Patent Application
20150022158
The present invention relates to a control device of a secondary battery and an SOC detection method of the secondary battery.
In recent years, for a secondary battery such as a lithium secondary battery, various kinds of materials for positive electrode active material have been studied with the aim of achieving high voltage and high capacity. As such positive electrode active material, for instance, Patent Document 1 discloses solid solution material such as Li2MnO3—LiMO2 (M is transition metal whose average oxidation state is 3+).
Regarding the solid solution material disclosed in Patent Document 1, depending on its composition etc., there is a case where a hysteresis phenomenon in which an open circuit voltage curve during charge and an open circuit voltage curve during discharge are quite different occurs. Then, when the positive electrode active material showing the occurrence of the hysteresis phenomenon is applied to the secondary battery, due to an influence of the hysteresis phenomenon, even if the open circuit voltage is the same, an SOC of the secondary battery is different between during charge and discharge. Thus, there is a problem that the SOC can not properly detected.
Patent Document 1: Japanese Patent Provisional Publication Tokkai No. 2008-270201
An object of the present invention, which solves the problem, is to properly detect, from the open circuit voltage, a current SOC of the secondary battery using, as the material of the positive electrode, the positive electrode active material that shows the difference of the open circuit voltage curve between during the charge and the discharge.
In the present invention, a control device of a secondary battery using, as a positive electrode material, a positive electrode active material that shows a difference of an open circuit voltage curve between during charge and discharge, detects whether the secondary battery is in a charge state or in a discharge state. When the secondary battery is in the charge state, the control device calculates, as a current SOC of the secondary battery, a value that is lower than a value of an SOC corresponding to a current open circuit voltage of the secondary battery on a predetermined reference SOC-open circuit voltage curve showing a relationship between the SOC and the open circuit voltage, which becomes a reference upon calculating the current SOC of the secondary battery. When the secondary battery is in the discharge state, the control device calculates, as the current SOC of the secondary battery, a value that is higher than the value of the SOC corresponding to the current open circuit voltage of the secondary battery on the reference SOC-open circuit voltage curve. With this calculation, the present invention solves the above problem.
According to the present invention, the reference SOC-open circuit voltage curve showing the relationship between the SOC and the open circuit voltage, which becomes the reference upon calculating the current SOC of the secondary battery is set, and the current SOC of the secondary battery is calculated according to whether the secondary battery is in the charge state or in the discharge state using this reference SOC-open circuit voltage curve. It is therefore possible to properly detect the SOCs during the charge and during the discharge of the secondary battery using, as the positive electrode material, the positive electrode active material that shows the difference of the open circuit voltage curve between during charge and discharge.
In the following description, embodiments of the present invention will be explained with reference to the drawings.
The controller 20 is a device to control the secondary battery 10. The controller 20 controls charge and discharge of the secondary battery 10 and also calculates an SOC (State of Charge) of the secondary battery 10 on the basis of a charge-discharge current flowing in the secondary battery 10 which is detected by the ammeter 40 and a terminal voltage of the secondary battery 10 which is detected by the voltmeter 50.
The load 30 is various devices that receive power supply from the secondary battery 10. For instance, in a case where the control system of the secondary battery of the present embodiment is applied to an electric vehicle, the load 30 is a load configured by an inverter and a motor. That is, in the case where the load 30 is configured by the inverter and the motor, a DC power supplied from the secondary battery 10 is converted to an AC power by the inverter, and is supplied to the motor. Further, in the case where the load 30 is configured by the inverter and the motor, a regenerative power generated by rotation of the motor is converted to the DC power through the inverter, and is used to charge the secondary battery 10.
The display device 60 is a device to display information of a current SOC of the secondary battery 10 calculated by the controller 20. For instance, in the case where the control system of the secondary battery of the present embodiment is applied to the electric vehicle, the display device 60 is used to inform an occupant of the electric vehicle of the current SOC of the secondary battery 10.
As the secondary battery 10, it is, for instance, a lithium-based secondary battery such as a lithium-ion secondary battery.
As shown in
Here, the number of each of the positive electrode plate 102, the separator 103 and the negative electrode plate 104 is not especially limited. The electrode stack 101 could be formed by one positive electrode plate 102, three separators 103 and one negative electrode plate 104. Further, the number of each of the positive electrode plate 102, the separator 103 and the negative electrode plate 104 could be selected as necessary.
