Battery state estimation apparatus, battery state estimation method, battery state estimation program, and battery pack

Abstract

An acquisition unit 15 acquires measured voltage and current of a secondary battery E1. A first SOC estimation unit 16 estimates a change in a first SOC at least up to the start of CV charging during CCCV charging of the secondary battery E1. A second SOC estimation unit 17 increases a second SOC for a CV charging section in correspondence with the pace of an increase in the current-time product of current curve characteristics, as a change in the second SOC from the SOC of the secondary battery E1 when CV charging is started to the SOC when a full charge is reached.

Description

Battery State Estimation Device, Battery State Estimation Method, Battery State Estimation Program, and Battery Pack 【0001】 The present disclosure relates to a battery state estimation device, a battery state estimation method, a battery state estimation program, and a battery pack for estimating the State Of Charge (SOC) of a secondary battery. 【0002】 Battery packs are used as power sources for electric mobility such as pedelecs and electric bicycles. A hand switch of a general electric mobility is equipped with a liquid crystal display, and the remaining amount of the battery pack is displayed as a numerical value (0 - 100%) on the liquid crystal display. Generally, the SOC of a battery pack is estimated by the current integration method, the OCV method using the SOC - OCV (Open Circuit Voltage) curve, or a combination of both. Errors occur in the SOC estimated by these methods, and an error close to 5% may occur. 【0003】 When the SOC estimation accuracy is low, SOC jumps and SOC holds occur. During charging, an SOC jump is a case where an error occurs in the downward direction of the SOC estimated value with respect to the true value. For example, it refers to a phenomenon where the SOC display value directly changes from a value of SOC 98% or less to 100%. During charging, an SOC hold is a case where an error occurs in the upward direction of the SOC estimated value with respect to the true value. For example, it refers to a phenomenon where the SOC display value sticks to 100% or exceeds 100% before the SOC display value reaches full charge. When an SOC jump or an SOC hold occurs in the SOC display value, it appears unnatural to the user. 【0004】 In addition, since the conditions for determining that full charge has been reached vary due to individual differences in the battery state and charger, it is difficult to match the timing of reaching full charge and the timing of the SOC estimated value reaching 100% even if the SOC estimation accuracy is improved. 【0005】Patent Document 1 discloses a method for calculating the current charge rate S [%] when the current voltage V of the battery is located between the first voltage V1 and the second voltage V2 when the battery is fully charged, in order to avoid unnatural operation from the user's perspective, using the following formula (Equation 1): S = X + (100 - X) × (V - V2) ÷ (V1 - V2) ... (Equation 1) The charge rate X is a value calculated by integrating the charge rate of 100 percent when the battery is fully charged and the current when the current voltage V becomes equal to the second voltage V2. 【0006】 This method is effective during CC (Constant Current) charging, but during CV (Constant Voltage) charging, the SOC hardly changes, and the increase in SOC becomes unnatural. 【0007】 Japanese Patent Publication No. 2016-080616 【0008】 This disclosure is made in light of these circumstances, and its purpose is to provide a technology that allows the SOC (State of Charge) of a secondary battery to increase naturally until it is fully charged. 【0009】 To solve the above problems, a battery state estimation device according to one embodiment of the present disclosure includes: an acquisition unit that acquires measured voltage and current of a secondary battery; a first SOC estimation unit that estimates the transition of a first SOC at least until the start of CV charging during CCCV charging of the secondary battery; and a second SOC estimation unit that maintains the current curve characteristics during CV charging of the secondary battery and increases the second SOC in accordance with the rate of increase of the current-time product of the current curve characteristics as the transition of a second SOC in the CV charging section from the SOC at the start of CV charging to the SOC at the time of full charge. 【0010】 Furthermore, any combination of the above components, as well as any conversion of the expressions of this disclosure between devices, systems, methods, computer programs, etc., are also valid forms of this disclosure. 【0011】 According to this disclosure, the State of Charge (SOC) for displaying the secondary battery can be naturally increased until it is fully charged. 【0012】This figure shows an example of the configuration of a battery pack and vehicle according to an embodiment. This figure shows an example of the operation display unit. This figure shows an example of the behavior of the charging voltage, charging current, and SOC during CCCV charging of the battery pack. This figure shows an example of the current curve characteristics during CV charging. This figure shows an example of the SOC behavior when the first SOC estimate is lower than the true SOC value at the start of CV charging of the battery pack according to this embodiment. This figure shows an example of the SOC behavior when the first SOC estimate is higher than the true SOC value at the start of CV charging of the battery pack according to this embodiment. This figure shows an example of the SOC and cell voltage behavior when the first SOC estimate is extremely higher than the true SOC value at the start of CV charging of the battery pack according to this embodiment. This flowchart shows the flow of the first operation example during CCCV charging of the battery pack according to this embodiment. This flowchart shows the flow of the second operation example during CCCV charging of the battery pack according to this embodiment. This figure shows an example of the behavior of the cell voltage and charging current during CC-pseudo-CV charging of the battery pack according to a modified example. 