Embodiments of the present invention relates to a storage system, a storage control method, and a storage control program.
As technology for ascertaining the charging rate of a storage battery, technology for estimating a state of charge (SOC) serving as one of indexes of the charging rate on the basis of a ratio of a battery capacity of the storage battery to an amount of energy by which the storage battery is charged is known. However, since a battery capacity of a storage battery varies in accordance with a use status, aging, and the like of the storage battery, the estimation accuracy of an SOC may be lowered in some cases in a conventional estimation technique.
Japanese Unexamined Patent Application, First Publication No. 2000-306613
Japanese Unexamined Patent Application, First Publication No. 2014-174050
An objective to be solved by the present invention is to provide a storage system, a storage control method, and a storage control program which can estimate an SOC of a storage battery with high accuracy.
A storage system in an embodiment includes a storage battery, a first deriver, a second deriver, and a corrector. The storage battery performs charging and discharging of electricity. The first deriver derives a first state of charge (SOC) on the basis of a voltage of the storage battery when a current is not flowing to the storage battery. The second deriver derives a second SOC on the basis of a battery capacity of the storage battery and an integrated value of a current flowing to the storage battery. The corrector corrects the battery capacity of the storage battery which is used by the second deriver on the basis of a difference between the second SOC derived by the second deriver and the first SOC derived by the first deriver after the derivation of the second SOC. Furthermore, the corrector changes a correction quantity of the correction in accordance with a state of the storage battery.
A storage system, a storage control method, and a storage control program according to an embodiment will be described below with reference to the drawings.
The battery modules 12(1) to 12(k) include, for example, secondary batteries such as lithium ion batteries, lead storage batteries, sodium sulfur batteries, redox flow batteries, and nickel metal hydride batteries. The characteristics of the secondary batteries are represented by, for example, parameters including a battery capacity C [Ah] and a current rate R [C]. For example, in a battery with a rated battery capacity of 20 [Ah], a current with a current rate of 1[C] (20 [A]) can be discharged for one hour at a time of a state of charge (SOC) of 100% (fully charged) in a state in which deterioration docs not occur such as immediately after shipment. In other words, a current with a current rate of 1[C] (20 [A]) can be charged for one hour at a time of an SOC of 0% in a state in which deterioration does not occur such as immediately after shipment.
Hereinafter, when the plurality of battery modules 12(1) to 12(k) are not distinguished, the plurality of battery modules 12(1) to 12(k) are simply referred to as battery modules 12. Furthermore, when the plurality of CMUs 20(1) to 20(k) are not distinguished, the plurality of CMUs 20(1) to 20(k) are simply referred to as CMUs 20. The CMUs 20(1) to 20(k) have the same constitution, and the CMUs are provided in accordance with the number k of battery modules.
The storage system 1 switches battery modules to be operated among the battery modules 12(1) to 12(k) on the basis of a charge and discharge electric power command sent form a high-order device 40. The storage system 1 charges and discharges the selected assembled battery unit 10 on the basis of the charge and discharge electric power command. Note that it is desirable to charge and discharge the battery modules 12 using a constant current. In this embodiment, charging and discharging of electricity performed using a constant current will be described below as an example.
The BMU 30 derives an SOC as one of indexes of a charging rate of each battery module 12 in accordance with an operation status of the assembled battery unit 10. A method of deriving the SOC performed using the BMU 30 will be described below.
Note that an SOC may be derived in the high-order device 40 or the CMU 20 instead of the SOC being derived in the BMU 30, and two or more processors included in the high-ordcr device 40, the BMU 30, and the CMU 20 may be configured to bear a part of an arithmetic process of deriving an SOC.
The storage system 1 is connected to, for example, an electric power system 60, the high-order device 40, a power conditioning system (PCS) 50, and the like. The high-order device 40 sends the charge and discharge electric power command sent to the assembled battery unit 10 controlled by the PCS 50 to the PCS 50.
