Battery pack degradation suppression device
The battery pack degradation suppression device addresses the issue of capacity loss in stored LFP batteries by using a voltage control system to equalize cell voltages, reducing power consumption, and activating the battery at the right time to prevent deterioration.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- MITSUBISHI MOTORS CORP
- Filing Date
- 2023-03-30
- Publication Date
- 2026-07-23
Smart Images
Figure 0007894064000001 
Figure 0007894064000002 
Figure 0007894064000003
Abstract
Description
Technical Field
[0001] The present invention relates to a device for suppressing deterioration of a battery pack.
Background Art
[0002] An LFP battery (lithium iron phosphate ion battery) using lithium iron phosphate for the positive electrode has high durability against repeated charge and discharge and use in a high-temperature environment, does not contain rare metals such as cobalt, and is low-cost. In recent years, its application to in-vehicle batteries of EVs (electric vehicles), PHEVs (plug-in hybrid vehicles) that can be externally charged or externally powered has been increasing.
[0003] The battery mounted in a vehicle in this way deteriorates rapidly when it is in an excessively high-temperature state, not only when the vehicle is running and the battery is being used, but also when the vehicle is stopped and the battery is not being used. Therefore, a vehicle battery cooling device has been disclosed that cools the battery using the power stored in the battery when the vehicle is stopped (see Patent Document 1). In this vehicle battery cooling device, even when the battery is at a high temperature and deteriorating when the vehicle is stopped, the cooling rate of the battery is increased to shorten the time the battery is left in a high-temperature state when the vehicle is stopped, thereby suppressing battery deterioration.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] On the other hand, even batteries that are stored without being used show a decrease in capacity and deteriorate (deterioration due to neglect). Furthermore, since deterioration of batteries was confirmed even in unused batteries, the applicant spoke to battery suppliers and learned that this phenomenon is also a problem in the market. Furthermore, a literature search on such battery degradation revealed that when batteries are stored without being powered from their initial state, degradation occurs due to the formation of a protective film on the electrode surface. This invention has been made in view of the above circumstances, and aims to provide a battery pack degradation suppression device that prevents a decrease in capacity and suppresses the deterioration of a battery pack by reducing power consumption from a stored battery pack. [Means for solving the problem]
[0006] To achieve the above-mentioned objective, one embodiment of the present invention is a device for suppressing degradation of a battery pack comprising a first energy storage device and a second energy storage device, comprising a voltage control unit that generates a potential difference between the voltage of the first energy storage device and the voltage of the second energy storage device, and a predetermined Potential difference When this occurs, the system includes a charge / discharge control unit that performs charging and discharging between the first and second energy storage devices and aligns the voltage of the first and second energy storage devices. The first energy storage device is a first battery cell group comprising a plurality of battery cells, and the second energy storage device is a second battery cell group comprising a plurality of battery cells, and the voltage control unit is a balancer circuit control unit that connects either the first battery cell group or the second battery cell group to a balancer resistor to discharge the voltage and generate the potential difference. It is characterized by the following. Furthermore, one embodiment of the present invention further includes a measuring unit that measures the elapsed time since the battery pack was stopped being used, and the voltage control unit generates the potential difference when a predetermined time has elapsed since the battery pack was stopped being used. Furthermore, one embodiment of the present invention further comprises a degradation state estimation unit for estimating the degradation state of the battery pack, and the voltage control unit generates the potential difference when the degradation state is above a predetermined first threshold. Furthermore, one embodiment of the present invention is as described above. Potential differenceThe range is defined from the minimum voltage difference that allows charging and discharging while considering overvoltage, to the maximum voltage difference that does not exceed the voltage at which the charged energy storage device (of the first and second energy storage devices) can store energy when charging and discharging is performed. 。 Ma Furthermore, one embodiment of the present invention further comprises a remaining capacity estimation unit for estimating the remaining capacity of the battery pack, and the balancer circuit control unit generates the potential difference when the remaining capacity is equal to or greater than a predetermined second threshold. Furthermore, in one embodiment of the present invention, the balancer circuit control unit disconnects the balancer resistor when the voltage of one of the battery cell groups reaches a predetermined target voltage, and the charge / discharge control unit, when the balancer resistor is disconnected, charges and discharges the battery cells of the first battery cell group and the second battery cell group to equalize the voltage of the first battery cell group and the voltage of the second battery cell group. 。 [Effects of the Invention]
[0007] According to one embodiment of the present invention, a voltage control unit generates a potential difference between the voltage of the first energy storage device and the voltage of the second energy storage device constituting the battery pack, and a predetermined Potential difference When this occurs, the charge / discharge control unit performs charging and discharging between the first and second energy storage devices to equalize the voltage of the first and second energy storage devices. The first energy storage device is a first battery cell group comprising multiple battery cells, and the second energy storage device is a second battery cell group comprising multiple battery cells, wherein the voltage control unit is a balancer circuit control unit that connects either the first battery cell group or the second battery cell group to a balancer resistor to discharge the voltage and generate a potential difference. Therefore, While utilizing the existing balancer function built into the battery pack, Reducing power consumption from stored battery packs helps prevent capacity degradation and is advantageous in suppressing battery pack deterioration. Furthermore, if the system is configured to generate a potential difference between the voltage of the first energy storage device and the voltage of the second energy storage device after a predetermined time has elapsed since the battery pack was stopped from being used, the battery pack can be activated at an appropriate time after it has been stored, which is advantageous in suppressing the deterioration of the battery pack. Furthermore, if the system is configured to estimate the degradation state of the battery pack and, if the estimated degradation state is above a predetermined first threshold, to create a potential difference between the voltage of the first energy storage device and the voltage of the second energy storage device, it becomes possible to determine whether or not to perform battery pack degradation suppression processing based on the degradation state of the battery pack, which is advantageous in performing effective battery pack degradation suppression processing. Also, Potential difference However, if the configuration is set within a range from the minimum voltage difference that allows charging and discharging while considering overvoltage, to the maximum voltage difference that does not exceed the voltage that the charged energy storage device (of the first and second energy storage devices) can store when charging and discharging is performed, it is advantageous in determining a potential difference that allows for proper charging and discharging between the first and second energy storage devices while avoiding battery pack failure. 。 Ma Furthermore, if the remaining capacity of the battery pack is estimated and the balancer circuit control unit generates a potential difference when the remaining capacity is above a predetermined second threshold, it becomes possible to determine whether or not to perform battery pack degradation suppression processing based on the remaining capacity of the battery pack, which is advantageous in performing degradation suppression processing on battery packs with an appropriate remaining capacity. Furthermore, if the voltage of one battery cell group (the discharged battery cell group) reaches a predetermined target voltage, the balancer circuit control unit disconnects the balancer resistor, and the charge / discharge control unit performs mutual charging and discharging between the battery cells of the first and second battery cell groups, thereby equalizing the voltages of the first and second battery cell groups, charging and discharging can be performed when an appropriate voltage difference is achieved, which is advantageous in suppressing battery pack degradation. 。 [Brief explanation of the drawing]
[0008] [Figure 1] This is a functional configuration diagram of a battery pack degradation control device according to the first embodiment. [Figure 2] This is a schematic diagram showing the flow of the battery pack degradation control process according to the first embodiment. [Figure 3] This is a circuit diagram of a battery pack degradation control device according to the first embodiment. [Figure 4] It is an explanatory diagram of power consumption during discharge by a balancer resistor. [Figure 5] It is a flowchart showing the flow of deterioration control processing of a battery pack according to the first embodiment. [Figure 6] It is a functional configuration diagram of a deterioration control device for a battery pack according to the second embodiment. [Figure 7] It is a schematic diagram showing the flow of deterioration control processing of a battery pack according to the second embodiment. [Figure 8] It is a circuit diagram of a deterioration control device for a battery pack according to the second embodiment. [Figure 9] It is a flowchart showing the flow of deterioration control processing of a battery pack according to the second embodiment.