【0013】 Figure 1 shows an example configuration of a battery pack 10 and a vehicle 20 according to an embodiment. Hereinafter, in this embodiment, the vehicle 20 is assumed to be a Pederec. The battery pack 10 may be a battery pack 10 fixed to the vehicle 20, or it may be a detachable, portable, and replaceable battery pack 10. When charging the battery pack 10, in the former case, the battery pack 10 and the charger 30 are connected by a charging cable. In the latter case, the battery pack 10 is removed from the mounting slot of the vehicle 20 and mounted in the mounting slot of the charger 30. In the following description, the former case will be assumed. 【0014】 The vehicle 20 includes a motor 21, an inverter 22, a control unit 23, and an operation display unit 24. A three-phase AC motor is used for the motor 21. During acceleration, the inverter 22 converts the DC power supplied from the battery pack 10 into AC power and supplies it to the motor 21. During regeneration, it converts the AC power supplied from the motor 21 into DC power and supplies it to the battery pack 10. During acceleration, the motor 21 rotates in accordance with the AC power supplied from the inverter 22. During regeneration, it converts the rotational energy due to deceleration into AC power and supplies it to the inverter 22. 【0015】 The control unit 23 is a microcontroller that controls the entire vehicle 20. The control unit 23 of the vehicle 20 is connected to the control unit 14 of the battery pack 10 via a communication line L2. The operation display unit 24 is provided on a hand switch fixed to the steering wheel. 【0016】 Figure 2 shows an example of the operation display unit 24. The operation display unit 24 includes a display unit 24a composed of a liquid crystal display, an organic EL display, a mini LED display, etc., and various operation buttons (power button, light button, mode switching button, assist switching button, etc.). The control unit 23 of the vehicle 20 can display the State of Control (SOC) of the battery pack 10, received from the control unit 14 of the battery pack 10, as a digital value on the display unit 24a. 【0017】 Returning to Figure 1, the battery pack 10 includes a battery module 11 and a battery management device 12. The battery module 11 includes a plurality of cells E1-En connected in series. The number of cells in series is determined by the specifications of the vehicle 20. For example, if the vehicle 20 is a pederec, a battery module 11 containing approximately 7-14 cells in series is used. Lithium-ion battery cells, nickel-metal hydride battery cells, lead-acid battery cells, etc., can be used for the cells. Hereinafter, this specification assumes the use of lithium-ion battery cells (nominal voltage: 3.6-3.7V). 【0018】 A power line L1 for supplying power to the vehicle 20 is connected to the discharge terminal Td of the battery pack 10. A discharge switch Q1 and a charge switch Q2 are inserted into the positive power line L1 that connects the positive terminal of the discharge terminal Td of the battery pack 10 and the positive terminal of the battery module 11 inside the battery pack 10. 【0019】 In this embodiment, N-channel MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are used for the discharge switch Q1 and the charge switch Q2, respectively. In an N-channel MOSFET, a parasitic diode is formed in the direction from source to drain. By connecting two N-channel MOSFETs in series in opposite directions, the current passing through the parasitic diode is blocked, and a bidirectional switch can be configured. 【0020】 When charging the battery pack 10, the charging terminal Tc of the battery pack 10 and the charger 30 are connected by a charging cable L3. The positive terminal of the charging terminal Tc of the battery pack 10 is connected by an internal charging wire to the connection point N1 between the discharge switch Q1 and the charge switch Q2. 【0021】 By turning off the discharge switch Q1, the discharge current from the battery module 11 to the vehicle 20 can be interrupted, and by turning off the charge switch Q2, the charging current from the charger 30 to the battery module 11 or the regenerative current from the vehicle 20 can be interrupted. 【0022】 The battery management device 12 is composed of multiple circuit components, including an IC, and these multiple circuit components are mounted on a circuit board. In this embodiment, we will focus on the SOC estimation function of the battery management device 12, and therefore, in this specification, the battery management device 12 is also referred to as a battery state estimation device. 【0023】 The battery management device 12 includes a measurement unit 13 and a control unit 14. The measurement unit 13 is composed of an AFE (Analog Front End) IC or an ASIC (Application Specific Integrated Circuit). The measurement unit 13 is connected to each node of a plurality of series-connected cells E1-En by a plurality of voltage measurement lines, and measures the voltage of each cell E1-En by measuring the voltage between two adjacent voltage measurement lines. 【0024】 The measurement unit 13 includes a multiplexer and an A / D converter. The multiplexer outputs the measured voltages of multiple cells E1-En in a predetermined order to the A / D converter. The A / D converter converts the analog measured voltages input from the multiplexer into digital values. The measurement unit 13 transmits the voltage values ​​of each cell E1-En, which have been converted into digital values, to the control unit 14 via a communication interface. 【0025】The measurement unit 13 can measure the current flowing through the battery module 11. A shunt resistor Rs is connected to the power line L1. A differential amplifier (not shown) amplifies the voltage across the shunt resistor Rs and outputs it to the A / D converter in the measurement unit 13. The A / D converter converts the analog voltage indicating the current flowing through the battery module 11, which is input from the differential amplifier, into a digital value. The measurement unit 13 transmits the digitally converted current value to the control unit 14 via a communication interface. A Hall element may be used instead of the shunt resistor Rs. 