Battery management system

Abstract

The present invention avoids influence by errors in communication between lower-level units and an upper-level unit and suppresses the cost of taking measures to avoid influence by such errors when functions are divided between the lower-level units and the upper-level unit and an SOC estimation function is delegated to the lower-level units. The present invention comprises: lower-level units (CMU) that are associated with and control respective battery modules (M) that have a plurality of battery cells (C); an upper-level unit (BMU) that oversees the lower-level units (CMU); and a current sensor (A) that detects the values of the current passing through the battery modules (M). The upper-level unit (BMU) calculates an integrated current value from the current values detected by the current sensor (A) and transmits the integrated current value to the lower-level units (CMU), and the lower-level units (CMU) compute initial SOC values for the battery cells (C) on the basis of voltage values for the battery cells (C) and update the initial SOC values on the basis of the integrated current value received from the upper-level unit (BMU).

Description

Battery Management System

[0001] Embodiments of the present invention relate to a battery management system.

[0002] Patent Document 1 discloses a configuration of a new battery monitoring system including a slave unit that receives voltage data and current data via a wired connection through an insulation circuit, and a master unit that receives data from the slave unit by wireless transmission.

[0003] According to this battery monitoring system, since the slave unit receives voltage data and current data via a wired connection, unlike the case of wireless reception of both, the detection timing does not shift. Therefore, it is said that synchronization of the detection timing can be achieved and the calculation accuracy of the state of charge of the cell can be improved.

[0004] Japanese Patent Application Laid-Open No. 2023-001121

[0005] However, in the configuration described in Patent Document 1, since data is wirelessly transmitted between the slave unit and the master unit, there may inevitably be a delay in data transfer between the slave unit and the master unit. Also, in the battery monitoring system of Patent Document 1, the calculation of the state of charge of the cell is executed on the master unit side. However, for example, when the calculation is executed on the slave unit side, it is necessary to transfer the data required for the calculation from the master unit. However, as described above, if the data transfer from the master unit is delayed, the accuracy of the calculation of the state of charge of the cell in the slave unit may decrease.

[0006] Further, in the battery monitoring system of Patent Document 1, the slave unit receives voltage data and current data via a wired connection. However, when such a configuration is adopted, insulation processing is required, for example, between a current sensor in a high voltage band and a slave unit (monitoring IC) in a low voltage band.

[0007] Therefore, in this battery monitoring system, an isolator (insulation circuit) is provided between the current sensor and the slave unit (monitoring IC). However, of course, an insulation circuit must be provided for each slave unit. In particular, in the case of a configuration where a plurality of slave units are provided, an increase in cost due to the provision of an insulation circuit is inevitable.

[0008] The present invention was made to solve the above problems, and the object of the present invention is to provide a battery management system that, when functions are divided between a lower unit and an upper unit, and the lower unit is responsible for estimating the state of care (SOC) of a cell, avoids the effects of errors caused by communication between the lower unit and the upper unit, and can suppress the costs incurred in taking measures to avoid the effects of such errors.

[0009] The battery management system in this embodiment is associated with each battery module having multiple battery cells and includes a lower unit that controls the battery module, a higher unit that manages the multiple lower units, and a current sensor that detects the current value passing through the battery module. The higher unit calculates an integrated current value from the current value detected by the current sensor and transmits it to the lower unit. The lower unit calculates the initial state of charge (SOC) value of the battery cell based on the voltage value of the battery cell and updates the initial SOC value based on the integrated current value received from the higher unit.

[0010] Because the present invention employs such a battery management system, when functions are divided between a lower unit and an upper unit, and the lower unit is responsible for estimating the cell's SOC, it is possible to avoid the effects of errors caused by communication between the lower unit and the upper unit, and to suppress the costs incurred in taking measures to avoid such errors.

[0011] This is a block diagram showing the overall configuration of a vehicle control system according to an embodiment of the present invention, particularly the internal configuration of the battery management system. This is a block diagram showing the internal configuration of the control device of the BMU (higher-level unit) according to an embodiment of the present invention. This is a block diagram showing the internal configuration of the control device of the CMU (lower-level unit) according to an embodiment of the present invention. This is an explanatory diagram illustrating the calculation process of the initial SOC value and the update process of the SOC value according to an embodiment of the present invention. This is a flowchart showing the flow of the calculation process of the initial SOC value and the update process of the SOC value according to an embodiment of the present invention. This is a block diagram showing a modified example of the internal configuration of the control device of the higher-level unit according to an embodiment of the present invention. This is a flowchart showing the control flow executed in the control device of the modified example of the higher-level unit according to an embodiment of the present invention.

[0012] Embodiments of the present invention will be described in detail below with reference to the drawings. Note that the drawings are schematic and may differ from actual ones. Furthermore, the embodiments of the present invention shown below are illustrative examples of devices and methods for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited to the structure, arrangement, etc., of the components described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims.

[0013] The overall configuration of the vehicle control system S according to an embodiment of the present invention will be described with reference to Figure 1. Figure 1 is a block diagram showing the overall configuration of the vehicle control system S according to an embodiment of the present invention, with particular emphasis on the internal configuration of the battery management system.

[0014] The Battery Management System (BMS) according to an embodiment of the present invention is installed in a vehicle and performs control such as estimating the state of a secondary battery, as well as charging the secondary battery and supplying power to loads provided in various parts of the vehicle.

[0015] Here, a secondary battery is a battery that can be charged and discharged multiple times. Examples include batteries installed in vehicles and storage batteries used in electric vehicles to provide driving force. There are various types of "secondary batteries," but here we can mention lithium-ion batteries as an example.

[0016] Furthermore, the vehicle on which the Battery Management System (BMS) in the embodiment of the present invention is installed is not limited to electric vehicles, hybrid vehicles, etc., as long as it is equipped with a secondary battery.

[0017] The vehicle control system S in this embodiment of the present invention comprises a battery management system (BMS) and a Vehicle Control Module (VCM) 2. The VCM 2 is a control device connected to the battery management system (BMS) that controls the entire vehicle.

[0018] The vehicle is equipped with a charging port (not shown), and by connecting the charger 3 to the charging port, the secondary battery (battery cell C) can be charged. The power charged to the secondary battery is then discharged from the secondary battery and transmitted to the drive motor via an inverter (not shown). The drive motor is connected to the vehicle's drive components, such as the tires, and the secondary battery provides driving force to the vehicle.

[0019] In Figure 1, the aforementioned drive motor and drive unit are collectively referred to as the "load." That is, the power stored in the secondary battery (battery cell C) by charging from the charger 3 is discharged to the load.

[0020] The battery management system (BMS) comprises a Battery Management Unit (BMU) 1, multiple battery modules M, and a current measuring device 4.

