Battery system

Abstract

The present invention provides a battery system capable of suppressing lithium deposition in energy storage devices, including lithium-ion batteries. [Solution] The battery system 100 includes a current sensor 30 for detecting ripple current and an ECU 10. Based on the decay curve, the ECU 10 reconstructs the actual amplitude of the ripple current flowing through the current sensor 30 from the amplitude of the ripple current detected by the current sensor 30. If the reconstructed amplitude is greater than the upper limit of the ripple current amplitude that can suppress lithium deposition in the battery 40, the ECU 10 reduces the amplitude of the ripple current.

Description

Technical Field

[0001] The present disclosure relates to a battery system.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2010-259217 (Patent Document 1) discloses a driving device that warms up a battery by flowing a ripple current through the battery. In the driving device, the warming of the battery is promoted by increasing the ripple current.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, when the battery includes a lithium-ion battery, lithium may be deposited when the amplitude of the ripple current exceeds a predetermined threshold value. In contrast, it is conceivable to reduce the amplitude of the ripple current so that the detected value (amplitude) of the current sensor becomes below the above-mentioned predetermined threshold value. However, the detected value (amplitude) of the current sensor may be attenuated with respect to the actual amplitude of the ripple current. In this case, there is a risk of lithium deposition.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a battery system capable of suppressing the deposition of lithium in a power storage device including a lithium-ion battery.

Means for Solving the Problems

[0006] A battery system according to one aspect of this disclosure comprises a ripple generation device connected to an energy storage device including a lithium-ion battery and configured to generate a ripple current in the energy storage device; a current detection device for detecting the ripple current generated by the ripple generation device; and a control device for controlling the ripple generation device. The upper limit of the amplitude of the ripple current that can suppress lithium deposition in the energy storage device is defined as the amplitude upper limit, and the attenuation curve is defined as the relationship between the attenuation rate from the first amplitude, which is the actual amplitude of the ripple current flowing through the current detection device, to the second amplitude, which is the amplitude of the value detected by the current detection device, and the frequency of the ripple current. Based on the attenuation curve, the control device restores the first amplitude from the second amplitude of the ripple current detected by the current detection device, and defines the restored first amplitude as the restored amplitude. If the restored amplitude is greater than the amplitude upper limit, the control device reduces the amplitude of the ripple current.

[0007] In a battery system according to one aspect of this disclosure, as described above, the control device restores the first amplitude from the second amplitude of the ripple current detected by the current detection device based on the decay curve, and when the restored first amplitude is taken as the restored amplitude, the control device reduces the amplitude of the ripple current if it is greater than the upper amplitude limit. As a result, even if the value detected by the current detection device has decayed, the amplitude can be restored using the decay curve, thereby adjusting the amplitude of the ripple current actually flowing through the current detection device so that it does not exceed the upper amplitude limit. Consequently, the deposition of lithium in the energy storage device can be suppressed.

[0008] The control device may reduce the amplitude of the ripple current so that the recovery amplitude is equal to or substantially equal to the upper amplitude limit when the recovery amplitude is greater than the upper amplitude limit. With this configuration, lithium deposition in the energy storage device can be easily suppressed. Furthermore, the amplitude of the ripple current can be made relatively large while suppressing lithium deposition. This makes it possible to efficiently dissipate the total heat of the energy storage device due to the ripple current.

[0009] The control device may maintain the ripple current amplitude at its current value without changing it if the recovery amplitude is below the upper limit of the amplitude. This configuration makes it easy to suppress lithium deposition in the energy storage device.

[0010] The current detection device includes a busbar and a magnetic field detection element that detects the magnetic field generated by the current flowing through the busbar. The busbar may have a rectangular cross-section intersecting the direction of current flow. Due to the skin effect, the current density near the center of the busbar's cross-section is relatively low. As a result, when the busbar has a rectangular cross-section, the magnetic field generated by the ripple current flowing through the busbar becomes uneven (the magnetic field concentrates at the ends). Therefore, it is conceivable that the current value detected by the current detection device will attenuate due to a decrease in the magnetic field input to the magnetic field detection element. Accordingly, reducing the amplitude of the ripple current based on the restored amplitude restored based on the attenuation curve is particularly effective when the busbar has a rectangular cross-section.

[0011] Furthermore, because the cross-section is rectangular, the cross-sectional area can be easily increased compared to cases where the cross-section is square, etc. As a result, the ripple current that can flow through the busbar can be easily increased.

