Charging state estimation device, charging state estimation system, and charging state estimation program

Abstract

To provide a charging state estimation device, a charging state estimation system and a charging state estimation program capable of improving the measurement accuracy of a charging state of a storage battery.SOLUTION: A control device 50 for estimating an SOC of a first storage battery 31 comprises: a storage unit 51 that stores a charge / discharge history of the first storage battery 31; a charge / discharge determination unit 52 that determines whether the first storage battery 31 is after charge or after discharge on the basis of the charge / discharge history stored in the storage unit 51; a charge / discharge control unit 53 that discharges the first storage battery 31 when the charge / discharge determination unit 52 determines that the first storage battery 31 is after charge, and charges the first storage battery 31 when the charge / discharge determination unit determines that the first storage battery is after discharge; an open voltage acquisition unit 54 that acquires an OCV of the first storage battery 31 after the charge / discharge of the first storage battery 31 is performed by the charge / discharge control unit 53; and a charging state estimation unit 55 that refers to an OCV-SOC curve to estimate the SOC from the OCV.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a state-of-charge estimation device, a state-of-charge estimation system, and a state-of-charge estimation program for estimating the state of charge of a storage battery.

Background Art

[0002] Conventionally, a technique for estimating the state of charge (SOC) from the open-circuit voltage (OCV) of a storage battery has been known. Among such techniques, there are those that consider the difference between the charge curve, which is the OCV-SOC curve during charging of the storage battery, and the discharge curve, which is the OCV-SOC curve during discharging of the storage battery, that is, the hysteresis characteristics of the storage battery. For example, there is one that always charges and then estimates the SOC from the OCV based on the charge curve. Such a technique is described in, for example, Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, it has been discovered that an error occurs in the OCV when the C (Capacity) rate during charging and discharging is high and when it is low. In particular, in the case of an LFP (lithium iron phosphate) battery, this tendency is remarkable. And there is a problem that the estimation accuracy of the SOC deteriorates as a result of estimating the SOC using the OCV having an error.

[0005] Furthermore, batteries used in electric vehicles and other applications require high-rate characteristics (charging and discharging at high currents). For example, rapid charging using a fast charger results in a higher C-rate compared to normal charging using a standard charger installed in a typical home. In other words, with such batteries, the error in OCV due to the difference in C-rate is expected to be larger. Consequently, the error in SOC is also expected to be larger, raising concerns that rapid charging may not be completed properly when controlled based on SOC.

[0006] The present invention has been made in view of the above circumstances, and its main objective is to provide a charge state estimation device, a charge state estimation system, and a charge state estimation program that can improve the accuracy of measuring the charge state of a storage battery. [Means for solving the problem]

[0007] The first means for solving the above problem is to provide a charge state estimation device for estimating the charge state of a storage battery, comprising: a storage unit for storing the charge and discharge history of the storage battery; a charge and discharge determination unit for determining whether the storage battery is charged or discharged based on the charge and discharge history stored by the storage unit; a charge and discharge control unit for discharging the storage battery by a predetermined amount if the charge and discharge determination unit determines that the storage battery is charged, and charging the storage battery by a predetermined amount if the charge and discharge determination unit determines that the storage battery is discharged; an open-circuit voltage acquisition unit for acquiring the open-circuit voltage of the storage battery after the charge and discharge of the storage battery has been performed by the charge and discharge control unit; and a charge state estimation unit for estimating the charge state of the storage battery from the open-circuit voltage acquired by the open-circuit voltage acquisition unit by referring to a charge and discharge curve showing the relationship between the open-circuit voltage of the storage battery and the charge state of the storage battery.

[0008] This makes it possible to suppress errors in open-circuit voltage due to differences in battery usage conditions and improve the accuracy of measuring the battery's charge state.

[0009] A second means for solving the above problem is a charge state estimation system comprising a first battery and a second battery, for estimating the charge state of the first battery and the second battery, comprising: a storage unit for storing the charge and discharge history of each battery; a charge / discharge determination unit for determining whether each battery is charged or discharged based on the charge / discharge history stored by the storage unit; and a charge / discharge determination unit for discharging the battery that the charge / discharge determination unit has determined to be charged, while discharging the battery that the charge / discharge determination unit has determined to be discharged The system comprises a charge / discharge control unit that charges the batteries, an open-circuit voltage acquisition unit that acquires the open-circuit voltage of each battery after the charge / discharge control unit has performed charging and discharging on each of the batteries, and a charge state estimation unit that estimates the charge state of each battery from the open-circuit voltage of each battery acquired by the open-circuit voltage acquisition unit by referring to a charge / discharge curve that shows the relationship between the open-circuit voltage of the batteries and the charge state of the batteries, and the essence of the charge / discharge control unit is to charge and discharge each of the batteries by transferring power between the first battery and the second battery.

[0010] This makes it possible to suppress errors in open-circuit voltage due to differences in battery usage conditions and improve the accuracy of measuring the battery's charge state.

[0011] A third means for solving the above problems is a charge state estimation program that causes a charge state estimation device for estimating the charge state of a storage battery to perform a storage process for storing the charge and discharge history of the storage battery; a charge and discharge determination process for determining whether the storage battery is charging or discharging based on the charge and discharge history stored by the storage process; a charge and discharge control process for discharging the storage battery if the charge and discharge determination process determines that the storage battery is charging, and charging the storage battery if the charge and discharge determination process determines that the storage battery is discharging; an open-circuit voltage acquisition process for acquiring the open-circuit voltage of the storage battery after the charge and discharge of the storage battery has been performed by the charge and discharge control process; and a charge state estimation process for estimating the charge state of the storage battery from the open-circuit voltage acquired by the open-circuit voltage acquisition process by referring to a charge and discharge curve showing the relationship between the open-circuit voltage of the storage battery and the charge state of the storage battery.

[0012] This makes it possible to suppress errors in open-circuit voltage due to differences in battery usage conditions and improve the accuracy of measuring the battery's charge state. [Brief explanation of the drawing]

[0013] [Figure 1] Configuration diagram of the power supply system according to the first embodiment. [Figure 2] (a) is a diagram showing the error in OCV after charging, and (b) is a diagram showing the error in OCV after discharging. [Figure 3] A figure showing the OCV-SOC curve. [Figure 4] A flowchart of memory processing. [Figure 5] Flowchart of the SOC estimation process. [Figure 6] A timing chart showing the charging and discharging timing. [Figure 7] A diagram illustrating the configuration of the power supply system in a modified example. [Figure 8] A diagram illustrating the configuration of the power supply system in a modified example. [Figure 9] A flowchart illustrating the memory processing of modified forms. [Modes for carrying out the invention]

[0014] Hereinafter, a first embodiment of the charge state estimation device, charge state estimation system, and charge state estimation program relating to this disclosure will be described with reference to the drawings. In the following embodiments and modifications, parts that are the same or equivalent to each other are denoted by the same reference numerals in the drawings, and the explanations for such parts will be based on those same reference numerals. The power supply system 100 as the charge state estimation system of this embodiment is mounted on electric vehicles such as electric cars and hybrid vehicles, electric aircraft, electric boats, and other mobile devices. In this embodiment, an electric vehicle is assumed.