[0021] For example, a microcontroller can be used as the BMU1. The BMU1 may also be installed near the battery module M, and may be configured for cloud-based management or remote management. The detailed configuration and functions of the BMU1 will be described later.

[0022] BMU1 is a device that manages the CMU (Cell Management Unit) provided for each battery module M, which will be described later. In other words, BMU1 is capable of understanding the status of multiple battery modules M, and estimates the status of multiple battery modules M, including the multiple CMUs managed by BMU1, as a single unit.

[0023] In other words, in the battery management system BMS that constitutes the vehicle control system S in the embodiment of the present invention, three battery modules M are connected in series, and these multiple battery modules M constitute a battery pack P. The following explanation will assume that multiple battery modules M are provided.

[0024] The battery module M comprises multiple battery cells C connected in series. Power is stored in the battery cells C via the charger 3. Furthermore, based on commands from the BMU 1 and VCM 3, the power stored in the battery cells C is discharged towards the load.

[0025] In the embodiment of the present invention, each of the multiple battery modules M constituting the vehicle control system S is provided with one CMU, and the battery module M is controlled by the CMU. As described above, the BMU1 manages the multiple CMUs, which are provided in a number equal to the number of battery modules M.

[0026] However, the relationship between the battery module M and the CMU does not necessarily have to be one-to-one. For example, a single battery module M may be divided into multiple groups, and a CMU may be provided for each group. In this case, multiple CMUs may be provided within a single battery module M. Alternatively, a single CMU may control multiple battery modules M. The detailed configuration of the battery module M will be described later.

[0027] Thus, one BMU1 manages multiple CMUs. In this embodiment of the present invention, the BMU1 that manages multiple CMUs is referred to as the "higher-level unit." On the other hand, the CMU that controls the battery module M managed by the BMU1 corresponds to the "lower-level unit."

[0028] The CMU controls the battery module M on which it is installed. The CMU is responsible for understanding and controlling the state of the associated battery module M, and the BMU1 calculates a total state estimate that represents the overall state of the battery pack P, which includes the battery module M, based on the state estimates transmitted from multiple CMUs that it oversees.

[0029] In other words, the BMU1 controls the entire battery pack P, which consists of multiple battery modules M, while each CMU controls only its own battery module M. The details of the division of functions between the BMU1 and the CMUs will be described later.

[0030] Furthermore, a current measuring device 4 is connected in series with the three battery modules M within the BMS. The current measuring device 4 includes a current detection circuit 41 that receives the value of the current passing through the multiple battery modules M detected by the current sensor A, and a communication circuit 42 that transmits the detected current value to the BMU 1.

[0031] As described above, the current measuring device 4 and the BMU 1 are connected by a wire, and the current value transmitted from the communication circuit 42 is received by the BMU 1 via the communication circuit 12, which will be described later.

[0032] As shown in Figure 1, the BMU1 includes a BMU control device 11 and a communication circuit 12. The communication circuit 12 transmits and receives information wirelessly between, for example, the BMUs provided in the multiple battery modules M.

[0033] On the other hand, information is transmitted and received via wired communication, for example, between the VCM3 or current measuring device 4 and the BMU1. Therefore, here, the communication circuit where wireless communication takes place and the communication circuit where wired communication takes place are collectively referred to as the communication circuit 12.

[0034] Therefore, in Figure 1, the connections between devices that transmit and receive information wirelessly, such as BMU1 and CMU, are shown with dashed lines. On the other hand, the connections between devices that transmit and receive information via wires, such as between BMU1 and VCM3, or between current measuring device 4 and BMU1, are shown with solid lines.

[0035] Figure 2 is a block diagram showing the internal configuration of the control device of the BMU (higher-level unit) 1 according to an embodiment of the present invention. The BMU control device 11 includes an information acquisition unit 111, an open state determination unit 112, a current value integration unit 113, an aggregation calculation unit 114, and an information transmission unit 115.

[0036] In Figure 1, the BMU 1 consists of a BMU control device 11 and a communication circuit 12, and the internal configuration of the BMU control device 11 is as shown in Figure 2. However, these configurations only show the configurations necessary to explain the functions of the BMU 1 in the embodiment of the present invention, and other configurations may also be included.

[0037] The information acquisition unit 111 acquires information transmitted from each CMU provided in the multiple battery modules M under its control, as well as information related to current values ​​transmitted from the current measuring device 4. Depending on the type of information, the various types of information acquired by the information acquisition unit 111 are transmitted to the open state determination unit 112, the current value integration unit 113, or the aggregation calculation unit 114 as appropriate.

[0038] The open state determination unit 112 determines whether the secondary battery (battery cell C) in each battery module M is in an open state. The reason the open state determination unit 112 determines whether the battery cell C is in an open state is that, as will be described later, the CMU uses the open-circuit voltage when calculating the state of charge (SOC) of the battery cell C.

[0039] However, when the vehicle is in use and battery cell C is charging and discharging, the secondary battery circuit is a closed circuit, and therefore the open-circuit voltage cannot be measured. In other words, the secondary battery installed in the vehicle is in an open-circuit state only when the ignition is OFF and before the ignition is turned ON.

[0040] On the other hand, since the vehicle control system S needs to be started in order to measure the open-circuit voltage, the timing for measuring the open-circuit voltage is limited to when the vehicle user turns the ignition ON. Therefore, the open-circuit state determination unit 112 determines whether or not the secondary battery is in an open-circuit state when the vehicle control system S (battery management system BMS) is started.

[0041] In other words, the open state determination unit 112 determines whether or not the ignition has been turned ON. Specifically, one possible method is to look at the current value transmitted from the current measuring device 4. In this case, if the current value is zero, it can be determined that the battery cell C is in an open state.

[0042] Alternatively, one could determine whether the secondary battery is open based on the connection status of the battery relay. In this case, for example, one could check whether an ON or OFF command has been issued to the battery relay. Furthermore, some battery relays have a function to check for connection status using current, etc., and if such a battery relay is used, the connection status can be determined by checking the current, etc.

[0043] The current value integration unit 113 calculates a current integration value [Asec] based on the values of currents that have passed through the plurality of battery modules M received from the current measurement device 4. For example, when the vehicle is in use, since it discharges during driving, the calculated current integration value is the current integration value due to discharge. Specifically, for example, the current integration value is calculated by performing time integration of the current value at a preset period such as 100 ms.

[0044] That is, the current integration value is calculated, for example, by adding a numerical value obtained by multiplying the current value received from the current measurement device 4 by 0.1 to the latest current integration value calculated by the current value integration unit 113. Further, the current value integration unit 113 transmits the resulting current integration value to the CMU at a preset period such as 100 ms.

