Battery management system

Abstract

According to the present invention, when functions are divided between a lower-level unit and an upper-level unit and the lower-level unit is made to handle the function of estimating the SOH of a cell, the effects of errors in communication between the lower-level unit and the upper-level unit are avoided and costs arising from measures for avoiding the effects of the errors are suppressed. The present invention comprises: lower-level units (CMU) which are respectively associated with battery modules (M) having a plurality of battery cells (C) and control the battery modules (M); an upper-level unit (BMU) that oversees the plurality of lower-level units (CMU); and current sensors (A) for detecting the value of currents passing through the battery modules (M). The upper-level unit (BMU) calculates a cumulative current value from the current values detected by the current sensors (A) and transmits the cumulative current value to the lower-level units (CMU). The lower-level units (CMU) calculate the SOH value of each of the battery cells (C) on the basis of the cumulative 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】 In Patent Document 1, as one method for estimating the degradation state of the capacity of a secondary battery mounted on a vehicle, a first degradation state using a storage degradation state and a cycle degradation state, and a second degradation state calculated based on the amount of change in the state of charge, etc. are used. 【0003】 On the other hand, Patent Document 2 shows a configuration of a new battery monitoring system including a slave unit that receives voltage data and current data via a wired connection and a master unit that receives data from the slave unit by wireless transmission. 【0004】 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, and synchronization can be achieved. Therefore, it is said that the calculation accuracy of the state of charge of the cell can be improved. 【0005】 Japanese Patent No. 6973488 Japanese Unexamined Patent Application Publication No. 2023-001121 【0006】 However, in the configuration described in Patent Document 2, since data is wirelessly transmitted between the slave unit and the master unit, there may inevitably be a delay in the data transfer between the slave unit and the master unit. Also, in the battery monitoring system of Patent Document 2, 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 necessary 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. 【0007】 Further, in the battery monitoring system of Patent Document 2, 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 range and a slave unit (monitoring IC) in a low voltage range. 【0008】Therefore, in this battery monitoring system, an isolator (isolation circuit) is provided between the current sensor and the slave unit (monitoring IC). However, an isolation circuit must naturally be provided for each slave unit, and especially in configurations where multiple slave units are provided, the cost increase due to the provision of isolation circuits is unavoidable. 【0009】 Therefore, when implementing the method disclosed in Patent Document 1 as a method for estimating the state of deterioration using the configuration disclosed in Patent Document 2, it is necessary to overcome the aforementioned problems. 【0010】 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 avoids the effects of errors caused by communication between a lower unit and an upper unit when functions are divided between the lower unit and the upper unit and the lower unit is responsible for estimating the state of health (SOH) of the cell, and that can suppress the costs incurred in taking measures to avoid the effects of such errors. 【0011】 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, and the lower unit calculates the State of Health (SOH) value for each battery cell based on the integrated current value received from the higher unit. 【0012】 Because the present invention employs such a battery management system, when functions are separated between a lower unit and an upper unit, and the lower unit is responsible for estimating the state of health (SOH) of the cells, 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 the effects of such errors. 【0013】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 SOH calculation process according to an embodiment of the present invention. This is a flowchart showing the flow of the SOH calculation process according to an embodiment of the present invention when a degradation characteristic formula is used. This is a flowchart showing the flow of the calculation process for the initial SOC value, which is a prerequisite for calculating the measured SOH value, according to an embodiment of the present invention. This is a flowchart showing the flow of the calculation process for the initial SOC value, which is a prerequisite for calculating the measured SOH value, according to an embodiment of the present invention. This is a flowchart showing the flow of the calculation process for the measured SOH value according to an embodiment of the present invention. This is a flowchart showing the flow of the calculation of the SOH value in the lower-level unit and the calculation of the SOH value of the entire battery pack in the higher-level unit using the SOH value of each battery cell transmitted from the lower-level unit. 【0014】 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. 【0015】 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. 【0016】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. 【0017】 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. 【0018】 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. 【0019】 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. 【0020】 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. 【0021】 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. 【0022】The battery management system (BMS) comprises a Battery Management Unit (BMU) 1, multiple battery modules M, and a current measuring device 4. 【0023】 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. 【0024】 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. 【0025】 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. 【0026】 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. 【0027】 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. 【0028】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. 【0029】 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." 【0030】 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. 【0031】 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. 【0032】 Furthermore, a current measuring device 4 is connected in series with the three battery modules M within the battery management system (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. 【0033】 As will be described later, 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. 【0034】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. 【0035】 On the other hand, for example, information is transmitted and received between the VCM3 or current measuring device 4 and the BMU1 via wired communication. 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. 【0036】 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 BMU1 and VCM3, or BMU1 and current measuring device 4, are shown with solid lines. 【0037】 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, a current value integration unit 112, a battery relay control unit 113, an open state determination unit 114, an aggregation calculation unit 115, and an information transmission unit 116. 【0038】 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. 【0039】 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 current value integration unit 112, the battery relay control unit 113, the open state determination unit 114, or the aggregation calculation unit 115 as appropriate. 【0040】The current value integration unit 112 calculates a current integration value [As] based on the values of currents that have passed through a 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. 【0041】 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 112. Further, the current value integration unit 112 transmits the resulting current integration value to the CMU at a preset period such as 100 ms. 【0042】 The battery relay control unit 113 controls the connection state of the battery relay. That is, upon receiving a signal of ignition ON from the user, it connects the battery relay, and when the ignition is turned OFF, it disconnects (releases) the connection of the battery relay. 【0043】 That is, by the control of the battery relay control unit 113, when the vehicle system is started, the circuit of the secondary battery (battery cell C), which has been an open circuit until now, becomes a closed circuit, and conversely, when the vehicle system is stopped, the circuit of the battery cell C, which has been a closed circuit until now, becomes an open circuit. 