Patent Application
20190043674
The present invention relates to an electric power storage apparatus including an electric storage device with a high energy density and an electric storage device with a high power (output) density.
As an electric power storage apparatus which can achieve a high energy density and a high power density, for example, an electric power storage system disclosed in Patent Literature 1 is conventionally known. This electric power storage system includes a power converter, a secondary battery, a capacitor, and a controller. A load terminal of the power converter is connected to a load. A power supply terminal of the power converter is connected to the secondary battery and connected to the capacitor in parallel with the secondary battery via the DC/DC converter. The DC/DC converter is controlled by the controller so that the capacitor is charged and discharged with a priority over the secondary battery.
Japanese Laid-Open Patent Application Publication No. 2016-001936
In the above-described electric power storage system, the capacitor is connected to the power converter via the DC/DC converter so that the capacitor is controlled to be charged and discharged with a priority over the secondary battery. For this reason, there is improvement in reduction of size and simplification of configuration of the electric power storage system.
The present invention has been developed to solve the above-described problem, and an object of the present invention is to provide an electric power storage apparatus which can achieve a high energy density and a high power density while reducing the size of the electric power storage apparatus and simplifying the configuration of the electric power storage apparatus.
According to an aspect of the present invention, an electric power storage apparatus comprises a first electric storage device; and a second electric storage device, wherein the first electric storage device has an inner resistance lower than an inner resistance of the second electric storage device, and has a power density higher than a power density of the second electric storage device, and the second electric storage device has an energy density higher than an energy density of the first electric storage device, wherein the first electric storage device and the second electric storage device are connected in parallel, and wherein a voltage (potential) window of the first electric storage device and a voltage window of the second electric storage device at least partially overlap with each other.
In accordance with this configuration, the first electric storage device and the second electric storage device are charged and discharged and thus a high energy density and a high power density can be achieved. In this case, the first electric storage device is charged and discharged with a priority over the second electric storage device. Therefore, in a case where the first electric storage device and the second electric storage device are connected to each other, it is not necessary to interpose a DC/DC converter between them. This makes it possible to reduce the size of the electric power storage system. In addition, since the DC/DC converter is not necessary, it is not necessary to control the DC/DC converter. As a result, the configuration of the electric power storage system can be simplified.
In the electric power storage apparatus, the first electric storage device may include one or a plurality of first electric storage cells connected to each other in series, the second electric storage device may include one or a plurality of second electric storage cells connected to each other in series, and the number of the first electric storage cells connected to each other in series and the number of the second electric storage cells connected to each other in series may be set so that the voltage window of the first electric storage device and the voltage window of the second electric storage device at least partially overlap with each other. In accordance with this configuration, depending on the number of the electric storage cells connected in series in each of the electric storage devices, the voltage (potential) window of each of the electric storage devices can be suitably adjusted.
In the electric power storage apparatus, the first electric storage device may include one or a plurality of first electric storage cells connected to each other in parallel, the second electric storage device may include one or a plurality of second electric storage cells connected to each other in parallel, and the number of the first electric storage cells connected to each other in parallel and the number of the second electric storage cells connected to each other in parallel may be set so that the internal resistance of the first electric storage device becomes lower than the internal resistance of the second electric storage device. In accordance with this configuration, depending on the number of the electric storage cells connected in parallel in each of the electric storage devices, the internal resistance of each of the electric storage devices can be suitably adjusted.
In the electric power storage apparatus, one or a plurality of first electric storage cells connected to each other and one or a plurality of second electric storage cells connected to each other may be connected to each other in parallel to construct an electric storage module. In accordance with this configuration, the first electric storage cell(s) is/are charged and discharged with a priority over the second electric storage cell(s). Therefore, the second electric storage cell(s) is/are charged and discharged in a state in which the second electric storage cell(s) is/are heated by heat generated by charging and discharging the first electric storage cell(s). As a result, under a low-temperature environment, the second electric storage device can be efficiently charged and discharged by heating the second electric storage cell(s).
The present invention has the above-described configuration, and can obtain an advantage that it is possible to provide an electric power storage apparatus which can achieve a high energy density and a high power density while reducing the size of the electric power storage apparatus and simplifying the configuration of the electric power storage apparatus.
The above and further objects, features and advantages of the present invention will more fully be apparent from the following detailed description of preferred embodiment with reference to the accompanying drawings.
Hereinafter, the embodiments of the present invention will be described with reference to the drawings. Throughout the drawings, the same or corresponding constituents are designated by the same reference symbols, and will not be described in repetition. Although the internal resistance of a capacitor cell and the internal resistance of a secondary battery cell are shown in
The configuration of an electric power storage apparatus 1 according to Embodiment 1 will be described with reference to
The first electric storage device 10 is an electric storage unit which has an internal resistance lower than that of the second electric storage device 20 and a power density higher than that of the second electric storage device 20. In contrast, the second electric storage device 20 is an electric storage unit which has an energy density higher than that of the first electric storage device 10. In this way, the first electric storage device 10 and the second electric storage device 20 have opposite specifications regarding the internal resistance, the power density, and the energy density.
