JP6958427B2 - Rechargeable battery system - Google Patents

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 a secondary battery.

Estimating the SOC of a secondary battery with high accuracy is important for properly protecting the secondary battery and making full use of the secondary battery. As a typical method for estimating SOC of a secondary battery, a method of estimating SOC from OCV using the SOC-OCV characteristic (SOC-OCV curve) of a secondary battery is widely used.

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

Japanese Unexamined Patent Publication No. 2015-166710 Japanese Unexamined Patent Publication No. 2015-021861

The state of the secondary battery represented by the combination of OCV and SOC of the secondary battery (OCV, SOC) shows that the state of the secondary battery is on the charge curve or the discharge curve, depending on the usage history of the secondary battery. There are cases where it is plotted and cases where it is not. In relation to this point, 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 called 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. The amount of electricity generated is referred to as a "second amount of electricity". When the magnitude of the first electric energy is equal to or greater than the first reference electric energy, 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 energy is the second reference electric energy, 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 charge curve, the SOC can be estimated with high accuracy from the OCV of the secondary battery using the charge 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 electric quantity is less than the first reference electric quantity, or when the magnitude of the second electric quantity is less than the second reference electric quantity, it is secondary. The state of the battery deviates from the charge curve and the discharge curve, and is plotted in the area 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 (a linear approximation relationship in the example described later) that complements the SOC-OCV characteristics of the secondary battery in the region. I found a point (details will be described later). Such SOC estimation processing is also referred to as "third estimation processing".

The charge curve and discharge curve can be strictly determined 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 of the third estimation process will be 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. Is not preferable to be longer than a predetermined period.

The present disclosure has been made to solve the above problems, and an object thereof is to improve the SOC estimation accuracy of a secondary battery in a secondary battery system.

(1) The secondary battery system according to a certain aspect of the present disclosure includes 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, and a first. A control device for estimating the SOC of the secondary battery by any of the third estimation processes is provided. The first estimation process uses a charging curve showing the SOC-OCV characteristics of the secondary battery when the secondary battery is charged from a fully discharged state to a fully charged state, from the OCV of the secondary battery to the secondary battery. This is a process for estimating SOC. The second estimation process uses a discharge curve showing the SOC-OCV characteristics of the secondary battery when the secondary battery is discharged from a fully charged state to a fully discharged state, from the OCV of the secondary battery to the secondary battery. This is a process for estimating SOC. The third estimation process is surrounded by the charge curve and the discharge curve in the region defined by the SOC and OCV of the secondary battery when the state of the secondary battery deviates from the charge curve and the discharge curve. This is a process of estimating the SOC of the secondary battery from the OCV of the secondary battery by using a predetermined correspondence relationship that complements the SOC-OCV characteristics of the secondary battery in the region. The control device controls the power conversion device so that the secondary battery is charged when the state of the secondary battery deviates from the charge curve and the discharge curve for a longer period than a predetermined period. The state of is positioned on the charge curve and the first estimation process is executed.

(2) The secondary battery system according to the other aspects of the present disclosure includes 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, and a second. It is provided with a control device that estimates the SOC of the secondary battery by any of the first to third estimation processes. The first estimation process uses a charging curve showing the SOC-OCV characteristics of the secondary battery when the secondary battery is charged from a fully discharged state to a fully charged state, from the OCV of the secondary battery to the secondary battery. This is a process for estimating SOC. The second estimation process uses a discharge curve showing the SOC-OCV characteristics of the secondary battery when the secondary battery is discharged from a fully charged state to a fully discharged state, from the OCV of the secondary battery to the secondary battery. This is a process for estimating SOC. The third estimation process is surrounded by the charge curve and the discharge curve in the region defined by the SOC and OCV of the secondary battery when the state of the secondary battery deviates from the charge curve and the discharge curve. This is a process of estimating the SOC of the secondary battery from the OCV of the secondary battery by using a predetermined correspondence relationship that complements the SOC-OCV characteristics of the secondary battery in the region. The control device controls the power conversion device so that the secondary battery is discharged when the state of the secondary battery deviates from the charge curve and the discharge curve for a longer period than a predetermined period. The state of is positioned on the discharge curve and the second estimation process is executed.