【0044】 The open state determination unit 114 determines whether the battery cell C in each battery module M is in an open state. The reason why the open state determination unit 114 determines whether the battery cell C is in an open state is that, as will be described later, the CMU may use the open voltage when calculating the capacity degradation rate (SOH: State of Health) of the battery cell C. 【0045】 However, since the circuit of the secondary battery is a closed circuit when the vehicle is in use and the battery cell C is also charging and discharging, the open voltage cannot be measured. That is, the secondary battery mounted on the vehicle is in an open state when the ignition is OFF and until the ignition is turned ON. 【0046】 On the other hand, since it is necessary for the vehicle control system S to be activated in order to measure the open-circuit voltage, as a result, the timing for measuring the open-circuit voltage is limited to when the user of the vehicle turns on the ignition. Therefore, the open-state determination unit 114 determines whether the secondary battery is in an open state when the vehicle control system S (battery management system BMS) is activated. 【0047】 That is, the open-state determination unit 114 determines whether or not this ignition has been turned on. Specifically, for example, a method of looking at the current value transmitted from the current measurement device 4 can be considered. In this case, if the current value is zero, it can be determined that the battery cell C is in an open state. 【0048】 Alternatively, a method of determining whether the secondary battery is in an open state based on the connection state of the battery relay can also be considered. In this case, for example, it is confirmed via the battery relay control unit 113 whether an ON or OFF command has been issued for the battery relay. Also, for example, there is a battery relay having a function of checking the presence or absence of connection using current or the like. When such a battery relay is used, the presence or absence of connection can be determined by checking the current or the like. 【0049】 The aggregation calculation unit 115 aggregates the SOH values calculated in each CMU and the state estimation values described later. That is, the aggregation calculation unit 115 calculates the total state estimation value of the entire battery pack P based on the information transmitted from the CMUs provided in each battery module M, rather than the state of each individual battery module M. 【0050】 The information transmission unit 116 transmits, for example, a signal indicating that the secondary battery is in an open state, which is determined by the open-state determination unit 114, to each battery module M (CMU). Alternatively, for the VCM 3 connected to the BMU 1, for example, the total state estimation value obtained by aggregating and calculating the state estimation values received from each CMU may be transmitted. 【0051】Next, the configuration of the battery module M will be explained using Figure 1. As shown in Figure 1, the battery management system BMS in the embodiment of the present invention has three battery modules M connected in series. In Figure 1, the first battery module M1, the second battery module M2, and the third battery module M3 are shown from left to right. 【0052】 The configurations of the first battery module M1 through the third battery module M3 are all the same in this context. Therefore, the configuration of battery module M will be explained below using the first battery module M1 as an example. However, when the explanation applies to any of the first battery module M1 through the third battery module M3, it will be referred to as "battery module M" as appropriate, as before. 【0053】 The first battery module M1 comprises multiple battery cells C and a CMU1. The multiple battery cells C are connected in series as shown in Figure 1. In the battery module M shown in Figure 1, four battery cells C are shown stacked on each side, but this is only for illustrative purposes. 【0054】 In other words, the number of these battery cells C stacked, and the number of stacked battery cells C that make up one battery module M, can be arbitrarily set according to the battery capacity required for the battery module M. Hereafter, whether referring to individual battery cells or multiple battery cells contained in the battery module M, the term "battery cell C" will be used as appropriate. 【0055】 Furthermore, a temperature sensor T for detecting the temperature of the battery module M is provided near the battery cell C. As shown in Figure 1, in the battery management system BMS according to 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 multiple sensors may be provided. 【0056】As shown in Figure 1, in the battery management system BMS of the present invention, a temperature sensor T is provided in each battery module M. However, it is not necessary for a battery module M without the temperature sensor T to be connected. 【0057】 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 SOH value and state estimate, 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. 【0058】 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. 【0059】 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. 【0060】 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. 【0061】 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. 【0062】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, a storage unit M124, and an information transmission unit M125. 【0063】 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 storage degradation information, cycle degradation information, or current integration value information 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. 【0064】 The cell state estimation unit M122 estimates the state of each battery cell C and calculates a state estimation value. The values ​​used to estimate the state of the battery cell C here include, for example, the State of Charge (SOC), the upper limit charging power, or at least one of the above-mentioned State of Health (SOH), as well as the upper limit discharging power. 【0065】 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. 【0066】 For example, when the measured SOH value is calculated, the calculation unit M123 calculates the SOC initial value. When the SOC initial value is calculated in this way, it may be necessary to determine whether the voltage value of the battery cell C can be used in the calculation of the SOC initial value. The cell state estimation unit M122 may perform this determination. These points will be described later. 【0067】 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. 【0068】The calculation unit M123 calculates the State of Health (SOH) value for each of the multiple battery cells C in the first battery module M1. Various methods can be considered for calculating the SOH value, but here we will describe a method that combines the calculation of the SOH value using the degradation characteristic formula with the calculation of the measured SOH value. 【0069】 First, let's explain the case where a degradation characteristic equation is used. A degradation characteristic equation is, for example, a map that shows the degradation characteristics of a battery cell C obtained experimentally, based on the storage degradation characteristics and cycle degradation characteristics of a secondary battery. Since these degradation characteristics differ for each secondary battery (battery cell C), a degradation characteristic equation is determined for each battery cell C. 【0070】 In other words, when the calculation unit M123 calculates the SOH value for each battery cell C using the degradation characteristic formula, it accesses the storage unit M124, for example, to obtain the degradation characteristic formula for the battery cell C for which it is trying to calculate the SOH value. 【0071】 Specifically, the BMU1 first obtains an estimated state value regarding the elapsed usage time of the secondary battery (battery cell C) and calculates the cumulative usage time. The "cumulative usage time" is a value determined by either the cumulative time the vehicle is operating, the cumulative time it is stopped, or both. 【0072】 During the elapsed usage time, the operation (closed state) or stop (open state) of battery cell C is determined by the ON / OFF state of the battery relay. Since the ON / OFF state of the battery relay (the connection state of the battery relay) is controlled by the battery relay control unit 113, the battery relay control unit 113 can determine the time that battery cell C is in the open state and the time that it is in the closed state. 【0073】 In other words, the elapsed usage time is determined in the BMU1. Therefore, for example, the open state determination unit 114 can accumulate the elapsed usage time by obtaining the above time information from the battery relay control unit 113. Accordingly, the calculated accumulated value of the elapsed usage time is transmitted from the BMU1 to each CMU. 