The positive electrode plate 102 forming the electrode stack 101 has a positive electrode side current collector 102a that extends up to the positive electrode tab 105 and positive electrode active material layers that are formed on both main surfaces of a part of the positive electrode side current collector 102a. As the positive electrode side current collector 102a forming the positive electrode plate 102, it is, for instance, electrochemically stable metal leaf (or electrochemically stable metal foil) such as aluminium leaf (or foil), aluminium alloy leaf (or foil), copper titanium leaf (or foil) and stainless leaf (or foil), each of which has about 20 μm thickness.
The positive electrode active material layer forming the positive electrode plate 102 is formed by applying a mixture of positive electrode active material, a conductive agent such as carbon black and a binding agent such as aqueous dispersion of polyvinylidene fluoride or polytetrafluoroethylene to the main surfaces of apart of the positive electrode side current collector 102a and by drying and pressing them.
The secondary battery 10 of the present embodiment contains, as the positive electrode active material in the positive electrode active material layer forming the positive electrode plate 102, at least positive electrode active material that shows a difference of an open circuit voltage curve between during the charge and the discharge, i.e. positive electrode active material having hysteresis in a charge-discharge curve. As such the positive electrode active material showing the difference of the open circuit voltage curve between during the charge and the discharge, it is not especially limited. It is, for instance, a compound expressed by the following general expression (1). In particular, since the compound expressed by the following general expression (1) has high potential (high voltage) and high capacity, using this compound as the positive electrode active material enables the secondary battery 10 to have high energy density. Here, the compound expressed by the following general expression (1) normally forms solid solution.
aLi[Li1/3 Mn2/3]O2·(1−a)Li[Niw Cox Mny Az]O2 (1)
In the compound expressed by the above general expression (1), as the “A”, it is not especially limited as long as the “A” is the metallic element (metallic element except Li, Ni, Co and Mn). However, at least one element selected from Fe, V, Ti, Al and Mg is preferable, and Ti is far preferable.
Further, in the compound expressed by the above general expression (1), although the “w”, “x”, “y”, “z” are not especially limited as long as the “w”, “x”, “y”, “z” meet w+x+y+z=1 and 0≦x, y, z≦1, it is preferable that z be 0 (z=0). That is, it is preferable that the compound be a compound expressed by the following general expression (2).
aLi[Li1/3 Mn2/3]O2·(1−a)Li[Niw Cox Mny]O2 (2)
Here, the positive electrode active material layer could contain positive electrode active material except the positive electrode active material showing the difference of the open circuit voltage curve between during the charge and the discharge, for instance, lithium compound oxide such as lithium nickelate (LiNiO2), lithium manganate (LiMn2O4) and lithium cobalt oxide (lithium cobaltate) (LiCoO2), LiFePO4 and LiMnPO4.
Each of the positive electrode side current collectors 102a forming the three positive electrode plates 102 is connected to the positive electrode tab 105. As the positive electrode tab 105, for instance, aluminium leaf (or foil), aluminium alloy leaf (or foil), copper leaf (or foil) and nickel leaf (or foil), each of which has about 0.2 mm thickness, could be used.
The negative electrode plate 104 forming the electrode stack 101 has a negative electrode side current collector 104a that extends up to the negative electrode tab 106 and negative electrode active material layers that are formed on both main surfaces of a part of the negative electrode side current collector 104a.
The negative electrode side current collector 104a of the negative electrode plate 104 is, for instance, electrochemically stable metal leaf (or electrochemically stable metal foil) such as nickel leaf (or foil), copper leaf (or foil), stainless leaf (or foil) and iron leaf (or foil), each of which has about 10 μm thickness.
The negative electrode active material layer forming the negative electrode plate 104 is formed, for example, as follows. By preparing a slurry by adding a binding agent such as polyvinylidene and a solvent such as N-2-methylpyrrolidone to negative electrode active material such as non-graphitizable carbon, graphitizable carbon and graphite, and by applying the slurry to the both main surfaces of a part of the negative electrode side current collector 104a, then by drying and pressing them, the negative electrode active material layer is formed.
In the secondary battery 10 of the present embodiment, the three negative electrode plates 104 are formed so that each of the negative electrode side current collectors 104a forming the negative electrode plates 104 is connected to the single negative electrode tab 106. That is, in the secondary battery 10 of the present embodiment, each negative electrode plate 104 is formed so as to connect to the single common negative electrode tab 106.
