JP2019148492A - Secondary battery system - Google Patents

Abstract

To improve the SOC estimation accuracy of a secondary battery.SOLUTION: First estimation processing estimates an SOC by using a charge curve CHG indicating an SOC-OCV characteristic when a main battery 110 is charged to a full-charge state from a complete-discharge state. Third estimation processing estimates the SOC by using a correspondence relationship (linear approximation relationship) for compensating for the SOC-OCV characteristic in a region D surrounded by the charge curve CHG and a discharge curve DCH when a state of the main battery 110 is deviated from above the charge curve CHG and above the discharge curve DCH. When a period in which the state of the main battery 110 is deviated from above the charge curve CHG and above the discharge curve DCH is longer than a prescribed period, an ECU 100 performs the first estimation processing by making the state of the main battery 110 located above the charge curve CHG by controlling converters 210, 220 so that the main bate 110 is charged.SELECTED DRAWING: Figure 13

Description

  The present disclosure relates to a secondary battery system, and more specifically, to a technique for estimating SOC from OCV using SOC (State Of Charge) -OCV (Open Circuit Voltage) characteristics of the secondary battery.

  Estimating the SOC of the secondary battery with high accuracy is important in properly protecting the secondary battery and fully utilizing the secondary battery. As a representative technique for estimating the SOC of a secondary battery, a technique for estimating the SOC from the OCV using the SOC-OCV characteristics (SOC-OCV curve) of the secondary battery is widely used.

  Among secondary batteries, a “charge curve” which is an SOC-OCV curve obtained when the secondary battery is charged from a fully discharged state and a secondary battery obtained when the secondary battery is discharged from a fully charged state There is a system in which the “discharge curve” which is the SOC-OCV curve is significantly different. Such a difference between the charge curve and the discharge curve is also referred to as “there is hysteresis” in the SOC-OCV curve. For example, Japanese Patent Laying-Open No. 2015-166710 (Patent Document 1) discloses a technique for estimating SOC from OCV in consideration of hysteresis.

JP2015-166710A Japanese Patent Laying-Open No. 2015-021861

  The state of the secondary battery represented by the combination of OCV and SOC of the secondary battery (OCV, SOC) depends on the usage history of the secondary battery, and the state of the secondary battery is on the charge curve or the discharge curve. There are cases where it is plotted and cases where it is not. In this regard, the present inventor has discovered the following behavior of the secondary battery.

  The amount of electricity charged in the secondary battery from the time of switching from discharging to charging of the secondary battery is referred to as the “first amount of electricity” and is discharged from the secondary battery from the time of switching from charging to discharging of the secondary battery. This amount of electricity is referred to as a “second amount of electricity”. When the magnitude of the first amount of electricity is equal to or greater than the first reference amount of electricity, the state of the secondary battery is plotted on the charging curve regardless of the SOC of the secondary battery. Even when the magnitude of the second electric quantity is the second reference electric quantity, the state of the secondary battery is plotted on the discharge curve regardless of the SOC of the secondary battery.

  When the state of the secondary battery is plotted on the charging curve, the SOC can be estimated with high accuracy from the OCV of the secondary battery using the charging curve. On the other hand, when the state of the secondary battery is plotted on the discharge curve, the SOC can be estimated with high accuracy from the OCV of the secondary battery using the discharge curve. The former SOC estimation process is referred to as “first estimation process”, and the latter SOC estimation process is referred to as “second estimation process”.

  On the other hand, when the magnitude of the first electricity quantity is less than the first reference electricity quantity, or when the magnitude of the second electricity quantity is less than the second reference electricity quantity, the secondary quantity The state of the battery deviates from the charge curve and the discharge curve, and is plotted in a region surrounded by the charge curve and the discharge curve. In these cases, the SOC of the secondary battery cannot be estimated by referring to the charge curve or the discharge curve as in the first or second estimation process. However, the present inventor can estimate the SOC from the OCV of the secondary battery by using a predetermined correspondence relationship (linear approximate relationship in the example described later) that complements the SOC-OCV characteristics of the secondary battery in the region. A point was found (details will be described later). Such SOC estimation processing is also referred to as “third estimation processing”.

  The charge curve and the discharge curve can be determined strictly by prior experiments. Therefore, the SOC estimation accuracy by the first and second estimation processes is relatively high. On the other hand, the third estimation process is a so-called approximation SOC estimation process using a correspondence relationship for complementing the SOC-OCV characteristics. Therefore, there is a concern that the SOC estimation accuracy by the third estimation process is lower than the SOC estimation accuracy of the first and second estimation processes, and the period during which the state of the secondary battery deviates from the charge curve and the discharge curve. It is not preferable that is longer than a predetermined period.

  This indication is made in order to solve the above-mentioned subject, and the object is to improve SOC estimation accuracy of a rechargeable battery in a rechargeable battery system.

  (1) A secondary battery system according to an aspect of the present disclosure includes a secondary battery, a power storage device, a power conversion device configured to be capable of power conversion between the secondary battery and the power storage device, and a first To a control device that estimates the SOC of the secondary battery by any one of the third estimation processes. The first estimation process uses the charging curve indicating the SOC-OCV characteristic of the secondary battery when the secondary battery is charged from the fully discharged state to the fully charged state, and determines the secondary battery from the OCV of the secondary battery. This is a process for estimating the SOC. The second estimation process uses the discharge curve indicating the SOC-OCV characteristic of the secondary battery when the secondary battery is discharged from the fully charged state to the fully discharged state, and determines the secondary battery from the OCV of the secondary battery. This is a process for estimating the SOC. In the third estimation process, when the state of the secondary battery deviates from the charge curve and the discharge curve, the charge curve and the discharge curve are surrounded by the region defined by the SOC and OCV of the secondary battery. This is a process of estimating the SOC of the secondary battery from the OCV of the secondary battery using a predetermined correspondence relationship that complements the SOC-OCV characteristics of the secondary battery in the region. The control device controls the power converter so that the secondary battery is charged when the period when the state of the secondary battery deviates from the charge curve and the discharge curve is longer than a predetermined period. The first estimation process is executed by positioning the state on the charging curve.

