Battery system, battery control device, vehicle, and recording medium storing computer program

Abstract

The present invention provides a battery system and the like that, with a lightweight and low-cost battery configuration, can avoid large voltage drops in a battery while also minimizing degradation. The battery system according to the present disclosure includes: a battery pack formed from a first battery group comprising a plurality of cells connected in series and a second battery group comprising a different number of cells than the first battery group connected in series and having, as an upper voltage limit, the voltage value of the first battery group in a low SOC state; a switch mechanism capable of switching to a first connection mode in which the first battery group is connected to a load or a second connection mode in which the first battery group and the second battery group are connected in parallel to the load; and a battery control device for controlling the switch mechanism, wherein the battery control device switches from the first connection mode to the second connection mode via the switch mechanism once the first battery group has entered a low SOC state.

Description

Battery system, battery control device, vehicle, and recording medium on which a computer program is recorded

[0001] The present disclosure relates to a battery system, a battery control device that controls the battery system, a vehicle that mounts the battery system, and a recording medium that records a computer program that controls the battery system.

[0002] Non-aqueous electrolyte secondary batteries (hereinafter also referred to simply as "nonaqueous secondary batteries") are known as chargeable and dischargeable power storage devices mounted on vehicles. Lithium-ion secondary batteries, an example of such non-aqueous secondary batteries, are being developed for vehicle applications due to their extremely high energy density. It is desirable for such vehicle-mounted battery systems to be able to maintain the voltage required by the vehicle regardless of the state of charge (SOC) of the mounted battery.

[0003] In this regard, for example, Patent Document 1 discloses that when it is determined that the state of charge SOC (MB) is equal to or less than a predetermined value A2, the main control unit 62 switches the power supply path so that the motor generator MG2 is driven using power from the auxiliary battery SB instead of the main battery MB. Similarly, Patent Document 2 discloses a battery control device that controls the output of power from the auxiliary battery when the remaining capacity of the main battery is less than a predetermined amount.

[0004] JP 2007-129799 A JP 2011-024322 A

[0005] However, the prior art, including the above-mentioned patent documents, does not yet meet market needs, and the following problems remain. Generally, when a battery is in a low SOC state where the battery's charging rate is low, its internal resistance increases, resulting in a significant drop in battery output. As proposed in Patent Document 1 and elsewhere, the above-mentioned significant voltage drop can be avoided by switching to a sub-battery when the main battery is in a low SOC state. However, this simple method of switching from the main battery to the sub-battery does not efficiently use the main battery's capacity and the sub-battery's charging rate quickly drops. This necessitates the installation of a relatively large-capacity sub-battery, which increases the vehicle's weight and costs, and is therefore not considered efficient.

[0006] The present disclosure has been made in consideration of the above-mentioned problem as an example, and provides a battery system, etc., in a vehicle equipped with a battery pack consisting of a first battery group and a second battery group, each having a different number of cells connected in series, that is capable of avoiding a significant voltage drop from the cells while suppressing battery deterioration as much as possible with a lightweight, low-cost battery configuration.

[0007] In order to solve the above problem, according to one aspect of the present disclosure, there is provided a battery system including: a battery pack consisting of a first battery group in which a plurality of cells are connected in series; and a second battery group in which a number of cells different from that of the first battery group are connected in series and in which the voltage value in a low SOC state of the first battery group is set as an upper limit voltage; a switch mechanism capable of switching at least between a first connection configuration in which the first battery group is connected to a load; and a second connection configuration in which the first battery group and the second battery group are connected in parallel to the load; and a battery control device that controls the switch mechanism, wherein the battery control device switches from the first connection configuration to the second connection configuration via the switch mechanism when the first battery group enters the low SOC state.