【0026】 At least one thermistor T1 is installed on the surface of the battery module 11. The thermistor T1 is a temperature-sensitive element whose resistance changes according to temperature. The voltage divided by the thermistor T1 and a voltage divider resistor (not shown) is output to the A / D converter in the measurement unit 13. The A / D converter converts the analog voltage indicating the surface temperature of the battery module 11, which is input from the voltage division point, into a digital value. The measurement unit 13 transmits the temperature value converted into a digital value to the control unit 14 via a communication interface. 【0027】 The control unit 14 is composed of a microcontroller, which performs the following functions by executing a firmware program. The control unit 14 includes an acquisition unit 15, a first SOC estimation unit 16, a second SOC estimation unit 17, a display SOC setting unit 18, and a switch control unit (not shown). 【0028】 The acquisition unit 15 acquires the voltage value of each cell E1-En included in the battery module 11, the current value flowing through the battery module 11, and the temperature value of the battery module 11 from the measurement unit 13. 【0029】 The switch control unit controls the conduction / interruption of the power line L1. When the switch control unit detects any of the following from the voltage, current, and temperature values ​​of each cell E1-En acquired by the acquisition unit 15: overcharge, overdischarge, overcurrent, high temperature abnormality, or low temperature abnormality, it sends an interruption signal for the discharge switch Q1 and the charge switch Q2 to the measurement unit 13, causing the discharge switch Q1 and the charge switch Q2 to turn off. 【0030】The first SOC estimation unit 16 estimates the first SOC of each cell E1-En based on the voltage and current values ​​acquired by the acquisition unit 15, using at least one of the current integration method or the OCV method using the cell's SOC-OCV curve. The current integration method is a method of estimating the SOC based on the OCV at the start of charging and discharging of the cell and the integrated value of the measured current. 【0031】 The cell's SOC-OCV curve is the same as that of cell E1-En included in the battery module 11. It is pre-created based on characteristic tests conducted by the battery manufacturer and registered in the control unit 14 (specifically, the ROM in the microcontroller) at the time of shipment. 【0032】 The first SOC estimation unit 16 estimates the cell's State of Core (SOC) from the measured voltage (OCV) and by referring to the cell's SOC-OCV curve when the cell is in a dormant state. The first SOC estimation unit 16 also estimates the cell's SOC during charging and discharging based on the cell's equivalent circuit model and the OCV method. 【0033】 The first SOC estimation unit 16 estimates the OCV of a cell based on the voltage (CCV(t)) and current I(t) measured at time t of the cell, using, for example, the simplified equivalent circuit model shown in (Equation 2) below. OCV = CCV(t) - I(t) * Ri ... (Equation 2) Ri is the internal resistance (ohmic resistance component) 【0034】 In the simplified equivalent circuit model defined above (Equation 2), only a DC resistor describing the ohmic resistance component is included. However, in a more detailed equivalent circuit model, in addition to the DC resistor, one or more stages of RC parallel circuits describing the non-ohmic resistance component (transient polarization characteristics) are added. The first SOC estimation unit 16 estimates the cell's SOC from the estimated OCV by referring to the cell's SOC-OCV curve. 【0035】In the current integration method described above, measurement errors in the current accumulate as the charge and discharge time increases. In the OCV method, the SOC-OCV curve is deformed due to the effects of cell degradation and temperature. Therefore, it is preferable for the first SOC estimation unit 16 to estimate the first SOC by taking a weighted average of the SOC estimated by the current integration method and the SOC estimated by the OCV method. 【0036】 The first SOC estimation unit 16 estimates the first SOC of each of the multiple cells E1-En when the battery pack 10 is being charged, and sets the first SOC with the largest value among them as the first SOC of the battery pack 10. 【0037】 This embodiment focuses on the scenario in which the battery pack 10 is CCCV charged from the charger 30. The charger 30 includes a rectifier that rectifies the AC voltage supplied from the commercial power grid (not shown) into a DC voltage, a smoothing filter that smooths the rectified DC voltage, a DC / DC converter capable of controlling the voltage or current of the DC power, and a control unit. A communication line L4 is included in the charging cable L3 connecting the battery pack 10 and the charger 30, and the control unit of the charger 30 is connected to the control unit 14 of the battery pack 10 via the communication line L4. 【0038】 The control unit of the charger 30 receives voltage and current values ​​from the control unit 14 of the battery pack 10. During charging, the control unit 14 of the battery pack 10 transmits the maximum value among the voltage values ​​of the multiple cells E1-En to the control unit of the charger 30. When charging the battery pack 10, the control unit of the charger 30 sets a preset current value as a current command value in the DC / DC converter and performs CC charging of the battery pack 10. 【0039】 The control unit of the charger 30 switches from CC charging to CV charging when the voltage value received from the control unit 14 of the battery pack 10 reaches a set voltage value. The control unit of the charger 30 sets the set voltage value as a voltage command value in the DC / DC converter and CV charges the battery pack 10. The set voltage value may be set to the full charge voltage value, a predetermined value lower than the full charge voltage value, or a predetermined value higher than the full charge voltage value, taking into account the wiring resistance. 