Battery monitoring system

Abstract

This corrects estimation errors in the battery's charge level without affecting normal battery control. [Solution] The battery monitoring system 1, which monitors multiple batteries 2 connected in parallel, comprises an estimation unit 11 that estimates the charge rate of each of the multiple batteries 2, an electrical energy transfer unit 13 that can transfer electrical energy between each of the multiple batteries 2, an error detection unit 12 that detects whether the estimation error, which is the estimation error by the estimation unit 11, is greater than or equal to a predetermined threshold error, and an error correction unit 14 that corrects the estimation error by the estimation unit 11. When the error detection unit 12 detects that the estimation error corresponding to a predetermined battery 2 is greater than or equal to a threshold error, the electrical energy transfer unit 13 transfers electrical energy between the target battery, which is the predetermined battery 2, and one or more correction batteries, which are batteries different from the target battery among the multiple batteries 2. The error correction unit 14 corrects the estimation error corresponding to the target battery after the transfer of electrical energy has taken place.

Description

【Technical Field】 【0001】 The present invention relates to a battery monitoring system for monitoring a plurality of batteries connected in parallel. 【Background Art】 【0002】 Conventionally, in a battery monitoring system for monitoring a battery mounted on a vehicle such as an automobile, for example, an SOC which is an index representing the state of charge of the battery is estimated. Note that SOC is an abbreviation of State Of Charge. The estimation of SOC is performed, for example, by the following method. That is, an SOC estimated based on the correlation between SOC and OCV which is the voltage in a state where the circuit is not energized is set as the initial SOC, an integrated SOC is obtained by integrating the current flowing through the battery, and the current SOC is estimated by adding the integrated SOC to the initial SOC. Note that OCV is an abbreviation of open circuit voltage, that is, Open Circuit Voltage. 【0003】 However, such an estimation method has a problem that the estimation error of SOC due to the offset error of the current sensor for detecting the current increases with time. Patent Document 1 discloses a technique for correcting such an estimation error of SOC. In the following description, the technique disclosed in Patent Document 1 may be referred to as the prior art. In the correlation between OCV and SOC, there are a minute change region which is a region where the change rate of OCV with respect to SOC is less than or equal to a reference value, and a steep change region which is a region where the above change rate is higher than the reference value. 【0004】 In conventional technology, if the measured OCV is determined to be within a steep change region, the SOC corresponding to the measured OCV is determined as the estimated SOC based on information regarding the correlation between the OCV and SOC within the steep change region. Furthermore, in conventional technology, if the measured OCV is determined not to be within a steep change region, it is prohibited to determine the SOC corresponding to the measured OCV as the estimated SOC. With such conventional technology, the determination of an estimated SOC even if the SOC obtained by the OCV-based SOC estimation method deviates from the actual SOC is suppressed. [Prior art documents] [Patent Documents] 【0005】 [Patent Document 1] Japanese Patent Publication No. 2014-199238 [Overview of the Initiative] [Problems that the invention aims to solve] 【0006】 In conventional technology, when the measured OCV is determined to be within a steep change region, the estimated SOC is determined based on information regarding the correlation between SOC and OCV. However, in order to maintain the SOC value within the steep change region, the battery is charged or discharged. Such charge / discharge operations can affect the normal control of the battery. Therefore, in conventional technology, there was a risk that the normal control of the battery would be restricted when correcting the estimation error of SOC. 【0007】 The present invention has been made in view of the above circumstances, and its object is to provide a battery monitoring system that can correct estimation errors of the battery's charge level without affecting normal battery control. [Means for solving the problem] 【0008】 The battery monitoring system described in claim 1 is a battery monitoring system for monitoring a plurality of batteries (2, 2A, 2B, 2C) connected in parallel, comprising: an estimation unit (11) for estimating the charge rate of each of the plurality of batteries; an electrical amount transfer unit (13) for transferring electrical amounts between each of the plurality of batteries; an error detection unit (12) for detecting whether the estimation error, which is the estimation error by the estimation unit, is greater than or equal to a predetermined threshold error; and an error correction unit (14) for correcting the estimation error by the estimation unit. 