The separator 103 of the electrode stack 101 is an element that prevents a short circuit between the positive electrode plate 102 and the negative electrode plate 104. The separator 103 might have a function of holding the electrolyte. This separator 103 is a macroporous film formed from, for instance, polyolefine such as polyethylene (PE) and polypropylene (PP) each having about 25 μm thickness, which also has a function of interrupting current by the fact that when overcurrent (excess current) flows, pores on the layer are closed by heat of the overcurrent.
As shown in
The electrolyte which the secondary battery 10 contains is liquid obtained by dissolving, as a solute, lithium salt such as lithium tetrafluoroborate (LiBF4) and lithium hexafluorophosphate (LiPF6) in organic liquid solvent. As the organic liquid solvent forming the electrolyte, it is, for instance, ester-based solvent such as propylene carbonate (PC), ethylene carbonate (EC), buthylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl formate (MF), methyl acetate (MA) and methyl propionate (MP). These could be used as a mixture.
The electrode stack 101 formed in this manner is accommodated between and sealed with the upper jacket member 107 (sealing means or element) and the lower jacket member 108 (sealing means or element). The upper jacket member 107 and the lower jacket member 108 to seal the electrode stack 101 are formed by material having flexibility, e.g. a resin film such as polyethylene and polypropylene or a resin-metal thin film laminate material obtained by bonding (or laminating) resin such as the polyethylene and the polypropylene onto both surfaces of metal foil such as aluminum. By thermal-bonding (heat-bonding) these upper jacket member 107 and lower jacket member 108, the electrode stack 101 is sealed with the positive electrode tab 105 and the negative electrode tab 106 coming out to the outside.
The positive electrode tab 105 and the negative electrode tab 106 are each provided with a seal film 109 to secure absolute contact with the upper jacket member 107 and the lower jacket member 108 at portions where each of the positive electrode tab 105 and the negative electrode tab 106 contacts the upper jacket member 107 and the lower jacket member 108. As the seal film 109, it is not especially limited. It can be formed from, for instance, synthetic resin material having excellent resistance of electrolyte and good thermal adhesion performance such as polyethylene, modified polyethylene, polypropylene, modified polypropylene and ionomer.
The secondary battery 10 of the present embodiment is formed in the manner described above.
Next, a charge-discharge characteristic of the secondary battery 10 of the present embodiment will be explained.
As described above, the secondary battery 10 uses, as the positive electrode active material, the positive electrode active material showing the difference of the open circuit voltage curve between during the charge and the discharge, i.e. the positive electrode active material having the hysteresis in the charge-discharge curve. Because of this, as shown in
That is, as shown in
Here, in
On the other hand, as shown in
Likewise, as shown in
Consequently, in the present embodiment, on the basis of such charge-discharge characteristics of the secondary battery 10, by previously storing the discharge basic open circuit voltage curve β that is a discharge curve when performing the discharge from the predetermined fully charged voltage Vmax in the controller 20 and by using this discharge basic open circuit voltage curve β, the SOC of the secondary battery 10 when performing the discharge from the predetermined fully charged voltage Vmax is calculated by the controller 20. A specific calculating manner of the SOC will be described later.
Further, in the present embodiment, as described above, as shown in
Because of this, in the present embodiment, on the basis of such charge-discharge characteristics of the secondary battery 10, the open circuit curve during the charge in the case where the discharge is performed according to or along the discharge basic open circuit voltage curve β and afterwards the charge is performed again by changing the state from the discharge to the charge is previously stored as a re-charge open circuit voltage curve γSOC for each charging changeover SOCcharge in the controller 20 together with the discharge basic open circuit voltage curve β described above. Then, in the present embodiment, in a situation where the discharge is performed according to or along the discharge basic open circuit voltage curve β and afterwards the charge is performed again by changing the state from the discharge to the charge, by using this re-charge open circuit voltage curve γSOC stored for each charging changeover SOCcharge, the calculation of the SOC of the secondary battery 10 is executed by the controller 20. A specific calculating manner of the SOC will be described later.