【0040】When the current value received by the control unit of the charger 30 from the control unit 14 of the battery pack 10 reaches the charge termination current value, the charging of the battery pack 10 is terminated. The charge termination current value may be set to 0 A, or may be set to a current value that is a predetermined value higher than 0 A. 【0041】 Incidentally, the charger 30 may be configured to be built into the battery pack 10. In that case, when charging the battery pack 10, the battery pack 10 and an AC outlet (not shown) installed outdoors or indoors are connected by an AC charging cable, and charging can be performed with alternating current. 【0042】 The second SOC estimation unit 17 holds the current curve characteristics (see FIG. 4 described later) during CV charging with the CC charging current as the initial value when the cells are charged in CCCV. The second SOC estimation unit 17 increases the second SOC in accordance with the increase pace of the current time integral of the current curve characteristics as the transition of the second SOC in the CV charging section from the SOC at the start of CV charging to the SOC at the arrival of full charge. 【0043】 The second SOC estimation unit 17 estimates the second SOC of each of the plurality of cells E1 - En during CV charging of the battery pack 10, and sets the second SOC with the largest value among them as the second SOC of the battery pack 10. 【0044】 When the plurality of cells E1 - En included in the battery module 11 are charged in CCCV, the display SOC setting unit 18 sets the first SOC estimated by the first SOC estimation unit 16 in the CC charging section as the display SOC, and sets the second SOC estimated by the second SOC estimation unit 17 in the CV charging section as the display SOC. 【0045】 The display SOC setting unit 18 transmits the set display SOC to the control unit 23 of the vehicle 20 via the communication line L2. The control unit 23 of the vehicle 20 causes the display unit 24a to display the display SOC of the battery pack 10 received from the control unit 14 of the battery pack 10. 【0046】Figure 3 shows an example of the behavior of the charging voltage, charging current, and SOC during CCCV charging of the battery pack 10. The SOC estimated value shown in Figure 3 represents the SOC estimated by the first SOC estimation unit 16. If the SOC estimated value is lower than the true SOC value, the SOC estimated value will fall below 100% when the true SOC value reaches 100%. If the SOC estimated value at that point is 98% or less, the SOC estimated value will switch to 100% upon reaching full charge, causing an SOC jump. 【0047】 If the SOC estimate is higher than the true SOC value, the SOC estimate may reach 100% before the true SOC value reaches 100%, and may remain stuck at 100%. If the user sees the 100% battery indicator and disconnects the charging cable L3, charging may end before the battery pack 10 is fully charged. 【0048】 Therefore, in this embodiment, this problem is solved by displaying the second SOC estimated by the second SOC estimation unit 17 during the CV charging section near full charge. 【0049】 Figure 4 shows an example of the current curve characteristics during CV charging. The designer obtains the current curve characteristics during CV charging of a cell of the same type as cell E1-En included in the battery module 11 through experimentation or simulation beforehand. The current value at the start of CV charging is the set current value for CC charging. 【0050】 The designer divides the acquired current curve into n (where n is an integer greater than or equal to 2) regions such that the current-time product (area) is equal. Figure 4 shows an example of dividing the current curve into 10 regions. Each region of the current-time product corresponds to the unit increase in SOC. Note that the current-time product (area) does not necessarily have to be divided into exactly equal regions; it is sufficient if the values ​​(areas) of each current-time product (area) are approximate. Furthermore, even if the values ​​(areas) of the current-time product (area) are not equal or approximate, it is sufficient if the relationship between the charging current value and the SOC increase rate corresponds to the current curve characteristics during CV charging. Specifically, even if the ratio of each area in Figure 4 is not equal, such as 1:1:1:...:1, but for example, 1:3:1.7:...:2, it is sufficient if the SOC increase rate corresponds. 【0051】The designer creates a current-SOC growth rate table that describes the relationship between the current value In at the start of each current-time product region obtained by equally dividing the current curve and the SOC growth rate Kn. The pre-prepared current-SOC growth rate table is registered in the control unit 14 (specifically, the ROM in the microcontroller) at the time of shipment. 【0052】 The second SOC estimation unit 17 obtains the SOC increase rate Kn from the current value flowing through the battery module 11 by referring to the current-SOC increase rate table in the CV charging section. The second SOC estimation unit 17 estimates the second SOC from the SOC increase rate Kn using the following equation (Equation 3). The initial value of the SOC in the CV charging section is the SOC ＣＶ０ This is the first SOC estimated by the first SOC estimation unit 16 at the start of CV charging, and it fluctuates depending on the degradation state of the cell and the charging environment. Second SOC = SOC ＣＶ０ + (100 - SOC) ＣＶ０ )×Kn...(Formula 3) 【0053】 The second SOC estimation unit 17 can recognize the start of CV charging by detecting at least one of the following: (1) receiving a notification of switching from the charger 30 to CV charging, (2) the measured voltage value reaching the full charge voltage, or (3) the measured current value falling from the set current value for CC charging. 