[0008] In order to solve the above problem, according to another aspect of the present disclosure, there is provided a battery control device that controls a battery pack consisting of a first battery group in which a plurality of cells are connected in series, and a second battery group in which a number of cells different from that of the first battery group are connected in series and in which the voltage value in a low SOC state of the first battery group is set as an upper limit voltage, the battery control device comprising: a processor; and a memory capable of storing a program executed by the processor, the program including instructions that cause the processor to detect the SOC of the first battery group, and when the first battery group enters the low SOC state, connect the first battery group and the second battery group in parallel and to a load via a switch mechanism.

[0009] In order to solve the above problem, according to another aspect of the present disclosure, there is provided a recording medium having recorded thereon a computer program applicable to a battery system consisting of a first battery group in which a plurality of cells mounted on a vehicle are connected in series, and a second battery group in which a number of cells different from that of the first battery group are connected in series and in which the voltage value in a low SOC state of the first battery group is set as an upper limit voltage, the recording medium having recorded thereon a computer program that causes one or more processors to execute processing including detecting the SOC of the first battery group, and connecting the first battery group and the second battery group in parallel via a switch mechanism when the first battery group enters the low SOC state.

[0010] According to the present disclosure, a lightweight, low-cost battery configuration can be used to maintain the vehicle's cruising range, while minimizing battery degradation due to loads such as the onboard electric motor, thereby achieving more stable battery output.

[0011] FIG. 1 is a schematic diagram showing an example configuration of a vehicle equipped with a battery system according to the present disclosure. FIG. 1 is a schematic diagram showing an example configuration of a battery system including a switch mechanism according to the present disclosure. FIG. 2 is a schematic diagram showing discharge rate characteristics of unit cells constituting a first battery group in a battery system according to the present disclosure. FIG. 3 is a schematic diagram showing a first connection configuration to a load of a battery system according to the present disclosure. FIG. 4 is a schematic diagram showing a third connection configuration to a load of a battery system according to the present disclosure. FIG. 5 is a schematic diagram showing a fourth connection configuration to a load of a battery system according to the present disclosure. FIG. 6 is a functional block diagram of a battery control device provided in a battery system according to the present disclosure. FIG. 7 is a flowchart showing a battery system control method executed by a battery control device according to the present disclosure.

[0012] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functions are designated by the same reference numerals, and redundant description will be omitted. Furthermore, for configurations other than those described in detail below, publicly known technologies, including those described in the patent documents listed above, and vehicle configurations may be appropriately applied.

[0013] 1 to 7, configuration examples of a battery system 100 and a vehicle 200 according to an embodiment of the present disclosure will be described. Fig. 1 is a schematic diagram showing a vehicle 200 equipped with an on-board load 50 and a battery system 100 capable of supplying power to the load 50. One example of such a load 50 is a known electric motor that is driven by receiving a supply of power from the battery system 100 via a known inverter 22.

[0014] In the following, an electric vehicle (BEV) equipped with a known electric motor will be illustrated as an example of vehicle 200. Note that vehicle 200 of the present embodiment is not limited to the above-described electric vehicle, and may be a hybrid electric vehicle (HEV) that also uses a known engine (internal combustion engine) in combination, or may be an electric vehicle equipped with another known power generation device such as a gas turbine.

[0015] 2 shows an example of the configuration of a battery system 100 according to this embodiment. As can be seen from the figure, the battery system 100 includes a battery pack 10, a switch mechanism 20, and a battery control device 30.

[0016] The battery pack 10 is composed of a first battery group 10A in which a plurality of cells are connected in series, and a second battery group 10B in which a different number of cells are connected in series than in the first battery group 10A. Note that the cells incorporated into the battery pack 10 of this embodiment are preferably known lithium-ion secondary batteries in which the positive electrode is made of a ternary material mainly composed of nickel, manganese, and cobalt, and the negative electrode is made of a carbon material.