Further, in the present embodiment, as shown in
Here, the charge-discharge curve C shown in
Furthermore, as indicated by a charge-discharge curve D in
Here, the charge-discharge curve D shown in
Here, as can be seen from
In addition, as indicated by the charge-discharge curve D in
That is, from the charge-discharge curves C and D shown in
Therefore, in the light of the above characteristic (A), the present embodiment is configured so that the open circuit curve during the discharge in the case where the charge is performed according to or along the re-charge open circuit voltage curve γSOC and afterwards the discharge is performed again by changing the state from the charge to the discharge is previously stored as a re-discharge open circuit voltage curve δγ-SOC for each charging changeover SOCcharge and each discharging changeover SOCdischarge in the controller 20. That is, in the present embodiment, the re-discharge open circuit voltage curve δγ-SOC corresponding to each discharging changeover SOCdischarge is previously stored for each charging changeover SOCcharge in the controller 20. Then, in the present embodiment, in a situation as shown in
Here, in the present embodiment, as the re-discharge open circuit voltage curve δγ-SOC mentioned above, it is determined in the light of the above characteristics of (B) and (C) in addition to the characteristic (A). That is, in the light of the characteristic of (B), before reaching the charging changeover SOCcharge according to the re-charge open circuit voltage curve γSOC, the open circuit curve during the discharge is the open circuit curve corresponding to the discharging changeover SOCdischarge, whereas when passing through the charging changeover SOCcharge, the open circuit curve during the discharge is the open circuit curve moving according to or along the discharge basic open circuit voltage curve β. Further, in the light of the characteristic of (C), when performing the charge again before reaching the charging changeover SOCcharge according to the re-charge open circuit voltage curve γSOC, the charge is performed according to or along the re-charge open circuit voltage curve γSOC. Thus, in the light of these characteristics, as the re-discharge open circuit voltage curve δγ-SOC, data of the open circuit curve during the discharge up to the corresponding charging changeover SOCcharge according to the re-charge open circuit voltage curve γSOC is stored. Accordingly, the present embodiment is configured so that the data up to the corresponding charging changeover SOCcharge according to the re-charge open circuit voltage curve γSOC is stored as the re-discharge open circuit voltage curve δγ-SOC.
Regarding the discharge basic open circuit voltage curve β, in the present embodiment, for instance, the discharge basic open circuit voltage curve β can be obtained by an actual measurement of data collected when actually charging the secondary battery 10 up to the predetermined fully charged voltage Vmax and afterwards actually discharging the secondary battery 10. Likewise, regarding the re-charge open circuit voltage curve γSOC and the re-discharge open circuit voltage curve δγ-SOC, they can also be obtained by an actual measurement of data collected when performing the charge and the discharge with a predetermined SOC being a starting point.
In
Next, an example of operation of the present embodiment will be explained.
First, at step S1, a judgment is made as to whether or not the discharge of the secondary battery 10 from the fully charged state is started by the controller 20. If the discharge is started, the routine proceeds to step S2. On the other hand, if the discharge is not started, the routine waits at step S1.
At step S2, an operation of reading the discharge basic open circuit voltage curve β previously stored in the controller 20 is performed by the controller 20.
Subsequently, at step S3, an operation of obtaining the terminal voltage of the secondary battery 10 measured by the voltmeter 50 and the current value of the secondary battery 10 measured by the ammeter 40 then calculating a current open circuit voltage of the secondary battery 10 from the terminal voltage obtained and the current value of the secondary battery 10 obtained is performed by the controller 20. Here, as a calculating manner of the current open circuit voltage of the secondary battery 10, it is not especially limited. For instance, it could be a manner in which, using a plurality of data of the terminal voltage and the current value of the secondary battery 10, a value of the terminal voltage when the current value is zero is estimated from the plurality of data of the terminal voltage and the current value using a regression line, and this value is calculated as the open circuit voltage.
At step S4, an operation of calculating a current SOC of the secondary battery 10 from the current open circuit voltage of the secondary battery 10 calculated at step S3 on the basis of the discharge basic open circuit voltage curve β read at step S2 is performed by the controller 20. When explaining the case shown in
At step S5, information of the current SOC of the secondary battery 10 calculated at step S4 is sent from the controller 20 to the display device 60, and an operation of displaying the information of the current SOC of the secondary battery 10 on the display device 60 is performed.
Subsequently, at step S6, a judgment is made as to whether or not an operation of the changeover from the discharge state to the charge state is performed by the controller 20. That is, a judgment is made as to whether or not the discharge is finished then the charge is started. If the operation of the changeover from the discharge state to the charge state is not performed, the routine proceeds to step S7. Then, until a predetermined finishing operation of the charge and discharge is performed (Yes at step 7), or until the operation of the changeover from the discharge state to the charge state is performed (Yes at step S6), processes at steps S2 to S7 are repeated. That is, the calculation of the current SOC of the secondary battery 10 during the discharge is repeated using the discharge basic open circuit voltage curve β.