The first electric storage device 10 includes one or a plurality of first electric storage cells 11 which are connected to each other. In the present embodiment, the first electric storage device 10 includes one first electric storage cell 11. More specifically, the first electric storage device 10 of
The second electric storage device 20 includes one or a plurality of second electric storage cells 21 connected to each other. In the present embodiment, the second electric storage device 20 includes three second electric storage cells 21. Specifically, the second electric storage device 20 of
The first electric storage cell 11 is not limited to the capacitor cell 11a. The second electric storage cells 21 are not limited to the secondary battery cells 21a. Other constituents may be used so long as the first electric storage device 10 and the second electric storage device 20 have opposite specifications as described above. For example, as the first electric storage cell 11, a secondary battery with a power density higher than that of the second electric storage cell 21 may be used.
The number of the first electric storage cells 11 and the number of the second electric storage cells 21 are set so that the electric storage devices 10, 20 meet both of the following conditions (1) and (2).
(1) The internal resistance of the first electric storage device 10 is lower than that of the second electric storage device 20.
(2) A part or all of the voltage (potential) window of the first electric storage device 10 overlaps with that of the second electric storage device 20.
In the present embodiment, to meet the above-described conditions, one capacitor cell 11a is provided to correspond to the three secondary battery cells 21a connected in series. The internal resistance of the first electric storage device 10 is an electric resistance included in one capacitor cell 11a. The internal resistance of the second electric storage device 20 is an electric resistance included in the three secondary battery cells 21a connected in series and is a sum of the internal resistances of the three secondary battery cells 21a.
The voltage (potential) window of the first electric storage device 10 is, for example, a voltage range which can be used in the first electric storage device 10, or a voltage use range set by a manufacturer or a user. The voltage (potential) window of the second electric storage device 20 is, for example, a voltage range which can be used, or a voltage use range set by the manufacturer or the user, in view of electrochemical characteristics of the second electric storage device 20.
In the present embodiment, the voltage (potential) window of each of the electric storage devices (first electric storage device 10 and second electric storage device 20) is set as a voltage range from an open circuit voltage (OCV) in a case where the state of charge (SOC) of the corresponding electric storage device is 0% to the OCV in a case where the SOC is 100%. For example, in a case where the electric storage devices 10, 20 have SOC-OCV characteristics shown in
The remaining capacity of the electric power storage apparatus 1 which is represented by a product of the SOC and the capacity is the amount of electric power which can be discharged by the electric power storage apparatus 1, and is estimated as follows, Here, it is assumed that the first electric storage device 10 includes the capacitor cell 11a and the second electric storage device 20 includes the secondary battery cells 21a, as in the case of the electric power storage apparatus 1 of
In a case where the capacity of the second electric storage device 20 is much larger than that of the first electric storage device 10 and hence the capacity of the first electric storage device 10 is negligible, the remaining capacity of the electric power storage apparatus 1 is almost equal to that of the second electric storage device 20. The remaining capacity of the second electric storage device 20 can be estimated by a known method disclosed in, for example, Japanese Laid-Open Patent Application Publication No. 2009-257775. Therefore, the remaining capacity of the second electric storage device 20 obtained in this way is estimated as the remaining capacity of the electric power storage apparatus 1.
On the other hand, in a case where the capacity of the first electric storage device 10 is not negligible, the remaining capacity of the second electric storage device 20 can be derived (found) in view of the remaining capacity of the first electric storage device 10. For example, in the example of
When the current value I is zero, the OCV of the first electric storage device 10 is equal to a terminal voltage V of the electric power storage apparatus 1. Therefore, a change amount ΔQc of the remaining capacity Qc of the first electric storage device 10 is represented by a formula (ΔQ c=Δ(CV̂2)/2=C/2·Δ(V̂2)). In this formula, C indicates electrostatic capacity (capacitance) of the capacitor cell 11a constituting the first electric storage device 10, and V indicates the voltage of the capacitor cell 11a. Therefore, the remaining capacity Qc of the first electric storage device 10 and the remaining capacity Qb of the second electric storage device 20 are derived based on the terminal voltage V of the electric power storage apparatus 1 and the current value I measured by the current meter 30.
In accordance with the electric power storage apparatus 1 with the above-described configuration, a part or all of the voltage (potential) window of the first electric storage device 10 overlaps with that of the second electric storage device 20. Therefore, the first electric storage device 10 with an internal resistance lower than that of the second electric storage device 20 is charged and discharged with a priority over the second electric storage device 20. For this reason, it is not necessary to actively perform a control for charging and discharging the first electric storage device 10 with a priority over the second electric storage device 20. This can eliminate a need for the DC/DC converter used to perform this control. As a result, the first electric storage device 10 and the second electric storage device 20 can be directly connected to each other (without the DC/DC converter interposed between them), which can reduce the size of the electric power storage apparatus 1 and simplify the configuration of the electric power storage apparatus 1. For example, the life of the second electric storage device 20, including the secondary battery cells 21a, depends on the number of times the second electric storage device 20 is charged and discharged. Since the number of times the second electric storage device 20 is charged and discharged can be reduced, and the depth of charging and discharging the second electric storage device 20 can be reduced, the life of the second electric storage device 20 can be extended.