[0045] The aggregation calculation unit 114 aggregates the values of the SOC calculated in each CMU and the state estimation values described later. That is, the aggregation calculation unit 114 calculates the total state estimation value for the entire battery pack P based on the information transmitted from the CMUs provided in the respective battery modules M, rather than the states of the individual battery modules M.

[0046] The information transmission unit 115 transmits, for example, a signal indicating that the secondary battery is in an open state, which is determined by the open state determination unit 112, to each battery module M (CMU). Alternatively, it may transmit the total state estimation value obtained by aggregating and calculating the state estimation values received from each CMU to the VCM 3 connected to the BMU 1.

[0047] Next, the configuration of the battery module M will be described with reference to FIG. 1. As shown in FIG. 1, in the battery management system BMS according to the embodiment of the present invention, three battery modules M are connected in series. In FIG. 1, the first battery module M1, the second battery module M2, and the third battery module M3 are shown from the left side to the right side.

[0048] Incidentally, the configurations of these first to third battery modules M1 to M3 are all the same here. Therefore, hereinafter, the configuration of the battery module M will be described by taking the first battery module M1 as an example. However, in the case of explanations applicable to any of the first battery module M1 to the third battery module M3, it will be represented as "battery module M" as appropriate as before.

[0049] The first battery module M1 includes a plurality of battery cells C and a CMU1. As shown in FIG. 1, the plurality of battery cells C are connected in series. In the battery module M shown in FIG. 1, it is shown that four battery cells C are stacked on top of each other, but this is only for the convenience of illustration.

[0050] That is, how many of these battery cells C are stacked and how many stacked battery cells C are grouped into one battery module M can be arbitrarily set according to the battery capacity required for the battery module M. Incidentally, hereinafter, for the battery cell C, whether it represents an individual battery cell or a plurality of battery cells included in the battery module M, it will be appropriately represented as "battery cell C".

[0051] Further, a temperature sensor T for detecting the temperature of the battery module M is provided near the battery cell C. As shown in FIG. 1, in the battery management system BMS in the embodiment of the present invention, one temperature sensor T is provided for each battery module M. However, the number of temperature sensors T is not limited to one, and a plurality of them may be provided.

[0052] As also shown in FIG. 1, in the battery management system BMS in the embodiment of the present invention, a temperature sensor T is provided in any battery module M. However, it is also possible that a battery module M without the temperature sensor T is connected.

[0053] The CMU1 is equipped with a communication circuit M11, a CMU control device M12, a voltage detection circuit M13, a balance circuit M14, and a temperature detection circuit M15. The communication circuit M11 plays the role of transmitting various information acquired in the first battery module M1, such as the calculated SOC value and state estimate value, to the BMU1. As described above, the above data is transmitted and received between the upper-level unit BMU1 and the lower-level unit CMU1 via wireless communication.

[0054] The CMU control unit M12 has the function of controlling the entire first battery module M1. Details of the functions of the CMU control unit M12 will be described later. The voltage detection circuit M13 detects the voltage of each of the multiple battery cells C provided in the first battery module M1.

[0055] Furthermore, the balance circuit M14 performs a balancing process to balance (equalize the voltage of) each battery cell C. Specifically, based on a command from the cell balancing control unit (not shown), the balance circuit M14 consumes power using an ON / OFF resistor and controls the voltage of each battery cell C to a value set as the cell balancing target value.

[0056] The temperature detection circuit M15 acquires information from the temperature sensor T that detects the temperature of the battery cell C and transmits it to the CMU control device M12.

[0057] In Figure 1, each CMU has the configuration described above. However, these configurations only show the configurations necessary to explain the function of the CMU in the embodiment of the present invention, and other configurations may also be included. The same applies to the internal configuration of the CMU control device M12 described below.

[0058] Figure 3 is a block diagram showing the internal configuration of the CMU control device M12 of the CMU (sub-unit) M1 according to an embodiment of the present invention. The CMU control device M12 includes a measurement value acquisition unit M121, a cell state estimation unit M122, a calculation unit M123, an update unit M124, and an information transmission unit M125.

[0059] The measurement value acquisition unit M121 acquires, for example, the voltage value detected by the voltage detection circuit M13 for each battery cell C. Alternatively, it acquires information on the integrated current value transmitted from the BMU1. The measurement value acquisition unit M121 may also acquire temperature information measured by the temperature sensor T via the temperature detection circuit M15.

[0060] The cell state estimation unit M122 estimates the state of each battery cell C and calculates a state estimation value. The value used to estimate the state of the battery cell C is, for example, a value indicating at least one of the following: the rate of capacity degradation (SOH: State of Health), the upper limit charging power, or the upper limit discharging power.

[0061] Furthermore, as state estimates, after calculating each value, these three types of indicators can be used in appropriate combinations, or all three types of indicators can be used. Alternatively, other indicators can also be used.

[0062] Furthermore, the cell state estimation unit M122 may also determine whether the voltage value of the battery cell C used by the calculation unit M123 when calculating the initial SOC value can be used in the calculation of the initial SOC value. This point will be discussed later.

[0063] The cell state estimation unit M122 calculates the state estimate for each of the multiple battery cells C provided in the first battery module M1. Therefore, for example, the state estimates for the second module M2 and the third battery module M3 are calculated in the respective CMU2 and CMU3.

[0064] The calculation unit M123 calculates the State of Control (SOC) value for each of the multiple battery cells C in the first battery module M1. Specifically, first, the calculation unit M123 acquires the open-circuit voltage of each battery cell C transmitted from the voltage detection circuit M13. The voltage detection circuit M13 transmits the measured value to the calculation unit M123 via the measurement value acquisition unit M121 at a predetermined period, for example, 100 ms.

[0065] Then, the calculation unit M123 calculates the SOC value using table data showing the relationship between the open-circuit voltage and the SOC value of the battery cell C, which is pre-stored in a memory unit (not shown). The table data showing the relationship between the open-circuit voltage and the SOC value is set based on results obtained in advance from characteristic acquisition experiments using the battery cell C that will actually be installed, for example.

[0066] Furthermore, for example, if the battery module M constituting the battery management system (BMS) is reused, the configuration of the battery management system (BMS) may change, or a new type of battery cell may be used, such as by changing the material constituting the battery cell C. In such cases, by replacing the table data described above with new characteristics, the CMU can be given the same functionality as the calculation unit M123 according to the embodiment of the present invention.

[0067] Thus, the calculation unit M123 calculates the SOC value using the open-circuit voltage value. As mentioned above, the timing for measuring the open-circuit voltage is when the user turns the ignition ON. On the other hand, after the ignition is turned ON, the circuit of battery cell C becomes a closed circuit as described above, so it is not possible to obtain the open-circuit voltage.

