Battery pressure active control

Abstract

A vehicle includes a propulsion system having a plurality of electric motors. The battery system is connected to the electric motor through a direct current-direct current (DC-DC) converter and an inverter. A battery system includes a battery assembly having a plurality of battery modules. Each battery module has a plurality of individual battery cells arranged in a battery pack, a set of sensors configured to monitor a set of parameters of each battery pack, and a plurality of battery pack holders. Each battery pack bracket includes a bottom plate and a top plate and an actuator configured to vary a distance between the plates. The monitoring unit is configured to monitor a value representative of a battery pack pressure, determine whether the value falls within a pressure threshold window, and maintain the value within the pressure threshold window by actively changing the battery pack pressure.

Description

Technical Field

[0001] The subject disclosure relates to methods and systems for actively managing pressure in lithium metal batteries or similar batteries. Background Art

[0002] Vehicles, including gasoline and diesel powered vehicles and electric and hybrid electric vehicles, have battery energy storage devices for purposes such as powering electric motors, electronic devices, and other vehicle subsystems. The vehicle battery system can be charged using a power source such as a charging station, other electric vehicle battery systems, and / or the electrical grid. Typically, during the charging process, the height of the battery pack is maintained at a constant state by a fixed gap constraint to prevent accidental expansion of the battery pack. However, as the battery pack ages, and as the battery pack charges and discharges, the pressure within the battery pack increases, and the constant maintained height exacerbates the pressure increase. The pressure increase can negatively affect the performance of the battery pack.

[0003] Therefore, it is desirable to provide a battery monitoring system that takes into account pressure buildup within the battery pack. Summary of the invention

[0004] In an exemplary embodiment, a method for operating a battery system includes monitoring a value representing battery pack pressure, determining whether the value falls within a pressure threshold window, and maintaining the value within the pressure threshold window by actively changing the battery pack pressure in response to the value falling outside the pressure window.

[0005] In addition to one or more features described herein, the value representative of the pressure of the battery pack is a length between a first pressure plate and a second pressure plate, wherein the battery pack is disposed between the first pressure plate and the second pressure plate.

[0006] In addition to one or more features described herein, the value representative of the battery pack pressure is a measured pressure of the battery pack.

[0007] In addition to one or more features described herein, at least one of an upper limit of the pressure threshold window and a lower limit of the pressure threshold window is dependent on a volume of the battery pack.

[0008] In addition to one or more features described herein, determining whether the value falls within the pressure threshold window includes calculating the pressure based on the target length and the feedback length.

[0009] In addition to one or more features described herein, the battery is a lithium metal battery.

[0010] In addition to one or more features described herein, the pressure threshold window is centered about the target pressure value such that an upper limit of the pressure threshold window and a lower limit of the pressure threshold window are equidistant from the target pressure value.

[0011] In addition to one or more features described herein, the upper and lower limits depend on at least one of the age of the battery pack, the state of charge of the battery pack, and the number of charge / discharge cycles the battery pack has undergone.

[0012] In another exemplary embodiment, a battery assembly includes a plurality of battery modules, each battery module including a plurality of individual battery cells arranged in a battery pack, a set of sensors configured to monitor a set of parameters of each battery pack, a plurality of battery pack brackets, each battery pack bracket including a bottom plate and a top plate disposed around the battery pack, each battery pack mount also including an actuator configured to change the distance between the top plate and the bottom plate, a monitoring unit including a processor and a memory, the monitoring unit configured to receive measurements from the sensor, the memory storing instructions for causing the processor to monitor a value representing a battery pack pressure, determine whether the value falls within a pressure threshold window, and maintain the value within the pressure threshold window by actively changing the battery pack pressure in response to the value falling outside the pressure window.

[0013] In addition to one or more features described herein, the value representative of the battery pack pressure is a measured pressure of the battery pack.

[0014] In addition to one or more features described herein, determining whether the value falls within the pressure threshold window includes calculating the pressure based on the target length and the feedback length.

[0015] In addition to one or more features described herein, the upper and lower limits depend on at least one of the age of the battery pack, the state of charge of the battery pack, and the number of charge / discharge cycles the battery pack has undergone.