According to the configurations (1) and (2) above, when the period in which 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 is estimated by the third estimation process. If the situation where the accuracy can be low continues for a long time, forced charge control or discharge control of the secondary battery is executed. By forcibly charging and discharging the secondary battery in this way, a state in which the state of the secondary battery is plotted on the charge curve or the discharge curve is created. As a result, the SOC is estimated by the first or second estimation process, so that the SOC estimation accuracy of the secondary battery can be improved.

According to the present disclosure, in the secondary battery system, the SOC estimation accuracy of the secondary battery can be improved.

It is a block diagram which shows schematic the whole structure of the vehicle which mounted the secondary battery system which concerns on this Embodiment. It is a circuit block diagram for explaining the structure of a secondary battery system in more detail. It is a figure for demonstrating the structure of each cell in more detail. It is a figure which shows an example of the change of the surface stress with charge and discharge of a main battery schematically. 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 of the 1st to 3rd estimation processing. It is a conceptual diagram for demonstrating the selection method of estimation processing. It is a figure for demonstrating the third estimation process in more detail. It is a figure which shows an example of the map for calculating the proportionality constant α. It is a flowchart which shows the 1st estimation process. It is a flowchart which shows the 2nd estimation process. It is a flowchart which shows the 3rd estimation process. It is a flowchart for demonstrating SOC estimation processing in this embodiment. It is a flowchart for demonstrating another SOC estimation processing in this embodiment.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals, and the 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 the hybrid vehicle, and may be a plug-in hybrid vehicle, an electric vehicle, or a fuel vehicle. May be good. Further, the use of the secondary battery system is not limited to that for vehicles, and may be for stationary use.

[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: Electronic Control Unit) 100, a main battery 110, a sub-battery 120, and a power control unit (PCU: Power Control Unit) 200.

Each of the motor generators 10 and 20 is, for example, a three-phase AC permanent magnet type motor. When starting the engine 60, the motor generator 10 uses the electric power of the main battery 110 and / or the sub-battery 120 to rotate the crankshaft of the engine 60. Further, the motor generator 10 can also generate electricity by 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 into the main battery 110 and / or the sub battery 120. Further, the AC power generated by the motor generator 10 may be supplied to the motor generator 20.

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

The power split mechanism 30 includes, 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 makes it possible to transmit power between the other two elements by using any one of the above three elements as a reaction force element.

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

The engine 60 is an internal combustion engine such as a gasoline engine or a diesel engine. The engine 60 generates power for the vehicle 1 to travel in response to a control signal from the 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 of (for example, several tens to several hundreds) cells 13, and the configuration of each cell 13 will be described with reference to FIG. The main battery 110 corresponds to the "secondary battery" according to the present disclosure.

In the following, the current direction when charging the main battery 110 is defined as the 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 hydrogen battery. However, as the sub-battery 120, a capacitor such as an electric double layer capacitor may be adopted. The sub-battery 120 corresponds to the "power storage device" according to the present disclosure.

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

Although not shown, the ECU 100 includes a CPU (Central Processing Unit), a memory, an input / output port, and the like. The ECU 100 controls each device so that the vehicle 1 and the secondary battery system 2 are in a desired state based on the signal received from each sensor and the map and the program stored in the memory. The main controls executed by the ECU 100 include 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. The PCU 200 includes converters 210 and 220, inverters 230 and 240, a capacitor C, and a voltage sensor 250. A system main relay (SMR) 400 is electrically connected to the power line connecting the main battery 110 and the converter 210. Further, the main battery 110 is provided with the monitoring unit 112, and the sub-battery 120 is provided with the monitoring unit 122.