【0074】Alternatively, the software used by the battery relay control unit 113 performs calculations at a cycle of, for example, 100ms. Therefore, each time this cycle occurs after the battery relay is turned ON, the count is incremented by one. The time can then be calculated by totaling how many times the count has incremented between the time the battery relay is turned OFF and the time itself. 【0075】 Furthermore, the BMU1 may be equipped with a timer, for example, or the battery relay control unit 113 may be equipped with a timer function to keep track of the date and time. 【0076】 In this way, depending on the open state determination unit 114, or the method of accumulating the elapsed usage time, the battery relay control unit 113, for example, acquires storage degradation information for each battery cell C. 【0077】 Furthermore, the BMU1 may also acquire temperature information from the temperature sensor T provided in the battery module M and transmit it to each CMU. This is because temperature has a significant impact on the degradation state of the battery cell C, and by using temperature information in addition to storage degradation information and cycle degradation information, the SOH value can be calculated with greater accuracy. 【0078】 Here, "storage degradation" refers to the degradation that occurs even when a secondary battery is not in use. "Cycle degradation," on the other hand, refers to the degradation caused by repeated charging and discharging of a secondary battery, i.e., by use. 【0079】 Next, the BMU1 acquires cycle degradation information for the secondary battery (battery cell C). Specifically, the current value integration unit 112 calculates the integrated value of the charge and discharge current for each battery cell C. That is, the current value integration unit 112 acquires the integrated value of the charge and discharge current by performing time integration based on the current value acquired from the current measuring device 4 at a predetermined period. By calculating the integrated value of the charge and discharge current in the current value integration unit 112, cycle degradation information for the battery cell C is acquired. 【0080】Furthermore, the integrated value of the charge and discharge current is calculated solely for use as a parameter in the degradation characteristic formula, and ultimately for calculating the State of Health (SOH) value of each battery cell C. Therefore, when the CMU calculates the initial SOC value as described later, and the current value integration unit 112 receives a signal from the CMU indicating that the calculation of the initial SOC value has been completed, the current value integration unit 112 does not reset the process of integrating the charge and discharge current values. 【0081】 The calculation unit M123 of the CMU1 applies the storage degradation information and cycle degradation information obtained from the BMU1 to the degradation characteristic formula corresponding to each battery cell C, and calculates the SOH value for each battery cell C. 【0082】 The storage degradation information and cycle degradation information acquired in BMU1 are transmitted to CMU1 via the information transmission unit 116. This storage degradation information and cycle degradation information are used as parameters in the degradation characteristic formula, as described above. 【0083】 In other words, for the CMU to calculate the SOH value, it needs to acquire the information necessary for calculating the SOH value. However, if this information is acquired via BMU1 as before, the calculation may end up being performed using values ​​that include errors due to communication delays. 【0084】 Therefore, in the battery management system BMS according to the embodiment of the present invention, the CMU collects the information necessary for calculating the SOH value in BMU1 and then transmits it to each CMU. This is the same whether the CMU calculates the SOH value using the degradation characteristic formula as described above, or whether the CMU, as described later, calculates the measured SOH value. 【0085】 Next, we will explain how to calculate the measured SOH value. The measured SOH value is obtained by calculating the SOC for each battery cell C from the voltage of each battery cell C, calculating the change in SOC and the integrated current value to determine the actual full charge capacity, and then comparing it with the full charge capacity when new. The specific procedure for calculating the measured SOH value in CMU1 will be explained in separate steps. 【0086】First, the process involves determining the change in SOC. The calculation unit M123 calculates the SOC value for each of the multiple battery cells C in the first battery module M1. Specifically, the calculation unit M123 first 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. 【0087】 Then, the calculation unit M123 calculates the SOC value using table data, which is pre-stored in the memory unit M124, that shows the relationship between the open-circuit voltage and the SOC value of the battery cell C. The table data showing the relationship between the open-circuit voltage and the SOC value is set, for example, based on results obtained in advance from characteristic acquisition experiments using the battery cell C that will actually be installed. 【0088】 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. 【0089】 Thus, the calculation unit M123 calculates the SOC value using the open-circuit voltage. 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 the open-circuit voltage cannot be obtained. Therefore, in the following, the SOC value calculated by the calculation unit M123 using the open-circuit voltage will be referred to as the "initial SOC value". 【0090】 Furthermore, when the calculation unit M123 calculates the initial SOC value, it may also send a signal to the current value integration unit 112 of the BMU1 indicating that the calculation of the initial SOC value has been completed (hereinafter referred to as the "completion signal" as appropriate). 【0091】The reason the calculation unit M123 transmits a completion signal to the current value integration unit 112 via the information transmission unit M125 is that the current value integration unit 112, upon receiving the completion signal, resets the process of integrating current values ​​that it has been performing up to that point. 【0092】 In other words, for example, after calculating the initial SOC value in CMU1, it is conceivable that the SOC value during the vehicle's operation may be updated starting from that initial SOC value. This is because the process of calculating the SOC value using the open-circuit voltage cannot be performed while the vehicle is in operation. In this case, the current integrated value obtained in the current value integration unit 112 is used. 【0093】 Therefore, the calculation unit M123 may send a completion signal to the current value integration unit 112 once the calculation of the SOC initial value is complete. Upon receiving the completion signal, the current value integration unit 112 resets the current value integration process it had been performing and starts the integration process again. This is different from the case where the current value integration unit 112 calculates the integrated value of the charge and discharge currents. 【0094】 The process between BMU1 and CUM when CMU1 calculates the measured SOH value, as described above, is explained below using diagrams. Figure 4 is an explanatory diagram illustrating the SOH calculation process according to an embodiment of the present invention. 【0095】 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 114. The indication "Open" shows 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. 【0096】 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 where it is being used, so battery cell C becomes a closed circuit. Therefore, the open state determination unit 114 determines that battery cell C is in an open state the moment the ignition is turned ON. 【0097】 In the explanatory diagram, the timing at which the open state determination unit 114 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. 【0098】 Here, for convenience, the first timing in the explanatory diagram of Figure 4 will be represented as "nth time," and the second timing will be represented as "n+1th time." Furthermore, for convenience in the following explanation, the time between the nth time and the (n+1th)th time will be represented as "1 Trip." 【0099】 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. 【0100】 The lower part of Figure 4 shows the change in the integrated current value. While the vehicle is in use, the value of the current flowing through battery cell C is accumulated, and this value gradually increases. The lower part shows this change in the integrated current value. 