battery system, according to the present disclosure. Detailed Implementation

[0009] Examples of this disclosure relate to systems and methods for automatically and safely connecting a large-capacity battery system online. The large-capacity battery system can be used, for example, in electric work machinery, and is connected by a direct current (DC) link to a DC-to-alternating current (AC) converter, which in turn connects to the electric drive system of the mobile work machinery. The DC link includes a large capacitor. Connecting a large-capacity battery system to an uncharged DC link capacitor can generate a large inrush current that could damage individual battery cells, interconnecting cables of the battery system, and components of the electric drive system.

[0010] Figure 1 An example machine 100 according to this disclosure is depicted. Figure 1 In this embodiment, machinery 100 includes a frame 102, wheels 104, implements 106, and a speed control system implemented in one or more onboard electronic devices (e.g., electronic control units or ECUs). Example machinery 100 is a wheel loader. However, in other examples, the machinery can be other types of machinery associated with various industries, including, for example, construction, agriculture, forestry, transportation, material handling, waste management, etc. Therefore, although several examples are described with reference to wheel loaders, examples according to this disclosure are also applicable to other types of machinery, including graders, scrapers, bulldozers, excavators, compactors, material handling vehicles such as dump trucks, and other example machinery types.

[0011] Mechanism 100 includes a frame 102 mounted on four wheels 104, although in other examples the mechanism may have more than four wheels. The frame 102 is configured to support and / or mount one or more components of the mechanism 100. For example, the mechanism 100 includes a housing 108 coupled to the frame 102. Among other components, the housing 108 may also house an electric motor for propelling the mechanism across various terrains via the wheels 104. In some examples, multiple electric motors are included in multiple housings at multiple locations within the mechanism 100.

[0012] Machinery 100 includes an implement 106 connected to a frame 102 via a linkage assembly 110 configured to be actuated to articulate the bucket 112 of the implement 106. The bucket 112 of the implement 106 may be configured to transfer material, such as soil or debris, from one location to another. The linkage assembly 110 may include one or more cylinders 114 configured to be actuated, for example, hydraulically or pneumatically, to articulate the bucket 112. For example, the linkage assembly 110 may be actuated by cylinders 114 to raise and lower relative to the frame 102 of machinery 100 and / or rotate the bucket 112.

[0013] Platform 116 is coupled to frame 102 and provides access to various locations on machinery 100 for operational and / or maintenance purposes. Machinery 100 also includes an operator's cabin 118, which may be open or closed and is accessible via platform 116. Operator's cabin 118 may include one or more control devices (not shown), such as joysticks, steering wheels, pedals, levers, buttons, switches, etc. The control devices are configured to enable the operator to control machinery 100 and / or implements 106. Operator's cabin 118 may also include an operator interface, such as a display device, sound source, light source, or a combination thereof.

[0014] Machinery 100 can be used in a variety of industrial, construction, commercial, or other applications. Machinery 100 can be operated by an operator in operator cabin 118. The operator can, for example, drive machinery 100 to and from various locations on the work site, and can also use the bucket 112 of implement 106 to pick up and store loads of materials. As an example, machinery 100 can be used to excavate a portion of the work site by means of actuating cylinder 114 to articulate bucket 112 via linkage assembly 110, to dig and remove dirt, rocks, sand, etc. from one part of the work site, and store the load at another location.

[0015] The mechanism 100 may include a battery compartment connected to the frame 102 and including a battery system 120. The battery system 120 is electrically connected to one or more electric motors of the mechanism 100.

[0016] Figure 2 This is a block diagram of a modular battery system. Battery system 120 can be used to supply power to machinery (such as...). Figure 1 The example machine 100 is powered by the battery system 120. The battery system 120 includes multiple battery packs 230 (e.g., two to eight battery packs). Each battery pack 230 includes multiple battery strings 232 (e.g., two to five battery strings). Each battery string 232 includes multiple high-capacity batteries 234 connected in series (e.g., two to twelve 58-volt, 80-ampere-hour batteries or 60-kilowatt-hour batteries).

[0017] Battery system 120 includes control circuitry 250 for keeping battery strings 232 and battery pack 230 in a discharged state to provide electrical energy to the operating machinery, and in a charging state to recharge the batteries. Control circuitry 250 may include processing circuitry including logic components for performing the described functions. The processing circuitry may include a microprocessor, application-specific integrated circuit (ASIC), programmable gate array (PGA), or other type of processor to interpret or execute instructions in software or firmware. In some examples, control circuitry 250 includes logic sequencer circuitry. A logic sequencer is a state machine or other circuitry that sequentially executes a fixed series of steps to perform the described functions. Logic sequencer circuitry can be implemented using hardware, firmware, or software.