Embodiments for Carrying Out the Invention
[0009] (First Embodiment) Hereinafter, embodiments of the present invention will be described with reference to the drawings. The deterioration control device 10A of the battery pack of the present embodiment shown in FIG. 1 suppresses the deterioration of the battery pack 12. As shown in FIG. 1, the battery pack 12 of the present embodiment includes a plurality of battery cells C1 to Cn and is applied to an in-vehicle battery of an EV.
[0010] First, referring to the schematic diagram of FIG. 2, an outline of the deterioration control processing of the battery pack 12 by the deterioration control device 10A of the battery pack will be described. FIG. 2 shows an example in which the battery pack 12 is provided with four battery cells C1 to C4, and the height of the battery cells C1 to C4 indicates the voltage (V). Note that the odd-numbered battery cells C1 and C3 correspond to the first battery cell group (first power storage device), and the even-numbered battery cells C2 and C4 correspond to the second battery cell group (second power storage device).
[0011] In Figure 2, the degradation control process for the battery pack 12 is performed in the order of (A) to (D). Figure 2(A) shows the state in which the voltages of battery cells C1 to C4 are the same. Here, in this embodiment, "the voltages are the same" includes the state in which the voltages between battery cells are the same, and the state in which the voltages between battery cells are approximately the same, that is, the state in which the voltages between battery cells are within a predetermined error range.
[0012] Figure 2(B) shows the state in which the even-numbered battery cells C2 and C4 of the battery pack are being discharged. Figure 2(C) shows the state in which the odd-numbered battery cells C1 and C3 and the even-numbered battery cells C2 and C4 are charging and discharging each other. Figure 2(D) shows the state in which the voltages of battery cells C1 to C4 are the same.
[0013] First, as shown in Figure 2(A), the voltages of battery cells C1 to C4 are equal. When the degradation control process of the battery pack 12 is started from this state, as shown in Figure 2(B), some of the battery cells C1 to C4, in this case the even-numbered battery cells C2 and C4, consume power, creating a voltage difference between them and the remaining odd-numbered battery cells C1 and C3.
[0014] Next, as shown in Figure 2(C), in order to balance the voltage between the odd-numbered battery cells C1 and C3 and the even-numbered battery cells C2 and C4, the odd-numbered battery cells C1 and C3 and the even-numbered battery cells C2 and C4 perform charging and discharging operations with each other. As a result, as shown in Figure 2(D), the voltages of battery cells C1 to C4 return to a state where they are equal.
[0015] Thus, in the degradation control process of the battery pack 12 of this embodiment, the stored battery pack is activated to intentionally create a potential difference between the odd-numbered battery cells C1 and C3 and the even-numbered battery cells C2 and C4, whose voltages are equal. Then, charging and discharging are performed between the odd-numbered battery cells C1 and C3 and the even-numbered battery cells C2 and C4 to equalize the voltages of the odd-numbered battery cells C1 and C3 and the even-numbered battery cells C2 and C4 again. Note that in Figure 2(B), the even-numbered battery cells C2 and C4 are being discharged and therefore have consumed power. Consequently, the voltages of the battery cells C1 to C4 in Figure 2(D), after which charging and discharging have been performed to equalize the voltages, are lower than the voltages of the battery cells C1 to C4 in Figure 2(A) (see the height of the battery cells C1 to C4 in Figure 2).
[0016] Next, with reference to Figure 3, the circuit diagram of the battery pack degradation control device 10A will be described. As shown in Figure 3, the battery pack degradation control device 10A is configured by connecting odd-numbered battery cells C1 (first battery cell group), even-numbered battery cells C2 (second battery cell group), switches S1 to S7, balancer resistors R1 and R2, and the battery control device 20.
[0017] Odd-numbered battery cells C1 are the odd-numbered battery cells among the multiple battery cells C1 to Cn (see Figure 1) provided in the battery pack 12. Similarly, even-numbered battery cells C2 are the even-numbered battery cells among the multiple battery cells C1 to Cn provided in the battery pack 12. In order to equalize the voltage between battery cells, charging and discharging are performed between battery cells. Therefore, in this embodiment, battery cells C1 and C2 are described as an example of a pair consisting of an odd-numbered battery cell and an even-numbered battery cell.
[0018] Switches S1 to S7 are used to mechanically switch electrical signals and are appropriately installed in the circuit. When switched ON (on state: closed position) based on a command from the battery control device 20, current flows, and when switched OFF (off state: open position), no current flows.
[0019] The balancer resistors R1 and R2 adjust the voltage balance between the odd-numbered battery cells C1 and the even-numbered battery cells C2. Balancer resistor R1 is connected in parallel to the odd-numbered battery cells C1, and balancer resistor R2 is connected in parallel to the even-numbered battery cells C2.