  (2) A secondary battery system according to another aspect of the present disclosure includes a secondary battery, a power storage device, a power conversion device configured to be capable of power conversion between the secondary battery and the power storage device, And a control device that estimates the SOC of the secondary battery by any one of the first to third estimation processes. The first estimation process uses the charging curve indicating the SOC-OCV characteristic of the secondary battery when the secondary battery is charged from the fully discharged state to the fully charged state, and determines the secondary battery from the OCV of the secondary battery. This is a process for estimating the SOC. The second estimation process uses the discharge curve indicating the SOC-OCV characteristic of the secondary battery when the secondary battery is discharged from the fully charged state to the fully discharged state, and determines the secondary battery from the OCV of the secondary battery. This is a process for estimating the SOC. In the third estimation process, when the state of the secondary battery deviates from the charge curve and the discharge curve, the charge curve and the discharge curve are surrounded by the region defined by the SOC and OCV of the secondary battery. This is a process of estimating the SOC of the secondary battery from the OCV of the secondary battery using a predetermined correspondence relationship that complements the SOC-OCV characteristics of the secondary battery in the region. The control device controls the power converter so that the secondary battery is discharged when the period when the state of the secondary battery deviates from the charge curve and the discharge curve is longer than a predetermined period. The second estimation process is executed by positioning the state of on the discharge curve.

  According to the configurations of (1) and (2) above, when the period when the state of the secondary battery deviates from the charge curve and the discharge curve is longer than the predetermined period, in other words, the SOC estimation is performed by the third estimation process. When the situation where the accuracy can be lowered continues for a long time, the secondary battery is forcibly charged or discharged. By forcibly charging and discharging the secondary battery in this way, a state is created in which the state of the secondary battery is plotted on the charge curve or the discharge curve. As a result, the SOC estimation by the first or second estimation process is performed, so that the SOC estimation accuracy of the secondary battery can be improved.

  According to the present disclosure, it is possible to improve the SOC estimation accuracy of the secondary battery in the secondary battery system.

It is a block diagram which shows roughly the whole structure of the vehicle by which the secondary battery system which concerns on this Embodiment is mounted. It is a circuit block diagram for demonstrating the structure of a secondary battery system in detail. It is a figure for demonstrating in detail the structure of each cell. It is a figure which shows typically an example of the change of the surface stress accompanying charging / discharging of a main battery. It is a figure which shows an example of the hysteresis of the SOC-OCV curve of the main battery in this Embodiment. It is a figure for demonstrating the outline | summary of the 1st-3rd estimation process. It is a conceptual diagram for demonstrating the selection method of an estimation process. It is a figure for demonstrating the 3rd estimation process in detail. It is a figure which shows an example of the map for calculating the proportionality constant (alpha). It is a flowchart which shows a 1st estimation process. It is a flowchart which shows a 2nd estimation process. It is a flowchart which shows a 3rd estimation process. It is a flowchart for demonstrating the SOC estimation process in this Embodiment. It is a flowchart for demonstrating the other SOC estimation process in this Embodiment.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  Hereinafter, a configuration in which the secondary battery system according to this embodiment is mounted on a hybrid vehicle will be described as an example. However, the vehicle on which the secondary battery system according to the present embodiment can be mounted is not limited to a hybrid vehicle, and may be a plug-in hybrid vehicle, an electric vehicle, or a fuel vehicle. Also good. Moreover, the use of the secondary battery system is not limited to a vehicle, and may be a stationary one.

[Embodiment]
<Vehicle configuration>
FIG. 1 is a block diagram schematically showing an overall configuration of a vehicle equipped with a secondary battery system according to the present embodiment. The vehicle 1 includes a secondary battery system 2, motor generators 10 and 20, a power split mechanism 30, a drive shaft 40, a speed reducer 50, an engine 60, and wheels 70. The secondary battery system 2 includes an electronic control unit (ECU) 100, a main battery 110, a sub battery 120, and a power control unit (PCU) 200.

  Each of motor generators 10 and 20 is, for example, a three-phase AC permanent magnet motor. When starting the engine 60, the motor generator 10 rotates the crankshaft of the engine 60 using the electric power of the main battery 110 and / or the sub-battery 120. The motor generator 10 can also generate power using the power of the engine 60. The AC power generated by the motor generator 10 is converted into DC power by the PCU 200 and charged in the main battery 110 and / or the sub battery 120. Further, AC power generated by the motor generator 10 may be supplied to the motor generator 20.

  Motor generator 20 rotates the output shaft using at least one of power supplied from main battery 110, power supplied from sub-battery 120, and power generated by motor generator 10. The motor generator 20 can also generate electric power by regenerative braking. The AC power generated by the motor generator 20 is converted into DC power by the PCU 200 and charged in the main battery 110 and / or the sub-battery 120.

  The power split mechanism 30 is configured to include, for example, a planetary gear mechanism (not shown), and mechanically connects the three elements of the crankshaft of the engine 60, the rotation shaft of the motor generator 10, and the drive shaft 40. The power split mechanism 30 can transmit power between the other two elements by using any one of the three elements as a reaction force element.

  Reducer 50 transmits power from at least one of power split mechanism 30 and motor generator 20 to wheels 70. Further, the reaction force from the road surface received by the wheels 70 is transmitted to the motor generator 20 via the speed reducer 50. As a result, the motor generator 20 generates power during regenerative braking.

  The engine 60 is an internal combustion engine such as a gasoline engine or a diesel engine. Engine 60 generates motive power for vehicle 1 to travel in response to a control signal from ECU 100. The power generated by the engine 60 is output to the power split mechanism 30.

  The main battery 110 is an assembled battery including a lithium ion secondary battery. This assembled battery includes a plurality (for example, several tens to several hundreds) of cells 13, and the configuration of each cell 13 will be described with reference to FIG. 3. The main battery 110 corresponds to a “secondary battery” according to the present disclosure.

  Hereinafter, the current direction during charging of the main battery 110 is defined as a positive direction. In the main battery 110 of the cell 13, the voltage monitoring unit may be a cell unit or a module unit including a plurality of cells 13. The same applies to the temperature monitoring unit. The same applies to the voltage monitoring unit and the temperature monitoring unit in the sub-battery 120.

  The sub battery 120 is an assembled battery including a secondary battery such as a lithium ion secondary battery or a nickel metal hydride battery. However, a capacitor such as an electric double layer capacitor may be adopted as the sub battery 120. The sub-battery 120 corresponds to a “power storage device” according to the present disclosure.

  PCU 200 boosts the DC power stored in main battery 110 and / or sub-battery 120, converts the boosted voltage to an AC voltage, and supplies it to motor generators 10 and 20. PCU 200 also converts AC power generated by motor generators 10 and 20 into DC power and supplies it to main battery 110 and / or sub-battery 120. Further, the PCU 00 is configured to be able to charge and discharge between the main battery 110 and the sub battery 120. The detailed configuration of the PCU 200 will be described with reference to FIG.

  The ECU 100 is configured to include a CPU (Central Processing Unit), a memory, an input / output port, and the like, although not shown. ECU 100 controls each device so that vehicle 1 and secondary battery system 2 are in a desired state based on a signal received from each sensor and a map and a program stored in the memory. The main control executed by the ECU 100 includes charge / discharge control of the main battery 110 and the sub battery 120, and SOC estimation processing of the main battery 110. These controls will be described in detail later.