[0015] As shown in Figure 1, the power supply system 100 comprises a motor 10, an inverter 20, and a battery pack 30. The motor 10 is a three-phase synchronous machine and comprises star-connected U, V, and W phase armature windings 11 and a rotor (not shown). The armature windings 11 of each phase are arranged with an electrical angle offset of 120°. The motor 10 is, for example, a permanent magnet synchronous machine. The rotor is capable of transmitting power to the vehicle's drive wheels. Therefore, the motor 10 is the source of torque that drives the vehicle.

[0016] The inverter 20 is equipped with three series connections of upper arm switches SWH and lower arm switches SWL. An upper arm diode DH, which is a freewheeling diode, is connected in antiparallel to the upper arm switch SWH, and a lower arm diode DL, which is a freewheeling diode, is connected in antiparallel to the lower arm switch SWL. Hereafter, the upper arm switch SWH and the lower arm switch SWL may be collectively referred to as switches SWH and SWL. In this embodiment, each switch SWH and SWL is a semiconductor switching element, for example, an IGBT (Insulated Gate Bipolar Transistor).

[0017] The inverter 20 includes a smoothing capacitor 21. The high-potential side terminal of the smoothing capacitor 21 is connected to the positive-side bus bar H1. The low-potential side terminal of the smoothing capacitor 21 is connected to the negative-side bus bar L1. Note that the smoothing capacitor 21 may be provided outside the inverter 20.

[0018] In each phase, the first end of the armature winding 11 is connected to the connection point between the emitter, which is the low-potential side terminal of the upper arm switch SWH, and the collector, which is the high-potential side terminal of the lower arm switch SWL, via a conductive member 23 such as a bus bar. The second ends of the armature windings 11 of each phase are connected at the neutral point.

[0019] The collector of the upper arm switch SWH of each phase is connected to the positive-side bus bar H1. The emitter of the lower arm switch SWL of each phase is connected to the negative-side bus bar L1. The battery pack 30 is connected to the inverter 20 via the positive-side bus bar H1 and the negative-side bus bar L1.

[0020] The battery pack 30 of the power supply system 100 includes a first storage battery 31 and a second storage battery 32. Each of the storage batteries 31 and 32 serves as a power supply for rotating the rotor of the motor 10. Each of the storage batteries 31 and 32 is an assembled battery configured as a series connection body of battery cells that are single cells. The positive terminal of the first storage battery 31 is connected to the positive-side bus bar H1, and the negative terminal of the second storage battery 32 is connected to the negative-side bus bar L1. The terminal voltages (e.g., rated voltages) of the battery cells constituting the assembled battery are set to be the same as each other, for example. The battery cell is a secondary battery such as a lithium-ion battery, for example. The terminal voltages (e.g., rated voltages) of each of the storage batteries 31 and 32 may be the same or different.

[0021] Each of the batteries 31 and 32 can be charged by an external charger 40 located outside the vehicle. The external charger 40 is, for example, a stationary charger. The external charger 40 may be either a standard charger or a fast charger. The positive terminal of the external charger 40 is connected to one end of the positive-side charging path 43, and the other end of the charging path 43 is connected to the positive-side busbar H1. The negative terminal of the external charger 40 is connected to one end of the negative-side charging path 44, and the other end of the charging path 44 is connected to the negative-side busbar L1.

[0022] The battery pack 30 of the power system 100 is equipped with a positive-side main switch SMRH for switching the energization and disconnection of the positive-side bus H1 connecting the first battery 31 and the inverter 20. The positive-side main switch SMRH is provided on the positive-side bus H1. The battery pack 30 of the power system 100 is also equipped with a negative-side main switch SMRL for switching the energization and disconnection of the negative-side bus L1 connecting the second battery 32 and the inverter 20. Furthermore, the positive-side charging path 43 of the power system 100 is equipped with a high-potential-side charging switch DCRH for switching the energization and disconnection of the positive-side charging path 43. Furthermore, the negative-side charging path 44 of the power system 100 is equipped with a low-potential-side charging switch DCRL for switching the energization and disconnection of the negative-side charging path 44. Note that the positive terminal main switch SMRH, the negative terminal main switch SMRL, the high-potential charging switch DCRH, and the low-potential charging switch DCRL may be collectively referred to as switches SMRH, SMRL, DCRH, and DCRL.

[0023] In this embodiment, each switch SMRH, SMRL, DCRH, and DCRL is a mechanical relay. When each switch SMRH, SMRL, DCRH, and DCRL is turned off, it prevents the flow of current in both directions, and when it is turned on, it allows the flow of current in both directions. Note that each switch SMRH, SMRL, DCRH, and DCRL is not limited to mechanical relays, but may also be, for example, semiconductor switching elements.

[0024] The battery pack 30 of the power system 100 is equipped with a first switch SW1, a second switch SW2, a third switch SW3, and a fourth switch SW4 as switches for switching the connection state of the first battery 31 and the second battery 32. In the following, the first switch SW1, the second switch SW2, the third switch SW3, and the fourth switch SW4 may be collectively referred to as switches SW1 to SW4.

[0025] In this embodiment, switches SW1 to SW4 are mechanical relays. When switches SW1 to SW4 are turned off, they block the flow of current in both directions, and when they are turned on, they allow the flow of current in both directions. Note that switches SW1 to SW4 are not limited to mechanical relays, but may also be semiconductor switching elements, for example.

[0026] The first switch SW1 is located in the first electrical path 24 that connects the negative terminal of the first battery 31 and the positive terminal of the second battery 32. When the first switch SW1 is turned on, the negative terminal of the first battery 31 and the positive terminal of the second battery 32 are electrically connected. Conversely, when the first switch SW1 is turned off, the negative terminal of the first battery 31 and the positive terminal of the second battery 32 are electrically disconnected.

[0027] The second switch SW2 is located in the second electrical path 25 that connects the negative terminal of the first battery 31 to the busbar L1 on the negative side. When the second switch SW2 is turned on, the negative terminal of the first battery 31 and the busbar L1 on the negative side are electrically connected. Conversely, when the second switch SW2 is turned off, the negative terminal of the first battery 31 and the busbar L1 on the negative side are electrically disconnected.