[0018] The DC link connecting to the operating machinery may have a large capacitance (e.g., 26,000 microfarads). In order to connect the battery system 120 to such a large capacitive load, the capacitance of the DC link is pre-charged to avoid generating a large inrush current that could potentially damage components of the battery system 120 and the electric operating machinery.

[0019] Figure 3 This is a circuit diagram of an example battery pack 330 of a modular battery system. The battery system 120 may include a plurality of battery packs 330 that can be connected in parallel to a load bus 340, which is connected to a DC link connected to an electric work machine. Figure 3 The example battery pack 330 includes three battery strings 332, each comprising multiple high-capacity battery cells 334 connected in series. Each battery string 332 includes a positive contactor 338 for connecting the positive terminal of the battery string 332 to a load bus 340. The battery strings 332 can be connected in parallel to the load bus 340. Each battery string 332 includes a negative contactor 342 for connecting the negative terminal of the battery string 332 to a negative load bus 344.

[0020] Battery system 120 includes a pre-charge circuit 346 connected to load bus 340. During pre-charging, the energy for pre-charging the DC link is provided by a battery string 332 connected to pre-charge circuit 346. The capacitor of the DC link is pre-charged to approximately the voltage of the battery string 332. The selected battery string 332 is connected to pre-charge circuit 346, and the DC link is pre-charged by the selected battery string 332 through pre-charge circuit 346. Pre-charge circuit 346 slows down the charging of the DC link capacitor to mitigate inrush current when the selected battery string 332 is connected to the DC link. Any battery string 332 of any battery pack 330 of battery system 120 can be connected to pre-charge circuit 346 to pre-charge the DC link.

[0021] The pre-charge circuit 346 may include a pre-charge resistor. This pre-charge resistor (e.g., multiple resistors) and the load capacitance form a time constant for pre-charging. In some examples, the pre-charge circuit 346 includes multiple positive temperature coefficient (PTC) thermistors. These PTC thermistors increase the resistance of the pre-charge circuit 346 as the temperature rises due to the increased inrush current, further limiting the inrush current. The pre-charge circuit 346 may be rated for 100 amperes or greater.

[0022] Each battery string 332 of the battery system 120 includes a pre-charge contactor 348 for connecting the battery string 332 to a pre-charge circuit 346. The contactor is activated or closed by a control circuit 250 of the battery system. The control circuit 250 can connect any battery string 332 of the battery system to the pre-charge circuit 346 and to a load bus 340 (and the positive side of the DC link) and a negative load bus 344 (and the negative side of the DC link). The battery system may include an isolated DC-DC converter connected to the pre-charge contactor 348, the positive contactor 338, and the negative contactor 342. When activated by the control circuit 250, the DC-DC converter 352 provides voltage to close the pre-charge contactor 348, the positive contactor 338, and the negative contactor 342. In the event of a contactor failure, the DC-DC converter 352 provides isolation. For example, the contactor can be an electromechanical switching device that includes a coil for achieving switching. In the event of a contactor failure that short-circuits the high-voltage connection of the contactor to the low-voltage coil, the DC-DC converter prevents the high-voltage contact from reaching the low-voltage side of the system.

[0023] The battery string 332 may include a voltage measurement circuit 354 and a current measurement circuit 356, which are used by the control circuit 250 to monitor the battery string 332. The battery string 332 may include a string disable circuit 358, which is used by the control circuit 250 to disable one or both of the positive contactor 338 and the negative contactor 342 of the battery string 332 based on the monitored voltage or current of the battery string 332. The battery string 332 may include a fuse 360.

[0024] Because the battery system 120 is modular, smaller battery packs 330 can be connected in parallel to the load bus 340, while larger battery systems can have more battery packs 330 connected in parallel. The control circuit 250 of the battery system 120 is responsible for subjecting the battery system to a pre-charge phase before bringing the battery strings 332 online to fully drive the load.

[0025] Industry Applicability

[0026] In one example of an online modular battery system for working machinery according to this disclosure, the battery packs 330 and battery strings 332 of the battery system 120 should be safely online. Control circuitry 236 can select any battery string 332 of the battery pack 330 to perform a pre-charge process to pre-charge the load to approximately the voltage of the selected battery string, thereby preventing large inrush currents from damaging components of the battery system 120 and the load. Control circuitry 250 can initiate the pre-charge process in response to a received command for bringing the battery system online in a discharged state to drive the load.