<Configuration of secondary battery system>
FIG. 2 is a circuit block diagram for explaining the configuration of the secondary battery system 2 in more detail. PCU 200 includes converters 210 and 220, inverters 230 and 240, a capacitor C, and a voltage sensor 250. A system main relay (SMR: System Main Relay) 400 is electrically connected to a power line connecting the main battery 110 and the converter 210. Further, the main battery 110 is provided with a monitoring unit 112, and the sub battery 120 is provided with a monitoring unit 122.

  SMR 400 is opened or closed in accordance with a control signal from ECU 100. Thereby, electrical connection and disconnection between the main battery 110 and the PCU 200 are switched.

  Monitoring unit 112 detects voltage VB1 of main battery 110, current IB1 input / output to / from main battery 110, and temperature TB1 of main battery 110, and outputs the detection results to ECU 100. Similarly, monitoring unit 122 detects voltage VB2 of sub battery 120, current IB2 input / output to / from sub battery 120, and temperature TB2 of sub battery 120, and outputs the detection results to ECU 100. ECU 100 controls charging / discharging of main battery 110 and sub-battery 120 based on the detection results by monitoring units 112 and 122.

  Converter 210 is, for example, a chopper converter, and includes a capacitor C1, a reactor L1, switching elements Q11 and Q12, and diodes D11 and D12. Capacitor C1 is connected in parallel to main battery 110, and smoothes voltage VB1 of main battery 110. Each of switching elements Q11 and Q12 is, for example, an IGBT (Insulated Gate Bipolar Transistor). Switching elements Q11 and Q12 are connected in series between power line PL and power line NL connecting converter 210 and inverter 230. Diodes D11 and D12 are connected in antiparallel between the collector and emitter of switching elements Q11 and Q12, respectively. One end of the reactor L1 is connected to the high potential side of the main battery 110. Reactor L1 has the other end connected to an intermediate point between switching element Q11 and switching element Q12 (a connection point between the emitter of switching element Q11 and the collector of switching element Q12).

  Converter 210 boosts voltage VB1 of main battery 110 and supplies it between power lines PL and NL in accordance with PWM (Pulse Width Modulation) control signal PWMC1 for switching operation of switching elements Q11 and Q12. Converter 210 steps down DC voltage between power lines PL and NL in accordance with control signal PWMC1 to charge main battery 110.

  Similarly to converter 210, converter 220 is, for example, a chopper converter, and is connected in parallel to converter 210 between power lines PL and NL. Since the configuration of converter 220 is basically the same as the configuration of converter 210, detailed description will not be repeated.

  By controlling converters 210 and 220, it is possible to control power transfer between main battery 110 and sub battery 120. That is, the sub battery 120 can be charged using the power discharged from the main battery 110, or the main battery 110 can be charged using the power discharged from the sub battery 120. Note that the configurations of converters 210 and 220 are not particularly limited, and other known configurations may be employed. Converters 210 and 220 correspond to a “power converter” according to the present disclosure.

  Capacitor C is connected in parallel to converter 210 between power lines PL and NL. Capacitor C smoothes the DC voltage supplied from one or both of converters 210 and 220 and supplies the smoothed voltage to inverters 230 and 240.

  Voltage sensor 250 detects the voltage across capacitor C, that is, voltage between power lines PL and NL (hereinafter also referred to as “system voltage”) VH, and outputs the detection result to ECU 100.

  When the system voltage VH is supplied, the inverter 230 converts a DC voltage into an AC voltage and supplies the AC voltage to the motor generator 10. Thereby, motor generator 10 is driven. Similarly, when the system voltage VH is supplied, the inverter 240 converts the DC voltage into an AC voltage and supplies it to the motor generator 20. Thereby, motor generator 20 is driven.

  ECU 100 sets target system voltage VHtag indicating the target value of system voltage VH, and controls converters 210 and 220 such that system voltage VH follows target system voltage VHtag. ECU 100 drives motor generators 10 and 20 by controlling inverters 230 and 240. Although FIG. 2 shows an example in which the ECU 100 is configured as a single unit, the ECU 100 may be configured to be divided into a plurality of units.

  FIG. 3 is a diagram for explaining the configuration of each cell 13 in more detail. The cell 13 in FIG. 2 is shown through the inside.

  Referring to FIG. 3, the cell 13 includes a battery case 131 having a square shape (substantially rectangular parallelepiped shape). The upper surface of the battery case 131 is sealed with a lid 132. One end of each of the positive terminal 133 and the negative terminal 134 protrudes from the lid 132 to the outside. The other ends of the positive electrode terminal 133 and the negative electrode terminal 134 are respectively connected to an internal positive electrode terminal and an internal negative electrode terminal (both not shown) inside the battery case 131. An electrode body 135 is accommodated in the battery case 131. The electrode body 135 is formed by laminating a positive electrode 136 and a negative electrode 137 via a separator 138 and winding the laminated body. The electrolytic solution is held by the positive electrode 136, the negative electrode 137, the separator 138, and the like.

As the positive electrode 136, the separator 138, and the electrolytic solution, conventionally known configurations and materials can be used as the positive electrode, the separator, and the electrolytic solution of the lithium ion secondary battery. As an example, for the positive electrode 136, a ternary material in which a part of lithium cobaltate is replaced by nickel and manganese can be used. A polyolefin (for example, polyethylene or polypropylene) can be used for the separator. The electrolyte includes an organic solvent (for example, a mixed solvent of DMC (dimethyl carbonate), EMC (ethyl methyl carbonate), and EC (ethylene carbonate)), a lithium salt (for example, LiPF ₆ ), and an additive (for example, LiBOB (lithium bis). (oxalate) borate) or Li [PF ₂ (C ₂ O ₄ ) ₂ ]). Instead of the electrolytic solution, a polymer electrolyte may be used, or an inorganic solid electrolyte such as an oxide or sulfide may be used.

  The configuration of the cell is not limited to the configuration shown in FIG. 3, and the electrode body may have a laminated structure instead of a wound structure. Moreover, not only a rectangular battery case but also a cylindrical or laminated battery case can be employed.

<Hysteresis of SOC-OCV curve>
Conventionally, a typical negative electrode active material of a lithium ion secondary battery has been a carbon material (for example, graphite). On the other hand, in the present embodiment, a silicon-based compound (Si or SiO) is employed as the active material (not shown) of the negative electrode 137. This is because the energy density and the like of the main battery 110 can be increased by adopting the silicon compound. On the other hand, in a system in which a silicon-based compound is employed, hysteresis can appear remarkably in the SOC-OCV characteristic (SOC-OCV curve). As the cause, as described below, the volume change of the negative electrode active material accompanying charge / discharge can be considered.