[0028] The third switch SW3 and the fourth switch SW4 are located in the third electrical path 26, which connects the second battery 32 side of the first electrical path 24 to the neutral point of the armature winding 11. The third switch SW3 is located on the side of the second battery 32, and the fourth switch SW4 is located on the neutral point side. When the third switch SW3 and the fourth switch SW4 are turned on, the neutral point of the armature winding 11 and the positive terminal of the second battery 32 are electrically connected. On the other hand, when the third switch SW3 or the fourth switch SW4 is turned off, the neutral point of the armature winding 11 and the positive terminal of the second battery 32 are electrically disconnected.

[0029] The power supply system 100 is also provided with a neutral point capacitor 22. The high-potential terminal of the neutral point capacitor 22 is connected to the neutral point (more specifically, the third electrical path 26 between the third switch SW3 and the fourth switch SW4). The low-potential terminal of the neutral point capacitor 22 is connected to the negative-side busbar L1.

[0030] Furthermore, the power supply system 100 is equipped with various sensors. As shown in Figure 1, a first current sensor A11 for measuring the current flowing through the first battery 31 is provided in the electrical path between the positive terminal main switch SMRH and the first battery 31. Note that it may be placed at any location in the electrical path as long as it is possible to measure the current flowing through the first battery 31.

[0031] Furthermore, in the first electrical path 24, a second current sensor A12 is provided between the first switch SW1 and the second battery 32 (more specifically, between the connection point with the third electrical path 26 and the positive terminal of the second battery 32) to measure the current flowing through the second battery 32. Note that it may be provided at any location in the electrical path as long as it is possible to measure the current flowing through the second battery 32. In addition, a first voltage sensor V11 for measuring the OCV (open circuit voltage) of the first battery 31 and a second voltage sensor V12 for measuring the OCV of the second battery 32 are provided.

[0032] The inverter 20 may be housed within the battery pack 30. Furthermore, some or all of the switches SMRH, SMRL, and SW1-SW4 may be located outside the battery pack 30.

[0033] The power supply system 100 includes a control device 50 as a charge state estimation device. The control device 50 is mainly composed of a microcontroller, which includes a CPU, RAM, ROM, etc. The functions provided by the control device 50 can be provided by software recorded in a physical memory device and the computer that executes it, by software only, by hardware only, or by a combination thereof. For example, if the microcontroller is provided by an electronic circuit which is hardware, it can be provided by a digital circuit including a large number of logic circuits, or by an analog circuit. For example, the microcontroller executes a program stored in a non-transitory tangible storage medium such as its own memory. The program includes, for example, a program for the processing shown in Figures 3 and 4 described later. When the program is executed, the method (process) corresponding to the program is executed. The memory is, for example, non-volatile memory. The program stored in the memory can be updated via a communication network such as the Internet, for example, OTA (Over The Air).

[0034] The control device 50 receives information (detected values) from various sensors. These sensors include, for example, the first current sensor A11, the second current sensor A12, the first voltage sensor V11, and the second voltage sensor V12 mentioned above. Other sensors, though not shown in the diagram, include, for example, a rotation angle sensor for detecting the rotation angle (electrical angle) of the rotor, and a phase current sensor for detecting the phase current flowing through the armature windings 11 of each phase.

[0035] The control device 50 performs various processes according to a program based on information such as detected values ​​input from various sensors. These processes include, for example, controlling the inverter 20. Specifically, the control device 50 performs switching control of the switches SWH, SWL, etc., that make up the inverter 20, in order to feed back the control amount of the motor 10 to a command value based on the detected values ​​of each sensor. The control amount is, for example, torque. In each phase, the upper arm switch SWH and the lower arm switch SWL are turned on alternately. Through this feedback control, the rotational power of the rotor is transmitted to the drive wheels, causing the vehicle to move.

[0036] Furthermore, when the external charger 40 is connected, the control device 50 performs on / off control of switches SMRH, SMRL, DCRH, DCRL, SW1~SW4 and switches SWH, SWL that make up the inverter 20 in order to charge the first battery 31 and the second battery 32. For example, if the external charger 40 is a fast charger, the control device 50 connects the first battery 31 and the second battery 32 in series and performs fast charging. In some cases, the control device 50 also connects the first battery 31 and the second battery 32 in parallel via the neutral point of the motor 10 and performs charging. In this case, the control device 50 may also use the inverter 20 and the armature winding 11 of the motor 10 as a voltage converter (DC-DC converter) to step down (or step up) the charging voltage of the external charger 40 and perform charging.

[0037] Furthermore, the control device 50 acquires the OCV of each battery 31 and 32 according to the charge state estimation program and performs a process to estimate the SOC (state of charge) of each battery 31 and 32 from the OCV.

[0038] Incidentally, the OCV and SOC of each battery 31 and 32 will vary depending on the usage conditions of each battery 31 and 32. To explain in more detail, in a vehicle, the torque required for the motor 10 may change significantly depending on the driving conditions. Also, each battery 31 and 32 may be charged with a fast charger or with a standard charger. For this reason, the discharge or charge speed, i.e., the C rate (ratio of charge / discharge current to battery capacity), may change significantly in each battery 31 and 32 used in a vehicle.

[0039] Furthermore, as shown in Figure 2(a), the Discloser has discovered that even if the SOC immediately after charging is the same "X%" (e.g., 50%), the OCV does not match depending on the C rate. In Figure 2, the OCV when the C rate is high is shown by a solid line, and the OCV when the C rate is low is shown by a dashed line. Similarly, as shown in Figure 2(b), the Discloser has discovered that even if the SOC immediately after discharge is the same "Y%" (e.g., 50%), the OCV does not match depending on the C rate. And it is obvious that estimating the SOC based on an OCV that includes errors cannot be done accurately.

[0040] In particular, the OCV-SOC curves (charge-discharge curves) of batteries 31 and 32 are known to have plateau regions where they temporarily become flat, as shown in Figure 3. When estimating SOC in such plateau regions, even a small error in OCV can lead to a large error in SOC.

[0041] Furthermore, as shown in Figure 3, the OCV-SOC curve C11, which is the charging curve during charging, and the OCV-SOC curve C13, which is the discharging curve during discharging, do not coincide. In other words, batteries 31 and 32 have hysteresis characteristics. For this reason, it is necessary to estimate the SOC while also considering the hysteresis characteristics of each battery 31 and 32.