The SMR 400 is opened or closed according to a control signal from the ECU 100. This switches the electrical connection and disconnection between the main battery 110 and the PCU 200.

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

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

The converter 210 boosts the voltage VB1 of the main battery 110 and supplies it between the power lines PL and NL in response to the PWM (Pulse Width Modulation) type control signal PWMC1 for switching the switching elements Q11 and Q12. Further, the converter 210 steps down the DC voltage between the power lines PL and NL in response to the control signal PWMC1 to charge the main battery 110.

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

By controlling the converters 210 and 220, it is possible to control the transfer of electric power between the main battery 110 and the sub battery 120. That is, the sub-battery 120 can be charged using the electric power discharged from the main battery 110, and conversely, the main battery 110 can be charged using the electric power discharged from the sub-battery 120. The configurations of the converters 210 and 220 are not particularly limited, and other known configurations may be adopted. The converters 210 and 220 correspond to the "power conversion device" according to the present disclosure.

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

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

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

The ECU 100 sets a target system voltage VHtag indicating a target value of the system voltage VH, and controls the converters 210 and 220 so that the system voltage VH follows the target system voltage VHtag. Further, the ECU 100 drives the motor generators 10 and 20 by controlling the inverters 230 and 240. Although FIG. 2 shows an example in which the ECU 100 is configured as one unit, the ECU 100 can also 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 thereof.

With reference to FIG. 3, cell 13 has a square (substantially rectangular parallelepiped) battery case 131. The upper surface of the battery case 131 is sealed by the lid 132. One end of each of the positive electrode terminal 133 and the negative electrode terminal 134 projects outward from the lid 132. The other ends of the positive electrode terminal 133 and the negative electrode terminal 134 are connected to the internal positive electrode terminal and the internal negative electrode terminal (neither of them is shown) inside the battery case 131, respectively. The electrode body 135 is housed inside 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 in the positive electrode 136, the negative electrode 137, the separator 138 and the like.

For 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, respectively. As an example, a ternary material in which a part of lithium cobalt oxide is replaced with nickel and manganese can be used for the positive electrode 136. Polyolefin (for example, polyethylene or polypropylene) can be used as the separator. The electrolytic solution is 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) carbonate) or Li [PF ₂ (C ₂ O ₄ ) ₂ ]) and the like. A polymer-based electrolyte may be used instead of the electrolytic solution, or an oxide-based or sulfide-based inorganic solid electrolyte may be used.

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

<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 compound (Si or SiO) is adopted as the active material (not shown) of the negative electrode 137. This is because the energy density of the main battery 110 and the like can be increased by adopting a silicon-based compound. On the other hand, in a system in which a silicon-based compound is adopted, hysteresis may appear remarkably in the SOC-OCV characteristics (SOC-OCV curve). As the cause, as will be described below, the volume change of the negative electrode active material due to charging / discharging can be considered.

The negative electrode active material expands with the insertion of lithium and contracts with the desorption of lithium. With such a volume change of the negative electrode active material, stress is generated on the surface and the inside of the negative electrode active material. The volume change of the silicon-based compound due to the insertion or desorption of lithium is larger than the volume change of graphite. Specifically, when the minimum volume in the state where lithium is not inserted is used as a reference, the volume change (expansion rate) of graphite due to the insertion of lithium is about 1.1 times, whereas it is about 1.1 times. The amount of change in volume of the silicon-based compound is about four times at the maximum. Therefore, when a silicon-based compound is used as the negative electrode active material, the stress generated on the surface of the negative electrode active material becomes larger than when graphite is used. Hereinafter, this stress is also referred to as "surface stress".