The PCS 50 includes a processor such as a central processing unit (CPU), a communication interface configured to bi-directionally communicate with the high-order device 40, and the like. The PCS 50 performs the following operations on the basis of a control signal sent from the high-order device 40. For example, the PCS 50 converts direct current (DC) electric power discharged from the battery module 12 into alternating current (AC) electric power, and steps up a voltage to a voltage (for example, 3.3 to 6.6 [kV]) used in an electric power system. Furthermore, for example, the PCS 50 converts AC electric power supplied from the electric power system into DC electric power, and steps down a voltage to a voltage (for example, 100 [V]) by which the battery module 12 can be charged.
A series circuit in which a plurality of battery modules 12, the BMU 30, a switch circuit 70, and switches 72 are connected in series to each other is constituted inside the assembled battery unit 10(1). The assembled battery unit 10(1) is connected to one terminal of the series circuit and the PCS 50 with the switch circuit 70. In the switch circuit 70, for example, a switch Si having no resistance (having, for example, a resistance value which is 1/10 or less that of a resistor R) and a switch S2 connected in series to the resistor R are connected in parallel to each other.
Also, the switches 72 may be provided between the battery modules 12. Each of the switches 72 is used for turning off the series circuit, for example, when any of the battery modules 12 is removed therefrom for the purpose of checking the battery module 12. The switch 72 is also used as a disconnecting unit (a service disconnect) in some cases and also functions as a fuse in some cases. In this case, wires used to notify the BMU 30 of an inserted and removal state and a state of fusing may be provided.
The BMU 30 includes, for example, a processor such as a CPU and a storage unit such as a read only memory (ROM), a random access memory (RANI), a flash memory, and a hard disk drive (HDD). The BMU 30 appropriately controls the switch circuit 70 and the switch 72 on the basis of the charge and discharge electric power command. The BMU 30 controls the switch circuit 70 such that the number of battery modules 12 and the number of assembled battery units 10 configured to charge and discharge are adjusted, for example, such that an amount of charging and discharging of electricity contained in the charge and discharge electric power command is satisfied.
Constitutions will be described in detail below by referring back to
Each of The CMUs 20(1) to 20(k) includes, for example, voltmeters 22(1) to 22(k) and first SOC derivers 24(1) to 24(k). Hereinafter, when the plurality of voltmeters 22(1) to 22(k) are not distinguished, the plurality of voltmeters 22(1) to 22(k) are simply referred to as voltmeters 22, and when the plurality of first SOC derivers 24(1) to 24(k) are not distinguished, the plurality of first SOC derivers 24(1) to 24(k) are simply referred to as first SOC derivers 24. The voltmeters 22 each measure voltages between positive electrode and negative electrode terminals in the battery modules 12.
Each of the first SOC derivers 24 acquires information indicating a voltage of each of the battery modules 12 from each of the voltmeters 22 at a timing at which each of the voltages is static and derives a first SOC. The timing at which the voltage is static is a time at which a voltage between terminals of the battery modules 12 is sufficiently stabilized and an open-circuit voltage which will be described below can be measured. The first SOC deriver 24 calculates a first SOC at both a timing at which a voltage is static before charging and discharging of electricity and a timing at which the voltage is static after the charging and discharging of electricity. The first SOC deriver 24 is an example of a “first deriver.” Note that the first SOC derivers 24(1) to 24(k) may he functional units of the BMU 30.
The first SOC deriver 24 determines that a voltage of the battery module 12 is static, for example, when a predetermined time Δt (for example, 10 minutes) has elapsed from a timing at which the charging and discharging of electricity has been completed and acquires information indicating the voltage of the battery modules 12 from the voltmeter 22. Note, when subsequent charging and discharging of electricity is started when a predetermined time Δt has not elapsed from the timing at which the charging and discharging of electricity has been completed, no first SOC derivers 24 acquire a voltage in the meantime.