[0016] In yet another exemplary embodiment, a vehicle includes a propulsion system having a first electric motor and a second electric motor, a battery system connected to the first electric motor and the second electric motor via a direct current-to-direct current (DC-DC) converter and an inverter, the battery system including a battery assembly having a plurality of battery modules, each battery module including a plurality of individual battery cells arranged in a battery pack, a set of sensors configured to monitor a set of parameters for each battery pack; a plurality of battery pack brackets, each battery pack bracket including a bottom plate and a top plate disposed around the battery pack, each battery pack bracket also including an actuator configured to change a distance between the top plate and the bottom plate; and a monitoring unit including a processor and a memory, the monitoring unit being configured to receive measurements from the sensors, the memory storing instructions for causing the processor to monitor a value representing a battery pack pressure, determine whether the value falls within a pressure threshold window, and maintain the value within the pressure threshold window by actively changing the battery pack pressure in response to the value falling outside the pressure window.

[0017] In addition to one or more features described herein, the value representative of the battery pack pressure is a measured pressure of the battery pack.

[0018] In addition to one or more features described herein, determining whether the value falls within the pressure threshold window includes calculating the pressure based on the target length and the feedback length.

[0019] In addition to one or more features described herein, the upper and lower limits depend on at least one of the age of the battery pack, the state of charge of the battery pack, and the number of charge / discharge cycles the battery pack has undergone.

[0020] The above features and advantages and other features and advantages of the present disclosure will become apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other features, advantages and details appear, by way of example only, in the following detailed description, which refers to the accompanying drawings, in which:

[0022] Figure 1 is a schematic diagram of the vehicle;

[0023] Figure 2 is a graph of battery pack pressure during charge / discharge cycles;

[0024] Figure 3 is a diagram illustrating the reversible pressure window;

[0025] Figure 4 is a highly schematic simplified battery pack bracket;

[0026] Figure 5 is an example process for actively controlling battery pack pressure;

[0027] Figure 6 is a more detailed example process for actively controlling battery pack pressure;

[0028] Figure 7 It is used to realize Figure 5 and 6 control systems for the processes;

[0029] Figure 8 Is configured for use in Figure 7 An example control loop in a control system. DETAILED DESCRIPTION

[0030] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or use. It should be understood that in all figures, corresponding reference numerals represent the same or corresponding parts and features. As used herein, the term module refers to a processing circuit, which may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated or group) and memory that executes one or more software or firmware programs, a combinational logic circuit and / or other suitable components that provide the described functions.

[0031] According to an exemplary embodiment, the battery monitoring system actively monitors a parameter of the battery pack, which represents the pressure of the battery pack. When the pressure drops below the lower limit of the pressure threshold window, or moves above the upper limit of the pressure threshold window, the battery monitoring system actively adjusts the pressure, thereby keeping the pressure of the battery pack within the pressure window and increasing the life of the battery pack. In this example, the upper and lower limits depend on the volume of the battery pack, and an increase in pressure will also cause the volume of the battery pack to increase.

[0032] Figure 1 One embodiment of a motor vehicle 10 is shown and includes a body 12 that at least partially defines an occupant compartment 14. The body 12 also supports various vehicle subsystems, including a propulsion system 16 and other subsystems to support the functions of the propulsion system 16 and other vehicle components, such as a braking subsystem, a suspension system, a steering subsystem, a fuel injection subsystem, an exhaust subsystem, etc.

[0033] The vehicle 10 may be an internal combustion vehicle, an electric vehicle (EV), or a hybrid vehicle. In one embodiment, the vehicle 10 is a hybrid vehicle that includes an internal combustion engine system 18 and at least one electric motor system. For example, the propulsion system 16 includes a first electric motor 20 and a second electric motor 21. The motors 20 and 21 may be configured to drive wheels on opposite sides of the vehicle 10. Any number of motors located in different locations may be used.

[0034] Vehicle 10 includes a battery system 22 that may be electrically connected to motors 20 and 21 and / or other components, such as vehicle electronics. Battery system 22 may be configured as a rechargeable energy storage system (RESS).

[0035] In one embodiment, the battery system 22 includes a battery assembly, such as a high voltage battery pack 24 having a plurality of battery modules 26. Each battery module 26 includes a plurality of individual battery cells arranged in a battery pack. The battery system 22 may also include a monitoring unit 28 (e.g., a RESS controller) configured to receive measurements from sensors 30. Each sensor 30 may be an assembly or system having one or more sensors for measuring various battery and environmental parameters, such as temperature, battery pack gap distance, battery pack pressure, current, voltage, and state of charge. The monitoring unit 28 includes various components, such as a processor, a memory, an interface, a bus, and / or other suitable components.