[0027] Figure 4 This is a flowchart illustrating an example of a method 400 for operating a battery system 120, which includes multiple battery packs 330 capable of being connected in parallel to a load bus 340. Each battery pack 330 includes multiple battery strings 332 capable of being connected in parallel to the load bus 340. The battery system 120 includes a pre-charge circuit 346 connected to the load bus 340. Method 400 can be executed by a control circuit 250 of the battery system.

[0028] At block 405, when a load is connected to battery system 120, control circuit 250 selects battery string 332 of battery system 120 to precharge the load. Control circuit 250 can use voltage measurement circuit 354 to determine the offline voltage of the battery string, and when all battery strings are disconnected from load bus 340, selects battery string 332 with the highest offline voltage to precharge the load. If the offline voltage of battery string 332 differs from the offline voltage of other battery strings by more than a threshold voltage difference, control circuit 250 may exclude battery string 332 from being used to precharge the load. If the offline voltage of battery string 332 differs from the offline voltage of other battery strings by more than a threshold voltage difference, control circuit 250 may exclude battery string 332 from being used to drive the load.

[0029] At block 410, control circuitry 250 connects the selected battery string 332 to a single precharge circuit 346 of battery system 120 and precharges the load. To connect battery string 332 to precharge circuit 346, control circuitry 250 closes precharge contactor 348 of battery string 332. Battery string 332 may include a single precharge contactor 348 located on the positive side of the battery string and a negative contactor 342 located on the negative side of battery string 332. Control circuitry 250 may also close both precharge contactor 348 and negative contactor 342 to connect battery string 332 to precharge circuit 346.

[0030] Any battery string from any battery pack 330 can be connected to the precharge circuit 346. This means that if the control circuit 250 (e.g., based on a measured voltage or current of the battery string 332) determines that the selected battery string is unsuitable for precharging the load, or for other reasons, the control circuit 250 can select a different battery string from a different battery pack to connect to the precharge circuit 346.

[0031] At block 415, when the load is pre-charged, control circuit 250 disconnects battery string 332 from pre-charge circuit 346 and directly connects the selected battery string 332 to load bus 340. When the load is pre-charged, control circuit 250 can connect the selected battery string 332 to load bus 340 by disconnecting the pre-charge contactor 348 of battery string 332 and closing the positive contactor 338 of battery string 332. When the load is pre-charged using the selected battery string, control circuit 250 closes the positive contactors 338 of other battery strings 332 in the battery pack 330, which includes the selected battery string 332. In this way, when the load is pre-charged, control circuit 250 keeps battery pack 330 online.

[0032] Other battery packs can be brought online together with the selected battery string 330, or selectively brought online. Control circuit 250 can simultaneously connect other battery strings 332 of other battery packs 330, or sequentially bring other battery packs 330 online (e.g., based on measured offline voltages of battery packs 330). Despite the complex multi-bus structure, the control logic of control circuit 250 monitors the activation of high-capacity battery cells 334 to prevent large inrush currents.

[0033] The detailed description above is intended to be illustrative and not restrictive. Therefore, the scope of the invention should be determined by reference to the appended claims and the full scope of their authorized equivalents.

Claims

1. A battery system (120), the battery system comprising: A load bus (340) for connecting to a direct current (DC) link; A single pre-charge circuit (346) is connected to the load bus; Multiple battery packs (330), each battery pack including multiple battery strings (332), the multiple battery strings being connectable to the load bus and the precharge circuit, wherein the battery strings include: Multiple battery cells (334) are connected in series; Positive contactor (338), the positive contactor being used to connect the battery string to the load bus; and A pre-charge contactor (348) is used to connect the battery string to the pre-charge circuit; and Control circuit (250), the control circuit being configured to: When the DC link is connected to the load bus, a battery string is selected to precharge the DC link; Close the pre-charge contactor of the battery string to connect the selected battery string to the pre-charge circuit; and When the DC link is precharged, the precharge contactor of the selected battery string is disconnected to disconnect the battery string from the precharge circuit, and the positive contactor of the selected battery string is closed to connect the battery string to the load bus.

2. The battery system according to claim 1, Each battery string includes a voltage measurement circuit (354) configured to measure the voltage of the battery string; and The control circuit is configured to select the battery string with the highest offline voltage to connect to the precharge circuit.

3. The battery system according to claim 1 or claim 2, wherein the control circuit is configured to: When it is determined that the selected battery string cannot precharge the DC link, the precharge contactor of the selected battery string is disconnected to disconnect the selected battery string from the precharge circuit; and Close the pre-charge contactors of different battery strings in different battery packs to pre-charge the DC link.

4. The battery system according to any one of claims 1 to 3, Each battery string includes a negative contactor (342) for connecting the battery string to a negative load bus (344); and The control circuit is configured to close the pre-charge contactor and the negative contactor of the selected battery string to connect the selected battery string to the pre-charge circuit.