【0009】 When the error detection unit detects that the estimated error corresponding to a predetermined battery is greater than or equal to the threshold error, the electrical energy transfer unit transfers electrical energy between the target battery, which is the predetermined battery, and one or more correction batteries, which are different from the target battery among the plurality of batteries. This allows the remaining capacity of the target battery to be adjusted to a steep change region without restricting the control of the normal battery. The error correction unit corrects the estimated error corresponding to the target battery after the electrical energy transfer has been performed. With this configuration, the estimation error of the battery's charge level can be corrected without affecting the control of the normal battery. [Brief explanation of the drawing] 【0010】 [Figure 1] A schematic diagram showing the configuration of a battery monitoring system according to one embodiment. [Figure 2] A diagram showing an example of the correlation between SOC and OCV of a typical battery according to one embodiment. [Figure 3] A diagram showing an example of the correlation between SOC and OCV of an LFP battery according to one embodiment. [Figure 4] A diagram showing an example of the specific details of the processing related to the correction of estimation errors according to one embodiment. [Figure 5] This figure shows an example of the specific details of the battery selection process for correction according to one embodiment. [Figure 6] A diagram showing an example of the specific details of the electrical energy transfer process according to one embodiment. [Figure 7]Figure 1 illustrates the specific operation of each part when the correction of the estimation error in the first pattern according to one embodiment is performed. [Figure 8] Figure 2 illustrates the specific operation of each part when the correction of the estimation error in the first pattern according to one embodiment is performed. [Figure 9] Figure 1 illustrates the specific operation of each part when the correction of the estimation error in the second pattern according to one embodiment is performed. [Figure 10] Figure 2 illustrates the specific operation of each part when the correction of the estimation error in the second pattern according to one embodiment is performed. [Figure 11] Figure 1 illustrates the specific operation of each part when the correction of the estimation error in the third pattern according to one embodiment is performed. [Figure 12] Figure 2 illustrates the specific operation of each part when the correction of the estimation error in the third pattern according to one embodiment is performed. [Figure 13] Figure 1 illustrates the specific operation of each part when the correction of the estimation error in the fourth pattern according to one embodiment is performed. [Figure 14] Figure 2 illustrates the specific operation of each part when the correction of the estimation error in the fourth pattern according to one embodiment is performed. [Figure 15] Figure 1 illustrates the specific operation of transferring an electric quantity by the operation of a bidirectional DC / DC converter according to one embodiment. [Figure 16] Figure 2 illustrates the specific operation of transferring an electric quantity by the operation of a bidirectional DC / DC converter according to one embodiment. [Figure 17] Figure 3 illustrates the specific operation of transferring an electric quantity by the operation of a bidirectional DC / DC converter according to one embodiment. [Modes for carrying out the invention] 【0011】 An embodiment of the battery monitoring system will be described below with reference to the drawings. <Overall Configuration of Battery Monitoring System> As shown in FIG. 1, the battery monitoring system 1 of the present embodiment is a system for monitoring a plurality of batteries 2 that are mounted on a vehicle such as an automobile and connected in parallel. In FIG. 1 and the like, only three of the plurality of batteries 2 are shown. Note that the number of batteries 2 to be monitored by the battery monitoring system 1 may be two or more. 【0012】 In FIG. 1 and the like, in order to distinguish the three batteries 2, an alphabet is attached to the end of the reference numeral. Also, for each component provided in the battery monitoring system 1 corresponding to each of these three batteries 2A, 2B, and 2C, a similar alphabet may be attached to the end of the reference numeral for distinction. However, when it is not necessary to distinguish these components, the alphabet at the end may be omitted and they may be collectively referred to. 【0013】 The battery 2 may be a single battery composed of one battery cell, or may be a battery pack in which a plurality of battery cells are connected in series. In this case, as the battery 2, a lithium iron phosphate ion battery can be adopted. Note that in this specification, the lithium iron phosphate ion battery may be referred to as an LFP battery. As shown in FIGS. 2 and 3, the value of the OCV changes correlatively according to the SOC of the battery. As shown in FIG. 2, in a general battery, the change in SOC is relatively large with respect to the change in OCV. On the other hand, as shown in FIG. 3, in an LFP battery, the change in SOC is relatively small with respect to the change in OCV. 【0014】 The high-potential side terminal of the battery 2A is connected to one terminal of the bidirectional DC / DC converter 3A. The other terminal of the bidirectional DC / DC converter 3A is connected to the DC power line L1 via the contactor 4A. The high-potential side terminal of the battery 2B is connected to one terminal of the bidirectional DC / DC converter 3B. The other terminal of the bidirectional DC / DC converter 3B is connected to the DC power line L1 via the contactor 4B. 【0015】 The high-potential terminal of battery 2C is connected to one terminal of bidirectional DC / DC converter 3C. The other terminal of bidirectional DC / DC converter 3C is connected to DC power line L1 via contactor 4C. DC power line L1 is connected to a DC / DC converter (not shown), and the output of the DC / DC converter is supplied to various load devices mounted on the vehicle. 【0016】 The bidirectional DC / DC converter 3 is a device that converts DC to DC, and is configured to include, for example, a boost circuit and a buck circuit. The bidirectional DC / DC converter 3 can perform a buck operation, which steps down the DC voltage supplied from the DC power line L1 via the contactor 4 to a DC voltage of a desired voltage value and outputs it to the battery 2, and a boost operation, which steps up the DC voltage supplied from the battery 2 to a DC voltage of a desired voltage value and outputs it to the DC power line L1 via the contactor 4. 