[0036] The battery system 22 is electrically connected to a direct current (DC)-DC converter module 32 and an inverter module 34. The inverter module 34 (e.g., a traction power inverter unit or TPIM) converts the direct current (DC) power from the battery assembly into three-phase alternating current (AC) power to drive the motor. In one embodiment, the inverter module 34 includes a first inverter 36 connected to the motor 20 and a second inverter 38 connected to the motor 21.

[0037] In some embodiments, the battery module 26 is composed of lithium metal batteries or similar types of battery cells. During vehicle operation, as the battery cells are charged and discharged (referred to as a charge / discharge cycle), the pressure on each battery cell changes. During each charge / discharge cycle, most of the pressure increase is reversible, however, a portion is irreversible. Irreversible pressure increases are undesirable and should be minimized in order to increase the life cycle of the battery pack.

[0038] Figure 2 100 is a graph showing the variation of battery pack pressure MPa (vertical axis) over time t (horizontal axis) over multiple charge / discharge cycles. A typical existing battery cell structure places one or more battery cells between two plates that are placed a fixed distance apart. In this configuration, pressure fluctuations during the charge / discharge cycle are shown by the solid line 102. Some attempts to minimize pressure fluctuations include the use of spring-loaded plates, in which the springs compress as the pressure increases, allowing the gap between the plates to move during the charge / discharge cycle. The dashed line 106 shows the pressure variation during the charge / discharge cycle of the spring-loaded variable distance structure. Combining spring loading and allowing the gap to move based on changes in battery pack pressure is referred to as using passive gap regulation and reducing peak pressure 108. In some examples, the reduction in peak pressure can be close to an order of magnitude.

[0039] Continue to refer Figure 2 , Figure 3A graph 200 illustrating the expansion of a given battery cell over multiple cycles is shown, with the vertical axis representing the battery cell pressure and the horizontal axis representing the number of charge / discharge cycles. A new battery pack (e.g., when the number of charge / discharge cycles is zero) starts with a pressure of a minimum pressure value 202. As the pressure increases during the charge / discharge cycle, the pressure approaches a maximum reversible pressure value 204. The distance between the minimum pressure 202 and the maximum reversible pressure 204 is called the reversible pressure window. Any pressure increase exceeding the maximum reversible value is irreversible and moves the minimum and maximum pressures 202, 204 upward by an irreversible amount to a new position 202', 204'. Over multiple cycles, the reversible pressure window moves upward, as shown by 202" and 204". Systems that incorporate passive gap adjustment (e.g., spring-loaded battery pack plates) have a lower but still stable increase in the reversible pressure window, and are shown by solid lines. In contrast, a fixed gap distance increases at a faster rate, resulting in a shorter life cycle of the battery pack, and the window increase is shown by a pair of dashed lines 212, 214.

[0040] In order to minimize the above irreversible pressure changes, Figure 1 The battery system 22 of the illustrated vehicle 10 includes a pressure management system that actively controls the pressure on the battery pack to ensure that the pressure is maintained at about Figure 3 The active management system includes a control module within the monitoring unit 28. The control module actively controls the gap distance between the plates that hold the battery pack in place, and the active control of the gap controls the pressure of the battery pack 330 (see Figure 4 ).

[0041] Continue to refer Figure 1-3 , Figure 4 A simplified example battery pack support 300 is shown. The simplified battery pack support 300 includes a bottom plate 310 and a top plate 320. The battery pack 330 is located between the bottom plate 310 and the top plate 320. A set of supports 340 separates the plates 310, 320 and maintains a desired distance l between the plates 310, 320. The actuation system 350 is configured to move the top plate 320 and the bottom plate 310 closer and farther. The actuation system can be any suitable actuator. In alternative examples, other types of actuators with similar controls and functions can also be used in the system. The movement of the plates 310, 320 increases or decreases the length l and the pressure / expansion experienced by the battery pack 330. For a given length l between the top plate 320 and the bottom plate 310, the pressure is a nonlinear function of the state of charge (SOC), with higher states of charge resulting in higher pressures and lower states of charge resulting in lower pressures. Actively controlled external pressure applied via an actuation system can reduce permanent expansion by determining the pressure, reduce the growth of dendrites within the battery, and can increase the life cycle of the battery.

[0042] Continue to refer Figure 1-4 , Figure 5 A control process 400 for controlling pressure by a target length l of the gap is shown. Initially, the monitoring unit 28 identifies a target pressure in a "read target pressure" step 410. The target pressure may be stored in memory, determined by the controller, or received from another control system, and may be either a constant value independent of the state of charge and age of the battery, or a variable value dependent on the current state of charge and position in the charge / discharge operation.