The first SOC deriver 24 determines that the charging and discharging of electricity has been completed when a current measured by a ammeter 32 exceeds a threshold value Iref (for example, 0.1 [mA]), and determines that the charging and discharging of electricity has not been completed when the current measured thereby is the threshold value Iref or less. Hereinafter, the voltage acquired at the timing at which the voltage is static is referred to as a “static voltage.”
Any timing may be used for a timing at which the static voltage is acquired as long as charging and discharging of electricity following corresponding charging and discharging of electricity is performed within a period before a scheduled time. Furthermore, a static voltage may be acquired multiple times within this period such that an average value is derived from a plurality of static voltages.
Also, the first SOC deriver 24 acquires open-circuit voltage (OCV)-SOC characteristics data from a storage unit (not shown) to derive an SOC. The OCV-SOC characteristics data is data indicating a correlation of an OCV and an SOC of the storage battery included in the battery module 12.
The first SOC deriver 24 applies the acquired static voltage to the OCV-SOC characteristics data to derive an SOC (a first SOC) of the battery modules 12. Hereinafter, for convenience, a first SOC derived on the basis of a static voltage acquired before the charging and discharging of electricity performed at any timing is referred to as an “SOC1b.” Furthermore, similarly, a first SOC derived on the basis of a static voltage acquired after the charging and discharging of electricity is referred to as an “SOC1a.” When the first SOCs are derived, the first SOC deriver 24 sends the first SOCs to the BMU 30.
The BMU 30 includes, for example, the ammeter 32, a second SOC deriver 34, and a Comparator and corrector 36. The ammeter 32 measures a current flowing to the battery module 12 for every battery module 12.
The second SOC deriver 34 derives an SOC (a second SOC) of the battery module 12 on the basis of an integrated value (hereinafter referred to as a “current integrated value ∫I”) of a current flowing to the battery module 12 during the charging and discharging of electricity, a battery capacity C of the battery module 12, and an SOC1b derived by the first SOC deriver 24. Hereinafter, the SOC derived by the second SOC deriver 34 is referred to as an “SOC2 .” Note that the second SOC deriver 34 is an example of a “second deriver.”
The second SOC deriver 34 calculates a current integrated value ∫I (for example, a unit is [Ah]), for example, using a period between an integration start time at which a current flowing to the battery module 12 has changed from a state in which the current is the threshold value Iref or less to a state in which the current exceeds the threshold value Iref and an integration end time at which the current flowing to the battery module 12 has changed from a state in which the current exceeds the threshold value Ircf to a state in which the current is the threshold value Iref or less as an integration period. The second SOC deriver 34 divides the calculated current integrated value ∫I by the battery capacity C of the battery module 12, adds the SOC1b derived by the first SOC deriver 24 to a value obtained by expressing the value obtained by this division as a percentage, and derives an SOC2 . The second SOC deriver 34 outputs the calculated current integrated value ∫I to the Comparator and corrector 36.
The first SOC deriver 24 derives an SOC1a on the basis of, for example, the static voltage acquired at the timing at which the predetermined time Δt has elapsed from the integration end time.
The Comparator and corrector 36 derives a difference ΔSOC between the SOC2 derived by the second SOC deriver 34 and the SOC1a derived by the first SOC deriver 24. The Comparator and corrector 36 corrects parameters associated with the battery capacity C of the battery module 12 so that a value of a ΔSOC is set to 0 when the derived ΔSOC is not 0. Note that the Comparator and corrector 36 is an example of a “corrector.”
The Comparator and corrector 36 corrects the parameters of the battery capacity C of the battery module 12 in a derivation equation of the SOC2 so that an SOC2 derived next time coincides with the SOC1a using the SOC1a as a true value, for example, when the ΔSOC is not 0. In other words, the storage system 1 derives the SOC2 using the corrected battery capacitor C (hereinafter referred to a “battery capacity C#” at a time at which electricity is charged and discharged after the charging and discharging of electricity. Thus, the storage system 1 can improve estimation accuracy of the SOC of the battery module 12. Note that the Comparator and corrector 36 may decide whether to perform correction, for example, in accordance with whether an absolute value of the ΔSOC has exceeded a threshold value (for example, 5%) or the like instead of deciding whether to perform correction in accordance with whether the ΔSOC is 0. The same applies to the following description.