Generally, the unipolar potential (positive electrode potential or negative electrode potential) is determined by the state of the surface of the active material, more specifically, the amount of lithium on the surface of the active material and the surface stress. For example, it is known that the negative electrode potential decreases as the amount of lithium on the surface of the negative electrode active material increases. When a material such as a silicon-based compound that causes a large volume change is adopted, the amount of change in surface stress due to an increase or decrease in the amount of lithium also becomes large. Here, there is hysteresis in the surface stress. Therefore, the negative electrode potential can be defined with high accuracy by considering the influence of the surface stress and its hysteresis. Then, when estimating the SOC 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.

The 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 surface of the negative electrode 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 peripheral material as the volume of the negative electrode active material changes. Can be thought of as the stress when is balanced in the entire system. The peripheral material is a substance existing around the active material such as a binder and a conductive auxiliary agent.

FIG. 4 is a diagram schematically showing an example of a change in the surface stress σ of the negative electrode active material with 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. The surface stress σ represents the tensile stress generated when the negative electrode active material contracts (when the main battery 110 is discharged) 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 a fully charged state to a fully charged state. An example of the change in surface stress σ when the main battery 110 is discharged at a constant discharge rate up to the discharged state is schematically shown.

Immediately after the start of charging from the fully discharged state, the surface stress σ (absolute value) increases linearly. It is considered that the surface of the negative electrode active material is elastically deformed in the SOC region (the region from SOC = 0% to SOC = Sa) during charging. On the other hand, in the subsequent region (the region from SOC = Sa to SOC = 100%), it is considered that the surface of the negative electrode active material exceeds the elastic deformation and reaches the plastic 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 (the region from SOC = 100% to SOC = Sb), and the region thereafter. In (the region from SOC = Sb to SOC = 0%), it is considered that the surface of the negative electrode active material is plastically deformed. In FIG. 4, all changes in the surface stress σ are shown by straight lines, but this is merely a schematic representation of the changes in the surface stress σ, and in reality, the plastic region after yielding (plastic deformation is Non-linear changes also occur in the SOC region where they occur (see, for example, FIG. 2 of Non-Patent Document 1).

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

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

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

The charging OCV can be obtained as follows. First, a fully discharged main battery 110 is prepared and charged with an amount of electricity (charge amount) corresponding to, for example, 5% SOC. After charging the amount of electricity, 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 elapse of the leaving time. Then, the combination (SOC, OCV) of the SOC (= 5%) after charging and the measured OCV is plotted in the figure.

Subsequently, charging of an amount of electricity corresponding to the next 5% SOC (charging from SOC = 5% to 10%) is started. When charging is completed, the OCV of the main battery 110 is similarly measured after the elapse of the leaving time. Then, the combination of SOC and OCV is plotted again from the measurement result of OCV. After that, the same procedure is repeated until the main battery 110 is fully charged. By carrying out such a measurement, the charging OCV can be obtained.

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

The charging OCV shows the highest value of OCV in each SOC, and the discharging OCV shows the lowest value of OCV in each SOC. Therefore, the state of the main battery 110 (combination of SOC and OCV) is either on the charging OCV, on the discharging OCV, or in the region D surrounded by the charging OCV and the discharging OCV in the SOC-OCV characteristic diagram. Will be plotted in. The outer circumference of the region D corresponds to the outer circumference of the parallelogram schematically shown in FIG.

<SOC estimation processing>
The state of the main battery 110 (combination of OCV and SOC) may or may not be plotted on the charging OCV or the discharging OCV, 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, the EUC 100 is configured to select any one of the first to third estimation processes described later. More specifically, the ECU 100 manages the flag F used for selecting the first to third estimation processes. The flag F takes any value of F = 1 to 3, and is non-volatilely stored in the memory in the ECU 100.