[0017] In the following, a battery pack 10 including battery groups in which the above-described lithium-ion secondary batteries are connected in series will be exemplified, but the battery pack 10 may also be configured using other known secondary batteries other than lithium-ion secondary batteries, such as other lithium-ion secondary batteries whose positive electrodes are iron phosphate or nickel-metal hydride batteries. Also, in the following, a battery pack 10 including two groups, a first battery group 10A and a second battery group 10B, will be described, but this is not limited to this example, and the battery pack 10 may also include three or more battery groups.

[0018] The first battery group 10A is formed by connecting a plurality of cells in series. The cells constituting the first battery group 10A may be, for example, known lithium-ion secondary batteries made of a ternary positive electrode material and a carbon-based negative electrode material, with an OCV (open circuit voltage) of approximately 4.0 to 4.2 V. In this embodiment, the output voltage from the battery system 100 is set to 350 to 360 V. Therefore, for example, the first battery group 10A may be configured with 96 of the above cells connected in series, with a rated voltage of 3.7 V.

[0019] The second battery group 10B is configured to have a first threshold V ｔｈ１is set as the upper limit voltage. Here, the "low SOC state" refers to a state of charge of a cell when the internal resistance is high and a relatively large voltage drop occurs during cell discharge, etc., even though the state is within the normal range (i.e., no significant cell degradation) of the cell discharge curve described below, as shown in FIG. 3 . As an example, in this embodiment, when the above-mentioned lithium-ion secondary battery is used, the above-mentioned voltage drop occurs when the SOC is around 20%, so in this embodiment, the low SOC state is defined as a state in which the cell SOC is between 10% and 20%. Note that although the charge rate indicating the "low SOC state" can be expected to be a value in the range of approximately 10% to 20%, the specific charge rate of the "low SOC state" may be determined in advance by experiment or simulation depending on the type of secondary battery, etc.

[0020] As an example of the upper limit voltage of the second battery group 10B, the first threshold voltage V ｔｈ１ The voltage value of the second battery group 10B may be determined based on 3.3V, which is the upper limit voltage of the cells constituting the second battery group 10B. As a result, if the upper limit voltage of the cells constituting the second battery group 10B is 4.2V, 75 (3.3 x 96 / 4.2) cells may be connected in series. In this manner, the battery pack 10 of this embodiment is configured so that the upper limit voltage of the second battery group 10B coincides with the voltage of each cell of the first battery group 10A when it reaches 3.3V. Furthermore, in the battery pack 10 of this embodiment, the number of cells constituting the first battery group 10A is set to be greater than the number of cells constituting the second battery group 10B.

[0021] As shown in Figure 2, the switch mechanism 20 is composed of a first switch 20A that controls the connection between the first battery group 10A and the load 50, a second switch 20B that controls the connection between the second battery group 10B and the load 50, and a third switch 20C that controls the electrical connection between at least the second battery group 10B and the boost circuit 21.

[0022] More specifically, the switch mechanism 20 is configured to be able to switch the power supply from the battery between a first connection configuration (see Figure 4) in which the first battery group 10A is connected to the load 50, and a second connection configuration (see Figure 5) in which the first battery group 10A and the second battery group 10B are connected in parallel to the load 50, by controlling the connection configuration of the first switch 20A to the third switch 20C.

[0023] The switch mechanism 20 of this embodiment may be capable of switching to a third connection configuration (see FIG. 6 ) in which the first battery group 10A is disconnected and the second battery group 10B is connected to the load 50. The switch mechanism 20 of this embodiment may be capable of switching to a fourth connection configuration (see FIG. 7 ) in which the first battery group 10A is disconnected and the second battery group 10B is connected to the load 50 in a manner that boosts the voltage via the boost circuit 21.

[0024] Note that there are no particular limitations on the specific example of the boost circuit 21 as long as it can boost the battery voltage to an arbitrary value, and for example, a known DC-DC converter may be applied. In this way, the battery system 100 of this embodiment may further include a boost circuit 21 connected to the second battery group 10B via the switch mechanism 20 and capable of boosting the voltage between the terminals of the second battery group 10B.