  The negative electrode active material expands as lithium is inserted and contracts as lithium is desorbed. Along with such a volume change of the negative electrode active material, stress is generated on the surface and inside of the negative electrode active material. The volume change amount of the silicon compound accompanying the insertion or desorption of lithium is larger than the volume change amount of graphite. Specifically, when the minimum volume in a state where lithium is not inserted is used as a reference, the volume change amount (expansion coefficient) of graphite accompanying the insertion of lithium is about 1.1 times, The maximum volume change of the silicon compound is about four times. Therefore, when a silicon compound is employed as the negative electrode active material, the stress generated on the surface of the negative electrode active material is greater than when graphite is employed. Hereinafter, this stress is also referred to as “surface stress”.

  In general, the unipolar potential (positive electrode potential or negative electrode potential) is determined by the state of the active material surface, more specifically, the amount of lithium and the surface stress on the active material surface. For example, it is known that the negative electrode potential decreases as the amount of lithium on the negative electrode active material surface increases. When a material that causes a large volume change, such as a silicon compound, is employed, the amount of change in surface stress accompanying an increase or decrease in the amount of lithium also increases. Here, there is a hysteresis in the surface stress. Therefore, it is possible to define the negative electrode potential with high accuracy by considering the influence of the surface stress and its hysteresis. Then, when the SOC is estimated from the OCV using the relationship between the SOC and the OCV, the SOC can be estimated with high accuracy by assuming the negative electrode potential in which the surface stress is taken into consideration.

  OCV means a voltage in a state where the voltage of the main battery 110 is sufficiently relaxed and the lithium concentration in the active material is relaxed. The stress remaining on the negative electrode surface in this relaxed state includes various forces including the stress generated inside the negative electrode active material and the reaction force acting on the negative electrode active material from the surrounding material as the volume of the negative electrode active material changes. Can be considered as stress when the entire system is balanced. Note that the peripheral material is a substance existing around the active material, such as a binder or a conductive additive.

  FIG. 4 is a diagram schematically showing an example of a change in the surface stress σ of the negative electrode active material accompanying charging / discharging of the main battery 110. In FIG. 4, the horizontal axis represents the SOC of the main battery 110, and the vertical axis represents the surface stress σ of the negative electrode active material. Regarding the surface stress σ, the tensile stress generated when the negative electrode active material contracts (when the main battery 110 is discharged) is expressed in the positive direction, and the compressive stress generated when the negative electrode active material expands (when the main battery 110 is charged). Is shown in the negative direction.

  In FIG. 4, first, the main battery 110 is charged at a constant charge rate from a fully discharged state (SOC = 0% state) to a fully charged state (SOC = 100% state), and then from the fully charged state to the fully charged state. An example of a change in the surface stress σ when the main battery 110 is discharged at a constant discharge rate until the discharge state is schematically shown.

  Immediately after the start of charging from the fully discharged state, the surface stress σ (the absolute value thereof) increases linearly. It is considered that elastic deformation of the surface of the negative electrode active material occurs in the SOC region during charging (region from SOC = 0% to SOC = Sa). On the other hand, in the area | region after that (area | region from SOC = Sa to SOC = 100%), it is thought that the surface of a negative electrode active material has reached elastic deformation exceeding elastic deformation. On the other hand, when the main battery 110 is discharged, elastic deformation occurs on the surface of the negative electrode active material in the region immediately after the start of discharge from the fully charged state (region from SOC = 100% to SOC = Sb), and the subsequent region In the region (SOC = Sb to SOC = 0%), it is considered that the plastic deformation of the surface of the negative electrode active material occurs. In FIG. 4, all changes in the surface stress σ are shown by straight lines, but this is merely a schematic illustration of changes in the surface stress σ. Actually, the plastic region after the yielding (plastic deformation is reduced). Non-linear changes occur even in the SOC region that occurs (see, for example, FIG. 2 of Non-Patent Document 1).

  When the main battery 110 is continuously charged, mainly, a compressive stress acts on the surface of the negative electrode active material (the surface stress σ becomes a compressive stress), and the negative electrode potential is reduced as compared with an ideal state where the surface stress σ is not generated. As a result, the OCV of the main battery 110 increases. On the other hand, when the discharge of the main battery 110 is continued, a tensile stress mainly acts on the surface of the negative electrode active material (the surface stress σ becomes a tensile stress), and the negative electrode potential increases compared to the ideal state. As a result, the OCV of the main battery 110 decreases. According to the above mechanism, hysteresis associated with charge / discharge appears in the SOC-OCV curve of the main battery 110.

  FIG. 5 is a diagram showing an example of the SOC-OCV curve hysteresis of main battery 110 in the present embodiment. 5 and FIGS. 6 to 8 described later, the horizontal axis indicates the SOC of the main battery 110, and the vertical axis indicates the OCV of the main battery 110.

  FIG. 5 shows a charging curve CHG obtained by repeatedly charging and stopping (charging stop) after the main battery 110 is completely discharged, and discharging and pausing (discharging) after the main battery 110 is fully charged. A discharge curve DCH obtained by repeating (stop) is shown. Hereinafter, the OCV on the charging curve CHG is referred to as “charging OCV”, and the OCV on the discharging curve DCH is referred to as “discharging OCV”. The deviation between the charge OCV and the discharge OCV (about 150 mV for silicon compounds) represents the hysteresis.

  The charge OCV can be acquired as follows. First, a fully discharged main battery 110 is prepared and charged with an amount of electricity (amount of charge) corresponding to, for example, 5% SOC. After charging the amount of electricity, the charging is stopped, and the main battery 110 is left for a time (for example, 30 minutes) until the polarization caused by the charging is eliminated. The OCV of the main battery 110 is measured after the standing time has elapsed. Then, the combination of SOC after charging (= 5%) and the measured OCV (SOC, OCV) is plotted in the figure.

  Subsequently, charging of the amount of electricity corresponding to the next 5% SOC (SOC = charging from 5% to 10%) is started. When the charging is completed, the OCV of the main battery 110 is similarly measured after the leaving time has elapsed. And the combination of SOC and OCV is plotted again from the measurement result of OCV. Thereafter, the same procedure is repeated until the main battery 110 reaches a fully charged state. The charging OCV can be acquired by performing such measurement.

  Next, the OCV of the main battery 110 in the SOC of 5% is measured while repeating the discharge and stop of the discharge of the main battery 110 until the main battery 110 reaches the fully discharged state from the fully charged state. The discharge OCV can be obtained by performing such measurement. The acquired charging OCV and discharging OCV are stored in a memory (not shown) of the ECU 100.

  The charge OCV indicates the highest OCV value in each SOC, and the discharge OCV indicates the lowest OCV value in each SOC. Therefore, the state of main battery 110 (combination of SOC and OCV) is any one of charge OCV, discharge OCV, or region D surrounded by charge OCV and discharge OCV in the SOC-OCV characteristic diagram. Will be plotted. The outer periphery of the region D corresponds to the outer periphery of the parallelogram schematically shown in FIG.