[0020] For example, when using the battery pack 12 under normal conditions, such as when operating a vehicle, set switches S1 to S7 as follows. S1:ON S2:OFF S3:ON S4:OFF S5:OFF S6:OFF S7:ON This connects the odd-numbered battery cells C1 (first battery cell group) and the even-numbered battery cells C2 (second battery cell group) in series.
[0021] Also, for example, when discharging an even-numbered battery cell C2 connected to balancer resistor R2, switches S1 to S7 should be set as follows. S1:OFF S2:OFF S3:OFF S4:OFF S5:ON S6:OFF S7:OFF This connects the even-numbered battery cell C2 to the balancer resistor R2.
[0022] Furthermore, for example, when charging an even-numbered battery cell C2 (second battery cell group) from an odd-numbered battery cell C1 (first battery cell group), switches S1 to S7 should be set as follows. S1:ON S2:OFF S3:ON S4:ON S5:OFF S6:ON S7:OFF This connects the odd-numbered battery cells C1 (first battery cell group) and the even-numbered battery cells C2 (second battery cell group).
[0023] Returning to Figure 1, the functional configuration of the battery pack degradation control device 10A will be described. As shown in Figure 1, the battery pack degradation control device 10A is configured to include a battery pack 12, a charging port 14, a balancer circuit 16, and a battery control device 20.
[0024] As described above, the battery pack 12 is composed of multiple battery cells C1 to Cn, with odd-numbered battery cells C1, C3, etc. corresponding to the first battery cell group (first energy storage device), and even-numbered battery cells C2, C4, etc. corresponding to the second battery cell group (second energy storage device).
[0025] The charging port 14 is a connection point to which the cable (connecting component) of the external charging equipment is connected. The battery pack 12 is charged via a converter (not shown) that converts the AC power supplied from the charging port 14 to DC power when charged by the external charging equipment (external charging).
[0026] The balancer circuit 16 is composed of a switch S and a balancer resistor R. In this embodiment, the balancer circuit 16 is configured such that balancer resistors R1, R3, and a switch are connected in parallel to odd-numbered battery cells C1, C3, etc., and balancer resistors R2, R4, etc. and a switch are connected in parallel to even-numbered battery cells C2, C4, etc.
[0027] The battery control device 20 further comprises a charge control unit 202, a measurement unit 204, a degradation state estimation unit 206, a remaining capacity estimation unit 208, a balancer circuit control unit 210, and a charge / discharge control unit 212. The battery control device 20 has a hardware configuration that utilizes a normal computer, including a control device such as a CPU (Central Processing Unit), a storage device such as a ROM (Read Only Memory) for storing the control program and a RAM (Random Access Memory) as the operating area for the control program, an output device, an input device, and a communication I / F (interface) for communicating with external devices, etc. The CPU executes the control program stored in the ROM, thereby enabling each of the above-mentioned units (charge control unit 202, measurement unit 204, degradation state estimation unit 206, remaining capacity estimation unit 208, balancer circuit control unit 210, and charge / discharge control unit 212) to function.
[0028] When the charging cable is connected to the charging port 14, the charging control unit 202 charges the battery cells C1 to Cn of the battery pack 12 with the power supplied from the charging port 14.
[0029] The measurement unit 204 measures the elapsed time since the battery pack 12 stopped being used. In other words, it does not measure while the battery pack 12 is charging or while the vehicle is running, but measures the time from the moment the battery pack 12 stops being used, such as when charging of the battery pack 12 is complete or when the vehicle stops.
[0030] The degradation state estimation unit 206 estimates the degradation state (SOH: State of Health) of the battery pack 12. The SOH can be estimated using the battery pack 12's capacity, voltage, current, and temperature storage data, and can be estimated using any known method such as the current integration method or the open-circuit voltage estimation method.
[0031] The remaining capacity estimation unit 208 estimates the remaining capacity (SOC: State of Charge) of the battery pack 12. The SOC can be estimated from the voltage between both terminals (OCV (Open Circuit Voltage)) when no load is applied to the battery cells, and can be estimated using any known method.
[0032] The balancer circuit control unit 210 is a voltage control unit that generates a potential difference between the voltages of the odd-numbered battery cells C1, C3... (first battery cell group) and the voltages of the even-numbered battery cells C2, C4... (second battery cell group). Specifically, the balancer circuit control unit 210 connects either the odd-numbered battery cells C1, C3... or the even-numbered battery cells C2, C4... to the balancer resistor R to discharge the voltage and generate a potential difference.
[0033] In this embodiment, the balancer circuit control unit 210 connects balancer resistors R2, R4, etc. to the even-numbered battery cells C2, C4, etc., and discharges them, thereby creating a potential difference. Therefore, as described above, when switch S5 is turned ON and the other switches are turned OFF, the balancer resistor R2 is connected to the even-numbered battery cell C2, and the even-numbered battery cell C2 (second battery cell group) is discharged.
[0034] Here, referring to Figure 4, we will explain the power consumption during discharge by the balancer resistor. In Figure 4, the current flowing through a circuit in which a balancer resistor (load resistance) R [Ω] is connected to a battery cell C with electromotive force E [V] is I [A]. The battery cell C generates an internal resistance r [Ω] when current flows due to the electromotive force E [V]. The terminal voltage of the battery cell C is V [V]. According to Ohm's Law, the relationship between them is: E = rI + V = (r + R)I This means that, I = E / (R+r). therefore, Power consumption P=VI=I 2 R = [E / (R + r)] 2 R This is the result. Thus, the power consumption P can be calculated using the electromotive force E and internal resistance r of the battery cell C, as well as the balancer resistance R.
[0035] The balancer circuit control unit 210 discharges the even-numbered battery cells C2, C4, etc. when predetermined conditions are met, creating a potential difference between the voltages of the odd-numbered battery cells C1, C3, etc. and the voltages of the even-numbered battery cells C2, C4, etc. Specifically, the balancer circuit control unit 210 creates a potential difference when a predetermined time has elapsed since the battery pack 12 has stopped being used. Since battery packs installed in vehicles deteriorate rapidly after 14 days of not being used, it is preferable to perform deterioration suppression treatment before 14 days have passed. For example, in this embodiment, when 7 days have elapsed since the battery pack 12 has stopped being used, the even-numbered battery cells C2, C4, etc. are discharged to create a potential difference.