[0025] The battery control device 30 is configured to have the function of controlling the switch mechanism 20. Such a battery control device 30 is also called a BMU (battery management unit), and is configured to include, for example, one or more processors such as a CPU (Central Processing Unit), and one or more memories such as a RAM (Random Access Memory) or a ROM (Read Only Memory) connected to the processor so as to be able to communicate with the processor.

[0026] In this way, the battery control device 30 can change the mode of power supply from the battery pack 10 to the load 50 via the switch mechanism 20 by having one or more processors execute a computer program. The computer program is a computer program for causing the processor to execute a battery control method (see FIG. 10 ) to be executed by the battery control device 30. The computer program executed by the processor may be recorded on a recording medium that functions as a storage unit (memory) provided in the battery control device 30, or may be recorded on another known recording medium that can be externally attached to the battery control device 30.

[0027] The recording medium for recording a computer program may be a magnetic medium such as a hard disk, a floppy disk, or a magnetic tape; an optical recording medium such as a CD-ROM (Compact Disk Read Only Memory), a DVD (Digital Versatile Disk), or a Blu-ray (registered trademark); a magneto-optical medium such as a floptical disk; a memory element such as a RAM or a ROM; a flash memory such as a USB (Universal Serial Bus) memory; an SSD (Solid State Drive); or any other medium capable of storing a program.

[0028] <Switching Control by Battery Control Device, Part 1> Figure 8 shows the discharge characteristics of a battery pack 10 that combines a first battery group 10A and a second battery group 10B. In the figure, the vertical axis indicates the voltage value (V) of the battery pack 10, and the horizontal axis indicates the capacity (Ah) of the battery pack 10. Figure 8 shows, as an example, the voltage values ​​of the first battery group 10A (only 96 cells connected in series) and the second battery group 10B (only 75 cells connected in series) of the above-mentioned embodiment. More specifically, in the example of the battery pack shown in Figure 8, the upper limit voltage is 403V (4.2 x 96), the first threshold V ｔｈ１ The voltage corresponding to the second threshold V ｔｈ２The voltage corresponding to the first battery group 10A is set to 288 V (3.0×96), and the lower limit voltage is set to 240 V (2.5×96). The battery control device 30 detects when the first battery group 10A is in a low SOC state (for example, when the cell voltage is below the first threshold V ｔｈ１ When the SOC at which the first battery group 10A reaches 20%, the first connection configuration (FIG. 4) is switched to the second connection configuration (FIG. 5) via the switch mechanism 20. That is, as shown in FIG. 8, when the SOC of the first battery group 10A falls below 20%, the first battery group 10A and the second battery group 10B are connected in parallel to the load 50.

[0029] This makes it possible to suppress as much as possible the deterioration of the first battery group 10A, which has entered a low SOC state where deterioration is likely to occur, while also utilizing the capacity of the first battery group 10A to provide a stable battery output to the load 50 compared to when current is drawn only from the second battery group 10B.

[0030] <Switching Control by Battery Control Device Part 2> Furthermore, the battery control device 30 of this embodiment may be configured to switch from the second connection configuration ( FIG. 5 ) to the third connection configuration ( FIG. 6 ) via the switch mechanism 20 when the SOC of the first battery group 10A falls below the normal lower limit. This makes it possible to perform battery output from the second battery group 10B to the load 50 while suppressing battery degradation that occurs when the first battery group 10A is used in an SOC range where a significant battery voltage drop occurs, as shown in FIG.