A process of correcting a parameter of a battery capacity C will be described below with reference to
Hereinafter, it is assumed that charging and discharging of electricity starts at time t0, and the charging and discharging of electricity ends at time t1. In this case, the second SOC deriver 34 derives an SOC2 on the basis of a current integrated value ∫I in a period from time t0 to time t1, the battery capacity C of the battery module 12, and an SOC1b derived by the first SOC deriver 24 on the basis of a static voltage before time t0.
The first SOC deriver 24 acquires a static voltage of the battery module 12 at time t2 at which a predetermined time Δt or more has elapsed from time t1 at which the charging and discharging of electricity has ended. The first SOC deriver 24 derives an SOC1a of the battery module 12 after the charging and discharging of electricity on the basis of the acquired static voltage and OCV-SOC characteristics data.
The Comparator and corrector 36 derives a difference ΔSOC between the SOC2 derived by the second SOC deriver 34 and the SOC1a derived by the first SOC deriver 24. Since the ΔSOC is not 0 in the illustrated example, the Comparator and corrector 36 corrects the parameters associated with the battery capacity C of the battery module 12, and notifies the second SOC deriver 34 that parameters of a battery capacity C# after the correction have changed. The battery capacity C# after the correction is derived using the following Expression (2).
First, the first SOC deriver 24 acquires a static voltage of the battery module 12 from the voltmeter 22 at a timing at which a voltage is static before charging and discharging of electricity, and derives an SOC1b on the basis of the acquired static voltage and OCV-SOC characteristics data (Step S100). Subsequently, the storage system 1 charges and discharges the battery module 12 on the basis of the charge and discharge electric power command (Step S102).
Subsequently, the second SOC deriver 34 calculates a current integrated value ∫I of the battery module 12 during charging and discharging of electricity on the basis of measured results of the ammeter 32 (Step S104). Subsequently, the second SOC deriver 34 derives an SOC2 on the basis of the calculated current integrated value JI, the battery capacity C of the battery module 12, and the SOC1b derived by the first SOC deriver 24 (Step S106).
Subsequently, the first SOC deriver 24 acquires a static voltage of the battery module 12 from the voltmeters 22 at a timing at which the voltage is static after the charging and discharging of electricity, and derives an SOC1a on the basis of the acquired static voltage and OCV-SOC characteristics data (Step S108).
Subsequently, the Comparator and corrector 36 derives a difference ΔSOC between the SOC2 derived by the second SOC deriver 34 and the SOC1a derived by the first SOC deriver 24 (Step S110).
Subsequently, the Comparator and corrector 36 determines whether the derived ΔSOC is not 0 (Step S112). The storage system 1 ends the process of this flowchart when it is determined that the derived ΔSOC is 0 (Step S112: NO). The Comparator and corrector 36 corrects the parameters of the battery capacity C of the battery module 12 so that a value of the ΔSOC is 0 (Step S114) when it is determined that the derived ΔSOC is not 0 (Step S112: YES). Thus, the storage system 1 ends the process of this flowchart.
According to the storage system 1 in the above-described first embodiment, the SOC1b is derived on the basis of the static voltage of the battery module 12 acquired at the time at which the voltage is static before the charging and discharging of electricity and the OCV-SOC characteristics data, the SOC2 is derived on the basis of the current integrated value II of the battery module 12 during the charging and discharging of electricity, the battery capacity C of the battery module 12, and the derived SOC1b, the SOC1a is derived on the basis of the static voltage of the battery module 12 acquired at the timing at which the voltage is static after the charging and discharging of electricity and the OCV-SOC characteristics data, and the parameters of the battery capacity C of the battery module 12 are corrected on the basis of the difference ΔSOC between the SOC2 and the SOC1a. As a result, the storage system 1 can estimate the SOC of the battery module 12 with high accuracy.