[0043] Subsequently, in a "measure or estimate current pressure" step 420, the pressure of the battery pack 330 is estimated or directly measured. In one example, the pressure is measured directly using a pressure sensor in the set of sensors 30. In another example, the pressure is estimated based on known or measurable factors including the length l. Once both the target pressure and the estimated pressure are identified, in a difference check 430, the control process determines whether the difference between the target and the reference is greater than an acceptable difference. The acceptable difference is half of the reversible pressure window, and when the difference exceeds the acceptable difference, the difference check 430 determines that the reference value is outside the reversible pressure window. If the target value and the reference value are within the acceptable difference, the process 400 returns to the beginning and no pressure adjustment is performed.

[0044] If the difference exceeds the acceptable difference, the monitoring unit 28 identifies that the pressure is outside the acceptable pressure window and determines whether the current pressure is greater than the target pressure in the comparison step 440. When the current pressure is greater than the target pressure, the process 400 reduces the volume of the battery chamber by reducing the length l in the reduce volume step 450. Alternatively, when the target pressure is not less than the current pressure, the monitoring system 28 increases the volume of the battery chamber in the increase volume step 460.

[0045] Figure 5 The control process shown is an actuation based system that controls the pressure by adjusting the gap (l) between the plates in order to attenuate long term and / or short term pressure variations throughout the charge / discharge operation.

[0046] In a more specific example, pressure control is achieved by controlling the gap to a target length l rather than a target pressure. Figure 1-5 , Figure 6 A flow chart 500 of an example process is shown in which battery pressure control is achieved by controlling the gap l to a target gap length. When a measured gap length l is available, such as by sensor 30, a simple feedback controller (e.g., a proportional-integral-derivative PID controller) can be used to control the gap to the target gap length. In alternative situations where the gap length l is not directly measurable or direct measurement is unavailable, the target pressure can be calculated based on the target length and feedback control to the desired pressure. The current battery pack pressure can be measured or estimated.

[0047] Referring to diagram 500, in a "read SOC, V, temperature" step 510, the initial state of charge of the battery pack 330, the voltage of the battery pack 330, and the temperature of the battery pack 330 are determined by the sensor 30 and / or derived from available sensor data. Once the parameters are determined, in a "calculate pressure increase due to irreversible expansion" step 520, the pressure increase in the battery pack 330 due to irreversible expansion is calculated. Based on the calculated pressure increase, a target length l of the gap is calculated in an "update target length" step 530.

[0048] Once the target length is determined, in an "update optimal pressure" step 540, the target pressure is updated based on the new target length, and in a "read current pressure step" 550, the current pressure is determined by direct measurement from the sensor 330 or derived from the sensor measurement. The difference between the current pressure and the target pressure is checked in a difference check 560. When the difference does not exceed the window size, the process restarts (510). When the difference exceeds the window size, it is determined that the pressure on the battery pack 330 needs to be adjusted, and the controller determines whether the current pressure is greater than the target pressure in a comparison step 570. When the current pressure is greater than the target pressure, in an "increase l" step 580, the length l is increased, thereby reducing the pressure. Conversely, when the current pressure is not greater than the target pressure, in a decrease l step 590, the length l is reduced, thereby reducing the pressure.

[0049] Continue to refer Figure 1-6 , and specific reference Figure 5 and 6 , Figure 7 Shown is the method for implementing Figure 5 and 6 The control diagram 600 of any of the control schemes described herein includes a set of state variables 610 as inputs, including a battery pack voltage 612, a state of charge 614 of the battery pack 330, and a temperature 616 of the battery pack 330. The state variables 610 are provided to a control block 620. In some examples, additional state variables 610 that are measured or derived may be provided to the control block 620. The control block 620 controls the battery pack 330 in accordance with the state variables 610. Figure 6 Steps 510 - 530 identify a desired pressure for the battery pack 330 and output a desired pressure 622 .

[0050] At combiner 630, the desired pressure is combined with the measured or derived current pressure. The output of combiner 630 is provided to actuator controller 640, and actuator controller 640 adjusts the position of the plate to control the length l, or to control the battery pack pressure, such as Figure 5 and 6As the actuator adjusts the plates, and therefore the pressure on the battery pack 330, the current pressure 650 is recirculated to the combiner 630 in a feedback loop.