[0012] The control device may be configured to adjust the frequency of the ripple current. The current detection device may detect a second amplitude corresponding to each of a plurality of frequencies within a predetermined frequency range, including a target frequency. Based on the second amplitude corresponding to each of the plurality of frequencies, the control device may calculate the rate of change of the second amplitude with respect to the frequency in the frequency range and determine whether the rate of change is abnormal or not based on the attenuation curve. If the control device determines that the rate of change is abnormal, it may stop the generation of the ripple current, and if it determines that the rate of change is not abnormal, it may set the frequency to the target value. The control device may calculate the recovery amplitude based on the attenuation curve and the second amplitude corresponding to the target value, and may reduce the amplitude of the ripple current if the recovery amplitude is greater than the upper limit of the amplitude. With such a configuration, it is possible to suppress the process of reducing the amplitude of the ripple current based on the recovery amplitude from being executed when the frequency of the ripple current is deviating from the target value. [Effects of the Invention]

[0013] According to this disclosure, it is possible to suppress the deposition of lithium in energy storage devices, including lithium-ion batteries. [Brief explanation of the drawing]

[0014] [Figure 1] This figure shows a vehicle equipped with the battery system according to this embodiment. [Figure 2] This is a schematic diagram showing the battery configuration according to this embodiment. [Figure 3] This figure shows the decay curve of a current sensor. [Figure 4] This is a flowchart illustrating the control of the battery system according to this embodiment. [Figure 5] Figure 4 is a flowchart showing the details of step S20. [Figure 6] Figure 4 is a flowchart showing the details of step S30. [Modes for carrying out the invention]

[0015] Embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0016] FIG. 1 is a diagram showing a vehicle 200 equipped with a battery system 100 according to an embodiment of the present disclosure.

[0017] The vehicle 200 is electrically connected to a power stand 300 through a cable 310, and power can be exchanged (charged and discharged) with the power stand 300. This power exchange is performed in a state where a plug 311 provided at an end of the cable 310 is connected to an inlet 210 of the vehicle 200. An alternating current is flowing between the power stand 300 and the vehicle 200. Note that the power stand 300 exchanges power with a power grid PG.

[0018] The vehicle 200 is equipped with a battery system 100, an MG (Motor Generator) 220, and a charger / discharger 230.

[0019] The battery system 100 includes an ECU (Electronic Control Unit) 10, a PCU (Power Control Unit) 20, a current sensor 30, a battery 40, an SMR (System Main Relay) 50, and a relay 60. Note that the ECU 10 and the battery 40 are examples of the "control device" and the "power storage device" of the present disclosure, respectively. Also, the PCU 20 and the current sensor 30 are examples of the "ripple generation device" and the "current detection device" of the present disclosure, respectively.

[0020] The ECU 10 includes a processor 11, a RAM (Random Access Memory) 12, and a storage device 13. The storage device 13 is configured to be able to store the stored information. In addition to programs, information used in the programs (for example, maps, mathematical formulas, and various parameters) are stored in the storage device 13. In the present embodiment, by the processor 11 executing the program stored in the storage device 13, various processes by the ECU 10 (for example, control of the ripple current described later) are executed. However, these processes may be executed only by hardware (electronic circuit) without using software.

[0021] The vehicle 200 is configured to be able to run using the electric power stored in the battery 40. The vehicle 200 is, for example, a battery electric vehicle (BEV) that does not include an engine (internal combustion engine). However, it is not limited to this, and the vehicle 200 may be a PHEV (plug-in hybrid vehicle) equipped with an internal combustion engine, or may be another electric vehicle (xEV).

[0022] The charger 230 and the relay 60 are located between the inlet 210 and the battery 40. Each of the charger 230 and the relay 60 is controlled by the ECU 10. In the present embodiment, a charging and discharging line including the inlet 210, the charger 230, and the relay 60 is connected between the SMR 50 and the PCU 20. However, it is not limited to this, and a charging and discharging line may be connected between the battery 40 and the SMR 50.

[0023] The charger 230 charges the battery 40 using the electric power input from the outside of the vehicle to the inlet 210. The charger 230 includes a power conversion circuit (for example, a converter including an inverter and a reactor) and is configured to be able to adjust the charging current. The relay 60 switches the connection / disconnection of the electric path from the inlet 210 to the battery 40.

[0024] In the plugged-in vehicle 200, external charging (i.e., charging of the battery 40 with power from outside the vehicle) and external discharging (i.e., discharging of power from the battery 40 to the outside of the vehicle) are possible. Note that the vehicle 200 may also be capable of performing only external charging. When external charging and external discharging are performed, the relay 60 is set to a closed state (connected state), and when external charging and external discharging are not performed, the relay 60 is set to an open state (disconnected state).