【0017】 Therefore, the bidirectional DC / DC converter 3 can change the terminal voltage of the corresponding battery. In other words, in this embodiment, the bidirectional DC / DC converter 3 functions as a voltage changing unit that can change the terminal voltage of each of the multiple batteries 2. The operation of the bidirectional DC / DC converter 3 is controlled by the power management device 5, which will be described later. 【0018】 The contactor 4 is an electronic device that can remotely generate or interrupt current, and is composed of, for example, a relay that opens and closes contacts using an electromagnetic coil. The operation of the contactor 4 is controlled by the BMU 6, which will be described later. The DC power line L1 is connected to the power conditioner 7. The power conditioner 7 is a device that converts DC power to AC power. The operation of the power conditioner 7 is controlled by the power management device 5, which will be described later. 【0019】 The power conditioner 7 is connected to the power generation device 8. The power generation device 8 includes, for example, an inverter connected to a motor that drives a vehicle, and drives the motor using the power supplied from the battery 2 via the power conditioner 7 and the like when the vehicle is running. At this time, the battery 2 will be discharged by the operation of the power generation device 8. Also, the power generation device 8 supplies the regenerative power regenerated from the motor to the battery 2 via the power conditioner 7 and the like, for example, when the vehicle is braking. At this time, the battery 2 will be charged by the operation of the power generation device 8. 【0020】 The BMU 6A is a device that monitors, controls, and protects the corresponding battery 2A, and is provided near the battery 2A. The BMU 6B is a device that monitors, controls, and protects the corresponding battery 2B, and is provided near the battery 2B. The BMU 6C is a device that monitors, controls, and protects the corresponding battery 2C, and is provided near the battery 2C. The BMU 6 is a device that performs various operations related to monitoring, controlling, and protecting the corresponding battery 2, and includes a battery monitoring IC which is an integrated circuit in which various circuits for performing those operations are integrated. Note that BMU is an abbreviation for Battery Management Unit, and IC is an abbreviation for Integrated Circuit. 【0021】 Thus, in the present embodiment, the plurality of BMUs 6 are provided corresponding to each of the plurality of batteries 2. That is, the battery monitoring system 1 of the present embodiment is a system in which a plurality of batteries 2 that store electricity from the power generation device 8 and the BMUs 6 that monitor, control, and protect those plurality of batteries 2 are connected in parallel as a set. The power management device 5 is a device that controls the overall operation in the battery monitoring system 1 and communicates with the plurality of BMUs 6. 【0022】 <Configuration and Function of BMU> The BMU6 includes functional blocks such as an estimation unit 11 and an error detection unit 12. In other words, in this embodiment, the estimation unit 11 and the error detection unit 12 are provided corresponding to each of the multiple batteries 2. The estimation unit 11 estimates the State of Charge (SOC), which is an index representing the charge level of the corresponding battery 2. The estimation unit 11 estimates the SOC using a method similar to that of the prior art. 【0023】 In other words, the estimation unit 11 uses the SOC estimated based on the correlation between SOC and OCV as the initial SOC. The estimation unit 11 detects the current flowing through the battery 2 using a current sensor (not shown) and calculates the integrated SOC by integrating the detected current. The estimation unit 11 estimates the constant SOC by adding the integrated SOC to the initial SOC. Note that the initial SOC corresponds to the initial charge rate, and the integrated SOC corresponds to the integrated charge rate. 【0024】 The error detection unit 12 detects whether the estimated error, which is the estimation error made by the estimation unit 11, is greater than or equal to a predetermined threshold error. The error detection unit 12 can perform specific detection operations, such as the following: The error detection unit 12 accumulates the offset error of the current sensor over time, and determines whether the estimated error is greater than or equal to a threshold error based on whether the accumulated value exceeds a threshold. The threshold can be set to a value corresponding to an accumulated value for which SOC estimation is considered difficult. 【0025】 <Configuration and Functions of Power Management Devices> The power management device 5 is equipped with functional blocks such as an electrical quantity transfer unit 13 and an error correction unit 14. The power management device 5 is a control device that acts as a higher-level control unit for multiple BMUs 6. The power management device 5 communicates with each of the multiple BMUs 6 and sends and receives various commands and data through this communication. The various commands include operation commands for the bidirectional DC / DC converter 3 and operation commands for the power conditioner 7. The various data include the SOC value estimated by the estimation unit 11 and the detection results by the error detection unit 12. 