On the other hand, if the predetermined finishing operation of the charge and discharge is performed at step S7, the present operation is terminated. Further, when judged that the operation of the changeover from the discharge state to the charge state is performed at step S6, the routine proceeds to step S8.
At step S8, an operation of setting the SOC of the secondary battery 10 when performing the operation of the changeover from the discharge state to the charge state to the charging changeover SOCcharge is performed by the controller 20. Further, an operation of reading the re-charge open circuit voltage curve γSOC corresponding to the charging changeover SOCcharge, which is previously stored in the controller 20, is performed by the controller 20. That is, for instance, as shown in
Subsequently, at step S9, an operation of obtaining the terminal voltage of the secondary battery 10 measured by the voltmeter 50 and the current value of the secondary battery 10 measured by the ammeter 40 then calculating a current open circuit voltage of the secondary battery 10 from the terminal voltage obtained and the current value of the secondary battery 10 obtained is performed by the controller 20. Here, as the calculating manner of the current open circuit voltage of the secondary battery 10, it could be the same manner as that at step S3 mentioned above.
At step S10, an operation of calculating a current SOC of the secondary battery 10 from the current open circuit voltage of the secondary battery 10 calculated at step S9 on the basis of the re-charge open circuit voltage curve γSOC corresponding to the charging changeover SOCcharge read at step S8 is performed by the controller 20. When explaining the case shown in
At step S11, information of the current SOC of the secondary battery 10 calculated at step S10 is sent from the controller 20 to the display device 60, and an operation of displaying the information of the current SOC of the secondary battery 10 on the display device 60 is performed.
Subsequently, at step S12, a judgment is made as to whether or not an operation of the changeover from the charge state to the discharge state is performed by the controller 20. That is, a judgment is made as to whether or not the charge is finished then the discharge is started. If the operation of the changeover from the charge state to the discharge state is not performed, the routine proceeds to step S13. Then, until a predetermined finishing operation of the charge and discharge is performed (Yes at step S13), or until the operation of the changeover from the charge state to the discharge state is performed (Yes at step S12), processes at steps S8 to S13 are repeated. That is, the calculation of the current SOC of the secondary battery 10 during the charge is repeated using the re-charge open circuit voltage curve γSOC corresponding to the charging changeover SOCcharge. For instance, when explaining the case shown in
On the other hand, if the predetermined finishing operation of the charge and discharge is performed at step S13, the present operation is terminated. Further, when judged that the operation of the changeover from the charge state to the discharge state is performed at step S12, the routine proceeds to step S14 shown in
At step S14, an operation of setting the SOC of the secondary battery 10 when performing the operation of the changeover from the charge state to the discharge state again to the discharging changeover SOCdischarge is performed by the controller 20. Further, an operation of reading the re-discharge open circuit voltage curve δγ-SOC corresponding to the charging changeover SOCcharge and the discharging changeover SOCdischarge, which is previously stored in the controller 20, is performed by the controller 20. For instance, when explaining the case shown in
Subsequently, at step S15, an operation of obtaining the terminal voltage of the secondary battery 10 measured by the voltmeter 50 and the current value of the secondary battery 10 measured by the ammeter 40 then calculating a current open circuit voltage of the secondary battery 10 from the terminal voltage obtained and the current value of the secondary battery 10 obtained is performed by the controller 20. Here, as the calculating manner of the current open circuit voltage of the secondary battery 10, it could be the same manner as that at step S3 mentioned above.
At step S16, an operation of calculating a current SOC of the secondary battery 10 from the current open circuit voltage of the secondary battery 10 calculated at step S15 on the basis of the re-discharge open circuit voltage curve δγ-SOC corresponding to the charging changeover SOCcharge and the discharging changeover SOCdischarge read at step S14 is performed by the controller 20. When explaining the case shown in
At step S17, information of the current SOC of the secondary battery 10 calculated at step S16 is sent from the controller 20 to the display device 60, and an operation of displaying the information of the current SOC of the secondary battery 10 on the display device 60 is performed.
Next, at step S18, a judgment is made as to whether or not a value of the current SOC of the secondary battery 10 calculated at step S16 is lower than the charging changeover SOCcharge by the controller 20. That is, when explaining the case shown in
On the other hand, if the value of the current SOC of the secondary battery 10 is higher than SOC2 that is the charging changeover SOCcharge, until the discharge is performed beyond SOC2 that is the charging changeover SOCcharge (Yes at step S18), or until the operation of the changeover from the discharge state to the charge state is performed (Yes at step S19), or until the charge and discharge finishing operation is performed (Yes at step S20), processes at steps S14 to S20 are repeatedly performed. That is, the calculation of the current SOC of the secondary battery 10 is repeatedly executed by the controller 20 using the re-discharge open circuit voltage curve δγ-SOC (i.e. the open circuit voltage curve corresponding to the charge-discharge curve C) corresponding to SOC2 that is the charging changeover SOCcharge and SOC4 that is the discharging changeover SOCdischarge.