【0054】 Figure 4 shows SOC ＣＶ０ This example shows the case where the charge level is 90%. The remaining SOC until full charge is 10%, and since the area of ​​the current curve is divided into 10 equal parts, each current-time product region corresponds to 1% of the SOC. The SOC growth rate Kn increases by 0.1 for each region of the current-time product that is advanced. If the area of ​​the current curve is divided into 20 equal parts, the SOC growth rate Kn increases by 0.05 for each region of the current-time product that is advanced. 【0055】 The second SOC estimation unit 17 can change the second SOC more smoothly by interpolating the current value In between two adjacent SOC increase rates Kn. 【0056】Figure 5 shows an example of SOC behavior according to this embodiment when the first SOC estimate is lower than the true SOC value at the start of CV charging of the battery pack 10. After the start of CV charging, the second SOC estimate increases at a faster pace than the true SOC value and the first SOC estimate, reaching 100% at the same time as the true SOC value. The second SOC estimate increases smoothly, and no SOC jumps occur. 【0057】 Figure 6 shows an example of SOC behavior according to this embodiment when the first SOC estimate is higher than the true SOC value at the start of CV charging of the battery pack 10. After the start of CV charging, the second SOC estimate increases at a slower pace than the true SOC value and the first SOC estimate, and reaches 100% at the same time as the true SOC value. Therefore, the second SOC estimate does not become fixed at 100% before the true SOC value reaches 100%. 【0058】 Up to this point, an example has been described in which the second SOC is set as the display SOC in the CV charging section. In this regard, the first SOC estimation unit 16 may use the second SOC in the CV charging section to correct the first SOC so that the first SOC approaches the second SOC. In this case, the display SOC setting unit 18 sets the corrected first SOC as the display SOC in the CV charging section. 【0059】 For example, the first SOC estimation unit 16 may use the weighted average value of the first SOC and the second SOC as the correction value for the first SOC in the CV charging section. Alternatively, the first SOC estimation unit 16 may compare the first SOC and the second SOC in the CV charging section, and if the first SOC is greater than the second SOC, it may calculate the correction value for the first SOC by multiplying the first SOC by a predetermined deceleration coefficient, and if the first SOC is smaller than the second SOC, it may calculate the correction value for the first SOC by multiplying the first SOC by a predetermined acceleration coefficient. 【0060】 When the first SOC estimate is significantly higher than the true SOC, there is a possibility that the first SOC estimate may reach 100% before CV charging begins. In such cases, the following control measures will be implemented. 【0061】When the first SOC reaches a preset SOCcv (for example, 80%) (hereinafter referred to as CV charging start SOCcv) corresponding to the set voltage at which CV charging should begin (CC charging section) before CV charging begins (CC charging section), the first SOC estimation unit 16 slows down the rate at which the first SOC increases so that the first SOC becomes less than 100% when the voltage measured by the measurement unit 13 reaches the set voltage. 【0062】 For example, the first SOC estimation unit 16 estimates the voltage at which the first SOC reaches 100% (hereinafter referred to as the virtual full charge voltage) at the current SOC increase rate. The first SOC estimation unit 16 sets the second virtual CV charging start voltage between the measured voltage when the CV charging start SOC cv is reached (hereinafter referred to as the first virtual CV charging start voltage) and the virtual full charge voltage (for example, at the halfway point between the two). The first SOC estimation unit 16 calculates the first voltage difference between the first virtual CV charging start voltage and the second virtual CV charging start voltage. 【0063】 The first SOC estimation unit 16 calculates a second voltage difference between the first CV virtual charging start voltage and the set voltage (true charging start voltage). The first SOC estimation unit 16 slows down the rate of increase of the first SOC by multiplying the first SOC by the ratio of the first voltage difference to the second voltage difference. 【0064】 Furthermore, if the first SOC reaches the CV charging start SOC cv before CV charging starts, the first SOC estimation unit 16 may simply reduce the current SOC increase rate to half the increase rate. The first SOC estimation unit 16 may set a larger reduction rate the higher the first virtual CV charging start voltage is. Furthermore, the CV charging start SOC cv may be reduced in accordance with the degradation of the cell. 【0065】Figure 7 shows an example of the behavior of SOC and cell voltage when the first SOC estimate is extremely high compared to the true SOC value at the start of CV charging of the battery pack 10 according to this embodiment. When the first SOC reaches CV charging start SOCcv before CV charging starts, the first SOC estimation unit 16 calculates the first SOC using, for example, the following equation (Equation 4). This example shows that the first SOC is increased in accordance with the voltage change rate so that it is half the rate of increase up to that point in the section from CV charging start SOCcv to 100%. First SOC = SOCcv + (100 - SOCcv) / 2 × (V - Vcv) / (Vfc - Vcv) ... (Equation 4) V: measured voltage, Vfc: fully charged voltage, Vcv: voltage corresponding to CV charging start SOCcv. 【0066】 By adding control to slow down the rate of increase of the first SOC in this way, the first SOC at the start of CV charging can be kept below 100%. After the start of CV charging, SOC skipping and SOC holding can be avoided by applying the control using the second SOC as described above. 