[0042] The following describes in detail the various functions of the control device 50 and the various processes performed by the control device 50 in order to estimate the State of Charge (SOC) of each battery 31 and 32 from the OCV of each battery 31 and 32. The various functions related to SOC estimation are realized by the microcontroller of the control device 50 executing a program (charge state estimation program) stored in the memory of the control device 50.

[0043] As shown in Figure 1, various functions related to SOC estimation include, for example, a memory unit 51, a charge / discharge determination unit 52, a charge / discharge control unit 53, an open-circuit voltage acquisition unit 54, and a charge state estimation unit 55. The following describes these functions in detail.

[0044] First, let's explain the memory unit 51. The memory unit 51 stores the charge and discharge history of each battery 31 and 32. The charge and discharge history is a history showing the charge and discharge trends of each battery 31 and 32. For example, the charge and discharge history can be stored as the integrated current value calculated by accumulating the amount of current that has flowed out or into each battery 31 and 32 during the period from the last SOC estimation to the present.

[0045] Here, the storage process for charge and discharge history in this embodiment will be explained with reference to Figure 4. The control device 50, which acts as a storage unit 51, performs storage processing at predetermined intervals. The storage processing is performed for each of the storage batteries 31 and 32. Here, the explanation will focus on the storage processing for the first storage battery 31, but the storage processing for the second storage battery 32 is similar.

[0046] When the memory processing starts, as shown in Figure 4, the control device 50 determines whether the current value of the first battery 31 has remained above the first threshold Th1 for a predetermined time (step S11). Here, the current value is represented by a positive value (plus) when current is flowing into the first battery 31 (i.e., when charging), and by a negative value (minus) when current is flowing out of the first battery 31 (i.e., when discharging). The predetermined time is any time, but for example, it may be the execution cycle of the memory processing. The first threshold Th1 is any positive value.

[0047] In other words, in step S11, it is determined whether the device has been charged to a current amount equal to or greater than the absolute value of the first threshold Th1 multiplied by a predetermined time. If this determination is positive, the control device 50 increments the charge / discharge counter stored in the control device 50's memory (step S12). Then, the memory processing is terminated.

[0048] If the result of step S11 is negative, the control device 50 determines whether the current value of the first storage battery 31 remained below the second threshold Th2 for a predetermined time (step S13). The second threshold Th2 is any negative value. That is, in step S13, it is determined whether the discharge amount was greater than or equal to the absolute value of the second threshold Th2 multiplied by the predetermined time. If this determination result is positive, the control device 50 counts down (subtracts 1) the charge / discharge counter (step S14). Then, it terminates the memory processing.

[0049] On the other hand, if the result of the determination in step S13 is negative, that is, if it cannot be determined that either charging or discharging was performed, the control device 50 decides to maintain the value of the charge / discharge counter (step S15) and terminates the storage process.

[0050] The charge / discharge determination unit 52 determines whether each battery 31, 32 has been charged or discharged based on the charge / discharge history obtained from the memory unit 51. For example, the charge / discharge determination unit 52 determines that the battery has been charged if the integrated current value is within the charging range that indicates a trend after charging, and determines that the battery has been discharged if the integrated current value is within the discharge range that indicates a trend after discharge. If the integrated current value is neither within the charging range nor the discharge range, it determines that the status is unknown.

[0051] In this embodiment, the charge / discharge determination unit 52 determines that charging has occurred if the charge / discharge counter stored by the storage unit 51 is equal to or greater than a first determination value J1, which indicates that it is within the charging range. On the other hand, the charge / discharge determination unit 52 determines that discharge has occurred if the charge / discharge counter is equal to or less than a second determination value J2, which indicates that it is within the discharging range. If the charge / discharge counter is greater than the second determination value J2 and less than the first determination value J1, it determines that the status is unknown.

[0052] If the charge / discharge determination unit 52 determines that the first battery 31 has been charged, the charge / discharge control unit 53 discharges the first battery 31. At this time, the control device 50 discharges the first battery 31 so that the State of Charge (SOC) decreases by a predetermined amount (for example, 5.0%).

[0053] On the other hand, if the charge / discharge control unit 53 determines that the first battery 31 has been discharged, it causes the first battery 31 to be charged. At this time, the control device 50 causes the first battery 31 to be charged so that the State of Charge (SOC) increases by a predetermined amount (for example, 2.5%).

[0054] In this case, the charge amount and discharge amount may be different, as in this embodiment, or they may be the same. Also, the charging and discharging speed (C rate) is predetermined, and in this embodiment, it is carried out at a low rate. The charging and discharging current and C rate are determined through experiments or other means to effectively suppress OCV errors.

[0055] Furthermore, the charge / discharge determination unit 52 of this embodiment performs charging and discharging of the first battery 31 by transferring power between the first battery 31 and the second battery 32. Specifically, the control device 50, acting as the charge / discharge determination unit 52, turns on switches SMRH, SW2~SW4 and controls the inverter 20 to convert (boost) the voltage of the second battery 32. As a result, the discharge power of the second battery 32 is supplied to the first battery 31, and the first battery 31 is charged. Similarly, the control device 50 turns on switches SMRH, SW2~SW4 and controls the inverter 20 to convert the voltage of the first battery 31. As a result, the discharge power of the first battery 31 is supplied to the second battery 32, and the second battery 32 is charged.

[0056] In this embodiment, charging and discharging of the first battery 31 was performed by exchanging power between the first battery 31 and the second battery 32, but this method is not limited to any method that allows for charging and discharging. For example, the first battery 31 may be discharged by connecting a predetermined electrical load to it and supplying power. Alternatively, the first battery 31 may be charged by connecting an external charger 40 or a generator (motor 10, etc.).

[0057] The open-circuit voltage acquisition unit 54 acquires the OCV (open-circuit voltage) of the first battery 31 after the first battery 31 has been charged and discharged by the charge / discharge control unit 53. For example, the open-circuit voltage acquisition unit 54 turns off switches SW1 to SW4 to put the first battery 31 into an unloaded state and acquires the open-circuit voltage of the first battery 31 from the first voltage sensor V11.

[0058] The charge state estimation unit 55 refers to the OCV-SOC curve (charge / discharge curve) which shows the relationship between the OCV of the first battery 31 and the SOC of the first battery 31, and estimates the SOC of the first battery 31 from the OCV of the first battery 31 obtained by the open-circuit voltage acquisition unit 54.