If the operation of the changeover from the discharge state to the charge state is performed by the controller 20 at step S19, as indicated by the charge-discharge curve D in
According to the present embodiment, the discharge curve when performing the discharge from the predetermined fully charged state, i.e. the fully charged voltage Vmax (SOC=100%) is previously stored as the discharge basic open circuit voltage curve β, then when the discharge is performed from the predetermined fully charged voltage Vmax, the current SOC of the secondary battery 10 is calculated from the current open circuit voltage of the secondary battery 10 on the basis of the discharge basic open circuit voltage curve β. Therefore, the current SOC of the secondary battery 10 when performing the discharge from the predetermined fully charged voltage Vmax can be accurately calculated. Especially when the control system of the secondary battery of the present embodiment is applied to the electric vehicle, since normally the secondary battery 10 is used after being charged up to the predetermined fully charged state, in this case, the discharge is performed according to or along the discharge basic open circuit voltage curve β. Thus, by using the discharge basic open circuit voltage curve β, it is possible to properly or rightly calculate the current SOC of the secondary battery 10.
Further, according to the present embodiment, the charge curve when the discharge is performed from the predetermined fully charged state and afterwards the state is changed from the discharge to the charge is previously stored as the re-charge open circuit voltage curve γSOC for each charging changeover SOCcharge. Then, in the case where the discharge is performed from the predetermined fully charged state and afterwards the charge is performed again, the current SOC of the secondary battery 10 is calculated from the current open circuit voltage of the secondary battery 10 on the basis of the re-charge open circuit voltage curve γSOC. Therefore, according to the present embodiment, in addition to the case where the discharge is performed from the predetermined fully charged state, even when the charge is performed again, the current SOC of the secondary battery 10 can be accurately calculated.
In addition, according to the present embodiment, the discharge curve when the discharge is performed from the predetermined fully charged state and the charge is performed again then afterwards the state is changed again from the charge to the discharge is previously stored as the re-discharge open circuit voltage curve δγ-SOC for each charging changeover SOCcharge and each discharging changeover SOCdischarge. Then, in the case where the discharge is performed from the predetermined fully charged state and the charge is performed then afterwards the discharge is performed again, the current SOC of the secondary battery 10 is calculated from the current open circuit voltage of the secondary battery 10 on the basis of the re-discharge open circuit voltage curve δγ-SOC. Therefore, according to the present embodiment, even when the discharge is performed from the predetermined fully charged state and the charge is performed then afterwards the discharge is performed again, the current SOC of the secondary battery 10 can be accurately calculated.
Especially when the control system of the secondary battery of the present embodiment is applied to the electric vehicle, normally the secondary battery 10 is used after being charged up to the predetermined fully charged state. Thus, by previously storing the re-discharge open circuit voltage curve δγ-SOC for each charging changeover SOCcharge and each discharging changeover SOCdischarge in addition to the discharge basic open circuit voltage curve β and the re-charge open circuit voltage curve γSOC for each charging changeover SOCcharge then by calculating the current SOC of the secondary battery 10 using these curves, the current SOC of the secondary battery 10 can be accurately calculated in a wide variety of situations.
Next, a second embodiment of the present invention will be explained.
In the second embodiment of the present invention, the SOC of the secondary battery 10 is calculated using a reference SOC-open circuit voltage curve δ explained below. Configuration and operation of the second embodiment except this calculation are the same as those of the first embodiment described above.