[0036] Furthermore, the balancer circuit control unit 210 generates a potential difference if the State of Health (SOH) of the battery pack 12 estimated by the degradation state estimation unit 206 is above a predetermined first threshold. Since a degraded battery pack 12 cannot be recovered, if the degradation has progressed too far, the degradation suppression treatment of the battery pack will not be effective. Therefore, the first threshold is a value that defines the lower limit for when the degradation suppression treatment of the battery pack 12 will be effective, for example, 20%.
[0037] Furthermore, the balancer circuit control unit 210 generates a potential difference if the State of Charge (SOC) of the battery pack 12 estimated by the remaining capacity estimation unit 208 is equal to or greater than a predetermined second threshold. Since power is consumed when performing degradation control processing on the battery pack 12, if it is determined that the vehicle cannot run with the SOC of the battery pack 12 after degradation control processing, the degradation control processing of the battery pack 12 is not performed. Therefore, the second threshold is a value that defines the lower limit for when the vehicle can run even after performing degradation control processing on the battery pack 12, for example, 20%.
[0038] Then, when the voltage of the battery cells that have been discharged (in this embodiment, the even-numbered battery cells C2, C4, etc.) from the odd-numbered battery cells C1, C3, etc. and the even-numbered battery cells C2, C4, etc. reaches a predetermined target voltage (for example, the current voltage - 0.2V), the balancer circuit control unit 210 turns off the switch S5 and disconnects the balancer resistor R2.
[0039] The target voltage is set each time, taking overvoltage into consideration, to determine the minimum voltage difference that allows for mutual charging and discharging between odd-numbered battery cells C1, C3... and even-numbered battery cells C2, C4.... This is to minimize power consumption due to the degradation control process of the battery pack 12, thereby minimizing the decrease in the remaining capacity (SOC) of the battery pack 12 and leaving enough power in the battery pack 12 for use the next time the vehicle is run. In other words, the degradation control process of the battery pack 12 is performed to prevent the remaining capacity of the battery pack 12 from falling below the lower limit of the remaining capacity required for the vehicle to run.
[0040] When a predetermined voltage difference occurs and the balancer circuit control unit 210 disconnects the balancer resistor R2, the charge / discharge control unit 212 performs charging and discharging between the odd-numbered battery cells C1, C3... and the even-numbered battery cells C2, C4... to equalize the voltages of the odd-numbered battery cells C1, C3... and the even-numbered battery cells C2, C4.... In this embodiment, when charging the even-numbered battery cells C2, C4... from the odd-numbered battery cells C1, C3..., switches S1, S3, S4, and S6 are turned ON, and switches S2, S5, and S7 are turned OFF.
[0041] The voltage difference generated by the balancer circuit control unit 210 is determined within a range from the minimum voltage difference that allows for mutual charging and discharging between odd-numbered battery cells C1, C3... and even-numbered battery cells C2, C4..., while taking overvoltage into consideration, to the maximum voltage difference that does not exceed the voltage at which the charged battery cell group (in this embodiment, even-numbered battery cells C2, C4...) among the odd-numbered battery cells C1, C3... and even-numbered battery cells C2, C4... can store energy when charging and discharging is performed.
[0042] Furthermore, because the degradation control process for the battery pack 12 in this embodiment has a short working time, even if a user requests the vehicle to be driven while the degradation control process is in progress, the time until the degradation control process is completed is short, and the user will not be kept waiting.
[0043] Next, with reference to Figure 5, the flow of the degradation control process for the battery pack 12 by the battery pack degradation control device 10A will be explained. First, when the measurement unit 204 measures the elapsed time since the battery pack 12 stopped being used, the balancer circuit control unit 210 determines whether a predetermined time has elapsed since the battery pack 12 stopped being used (step S10). If the time has not elapsed (step S10: NO), it waits until the time has elapsed.
[0044] On the other hand, if a predetermined time has elapsed since the battery pack 12 was stopped from being used (step S10: YES), the balancer circuit control unit 210 determines whether the State of Health (SOH) of the battery pack 12 estimated by the degradation state estimation unit 206 is equal to or greater than the first threshold (step S12). If the SOH of the battery pack 12 is less than the first threshold (step S12: NO), the degradation of the battery pack 12 is progressing and degradation suppression processing will not be effective, so the process is terminated.
[0045] On the other hand, if the State of Health (SOH) of the battery pack 12 is greater than or equal to the first threshold (step S12: YES), the balancer circuit control unit 210 determines whether the State of Charge (SOC) of the battery pack 12, estimated by the remaining capacity estimation unit 208, is greater than or equal to the second threshold (step S14). If the SOC of the battery pack 12 is less than the second threshold (step S14: NO), the process returns to step S10.
[0046] On the other hand, if the State of Charge (SOC) of the battery pack 12 is above the second threshold (step S14: YES), the balancer circuit control unit 210 connects the balancer resistor R2 to the even-numbered battery cells C2, C4... (step S16) and discharges the even-numbered battery cells C2, C4... (step S18). Then, the balancer circuit control unit 210 determines whether the even-numbered battery cells C2, C4... have reached the target voltage (step S20). If they have not reached the target voltage (step S20: NO), it returns to step S18 and continues discharging until the target voltage is reached.
[0047] On the other hand, when the even-numbered battery cells C2, C4, etc. reach the target voltage (step S20: YES), the balancer circuit control unit 210 disconnects the balancer resistor R2 from the even-numbered battery cells C2, C4, etc. (step S22). Once the balancer resistor R2 is disconnected from the even-numbered battery cells C2, C4, etc., the charge / discharge control unit 212 performs charging and discharging between the odd-numbered battery cells C1, C3, etc. and the even-numbered battery cells C2, C4, etc. (step S24).
[0048] The charge / discharge control unit 212 determines whether the voltages of the odd-numbered battery cells C1, C3... and the voltages of the even-numbered battery cells C2, C4... are the same (step S26). If they are not the same (step S26: NO), it continues charging and discharging (step S24). If they are the same (step S26: YES), it returns to step S10 and repeats the process.