【0101】 Furthermore, when the calculation unit M123 sends a completion signal to the current value integration unit 112 of the BMU1 indicating that it has completed the calculation of the SOC initial value, the current value integration unit 112 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 nth open state, decreases along the vertical line at the timing of the (n+1)th open state, and then turns to increase again. 【0102】 The reason the current integration value decreases along the vertical line at the point where the (n+1)th open state occurs is that the current value integration unit 112 receives a completion signal and resets the integration process. At this point, the integration process is reset, and then the current value integration unit 112 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]. 【0103】 The reason the integrated current gradually increases is that when the ignition is turned ON, the vehicle is put into use, and since this basically involves discharge to battery cell C, the integrated current also moves in a positive direction. 【0104】 Furthermore, as described above, the explanatory diagram in Figure 4 shows two timings for the open state determination unit 114 to determine whether or not the battery cell C is in an open state. At the timing of the (n+1)th determination by the open state determination unit 114 that the battery cell C is in an open state, the initial SOC value is calculated by the calculation unit M123, as explained earlier. 【0105】 In this way, the SOC initial value is calculated by the calculation unit M123 at the moment the battery cell C is opened. This value is then stored in the storage unit M124 each time. The calculation unit M123 also calculates the change in the SOC initial value from the most recently calculated SOC initial value (hereinafter referred to as "change in SOC" as appropriate). 【0106】 In other words, the "change in SOC" is the difference between the initial SOC value calculated at the nth timing and the initial SOC value calculated at the (n+1)th timing. In the explanatory diagram in Figure 4, this change (difference) is represented as "Delta SOC". 【0107】 Furthermore, as described above, the current integrated value calculated by the current value integration unit 112 of the BMU1 is reset at the same time that the SOC initial value is calculated in the calculation unit M123. Therefore, the difference between the previously accumulated current integrated value at the time of the reset and the reset value corresponds to the current integrated value in one trip. In the explanatory diagram of Figure 4, this current integrated value is represented as "Ah". 【0108】The calculation unit M123 then uses the integrated current value received from the BMU1 to calculate the current full charge capacity of the corresponding battery cell C by dividing the integrated current value by the change in SOC. Furthermore, the calculation unit M123 retrieves the information on the new full charge capacity of the battery cell C, which is stored in the storage unit M124, and divides the current full charge capacity by the new full charge capacity. By performing this calculation, the calculation unit M123 calculates the measured SOH value of the battery cell C. 【0109】 In the CMU1, the SOH value obtained using the degradation characteristic formula and the measured SOH value obtained using the change in SOC can be acquired using the method described above. Then, the calculation unit M123 calculates the final SOH value of the corresponding battery cell C. Specifically, for example, the SOH value is obtained by correcting the SOH value obtained using the degradation characteristic formula with the measured SOH value. 【0110】 In other words, the degradation characteristic formula is merely a value obtained through experiments, and is a so-called representative value. Therefore, from this perspective, the measured SOH value is considered to reflect the usage state of each battery cell C more accurately than the SOH calculated using the degradation characteristic formula. For this reason, the battery management system (BMS) in the embodiment of the present invention uses both the SOH value obtained using the degradation characteristic formula and the measured SOH value. 【0111】 When calculating the final SOH value using both values ​​in this way, an averaging process may be performed, for example, by taking a weighted average of the measured SOH values. 【0112】 Furthermore, in the embodiment of the present invention, the calculation of SOH was explained using the two methods described above as examples. However, the method is not necessarily limited to these methods; for example, it is also possible to use only the degradation characteristic formula, or to determine only the measured SOH value, or to use only one of these methods. 【0113】For example, if a vehicle is not used daily and is left unused for a long period, it is impossible to obtain the measured SOH value during that time. Therefore, in such cases, it is necessary to calculate the SOH value using the degradation characteristic formula. Accordingly, depending on the situation, it is also possible to calculate the SOH for each battery cell C using only one of the calculation methods. 【0114】 Furthermore, this explanation assumes a method of calculating the final SOH value for each battery cell after calculating the SOH value obtained by calculation using the degradation characteristic formula and the measured SOH value. However, it is also possible to configure the calculation unit M123 to calculate the SOH value from the beginning. 【0115】 The memory unit M124 stores various information used by the calculation unit M123 when calculating the SOH value of the battery cell C. For example, the memory unit M124 stores the degradation characteristic formula for each battery cell C used when calculating the SOH value of the battery cell C using the degradation characteristic formula described above. In addition, as described above, it also stores information regarding the initial SOC value and the full charge capacity when new, which are calculated by the calculation unit M123. 【0116】 The information transmission unit M125 transmits information such as state estimates and SOH 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. 【0117】 As explained above, the functions assigned to BMU1 (the upper unit) and each CMU (lower unit) are different. Specifically, the SOH value of the battery cells C in the battery module M is calculated by the CMU located in each battery module M. 【0118】 On the other hand, the storage degradation information, cycle degradation information, and current integration value used as parameters in the degradation characteristic formula necessary for calculating the SOH value in the CMU are calculated in the BMU1 and transmitted to the CMU. The BMU1 then uses these SOH values ​​to calculate the overall SOH value of the battery pack P. 【0119】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. 【0120】 First, we will explain the case where the CMU1 calculates the SOH value for each secondary battery (battery cell C) using a degradation characteristic formula. In the BMU1, the battery relay control unit 113 and the open state determination unit 114 calculate the cumulative value related to the elapsed usage time of the battery cell C. Through this process, storage degradation information of the battery cell C is obtained. 【0121】 Furthermore, the current value integration unit 112 of the BMU1 calculates the integrated value of the charge and discharge current in the battery cell C. This allows for the acquisition of cycle degradation information for the battery cell C. This storage degradation information and cycle degradation information are then transmitted wirelessly from the BMU1 to each CMU. 【0122】 Each CMU that receives the storage degradation information and cycle degradation information calculates the SOH value of each battery cell C in the battery module M in which it is installed. Specifically, as described above, the calculation unit M123 calculates the SOH value using the degradation characteristic formula stored in the storage unit M124. 【0123】 Next, we will explain the case in which the CMU1 calculates the measured SOH value using the SOC initial value. First, the open state determination unit 114 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 determination in the open state determination unit 114 continues. 【0124】 On the other hand, if the open state determination unit 114 determines that the battery cell C is in an open state, the open state determination unit 114 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 116. 【0125】 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. 【0126】 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 and is stored in the storage unit M124. 【0127】 It should be noted that the SOC initial value calculated here is assumed to be the SOC initial value calculated at the (n+1) timing in the explanatory diagram in Figure 4. 【0128】 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 112, which then resets the current value integration process it has been performing. It then restarts the current value integration process. 