【0067】 Figure 8 is a flowchart showing the flow of a first operation example during CCCV charging of the battery pack 10 according to this embodiment. The acquisition unit 15 acquires the voltage and current values ​​of each cell E1-En included in the battery module 11 from the measurement unit 13 (S10). The maximum value of the voltage of each cell E1-En is treated as the voltage value of the battery pack 10. The first SOC estimation unit 16 estimates the first SOC based on the acquired voltage and current values ​​of the battery pack 10 (S11). The display SOC setting unit 18 notifies the control unit 23 of the vehicle 20 of the first SOC as the display SOC (S12). 【0068】If the voltage value of the battery pack 10 is less than the set voltage value (N in S13), the system proceeds to step S10. If the voltage value of the battery pack 10 becomes equal to or greater than the set voltage (Y in S13), the system proceeds to step S14. The acquisition unit 15 acquires the voltage and current values ​​of each cell E1-En from the measurement unit 13 (S14). The maximum voltage value of each cell E1-En is treated as the voltage value of the battery pack 10. The second SOC estimation unit 17 estimates the second SOC based on the current-SOC increase rate table and the acquired current value of the battery pack 10 (S15). The display SOC setting unit 18 notifies the control unit 23 of the vehicle 20 of the second SOC as the display SOC (S16). 【0069】 If the current value of the battery pack 10 is greater than the charging termination current value (N in S17), the process proceeds to step S14. When the current value of the battery pack 10 becomes less than or equal to the charging termination current value (Y in S17), CCCV charging is terminated. 【0070】 Figure 9 is a flowchart showing the flow of a second operation example during CCCV charging of the battery pack 10 according to this embodiment. The processing from step S20 to step S23 is the same as the processing from step S10 to step S13 in the first operation example. 【0071】 The acquisition unit 15 acquires the voltage and current values ​​of each cell E1-En from the measurement unit 13 (S24). The maximum voltage value of each cell E1-En is treated as the voltage value of the battery pack 10. The first SOC estimation unit 16 estimates the first SOC based on the acquired voltage and current values ​​of the battery pack 10, and the second SOC estimation unit 17 estimates the second SOC based on the current-SOC increase rate table and the acquired current value of the battery pack 10 (S25). The first SOC estimation unit 16 corrects the first SOC using the second SOC (S26). The display SOC setting unit 18 notifies the control unit 23 of the vehicle 20 of the corrected first SOC as the display SOC (S27). 【0072】 If the current value of the battery pack 10 is greater than the charging termination current value (N in S28), the process proceeds to step S24. When the current value of the battery pack 10 falls below the charging termination current value (Y in S28), CCCV charging is terminated. 【0073】As described above, according to this embodiment, by using the current-SOC increase rate table and the remaining SOC from the start of CV charging to control the SOC increase rate in the CV charging section, the display SOC of the battery pack 10 during CCCV charging can be naturally increased to full charge. 【0074】 The present disclosure has been described above based on embodiments. The embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of their components and processing processes, and that such modifications are also within the scope of the present disclosure. 【0075】 For example, the following equation (5) may be used instead of the above equation (3). Second SOC = SOC ＣＶ０ +(100+α-SOC ＣＶ０ )×Kn...(Formula 5) 【0076】 The second SOC estimation unit 17 sets the SOC at full charge to a value greater than 100 (100 + α), and the SOC at the start of CV charging ＣＶ０ The second SOC is estimated for the CV charging section from the SOC at full charge (100 + α). In this case, it is desirable that the first SOC estimation unit 17 also estimates the first SOC by setting the SOC at full charge to a value greater than 100 (100 + α). α may be set to, for example, 0.5. 【0077】 For example, if the discharge switch Q1 and charge switch Q2 are turned off when the SOC of the battery pack 10 reaches 100%, then when the SOC of the battery pack 10 reaches 100%, the power to the control unit 23 and the operation display unit 24 will be lost, and the battery level display on the display unit 24a will switch from 99% to 100% and at the same time the battery level display will disappear. By setting the SOC at full charge to a value greater than 100, it is possible to ensure that the user has time to confirm that the battery level has reached 100%. 【0078】In the embodiment described above, an example was explained in which the display unit 24a displays the display SOC as a digital value. However, in some cases, a battery level indicator consisting of multiple LED lamps whose number of lights changes according to the remaining battery level may be used in place of the display unit 24a on the hand switch. In that case as well, by controlling the lighting state of the battery level indicator using the display SOC according to this embodiment, it is possible to avoid SOC hold. This makes it possible to avoid a situation in which the charging cable L3 is disconnected by the user before the battery pack 10 is fully charged. 【0079】 In the embodiment described above, an example was explained in which a current-SOC growth rate table was created to describe the relationship between the current value In at the start of each current-time product region obtained by equally dividing the current curve during CV charging, and the SOC growth rate Kn. In this regard, it may also be defined as a current-SOC growth rate function with current as the explanatory variable and SOC growth rate as the dependent variable. The designer obtains many plots of current and SOC growth rate during CV charging of cells of the same type as cells E1-En included in the battery module 11 through experiments or simulations in advance, generates an approximate curve, and derives the current-SOC growth rate function. 