[0059] In this embodiment, as shown in Figure 3, three types of OCV-SOC curves are provided. Specifically, an OCV-SOC curve C11 is provided for charging, an OCV-SOC curve C12 is provided for idle (complete idle), and an OCV-SOC curve C13 is provided for discharging. The OCV-SOC curve C11 is a charging curve that can be obtained as a result of continuously charging the SOC from a specified lower limit to a specified upper limit at a predetermined current (C rate). The OCV-SOC curve C12 is a curve that can be obtained as a result of naturally discharging the SOC from a specified upper limit to a specified lower limit at a predetermined current (C rate). The OCV-SOC curves are determined by simulation or experimentation and are pre-stored in the memory of the control device 50.

[0060] The control device 50, acting as a charge state estimation unit 55, reads the OCV-SOC curve C11 during charging if the charge / discharge determination unit 52 determines that the first battery 31 has been charged. The control device 50 then refers to the OCV-SOC curve C11 and estimates the SOC of the first battery 31 from the OCV of the first battery 31 obtained by the open-circuit voltage acquisition unit 54.

[0061] Furthermore, if the charge / discharge determination unit 52 determines that the first battery 31 has been discharged, the control device 50, acting as the charge state estimation unit 55, reads out the OCV-SOC curve C13 during discharge. The control device 50 then refers to the OCV-SOC curve C13 and estimates the SOC of the first battery 31 from the OCV of the first battery 31 obtained by the open-circuit voltage acquisition unit 54.

[0062] Then, if the charge / discharge determination unit 52 determines that the first battery 31 is neither charged nor discharged, the control device 50 reads out the OCV-SOC curve C12 during the idle period. The control device 50 then refers to the OCV-SOC curve C12 and estimates the SOC of the first battery 31 from the OCV of the first battery 31 obtained by the open-circuit voltage acquisition unit 54.

[0063] Next, the SOC estimation process for estimating the State of Charge (SOC) will be explained with reference to Figure 5. The SOC estimation process is performed by the control device 50 after receiving an SOC estimation instruction signal from the higher-level control device and after the charging and discharging of the first battery 31 is completed. The SOC estimation supply signal is output at a predetermined timing, for example, when the vehicle is stopped.

[0064] When the SOC estimation process is started, as shown in Figure 5, the control device 50 determines whether the charge / discharge counter stored in the memory by the storage unit 51 is greater than or equal to a first determination value J1, which indicates that it is within the charging range (step S101).

[0065] If the result of this determination is positive, the control device 50 discharges the first battery 31 so that the SOC decreases by a predetermined amount (approximately 5.0%) (step S102). After the first battery 31 has been discharged, the control device 50 obtains the OCV of the first battery 31 from the first voltage sensor V11 (step S103).

[0066] Then, the control device 50 refers to the OCV-SOC curve C11 during charging and estimates the SOC of the first battery 31 from the OCV of the first battery 31 obtained in step S103 (step S104). Then, the SOC estimation process is terminated.

[0067] On the other hand, if the determination result in step S101 is negative, the control device 50 determines whether the charge / discharge counter stored in memory by the memory unit 51 is less than or equal to the second determination value J2, which indicates that it is within the discharge range (step S105). If this determination result is positive, the control device 50 charges the first battery 31 so that the SOC increases by a predetermined amount (approximately 2.5%) (step S106). After charging the first battery 31, the control device 50 obtains the OCV of the first battery 31 from the first voltage sensor V11 (step S107).

[0068] Then, the control device 50 refers to the OCV-SOC curve C13 during discharge and estimates the SOC of the first battery 31 from the OCV of the first battery 31 obtained in step S107 (step S108). Then, the SOC estimation process is terminated.

[0069] On the other hand, if the determination result in step S105 is negative, the control device 50 charges the first battery 31 so that the SOC increases by a predetermined amount, and then discharges the first battery 31 so that the SOC decreases by a predetermined amount (step S109). In step S109, it is desirable that the charge amount and the discharge amount are the same, but they may be different. The control device 50 may also discharge the first battery 31 so that the SOC decreases by a predetermined amount, and then charge the first battery 31 so that the SOC increases by a predetermined amount.

[0070] After charging and discharging the first battery 31, the control device 50 obtains the OCV of the first battery 31 from the first voltage sensor V11 (step S110). Then, the control device 50 refers to the OCV-SOC curve C12 during idle time and estimates the SOC of the first battery 31 from the OCV of the first battery 31 obtained in step S110 (step S111). Then, the SOC estimation process ends.

[0071] Steps S101 and S105 correspond to charge / discharge determination processes, and by performing these processes, the control device 50 functions as a charge / discharge determination unit 52. Steps S102, S106, and S109 correspond to charge / discharge control processes, and by performing these processes, the control device 50 functions as a charge / discharge control unit 53. Steps S103, S107, and S110 correspond to open-circuit voltage acquisition processes, and by performing these processes, the control device 50 functions as an open-circuit voltage acquisition unit 54. Steps S104, S108, and S111 correspond to charge state estimation processes, and by performing these processes, the control device 50 functions as a charge state estimation unit 55.

[0072] The flow of the SOC estimation process will be explained using a specific example shown in Figure 6. Here, Figure 6(a) shows the charge and discharge current of the first battery 31. Figure 6(b) shows the increase and decrease patterns of the charge and discharge counter, and Figure 6(c) shows the result when charge and discharge is determined. In Figure 6(c), the positive side (upper side) is determined to be after charging, and the negative side (lower side) is determined to be after discharge. Figure 6(d) shows the OCV acquisition request flag, which is turned on (H level) when the SOC estimation process is started and turned off (L level) when the OCV is acquired. Figure 6(e) shows the charge and discharge completion flag, which is turned off (L level) when the first battery 31 is charging or discharging and turned on (H level) when it is not charging or discharging. Figure 6(f) shows the resolution control flag, which is turned on (H level) when charge and discharge control is requested to suppress OCV errors and turned off (L level) when charge and discharge control is completed. The charge / discharge control for suppressing OCV errors refers, for example, to the control processes in steps S102, S106, and S109. Figure 6(g) shows the OCV acquisition flag, which is ON (H level) during the period from the start to the end of the process for acquiring the OCV (steps S103, S107, S110).

[0073] As shown in Figures 6(a) and 6(b), from time point T1 to time point T10, the charge / discharge counter increases or decreases according to the current value of the charge / discharge current of the first battery 31. For example, at time points T2 to T4 and T7 to T9, the current value of the first battery 31 is continuously greater than or equal to the first threshold Th1, so the charge / discharge counter counts up at predetermined intervals. Similarly, at time points T5 to T6, the current value of the first battery 31 is continuously less than or equal to the second threshold Th2, so the charge / discharge counter counts down at predetermined intervals. At time points T1 to T2, T4 to T5, T6 to T7, and T9 to T10, the current value of the first battery 31 is greater than the second threshold Th2 and less than the first threshold Th1, so the value of the charge / discharge counter is maintained.