【0129】 The current value integration unit 112 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. 【0130】 As described above, the initial SOC value is calculated at the (n+1)th timing. The calculation unit M123 then retrieves the initial SOC value calculated at the (n)th timing from the storage unit M124. The calculation unit M123 subtracts the initial SOC value at the (n+1)th timing from the initial SOC value at the (n)th timing to calculate the change between the two. Then, by dividing the integrated current value transmitted from the BMU1 by the change in the SOC, the current full charge capacity of the battery cell C is calculated. 【0131】 The calculation unit M123 further accesses the storage unit M124 to obtain information on the new full charge capacity of the battery cell C. Then, it divides the current full charge capacity of the battery cell C by the new full charge capacity. By performing this process, the measured SOH value of the corresponding battery cell C can be obtained. 【0132】Through the calculations performed so far, the SOC value using the degradation characteristic formula for battery cell C and the measured SOH value have been obtained. The calculation unit M123 then performs further processing, such as correcting the former SOH value with the measured SOH value, to calculate the final SOH value for battery cell C. The calculated SOH value is then transmitted from CMU1 to BMU1 via the information transmission unit M125. 【0133】 The BMU1 checks whether the received SOH value was transmitted from all CMUs under its control. If SOH values ​​are received from all CMUs, the aggregation calculation unit 115 uses these SOH values ​​to calculate the total SOH value of the battery pack P. This makes it possible to determine the total SOH of the battery cells C provided by the vehicle control system S. 【0134】 Various methods can be used to calculate the SOH value of the entire battery pack P, such as taking the average of the SOH values ​​transmitted from each CMU. Furthermore, the SOH value of the entire battery pack P may be displayed, for example, on the vehicle's meter as a "battery capacity degradation rate." 【0135】 The roles of BMU1 and CMU in the CMU's calculation of the SOH value are as described above. For the CMU to calculate the SOH value accurately, the accuracy of the initial SOC value, especially for the measured SOH value, is crucial. Specifically, when the CMU calculates the initial SOC value, it uses the open-circuit voltage value. However, whether this 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. 【0136】 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. 【0137】Therefore, if it is determined that the voltage value of battery cell C is unstable, it is actually better not to perform the calculation of the initial SOC value in order to ensure the accuracy of the final SOH value. 【0138】 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. 【0139】 Furthermore, if it is determined that the voltage value of battery cell C is unstable, the calculation of the initial state of charge (SOC) value is not performed. However, for example, it is also possible to perform the calculation of the initial SOC value but not the calculation of the change in SOC. 【0140】 Furthermore, 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. 【0141】 Alternatively, to eliminate the effects of polarization, etc., it is possible to employ a method different from the one described above. As mentioned above, when calculating the measured SOH value, it is conceivable to perform an averaging process. However, even when performing this averaging process, it is conceivable to consider the effects of polarization. In other words, it is necessary to ensure the reliability of the initial SOC value required when calculating the measured SOH value. 【0142】 As a specific method, for example, if there is no effect of polarization (when the stopping time is very long), the weighting coefficient is set to a large value (e.g., 1). On the other hand, if the effect of polarization is strong, the weighting coefficient is set to a small value (e.g., a value close to 0). By performing processing that takes into account the reliability of the initial SOC value in this way, the measured SOH value can be calculated with greater accuracy. 【0143】Alternatively, as a method for calculating the SOH value using confidence, instead of considering the confidence level relative to the initial SOC value when calculating the measured SOH value, one can adopt a method such as multiplying the value obtained by subtracting the SOH value obtained using the degradation characteristic formula from the measured SOH value by a weighting coefficient. In this case, the final SOH value is calculated by adding the SOH value obtained using the degradation characteristic formula to the calculated value. 【0144】 Furthermore, this method considers reliability to improve the accuracy of the initial SOC value, which is the premise for calculating the measured SOH value. However, this concept of reliability can also be applied when calculating the SOH value using the degradation characteristic formula. That is, for example, the SOH value can be calculated by weighting the calculation by improving the accuracy of the temperature information used in the degradation characteristic formula. 【0145】 As explained above, the calculation of the SOH value in the CMU is performed when the ignition is turned ON, that is, when the vehicle control system S is started, whether using the degradation characteristic formula or calculating the measured SOH value. In other words, when both methods are used in combination, the calculation processes for each are executed in parallel. 【0146】 On the other hand, since the SOH value is merely a value indicating the capacity degradation of the battery cell C, its change is gradual, unlike in the case of SOC. Therefore, calculation processing does not necessarily have to be performed every time the device is started, and it is permissible for calculation processing to be omitted for some reason. 【0147】 Furthermore, in the calculation of the SOH value using the degradation characteristic formula, information such as the cumulative value of the elapsed usage time input to the degradation characteristic formula is calculated in BMU1 and transmitted to each CMU. This method is adopted because when transmitting information from BMU1 to the CMU, errors may occur due to delays in wireless communication, and the accuracy of the SOH value calculated based on information containing errors may decrease. 【0148】On the other hand, when calculating the SOH value using the degradation characteristic formula, as mentioned above, the SOH value is used to estimate the degradation state of the battery cell C, so it is unlikely that the SOH value will differ significantly from one battery cell C to another, compared to the SOC value. 【0149】 Therefore, if there is no variation in the degradation state of battery cell C, the information such as the cumulative value of the elapsed usage time to be input into the degradation characteristic formula may be obtained by each CMU instead of BMU1, and the SOH value may be calculated based on the obtained information. 【0150】 Furthermore, if, for example, each battery cell C in the battery module M is replaced or otherwise modified to use a battery cell C with a different composition than before, a new degradation characteristic formula will be adopted, particularly for the degradation characteristic formula used when calculating the SOH value. 【0151】 In other words, if a battery cell C constituting the battery management system (BMS) is replaced with a new one, the SOH value is calculated using a degradation characteristic formula tailored to the characteristics of the new battery cell C. By doing so, the SOH value can be calculated with high accuracy, and a highly flexible battery management system (BMS) can be constructed. 【0152】 [Operation] Next, we will explain the process of calculating the SOH value in the CMU described above, following the flow of the process. First, we will explain the flow of the process using the degradation characteristic formula. Figure 5 is a flowchart showing the flow of the SOH calculation process according to an embodiment of the present invention when using the degradation characteristic formula. 【0153】 Furthermore, in order to clarify the respective roles of the upper unit (BMU) and lower unit (CMU) according to the embodiment of the present invention, the flowcharts shown in Figure 5 and subsequent drawings show the processing of the upper unit (BMU) with dashed lines, while the processing of the lower unit (CMU) is shown with solid lines. 【0154】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." 【0155】 First, in the BMU1, the battery relay control unit 113 and the open state determination unit 114 calculate an accumulated value related to the elapsed usage time of the battery cell C (ST1). Through this process, storage degradation information of the battery cell C is obtained (ST2). 