[0051] Continue to refer Figure 1-7 , Figure 8 An example implementation of the control block 620 is shown. The control block receives the charge voltage and discharge voltage from the state variable 610 and determines the current pressure change Δcp in the pressure change block 710. The pressure change and the measured state of charge (SOC) are provided to the target gap length determiner 720, which converts the target gap length l ref Output to the target pressure determiner 730, the target pressure determiner 730 uses the target gap length l ref , state of charge SOC and temperature (t) to determine the target pressure. Then Figure 7 The system provides the target pressure forward.

[0052] use Figure 1-8 The described system and method implement active pressure control of battery charging and discharging operations. Active pressure control controls the pressure of the battery pack during battery operation to accommodate pressure buildup in the battery as the battery ages, as well as to accommodate short-term pressure changes due to charging / discharging operations. Active control of pressure reduces the occurrence of dendrite formation or similar degradation in other battery types, and increases the operating life of the battery pack.

[0053] The terms "one" and "an" do not indicate a limitation of quantity, but rather indicate the presence of at least one of the referenced items. The term "or" means "and / or", unless the context clearly indicates otherwise. References to "an aspect" throughout the specification mean that a particular element (e.g., feature, structure, step, or characteristic) described in conjunction with that aspect is included in at least one aspect described herein, and may or may not be present in other aspects. In addition, it should be understood that the described elements may be combined in any suitable manner in various aspects.

[0054] When an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

[0055] Unless otherwise indicated herein, all test standards are the most recent standards in effect as of the filing date of the present application or, if priority is claimed, the filing date of the earliest priority application in which the test standards appear.

[0056] Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0057] Although the above disclosure has been described with reference to exemplary embodiments, it will be appreciated by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from the scope thereof. In addition, many modifications may be made to adapt specific situations or materials to the teachings of the disclosure without departing from the essential scope of the disclosure. Therefore, it is intended that the disclosure is not limited to the specific embodiments disclosed, but will include all embodiments falling within its scope.

Claims

1. A method for operating a battery system, comprising: monitoring a value representative of pressure of a battery pack, optionally wherein the battery pack is a lithium metal battery; determining whether the value falls within a pressure threshold window; as well as The value is maintained within the pressure threshold window by actively changing the pressure of the battery pack in response to the value falling outside of the pressure threshold window.

2. The method according to claim 1, wherein: The value representing the pressure of the battery pack is a length between the first pressing plate and the second pressing plate, and wherein the battery pack is disposed between the first pressing plate and the second pressing plate.

3. The method according to claim 1, wherein: The value representing the pressure of the battery pack is the measured pressure of the battery pack.

4. The method according to claim 1, wherein: At least one of an upper limit of the pressure threshold window and a lower limit of the pressure threshold window depends on a volume of the battery pack.

5. The method according to claim 1, wherein: Determining whether the value falls within a pressure threshold window includes calculating a pressure based on a target length and a feedback length.

6. The method according to claim 1, wherein: The pressure threshold window is centered on the target pressure value so that an upper limit of the pressure threshold window and a lower limit of the pressure threshold window are equidistant from the target pressure value, and wherein the upper limit and the lower limit depend on at least one of the life of the battery pack, the state of charge of the battery pack, and the number of charge / discharge cycles the battery pack has undergone.

7. A battery assembly comprising: a plurality of battery modules, each battery module comprising a plurality of individual battery cells arranged in a battery pack; a set of sensors configured to monitor a set of parameters for each battery pack; a plurality of battery pack brackets, each battery pack bracket including a bottom plate and a top plate disposed around the battery pack, each battery pack bracket further comprising an actuator configured to change a distance between the top plate and the bottom plate; A monitoring unit comprising a processor and a memory, the monitoring unit being configured to receive measurements from a sensor, the memory storing instructions for causing the processor to monitor a value representing the pressure of a battery pack, determine whether the value falls within a pressure threshold window, and maintain the value within the pressure threshold window by actively changing the pressure of the battery pack in response to the value falling outside the pressure threshold window.

8. The battery assembly according to claim 7, wherein: The value representing the pressure of the battery pack is one of a measured pressure of the battery pack and a length between a first pressure plate and a second pressure plate, and wherein the battery pack is disposed between the first pressure plate and the second pressure plate.

9. The battery assembly according to claim 8, wherein: Determining whether the value falls within a pressure threshold window includes calculating a pressure based on a target length and a feedback length.

10. The battery assembly according to claim 9, wherein: The upper and lower limits depend on at least one of the age of the battery pack, the state of charge of the battery pack, and the number of charge / discharge cycles the battery pack has undergone.

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