[0031] Here, the "lower limit of normal use SOC" is the lower end of the normal use region where the slope of the discharge curve of the cell, exemplified by the plateau region, is gentle, and corresponds to the lower limit of the low SOC state described above, and is the second threshold V at which a significant voltage drop occurs. ｔｈ２ As an example, in this embodiment, the SOC state corresponds to the second threshold V ｔｈ２ 3.0V, this second threshold V ｔｈ２In other words, in this embodiment, if the SOC of the first battery group 10A exceeds 20%, the required current is supplied to the load 50 from the first battery group 10A in the first connection configuration via the switch mechanism 20. If the SOC of the first battery group 10A is within the range of 10% to 20%, the current is supplied to the load 50 in parallel from both the first battery group 10A and the second battery group 10B in the second connection configuration via the switch mechanism 20.

[0032] <Third Switching Control by Battery Control Device> As described above, when the SOC of the first battery group 10A falls below 10%, the necessary current is supplied to the load 50 from the second battery group 10B in the third connection configuration via the switch mechanism 20. At this time, the battery control device 30 may switch from the second connection configuration ( FIG. 5 ) to the fourth connection configuration ( FIG. 7 ) via the switch mechanism 20. That is, the battery control device 30 can boost the voltage output from the second battery group 10B via the boost circuit 21.

[0033] 8, when the first battery group 10A is disconnected from the load 50 and the second battery group 10B continues to output to the load 50, the output from the battery pack 10 drops slightly. In response to this, by switching from the second connection configuration to the fourth connection configuration via the switch mechanism 20, the voltage can be boosted to, for example, a voltage equivalent to the rated voltage of the first battery group 10A, thereby realizing a stable power supply from the second battery group 10B to the load 50.

[0034] <Functional Blocks of Battery Control Device> FIG. 9 shows functional blocks of the battery control device 30 in this embodiment. The battery control device 30 is configured with one or more processors, such as the CPUs, described above, and includes a voltage value acquisition unit 31, an SOC monitoring unit 32, a switch control unit 33, and a display control unit 34. These components of the battery control device 30 are functions realized by the execution of programs by the processors described above. However, some of the voltage value acquisition unit 31, the SOC monitoring unit 32, the switch control unit 33, and the display control unit 34 may be configured with known analog circuits. As described below, the battery control device 30 in this embodiment can perform processes such as detecting the SOC of the first battery group 10A and connecting the first battery group 10A and the second battery group 10B in parallel to a load via the switch mechanism 20 when the first battery group 10A enters a low SOC state.

[0035] 9, the battery control device 30 may be configured to be able to communicate with a vehicle control device 40 configured with other known ECUs mounted on the vehicle. The vehicle control device 40 may have a function of controlling the driving of the vehicle 200 based on detection values ​​of known vehicle state sensors including, for example, a vehicle speed sensor, an acceleration sensor, an angular velocity sensor, a steering angle sensor, an accelerator pedal sensor, and a brake pedal sensor. The battery control device 30 may also be configured to be able to communicate information with a known external network NET such as the Internet via a known on-board communication device CD.

[0036] The storage unit MD may be configured to include a known memory such as a RAM that temporarily stores information, and a known recording device such as a hard disk or SSD that can store programs, etc. The storage unit MD of this embodiment may store programs executed by the battery control device 30, various parameters used to execute the programs, acquired data, data of calculation results, etc.

[0037] (Voltage Value Acquisition Unit) The voltage value acquisition unit 31 executes a process of acquiring the voltage value of each battery group in the battery pack 10 mounted on the vehicle 200. Specifically, the voltage value acquisition unit 31 acquires the voltage value of each battery group in the battery pack 10 mounted on the vehicle 200 using a known voltage sensor SR １ The battery control device 30 of this embodiment has a function of detecting the voltage values ​​of the first battery group 10A and the second battery group 10B in the vehicle 200 while the vehicle is running or stopped, via the voltage sensor SR. １ The voltage values ​​of the first battery group 10A and the second battery group 10B are detected via the known current sensor SR. ２ Alternatively, the state values ​​of the batteries (current value, voltage value, etc.) may be detected by acquiring the current value flowing through the first battery group 10A and the second battery group 10B via the respective terminals.