【0156】 Furthermore, the current value integration unit 112 of the BMU1 calculates the integrated value of the charge and discharge current in the battery cell C (ST3). This allows for the acquisition of cycle degradation information of the battery cell C (ST4). This storage degradation information and cycle degradation information are then transmitted wirelessly from the BMU1 to each CMU (ST5). 【0157】 Each CMU that receives the storage degradation information and cycle degradation information calculates the SOH value of each battery cell C in the battery module M in which it is installed. Specifically, as described above, the calculation unit M123 calculates the SOH value using the degradation characteristic formula stored in the storage unit M124 (ST6). 【0158】 Next, we will explain the process for calculating the measured SOH value in CMU1. In order to calculate the measured SOH value, it is necessary to calculate the SOC initial value as described above. Therefore, we will first explain the process for calculating the SOC initial value using Figures 6 and 7. Figures 6 and 7 are flowcharts showing the process for calculating the SOC initial value, which is a prerequisite for calculating the measured SOH value, in the SOH calculation process according to an embodiment of the present invention. 【0159】 First, the open state determination unit 114 of the BMU1 determines the open state of the secondary battery (battery cell C) (ST11). If the determination result shows that the battery cell C is not in an open state (NO in ST12), the current value integration unit 112 calculates the current integration value, as will be described later. 【0160】On the other hand, if the open state determination unit 114 determines that the battery cell C is in an open state (YES in ST12), 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 116 (ST13). Each CMU receives the signal from the BMU1 (ST14). 【0161】 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 (ST15). The open-circuit voltage of each battery cell C is then calculated (ST16). 【0162】 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. 【0163】 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 (ST17). 【0164】 If the cell state estimation unit M122 determines that the open-circuit voltage value can be used to calculate the initial SOC value (YES in ST18), 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 for each battery cell C (ST19). The calculated initial SOC value is stored in the storage unit M124. 【0165】 This explanation assumes that the procedure used here is to determine whether the voltage value of battery cell C can be used in the calculation of the initial state of charge (SOC). However, as mentioned above, it is also possible to adopt a method that reflects the stability of the voltage value due to polarization in the form of a reliability level in the averaging process of the initial SOC. 【0166】The SOC initial value calculated by the calculation unit M123 here is the SOC initial value calculated at the (n+1) timing in the explanatory diagram of Figure 4, as described above. Therefore, any SOC initial values ​​calculated before the nth timing are already stored in the storage unit M124. 【0167】 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 (ST20). When the BMU1 receives the completion signal (ST21 in Figure 6), it sends the same completion signal to the current value integration unit 112, and the current value integration unit 112 resets the current value integration process that has been performed up to that point (ST22). Then it starts the current value integration process again (ST23). 【0168】 The current value integration unit 112 performs the current value integration process and determines whether a predetermined period has arrived for transmitting the current integrated value to each CMU (ST24). If it is determined that the predetermined period has not arrived (NO in ST24), the process returns to step ST23, and the current value integration unit 112 continues the current value integration process. 【0169】 On the other hand, if the current value integration unit 112 determines that a predetermined period has arrived (YES in ST24), the current value integration unit 112 transmits the calculated current integration value to the CMU 1 (ST25). The current integration value transmitted from the current value integration unit 112 is received by each CMU (ST26). 【0170】 With the above steps, we have determined the initial SOC value and integrated current value necessary to calculate the measured SOH value for each battery cell C in CMU1. Next, we will explain the process of actually calculating the measured SOH value using this information. Figure 8 is a flowchart showing the calculation process for the measured SOH value according to an embodiment of the present invention. 【0171】 As described above, the initial SOC value is calculated at the (n+1)th timing. The calculation unit M123 then retrieves the initial SOC value calculated at the nth timing from the storage unit M124 (ST31). 【0172】The calculation unit M123 calculates the change in SOC by subtracting the (n+1)th SOC initial value from the nth SOC initial value (ST32). Then, by dividing the current integrated value transmitted from BMU1 by the change in SOC, it calculates the current full charge capacity of the battery cell C (ST33). 【0173】 The calculation unit M123 further accesses the storage unit M124 to obtain information on the new full charge capacity of the battery cell C (ST34). Then, it divides the current full charge capacity of the battery cell C by the new full charge capacity. By performing this process, the measured SOH value of the corresponding battery cell C can be obtained (ST35). 【0174】 Through the calculations performed so far, we have obtained the SOC value using the degradation characteristic formula for battery cell C and the measured SOH value. Next, we will explain the process for calculating the final SOH value for battery cell C and the entire battery pack P. 【0175】 Figure 9 is a flowchart illustrating the process of calculating the SOH value in a lower-level unit and the process by which the upper-level unit calculates the SOH value of the entire battery pack P using the SOH values ​​of each battery cell C transmitted from the lower-level unit. 【0176】 First, the calculation unit M123 of the CMU1 calculates the SOH value for each battery cell C using the SOH value calculated using the degradation characteristic formula and the measured SOH value (ST41). Specifically, for example, a method can be considered in which the SOH value calculated using the degradation characteristic formula is corrected with the measured SOH value. 【0177】 The SOH value is the final SOH value of battery cell C. The calculated SOH value is then transmitted from CMU1 to BMU1 via the information transmission unit M125 (ST42). 【0178】 BMU1 checks whether the received SOH value was transmitted from all CMUs under its control (ST43). If the check reveals that there are CMUs that have not yet transmitted the SOH value (NO in ST43), BMU1 remains in standby mode. 【0179】On the other hand, if it is determined that SOH values ​​have been received from all CMUs (YES in ST43), the aggregation calculation unit 115 uses these SOH values ​​to calculate the total SOH value of the battery pack P (ST44). This makes it possible to determine the total SOH of the battery cells C provided by the vehicle control system S. 【0180】 [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 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 SOH value for each battery cell based on the integrated current value received from the higher unit. 【0181】 By adopting such a battery management system, when functions are divided between a lower-level unit and a higher-level unit, with the lower-level unit responsible for estimating the State of Health (SOH) of the battery cells, the effects of communication errors between the lower-level and higher-level units can be avoided, and the costs incurred in taking measures to avoid such errors can be reduced. 【0182】 In other words, when transferring part of the function that the higher-level unit originally had, such as calculating the State of Health (SOH) value of a battery cell, to the lower-level unit, the higher-level unit obtains information such as the integrated current value necessary for calculating the SOH value and then transmits it 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. 【0183】 Specifically, if the function for calculating the State of Health (SOH) is moved from the higher-level unit to the lower-level unit, the function for calculating the integrated current value necessary for calculating the SOH will also be moved to the lower-level unit. However, even with this separation of functions, 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. 