<SOC estimation processing>
The state of the main battery 110 (in combination with OCV and SOC) includes a case where the state P is plotted on the charge OCV or the discharge OCV and a case where it is not, depending on the usage history of the main battery 110. This means that the SOC estimation method should be appropriately selected (switched) according to the usage history of the main battery 110. Therefore, in the present embodiment, EUC 100 is configured to select any one estimation process from first to third estimation processes described later. More specifically, the ECU 100 manages a flag F used for selecting the first to third estimation processes. The flag F takes any value of F = 1 to 3, and is stored in a nonvolatile manner in a memory in the ECU 100.

  FIG. 6 is a diagram for explaining an overview of the first to third estimation processes. The state of the main battery 110 determined by the estimation process of the mth (m is a natural number) calculation cycle is represented as “P (m)”. FIG. 6A shows an example in which the main battery 110 is charged and the state P (m) of the main battery 110 is plotted on the charge OCV.

  When charging of the main battery 110 is continued from the state P (m), the state P (m + 1) in the (m + 1) th arithmetic cycle is maintained on the charging OCV as shown in FIG. 6B. Thus, when the main battery 110 is further charged from the state P on the charging OCV, the flag F is set to F = 1. In the case of F = 1, the first estimation process (see FIG. 10) is executed.

  On the other hand, when the main battery 110 is discharged from the state P (m) shown in FIG. 6A, as shown in FIG. 6C, the state P (m + 1) in the (m + 1) th operation cycle deviates from the charge OCV. And plotted between the charge OCV and the discharge OCV. Thus, in the state P plotted between the charge OCV and the discharge OCV (in the region D), the flag F is set to F = 3. In this case, the third estimation process (see FIG. 12) is executed.

  Thereafter, when the main battery 110 continues to be discharged, for example, in the (m + 2) th calculation cycle, the state P (m + 2) reaches the discharge OCV (see FIG. 6D). Thus, when the main battery 110 is further discharged from the state P on the discharge OCV, the flag F is set to F = 2. Then, the second estimation process (see FIG. 11) is executed.

<Selection of first to third estimation processes>
How the appropriate estimation process is selected from the first to third estimation processes in the present embodiment will be described in more detail with reference to FIGS. 7 and 8.

  FIG. 7 is a conceptual diagram for explaining a selection method of estimation processing. FIG. 7A shows an example in which the main battery 110 is charged and discharged in the order of the states indicated by P (1) to P (8) (see arrows in the figure). More specifically, first, the main battery 110 in the state P (1) is discharged, and the discharge is continued until the state P (3). In state P (3), switching from discharging to charging is performed. Thereafter, charging of main battery 110 is continued until state P (8) is reached. In FIG. 7A, only the symbols P (1), P (3), P (6), and P (8) are attached to avoid the drawing from becoming complicated.

  As described in FIG. 6, when the main battery 110 is further discharged from the state P (1) on the discharge OCV, the state P of the assembled battery is maintained on the discharge OCV (state P (2 ), P (3)). Therefore, the flag F may be set to F = 2, the second estimation process may be executed, and the SOC may be estimated with reference to the discharge OCV. Similarly, when the main battery 110 is further charged from the state P (6) on the charging OCV, the state P of the assembled battery is maintained on the charging OCV (states P (7), P (8)). reference). Therefore, the flag F may be set to F = 1, the first estimation process may be executed, and the SOC may be estimated with reference to the discharge OCV.

  On the other hand, in the SOC estimation between the states P (3) to P (6), the following two points are problems. The first problem is how to determine that the state P of the main battery 110 has reached the charge OCV (see state P (6)). The second problem is how to estimate the SOC when the state P of the main battery 110 is not plotted on the charge OCV or the discharge OCV (see states P (4) and P (5)). The question is whether it should be.

  Here, this inventor discovered the following behavior of the main battery 110 by experiment. Regarding the first problem, the present inventor measured the amount of electricity ΔAh charged in the main battery 110 from the time of switching from discharging to charging (see state P (3)). As a result, when the amount of electricity ΔAh is less than the predetermined amount, the state P of the main battery 110 may not reach the charge OCV. On the other hand, if the amount of electricity ΔAh exceeds the predetermined amount, even on the discharge OCV It was found that the state P can be regarded as having reached the charge OCV even when charging from. Here, “can be regarded as having reached” is not only the case where the state P has completely reached the charging OCV but also the difference between the OCV in the state P and the charging OCV is equal to or less than a certain amount, and approximates to “having reached” It may include cases where possible. Such a predetermined amount (hereinafter referred to as “reference charge amount X1”) can be set as follows based on experimental results.

  First, as shown in FIG. 7A, when the SOC of the main battery 110 is in the low SOC region (SOC is approximately 20%), the amount of electricity ΔAh required for the state P to reach the charge OCV (predetermined amount) Ask for. Similarly, when the SOC of the main battery 110 is in the middle SOC region (SOC region of about 50%) (see FIG. 7B), the amount of electricity ΔAh required for the state P to reach the charging OCV is also tested. Is required. The same applies to the case where the SOC of the main battery 110 is in the high SOC region (the region where the SOC is approximately 80%) as shown in FIG. 7C.

  As described above, when the amount of electricity ΔAh required for the state P to reach the charging OCV in various SOC regions is experimentally obtained, the amount of electricity ΔAh corresponds to, for example, several percent of the SOC of the main battery 110. It was found that the amount of electricity was almost constant regardless of the SOC region. Therefore, the amount of electricity ΔAh determined in this way can be set as the reference charge amount X1. By doing so, it becomes possible to use a common value as the reference charge amount X1 regardless of the SOC.

  However, since there may be a slight difference in the amount of electricity ΔAh depending on the SOC region, it is preferable to set the maximum value in all SOC regions as the reference charge amount X1. Or you may store the relationship between SOC at the time of switching of charging / discharging and the reference electric energy X1 in the memory (not shown) of ECU100 as a map.

  In this way, the reference charge amount X1 is set based on the experimental results, and the state P is determined by comparing the amount of electricity ΔAh charged in the main battery 110 from the time of switching from discharging to charge and the reference charge amount X1. It can be determined whether the charging OCV has been reached, or whether the state P may have not yet reached the charging OCV.