[0068] Therefore, in the following, the SOC value calculated using the open-circuit voltage in the calculation unit M123 will be referred to as the "initial SOC value". During periods when the vehicle is in use and the open-circuit voltage cannot be obtained, the SOC value is calculated by updating the initial SOC value. The update unit M124 is responsible for updating the SOC value in this way.

[0069] The update unit M124 receives the integrated current value transmitted from the BMU1 via the measurement value acquisition unit M121 and updates the initial SOC value calculated by the calculation unit M123. In other words, since the calculation unit M123 calculates the initial SOC value for each of the multiple battery cells C, it updates the value of each SOC based on the integrated current value, starting from these multiple initial SOC values.

[0070] Specifically, the update unit M124 calculates the updated SOC value by adding the initial SOC value to the value obtained by dividing the current integrated value [Asec] by the current full charge capacity [Asec] of the battery cell C and multiplying by 100. The full charge capacity here is determined by multiplying the full charge capacity of the new battery cell C by the capacity degradation rate (SOH).

[0071] Regarding the calculation method for SOH, known methods can be used. For example, one method involves calculating SOH from the perspective of storage degradation and cycle degradation based on the storage time and the number of charge cycles for the battery cell C, using characteristic formulas obtained experimentally in advance.

[0072] As described above, after the calculation unit M123 calculates the initial SOC value using the open-circuit voltage, the battery cell C becomes a closed circuit because the vehicle itself is in use, and the open-circuit voltage cannot be obtained. Therefore, the update unit M124 updates the SOC value using the integrated current value transmitted from the BMU1, starting from the initial SOC value.

[0073] By having the CMU1 perform this process, the SOC value can be updated in real time even while the vehicle is in use, and the status of the battery cell C (battery module M) can be monitored.

[0074] The information transmission unit M125 transmits information such as state estimates and SOC values ​​obtained from various parts of the CMU control device M12, including the cell state estimation unit M122 and the calculation unit M123, to the BMU1.

[0075] As described above, when the calculation unit M123 calculates the initial SOC value, it transmits the result to the update unit M124, and the update unit M124 updates the SOC value starting from the received initial SOC value. Furthermore, when the calculation unit M123 calculates the initial SOC value, it also transmits a signal (hereinafter referred to as the "completion signal") to the current value integration unit 113 of the BMU1 indicating that the calculation of the initial SOC value has been completed.

[0076] The reason the calculation unit M123 transmits a completion signal to the current value integration unit 113 via the information transmission unit M125 is that the current value integration unit 113, upon receiving the completion signal, resets the process of integrating current values ​​that it has been performing up to that point.

[0077] As described above, the current value integration unit 113 obtains information on the current value from the current measuring device 4 and calculates the current integrated value. However, it does not continue the integration process without a set period after starting the integration process at a certain timing. In other words, the current value integration unit 113 calculates the current integrated value because the current integrated value is used when updating the SOC value of the battery cell C calculated on the CMU side.

[0078] Therefore, once the calculation of the SOC initial value is complete, the calculation unit M123 sends a completion signal to the current value integration unit 113. Upon receiving this completion signal, the current value integration unit 113 resets the current value integration process it had been performing and starts the integration process again.

[0079] As described above, the BMU1 is equipped with an open state determination unit 112, and the calculation unit M123 receives a signal from the open state determination unit 112 indicating that the battery cell C is in an open state, obtains the open-circuit voltage, and starts calculating the initial SOC value. Therefore, it is also conceivable that the current value integration unit 113 may reset the current value integration process when it receives a signal from the open state determination unit 112 indicating that the battery cell C is in an open state.

[0080] However, if this process is implemented, there is a possibility that the CMU may not be able to properly update the SOC value if it fails to calculate the initial SOC value for some reason.

[0081] In other words, for example, the current value integration unit 113 may be reset when it receives a signal from the open state determination unit 112 indicating that the battery cell C is in an open state, while the calculation unit M123 does not calculate the initial SOC value. In this case, the update unit M124 performs an update process for the SOC value starting from the most recently calculated initial SOC value. This update process by the update unit M124 is performed based on the current integration value calculated after the reset and restart of the integration process.

[0082] As described above, the update unit M124 uses the integrated current value when updating the SOC value. The integrated current value after the current value integration process is reset will be smaller than the integrated current value when it is not reset. Therefore, as shown in the formula above, since the formula used when updating the SOC value includes an item that divides the integrated current value by the current full charge capacity of the battery cell C, the value of this item will also become smaller. As a result, the update unit M124 will not be able to perform a more accurate update process, and the accuracy of the updated SOC value will decrease.

[0083] Therefore, upon receiving the completion signal, the current value integration unit 113 resets the current value integration process it had been performing and restarts the integration process. The processes between the BMU1 and CUM described above are explained below using diagrams. Figure 4 is an explanatory diagram illustrating the calculation process of the initial SOC value and the update process of the SOC value according to an embodiment of the present invention.

[0084] The explanatory diagram shown in Figure 4 is divided into three main sections. The upper section first shows the open state determination of the battery cell C performed by the open state determination unit 112. The indication "Open" indicates that the battery cell C is in an open state. As mentioned above, the battery cell C is in an open state when the ignition is turned ON for the vehicle.

[0085] On the other hand, "closed" indicates that battery cell C is in a closed state. As mentioned above, once the ignition is turned ON and battery cell C is in an open state, the vehicle is in a state of use, so battery cell C becomes a closed circuit. Therefore, the open state determination unit 112 determines that battery cell C is in an open state the moment the ignition is turned ON.

[0086] In the explanatory diagram, the timing at which the open state determination unit 112 determined that the battery cell C was in an open state is shown twice. The timing of the first and second open states are indicated by solid vertical lines.

[0087] The middle section of the explanatory diagram shows the state of charge (SOC) of battery cell C. Since SOC represents the charge level, dashed lines indicating SOC 100% and SOC 0% are shown in the middle section. Therefore, the line indicating the state of SOC is contained between these dashed lines representing 100% and 0%. The period between the timing of the first and second opening states described above is when the vehicle is in use.

[0088] In reality, the ignition of a vehicle is not always ON; there are naturally times when the ignition is OFF. However, for the sake of explanation, the diagram in Figure 4 omits the illustration of the ignition OFF state.

[0089] As the vehicle is used, the State of Charge (SOC) decreases, so the graph shows a gradual decrease in SOC between the first and second times when battery cell C is open. Two black circles are shown on the vertical lines indicating these timings. These black circles indicate the initial SOC value calculated by the calculation unit M123.