FIG. 6 is a diagram for explaining the outline of the first to third estimation processes. The state of the main battery 110 found by the estimation process of the m (m is a natural number) th calculation cycle is represented by "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 charging 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 calculation cycle is maintained on the charging OCV as shown in FIG. 6B. In this way, when the main battery 110 is further charged from the state P on the charging OCV, the flag F is set to F = 1. When 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, the state P (m + 1) in the (m + 1) th calculation cycle deviates from the charging OCV as shown in FIG. 6C. Then, it will be plotted between the charging OCV and the discharging OCV. In this way, in the state P plotted between the charging OCV and the discharging OCV (in the region D), the flag F is set to F = 3. In this case, a third estimation process (see FIG. 12) is executed.

After that, when the discharge of the main battery 110 is continued, the state P (m + 2) reaches the discharge OCV in, for example, the (m + 2) th calculation cycle (see FIG. 6D). In this way, 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 the first to third estimation processes>
How an 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 shown by P (1) to P (8) (see the arrow 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). Then, in the state P (3), switching from discharging to charging is performed. After that, charging of the main battery 110 is continued until the state P (8) is reached. In FIG. 7A, only the reference numerals P (1), P (3), P (6), and P (8) are attached in order to avoid complicating the drawings.

As described with reference to FIG. 6, when the main battery 110 is further discharged from the state P (1) on the discharged OCV, the state P of the assembled battery is maintained on the discharged 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, the following two points are problems in the SOC estimation between the states P (3) and P (6). The first problem is how to determine that the state P of the main battery 110 has reached the charging 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 charging OCV or the discharging OCV (see states P (4) and P (5)). The question is whether it should be done.

Here, the present inventor has discovered the following behavior of the main battery 110 by experiments. 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 charging OCV, while when the amount of electricity ΔAh exceeds the predetermined amount, even if the amount of electricity ΔAh exceeds the predetermined amount, it is on the discharge OCV. It was found that the state P can be regarded as having reached the charging OCV even if the charging is performed from. Here, "it can be regarded as reached" is not only when the state P completely reaches the charging OCV, but also when the difference between the OCV of the state P and the charging OCV is equal to or less than a certain amount, and is approximated as "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 the experimental results.

First, when the SOC of the main battery 110 is within the low SOC region (the region where the SOC is about 20%) as shown in FIG. 7A, the amount of electricity ΔAh (predetermined amount) required for the state P to reach the charging OCV. Ask for. Similarly, when the SOC of the main battery 110 is within the medium SOC region (the region where the SOC is about 50%) (see FIG. 7B), the amount of electricity ΔAh required for the state P to reach the charging OCV is similarly tested. Demanded by. The same applies to the case where the SOC of the main battery 110 is within the high SOC region (the region where the SOC is about 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 determined, the amount of electricity ΔAh corresponds to, for example, a few 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 electric energy ΔAh thus obtained can be set as the reference electric energy 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 the SOC regions as the reference charge amount X1. Alternatively, the relationship between the SOC and the reference electric energy X1 at the time of switching between charging and discharging may be stored in the memory (not shown) of the ECU 100 as a map.

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

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

The reason why such linearity appears will be described. As described with reference to FIG. 4, it is considered that elastic deformation occurs on the surface of the negative electrode active material immediately after the charge / discharge direction is switched. In general, Hooke's law holds within the elastic deformation region of a substance, and strain is directly proportional to stress. On the other hand, a linear relationship is also established between the OCV change amount ΔOCV and the surface stress σ. Specifically, this linear relationship is expressed by the following equation (2).
ΔOCV = k × Ω × σ / F ・ ・ ・ (2)

In formula (2), the volume increase of the negative electrode active material when 1 mol of lithium is inserted ^{is indicated by Ω (unit: m 3} / mol), and the Faraday constant is indicated by F (unit: C / mol). Has been done. k is an experimentally determined constant. By using the above linear relationship, it becomes possible to easily execute the third estimation process.

<Details of the 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 charging OCV nor on the discharging OCV. The slope of the straight line L is the above-mentioned proportionality constant α.