Next, regarding the second problem, if the state P of the main battery 110 is not plotted on the charge OCV or the discharge OCV as a result of an experiment by the present inventor, the amount of change in OCV and the change in SOC It was found that the relationship between quantities can be approximated linearly. More specifically, an approximate expression such as the following expression (1) is established between the OCV change amount ΔOCV (hysteresis) and the SOC change amount ΔSOC from the time of switching from discharging to charging using a proportional constant α. To establish.
ΔOCV = α × ΔSOC (1)

The reason why such linearity appears will be described. On the surface of the negative electrode active material immediately after the charge / discharge direction is switched, it is considered that elastic deformation occurs as described in FIG. In general, Hooke's law is established within the elastic deformation region of a material, and strain is directly proportional to stress. On the other hand, a linear relationship is also established between the OCV variation ΔOCV and the surface stress σ. Specifically, this linear relationship is expressed as the following formula (2).
ΔOCV = k × Ω × σ / F (2)

In the formula (2), the volume increase amount of the negative electrode active material when 1 mol of lithium is inserted is represented by Ω (unit: m ³ / mol), and the Faraday constant is represented by F (unit: C / mol). Has been. k is a constant obtained experimentally. By using the linear relationship, it is possible to easily execute the third estimation process.

<Details of third estimation process>
FIG. 8 is a diagram for explaining the third estimation process in more detail. As shown in FIG. 8, the state P of the main battery 110 is plotted on a straight line L in the region D when it is neither on the charge OCV nor on the discharge OCV. The slope of the straight line L is the above-described proportionality constant α.

  The proportionality constant α is a parameter determined according to the mechanical characteristics of the negative electrode active material (and its surrounding materials), and is obtained by experiments. More specifically, the proportionality constant α may vary depending on the temperature of the negative electrode active material (≈the temperature TB of the main battery 110) and the lithium content in the negative electrode active material (in other words, the SOC of the main battery 110). . Therefore, it is preferable to determine the proportionality constant α for each of various combinations of the temperature TB and SOC of the main battery 110 and prepare the map MP.

  FIG. 9 is a diagram illustrating an example of a map MP for calculating the proportionality constant α. A map MP as shown in FIG. 9 is prepared and stored in the memory of the ECU 100 in advance. By referring to the map MP, the proportionality constant α can be calculated from the temperature TB (value acquired by the temperature sensor) of the main battery 110 and the SOC (the estimated result of the SOC in the previous calculation cycle).

  The map MP may indicate a correlation between only one of the temperature TB and the SOC and the proportionality constant α. Although the example using the map MP has been described with reference to FIG. 8, the proportionality constant α can be set (or predicted by simulation) from the physical property values (such as Young's modulus) of the negative electrode active material and the surrounding materials. A fixed value may be used as the proportionality constant α.

Returning to FIG. 7, both SOC and OCV in the state P (3) in which the charge / discharge direction of the main battery 110 is switched from the discharge direction to the charge direction are estimated by the second SOC estimation process. Therefore, when the SOC in the state P (3) is described as “reference SOC _REF ” and the OCV is described as “reference OCV _REF ”, the proportionality constant α, the reference SOC _REF, and the reference OCV _REF are substituted into the following formula (3). In addition, the SOC can be estimated by substituting the estimated OCV (estimated OCV _ES ) of the main battery 110 into the equation (3).
α = (OCV _ES −OCV _REF ) / (SOC−SOC _REF ) (3)

In this way, the proportional constant α of the straight line L is obtained by using the map MP. Then, the SOC of the main battery 110 can be estimated by substituting the reference SOC _REF , the reference OCV _REF, and the estimated OCV _ES into Equation (3) that holds for the proportionality constant α.

  7 to 9, the case where the specific charging / discharging indicated by the states P (1) to P (8) of the main battery 110 is described is merely an example. Although the detailed description will not be repeated, the SOC of the main battery 110 can be estimated regardless of the charge / discharge direction of the main battery 110 by performing the same as the description with reference to FIGS.

<First to third estimation processing flows>
FIG. 10 is a flowchart showing the first estimation process. Each step (hereinafter abbreviated as “S”) included in the flowcharts shown in FIG. 10 and FIGS. 11 to 14 to be described later is basically realized by software processing by the ECU 100. It may be realized by hardware (electric circuit). It is assumed that the reference SOC _REF and the reference OCV _REF are stored in the memory of the ECU 100 together with the flag F obtained in the previous calculation cycle ((n-1) th calculation cycle).

  1 and 10, in S101, ECU 100 obtains voltage VB, current IB, and temperature TB of main battery 110 from each sensor (voltage sensor, current sensor, and temperature sensor) in monitoring unit 112. Each acquired parameter is stored in the memory.

In S102, ECU 100 estimates the OCV of main battery 110. The estimated OCV _ES can be calculated according to the following equation (4).
OCV _ES = VB−IB × R−ΣΔV _i (4)

In Expression (4), the internal resistance of the main battery 110 is represented by R, and a correction term for correcting the influence of polarization generated in the main battery 110 is represented by ΣΔV _i (i is a natural number). This correction term ΣΔV _i corrects polarization caused by lithium diffusion in the positive electrode active material and the negative electrode active material and lithium salt diffusion in the electrolytic solution. In consideration of lithium diffusion in the negative electrode active material, it is desirable to consider the influence of both the lithium concentration difference in the negative electrode active material and internal stress. It is assumed that the correction term ΣΔV _i is obtained in a preliminary experiment and stored in the memory. The correction term ΣΔV _{i is} also determined so that the value when the main battery 110 is charged is positive.

  In S103, the ECU 100 estimates the SOC from the estimated OCV by referring to the charging OCV.

In step S104, the ECU 100 stores the SOC estimated in step S103 in the memory as the reference SOC _REF . Further, the ECU 100 stores the OCV _ES estimated in S102 in the memory as the reference OCV _REF . That is, ECU 100 updates reference SOC _REF and reference OCV _REF .

  FIG. 11 is a flowchart showing the second estimation process. Referring to FIG. 11, the second estimation process is basically the same as the first estimation process except that the discharge OCV is used instead of the charge OCV in the process of S <b> 203. Do not repeat.

  FIG. 12 is a flowchart showing the third estimation process. Referring to FIGS. 1 and 12, the processes of S301 and S302 are respectively equivalent to the processes of S101 and S102 in the first estimation process (see FIG. 10).

  In step S303, the ECU 100 reads the SOC (n−1) calculated in the previous calculation cycle from the memory.

In S304, the ECU 100 calculates the proportionality constant α from the temperature TB of the main battery 110 and the SOC (n−1) in the previous calculation cycle by referring to the map MP shown in FIG. Regarding the temperature TB of the main battery 110, in addition to using the current temperature TB as it is, a time average value within a predetermined period (for example, 30 minutes) immediately before a predetermined time may be used. Further, the reference SOC _REF may be used as the SOC when referring to the map MP.