[0090] In other words, once the open state determination unit 112 determines that the battery cell C is in an open state, the calculation unit M123 calculates the initial SOC value based on the acquired open-circuit voltage. Therefore, the black circles shown in Figure 4 are indicated on the vertical line that shows the timing when the open state determination unit 112 determines that the battery cell C is in an open state.

[0091] As described above, after the initial SOC value is calculated, the update unit M124 performs an update process for the SOC value using the integrated current value at a predetermined interval. As the vehicle is used, the integrated current value increases, so the SOC value decreases from the initial SOC value each time it is updated. The middle section of Figure 4 shows this change in the SOC value.

[0092] The lower part of Figure 4 shows the change in the integrated current value. As mentioned above, when the value of the current flowing through battery cell C is accumulated while the vehicle is in use, the value gradually increases. The lower part shows this change in the integrated current value.

[0093] Furthermore, when the calculation unit M123 sends a completion signal to the current value integration unit 113 of the BMI1 indicating that it has completed the calculation of the SOC initial value, the current value integration unit 113 resets the current value integration process. In the transition of the current integrated value shown in the lower part of Figure 4, the current integrated value, which is shown to gradually increase from the timing of the first open state, decreases along the vertical line at the timing of the second open state, and then turns to increase again.

[0094] The reason the current integration value decreases along the vertical line at the point where the circuit is opened for the second time is that the current value integration unit 113 receives a completion signal and resets the integration process. At this point, the integration process is reset, and then the current value integration unit 113 restarts the integration process. Therefore, in the lower part of Figure 4, the current integration value in the reset state is shown as 0 [Asec].

[0095] The reason the integrated current gradually increases is that when the ignition is turned ON, the vehicle is put into use, but basically, discharge occurs to the battery cell C, so the integrated current also moves in a positive direction.

[0096] Furthermore, as described above, the explanatory diagram in Figure 4 shows the timing at which the open state determination unit 112 determines whether or not the battery cell C is in an open state twice. At the timing of the second determination by the open state determination unit 112 that it is in an open state, the initial SOC value is calculated by the calculation unit M123, as explained earlier.

[0097] However, looking at the explanatory diagram, a difference d can be observed between the intersection of the SOC value, which gradually decreases from the initial SOC value calculated at the timing of the first opening, and the vertical line indicating the second timing, and the initial SOC value actually calculated at the second timing.

[0098] After the initial SOC value is calculated by the calculation unit M123, the update unit M124 performs an update process for the SOC value based on the current integrated value transmitted from the BMU1. This current integrated value is obtained by integrating the current values ​​transmitted from the current measuring device 4 in the current value integration unit 113 of the BMU1.

[0099] However, the current value measured by current sensor A may include errors in current sensor A itself. Therefore, the integrated current value is calculated based on the current value including such errors in current sensor A, and the update process starting from the initial SOC value is performed using this integrated current value. As a result, a difference arises between the updated SOC value and the initial SOC value calculated based on the open-circuit voltage due to this error. This difference is the difference d in the explanatory diagram of Figure 4.

[0100] As explained above, different functions are assigned to the BMU1 (higher-level unit) and each CMU (lower-level unit). Specifically, the SOC value of the battery cells C in each battery module M is calculated by the CMU located in that module M. On the other hand, the integrated current value necessary for the CMU to calculate the SOC value is calculated by the BMU1 and transmitted to the CMU.

[0101] Next, we will explain the exchange of information between the upper and lower units when calculating the SOC value in the CMU. Here again, we will use the CMU1 of the first battery module M1 as an example of the CMU.

[0102] First, the open state determination unit 112 of the BMU1 determines the open state of the secondary battery (battery cell C). If the determination result shows that the battery cell C is not in an open state, the open state determination unit 112 continues to perform its determination.

[0103] On the other hand, if the open state determination unit 112 determines that the battery cell C is in an open state, the open state determination unit 112 transmits a signal indicating that it is in an open state to each CMU provided in each battery module M via the information transmission unit 115.

[0104] Upon receiving the signal from BMU1, the measurement value acquisition unit M121 of CMU1 transmits the signal to the cell state estimation unit M122. Alternatively, it transmits a signal indicating that the signal has been received.

[0105] The cell state estimation unit M122, upon receiving the signal, acquires the open-circuit voltage of each battery cell C via the voltage detection circuit M13. The acquired open-circuit voltage value is transmitted to the calculation unit M123, which uses the open-circuit voltage value to calculate the SOC value. The SOC value calculated here is the initial SOC value, as described above.

[0106] When the calculation unit M123 calculates the initial SOC value, it sends a signal (completion signal) to the BMU1 indicating that the calculation is complete. Upon receiving the completion signal, the BMU1 sends the same completion signal to the current value integration unit 113, which then resets the current value integration process it has been performing. It then restarts the current value integration process.

[0107] The current value integration unit 113 transmits the current integration value calculated at a preset period to the CMU 1. As mentioned above, the transmission of the current integration value from the BMU 1 to each CMU, including the CMU 1, is performed wirelessly.

[0108] Upon receiving the integrated current value, the CMU1 transmits the integrated current value from the measurement value acquisition unit M121 to the update unit M124. The update unit M124 uses the received integrated current value to update the SOC value, starting from the initial SOC value calculated by the calculation unit M123. Through this process, the SOC value is updated (calculated) with high accuracy to reflect the conditions under which the vehicle is used.

[0109] The SOC value updated by the update unit M124 is then transmitted to the BMU1. The aggregation calculation unit 114 of the BMU1 uses the SOC values ​​transmitted from each CMU to calculate the SOC value for the entire battery pack P.

[0110] Here, various methods can be used to calculate the SOC value of the entire battery pack P, such as taking the average of the SOC values ​​transmitted from each CMU.

[0111] The roles of BMU1 and CMU in the CMU's calculation of the SOC value are as described above. When the CMU calculates the initial SOC value, it uses the open-circuit voltage value. However, whether the open-circuit voltage value can be used when calculating the initial SOC value may be determined before the calculation of the initial SOC value by the calculation unit M123.

[0112] For example, if the ignition is turned ON shortly after being turned OFF, a change in voltage due to polarization may occur in battery cell C. In such cases where the voltage value is unstable, it is difficult to say that the accuracy of the calculated SOC initial value can be ensured if the SOC initial value is calculated using the unstable voltage value.

[0113] Therefore, if it is determined that the voltage value of battery cell C is unstable, it is actually better to not perform the calculation of the initial state of control (SOC) value in order to ensure the accuracy of the SOC value.

[0114] Therefore, the cell state estimation unit M122 may determine whether the voltage value of the battery cell C used by the calculation unit M123 when calculating the initial SOC value can be used in the calculation of the initial SOC value, and only if the voltage value can be used in the calculation of the initial SOC value, the calculation unit M123 may perform the calculation of the initial SOC value.