The proportionality constant α is a parameter determined according to the mechanical properties of the negative electrode active material (and its peripheral materials), and is obtained experimentally. More specifically, the proportionality constant α can change depending on the temperature of the negative electrode active material (≈ 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 obtain the proportionality constant α for each of the various combinations of the temperature TB and SOC of the main battery 110 and prepare the map MP.

FIG. 9 is a diagram showing 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 (estimation result of the SOC in the previous calculation cycle).

The map MP may show the correlation between only one of the temperature TB and the SOC and the proportionality constant α. Further, although an example of using the map MP has been described in FIG. 8, it is also possible to set the proportionality constant α (or perform simulation prediction) from the physical property values (Young's modulus, etc.) of the negative electrode active material and the peripheral material. A fixed value may be used as the proportionality constant α.

Returning to FIG. 7, the 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 both estimated by the second SOC estimation process. Therefore, if 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 equation (3). At the same time, 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 proportionality constant α of the straight line L can be 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 the equation (3) that holds for the proportionality constant α.

Note that, in FIGS. 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 performed has been described, but this is only 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 the same as the description of FIGS. 7 to 9.

<Third first to third estimation processing flow>
FIG. 10 is a flowchart showing the first estimation process. Each step (hereinafter abbreviated as "S") included in the flowcharts shown in FIGS. 10 and 11 to 14 described later is basically realized by software processing by the ECU 100, but is dedicated to 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).

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

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

In the formula (4), the internal resistance of the main battery 110 is represented by R, and the 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 the polarization caused by the diffusion of lithium in the positive electrode active material and the negative electrode active material and the diffusion of the lithium salt in the electrolytic solution. When considering the diffusion of lithium in the negative electrode active material, it is desirable to consider the effects of both the difference in lithium concentration in the negative electrode active material and the internal stress. It is assumed that the correction term ΣΔV _i is obtained in the preliminary experiment in advance and is 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 S104, the ECU 100 stores the SOC estimated in S103 as a reference SOC _REF in the memory. Further, the ECU 100 _{stores the OCV ES} estimated in S102 as a reference OCV _REF in the memory. That is, the ECU 100 updates the _{reference SOC REF} and the reference OCV _REF.

FIG. 11 is a flowchart showing the second estimation process. With reference 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 S203. Do not repeat.

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

In 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 temperature TB at the current time as it is, a time average value within a predetermined period immediately before a predetermined period (for example, 30 minutes) may be used. _{Further, the reference SOC REF} may be used as the SOC when referring to the map MP.

In S305, the ECU 100 is acquired by the processing of the reference SOC _REF and the reference OCV _REF obtained by the first estimation processing or the second estimation processing, the proportionality constant α set in the processing of S304, and the processing of S302. Substitute the estimated OCV _ES 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 charge curve CHG and the discharge curve DCH can be strictly determined 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, so to speak, the SOC estimation process by approximation, the SOC estimation accuracy thereof is lower than the SOC estimation accuracy by the first and second estimation processes. Therefore, it is not preferable that the period in 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 in which 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, between the main battery 110 and the sub-battery 120. By forcibly charging and discharging the main battery 110 by power conversion in, 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. Is adopted. When the state P of the main battery 110 is on the charge curve CHG, the first estimation process is executed, and when the state P of the main battery 110 is on the discharge curve DCH, the second estimation process is executed. As a result, the SOC estimation accuracy can be improved as compared with the case where the execution of the third estimation process is continued for a long period of time. 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 process according to 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.