In step S305, the ECU 100 acquires the reference SOC _REF and the reference OCV _REF obtained by the first estimation process or the second estimation process, the proportionality constant α set in the process of S304, and the process of S302. The estimated OCV _ES is substituted into the above equation (3). As a result, the SOC (n) of the main battery 110 in the current calculation cycle is calculated. The calculated SOC (n) is stored in the memory in preparation for the next calculation cycle (S306).

<Comparison of SOC estimation accuracy>
The charging curve CHG and the discharging curve DCH can be determined strictly by the preliminary experiment described with reference to FIG. Therefore, the SOC estimation accuracy by the first and second estimation processes is relatively high. On the other hand, since the third estimation process is a so-called approximate SOC estimation process, the SOC estimation accuracy is lower than the SOC estimation accuracy by the first and second estimation processes. Therefore, it is not preferable that the period during which the state P of the main battery 110 deviates from the charge curve CHG and the discharge curve DCH is longer than the predetermined period.

  Therefore, in the present embodiment, when the period when the state P of the main battery 110 deviates from the charge curve CHG and the discharge curve DCH becomes longer than a predetermined period, the main battery 110 and the sub-battery 120 are not connected. Configuration in which the SOC of the main battery 110 is estimated after the state P of the main battery 110 is positioned on the charge curve CHG or the discharge curve DCH by forcibly charging and discharging the main battery 110 by power conversion at Is adopted. When the state P of the main battery 110 is on the charge curve CHG, a first estimation process is executed, and when the state P of the main battery 110 is on the discharge curve DCH, a second estimation process is executed. Thereby, the estimation accuracy of the SOC can be improved as compared with the case where the execution of the third estimation process is continued for a long period of time. Note that the SOC estimation error can be reset by executing the first process or the second process.

  FIG. 13 is a flowchart for explaining the SOC estimation processing in the present embodiment. The flowchart shown in FIG. 13 and FIG. 14 to be described later is called from a main routine (not shown) every time a predetermined calculation cycle elapses and is repeatedly executed by the ECU 100, for example.

  Referring to FIG. 13, in S401, ECU 100 reads flag F stored in the memory. When flag F is F = 1 (YES in S402), ECU 100 executes the first estimation process shown in FIG. 10 (S100). When flag F is F = 2 (YES in S403), ECU 100 executes the second estimation process shown in FIG. 11 (S200).

  When the flag F is neither F = 1 nor F = 2 (NO in S402 and S403), that is, when the flag F is F = 3, the ECU 100 has passed a predetermined period in a state where F = 3. Is determined (S404). The length of the predetermined period can be determined experimentally in consideration of factors such as the cycle of the calculation cycle, the magnitude of the estimation error due to linear approximation in the third estimation process, and the required SOC estimation accuracy.

  When the predetermined period has not elapsed in the state of F = 3 (NO in S404), it is considered that the influence on the estimation error of the SOC derived from the linear approximation in the third estimation process is relatively small. Therefore, the ECU 100 executes the third estimation process shown in FIG. 12 (S300).

  On the other hand, when a predetermined period or more has elapsed in the state of F = 3 (YES in S404), the SOC estimation error may be large due to the linear approximation. Therefore, the ECU 100 advances the process to S405 and starts the forced charging control of the main battery 110. More specifically, ECU 100 controls converters 210 and 220 such that main battery 110 is forcibly charged with electric power stored in sub battery 120. If the forced charging control has already been started, the forced charging control is continued.

  Thereafter, ECU 100 continues the forced charging control until state P of main battery 110 reaches charging OCV (NO in S406). As described with reference to FIG. 6, if the amount of electricity ΔAh charged in the main battery 110 from the time of switching from discharging to charging becomes equal to or greater than a predetermined amount, the state P is charged even when charging from the discharging OCV. It can be considered that the OCV has been reached. Therefore, when the amount of electricity ΔAh charged in main battery 110 is equal to or greater than the predetermined amount, ECU 100 determines that state P of main battery 110 has reached charging OCV (YES in S406), and forced charging control. Is stopped (S407). Then, ECU 100 estimates the SOC of main battery 110 by executing the first estimation process (S100).

  Depending on the running state of the vehicle 1, regenerative electric power may be generated by the motor generator 20 during execution of forced charging control of the main battery 110. In such a case, both the main battery 110 and the sub battery 120 may be charged with regenerative power. That is, the charging power of the main battery 110 during execution of the forced charging control is not limited to the discharging power from the sub-battery 120, and may include regenerative power from the motor generator 20.

  Although not shown in the flowchart, ECU 100 may execute discharge control for returning the power of main battery 110 charged by forced charge control to sub-battery 120 after SOC estimation by the first estimation process. Good. Thereby, the SOC increase amount accompanying forced charge control can be reset.

  Although the example in which the first estimation process is executed after execution of the forced charging control of the main battery 110 has been described in FIG. 13, the second estimation process is executed after the execution of the forced discharge control of the main battery 110 as described below. May be executed.

  FIG. 14 is a flowchart for explaining another SOC estimation process in the present embodiment. In this flowchart, it is determined whether forced discharge control is executed instead of forced charge control in the processes of S505 and S507, and whether or not the state P of the main battery 110 has reached the discharge OCV in the process of S506. 13 and that the second estimation process is executed instead of the first estimation process after the forced discharge control is stopped (after the process of S507), is different from the flowchart shown in FIG. Other processes are basically the same as the corresponding processes in the flowchart shown in FIG. 13, and thus detailed description will not be repeated.

  ECU 100 may be configured to execute any one of the flowchart shown in FIG. 13 and the flowchart shown in FIG. 14. Alternatively, ECU 100 may be configured to select an appropriate flowchart from the two flowcharts according to, for example, the SOC of main battery 110 (and the SOC of sub battery 120). As an example, when the SOC of the main battery 110 is less than a predetermined value (when the SOC is low), in order to recover the SOC of the main battery 110, the flowchart shown in FIG. When the SOC of the main battery 110 is equal to or higher than a predetermined value (when the SOC is high), the flowchart shown in FIG. 14 can be preferentially executed.

  As described above, according to the present embodiment, when the state of flag F = 3 continues for a predetermined period or longer, forced charging control or forced discharging control of main battery 110 is executed. When the state P of the main battery 110 becomes the charge OCV by the forced charge control of the main battery 110, the SOC of the main battery 110 is estimated by the first estimation process. Further, when the state P of the main battery 110 becomes the discharge OCV by the forced discharge control of the main battery 110, the SOC of the main battery 110 is estimated by the second estimation process. Since the first or second estimation process has higher SOC estimation accuracy than the third estimation process, the SOC estimation accuracy can be improved.

Furthermore, when the first or second estimation process is executed, the reference SOC _REF and the reference OCV _REF are updated as described with reference to FIGS. 10 and 11 (see the processes of S104 and S204). Thereby, it is possible to recover the execution of the subsequent third estimation process from the state where the SOC estimation accuracy is high.