As explained above, the secondary battery 10 of the present embodiment has the characteristics or properties that, as shown in
In addition to the characteristics or properties above, the secondary battery 10 of the present embodiment has the following characteristics or properties. That is, when comparing the SOC during the charge and the SOC during the discharge at the same open circuit voltage, the SOC during the charge is lower, and the SOC during the discharge is higher. For instance, as shown in
Therefore, in the present embodiment, the current SOC of the secondary battery 10 is calculated using these characteristics or properties. That is, in the present embodiment, as shown in
Then, in the present embodiment, as shown in
Therefore, in the present embodiment, an SOC corresponding to the open circuit voltage of the secondary battery 10 on the reference SOC-open circuit voltage curve δ is determined as a corresponding SOCref. Then, during the charge, an SOC (=SOCref×Ccharge) that is calculated by correcting the corresponding SOCref by a predetermined correction factor Ccharge that is less than 1 (Ccharge<1) is calculated as the current SOC of the secondary battery 10. Further, during the discharge, an SOC (=SOCref×Cdischarge) that is calculated by correcting the corresponding SOCref by a predetermined correction factor Cdischarge that is greater than 1 (Cdischarge>1) is calculated as the current SOC of the secondary battery 10. Here, as the correction factors Ccharge and Cdischarge used for this calculation, they are not especially limited. Each of them could be a predetermined certain constant, or might be a variable that is set with consideration given to the charge-discharge characteristic of the secondary battery 10.
For instance, as shown in
As explained above, according to the second embodiment, the reference SOC-open circuit voltage curve δ is set, then on the basis of the reference SOC-open circuit voltage curve δ, the current SOC of the secondary battery 10 is calculated according to whether the secondary battery 10 is in the charge state or in the discharge state. Thus, the current SOC of the secondary battery 10, using the positive electrode active material showing the difference of the open circuit voltage curve between during the charge and the discharge, can be calculated accurately and relatively easily.
Although the embodiments of the present invention has been explained above, the embodiments are described in order to facilitate an understanding of the present invention, and are not described to limit the present invention. Thus, each element or component disclosed in the above embodiments includes all design modifications and equivalents belonging to the technical scope of the present invention.
For instance, the above first embodiment shows the example in which, as the discharge basic open circuit voltage curve β when performing the discharge from the predetermined fully charged state, the open circuit voltage curve when performing the discharge from the fully charged voltage Vmax of SOC=100% is used. However, as the discharge basic open circuit voltage curve β, an open circuit voltage curve according to a battery design of the secondary battery 10 or a charge-discharge system design that actually uses the secondary battery 10 could be set. That is, for instance, it is not necessarily required that the predetermined fully charged state be set to an ideal fully charged state (this is a 100% charged state) that is considered from the positive electrode active material and the negative electrode active material forming the secondary battery 10. For example, a 95% charged state, which is slightly lower than the ideal fully charged state, could be set as the predetermined fully charged state. However, from the viewpoint of enhancing the effects of the present embodiments, it is desirable to set the predetermined fully charged state to a state that is close to the 100% charged state.
Further, in the above first present embodiment, instead of the discharge basic open circuit voltage curve β, the re-charge open circuit voltage curve γSOC and the re-discharge open circuit voltage curve δγ-SOC obtained by the actual measurement of data collected when actually charging and discharging the secondary battery 10, intermittent data that is obtained by getting or sampling corresponding open circuit voltages at each certain SOC interval (e.g. at each 1% interval) from the data could be used as the discharge basic open circuit voltage curve the re-charge open circuit voltage curve γSOC and the β, re-discharge open circuit voltage curve δγ-SOC. By using such intermittent data, a data capacity in the controller 20 can be further reduced.
In the case where the intermittent data is used, a method for determining the current SOC of the secondary battery 10 from the calculated open circuit voltages using data approximation can be employed in the controller 20. For instance, as shown in
If 0≦(E−En)/(En+1−En)<0.5, SOC(E)=SOCn (3)
If 0.5≦(E−En)/(En+1−En)≦1, SOC(E)=SOCn+1 (4)
Or, the first embodiment could be configured so that, as the re-charge open circuit voltage curve γSOC set for each charging changeover SOCcharge, the voltage curve is intermittently set at each predetermined SOC interval (e.g. at each 1% interval) and this data is stored. Also in this case, the current SOC of the secondary battery 10 could be calculated according to the above expressions (3) and (4) using the re-charge open circuit voltage curve γSOC having a closest charging changeover SOCcharge, which is stored in the controller 20. Further, likewise, the first embodiment could be configured so that, as the re-discharge open circuit voltage curve δγ-SOC set for each charging changeover SOCcharge and each discharging changeover SOCdischarge, the voltage curve is intermittently set at each predetermined SOC interval (e.g. at each 1% interval) and this data is stored. Also in this case, in the same manner as the above, the current SOC of the secondary battery 10 could be calculated. Especially by intermittently storing the re-charge open circuit voltage curve γSOC and the re-discharge open circuit voltage curve δγ-SOC in this way, the data capacity in the controller 20 can be further reduced.