[0025] The MG220 is, for example, a three-phase AC motor generator. The MG220 functions as a drive motor for the vehicle 200. The MG220 is driven by the PCU20 and rotates the drive wheels of the vehicle 200. The MG220 also performs regenerative power generation and outputs the generated power to the battery 40. The number of drive motors equipped on the vehicle 200 is arbitrary.

[0026] The PCU20 includes a circuit (e.g., an inverter and converter) that drives the MG220 using power supplied from the battery 40. The SMR50 switches the connection / disconnection of the circuit from the battery 40 to the PCU20. Both the SMR50 and the PCU20 are controlled by the ECU10. The SMR50 is closed (connected) when the vehicle 200 is running. The SMR50 is also closed when power is exchanged between the battery 40 and the inlet 210 (and thus outside the vehicle).

[0027] The battery 40 includes a plurality of energy storage cells (not shown). The energy storage cells are secondary batteries, typically lithium-ion secondary batteries. Lithium-ion secondary batteries are batteries that use lithium as a charge carrier, and may include not only lithium-ion secondary batteries with a liquid electrolyte, but also all-solid-state batteries that use a solid electrolyte.

[0028] The ripple current may be generated by the control of the PCU20 by the ECU10. Specifically, the ripple current is generated when a switching element provided in the PCU20 is switched by the ECU10. The ECU10 may be able to adjust the frequency of the ripple current by adjusting the on / off period of the switching element. Note that the method of generating the ripple current is not limited to this example.

[0029] Figure 2 is a schematic diagram showing the configuration of the current sensor 30. The current sensor 30 detects the current flowing between the battery 40 and the SMR 50.

[0030] The current sensor 30 includes a magnetic field detection element 31 and a busbar 32. The current (ripple current) flows through the busbar 32 in the direction of the dashed arrow in Figure 2. In this case, the current flowing through the busbar 32 forms a magnetic field (dashed arrow). As shown in Figure 2, the busbar 32 has a rectangular cross-section 32a that intersects (orthogonal to) the direction in which the current flows. For example, the length of the longer side of the cross-section 32a may be five times or more the length of the shorter side of the cross-section 32a.

[0031] Here, the current near the center of the cross-section 32a decreases as the frequency of the ripple current increases due to the skin effect. Consequently, the higher the frequency of the ripple current, the greater the bias in the magnetic field generated by the ripple current. As a result, the magnetic field input to the magnetic field detection element 31 decreases, and consequently, the current value detected by the current sensor 30 is attenuated.

[0032] Furthermore, the current value detected by the current sensor 30 is also attenuated by low-pass filters (not shown) provided in both the current sensor 30 and the battery ECU 10. The amount of attenuation by the low-pass filter increases as the frequency of the ripple current increases.

[0033] Figure 3 is an attenuation curve showing the relationship between the frequency of the ripple current (horizontal axis) and the attenuation rate in the current sensor 30 (vertical axis). The attenuation rate refers to the rate attenuation from the actual amplitude of the ripple current flowing through the current sensor 30 (busbar 32) to the amplitude of the value detected by the current sensor 30. The data of this attenuation curve may be stored in the storage device 13 of the ECU 10. As shown in Figure 3, the attenuation rate of the current sensor 30 increases as the frequency of the ripple current increases.

[0034] In lithium-ion batteries, lithium may be deposited if the amplitude of the ripple current exceeds a predetermined threshold. To address this, one might consider reducing the amplitude of the ripple current so that the detected value (amplitude) of the current sensor is below the predetermined threshold. However, the detected value (amplitude) of the current sensor may be attenuated relative to the actual amplitude of the ripple current. In this case, lithium deposition may occur.

[0035] Therefore, in this embodiment, the ECU 10 calculates the actual (pre-attenuation) amplitude based on the attenuation curve and the amplitude of the ripple current detected by the current sensor 30. The ECU 10 reduces the amplitude of the ripple current when the calculated amplitude (hereinafter referred to as the restored amplitude) is greater than the upper limit of the amplitude at which lithium deposition is suppressed (hereinafter referred to as the amplitude upper limit). Details will be explained later with reference to Figure 6.

[0036] (Control flow) Figure 4 is a flowchart showing the control performed by the ECU 10. The control flow shown in Figure 4 is executed when raising the temperature of the battery 40 using ripple current.

[0037] In step S10, the ECU10 generates a ripple current by controlling the PCU20, SMR50, and relay 60, etc. At this time, the ECU10 sets the frequency of the ripple current to a predetermined target value (for example, 1000Hz). Next, the process proceeds to step S20.

[0038] In step S20, the ECU10 determines whether there is an abnormality in the frequency of the ripple current. Next, the process proceeds to step S30.