  A typical hybrid vehicle has only one traveling battery. The charging / discharging of the traveling battery is basically switched as appropriate according to the traveling state (or load state) of the vehicle. It is difficult to forcibly discharge the traveling battery when there is no load that consumes the discharged power from the traveling battery. Further, for example, it is conceivable to drive the engine and forcibly charge the traveling battery with electric power generated by a motor generator (a generator corresponding to the motor generator 10 of the vehicle 1). It can cause the fuel consumption of the car to deteriorate.

  In contrast, in the present embodiment, sub battery 120 is provided in addition to main battery 110, and charging / discharging of main battery 110 is realized by power transfer between main battery 110 and sub battery 120. . Since there is always a sub-battery 120 that can receive discharge power from the main battery 110, the main battery 110 can be forcibly discharged at an arbitrary timing. Further, the forced charging of the main battery 110 from the sub-battery 120 via the converters 210 and 220 has higher energy efficiency than the power generation by the engine driving described above, although power conversion loss may occur in the converters 210 and 220. . Thus, according to the present embodiment, it is possible to provide a method for improving the SOC estimation accuracy with a high degree of freedom in execution timing of forced charge control and forced discharge control and high energy efficiency.

  In general, plug-in charging is periodically performed in plug-in hybrid vehicles and electric vehicles. When plug-in charging that is greater than or equal to the reference electricity amount is performed, the state of the main battery 110 is plotted on the charging OCV, so that the SOC estimation accuracy increases. On the other hand, in the vehicle 1 that is a normal hybrid vehicle (a hybrid vehicle that is not configured to perform plug-in charging), a situation in which the state of the main battery 110 is plotted on the charging OCV is relatively unlikely to occur. Therefore, the SOC estimation process in the present disclosure is particularly effective for a normal hybrid vehicle in that it is possible to actively create an opportunity for the state of the main battery 110 to be plotted on the charge OCV. However, since there are users of plug-in hybrid vehicles that do not perform much plug-in charging, it can be said that the SOC estimation processing according to the present disclosure is effective even for such plug-in hybrid vehicles with low frequency of plug-in charging. .

  3 and 4, the example in which the silicon compound is used as the negative electrode active material having a large volume change amount due to charge / discharge has been described. However, the negative electrode active material having a large volume change amount due to charge / discharge is not limited thereto. In the present specification, the “negative electrode active material having a large volume change amount” means a material having a large volume change amount as compared with the volume change amount (about 10%) of graphite accompanying charge / discharge. Examples of the negative electrode material of such a lithium ion secondary battery include a tin-based compound (such as Sn or SnO), a germanium (Ge) -based compound, or a lead (Pb) -based compound. Moreover, although the silicon-type compound was raised as an example of a negative electrode active material, you may use the composite material of a silicon-type compound and another material. Examples of the composite material include a composite material containing a silicon compound and graphite, and a composite material containing a silicon compound and lithium titanate.

  Furthermore, the secondary battery to which the SOC estimation process according to the present disclosure can be applied is not limited to a lithium ion secondary battery, and may be another secondary battery (for example, a nickel metal hydride battery). Further, when the volume change amount of the positive electrode active material is large, the surface stress can be generated also on the positive electrode side of the secondary battery. Therefore, the SOC estimation process described in the present embodiment may be used in order to take into account the hysteresis derived from the positive electrode in the SOC estimation. Further, in the present embodiment, the SOC estimation process of main battery 110 has been described, but it is also possible to estimate the SOC of sub battery 120 by a similar method.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present disclosure is shown not by the above description of the embodiments but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

  1 vehicle, 2 secondary battery system, 10, 20 motor generator, 30 power split mechanism, 40 drive shaft, 50 reducer, 60 engine, 70 wheels, 100 ECU, 110 main battery, 120 sub battery, 112, 122 monitoring unit , 13 cells, 131 battery case, 132 lid body, 133 positive electrode terminal, 134 negative electrode terminal, 135 electrode body, 136 positive electrode, 137 negative electrode, 138 separator, 200 PCU, 210, 220 converter, 230, 240 inverter, 250 voltage sensor, C, C1 capacitor, D11, D12 diode, L1 reactor, Q11, Q12 switching element.

Claims (2)

A secondary battery,
A power storage device;
A power conversion device configured to enable power conversion between the secondary battery and the power storage device;
A controller that estimates the SOC of the secondary battery by any one of the first to third estimation processes;
The first estimation process is performed from the OCV of the secondary battery using a charging curve indicating an SOC-OCV characteristic of the secondary battery when the secondary battery is charged from a fully discharged state to a fully charged state. A process for estimating the SOC of the secondary battery;
The second estimation process uses a discharge curve indicating an SOC-OCV characteristic of the secondary battery when the secondary battery is discharged from the fully charged state to the fully discharged state. A process of estimating the SOC of the secondary battery from OCV;
In the third estimation process, when the state of the secondary battery deviates from the charge curve and the discharge curve, the charge curve in the region defined by the SOC and OCV of the secondary battery A process of estimating the SOC of the secondary battery from the OCV of the secondary battery using a predetermined correspondence relationship that complements the SOC-OCV characteristics of the secondary battery in a region surrounded by the discharge curve. ,
The control device controls the power conversion device so that the secondary battery is charged when a period in which the state of the secondary battery deviates from the charge curve and the discharge curve is longer than a predetermined period. By doing so, the state of the secondary battery is positioned on the charging curve, and the first estimation process is executed. A secondary battery,
A power storage device;
A power conversion device configured to enable power conversion between the secondary battery and the power storage device;
A controller that estimates the SOC of the secondary battery by any one of the first to third estimation processes;
The first estimation process is performed from the OCV of the secondary battery using a charging curve indicating an SOC-OCV characteristic of the secondary battery when the secondary battery is charged from a fully discharged state to a fully charged state. A process for estimating the SOC of the secondary battery;
The second estimation process uses a discharge curve indicating an SOC-OCV characteristic of the secondary battery when the secondary battery is discharged from the fully charged state to the fully discharged state. A process of estimating the SOC of the secondary battery from OCV;
In the third estimation process, when the state of the secondary battery deviates from the charge curve and the discharge curve, the charge curve in the region defined by the SOC and OCV of the secondary battery A process of estimating the SOC of the secondary battery from the OCV of the secondary battery using a predetermined correspondence relationship that complements the SOC-OCV characteristics of the secondary battery in a region surrounded by the discharge curve. ,
The control device controls the power conversion device so that the secondary battery is discharged when a period in which the state of the secondary battery deviates from the charge curve and the discharge curve is longer than a predetermined period. By doing so, the state of the secondary battery is positioned on the discharge curve, and the second estimation process is executed.

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