[0049] As described above, the battery pack degradation control device 10A of this embodiment generates a potential difference between the voltages of the odd-numbered battery cells C1, C3... and the voltages of the even-numbered battery cells C2, C4... that make up the battery pack 12 using the balancer circuit control unit 210 (voltage control unit). When a predetermined voltage difference is generated, the charge / discharge control unit 212 charges and discharges the battery cells C1, C3... and the even-numbered battery cells C2, C4... to equalize the voltages of the odd-numbered battery cells C1, C3... and the even-numbered battery cells C2, C4.... This suppresses power consumption from the stored battery pack 12, prevents a decrease in capacity, and is advantageous in suppressing the degradation of the battery pack 12. Furthermore, performing the degradation control processing of the battery pack 12 in this embodiment consumes less power than turning on the power to devices such as the navigation system, meters, and motors to activate the battery cells C1 to Cn of the battery pack 12. This is advantageous in preventing a decrease in capacity and suppressing the degradation of the battery pack 12. In other words, when the power to other devices is turned on, power is consumed evenly from all the battery cells C1 to Cn. However, when performing the degradation control processing of the battery pack 12 in this embodiment, power is consumed from some of the battery cells C1 to Cn to create a voltage imbalance, and then the voltages of the battery cells C1 to Cn are equalized by charging and discharging. Therefore, the power consumption is less compared to when other devices are turned on. In addition, since a balancer resistor with a smaller resistance than other devices is used, power consumption can be reduced, and there is also the advantage that the power consumed in a single process can be easily controlled. Furthermore, since the battery pack 12 is configured to create a potential difference between the voltages of odd-numbered battery cells C1, C3, etc. and the voltages of even-numbered battery cells C2, C4, etc. after a predetermined time has elapsed since the battery pack 12 was stopped from being used, the battery pack 12 can be activated at an appropriate time after it has been stored, which is advantageous in suppressing the deterioration of the battery pack 12. Furthermore, the system is configured to estimate the State of Health (SOH) of the battery pack 12, and if the estimated SOH is above a predetermined first threshold, a potential difference is created between the voltages of the odd-numbered battery cells C1, C3, etc. and the voltages of the even-numbered battery cells C2, C4, etc. Therefore, it is possible to determine whether or not to perform battery pack degradation suppression processing based on the SOH of the battery pack 12, which is advantageous in performing effective battery pack degradation suppression processing. Furthermore, the voltage difference is set to a range from the minimum voltage difference that allows charging and discharging while considering overvoltage, to the maximum voltage difference that does not exceed the voltage that the charging side of the odd-numbered battery cells C1, C3... and even-numbered battery cells C2, C4... can store when charging and discharging is performed. This configuration is advantageous in determining a potential difference that allows for proper charging and discharging between the odd-numbered battery cells C1, C3... and even-numbered battery cells C2, C4... while avoiding failure of the battery pack 12. Furthermore, the first energy storage device is configured with a first battery cell group (odd-numbered battery cells C1, C3…) comprising multiple battery cells, and the second energy storage device is configured with a second battery cell group (even-numbered battery cells C2, C4…) comprising multiple battery cells, and the balancer circuit control unit 210 is configured to connect either the odd-numbered battery cells C1, C3… or the even-numbered battery cells C2, C4… (in this embodiment, the even-numbered battery cells C2, C4…) to the balancer resistor R2 to discharge the voltage and generate a potential difference. As a result, the existing balancer function installed in the battery pack 12 can be utilized, which is advantageous in suppressing the degradation of the battery pack 12. Furthermore, the system is configured to estimate the State of Charge (SOC) of the battery pack 12, and if the SOC is above a predetermined second threshold, the balancer circuit control unit 210 generates a potential difference. This allows for a decision to be made whether or not to perform battery pack degradation suppression processing based on the SOC of the battery pack 12, which is advantageous for performing degradation suppression processing on battery packs with appropriate remaining capacity. Furthermore, if the voltage of one group of battery cells (the even-numbered battery cells C2, C4, etc. that have been discharged) reaches a predetermined target voltage, the balancer circuit control unit 210 disconnects the balancer resistor R2, and the charge / discharge control unit 212 charges and discharges the odd-numbered battery cells C1, C3, etc. and the even-numbered battery cells C2, C4, etc. from each other, and the voltages of the odd-numbered battery cells C1, C3, etc. and the even-numbered battery cells C2, C4, etc. are matched, then charging and discharging can be performed when an appropriate voltage difference is reached, which is advantageous in suppressing the degradation of the battery pack 12.
[0050] (Second Embodiment) The first embodiment uses a balancer function to perform charging and discharging between battery cells, whereas the second embodiment differs in that it uses a booster to perform charging and discharging between module blocks. In the following description of the embodiments, the same reference numerals are used for parts and components as in the first embodiment, and their descriptions are omitted. The description will focus on the parts that differ from the first embodiment.
[0051] The battery pack degradation control device 10B of this embodiment, shown in Figure 6, suppresses the degradation of the battery pack 32. As shown in Figure 6, the battery pack 32 of this embodiment is configured with a first module block MB1 and a second module block MB2, and, like the first embodiment, is applied to the on-board battery of an EV.
[0052] First, with reference to the schematic diagram in Figure 7, an overview of the degradation control process of the battery pack 32 by the battery pack degradation control device 10B will be explained. Figure 7 shows an example in which the battery pack 32 is equipped with a first module block MB1 and a second module block MB2, and the height of the first module block MB1 and the second module block MB2 indicates the voltage (V). In this embodiment, the first module block MB1 and the second module block MB2 each consist of five modules, and these modules are further composed of 10 battery cells.
[0053] The number of modules in a module block and the number of battery cells in each module are arbitrary, but the relationship between the first module block MB1 and the second module block MB2 is maintained at 1:1. Furthermore, the first module block MB1 corresponds to the first energy storage device, and the second module block MB2 corresponds to the second energy storage device.
[0054] In Figure 7, the degradation control process for the battery pack 32 is performed in the order of (A) to (E). Figure 7(A) shows the state in which the voltages of the first module block MB1 and the second module block MB2 are the same. Figure 7(B) shows the state in which charging and discharging are performed between the boosted first module block MB1 and the second module block MB2.
[0055] Figure 7(C) shows the state where the voltage of the boosted first module block MB1 and the voltage of the second module block MB2 are the same. Figure 7(D) shows the state where the voltage of the first module block MB1 has been stepped down. Figure 7(E) shows the state where the first module block MB1 and the second module block MB2 are charging and discharging each other.