[0038] (SOC monitoring unit) The SOC monitoring unit 32 monitors the voltage sensor SR １ and current sensor SR ２ and executes a process of detecting and monitoring the SOC (charging rate) of each of the battery groups (first battery group 10A and second battery group 10B) of the battery pack 10 mounted on the vehicle 200 via the SOC monitor 32. Note that the specific method of detecting the SOC by the SOC monitor 32 is not particularly limited as long as it does not deviate from the spirit of the present embodiment, and various known SOC estimation techniques such as those disclosed in Japanese Patent Laid-Open No. 2021-68637 and International Publication No. WO2019 / 193471 may be applied.

[0039] (Switch Control Unit) The switch control unit 33 executes a process of switching the above-described connection state of the battery system 100 with respect to the above-described load 50. For example, the switch control unit 33 may execute a process of switching between the first connection mode and the second connection mode, a process of switching between the second connection mode and the third connection mode, a process of switching between the second connection mode and the fourth connection mode, etc., via the above-described switch mechanism 20.

[0040] (Presentation Control Unit) The presentation control unit 34 executes a process of displaying various information, such as the connection status of the battery system 100 to the load 50, on the presentation device PD. Here, examples of the presentation device PD in this embodiment include a known in-vehicle display and in-vehicle speaker. Note that the presentation control unit 34 may execute control to display the above-described various information on an external terminal, such as a smartphone carried by the occupant.

[0041] The computer program for realizing each function of the battery control device 30 may be, for example, a computer program applied to a battery system including a first battery group mounted on a vehicle and including a plurality of cells connected in series, and a second battery group having a different number of cells connected in series from the first battery group and having an upper limit voltage set to a voltage value in a low SOC state of the first battery group, and may cause one or more processors to execute processes including detecting the SOC of the first battery group and, when the first battery group enters the low SOC state, connecting the first battery group and the second battery group in parallel via a switch mechanism. Furthermore, such a computer program may be stored in a known recording medium such as an optical disk or various types of memory, or may be downloaded to the vehicle 200 from a known server such as a cloud.

[0042] <Other On-Vehicle Equipment> The vehicle 200 of this embodiment may further include a vehicle control device 40 that cooperates with the battery control device 30 to control the load 50, the generator, etc. Such a vehicle control device 40 is configured to have a function of controlling the driving of the vehicle 200 based on, for example, state information of the vehicle 200 detected by sensors SR mounted on the vehicle 200. Specific examples of such sensors SR include well-known acceleration sensors, GPS sensors, and angular velocity sensors. The sensors SR may further include a steering angle sensor, an accelerator pedal sensor, a brake pedal sensor, etc.

[0043] <Control Method of Battery System> Next, a control method of the battery system 100 of this embodiment will be specifically described with reference to Fig. 10 as well. Note that the control method may be used as a program algorithm that can be executed by the battery control device 30. A program having such an algorithm may be distributed, for example, in a downloadable manner via a known network, or in a form stored on a recording medium.

[0044] The following description will be given assuming that, for example, a user gets into vehicle 200, activates the system power supply, and starts driving. The following description will also be given of an example in which the first battery group 10A of battery pack 10 is used as a main battery that is primarily used, and the second battery group 10B is used as a sub-battery.

[0045] First, in step 11, the battery control device 30 determines whether the voltage of the main battery (first battery group 10A) that is normally used is equal to or exceeds the first threshold value V ｔｈ１ More specifically, in this example, the battery control device 30 determines whether the voltage sensor SR １ 10A。 It is determined whether the voltage value detected in the first battery group 10A is 3.3V or more (20% or more in terms of SOC) via.

[0046] In this example, the first threshold value V ｔｈ１ However, an optimum value may be determined in advance by experiment or simulation depending on the type of secondary battery used in the battery pack 10 and the specifications of the battery system 100. In addition, in step 11 described above, the battery control device 30 determines the state of the first battery group 10A based on the voltage value detected by the voltage sensor, but the determination may be made based on the SOC value of the battery instead of this voltage value.