A storage system 1 in a second embodiment will be described below. In the storage system 1 in the second embodiment, functions of a Comparator and corrector 36 are different from those of the first embodiment. Therefore, description thereof will be provided focusing on associated differences, and description of the same parts will be omitted. Here, a process of the Comparator and corrector 36 will be described as one of differences from the first embodiment.
In the storage system 1 in this embodiment, a correction quantity to be corrected is appropriately changed on the basis of a use state of a battery module 12 when a battery capacity C is corrected on the basis of a ΔSOC derived by the Comparator and corrector 36. The use state includes, for example, (1) a current rate R at a time at which electricity is charged and discharged, (2) a derived ΔSOC, and any one or more other states. In this embodiment, for example, a use state in which charging and discharging of electricity is performed using a current rate R of 1C and a constant current while an SOC of the battery module 12 is being changed from 100% to 0% is set as a reference state, and various parameters at that time are set as reference values. Hereinafter, a process of changing a correction quantity will be described with reference to the drawings.
In an example of
Also, when the current rate R is 1/2C or 2C, the reduction rate of the ΔSOC is set to, for example, 1/2. In other words, when the current rate R is 1/2C or 2C, the Comparator and corrector 36 corrects the parameters of the battery capacity C of the battery module 12 so that a contribution rate associated with the correction quantity of the ΔSOC is 1/2 that of a case in which the current rate R is IC.
Correspondences between the current rate R and the reduction rate of the ΔSOC may have relationships illustrated as in the graphs of
Also, the Comparator and corrector 36 in this embodiment may perform a correction process of changing the reduction rate of the ΔSOC in accordance with the above-described current rate R as well as, for example, the Comparator and corrector 36 correcting the parameters of the battery capacity C of the battery module 12 in accordance with the derived ΔSOC. Hereinafter, description will be provided with reference to the drawings.
In an example of
Also, the Comparator and corrector 36 in this embodiment may decide the reduction rate of the ΔSOC on the basis of the current rate R and the derived ΔSOC. In this case, the Comparator and corrector 36 multiplies parameters of the current rate R and the ΔSOC by an associated reduction rate of the ΔSOC, and derives the values obtained by multiplication as the reduction rates of the ΔSOC. The Comparator and corrector 36 corrects the parameters of the battery capacity C of the battery module 12 such that the ΔSOC multiplied by the reduction rate is obtained.
The Comparator and corrector 36 derives a value (=1/5) obtained by multiplying 1/4 and 0.8 as a reduction rate of the ΔSOC when the current rate R is 4C and the ΔSOC is 80%, for example, in numerical value examples of
First, the Comparator and corrector 36 determines whether the various parameters including the derived ΔSOC and the current rate R are reference values (Step S200). The Comparator and corrector 36 decides a reduction rate by which the derived ΔSOC is multiplied to be 1 when it is determined that the various parameters are the reference values (Step S200: YES) (Step S202). The Comparator and corrector 36 decides and changes a reduction rate by which the derived ΔSOC is multiplied on the basis of any parameter which is not a reference value (Step S204) when it is determined that the various parameters are not the reference values (Step S200: NO).
Subsequently, the Comparator and corrector 36 corrects the parameters of the battery capacity C of the battery module 12 such that the ΔSOC value is 0 or small on the basis of the decided reduction rate of the ΔSOC (Step S206). Thus, the Comparator and corrector 36 ends the process of this flowchart.
According to the storage system 1 in the above-described second embodiment, a correction quantity of the battery capacity C is changed on the basis of the use state of the battery module 12 so that the SOC of the battery module 12 can be estimated with higher accuracy.
A storage system 1 in a third embodiment will be described below. The storage system 1 in the third embodiment includes thermometers 26(1) to 26(k) in addition to the constituent elements included in the first or second embodiment. Hereinafter, description of functions the same as those of the first or second embodiment will be omitted.