[0039] In step S30, the ECU10 adjusts the amplitude of the ripple current. After that, the process ends.

[0040] Figure 5 is a flowchart showing the details of step S20. Step S20 includes steps S21 to S26.

[0041] In step S21, the ECU 10 changes the frequency of the ripple current within a predetermined frequency range centered on the target value, and acquires information on the amplitude of the ripple current at each frequency from the current sensor 30. For example, with the ripple current amplitude set to a predetermined value (e.g., 500A), the ECU 10 acquires information on the amplitude at frequencies of 900Hz, 1000Hz (target value), and 1100Hz from the current sensor 30.

[0042] In step S22, the ECU 10 calculates the rate of change of amplitude with respect to frequency based on the information obtained from the current sensor 30. Specifically, the ECU 10 calculates the rate of change from the amount of change in amplitude (detected value) in the frequency band from 900 Hz to 1100 Hz. The ECU 10 may calculate the rate of change using, for example, the least squares method.

[0043] In step S23, the ECU10 calculates the rate of change (expected value) of the amplitude in the above frequency range based on the attenuation curve. For example, if the attenuation curve shows that the attenuation rate at 900Hz is 30%, the attenuation rate at 1000Hz is 35%, and the attenuation rate at 1100Hz is 40%, then the rate of change when the amplitude setting is 500A is (500 × 0.7 - 500 × 0.6) / (900 - 1100) = -0.25.

[0044] In step S24, the ECU 10 determines whether the magnitude (absolute value) of the difference between the rate of change (expected value) calculated in step S23 and the rate of change calculated in step S22 is less than or equal to the threshold Th1. If the difference is less than or equal to the threshold Th1 (Yes in S23), the process proceeds to step S25. If the difference is greater than the threshold Th1 (No in S23), the process proceeds to step S26.

[0045] The threshold Th1 may vary based on the amplitude set value and frequency. For example, the threshold Th1 may increase as each of the amplitude set value and frequency increases. The threshold Th1 may be calculated by the ECU10, or it may be determined by the ECU10 based on a map showing the relationship between the amplitude set value and frequency and the threshold Th1.

[0046] In step S25, the ECU 10 sets the frequency of the ripple current to a target value (1000 Hz in this embodiment). Next, the process proceeds to step S30.

[0047] In step S26, the ECU 10 stops generating ripple current. Specifically, the ECU 10 may stop generating ripple current by stopping the switching of the switching element provided in the PCU 20. After that, the process ends.

[0048] Figure 6 is a flowchart showing the details of step S30. Step S30 includes steps S31 to S33.

[0049] In step S31, the ECU 10 restores the amplitude of the ripple current based on the attenuation curve. As described above, if the attenuation rate corresponding to 1000 Hz is 35% based on the attenuation curve, the ECU 10 may restore the amplitude by multiplying the amplitude detected by the current sensor 30 by 100 / 65.

[0050] In step S32, the ECU 10 determines whether the amplitude restored in step S31 is less than or equal to the lithium deposition protection amplitude Th2. The protection amplitude Th2 is the upper limit of the amplitude at which lithium deposition can be suppressed in the battery 40. If the restored amplitude is less than or equal to the protection amplitude Th2 (Yes in S32), the process ends. In this case, the ECU 10 maintains the ripple current amplitude at its current value without changing it. If the restored amplitude is greater than the protection amplitude Th2 (No in S32), the process proceeds to step S33. Note that in step S31, different protection amplitude Th2 values ​​may be used depending on the frequency. A map showing the relationship between the protection amplitude Th2 used in step S31 and the frequency may be stored in the storage device 13 (Figure 1).

[0051] In step S33, the ECU 10 reduces the amplitude setting so that the restored amplitude is the protection amplitude Th2 or substantially equivalent to the protection amplitude Th2. For example, the ECU 10 may gradually reduce the amplitude of the ripple current until the restored amplitude is the protection amplitude Th2 or substantially equivalent to the protection amplitude Th2. After that, the process ends. Substantially equivalent to the protection amplitude Th2 may mean, for example, a range of at least a predetermined percentage of the protection amplitude Th2 (e.g., 95%) and less than the protection amplitude Th2. Furthermore, the reduction of the ripple current amplitude may be achieved by known methods.

[0052] As described above, in this embodiment, the ECU 10 restores the amplitude of the ripple current actually flowing through the current sensor 30 from the amplitude of the ripple current detected by the current sensor 30 based on the attenuation curve, and reduces the amplitude of the ripple current (set value) if the restored amplitude is greater than the upper limit of the amplitude. This makes it possible to suppress lithium deposition in the battery 40 even if the value detected by the current sensor 30 is attenuated more than the actual amplitude.