5. The battery system according to any one of claims 1 to 4, Each battery string includes a voltage measurement circuit configured to measure the voltage of the battery string; and The control circuit is configured to not select the battery string to precharge the DC link when the offline voltage of the battery string differs from the offline voltage of other battery strings by more than a threshold voltage difference.

6. The battery system according to any one of claims 1 to 5, wherein the pre-charge circuit includes a pre-charge resistor that is directly connected to the load bus without using a contactor.

7. The battery system according to any one of claims 1 to 6, wherein the pre-charge circuit comprises a plurality of positive temperature coefficient (PTC) thermistors.

8. The system according to any one of claims 1 to 7, wherein the rated current of the pre-charge circuit is 100 amperes or greater.

9. The system according to any one of claims 1 to 8, Each battery string includes a negative contactor for connecting the battery string to a negative load bus; and The control circuit is configured to close the positive and negative contactors of the other battery strings in the battery pack that includes the selected battery string when the load is precharged using the selected battery string.

10. The system according to any one of claims 1 to 9, wherein the system comprises: An isolated DC-DC converter is connected to the pre-charge contactor and the positive contactor and is configured to provide a voltage to close the pre-charge contactor and the positive contactor when activated by the control circuit.

11. A method of operating a battery system (120) having a pre-charge circuit (346) connected to a load bus (340) and a plurality of battery packs (330), each battery pack comprising a plurality of battery strings (332) of a plurality of battery cells connected in series, the method comprising: When the battery system is connected to the DC link, the battery string of the battery system is selected to precharge the DC link; Connect the selected battery string to the pre-charge circuit and pre-charge the DC link; as well as When the selected battery string is used to precharge the DC link, the battery string is disconnected from the precharge circuit and the selected battery string is connected to the load bus.

12. The method of claim 11, wherein selecting the battery string comprises selecting the battery string with the highest offline voltage from the plurality of battery packs to connect to the one precharge circuit when all the battery strings are disconnected from the load bus.

13. The method according to claim 11 or claim 12, Connecting the selected battery string to the precharge circuit includes closing the precharge contactor (348) of the selected battery string and closing the negative contactor (342) to connect the selected battery string to the negative load bus; and Connecting the selected battery string to the load bus includes disconnecting the pre-charge contactor of the battery string and closing the positive contactor (338) of the battery string.

14. The method of claim 13, the method comprising closing the positive contactors of other battery strings in a battery pack including the selected battery string when the DC link is precharged using the selected battery string.

15. The method according to any one of claims 11 to 14, Connecting the selected battery string to the precharge circuit includes connecting the selected battery to multiple positive temperature coefficient (PTC) thermistors.

16. The method according to any one of claims 11 to 15, the method comprising: Measure the offline voltage of the battery strings in the plurality of battery packs; as well as When the offline voltage of a battery string differs from the offline voltage of other battery strings by more than a threshold voltage difference, the use of the battery string for pre-charging of the DC link is excluded.

17. The method according to any one of claims 11 to 16, the method comprising: The battery system control circuit determines that the selected battery string cannot precharge the DC link; as well as Different battery strings from different battery packs are connected to the precharge circuit.

18. A non-transitory computer-readable storage medium comprising instructions that, when executed by a hardware processor comprising a battery system (120) including a pre-charge circuit (346) and multiple battery packs (330) each comprising a plurality of battery strings (332), cause the battery system to perform operations, the operations comprising: Receive a command to put the battery system into a discharged state online; Select the battery string of the battery system to precharge the DC link; Connect the selected battery string to the pre-charge circuit and pre-charge the DC link; as well as When the selected battery string is used to precharge the DC link, the battery string is disconnected from the precharge circuit and the selected battery string is connected to the load bus (340).

19. The non-transitory computer-readable storage medium of claim 18, wherein the non-transitory computer-readable storage medium includes instructions that cause the battery system to perform operations, the operations including: The selected battery string is connected to the pre-charge circuit by closing the pre-charge contactor (348) of the selected battery string and closing the negative contactor (342) of the selected battery string to connect the battery string to the negative load bus (344). as well as The selected battery string is directly connected to the load bus by disconnecting the pre-charge contactor of the battery string and closing the positive contactor (338) of the battery string.

20. The non-transitory computer-readable storage medium of claim 18 or claim 19, wherein the non-transitory computer-readable storage medium includes instructions that cause the battery system to perform an operation, the operation comprising: It was determined that the selected battery string was unable to precharge the DC link; as well as Different battery strings from different battery packs are connected to the precharge circuit.

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