[0074] Then, as shown in Figure 6(b), from time T3 onward, the value of the charge / discharge counter becomes equal to or greater than the first determination value J1. Therefore, as shown in Figure 6(c), if a charge / discharge determination is made from time T3 onward, it will be determined that the device has been charged.

[0075] Here, as shown in Figure 6(d), when the SOC estimation instruction signal is input at time T8, the OCV acquisition request flag is turned on. However, as shown in Figures 6(a) and 6(e), since charging and discharging are in progress (the charge / discharge completion flag is not turned on), the SOC estimation process is not started and the device enters a standby state.

[0076] Subsequently, at time T10, when the charging and discharging of the first battery 31 is completed and the charging / discharging completion flag is turned on, the SOC estimation process is started. At the same time, the deactivation control flag is turned on. Then, at time T11, after a predetermined time has elapsed since the charging / discharging completion flag and the deactivation control flag were turned on, charging / discharging control is performed to suppress OCV errors. At this time, as shown in Figure 6(c), it is determined that charging has been completed, so discharging is performed to suppress OCV errors (times T11-T12). Subsequently, at time T13-T14, processing is performed to acquire the OCV. After acquiring the OCV, the SOC is estimated.

[0077] Next, we will explain the effects of this process. As shown in Figure 2(a), even if the SOC immediately after charging is the same "X%", errors occur in OCV depending on the C rate. However, by discharging the battery so that the SOC decreases by a predetermined amount (by moving it to the left in Figure 2(a)), the error in OCV is reduced. This makes it possible to reduce the error in OCV caused by differences in C rate.

[0078] Furthermore, as shown in Figure 2(a), even when it is determined that the first battery 31 has been charged, it is known that the error in OCV can be reduced by charging the first battery 31 in such a way that the SOC increases by a predetermined amount (moves to the right). However, as shown in Figure 2(a), compared to discharging (left side), it is more difficult to eliminate the error when charging (right side), and a larger amount of charging current is required.

[0079] Therefore, in this embodiment, when it is determined that the first storage battery 31 has been charged, it is discharged so that the State of Charge (SOC) decreases by a predetermined amount. This reduces the time required to correct the OCV error and suppresses the amount of SOC fluctuation associated with error correction (or error reduction, hereinafter the same).

[0080] Furthermore, as shown in Figure 2(b), even if the SOC immediately after discharge is the same "Y%", errors occur in OCV depending on the C rate. However, by subsequently charging the battery so that the SOC increases by a predetermined amount, the error in OCV is reduced. This makes it possible to reduce the error in OCV caused by differences in C rate.

[0081] Furthermore, as shown in Figure 2(b), it is known that even when it is determined that the first battery 31 has been discharged, the error in OCV can be reduced by discharging the first battery 31 so that the SOC decreases by a predetermined amount. However, as shown in Figure 2(b), compared to charging, it is more difficult to eliminate errors when discharging, and a larger discharge current is required.

[0082] Therefore, in this embodiment, when it is determined that the first storage battery 31 has been discharged, it is charged in such a way that the State of Charge (SOC) increases by a predetermined amount. This reduces the time required to correct the OCV error and suppresses the amount of SOC fluctuation associated with the error reduction.

[0083] The effects of the power supply system 100 in the first embodiment will be described below. The explanation will focus on the effects when the first battery 31 is the target of measurement, but similar effects can be obtained when the second battery 32 is the target of measurement.

[0084] If the control device 50 determines that the first battery 31 has been charged, it discharges the first battery 31. If it determines that the first battery 31 has been discharged, it charges the first battery 31, and then detects and acquires the OCV of the first battery 31. This makes it possible to suppress the OCV error due to differences in C rate. Since the OCV error can be reduced, the error in the SOC estimated based on the OCV can also be reduced.

[0085] The charge / discharge history is a current integration value calculated by accumulating the current that flows out or into the first battery 31. Specifically, the current integration value is measured by adding 1 to the charge / discharge counter when a predetermined amount of current is charged, and subtracting 1 from the charge / discharge counter when a predetermined amount of current is discharged.

[0086] The control device 50 determines that the battery has been charged if the integrated current value is within the charging range that indicates the trend after charging, and determines that the battery has been discharged if the integrated current value is within the discharge range that indicates the trend after discharging. Specifically, the control device 50 determines that the battery has been charged if the charge / discharge counter is equal to or greater than the first determination value J1, and determines that the battery has been discharged if it is equal to or less than the second determination value J2. This allows the device to make a determination by referring to the charge / discharge history over a certain period of time, thereby accurately determining the usage status of the first storage battery 31.

[0087] If the control device 50 cannot determine from the charge / discharge history whether the battery has been charged or discharged, that is, if the determination result in step S105 is negative, it will either charge the first battery 31 once and then discharge it, or discharge the first battery 31 once and then charge it, as shown in step S109. This makes it possible to suppress errors in OCV due to the C rate even if the usage status of the first battery 31 is unknown.

[0088] As can be seen by comparing Figure 2(a) and Figure 2(b), the OCV error is more difficult to eliminate when discharging after charging (Figure 2(a)) compared to when charging after discharging (Figure 2(b)). Therefore, the control device 50 made the amount of current discharged when it was determined that charging had been completed different from the amount of current discharged when it was determined that charging had been completed. Specifically, as shown in steps S102 and S105, when the control device 50 was determined that charging had been completed, it discharged the battery so that the SOC decreased by about 5.0%, and when it was determined that discharged the battery was completed, it charged the battery so that the SOC increased by about 2.5%. This makes it possible to reduce the amount of current and charging time in step S105 in order to eliminate the OCV error.

[0089] If the control device 50 determines that the first battery 31 has been charged (if the determination result in step S101 is positive), it estimates the SOC by referring to the OCV-SOC curve C11 during charging (step S104). If the control device 50 determines that the first battery 31 has been discharged (if the determination result in step S105 is positive), it estimates the SOC by referring to the OCV-SOC curve C13 during discharge (step S108). If the control device 50 determines that the usage state of the first battery 31 is unknown (if the determination results in steps S101 and S105 are negative), it estimates the SOC by referring to the OCV-SOC curve C12 during idle (step S111). This allows the SOC to be estimated while considering the effect of the hysteresis characteristics of the first battery 31 during charging and discharging, thereby suppressing errors in the SOC.

[0090] (modified version) A modified example in which some of the configurations of the power supply system 100 of the above embodiment are changed will be described below.