[0056] First, as shown in Figure 7(A), the voltages of the first module block MB1 and the second module block MB2 are equal. From this state, the degradation control process of the battery pack 32 is started, and by connecting a booster to the first module block MB1, the voltage of the first module block MB1 is increased. As a result, as shown in Figure 7(B), a voltage difference is created between the first module block MB1 and the second module block MB2, causing them to charge and discharge each other. Consequently, as shown in Figure 7(C), the voltages of the first module block MB1 and the second module block MB2 become equal.
[0057] From this state, disconnecting the boost converter from the first module block MB1 causes the first module block MB1 to be stepped down. As a result, as shown in Figure 7(D), a voltage difference is again created between the first module block MB1 and the second module block MB2, and as shown in Figure 7(E), the first module block MB1 and the second module block MB2 charge and discharge each other. Consequently, as shown in Figure 7(A), the voltages of the first module block MB1 and the second module block MB2 return to being equal.
[0058] Thus, in the degradation control process of the battery pack 32 of this embodiment, the stored battery pack is activated to intentionally create a potential difference between the first module block MB1 and the second module block MB2, whose voltages are the same. Then, charging and discharging are performed between the first module block MB1 and the second module block MB2 to equalize the voltages of the first module block MB1 and the second module block MB2.
[0059] In Figure 7(B), the voltage of the first module block MB1 is increased by connecting the boost converter, and in Figure 7(D), the voltage of module block MB1 is decreased by disconnecting the boost converter; therefore, theoretically, no power is consumed. Consequently, if the degradation control process is started from the state shown in Figure 7(A), the voltages of the first module block MB1 and the second module block MB2 after the process is completed will be the same as the voltages of the first module block MB1 and the second module block MB2 in Figure 7(A).
[0060] Next, with reference to Figure 8, the circuit diagram of the battery pack degradation control device 10B will be described. As shown in Figure 8, the battery pack degradation control device 10B is configured by connecting a first module block MB1 (first energy storage device), a second module block MB2 (second energy storage device), switches S11 to S14, a boost converter 36, and a battery control device 40.
[0061] The first module block MB1 (first energy storage device) and the second module block MB2 (second energy storage device) are provided in the battery pack 32 and are composed of multiple modules, each consisting of multiple battery cells. In this embodiment, the first module block MB1 and the second module block MB2 each consist of five modules, and these modules are further composed of 10 battery cells.
[0062] Switches S11 to S14 are used to mechanically switch electrical signals. They are installed appropriately within the circuit and are configured to allow current to flow when turned ON (on state: closed position) based on a command from the battery control device 40, and to prevent current from flowing when turned OFF (off state: open position).
[0063] The boost converter 36 is used to boost the voltage of the first module block MB1 and is connected in parallel to the first module block MB1 together with the switch S14. When the switch S14 is turned ON, the boost converter 36 is connected to the first module block MB1 and the voltage is boosted. When the switch S14 is turned OFF, the connection of the boost converter 36 to the first module block MB1 is released, and the voltage of the first module block MB1 is lowered.
[0064] For example, when using the battery pack 32 under normal conditions, such as when operating a vehicle, set switches S11 to S14 as follows. S11:OFF S12:OFF S13:ON S14:OFF This connects the first module block MB1 and the second module block MB2 in series.
[0065] Furthermore, for example, when connecting the first module block MB1 to the boost converter 36 to boost the voltage, switches S11 to S14 should be set as follows. S11:OFF S12:OFF S13:ON S14:ON This connects the first module block MB1 and the boost converter 36.
[0066] Furthermore, for example, when charging the second module block MB2 from the boosted first module block MB1, switches S11 to S14 should be set as follows. S11:ON S12:ON S13:OFF S14:ON This connects the first module block MB1, the second module block MB2, and the boost converter 36.
[0067] Furthermore, for example, when charging the first module block MB1 from the second module block MB2, switches S11 to S14 should be set as follows. S11:ON S12:ON S13:OFF S14:OFF This connects the first module block MB1 and the second module block MB2.
[0068] Returning to Figure 6, the functional configuration of the battery pack degradation control device 10B will be explained. As shown in Figure 6, the battery pack degradation control device 10B is configured to include a battery pack 32, a charging port 14, a boost converter 36, and a battery control device 40. Note that the battery pack degradation control device 10B in this embodiment does not have a remaining capacity estimation unit because theoretically no power is consumed in the degradation control process of the battery pack 32 in this embodiment.
[0069] As described above, the battery pack 32 is composed of a first module block MB1 and a second module block MB2, each comprising multiple modules consisting of multiple battery cells. The first module block MB1 corresponds to the first energy storage device, and the second module block MB2 corresponds to the second energy storage device.
[0070] The booster 36 increases the pressure and, in this embodiment, is configured to be connected in parallel to the first module block MB1.
[0071] The battery control device 40 further comprises a charge control unit 202, a measurement unit 204, a degradation state estimation unit 206, a booster control unit 410, and a charge / discharge control unit 412. Similar to the first embodiment, the battery control device 40 has a hardware configuration using a normal computer, and the CPU executes a control program stored in ROM, thereby enabling each of the above-mentioned units (charge control unit 202, measurement unit 204, degradation state estimation unit 206, booster control unit 410, and charge / discharge control unit 412) to function.
[0072] The boost converter control unit 410 is a voltage control unit that generates a potential difference between the voltage of the first module block MB1 and the voltage of the second module block MB2. Specifically, the boost converter control unit 410 generates a potential difference by connecting either the first module block MB1 or the second module block MB2 to the boost converter 36 to boost the voltage, or by disconnecting the boost converter 36 from one of the module blocks to lower the voltage.
[0073] In this embodiment, the boost converter control unit 410 connects the first module block MB1 to the boost converter 36 to boost the voltage and create a potential difference. Therefore, as described above, when switches S11 and S12 are turned OFF and switches S13 and S14 are turned ON, the boost converter 36 is connected to the first module block MB1, and the voltage of the first module block MB1 is boosted.
[0074] In this embodiment, the boost converter control unit 410 generates a potential difference by disconnecting the boost converter 36 from the first module block MB1 and causing it to step down. Therefore, when switch S14 is turned OFF, the boost converter 36 is disconnected from the first module block MB1, and the voltage of the first module block MB1 is stepped down. Furthermore, after the voltage of the first module block MB1 has been boosted, the boost converter control unit 410 disconnects the boost converter 36 when the voltage of the first module block MB1 and the voltage of the second module block MB2 become equal due to charging and discharging.