【0080】 Figure 10 shows an example of the behavior of cell voltage and charging current during CC-pseudo-CV charging of the battery pack 10, according to a modified example. When a charger 30 that does not support CV charging is used, multi-stage CC charging may be used as pseudo-CV charging. The finer the step width of the multi-stage CC charging, the closer it approaches the characteristics of CV charging. 【0081】When the first SOC reaches the CV charging start SOC cv, the control unit of the charger 30 switches from CC charging to multi-stage CC charging. In multi-stage CC charging, the control unit of the charger 30 reduces the CC charging current value by a predetermined step width each time the cell voltage reaches the full charge voltage Vfc. As the current decreases, the IR component decreases, and the cell voltage decreases accordingly. Also, as the CC charging current value decreases, the rate of increase of the first SOC, estimated using the current integration method, slows down. When the CC charging current value reaches the charging termination current, the first SOC estimation unit 16 increases the first SOC in accordance with the voltage increase. For example, the first SOC estimation unit 16 calculates the first SOC using the above equation (4), after replacing the voltage Vcv corresponding to the CV charging start SOC cv in (Equation 4) with the voltage at the time the CC charging current value reaches the charging termination current. 【0082】 When a detachable, portable, and replaceable battery pack 10 is used, a remaining charge indicator is often installed on the battery pack 10. In this case as well, by controlling the illumination state of the remaining charge indicator using the display SOC according to this embodiment, SOC hold can be avoided. This prevents the situation in which the battery pack 10 is removed from the charger 30 by the user before it is fully charged. 【0083】 The above-described embodiment assumes a State of Condition (SOC) display for a battery pack 10 mounted on a Pedelec. However, this disclosure can also be applied to the SOC display of battery packs 10 mounted on other electric mobility devices such as electric motorcycles, electric kick scooters, EVs, HVs, ultra-compact EVs, hybrid railway vehicles, and multicopters. Furthermore, this disclosure can also be applied to the SOC display of battery packs 10 mounted on information terminals (e.g., smartphones, tablets, and notebook PCs). In addition, this disclosure can be applied to any device that incorporates a battery pack 10, such as electric shavers, electric toothbrushes, wireless earphones, wireless headphones, portable game consoles, and mobile batteries. In this case, the controller on which the battery state estimation program related to this disclosure is installed may be a controller within the battery pack 10 or a controller on the device itself. 【0084】The embodiments may be specified by the following items. 【0085】[Item 1] A battery state estimation device (12) comprising: an acquisition unit that acquires the measured voltage and current of a secondary battery (E1); a first SOC estimation unit (16) that estimates the transition of a first SOC from the start of CCCV charging of the secondary battery (E1) until the start of CV charging; and a second SOC estimation unit (17) that increases the second SOC in accordance with the rate of increase of the current-time product of the current curve characteristics, as the transition of a second SOC in the CV charging section from the SOC at the start of CV charging of the secondary battery (E1) to the SOC when it reaches full charge. According to this, by controlling the rate of increase of SOC in the CV charging section, the display SOC can be naturally increased until full charge. [Item 2] The battery state estimation device (12) according to Item 1, further comprising a display SOC setting unit (18) that sets the first SOC to a display SOC in the CC charging section and the second SOC to a display SOC in the CV charging section when the secondary battery (E1) is CCCV charged. With this, by controlling the rate of increase of SOC in the CV charging section, the timing at which the true SOC value and the display SOC reach 100% can be synchronized. [Item 3] The battery state estimation device (12) according to Item 1, further comprising: the first SOC estimation unit (16) corrects the first SOC using the second SOC in the CV charging section so that the first SOC approaches the second SOC; and the battery state estimation device (12) further comprises: a display SOC setting unit (18) that sets the first SOC in the CC charging section as the display SOC when the secondary battery (E1) is CCCV charged, and sets the corrected first SOC as the display SOC in the CV charging section. This makes it possible to improve the estimation accuracy of the first SOC in the CV charging section. [Item 4] The battery state estimation device (12) according to Item 1, wherein the second SOC estimation unit (17) sets a value greater than 100 for the SOC when full charge is reached, and estimates the second SOC for the CV charging section from the SOC at the start of CV charging to the SOC when full charge is reached. This allows users to have enough time to confirm that the battery level has reached 100%.