【0184】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 State of Health (SOH) 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. 【0185】 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 SOH calculation is improved accordingly. 【0186】 In particular, the State of Health (SOH) value, which indicates the degradation state of a secondary battery, changes in this value are small (gradual) compared to, for example, the State of Cost (SOC) value. Therefore, even if the information used to calculate the SOH value in the lower-level unit is collected and transmitted from the higher-level unit, the impact on the calculated SOH value is small. 【0187】 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. 【0188】 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. 【0189】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. 【0190】 (2) In the battery management system described in (1) above, the higher-level unit includes a current value integration unit that calculates a current integrated value based on the current value acquired by a current sensor that detects the current value passing through the battery module. 【0191】 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 SOH values ​​and state estimates calculated by the lower-level units. 【0192】 Furthermore, by transmitting information necessary for calculating the SOH value in the lower-level unit, such as the integrated current value, wireless communication delays can be avoided. This makes it possible to calculate the SOH value with greater accuracy. 【0193】 (3) In the battery management system described in (2) above, the upper unit includes an open state determination unit that grasps the elapsed time of use of the battery module and determines whether or not the battery cell is in an open state, and an aggregation calculation unit that aggregates the SOH values ​​transmitted from multiple lower units and calculates the SOH value of the entire battery pack composed of multiple battery modules. 【0194】 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 SOH values ​​and state estimates calculated by the lower-level units. 【0195】(4) In any of the battery management systems described in (1) to (3) above, the lower unit comprises 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 a SOH value based on the current integrated value transmitted from the upper unit, and a storage unit that stores at least a degradation characteristic formula used when calculating the SOH value. 【0196】 Of the functions originally possessed by the higher-level unit, the lower-level unit now includes the function to estimate the state of the battery module and the function to calculate the State of Health (SOH). This allows the lower-level unit to acquire more information necessary for controlling the battery module it is installed in. 【0197】 (5) In the battery management system described in (4) above, the calculation unit calculates the value of SOH using a degradation characteristic formula based on the information transmitted from the higher-level unit, which is the elapsed usage time and the integrated current value of the battery module. 【0198】 By using a degradation characteristic formula to calculate the State of Health (SOH), it is possible to roughly determine the SOH value of a battery cell. This is particularly useful when the vehicle containing the battery cell in question has been inactive for a long period of time, as it is impossible to determine the actual SOH value. 【0199】 (6) In the battery management system described in (4) above, the calculation unit calculates the initial SOC value of the battery cell based on the voltage value of the battery cell, and calculates the measured SOH value based on the change in the initial SOC value between the initial SOC value calculated on the nth time and the initial SOC value calculated on the (n+1)th time and the integrated current value obtained from the higher-level unit. 【0200】 By determining the measured SOH value, it is possible to calculate an SOH value that more accurately reflects the actual condition of the battery cell compared to calculating the SOH value using the degradation characteristic formula. Furthermore, by using the SOH value calculated using the degradation characteristic formula in conjunction as appropriate, the SOH value can be calculated with even greater accuracy. 【0201】(7) In the battery management system described in (6) above, the calculation unit considers the reliability of the initial SOC value when calculating the measured SOH value. By considering the reliability, the measured SOH value can be calculated with greater accuracy, and as a result, the accuracy of the final SOH value can be improved. 【0202】 (8) In the battery management system described in any of (4) to (7) above, the calculation unit calculates the SOH value for each battery cell using the SOH value obtained by calculation using the degradation characteristic formula and the measured SOH value. By calculating the final SOH value using the SOH value calculated by the degradation characteristic formula and the measured SOH value in this way, the SOH value can be calculated with greater accuracy. 【0203】 (9) In any of the battery management systems described in (2) through (4) or (6) through (8) above, the calculation of the initial SOC value is initiated when the higher-level unit determines that the secondary battery is in an open-circuit state. By initiating the calculation of the initial SOC value based on the determination that the battery is in an open-circuit state, the open-circuit voltage value can be used, and the initial SOC value can be calculated with greater accuracy. As a result, the measured SOH value can also be calculated with greater accuracy. 【0204】 (10) In the battery management system described in any of (4), (6) to (9) above, when the lower unit completes the calculation of the change in the initial SOC value in the calculation unit, it sends a signal to the upper unit indicating completion, and the current value integration unit in the upper unit, upon receiving the signal from the lower unit indicating completion, resets the current value integration process and starts the process of calculating the current integrated value again. 【0205】 The current value integration unit of the higher-level unit does not have information on whether the lower-level unit has calculated the change in 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. 【0206】(11) In the battery management system described in any of (4), (6), (8) to (10) 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 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. 【0207】 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. 【0208】 (12) In any of the battery management systems described in (3) to (6) or (8) to (11) 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. 【0209】 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 circuit can be reliably determined without changing the configuration of the existing battery management system. 【0210】 (13) In any of the battery management systems described in (3) to (6) or (8) to (12) above, 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. 【0211】 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. 【0212】 (14) In any of the battery management systems described in (3) to (6) or (8) to (13) above, the open state determination unit determines the open state of the secondary battery when the battery management system is started. 【0213】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. 【0214】 (15) In the battery management system described in (2) or (3) above, the higher-level unit further comprises a battery relay control unit that performs connection control of a battery relay to create an open state or a closed state of a battery cell. 【0215】 (16) In the battery management system described in (15) above, 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 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 change in the initial SOC value has been completed. 【0216】 By performing control in the lower-level unit to disconnect the battery relay until the calculation of the change in the initial state of charge (SOC) is completed, the battery cell circuit is kept open. Therefore, the lower-level unit can perform calculations of the initial SOC value and the change in the initial SOC value with greater reliability. 【0217】 1...BMU, 11...BMU control device, 111...Information acquisition unit, 112...Current value integration unit, 113...Battery relay control unit, 114...Open state determination unit, 115...Aggregation calculation unit, 116...Information transmission 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...Storage 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 State of Health (SOH) value for each battery cell 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 includes a current value integration unit that calculates a current integrated value based on the current value acquired by a current sensor that detects the current value passing through the battery module.