[0075] The boost converter control unit 410 connects the first module block MB1 to the boost converter 36 and boosts the voltage when predetermined conditions are met, thereby creating a potential difference between the first module block MB1 and the second module block MB2. Specifically, the boost converter control unit 410 creates a potential difference when a predetermined time has elapsed since the battery pack 32 was stopped from being used. For example, in this embodiment, similar to the first embodiment, the boost converter 36 is connected to the first module block 1 and a potential difference is created when 7 days have elapsed since the battery pack 32 was stopped from being used.
[0076] Furthermore, similar to the first embodiment, the boost converter control unit 410 generates a potential difference when the State of Health (SOH) of the battery pack 32, as estimated by the degradation state estimation unit 206, is equal to or greater than a predetermined first threshold.
[0077] When a predetermined voltage difference occurs, the charge / discharge control unit 412 performs charging and discharging between the first module block MB1 and the second module block MB2 to equalize the voltage of the first module block MB1 and the voltage of the second module block MB2. In this embodiment, when charging the second module block MB2 from the first module block MB1, switches S11, S12, and S14 are turned ON and switch S13 is turned OFF. Also in this embodiment, when charging the first module block MB1 from the second module block MB2, switches S11 and S12 are turned ON and switches S13 and S14 are turned OFF.
[0078] In this embodiment, the charge / discharge control unit 412, when the boost converter 36 is connected to the first module block MB1 and the voltage is boosted to a predetermined target voltage (for example, the current voltage + 10V), performs charging and discharging between the first module block MB1 and the second module block MB2 to equalize the voltage of the first module block MB1 and the voltage of the second module block MB2.
[0079] The target voltage is set so that when the voltage is boosted by the booster 36, the voltage of the module block does not exceed the upper limit of the charging capacity. Furthermore, the target voltage is set so that when the module block is charged by charging and discharging, the voltage of the module block does not exceed the upper limit of the charging capacity. This is because if the voltage of the module block exceeds the upper limit of the charging capacity, it will lead to a failure of the battery pack 32.
[0080] Furthermore, the target voltage may be configured to be determined based on user instructions. The degradation control process for the battery pack 32 in this embodiment takes longer to operate compared to the first embodiment. Therefore, if the target voltage is set high, the process of matching the voltage of the first module block MB1 and the voltage of the second module block MB2 also takes time. As a result, even if a user gives a command to drive the vehicle while the degradation control process is running, the vehicle cannot be driven immediately. Also, if the vehicle is driven while there is a voltage difference between the first module block MB1 and the second module block, the degradation of the battery pack 32 will progress. Therefore, if the vehicle is to be driven, the user can set the target voltage low to minimize the operating time for the degradation control process. On the other hand, if the vehicle is not to be driven, the user can set the target voltage high, which will increase the operating time, but will enhance the effect of preventing the battery pack 32 from degrading due to neglect.
[0081] Furthermore, in this embodiment, when the connection to the boost converter 36 is disconnected and the voltage of the first module block MB1 drops, the charge / discharge control unit 412 performs charging and discharging between the first module block MB1 and the second module block MB2 to equalize the voltage of the first module block MB1 and the voltage of the second module block MB2.
[0082] The voltage difference caused by connecting or disconnecting the booster 36 is determined within a range from the minimum voltage difference that allows charging and discharging between the first module block MB1 and the second module block MB2, taking overvoltage into consideration, to the maximum voltage difference that does not exceed the voltage at which the charged module block of the first module block MB1 or the second module block MB2 can store energy when charging and discharging is performed.
[0083] Next, with reference to Figure 9, the flow of the degradation control process for the battery pack 32 by the battery pack degradation control device 10B will be explained. First, when the measurement unit 204 measures the elapsed time since the battery pack 32 was stopped from being used, the booster control unit 410 determines whether a predetermined time has elapsed since the battery pack 32 was stopped from being used (step S30). If the time has not elapsed (step S30: NO), it waits until the time has elapsed.
[0084] On the other hand, if a predetermined time has elapsed since the battery pack 32 was stopped from being used (step S30: YES), the boost converter control unit 410 determines whether the State of Health (SOH) of the battery pack 32 estimated by the degradation state estimation unit 206 is equal to or greater than the first threshold (step S32). If the SOH of the battery pack 32 is less than the first threshold (step S32: NO), the degradation of the battery pack 32 is progressing and degradation suppression processing will not be effective, so the process is terminated.
[0085] On the other hand, if the SOH of the battery pack 32 is above the first threshold (step S32: YES), the boost converter control unit 410 connects the boost converter 36 to the first module block MB1 (step S34) and boosts the voltage of the first module block MB1 (step S36). Then, the boost converter control unit 410 determines whether the first module block MB1 has reached the target voltage (step S38), and if it has not reached the target voltage (step S38: NO), it returns to step S36 and boosts the voltage until it reaches the target voltage.
[0086] On the other hand, if the first module block MB1 reaches the target voltage (step S38: YES), the charge / discharge control unit 412 performs charging and discharging between the first module block MB1 and the second module block MB2 (step S40).
[0087] The charge / discharge control unit 412 determines whether the voltage of the first module block MB1 and the voltage of the second module block MB2 are the same (step S42). If they are not the same (step S42: NO), it continues charging and discharging (step S40). If they are the same (step S42: YES), the boost converter control unit 410 disconnects the boost converter 36 from the first module block MB1 (step S44).
[0088] When the connection of the booster 36 to the first module block MB1 is disconnected and the first module block MB1 is stepped down, the charge / discharge control unit 412 performs charging and discharging between the first module block MB1 and the second module block MB2 (step S46).
[0089] The charge / discharge control unit 412 determines whether the voltage of the first module block MB1 and the voltage of the second module block MB2 are the same (step S48). If they are not the same (step S48: NO), it continues charging and discharging (step S46). If they are the same (step S48: YES), it returns to step S30 and repeats the process.