【0026】 The electrical energy transfer unit 13 can transfer electrical energy between each of the multiple batteries 2. In this case, when the error detection unit 12 detects that the estimated error corresponding to a predetermined battery 2 is greater than or equal to a threshold error, the electrical energy transfer unit 13 transfers electrical energy between the target battery, which is the predetermined battery 2, and one or more correction batteries, which are different from the target battery among the multiple batteries 2. In this case, the electrical energy transfer unit 13 transfers electrical energy until the target battery reaches a region in which the estimated error can be corrected, specifically, until the target battery reaches the high SOC region or low SOC region described later. The electrical energy transfer unit 13 transfers electrical energy by changing the terminal voltage of the batteries 2 using the bidirectional DC / DC converter 3 to generate a potential difference between each of the multiple batteries 2. 【0027】 The error correction unit 14 corrects the estimation error made by the estimation unit 11. In this case, the error correction unit 14 corrects the estimation error corresponding to the target battery after the electrical quantity transfer has been performed by the electrical quantity transfer unit 13. Specifically, the error correction unit 14 estimates the SOC of the target battery based on the correlation between SOC and OCV after the electrical quantity transfer has been performed. The error correction unit 14 corrects the estimation error corresponding to the target battery by replacing the estimated SOC with the initial SOC corresponding to the target battery. 【0028】 After the error correction unit 14 corrects the estimated error corresponding to the target battery, the electrical quantity transfer unit 13 performs a re-transfer operation to move the electrical quantity so that the SOC of the target battery and the correction battery return to their pre-correction state if the determination conditions described later are not met. If the conditions are met, the re-transfer operation is not performed. The determination conditions are that the estimated error corresponding to the correction battery is greater than or equal to the threshold error, and the SOC of the correction battery is close to a high region where the SOC is relatively higher than before correction, or a low region where the SOC is relatively lower. 【0029】 The high region, where SOC is relatively high, corresponds to the high SOC region shown in Figures 2 and 3. The low region, where SOC is relatively low, corresponds to the low SOC region shown in Figures 2 and 3. These high and low SOC regions correspond to the steep change region, where the rate of change of OCV with respect to SOC is higher than the baseline value. The region excluding the high and low SOC regions corresponds to the minute change region, where the rate of change of OCV with respect to SOC is below the baseline value. 【0030】 <Processing related to correcting estimation errors> Specific details of the processing related to correcting the SOC estimation error in the above configuration can be as follows, for example, as shown in Figures 4 to 6. As shown in Figure 4, in step S101, the operation of the estimation unit 11, that is, the operation to estimate the SOC, is started. After the execution of step S101, the process proceeds to step S102, where it is determined whether the SOC estimation error of each of the multiple estimation units 11 is greater than or equal to the threshold error. 【0031】 Here, if the SOC estimation error for all estimation units 11 is less than the threshold error, the result in step S102 is "NO", and step S102 is executed again. On the other hand, if the SOC estimation error for at least one estimation unit 11 is greater than or equal to the threshold error, the result in step S102 is "YES", and the process proceeds to step S103. In step S103, the target battery to be corrected is selected as follows. 【0032】 In other words, if the SOC estimation error for one estimation unit 11 is greater than or equal to the threshold error, the battery 2 corresponding to that estimation unit 11 is selected as the target battery. Also, if the SOC estimation errors for multiple estimation units 11 are greater than or equal to the threshold error, the battery 2 corresponding to the estimation unit 11 with the largest estimation error is selected as the target battery. After step S103 is executed, the process proceeds to step S104. In step S104, a correction battery selection process is performed to select a correction battery to be used to correct the estimation error. 【0033】 The process for selecting a correction battery can be as shown in Figure 5, for example. First, in step S201, one battery 2 from among several batteries 2 that is different from the target battery is selected as the correction battery. After step S201 is executed, the process proceeds to step S202, where it is measured whether the target battery can be transitioned to a high SOC region or a low SOC region by transferring an amount of electricity between the target battery and the currently selected correction battery. 【0034】 If the target battery cannot be transitioned to the high SOC region or the low SOC region, the result in step S202 is "NO", and the process proceeds to step S203. In step S203, one battery 2 from among the multiple batteries 2, different from the target battery and the currently selected correction battery, is added as a correction battery. After the execution of step S203, the process returns to step S202. On the other hand, if the target battery can be transitioned to the high SOC region or the low SOC region, the result in step S202 is "YES", and the correction battery selection process is completed. 【0035】 After the selection process for the correction battery is completed, that is, after step S104 is completed, the process proceeds to step S105. In step S105, an electrical energy transfer process is performed to transfer electrical energy between the target battery and the correction battery. The electrical energy transfer process can be as shown in Figure 6, for example. First, in step S301, it is determined whether the remaining capacity of the target battery is closer to the SOC value in the high SOC region than to the SOC value in the low SOC region. Note that the remaining capacity refers to the amount of electrical energy remaining in battery 2. 