[0047] In step 11, the voltage at the main battery exceeds a first threshold V ｔｈ１If this is the case (Yes in step 11), the battery control device 30 proceeds to step 12A and executes control to set the switch to the first connection configuration (see FIG. 4) described above via the switch mechanism 20. That is, in this case, the SOC of the first battery group 10A is 20% or more, the voltage value is close to the rated voltage, and the battery capacity is sufficient, so that the required power is supplied to the load 50 from the first battery group 10A.

[0048] On the other hand, if the voltage at the main battery exceeds the first threshold V ｔｈ１ If the voltage of the main battery is not equal to or greater than the second threshold value V (No in step 11), the battery control device 30 proceeds to step 12B. ｔｈ２ More specifically, in this example, the battery control device 30 determines whether the voltage sensor SR １ It is determined whether the voltage value detected in the first battery group 10A is 3.0 V or more (10% or more in terms of SOC) via the first threshold value V ｔｈ１ Similarly, the second threshold V ｔｈ２ Regarding the above, the optimum value can be determined in advance by experiment or simulation depending on the type of secondary battery used in the battery pack 10, the specifications of the battery system 100, and the like.

[0049] In step 12B, the voltage at the main battery reaches a second threshold V ｔｈ２ If the SOC is equal to or greater than this (Yes in step 12B), the battery control device 30 proceeds to step 13A and executes control to set the switch to the second connection configuration (see FIG. 5) via the switch mechanism 20. That is, in this case, the SOC of the first battery group 10A is equal to or greater than 10% but less than 20%, and the voltage value falls within a range in which it drops as the battery capacity decreases. In this case, the first battery group 10A and the second battery group 10B are connected in parallel to supply the required power to the load 50. As a result, although there is a possibility that the first battery group 10A may deteriorate slightly as the voltage and battery capacity decrease, a more stable battery output to the load 50 can be achieved compared to simply switching to the second battery group 10B.

[0050] On the other hand, if the voltage at the main battery exceeds the second threshold V ｔｈ２ If not (No in step 12B), the battery control device 30 proceeds to step 13B and executes control to set the switch to the third connection configuration (see FIG. 6) or the fourth connection configuration (see FIG. 7) via the switch mechanism 20. That is, in this case, the SOC of the first battery group 10A is less than 10%, and if it continues to be used as is, it will enter a region where battery deterioration will become significant. Therefore, the first battery group 10A is disconnected from the load 50, and the required power is supplied to the load 50 from the second battery group 10B.

[0051] At this time, the battery control device 30 may determine whether to set the third or fourth connection configuration depending on, for example, the required power for the load 50 of the battery system 100 and the driving condition of the vehicle 200 (for example, the acceleration value, the speed value, whether or not the vehicle is climbing, the accelerator opening degree at the time of determination, etc.).

[0052] As a result, by going through the above-mentioned step 13B, it becomes possible to suppress deterioration of the first battery group 10A while continuing to supply power from the second battery group 10B to the load 50 when the battery control device 30 selects the third connection configuration, and it becomes possible to supply sufficient power equivalent to that of the first battery group 10A from the second battery group 10B to the load 50 when the battery control device 30 selects the fourth connection configuration.

[0053] In this way, in the battery system 100 of this embodiment, by first using the second battery group 10B when the battery capacity of the first battery group 10A, which is the main battery, decreases, weight and cost can be reduced without making the capacity of the second battery group 10B excessively large compared to the case where the battery system 100 simply switches to the second battery group 10B. Furthermore, in the battery system 100 of this embodiment, if the boost circuit 21 is also provided in the battery pack 10, sufficient power equivalent to that of the first battery group 10A can be supplied to the load 50 from the second battery group 10B even in a situation where the first battery group 10A cannot be used.