[0091] In the above embodiment, the magnitude of the OCV error differs depending on the magnitude of the integrated current value. Therefore, in steps S102 and S105, the control device 50 may determine the amount of current to charge and discharge based on the integrated current value. That is, the control device 50 may increase the amount of current to charge and discharge when the integrated current value is large, and decrease the amount of current to charge and discharge when the integrated current value is small. For example, the control device 50 may increase the amount of current to charge and discharge when the absolute value of the charge / discharge counter indicating the integrated current value is large, compared to when it is small.

[0092] In the above embodiment, the OCV-SOC curve (charge / discharge curve) differs depending on the usage state of the batteries 31 and 32, i.e., the amount of current charged and discharged, due to the hysteresis characteristics of the batteries 31 and 32. Therefore, four or more OCV-SOC curves may be prepared, and an OCV-SOC curve may be associated with each integrated current value, and the associated OCV-SOC curve may be identified from the integrated current value.

[0093] For example, four or more OCV-SOC curves associated with each charge / discharge counter showing the integrated current value may be stored, and in steps S104, S108, and S111, the control device 50 may identify the associated OCV-SOC curve from the value of the charge / discharge counter showing the integrated current value, and estimate the SOC based on the identified charge / discharge curve.

[0094] In the above embodiment, the storage batteries 31 and 32 may be just one or three or more. Also, as shown in Figure 7, DC-DC converters 121 and 122 may be used instead of the motor 10 and inverter 20 to perform voltage conversion. Furthermore, as shown in Figure 8, the storage batteries 31 and 32 may be connected in parallel to the inverter 20 without going through the motor 10.

[0095] In the memory processing of the above embodiment, the results are accumulated, but the decision may be made based on the most recent result. Specifically, the memory processing may be as shown in Figure 9. This will be explained in detail below. When the memory processing of the modified example shown in Figure 9 is started, the control device 50 determines whether the current value of the first storage battery 31 has remained above the first threshold Th1 for a predetermined time (step S21). That is, in step S21, it is determined whether the amount of current represented by the absolute value of the first threshold Th1 multiplied by a predetermined time has been charged. If this determination result is positive, the control device 50 sets a value (for example, 1) indicating that charging has been completed in the charge / discharge counter stored in the memory of the control device 50 (step S22). Then, the memory processing is terminated.

[0096] If the result of step S21 is negative, the control device 50 determines whether the current value of the first storage battery 31 remained below the second threshold Th2 for a predetermined time (step S23). That is, in step S23, it determines whether the amount of current represented by the absolute value of the second threshold Th2 multiplied by the predetermined time has been discharged. If this determination result is positive, the control device 50 sets a value in the charge / discharge counter to indicate that discharge has occurred (for example, -1) (step S24). Then, it terminates the storage process.

[0097] On the other hand, if the determination result in step S23 is negative, that is, if it cannot be determined that either charging or discharging was performed, the control device 50 sets a value indicating unknown (for example, zero) in the charge / discharge counter (step S25) and terminates the memory processing. Then, in the SOC estimation processing wave, based on the value of the charge / discharge counter, it is determined whether it is after charging, after discharging, or unknown, and charge / discharge control and OCV-SOC curve identification are performed. In this way, the charge / discharge history can be stored with simple control.

[0098] In the above embodiment, the integrated current value may be measured using a well-known method and used as the charge / discharge history.

[0099] The control unit and its method described herein may be implemented by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. Alternatively, the control unit and its method described herein may be implemented by a dedicated computer provided by configuring a processor by one or more dedicated hardware logic circuits. Alternatively, the control unit and its method described herein may be implemented by one or more dedicated computers configured by a combination of a processor and memory programmed to perform one or more functions and a processor configured by one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by the computer on a computer-readable non-transitional tangible recording medium.

[0100] The following describes the characteristic configurations extracted from each of the embodiments described above. [Configuration 1] In a charge state estimation device (50) that estimates the charge state of a storage battery, A storage unit (51) that stores the charge and discharge history of the aforementioned storage battery, A charge / discharge determination unit (52) determines whether the battery has been charged or discharged based on the charge / discharge history stored in the memory unit, A charge / discharge control unit (53) that, when the charge / discharge determination unit determines that the battery has been charged, discharges the battery by a predetermined amount, and when the charge / discharge determination unit determines that the battery has been discharged, charges the battery by a predetermined amount, After the battery has been charged and discharged by the charge / discharge control unit, an open-circuit voltage acquisition unit (54) acquires the open-circuit voltage of the battery, A charge state estimation device comprising: a charge state estimation unit (55) that estimates the charge state of the storage battery from the open-circuit voltage acquired by the open-circuit voltage acquisition unit, by referring to a charge-discharge curve showing the relationship between the open-circuit voltage of the storage battery and the charge state of the storage battery. [Configuration 2] The charge-discharge history is a current integration value calculated by accumulating the current that flows out of or into the battery. The charge / discharge determination unit determines that the device is charged if the integrated current value is within the charging range that indicates the trend after charging, and determines that the device is discharged if the integrated current value is within the discharge range that indicates the trend after discharging, according to configuration 1 of the charge state estimation device. [Configuration 3] The charge / discharge control unit determines the amount of current to be used for charging and discharging based on the integrated current value, as described in configuration 2 of the charge state estimation device. [Structure 4] A charge / discharge curve is pre-associated for each of the aforementioned integrated current values. The charge state estimation device according to configuration 2, wherein the charge state estimation unit identifies a charge / discharge curve associated with the current integrated value and estimates the charge state based on the identified charge / discharge curve. [Composition 5] If the charge / discharge determination unit cannot determine from the charge / discharge history whether the battery has been charged or discharged, the charge / discharge control unit may, in any of configurations 1 to 4, charge the battery once and then discharge it by a predetermined amount, or discharge the battery once and then charge the battery by a predetermined amount, thereby estimating the charge state. [Composition 6] The charge state estimation device according to any one of configurations 1 to 5, wherein the charge / discharge control unit determines that the amount of current to be discharged when it is determined that the device has been charged is different from the amount of current to be discharged when it is determined that the device has been charged. [Composition 7] The charge state estimation device according to any one of configurations 1 to 6, wherein the charge state estimation unit estimates the charge state by referring to a charge curve showing the relationship between the open-circuit voltage and the charge state during charging when the charge / discharge determination unit determines that the battery has been charged, and estimates the charge state by referring to a discharge curve showing the relationship between the open-circuit voltage and the charge state during discharge when the charge / discharge determination unit determines that the battery has been discharged. [Structure 8] A charge state estimation system (100) comprising a first storage battery and a second storage battery, which estimates the charge state of the first storage battery and the second storage battery, A storage unit (51) that stores the charge and discharge history of each of the aforementioned storage batteries, A charge / discharge determination unit (52) determines, for each of the storage batteries, whether it has been charged or discharged based on the charge / discharge history stored in the storage unit, A charge / discharge control unit (53) discharges the battery that the charge / discharge determination unit has determined to be charged, while charging the battery that the charge / discharge determination unit has determined to be discharged. After each of the storage batteries has been charged and discharged by the charge / discharge control unit, an open-circuit voltage acquisition unit (54) acquires the open-circuit voltage of each storage battery, The system includes a charge state estimation unit (55) that estimates the charge state of each of the batteries from the open-circuit voltages of each of the batteries obtained by the open-circuit voltage acquisition unit, by referring to a charge / discharge curve showing the relationship between the open-circuit voltage of the battery and the charge state of the battery, The charge / discharge control unit is a charge state estimation system that charges and discharges each of the first and second storage batteries by transferring power between them. [Composition 9] The charge state estimation device (50) A storage process for storing the charge and discharge history of the aforementioned battery, A charge / discharge determination process that determines whether the battery is charging or discharging based on the charge / discharge history stored in the memory unit, If the charge / discharge determination unit determines that the battery is being charged, the battery is discharged; and if the charge / discharge determination unit determines that the battery is being discharged, the battery is charged. After the battery has been charged and discharged by the charge / discharge control unit, an open-circuit voltage acquisition process is performed to acquire the open-circuit voltage of the battery, A charge state estimation program that performs a charge state estimation process, which estimates the charge state of the battery from the open-circuit voltage acquired by the open-circuit voltage acquisition unit, by referring to a charge / discharge curve showing the relationship between the open-circuit voltage of the battery and the charge state of the battery. [Explanation of Symbols]