The Comparator and corrector 36 acquires the temperature T of each of the battery modules 12 from the thermometer 26, and decides the reduction rate of the ΔSOC on the basis of the acquired temperature T. The significance of reducing the ΔSOC is the same as that of the second embodiment.
Also, it is desirable that a correspondence between the temperature T and the reduction rate of the ΔSOC is decided in consideration of a type of battery, individual differences, and the like of the battery module 12 to be used. For example, when the battery to be used is a lithium ion battery, a reduction rate is decided on the basis of temperature characteristics of the lithium ion battery. In the case of the lithium ion battery, for example, a reduction rate at a temperature less than 0° C. is reduced compared to a reduction rate at a temperature of 0° C. or higher. Thus, the SOC can be estimated for every battery module 12 to be used with higher accuracy. Note that it is assumed that data indicating the above-described correspondence is stored in any storage unit (a storage device) of a BMU 30, a CMU 20, a high-order device 40, and the like.
The Comparator and corrector 36 in this embodiment may decide a reduction rate of a ΔSOC on the basis of a current rate R, the ΔSOC, and a temperature T. In this case, the Comparator and corrector 36 multiplies parameters of the current rate R, the ΔSOC, and the temperature T by an associated reduction rate of the ΔSOC, and derives the value obtained by multiplication as a reduction rate of the ΔSOC. The Comparator and corrector 36 corrects the parameters of the battery capacity C of the battery module 12 so that a value obtained by multiplying the ΔSOC by the reduction rate is corrected to be 0.
For example, when the current rate R is 1/2C, the ΔSOC is 40%, and the temperature is 10 to 20° C. in the numerical examples of
According to the storage system 1 in the above-described third embodiment, like in the second embodiment, a correction quantity of the battery capacity C is changed on the basis of the use state of the battery module 12 so that the SOC of the battery module 12 can be estimated with higher accuracy.
Other examples (modified examples) will be described below.
Although a case in which the voltmeters 22, the first SOC deriver 24, the ammeter 32, and the second SOC deriver 34 perform various measurements and derivation of an SOC on each of the battery modules 12 has been described in the above-described embodiment, the present invention is not limited thereto. For example, a voltage and a current between terminals may be measured for each assembled battery unit 10, and various SOCs may be derived for each assembled battery unit 10 on the basis of the measured voltage current.
According to at least one of the above-described embodiments, an SOC1b is derived on the basis of a static voltage of the battery module 12 acquired at a timing at which the voltage is static before charging and discharging of electricity and OCV-SOC characteristics data, an SOC2 is derived on the basis of a current integrated value ∫I of the battery module 12 during charging and discharging of electricity, a battery capacity C of the battery module 12, and a derived SOC1b, an SOC1a is derived on the basis of the static voltage of the battery module 12 acquired at the timing at which the voltage is static after charging and discharging of electricity and the OCV-SOC characteristics data, and parameters of the battery capacity C of the battery module 12 are corrected on the basis of a difference ΔSOC between the SOC2 and the SOC1a. As a result, the storage system 1 can estimate the SOC of the battery module 12 with high accuracy.
Although several embodiments of the present invention have been described, such embodiments are presented as examples and are not intended to limit the scope of the invention. Such embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. Such embodiments and modifications thereof are included in the scope and the gist of the invention as well as being included within the invention described in the claims and the equivalent scope thereof.
1 Storage system
10, 10(1) to 10(k) Assembled battery unit
12, 12(1) to 12(k) Battery module
20, 20(1) to 20(k) CMU
22, 22(1) to 22(k) Voltmeter
24, 24(1) to 24(k) First SOC deriver
26, 26(1) to 26(k) Thermometer
30 BMU
32 Ammeter
34 Second SOC deriver
36 Comparator and corrector
40 High-order device
50 PCS
60 Electric power system
70 Switch circuit
72 Switch
Filing Document | Filing Date | Country | Kind |
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PCT/JP2015/054650 | 2/19/2015 | WO | 00 |