【0036】 Here, if the remaining capacity of the target battery is closer to the SOC value in the high SOC region than the SOC value in the low SOC region, the answer in step S301 is "YES", and the process proceeds to step S302. In step S302, the voltage on the target battery side is lowered by controlling the operation of the bidirectional DC / DC converter 3 corresponding to the target battery. After step S302 is executed, the process proceeds to step S303, where the voltage on the correction battery side is raised by controlling the operation of the bidirectional DC / DC converter 3 corresponding to the correction battery. 【0037】 On the other hand, if the remaining capacity of the target battery is closer to the SOC value in the low SOC region than the SOC value in the high SOC region, the result in "NO" in step S301, and the process proceeds to step S304. In step S304, the voltage on the target battery side is increased by controlling the operation of the bidirectional DC / DC converter 3 corresponding to the target battery. After step S304 is executed, the process proceeds to step S305, where the voltage on the correction battery side is decreased by controlling the operation of the bidirectional DC / DC converter 3 corresponding to the correction battery. After step S303 or S305 is executed, the electrical energy transfer process is completed. 【0038】 After the electrical energy transfer process is completed, that is, after step S105 is completed, the process proceeds to step S106. In step S106, the estimation error correction is performed when the target battery reaches a region where correction is possible. Specifically, if the answer in step S301 is "YES", the estimation error correction is performed when the remaining capacity of the target battery reaches a State of Charge (SOC) value in the high SOC region. If the answer in step S301 is "NO", the estimation error correction is performed when the remaining capacity of the target battery reaches a State of Charge (SOC) value in the low SOC region. 【0039】 After step S106 is executed, the process proceeds to step S107, where it is determined whether the judgment conditions are met. As previously described, the judgment conditions are that the estimated error corresponding to the correction battery is greater than or equal to the threshold error, and the SOC of the correction battery is closer to the high SOC region or low SOC region than before correction. If the judgment conditions are not met, the result in step S107 is "NO", and the process proceeds to step S108. 【0040】 In step S108, a re-transfer operation is performed to move the amount of electricity so that the State of Charge (SOC) of the target battery and the correction battery return to their state before correction. For the re-transfer operation, an operation can be adopted in which the relationship between discharge and charge is reversed for each operation performed in the amount of electricity transfer process, and the operation time is equal. After the execution of step S108, this series of processes ends. On the other hand, if the judgment condition is met, the result in step S107 is "YES", and this series of processes ends without step S108 being executed. 【0041】 <Specific operation of each part when correction of estimation error is performed> The specific operation of each part when the estimation error correction is performed will be explained below with reference to Figures 7 to 14. Here, we will explain each of the four representative patterns. 【0042】 [1] Pattern 1 As shown in Figure 7, the first pattern has the following conditions. Applicable battery: Battery 2C Correction battery: Battery 2A Remaining capacity of the target battery: Close to the SOC value in the high SOC region. 【0043】 The operation in the first pattern is as follows: Since the estimation error of battery 2C exceeds the threshold error, battery 2C is selected as the target battery. Subsequently, battery 2A is selected as the correction battery. In this case, as shown in [Before Control] in Figure 7, the target battery can be transitioned to the high SOC region by transferring the amount of electricity between the target battery 2C and the correction battery 2A. 【0044】 Therefore, the battery monitoring system 1 controls the operation of the bidirectional DC / DC converter 3C to lower the voltage on the target battery 2C side, and controls the operation of the bidirectional DC / DC converter 3A to raise the voltage on the correction battery 2A side. As a result, the correction battery 2A is discharged and the target battery 2C is charged, and an amount of electricity is transferred from battery 2A to battery 2C. This transfer of electricity continues until the target battery 2C reaches a high SOC region, as shown in [After Control] in Figure 7. 【0045】 In this case, as shown in Figure 8, the estimation error correction is performed at time ta, which is the timing after the remaining capacity of the target battery, battery 2C, reaches the SOC value in the high SOC region. As previously described, the estimation error correction involves estimating the SOC of the target battery based on the correlation between SOC and OCV, and replacing it with the initial SOC corresponding to the target battery. As shown in Figure 8, by performing this estimation error correction at time ta, the estimation error of the target battery, battery 2C, becomes zero. Note that in Figure 8 and other documents, the estimation error of SOC is referred to as the SOC error. 【0046】 [2] Second pattern As shown in Figure 9, the second pattern has the following conditions. Applicable battery: Battery 2C Correction battery: Battery 2A Remaining capacity of the target battery: Close to the SOC value in the low SOC region. 