[0090] As described above, the battery pack degradation control device 10B of this embodiment generates a potential difference between the voltage of the first module block MB1 and the voltage of the second module block MB2 constituting the battery pack 32 using the booster control unit 410 (voltage control unit). When a predetermined voltage difference is generated, the charge / discharge control unit 412 charges and discharges the first module block MB1 and the second module block MB2 to equalize the voltage of the first module block MB1 and the voltage of the second module block MB2. This suppresses power consumption from the stored battery pack 32, prevents a decrease in capacity, and is advantageous in suppressing the degradation of the battery pack 32. Furthermore, power is consumed when the power to devices such as the navigation system, meters, and motors is turned on to activate the module blocks of the battery pack 32. However, the degradation control process of the battery pack 32 in this embodiment theoretically consumes no power, which is advantageous in preventing a decrease in capacity and suppressing the degradation of the battery pack 32. In other words, when the power to other devices is turned on, power is consumed equally from all the battery cells of the battery pack 32. However, when the degradation control process of the battery pack 32 in this embodiment is performed, the voltage of one module block is boosted or lowered to create a voltage imbalance, and then the voltages of the two module blocks are equalized by charging and discharging, so theoretically no power is consumed. Furthermore, since the configuration is such that a potential difference is generated between the voltage of the first module block MB1 and the voltage of the second module block MB2 after a predetermined time has elapsed since the battery pack 32 was stopped from being used, the battery pack 32 can be started at an appropriate time after it has been stored, which is advantageous in suppressing the deterioration of the battery pack 32. Furthermore, the system is configured to estimate the State of Health (SOH) of the battery pack 32, and if the estimated SOH is above a predetermined first threshold, a potential difference is created between the voltage of the first module block MB1 and the voltage of the second module block MB2. This allows for a decision on whether or not to perform degradation suppression processing for the battery pack 32 based on its degradation state, which is advantageous for performing effective battery pack degradation suppression processing. Furthermore, since the voltage difference is set to a range from the minimum voltage difference that allows charging and discharging while considering overvoltage, to the maximum voltage difference that does not exceed the voltage at which the charged module block of the first module block MB1 and the second module block MB2 can store energy when charging and discharging is performed, it is advantageous in setting a potential difference that allows for proper charging and discharging between the first module block MB1 and the second module block MB2 and avoids failure of the battery pack 32. Furthermore, the first energy storage device is a first module block comprising multiple modules consisting of multiple battery cells, and the second energy storage device is a second module block comprising multiple modules consisting of multiple battery cells. The booster control unit 410 generates a potential difference by connecting either the first module block MB1 or the second module block MB2 to the booster 36 to boost the voltage, or by disconnecting the booster 36 from the first module block MB1 to lower the voltage. As a result, a potential difference can be generated by boosting or lowering the voltage without consuming power, which is advantageous in suppressing the deterioration of the battery pack 32. Furthermore, when the first module block MB1 (the module block connected to the booster) is boosted and reaches a predetermined target voltage, the charge / discharge control unit 412 performs charging and discharging between the first module block MB1 and the second module block MB2 to equalize the voltage of the first module block MB1 and the voltage of the second module block MB2. When the voltage of the first module block MB1 and the voltage of the second module block MB2 are equalized through charging and discharging, the booster control unit 410 disconnects the booster 36. When the voltage of the first module block MB1 drops due to the disconnection of the booster 36, the charge / discharge control unit 412 performs charging and discharging between the first module block MB1 and the second module block MB2 to equalize the voltage of the first module block MB1 and the voltage of the second module block MB2. This configuration allows charging and discharging to occur when an appropriate voltage difference is achieved, which is advantageous in suppressing the degradation of the battery pack 32. Furthermore, if the target voltage is set based on user instructions, the battery pack 32 can be subjected to degradation suppression treatment for a short time if it is to be used immediately, and the degradation suppression treatment can be performed for a longer time if the effect of suppressing degradation is to be enhanced. This is advantageous in suppressing the degradation of the battery pack 32 in accordance with the usage conditions of the battery pack 32.
[0091] In the embodiment described above, an example was shown in which the degradation control process of the battery pack 32 was applied to a battery using LFP. However, it can also be applied to batteries other than those using LFP, as long as the degradation due to standing up is greater than the degradation due to cycles. [Explanation of Symbols]
[0092] 10A, 10B Degradation Control Device 12, 32 battery packs 14 Charging port 16. Balancer Circuit 20, 40 Battery control device 36. Step-up transformer 202 Charging Control Unit 204 Measurement Unit 206 Deterioration state estimation unit 208 Remaining capacity estimation section 210 Balancer Circuit Control Unit 212 Charge / Discharge Control Unit 410 Booster Control Unit 412 Charge / Discharge Control Unit C1~Cn Battery Cells MB1 1st Module Block MB2 Second Module Block
Claims
1. A device for suppressing degradation of a battery pack, comprising a first energy storage device and a second energy storage device, A voltage control unit that generates a potential difference between the voltage of the first energy storage device and the voltage of the second energy storage device, The system includes a charge / discharge control unit that, when a predetermined potential difference occurs, performs charging and discharging between the first and second energy storage devices to equalize the voltage of the first and second energy storage devices, The first energy storage device is a first battery cell group comprising a plurality of battery cells, The second energy storage device is a second battery cell group comprising a plurality of battery cells, The voltage control unit is a balancer circuit control unit that connects either the first battery cell group or the second battery cell group to a balancer resistor to discharge the voltage and generate the potential difference. A battery pack degradation suppression device characterized by the above.
2. The system further includes a measuring unit that measures the elapsed time since the battery pack was stopped being used. The voltage control unit generates the potential difference when a predetermined time has elapsed since the battery pack was stopped being used. The battery pack degradation suppression device according to claim 1.
3. The battery pack further comprises a degradation state estimation unit for estimating the degradation state of the battery pack, The voltage control unit generates the potential difference if the degradation state is above a predetermined first threshold. The battery pack degradation suppression device according to feature 2.
4. The aforementioned potential difference is defined within a range from the minimum voltage difference that allows charging and discharging while considering overvoltage, to the maximum voltage difference that does not exceed the voltage at which the charged energy storage device (of the first and second energy storage devices) can store energy when charging and discharging is performed. A battery pack degradation suppression device according to claim 3, characterized in that...
5. The battery pack further comprises a remaining capacity estimation unit for estimating the remaining capacity, The balancer circuit control unit generates the potential difference when the remaining capacitance is equal to or greater than a predetermined second threshold. The battery pack degradation suppression device according to claim 1.
6. The balancer circuit control unit disconnects the balancer resistor when the voltage of one of the battery cell groups reaches a predetermined target voltage. When the balancer resistor is disconnected, the charge / discharge control unit performs charging and discharging between the battery cells of the first battery cell group and the second battery cell group to equalize the voltage of the first battery cell group and the voltage of the second battery cell group. Battery pack degradation control device according to claim 5.