[0054] As described above, the vehicle 200 equipped with the battery system 100 according to an embodiment of the present disclosure can maintain the vehicle's cruising range with a lightweight, low-cost battery configuration, while suppressing battery degradation as much as possible in response to loads such as the on-board electric motor, thereby achieving more stable battery output.

[0055] Although the preferred embodiments of the present disclosure have been described in detail above with reference to the accompanying drawings, the technology of the present disclosure is not limited to such examples. It is clear that a person skilled in the art of the technology to which the present disclosure pertains can conceive of various modified or altered examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0056] For example, in the second connection configuration described above, the battery control device 30 connects the first battery group 10A and the second battery group 10B in parallel, but when the voltage difference between the cells constituting the first battery group 10A and the cells constituting the second battery group 10B exceeds a predetermined value (for example, immediately after the vehicle suddenly accelerates), the battery control device 30 may perform control to temporarily disconnect the first battery group 10A from the load 50. This makes it possible to suppress unintended deterioration of the first battery group 10A. Note that the "predetermined value" that specifies the voltage difference described above can be set appropriately through experiments or simulations.

[0057] In the fourth connection configuration described above, the battery control device 30 boosts the voltage of the second battery group 10B via the boost circuit 21. However, the present disclosure is not limited to the above configuration, and may execute control to boost the voltage of the first battery group 10A via the boost circuit 21 under predetermined conditions, for example. Examples of such "predetermined conditions" include an uphill road or a certain accelerator pedal position.

[0058] 10: Battery pack, 10A: First battery group, 10B: Second battery group, 20: Switch mechanism, 20A: First switch, 20B: Second switch, 20C: Third switch, 30: Battery control device, 100: Battery system, 200: Vehicle

Claims

1. A battery system comprising: a battery pack consisting of a first battery group in which a plurality of cells are connected in series; and a second battery group in which a number of cells different from that of the first battery group are connected in series and in which the voltage value in a low SOC state of the first battery group is set as an upper limit voltage; a switch mechanism that can switch at least between a first connection configuration in which the first battery group is connected to a load, and a second connection configuration in which the first battery group and the second battery group are connected in parallel to the load; and a battery control device that controls the switch mechanism, wherein the battery control device switches from the first connection configuration to the second connection configuration via the switch mechanism when the first battery group enters the low SOC state.

2. The battery system of claim 1, wherein the switch mechanism is further capable of switching to a third connection configuration in which the first battery group is disconnected and the second battery group is connected to the load, and the battery control device switches from the second connection configuration to the third connection configuration via the switch mechanism when the SOC of the first battery group falls below a normal lower limit.

3. The battery system according to claim 2, further comprising a boost circuit connected to the second battery group via the switch mechanism and capable of boosting the voltage between the terminals of the second battery group, wherein the battery control device boosts the voltage of the second battery group via the boost circuit.

4. A battery control device for controlling a battery pack consisting of a first battery group in which a plurality of cells are connected in series, and a second battery group in which a different number of cells from the first battery group are connected in series and in which the upper limit voltage is the voltage value in a low SOC state of the first battery group, the battery control device comprising: a processor; and a memory capable of storing a program executed by the processor, the program including instructions that cause the processor to detect the SOC of the first battery group, and when the first battery group enters the low SOC state, connect the first battery group and the second battery group in parallel to a load via a switch mechanism.

5. A vehicle equipped with the battery system according to any one of claims 1 to 3 or the battery control device according to claim 4.

6. A recording medium on which a computer program is recorded that is applicable to a battery system that is composed of a first battery group in which a plurality of cells mounted on a vehicle are connected in series, and a second battery group in which a different number of cells than the first battery group are connected in series and in which the upper limit voltage is the voltage value in a low SOC state of the first battery group, the recording medium on which a computer program is recorded that causes one or more processors to execute processes including: detecting the SOC of the first battery group; and, when the first battery group enters the low SOC state, connecting the first battery group and the second battery group in parallel via a switch mechanism.

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