3. The battery management system according to claim 2, characterized in that the upper unit comprises: an open state determination unit that grasps the elapsed usage time of the battery module and determines whether or not the battery cell is in an open state; and an aggregation calculation unit that aggregates the SOH values ​​transmitted from a plurality of lower units and calculates the SOH value of the entire battery pack composed of a plurality of battery modules.

4. The battery management system according to claim 1, wherein 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 SOH value based on the current integrated value transmitted from the upper unit; and a storage unit that stores at least a degradation characteristic formula used when calculating the SOH value.

5. The battery management system according to claim 4, characterized in that the calculation unit calculates the value of the State of Health (SOH) using the degradation characteristic formula based on the information transmitted from the higher-level unit, which is the elapsed usage time and the integrated current value of the battery module.

6. The battery management system according to claim 4, characterized in that the calculation unit calculates the initial SOC value of the battery cell based on the voltage value of the battery cell, and calculates the measured SOH value based on the amount of change in the initial SOC value between the initial SOC value calculated on the nth time and the initial SOC value calculated on the (n+1)th time and the integrated current value obtained from the higher-level unit.

7. The battery management system according to claim 6, characterized in that the calculation unit takes into account the reliability of the initial SOC value when calculating the measured SOH value.

8. The battery management system according to claim 4, characterized in that the calculation unit calculates the SOH value for each battery cell using the SOH value obtained by calculation using the degradation characteristic formula and the measured SOH value.

9. The battery management system according to claim 4, 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.

10. The battery management system according to claim 4, characterized in that the lower unit transmits a signal to the upper unit indicating completion when the calculation of the change amount 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.

11. The battery management system according to claim 4, 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.

12. The battery management system according to claim 3, 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.

13. The battery management system according to claim 3, 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.

14. The battery management system according to claim 3, 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.

15. The battery management system according to claim 2 or 3, wherein the higher-level unit further comprises a battery relay control unit that performs connection control of a battery relay that creates an open state or a closed state of the battery cell.

16. The battery management system according to claim 15, characterized in that 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 change amount of the SOC initial value has been completed.

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