With reference to FIG. 13, in S401, the ECU 100 reads the flag F stored in the memory. When the flag F is F = 1 (YES in S402), the ECU 100 executes the first estimation process shown in FIG. 10 (S100). When the flag F is F = 2 (YES in S403), the 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 both S402 and S403), that is, when the flag F is F = 3, the ECU 100 has passed a predetermined period or more in the state of F = 3. Whether or not it is determined (S404). The length of this predetermined period can be experimentally determined in consideration of factors such as the period of the calculation cycle, the magnitude of the estimation error due to the 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), the influence on the estimation error of the SOC derived from the linear approximation in the third estimation process is considered to be 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 elapses in the state of F = 3 (YES in S404), there is a possibility that the SOC estimation error is 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, the ECU 100 controls the converters 210 and 220 so that the main battery 110 is forcibly charged by the electric power stored in the sub-battery 120. If the forced charge control has already been started, the forced charge control is continued.

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

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

Further, although not shown in the flowchart, the ECU 100 may execute discharge control for returning the electric power of the main battery 110 charged by the forced charge control to the sub-battery 120 after the SOC is estimated by the first estimation process. good. As a result, the amount of SOC increase associated with the forced charge control can be reset.

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

FIG. 14 is a flowchart for explaining another SOC estimation process in the present embodiment. In this flowchart, it is determined that the forced discharge control is executed instead of the 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. This is different from the flowchart shown in FIG. 13 in 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). Since the processes other than these are basically the same as the corresponding processes in the flowchart shown in FIG. 13, detailed description will not be repeated.

The ECU 100 may be configured to execute either the flowchart shown in FIG. 13 or the flowchart shown in FIG. Alternatively, the ECU 100 may be configured to select an appropriate flowchart from the above two flowcharts according to, for example, the SOC of the main battery 110 (and the SOC of the 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), the flowchart shown in FIG. 13 is preferentially executed in order to recover the SOC of the main battery 110. 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 the flag F = 3 continues for a predetermined period or more, the forced charge control or the forced discharge control of the main battery 110 is executed. When the state P of the main battery 110 becomes on the charging 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 on 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 a higher SOC estimation accuracy than the third estimation process, the SOC estimation accuracy can be improved.

Further, 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). As a result, it is possible to recover from the state in which the SOC estimation accuracy is high to execute the subsequent third estimation process.

A typical hybrid vehicle has only one running battery. The charging / discharging of the traveling battery is basically switched as appropriate according to the traveling state (or load state) of the vehicle. Forcibly discharging the traveling battery is difficult in the absence of a load that consumes the discharge power from the traveling battery. Further, for example, it is conceivable to drive the engine and forcibly charge the traveling battery with the electric power generated by the motor generator (generator corresponding to the motor generator 10 of the vehicle 1), but such power generation is a hybrid. It can cause deterioration of the fuel efficiency of the car.

On the other hand, in the present embodiment, the sub-battery 120 is provided in addition to the main battery 110, and charging / discharging of the main battery 110 is realized by exchanging electric power between the main battery 110 and the sub-battery 120. .. Since there is always a sub-battery 120 capable of receiving the discharge power from the main battery 110, it is possible to forcibly discharge the main battery 110 at an arbitrary timing. Further, forced charging of the main battery 110 from the sub-battery 120 via the converters 210 and 220 is more energy efficient than the above-mentioned power generation by engine drive, although power conversion loss may occur in the converters 210 and 220. .. As described above, according to the present embodiment, it is possible to provide a method for improving the SOC estimation accuracy, which has a high degree of freedom in execution timing of forced charge control and forced discharge control, and also has high energy efficiency.

Generally, in plug-in hybrid vehicles and electric vehicles, plug-in charging is performed on a regular basis. When the plug-in is charged with the reference electric energy or more, the state of the main battery 110 is plotted on the charging OCV, so that the SOC estimation accuracy is improved. On the other hand, in the vehicle 1 which is a normal hybrid vehicle (a hybrid vehicle that is not configured to enable 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 can positively create an opportunity for the state of the main battery 110 to be plotted on the charging OCV. However, since there are users of plug-in hybrid vehicles that do not charge plug-ins very often, it can be said that the SOC estimation process in the present disclosure is effective even for plug-in hybrid vehicles in which the frequency of such plug-in charging is low. ..