【0047】 The operation in the second pattern is as follows: Since the estimation error of battery 2C exceeds the threshold error, battery 2C is selected as the target battery. Subsequently, battery 2A is selected as the correction battery. In this case, as shown in [Before Control] in Figure 9, the target battery can be transitioned to the low SOC region by transferring the amount of electricity between the target battery 2C and the correction battery 2A. 【0048】 Therefore, the battery monitoring system 1 controls the operation of the bidirectional DC / DC converter 3C to increase the voltage on the target battery 2C side, and controls the operation of the bidirectional DC / DC converter 3A to decrease the voltage on the correction battery 2A side. As a result, the target battery 2C is discharged and the correction battery 2A is charged, and an amount of electricity is transferred from battery 2C to battery 2A. This transfer of electricity continues until the target battery 2C reaches a low SOC region, as shown in [After Control] in Figure 9. 【0049】 In this case, as shown in Figure 10, the estimation error correction is performed at time tb, which is the timing after the remaining capacity of the target battery, battery 2C, reaches the SOC value in the low SOC region. As previously described, the estimation error correction involves estimating the SOC of the target battery based on the correlation between SOC and OCV, and replacing it with the initial SOC corresponding to the target battery. As shown in Figure 10, by performing this estimation error correction at time tb, the estimation error of the target battery, battery 2C, becomes zero. 【0050】 [3] Third pattern As shown in Figure 11, the third pattern has the following conditions. Applicable battery: Battery 2C Correction batteries: Battery 2A, Battery 2B Remaining capacity of the target battery: Close to the SOC value in the high SOC region. 【0051】 The operation in the third pattern is as follows: Since the estimation error of battery 2C exceeds the threshold error, battery 2C is selected as the target battery. Subsequently, batteries 2A and 2B are selected as correction batteries. In this case, as shown in Figure 11 [Before Control], the target battery can be transitioned to the high SOC region by transferring the amount of electricity between the target battery 2C and the correction batteries 2A and 2B. 【0052】 Therefore, the battery monitoring system 1 controls the operation of the bidirectional DC / DC converter 3C to lower the voltage on the target battery 2C side, and controls the operation of the bidirectional DC / DC converters 3A and 3B to raise the voltage on the correction batteries 2A and 2B side. As a result, the correction batteries 2A and 2B are discharged and the target battery 2C is charged, and an amount of electricity is transferred from batteries 2A and 2B to battery 2C. This transfer of electricity continues until the target battery 2C reaches a high SOC region, as shown in [After Control] in Figure 11. 【0053】 In this case, as shown in Figure 12, the estimation error correction is performed at time tc, which is the timing after the remaining capacity of the target battery, battery 2C, reaches the SOC value in the high SOC region. As previously described, the estimation error correction involves estimating the SOC of the target battery based on the correlation between SOC and OCV, and replacing it with the initial SOC corresponding to the target battery. As shown in Figure 12, by performing this estimation error correction at time tc, the estimation error of the target battery, battery 2C, becomes zero. 【0054】 [4] Fourth pattern As shown in Figure 13, the fourth pattern has the following conditions. Applicable battery: Battery 2C Correction batteries: Battery 2A, Battery 2B Remaining capacity of the target battery: Close to the SOC value in the low SOC region. 【0055】 The operation in the fourth pattern is as follows: Since the estimation error of battery 2C exceeds the threshold error, battery 2C is selected as the target battery. Subsequently, batteries 2A and 2B are selected as correction batteries. In this case, as shown in Figure 13 [Before Control], the target battery can be transitioned to the low SOC region by transferring the amount of electricity between the target battery 2C and the correction batteries 2A and 2B. 【0056】 Therefore, the battery monitoring system 1 controls the operation of the bidirectional DC / DC converter 3C to increase the voltage on the target battery 2C side, and controls the operation of the bidirectional DC / DC converters 3A and 3B to decrease the voltage on the correction batteries 2A and 2B sides. As a result, the target battery 2C is discharged and the correction batteries 2A and 2B are charged, and an amount of electricity is transferred from battery 2C to battery 2A. This transfer of electricity continues until the target battery 2C reaches a low SOC region, as shown in [After Control] in Figure 13. 【0057】 In this case, as shown in Figure 14, the estimation error correction is performed at time td, which is the timing after the remaining capacity of the target battery, battery 2C, reaches the SOC value in the low SOC region. As previously described, the estimation error correction involves estimating the SOC of the target battery based on the correlation between SOC and OCV, and replacing it with the initial SOC corresponding to the target battery. As shown in Figure 14, by performing this estimation error correction at time td, the estimation error of the target battery, battery 2C, becomes zero. 【0058】 <Specific actions of the transfer of electrical energy> According to the above configuration, the operation of the bidirectional DC / DC converter 3 allows for the transfer of electrical energy. The specific operation will be explained with reference to Figures 15 to 17. Here, the second pattern described above will be used as an example, but the operation will be similar for other patterns. When transferring electrical energy from battery 2C to battery 2A, as in the second pattern, the battery monitoring system 1 controls the operation of the bidirectional DC / DC converter 3C to make the voltage VcC of node NcC, which corresponds to one terminal of the bidirectional DC / DC converter 3C, higher than the voltage VbC of node NbC, which corresponds to the high-potential terminal of battery 2C, as shown in Figures 15 and 16. 