The above first embodiment employs a method for determining the current SOC of the secondary battery 10 from the current open circuit voltage of the secondary battery 10 on the basis of the discharge basic open circuit voltage curve β, the re-charge open circuit voltage curve γSOC and the re-discharge open circuit voltage curve δγ-SOC. However, instead of this method, it is possible to calculate the current SOC of the secondary battery 10 on the basis of a current summation. That is, the charge-discharge current detected by the ammeter 40 from a discharge start time is continuously summed up, and on the basis of a summation result, the current SOC of the secondary battery 10 can be calculated. In this case, for instance, by making a calculation of the SOC by the current summation at a predetermined first interval (e.g. 10 m sec interval) and also by making a calculation of the SOC based on the above-mentioned discharge basic open circuit voltage curve β, the re-charge open circuit voltage curve γSOC and the re-discharge open circuit voltage curve δγ-SOC at a predetermined second interval (e.g. several minutes˜several tens of minutes) which is longer than the first interval, a calculation result of the SOC by the current summation can be corrected according to a calculation result of the SOC based on the discharge basic open circuit voltage curve β, the re-charge open circuit voltage curve γSOC and the re-discharge open circuit voltage curve δγ-SOC. Especially by using this method in particular, while the calculation of the SOC is made by the current summation which has a relatively light operation load, the calculation result of the SOC by the current summation is corrected according to the calculation result of the SOC based on the discharge basic open circuit voltage curve β, the re-charge open circuit voltage curve γSOC and the re-discharge open circuit voltage curve δγ-SOC. This increases the calculation accuracy of the SOC.
Further, the above first embodiment shows, as the example, the configuration in which the re-discharge open circuit voltage curve δγ-SOC is set for each charging changeover SOCcharge and each discharging changeover SOCdischarge. However, the first embodiment could be configured to set one re-discharge open circuit voltage curve δγ-SOC for only the charging changeover SOCcharge. That is, one re-charge open circuit voltage curve γSOC and one re-discharge open circuit voltage curve δγ-SOC could be set for the charging changeover SOCcharge. Here, when referring to
Therefore, in the present embodiment, one re-charge open circuit voltage curve γSOC and one re-discharge open circuit voltage curve δγ-SOC are set for each charging changeover SOCcharge. Then, except that this is used, the current SOC of the secondary battery 10 could be calculated in the same manner as the first embodiment. Especially when such configuration is employed, the current SOC of the secondary battery 10, using the positive electrode active material showing the difference of the open circuit voltage curve between during the charge and the discharge, can be calculated accurately while reducing the data to be stored and lightening an operation load.
The method of setting one re-charge open circuit voltage curve γSOC and one re-discharge open circuit voltage curve δγ-SOC soc for each charging changeover SOCcharge is not especially limited. For instance, in the same manner as the first embodiment, one re-charge open circuit voltage curve γSOC and one re-discharge open circuit voltage curve δγ-SOC are stored for each charging changeover SOCcharge in the controller 20, then this could be obtained when the state is changed from the charge to the discharge. Or alternatively, each time the state is changed from the charge to the discharge, one re-charge open circuit voltage curve γSOC and one re-discharge open circuit voltage curve δγ-SOC which correspond to the charging changeover SOCcharge could be calculated. Furthermore, the method of setting the re-discharge open circuit voltage curve δγ-SOC corresponding to the charging changeover SOCcharge is not especially limited. For instance, a middle SOCmid (SOCmid=(100−SOCcharge)/2) from the charging changeover SOCcharge to the full charge is calculated. Then, from the middle SOCmid, the open circuit voltage curve during the discharge when performing the discharge can be the re-discharge open circuit voltage curve δγ-SOC.
In the above embodiments, the secondary battery 10 corresponds to a secondary battery of the present invention, the controller 20 corresponds to a storing unit or means, an SOC calculating unit or means, a charging start SOC detecting unit or means, first and second obtaining units or means, first to third storing units or means, first to third SOC calculating units or means, a charge-discharge current summing unit or means and a correcting unit or means of the present invention.
Although the embodiments of the present invention has been explained above, the embodiments are described in order to facilitate an understanding of the present invention, and are not described to limit the present invention. Thus, each element or component disclosed in the above embodiments includes all design modifications and equivalents belonging to the technical scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-051171 | Mar 2012 | JP | national |
| 2012-268036 | Dec 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/055303 | 2/28/2013 | WO | 00 |