[0053] (modified version) In the above embodiment, an example was shown in which, when the restored amplitude is greater than the upper amplitude limit, the amplitude of the ripple current is reduced so that the restored amplitude is equal to or substantially equal to the upper amplitude limit. However, the disclosure is not limited thereto. In the above case, for example, the amplitude of the ripple current may be reduced so that the restored amplitude is smaller than the upper amplitude limit by a predetermined amount.

[0054] In the above embodiment, an example was shown in which the amplitude of the ripple current is not changed when the restored amplitude is less than or equal to the upper amplitude limit, but the disclosure is not limited thereto. In the above case, the amplitude of the ripple current may be increased so that the restored amplitude is equal to or substantially equivalent to the upper amplitude limit.

[0055] In the above embodiment, an example was shown in which the cross-section 32a of the busbar 32 of the current sensor 30 has a rectangular shape, but the disclosure is not limited thereto. The cross-section of the busbar may have a shape other than a rectangle (for example, circular or square).

[0056] In the above embodiment, an example was shown in which an abnormality in the rate of change of the amplitude of the ripple current is determined based on the detected value of the current sensor 30 corresponding to each of multiple frequencies, but the disclosure is not limited thereto. The above determination may also be made based on the detected value of the current sensor 30 corresponding to only one frequency (target value).

[0057] In the above embodiment, an example was shown in which a ripple current is generated by controlling the switching elements of the PCU 20, but the disclosure is not limited thereto. For example, a ripple current may be generated by controlling the switching elements of the charger / discharger 230.

[0058] In the above embodiment, an example is shown in which a current sensor 30 is provided that detects the current value based on the magnitude of the magnetic field, but the disclosure is not limited thereto. A current sensor that detects the current value based on the magnitude of the voltage drop due to the shunt resistor may also be provided.

[0059] The configurations of each of the above embodiments and each of the modified examples may be combined with each other.

[0060] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0061] 10 ECU (control unit), 20 PCU (ripple generator), 30 current sensor (current detection device), 31 magnetic field detection element, 32 busbar, 32a cross section, 40 battery (energy storage device), 100 battery system.

Claims

1. A ripple generation device connected to an energy storage device including a lithium-ion battery, and configured to generate a ripple current in the energy storage device, A current detection device for detecting the ripple current generated by the ripple generation device, The system comprises a control device for controlling the ripple generation device, The upper limit of the amplitude of the ripple current that can suppress lithium deposition in the energy storage device is set as the amplitude upper limit. If the curve showing the relationship between the attenuation rate from the first amplitude, which is the actual amplitude of the ripple current flowing through the current detection device, to the second amplitude, which is the amplitude of the value detected by the current detection device, and the frequency of the ripple current is defined as the attenuation curve, The control device is Based on the decay curve, the first amplitude of the ripple current detected by the current detection device is restored from the second amplitude. A battery system that, when the restored first amplitude is defined as the restored amplitude, reduces the amplitude of the ripple current if the restored amplitude is greater than the upper limit of the amplitude.

2. The battery system according to claim 1, wherein the control device reduces the amplitude of the ripple current so that the restoration amplitude becomes equal to or substantially equal to the amplitude upper limit when the restoration amplitude is greater than the amplitude upper limit.

3. The battery system according to claim 1 or 2, wherein the control device maintains the amplitude of the ripple current at its current value without changing it when the restoration amplitude is less than or equal to the upper limit of the amplitude.

4. The current detection device is Bassba and, The system includes a magnetic field detection element that detects the magnetic field generated by the current flowing through the busbar, The battery system according to claim 1 or 2, wherein the busbar has a rectangular cross-section that intersects the direction in which the current flows.

5. The control device is configured to be able to adjust the frequency of the ripple current, The current detection device detects the second amplitude corresponding to each of a plurality of frequencies within a predetermined frequency range including the target value of the frequency, The control device is Based on the second amplitude corresponding to each of the plurality of frequencies, the rate of change of the second amplitude with respect to the frequency in the frequency range is calculated. Based on the aforementioned damping curve, it is determined whether the rate of change is abnormal or not. If the rate of change is determined to be abnormal, the generation of the ripple current is stopped. If it is determined that the rate of change is not abnormal, the frequency is set to the target value. The battery system according to claim 1 or 2, wherein the recovery amplitude is calculated based on the damping curve and the second amplitude corresponding to the target value, and the amplitude of the ripple current is reduced when the recovery amplitude is greater than the upper limit of the amplitude.

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