[0115] Here, the cell state estimation unit M122 determines whether the open-circuit voltage value can be used when calculating the initial SOC value. Specifically, the cell state estimation unit M122 makes this determination based on conditions such as whether the time between ignition ON and ignition ON is below a threshold.

[0116] [Operation] Next, the process for calculating the SOC value in the CMU described above will be explained in accordance with the processing flow. Figures 5 and 6 are flowcharts showing the flow of the SOC initial value calculation process and the SOC value update process according to the embodiment of the present invention.

[0117] To clarify the respective roles of the upper unit (BMU) and lower unit (CMU) in the embodiment of the present invention, the flowcharts shown in Figures 5 and 6 show the processing of the upper unit (BMU) with dashed lines, while the processing of the lower unit (CMU) is shown with solid lines.

[0118] Again, among the multiple CMUs, we will primarily use CMU1, which is located in the first battery module M1, as an example. However, if it is not necessary to mention a specific CMU, we will continue to use the phrase "multiple CMUs."

[0119] First, the open state determination unit 112 of the BMU1 determines the open state of the secondary battery (battery cell C) (ST1). If the determination result shows that the battery cell C is not in an open state (NO in ST2), the current value integration unit 113 calculates the current integration value, as will be described later.

[0120] On the other hand, if the open state determination unit 112 determines that the battery cell C is in an open state (YES in ST2), it transmits a signal indicating that it is in an open state to each CMU provided in each battery module M via the information transmission unit 115 (ST3). Each CMU receives the signal from the BMU1 (ST4).

[0121] For example, the measurement value acquisition unit M121 of the CMU1 transmits the signal to the cell state estimation unit M122. Alternatively, it transmits a signal indicating that the signal has been received. The cell state estimation unit M122, triggered by the receipt of the signal, acquires the open-circuit voltage of each battery cell C via the voltage detection circuit M13 (ST5). The open-circuit voltage of each battery cell C is then calculated (ST6).

[0122] However, if the open-circuit voltage value is unstable, calculating the SOC initial value using the unstable voltage value may compromise the accuracy of the calculated SOC initial value. Therefore, after the open-circuit voltage value is calculated, a determination is made before the calculation of the SOC initial value by the calculation unit M123 to determine whether that open-circuit voltage value can be used in calculating the SOC initial value.

[0123] In other words, the cell state estimation unit M122 determines whether the voltage value of the battery cell C used by the calculation unit M123 when calculating the initial SOC value can be used in the calculation of the initial SOC value (ST7). If the cell state estimation unit M122 determines that the open-circuit voltage value can be used in the calculation of the initial SOC value (YES in ST8), the acquired open-circuit voltage value is transmitted to the calculation unit M123. The calculation unit M123 uses the open-circuit voltage value to calculate the initial SOC value of each battery cell C (ST9).

[0124] When the calculation unit M123 calculates the initial SOC value, it sends a signal (completion signal) to the BMU1 indicating that the calculation is complete (ST10). When the BMU1 receives the completion signal (ST11 in Figure 6), it sends the same completion signal to the current value integration unit 113, and the current value integration unit 113 resets the current value integration process that has been performed up to that point (ST12). Then it starts the current value integration process again (ST13).

[0125] The current value integration unit 113 performs the current value integration process and determines whether a predetermined period has arrived for transmitting the current integrated value to each CMU (ST14). If it is determined that the predetermined period has not arrived (NO in ST14), the process returns to step ST13, and the current value integration unit 113 continues the current value integration process.

[0126] On the other hand, if the current value integration unit 113 determines that a predetermined period has arrived (YES in ST14), the current value integration unit 113 transmits the calculated current integrated value to the CMU 1. The current integrated value transmitted from the current value integration unit 113 is received by each CMU (ST16).

[0127] Upon receiving the integrated current value, the CMU1 transmits the integrated current value from the measurement value acquisition unit M121 to the update unit M124. The update unit M124 uses the received integrated current value to update the SOC value, starting from the initial SOC value calculated by the calculation unit M123 (ST17).

[0128] The SOC value updated by the update unit M124 is transmitted to the BMU1 (ST18). The aggregation calculation unit 114 of the BMU1 determines whether or not it has received the SOC value for each battery cell C from all CMUs (ST19). If it has not received the SOC value from all CMUs (NO in ST19), it waits until the SOC values ​​transmitted from all CMUs are complete.

[0129] On the other hand, if the aggregation calculation unit 114 determines that it has received SOC values ​​from all CMUs (YES in ST19), the SOC value for the entire battery pack P is calculated using the SOC values ​​transmitted from each CMU (ST20).

[0130] The process when the cell state estimation unit M122 determines that the open-circuit voltage value can be used in the calculation of the SOC initial value (YES in ST8) is as described above. On the other hand, when the cell state estimation unit M122 determines that the open-circuit voltage value cannot be used in the calculation of the SOC initial value (NO in ST8), the calculation unit M123 does not perform the calculation of the SOC initial value.

[0131] In this case, although the circuit of battery cell C is determined to be open-circuited, the open-circuit voltage value necessary to calculate the initial SOC value cannot be obtained. Therefore, it is not possible to forcibly calculate the initial SOC value in this state, and even if the initial SOC value is obtained by calculation, it is not appropriate from the standpoint of accuracy.

[0132] Therefore, in such cases, the SOC initial value is not calculated, and the SOC value is updated using the SOC initial value calculated immediately before, based on the integrated current value received from BMU1 (ST16, ST17). Consequently, the calculation of the SOC initial value is skipped once, but this can be compensated for by calculating the SOC initial value when the circuit of battery cell C becomes open again.

[0133] The above describes the process for calculating the SOC value in the lower-level unit (CMU). However, it is possible to add the processes described below to this process. Figure 7 is a block diagram showing a modified example of the internal configuration of the control device 11A of the upper-level unit (BMU1) according to an embodiment of the present invention.

[0134] In the modified configuration of the BMU control device 11A, a battery relay control unit 116 is added to the configuration of the BMU control device 11 of the conventional BMU1. The battery relay control unit 116 controls the connection state of the battery relay. That is, it connects the battery relay when it receives an ignition ON signal from the user, and disconnects (opens) the battery relay when the ignition is turned OFF.

[0135] In other words, under the control of the battery relay control unit 116, the circuit of battery cell C, which was previously an open circuit, is closed when the vehicle system starts up, and conversely, when the vehicle system stops, the circuit of battery cell C, which was previously a closed circuit, is opened.