[Item 5] The battery state estimation device (12) described in Item 1, wherein when the first SOC reaches a preset SOC corresponding to the voltage at which CV charging should be started before CV charging begins, the first SOC estimation unit (16) slows down the rate of increase of the first SOC so that when the measured voltage reaches the voltage at which CV charging should be started, the first SOC reaches less than 100%. According to this, even if the first SOC is extremely high compared to the true SOC value, the displayed SOC can be increased naturally. [Item 6] A battery state estimation method comprising: a step of acquiring the measured voltage and current of a secondary battery (E1); a step of estimating the transition of the first SOC up to the start of CV charging during CCCV charging of the secondary battery (E1); and a step of increasing the second SOC in accordance with the rate of increase of the current-time product of the current curve characteristic as the transition of the second SOC in the CV charging section from the SOC at the start of CV charging to the SOC at the time of full charge of the secondary battery (E1). According to this, by controlling the rate at which the SOC increases in the CV charging section, the displayed SOC can be naturally increased until it is fully charged. [Item 7] A battery state estimation program that causes a computer to perform the following: a process of acquiring the measured voltage and current of a secondary battery (E1); a process of estimating the transition of a first SOC from the start of CCCV charging of the secondary battery (E1) until the start of CV charging; and a process of increasing the second SOC in accordance with the rate of increase of the current-time product of the current curve characteristics, as the transition of a second SOC in the CV charging section from the SOC at the start of CV charging of the secondary battery (E1) to the SOC when it is fully charged. According to this, by controlling the rate at which the SOC increases in the CV charging section, the displayed SOC can be naturally increased until it is fully charged. [Item 8] A battery pack (10) comprising a secondary battery (E1), a battery state estimation device (12) described in any one of items 1 to 5. According to this, by controlling the rate at which the SOC increases in the CV charging section, the displayed SOC can be naturally increased until it is fully charged. 【0086】 This disclosure can be used for SOC (State of Charge) display during CCCV (Critical Control Volume) charging of a battery pack. 【0087】10 Battery pack, 11 Battery module, E1-En cell, 12 Battery management device, 13 Measurement unit, 14 Control unit, 15 Acquisition unit, 16 First SOC estimation unit, 17 Second SOC estimation unit, 18 Display SOC setting unit, Rs Shunt resistor, T1 Thermistor, Q1 Discharge switch, Q2 Charge switch, 20 Vehicle, 21 Motor, 22 Inverter, 23 Control unit, 24 Operation display unit, 24a Display unit, 30 Charger.

Claims

1. A battery state estimation device comprising: an acquisition unit for acquiring measured voltage and current of a secondary battery; a first SOC estimation unit for estimating the transition of a first SOC (State of Charge) at least until the start of CV charging during CCCV (Constant Current Constant Voltage) charging of the secondary battery; and a second SOC estimation unit for maintaining the current curve characteristics of the secondary battery during CV charging and increasing the second SOC in accordance with the rate of increase of the current-time product of the current curve characteristics as the transition of a second SOC in the CV charging section from the SOC at the start of CV charging to the SOC at the time of full charge.

2. The battery state estimation device according to claim 1, further comprising a display SOC setting unit that, when the secondary battery is CCCV charged, sets the first SOC to a display SOC in the CC charging section and sets the second SOC to a display SOC in the CV charging section.

3. The battery state estimation device according to claim 1, further comprising: the first SOC estimation unit corrects the first SOC using the second SOC in the CV charging section so that the first SOC approaches the second SOC; and the battery state estimation device further comprising a display SOC setting unit that, when the secondary battery is CCCV charged, sets the first SOC as the display SOC in the CC charging section and sets the corrected first SOC as the display SOC in the CV charging section.

4. The battery state estimation device according to claim 1, wherein the second SOC estimation unit sets a value greater than 100 for the SOC at the time of full charge and estimates the second SOC for the CV charging interval from the SOC at the start of CV charging to the SOC at the time of full charge.

5. The battery state estimation device according to claim 1, wherein when the first SOC reaches a preset SOC corresponding to the voltage at which CV charging should be started before CV charging is started, the first SOC estimation unit slows down the rate of increase of the first SOC so that when the measured voltage reaches the voltage at which CV charging should be started, the first SOC estimation unit slows down the rate of increase of the first SOC so that the first SOC is less than 100%.

6. A battery state estimation method comprising: a step of acquiring the measured voltage and current of a secondary battery; a step of estimating the transition of a first SOC (State of Charge) at least until the start of CV charging during CCCV (Constant Current Constant Voltage) charging of the secondary battery; and a step of maintaining the current curve characteristics of the secondary battery during CV charging and increasing the second SOC in accordance with the rate of increase of the current-time product of the current curve characteristics as the transition of a second SOC in the CV charging section from the SOC at the start of CV charging to the SOC at the time of full charge.

7. A battery state estimation program that causes a computer to perform the following steps: a process to acquire the measured voltage and current of a secondary battery; a process to estimate the transition of a first SOC (State of Charge) at least until the start of CV charging during CCCV (Constant Current Constant Voltage) charging of the secondary battery; and a process to maintain the current curve characteristics of the secondary battery during CV charging and increase the second SOC in accordance with the rate of increase of the current-time product of the current curve characteristics as the transition of a second SOC in the CV charging interval from the SOC at the start of CV charging to the SOC at the time of full charge.

8. A battery pack comprising a secondary battery and a battery state estimation device according to any one of claims 1 to 5.

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