【0059】 In this case, the battery monitoring system 1 controls the operation of the bidirectional DC / DC converter 3A to lower the voltage VcA of node NcA, which corresponds to one terminal of the bidirectional DC / DC converter 3A, to a lower voltage VbA of node NbA, which corresponds to the high-potential terminal of battery 2A, as shown in Figures 15 and 17. As a result, as shown in Figure 15, a discharge current I_C is generated to discharge electricity from battery 2C, and a charging current I_A is generated to charge battery 2A. Consequently, battery 2C is discharged and battery 2A is charged, and an amount of electricity is transferred from battery 2C to battery 2A. 【0060】 <Effects obtained by this embodiment> According to the embodiment described above, the following effects can be obtained. The battery monitoring system 1 monitors multiple batteries 2 connected in parallel and includes an estimation unit 11 that estimates the State of Charge (SOC) of each of the batteries 2, an electrical energy transfer unit 13 that can transfer electrical energy between each of the batteries 2, an error detection unit 12 that detects whether the estimation error, which is the estimation error by the estimation unit 11, is greater than or equal to a predetermined threshold error, and an error correction unit 14 that corrects the estimation error by the estimation unit 11. 【0061】 When the error detection unit 12 detects that the estimated error corresponding to a predetermined battery 2 is greater than or equal to a threshold error, the electrical quantity transfer unit 13 transfers electrical quantity between the target battery, which is the predetermined battery 2, and one or more correction batteries, which are different from the target battery among the multiple batteries 2. This allows the remaining capacity of the target battery to be adjusted to a steep change region without restricting the control of the normal battery. The error correction unit 14 corrects the estimated error corresponding to the target battery after the electrical quantity transfer has been performed. With this configuration, the estimated error of the State of Charge (SOC) of the battery 2 can be corrected without affecting the control of the normal battery 2. 【0062】 The battery monitoring system 1 includes a bidirectional DC / DC converter 3 that functions as a voltage changing unit capable of changing the terminal voltage of each of the multiple batteries 2, and the electric quantity transfer unit 13 transfers electric quantity by changing the terminal voltage using the bidirectional DC / DC converter 3 to generate a potential difference between each of the multiple batteries 2. 【0063】 With this configuration, since only the amount of electricity in each battery 2 is transferred, the remaining capacity of the target battery can be efficiently changed to either the high-SOC region or the low-SOC region, which are steep change regions, without changing the total SOC of multiple batteries 2 connected in parallel. Furthermore, with the above configuration, since the amount of electricity can be transferred by controlling the operation of the bidirectional DC / DC converter 3, estimation errors can be corrected without restricting the control of the batteries 2, even when a system that operates using multiple batteries 2 is in operation. 【0064】 After the error correction unit 14 corrects the estimated error corresponding to the target battery, if the conditions are not met—that the estimated error corresponding to the correction battery is greater than or equal to the threshold error and the state of charge (SOC) of the correction battery is closer to the high SOC region or low SOC region than before the correction—the electrical quantity transfer unit 13 performs a re-transfer operation to transfer the electrical quantity so that the SOC of both the target battery and the correction battery return to their pre-correction states. 【0065】 Furthermore, the electrical quantity transfer unit 13 is configured not to perform a re-transfer operation if the above-mentioned conditions are met. In this way, when the remaining capacity of the correction battery is close to the high SOC region or the low SOC region, it is possible to minimize the amount of electrical quantity that needs to be transferred to correct the estimation error. As a result, the time required for the transfer of electrical quantity is shortened, and the estimation error can be corrected efficiently. 【0066】 In the battery monitoring system 1, the estimation unit 11 and the error detection unit 12 are provided in the BMU 6 corresponding to each of the multiple batteries 2. In other words, in the battery monitoring system 1, the estimation of the SOC of each battery 2 and the detection of the estimation error are performed independently by each BMU 6. 【0067】 With this configuration, for example, a higher-level control device such as the power management device 5 does not need to sequentially measure the estimation error of all batteries 2. Therefore, when the estimation error of any of the estimation units 11 corresponding to each of the batteries 2 exceeds the threshold error, this can be detected, and subsequent processing such as moving the amount of electricity and correcting the estimation error can be performed immediately. Error correction processing can be performed immediately. Accordingly, with the above configuration, the time during which the estimated value of SOC and the actual value diverge due to the increase in estimation error can be kept short. 