[0136] As explained above, upon receiving a determination from the open state determination unit 112 of the BMU1 that the circuit of the battery cell C is in an open state, the cell state estimation unit M122 in the CMU obtains the open-circuit voltage value of each battery cell C, and the calculation unit M123 calculates the initial SOC value.

[0137] In other words, if the open state of the battery cell C is maintained until the initial SOC value is calculated in the CMU, the calculation of the initial SOC value in the CMU can be performed more reliably. Therefore, in the modified example, the determination result that the circuit of the battery cell C is in an open state, made by the open state determination unit 112, is transmitted not only to the CMU but also to the battery relay control unit 116.

[0138] Upon receiving the determination result, the battery relay control unit 116 does not connect the battery relay and maintains the battery relay disconnected state until the BMU1 receives a completion signal from the CMU indicating that the calculation of the SOC initial value has been completed. Then, when the battery relay control unit 116 receives the completion signal, it connects the battery relay.

[0139] Figure 8 is a flowchart showing the control flow performed in a modified control device (11A) of the upper unit (BMU1) according to an embodiment of the present invention. All processes shown in the flowchart of Figure 8 are processes performed in the BMU1, and are therefore shown with dashed lines.

[0140] First, the process by which the open state determination unit 112 determines the open state of the secondary battery (battery cell C) is as previously explained (ST1, ST2). If it is determined that the circuit of battery cell C is in an open state (YES in ST2), the determination result is transmitted to each CMU and also to the battery relay control unit 116.

[0141] The battery relay control unit 116 maintains the state of the battery relay when the ignition is turned ON (ST31). That is, at the moment the ignition is turned ON, the circuit of battery cell C is still open, so the battery relay is not connected. Therefore, this state is maintained.

[0142] The battery relay control unit 116 maintains the state in which the battery relay is disconnected and determines whether or not a signal has been sent from the CMU to the calculation unit M123 indicating that the calculation of the initial SOC value has been completed (ST32).

[0143] If a completion signal has not been received from the calculation unit M123 (NO in ST32), the battery relay remains disconnected, and the circuit of battery cell C remains open.

[0144] On the other hand, if a completion signal is received from the calculation unit M123 (YES in ST32), the calculation of the SOC initial value is completed in the calculation unit M123, so the battery relay control unit 116 connects the battery relay (ST33). After this, the processes from step ST12 onwards in Figure 6 are executed.

[0145] [Effects of the Embodiment] (1) The battery management system includes a lower unit that controls the battery module and is associated with each battery module having multiple battery cells, a higher unit that manages the multiple lower units, and a current sensor that detects the current value passing through the battery module. The higher unit calculates the integrated current value from the current value detected by the current sensor and transmits it to the lower unit. The lower unit calculates the initial SOC value of the battery cell based on the voltage value of the battery cell and updates the initial SOC value based on the integrated current value received from the higher unit.

[0146] By adopting such a battery management system, when functions are divided between lower and upper units, with the lower unit responsible for estimating the cell's SOC, the effects of communication errors between the lower and upper units can be avoided, and the costs incurred in taking measures to avoid such errors can be reduced.

[0147] In other words, when transferring part of the function that the higher-level unit originally had—calculating the State of Charge (SOC) value of a battery cell—to the lower-level unit, the current value necessary for calculating the SOC value is not the current value obtained directly from the current measuring device, but rather the current is integrated in the higher-level unit before being transmitted to the lower-level unit. By performing this process, communication errors caused by delays in wireless communication between the higher-level and lower-level units can be avoided.

[0148] Specifically, if the function for calculating the SOC value is moved from the higher-level unit to the lower-level unit, the function for calculating the current integration value necessary for calculating the SOC value will also be moved to the lower-level unit. However, even if such a separation of functions is performed, the current value detection function is still located in the higher-level unit, so the current value still needs to be transmitted wirelessly from the higher-level unit to the lower-level unit.

[0149] If the current value is integrated in the lower unit under these conditions, the communication errors that occur when transmitting the current value from the upper unit to the lower unit may accumulate as the number of transmissions increases. If the SOC value is calculated using the current integrated value with accumulated communication errors, the accuracy of the calculation may deteriorate. Therefore, in the battery management system of the embodiment of the present invention, the calculation of the current integrated value is performed in the upper unit.

[0150] It should be noted that communication errors occur when transmitting information between upper and lower units, and indeed, there is a possibility that communication errors may occur when transmitting the integrated current value from the upper unit to the lower unit. However, since the impact of communication errors on the lower unit is limited to the single reception of the integrated current value, the communication errors do not accumulate as much as when the lower unit performs the integration of current values ​​based on the current values ​​transmitted from the upper unit, and the accuracy of the SOC value calculation is improved accordingly.

[0151] Furthermore, by dividing functions between the upper and lower units in this way, even when reusing the batteries after their use in a vehicle has ended, for example, they can be divided and used individually as needed. Therefore, when reusing secondary batteries, they can be used without major modifications, regardless of whether only individual battery modules are reused or not. This promotes the reuse of secondary batteries.

[0152] Therefore, for example, one possible use case for reusable secondary batteries is a battery storage system that is connected to the grid current, can charge with generated electricity, and can discharge it to a load.

[0153] In other words, this battery storage system stores grid current generated and transmitted from various power plants, such as thermal power plants, or renewable energy sources such as wind power, in battery modules. Simultaneously, the electricity stored in the battery modules can be transmitted to loads such as homes, offices, and factories as needed.

[0154] (2) In the battery management system described in (1) above, the upper unit includes an open state determination unit that determines whether or not a battery cell is in an open state, a current value integration unit that calculates an integrated current value based on the current value acquired by the current sensor, and an aggregation calculation unit that aggregates the SOC values ​​transmitted from multiple lower units and calculates the SOC value of the entire battery pack composed of multiple battery modules.

[0155] By limiting the functions previously assigned to higher-level units to those required for overseeing lower-level units, the higher-level units can now understand the overall state of the battery pack using the SOC values ​​and state estimates calculated by the lower-level units.

[0156] Furthermore, by transmitting the current value necessary for calculating the SOC value in the lower-level unit as a current integration value, delays in wireless communication can be avoided. Therefore, it becomes possible to calculate the SOC value with greater accuracy.

[0157] (3) In the battery management system described in (1) or (2) above, the lower unit includes a cell state estimation unit that calculates a state estimate value indicating the state of the battery cells of the corresponding battery module, a calculation unit that calculates an initial SOC value, and an update unit that updates the SOC value starting from the initial SOC value based on the integrated current value received from the upper unit.

[0158] Of the functions originally possessed by the higher-level unit, the lower-level unit now includes functions to estimate the state of the battery module and to calculate and update the SOC value. This allows the lower-level unit to acquire more information necessary for controlling the battery module it is installed in.