[0101] 10...Motor, 20...Inverter, 31...First battery, 32...Second battery, 40...External charger, 50...Control device, 51...Memory unit, 52...Charge / discharge determination unit, 53...Charge / discharge control unit, 54...Open circuit voltage acquisition unit, 55...Charge state estimation unit, 100...Power supply system.

Claims

1. In a charge state estimation device (50) that estimates the charge state of a storage battery, A storage unit (51) that stores the charge and discharge history of the aforementioned storage battery, A charge / discharge determination unit (52) determines whether the battery has been charged or discharged based on the charge / discharge history stored in the memory unit, A charge / discharge control unit (53) that, when the charge / discharge determination unit determines that the battery has been charged, discharges the battery by a predetermined amount, and when the charge / discharge determination unit determines that the battery has been discharged, charges the battery by a predetermined amount, After the battery has been charged and discharged by the charge / discharge control unit, an open-circuit voltage acquisition unit (54) acquires the open-circuit voltage of the battery, A charge state estimation device comprising: a charge state estimation unit (55) that estimates the charge state of the storage battery from the open-circuit voltage acquired by the open-circuit voltage acquisition unit, by referring to a charge-discharge curve showing the relationship between the open-circuit voltage of the storage battery and the charge state of the storage battery.

2. The charge-discharge history is a current integration value calculated by accumulating the current that flows out of or into the battery. The charge state estimation device according to claim 1, wherein the charge / discharge determination unit determines that the device is charged if the integrated current value is within a charging range that indicates a trend after charging, and determines that the device is discharged if the integrated current value is within a discharge range that indicates a trend after discharge.

3. The charge state estimation device according to claim 2, wherein the charge / discharge control unit determines the amount of current to be used for charging and discharging based on the integrated current value.

4. A charge / discharge curve is pre-associated for each of the aforementioned integrated current values. The charge state estimation device according to claim 2, wherein the charge state estimation unit identifies a charge / discharge curve associated with the current integrated value and estimates the charge state based on the identified charge / discharge curve.

5. If the charge / discharge determination unit cannot determine from the charge / discharge history whether the battery has been charged or discharged, the charge / discharge control unit charges the battery once and then discharges it by a predetermined amount, or discharges the battery once and then charges the battery by a predetermined amount, according to any one of claims 1 to 4.

6. The charge state estimation device according to any one of claims 1 to 4, wherein the charge / discharge control unit determines that the amount of current to be discharged when it is determined that the device has been charged is different from the amount of current to be discharged when it is determined that the device has been charged.

7. The charge state estimation device according to any one of claims 1 to 3, wherein the charge state estimation unit estimates the charge state by referring to a charge curve showing the relationship between the open-circuit voltage and the charge state during charging when the charge / discharge determination unit determines that the storage battery has been charged, and estimates the charge state by referring to a discharge curve showing the relationship between the open-circuit voltage and the charge state during discharge when the charge / discharge determination unit determines that the storage battery has been discharged.

8. A charge state estimation system (100) comprising a first storage battery and a second storage battery, which estimates the charge state of the first storage battery and the second storage battery, A storage unit (51) that stores the charge and discharge history of each of the aforementioned storage batteries, A charge / discharge determination unit (52) determines whether each of the storage batteries has been charged or discharged based on the charge / discharge history stored in the storage unit, A charge / discharge control unit (53) discharges the battery that the charge / discharge determination unit has determined to be charged, while charging the battery that the charge / discharge determination unit has determined to be discharged. After each of the batteries has been charged and discharged by the charge / discharge control unit, an open-circuit voltage acquisition unit (54) acquires the open-circuit voltage of each battery, The system includes a charge state estimation unit (55) that estimates the charge state of each of the batteries from the open-circuit voltages of each of the batteries obtained by the open-circuit voltage acquisition unit, by referring to a charge / discharge curve showing the relationship between the open-circuit voltage of the battery and the charge state of the battery, The charge / discharge control unit is a charge state estimation system that charges and discharges each of the first and second storage batteries by transferring power between them.

9. A charge state estimation device (50) that estimates the charge state of a storage battery, A storage process for storing the charge and discharge history of the aforementioned battery, A charge / discharge determination process that determines whether the battery has been charged or discharged based on the charge / discharge history stored by the memory process, If the charge / discharge determination process determines that the battery has been charged, the charge / discharge control process discharges the battery; if the charge / discharge determination process determines that the battery has been discharged, the charge / discharge control process charges the battery. After the battery has been charged and discharged by the charge / discharge control process, an open-circuit voltage acquisition process is performed to acquire the open-circuit voltage of the battery. A charge state estimation program that performs a charge state estimation process, which estimates the charge state of the battery from the open-circuit voltage obtained by the open-circuit voltage acquisition process, by referring to a charge / discharge curve showing the relationship between the open-circuit voltage of the battery and the charge state of the battery.

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