【0068】 Various types of batteries, including LFP batteries, can be used as the battery 2 to be monitored by the battery monitoring system 1. Compared to general batteries, LFP batteries have a narrower steep change region because the change in SOC is less in response to the change in OCV, making it difficult to correct estimation errors. However, according to this embodiment, estimation errors are corrected by adjusting the remaining capacity by moving the amount of electricity so that the remaining capacity of the target battery is in the high SOC region or low SOC region, which are steep change regions, by utilizing the correlation between SOC and OCV. Therefore, estimation errors can be corrected even for batteries such as LFP batteries that have a narrow steep change region. 【0069】 (Other embodiments) It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, and can be arbitrarily modified, combined, or expanded without departing from its essence. The numerical values ​​and other figures shown in the above embodiments are illustrative and not limiting. The present invention is not limited to battery monitoring system 1, but can be applied to battery monitoring systems in general that monitor multiple batteries connected in parallel. 【0070】 The battery 2 that the battery monitoring system 1 monitors can be any type of battery, as long as it exhibits a region of sharp change in the correlation between SOC and OCV. The voltage changing section is not limited to the bidirectional DC / DC converter 3; it can be changed as appropriate as long as it can change the terminal voltage of each of the multiple batteries 2. 【0071】 The estimation unit 11 and the error detection unit 12 can also be installed in a control device higher up than the BMU 6, such as the power management device 5. In other words, in the battery monitoring system 1, the estimation of the SOC of each battery 2 and the detection of estimation errors can be performed collectively by a control device higher up than the BMU 6, such as the power management device 5. 【0072】 This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure. [Explanation of symbols] 【0073】 1...Battery monitoring system, 2, 2A, 2B, 2C...Batteries, 3, 3A, 3B, 3C...Bidirectional DC / DC converters, 5...Power management device, 6, 6A, 6B, 6C...BMU, 11...Estimation unit, 12...Error detection unit, 13...Electric quantity transfer unit, 14...Error correction unit.

Claims

[Claim 1] A battery monitoring system that monitors multiple batteries (2, 2A, 2B, 2C) connected in parallel, An estimation unit (11) that estimates the charge level of each of the aforementioned multiple batteries, An electric charge transfer unit (13) that can transfer electric charge between each of the aforementioned plurality of batteries, An error detection unit (12) detects whether the estimation error, which is the estimation error by the estimation unit, is greater than or equal to a predetermined threshold error, An error correction unit (14) corrects the estimation error by the estimation unit, Equipped with, When the error detection unit detects that the estimated error corresponding to a predetermined battery is greater than or equal to the threshold error, the electrical quantity transfer unit transfers electrical quantity between the target battery, which is the predetermined battery, and one or more correction batteries, which are different from the target battery among the plurality of batteries. The error correction unit is a battery monitoring system that corrects the estimated error corresponding to the target battery after the transfer of the amount of electricity has occurred. [Claim 2] Furthermore, it includes voltage changing units (3, 3A, 3B, 3C) that can change the terminal voltage of each of the multiple batteries, The battery monitoring system according to claim 1, wherein the amount of electricity transfer unit transfers the amount of electricity by changing the terminal voltage with the voltage change unit to generate a potential difference between each of the plurality of batteries. [Claim 3] The aforementioned electric quantity transfer unit is After the error correction unit corrects the estimated error corresponding to the target battery, If the estimation error corresponding to the correction battery is greater than or equal to the threshold error and the charge level of the correction battery is not close to a high region where the charge level is relatively higher than before correction, or to a low region where the charge level is relatively lower, then a re-transfer operation is performed to move the amount of electricity so that the charge levels of the target battery and the correction battery return to the state before correction. The battery monitoring system according to claim 1 or 2, wherein the repositioning operation is not performed when the above conditions are met. [Claim 4] The battery monitoring system according to claim 1 or 2, wherein the estimation unit and the error detection unit are provided in correspondence with each of the plurality of batteries. [Claim 5] The battery monitoring system according to claim 1 or 2, wherein the battery is a lithium iron phosphate battery. [Claim 6] The estimation unit uses the estimated charge rate, determined based on the correlation between the battery's charge rate and the open-circuit voltage, as the initial charge rate. It then calculates the integrated charge rate by integrating the current flowing through the battery, and estimates the charge rate by adding the integrated charge rate to the initial charge rate. The battery monitoring system according to claim 1 or 2, wherein the error correction unit estimates the charge rate of the target battery based on the correlation between the charge rate of the battery and the open-circuit voltage after the transfer of the amount of electricity has occurred, and corrects the estimation error corresponding to the target battery by replacing the estimated charge rate with the initial charge rate corresponding to the target battery.

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