[0159] (4) In the battery management system described in (3) above, the calculation unit starts calculating the initial SOC value after receiving a determination from the higher-level unit that the secondary battery is in an open state. By starting the calculation of the initial SOC value based on the determination that the battery is in an open state, the value of the open-circuit voltage can be used, and the initial SOC value can be calculated with greater accuracy.

[0160] (5) In the battery management system described in any of (2) to (4) above, when the calculation of the initial SOC value in the calculation unit of the lower unit is completed, the lower unit sends a signal to the upper unit indicating completion, and the current value integration unit in the upper unit resets the current value integration process upon receiving the signal from the lower unit indicating completion and starts the process of calculating the current integrated value again.

[0161] The current value integration unit of the higher-level unit does not have information on whether the lower-level unit has calculated the initial SOC value. Therefore, when the current value integration unit receives a completion signal, it can reset the current value integration process and start the integration process again.

[0162] (6) In the battery management system described in any of (3) to (5) above, the cell state estimation unit determines whether the voltage value of the battery cell used by the calculation unit when calculating the initial SOC value can be used in the calculation of the initial SOC value, and only if the voltage value can be used in the calculation of the initial SOC value the calculation unit performs the calculation of the initial SOC value.

[0163] By determining before the calculation whether the open-circuit voltage value necessary for calculating the initial SOC value in the lower-level unit is available, the initial SOC value can be calculated with greater accuracy.

[0164] (7) In any of the battery management systems described in (2) to (6) above, the higher-level unit further includes a battery relay control unit that performs connection control of a battery relay to create an open or closed state of the secondary battery, and the battery relay control unit performs control to disconnect the battery relay from the time the open state determination unit sends a determination signal to the lower-level unit indicating that the secondary battery is in an open state until it receives a signal from the lower-level unit indicating that the calculation of the SOC initial value has been completed.

[0165] By performing control in the lower-level unit to disconnect the battery relay until the calculation of the SOC initial value is complete, the battery cell circuit is kept open. Therefore, the lower-level unit can perform the calculation of the SOC initial value with greater reliability.

[0166] (8) In the battery management system described in any of (2) to (7) above, the open state determination unit determines whether or not the secondary battery is in an open state based on the current value acquired by the current sensor.

[0167] The current values ​​transmitted from the current measuring device are received only by the higher-level unit. Therefore, the open-circuit state of the battery cell's circuit can be reliably determined without changing the configuration of the existing battery management system.

[0168] (9) In the battery management system described in any of (2) to (8) above, the open state determination unit determines whether the secondary battery is in an open state or not based on the connection state of the battery relay that creates an open state or a closed state of the secondary battery.

[0169] By determining the open-circuit state of a battery cell circuit based on the connection status of the battery relay, the determination can be made in a shorter time and with higher reliability.

[0170] (10) In the battery management system described in any of (2) to (9) above, the discharge state determination unit determines the open state of the secondary battery when the battery management system is started.

[0171] Without changing the configuration of the existing battery management system, it is possible to determine the open circuit state of the battery cells with a high probability and greater reliability.

[0172] 1...BMU, 11...BMU control device, 111...Information acquisition unit, 112...Open state determination unit, 113...Current value integration unit, 114...Aggregation calculation unit, 115...Information transmission unit, 116...Battery relay control unit, 12...Communication circuit, 2...VCM, 3...Charger, 4...Current measuring device, 41...Current detection circuit, 42...Communication circuit, A...Current sensor, C...Battery cell, M...Battery module, M1...First battery module, M11...Communication circuit, M12...CMU control device, M121...Measurement value acquisition unit, M122...Cell state estimation unit, M123...Calculation unit, M124...Update unit, M125...Information transmission unit, M13...Voltage detection circuit, M14...Balance circuit, M15...Temperature detection circuit, P...Pack, T...Temperature sensor

Claims

1. A battery management system comprising: a lower unit associated with each battery module having multiple battery cells and controlling the battery module; a higher unit that manages the multiple lower units; and a current sensor that detects the current value passing through the battery module, wherein the higher unit calculates an integrated current value from the current value detected by the current sensor and transmits it to the lower unit; and the lower unit calculates the initial state of charge (SOC) value of the battery cell based on the voltage value of the battery cell and updates the initial SOC value based on the integrated current value received from the higher unit.

2. The battery management system according to claim 1, characterized in that the upper unit comprises: an open state determination unit that determines whether or not the battery cell is in an open state; a current value integration unit that calculates an integrated current value based on the current value acquired by the current sensor; and an aggregation calculation unit that aggregates the SOC values ​​transmitted from a plurality of lower units and calculates the SOC value of the entire battery pack composed of a plurality of battery modules.

3. The battery management system according to claim 1, characterized in that the lower unit comprises: a cell state estimation unit that calculates a state estimate value indicating the state of the battery cells in the corresponding battery module; a calculation unit that calculates the initial SOC value; and an update unit that updates the SOC value starting from the initial SOC value based on the current integration value received from the upper unit.

4. The battery management system according to claim 3, characterized in that the calculation unit starts calculating the initial SOC value upon receiving a determination made by the higher-level unit that the secondary battery is in an open state.

5. The battery management system according to claim 2 or 3, characterized in that the lower unit transmits a signal to the upper unit indicating completion when the calculation of the SOC initial value in the calculation unit is completed, and the current value integration unit in the upper unit resets the current value integration process upon receiving the completion signal from the lower unit and starts the process of calculating the current integrated value again.

6. The battery management system according to claim 3, wherein the cell state estimation unit determines whether the voltage value of the battery cell used by the calculation unit when calculating the initial SOC value can be used in the calculation of the initial SOC value, and the calculation unit performs the calculation of the initial SOC value only if the voltage value can be used in the calculation of the initial SOC value.

7. The battery management system according to claim 2, wherein the upper unit further comprises a battery relay control unit that performs connection control of a battery relay to create an open or closed state of the secondary battery, and the battery relay control unit performs control to disconnect the battery relay from the time the open state determination unit transmits a determination signal to the lower unit indicating that the secondary battery is in an open state until it receives a signal from the lower unit indicating that the calculation of the SOC initial value has been completed.

8. The battery management system according to claim 2, characterized in that the open state determination unit determines whether or not the secondary battery is in an open state based on the current value acquired by the current sensor.

9. The battery management system according to claim 2, characterized in that the open state determination unit determines whether the secondary battery is in an open state or closed state based on the connection state of the battery relay that creates the open state or closed state of the secondary battery.

10. The battery management system according to claim 2, characterized in that the open state determination unit performs a determination of the open state of the secondary battery when the battery management system is started.

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