In addition, in FIG. 3 and FIG. 4, an example in which a silicon-based compound is used as a negative electrode active material having a large volume change due to charge / discharge has been described. However, the negative electrode active material having a large volume change due to charging / discharging is not limited to this. 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 due to charging / discharging. Examples of the negative electrode material of such a lithium ion secondary battery include tin compounds (Sn, SnO, etc.), germanium (Ge) compounds, and lead (Pb) compounds. Moreover, although the silicon-based compound is mentioned as an example of the negative electrode active material, a composite material of the silicon-based compound and another material may be used. Examples of the composite material include a composite material containing a silicon-based compound and graphite, a composite material containing a silicon-based compound and lithium titanate, and the like.

Further, the secondary battery to which the SOC estimation process in the present disclosure can be applied is not limited to the lithium ion secondary battery, and may be another secondary battery (for example, a nickel hydrogen battery). Further, when the volume change amount of the positive electrode active material is large, surface stress may 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 the hysteresis derived from the positive electrode into consideration when estimating the SOC. Further, in the present embodiment, the SOC estimation process of the main battery 110 has been described, but it is also possible to estimate the SOC of the sub-battery 120 by the same method.

The embodiments disclosed this time should be considered to be exemplary in all respects and not restrictive. The scope of the present disclosure is shown by the scope of claims rather than the description of the embodiment described above, 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 speed 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 capacitors, D11, D12 diodes, L1 reactors, Q11, Q12 switching elements.

Claims (2)

With a rechargeable battery
Power storage device and
A power conversion device configured to enable power conversion between the secondary battery and the power storage device,
A control device for estimating the SOC of the secondary battery by any of the first to third estimation processes is provided.
The first estimation process is performed from the OCV of the secondary battery by using a charging curve showing the SOC-OCV characteristics of the secondary battery when the secondary battery is charged from a fully discharged state to a fully charged state. This is a process for estimating the SOC of the secondary battery.
The second estimation process uses a discharge curve showing the SOC-OCV characteristics of the secondary battery when the secondary battery is discharged from the fully charged state to the fully discharged state of the secondary battery. This is a process of estimating the SOC of the secondary battery from the 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 is included in the region defined by the SOC and OCV of the secondary battery. It is a process of estimating the SOC of the secondary battery from the OCV of the secondary battery by using a predetermined correspondence relationship that complements the SOC-OCV characteristics of the secondary battery in the region surrounded by the discharge curve. ,
The control device controls the power conversion device so that the secondary battery is charged when the state of the secondary battery deviates from the charge curve and the discharge curve for a longer period than a predetermined period. A secondary battery system that positions the state of the secondary battery on the charging curve and executes the first estimation process. With a rechargeable battery
Power storage device and
A power conversion device configured to enable power conversion between the secondary battery and the power storage device,
A control device for estimating the SOC of the secondary battery by any of the first to third estimation processes is provided.
The first estimation process is performed from the OCV of the secondary battery by using a charging curve showing the SOC-OCV characteristics of the secondary battery when the secondary battery is charged from a fully discharged state to a fully charged state. This is a process for estimating the SOC of the secondary battery.
The second estimation process uses a discharge curve showing the SOC-OCV characteristics of the secondary battery when the secondary battery is discharged from the fully charged state to the fully discharged state of the secondary battery. This is a process of estimating the SOC of the secondary battery from the 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 is included in the region defined by the SOC and OCV of the secondary battery. It is a process of estimating the SOC of the secondary battery from the OCV of the secondary battery by using a predetermined correspondence relationship that complements the SOC-OCV characteristics of the secondary battery in the region surrounded by the discharge curve. ,
The control device controls the power conversion device so that the secondary battery is discharged when the state of the secondary battery deviates from the charge curve and the discharge curve for a longer period than a predetermined period. A secondary battery system that positions the state of the secondary battery on the discharge curve and executes the second estimation process.

Images