The first electric storage device 10 includes the first electric storage cell 11 with a high power density. The second electric storage device 20 includes the second electric storage cells 21 with a high energy density. The voltage (potential) windows of the electric storage devices 10, 20 are adjusted depending on the number of electric storage cells 11, 21 (one or a plurality of electric storage cells 11 are connected to each other in series, and one or a plurality of electric storage cells 21 are connected to each other in series). This makes it possible to easily realize the electric power storage apparatus 1 with a high power density and a high energy density.
(Modified Example 1)
In a case where an electric storage pack 2 includes the first electric storage device 10 and the second electric storage device 20 which are connected in parallel, the electric power storage apparatus 1 of
(Modified Example 2)
Although in the electric power storage apparatus 1 of
(Modified Example 3)
In the electric power storage apparatus 1 of
For example, as shown in
As described above, the internal resistance of the first electric storage device 10 is required to be lower than that of the second electric storage device 20. For this reason, the internal resistances of the electric storage devices 10, 20 may be adjusted (set) by utilizing a design idea described in Embodiment 2 below, as desired.
As shown in
The configuration of the electric power storage apparatus 1 according to Embodiment 2 will be described with reference to
In a case where the first electric storage cells 11 are not connected in series and connected in parallel in the first electric storage device 10 and the second electric storage cells 21 are not connected in series and connected in parallel in the second electric storage device 20, the reciprocal of the internal resistance of the first electric storage device 10 is a sum of the reciprocals of the internal resistances of the first electric storage cells 11, and the reciprocal of the internal resistance of the second electric storage device 20 is a sum of the reciprocals of the internal resistances of the second electric storage cells 21. As the number of the first electric storage cells 11 connected in parallel and the number of the second electric storage cells 21 connected in parallel are increased, the internal resistance of the first electric storage device 10 and the internal resistance of the second electric storage device 20 are reduced. For example, in the example of
As described above, depending on a ratio between the number of the first electric storage cells 11 connected in parallel and the number of the second electric storage cells 21 connected in parallel, a power (output) ratio between the first electric storage device 10 and the second electric storage device 20 can be adjusted as desired. Further, in a case where the plurality of first electric storage cells 11 are connected in series in the first electric storage device 10 and the plurality of second electric storage cells 21 are connected in series in the second electric storage device 20, the internal resistance of the first electric storage device 10 is a sum of the internal resistances of the first electric storage cells 11, and the internal resistance of the second electric storage device 20 is a sum of the internal resistances of the second electric storage cells 21. Therefore, depending on the ratio between the number of the first electric storage cells 11 connected in parallel and the number of the second electric storage cells 21 connected in parallel, and the ratio between the number of the first electric storage cells 11 connected in series and the number of the second electric storage cells 21 connected in series, the power (output) ratio between the first electric storage device 10 and the second electric storage device 20 can be adjusted more flexibly.
The configuration of the electric power storage apparatus 1 according to Embodiment 3 will be described with reference to
In the electric power storage apparatus 1 according to Embodiment 1, one or the plurality of first electric storage cells 11 is/are accommodated in the first case 13, and one or the plurality of second electric storage cells 21 is/are accommodated in the second case 23. In contrast, in the electric storage devices 10, 20 of the electric power storage apparatus 1 according to Embodiment 3, one or the plurality of first electric storage cells 11 connected to each other and one or the plurality of second electric storage cells 21 connected to each other are connected to each other in parallel, and these electric storage cells 11, 12 are packaged and accommodated together in a case (package case) 3.
In the package case 3, the first electric storage cell(s) 11 and the second electric storage cell(s) 21 are not thermally insulated and are accommodated in the same space of one (single) package case 3. The first electric storage cell(s) 11 is/are charged and discharged before the second electric storage cell(s) 21 is/are charged and discharged. In this configuration, during charge and discharge, the second electric storage cell(s) 21 can operate in a state in which the second electric storage cell(s) 21 is/are heated by reaction heat of the first electric storage cell(s) 11. For example, performance and quality of the first electric storage cell 11 such as the capacitor cell 11a do not depend on the temperature. On the other hand, performance of the second electric storage cell 21 such as the secondary battery cell 21a is reduced or degradation of the second electric storage cell 21 progresses, due to an operation in a low-temperature state. With the above-described configuration, reduction of the performance and quality of the second electric storage cell 21 can be suppressed. As a result, reduction of the performance and life of the electric power storage apparatus 1 can be suppressed.
Alternatively, as shown in
As to the characteristics of the electric power storage apparatus 1 with the above-described configuration, test result of the electric power storage apparatus 1 of
As shown in
As described above, the first electric storage device 10 with a power density higher than that of the second electric storage device 20 output (discharged) an electric current with a priority over the second electric storage device 20. After that, the second electric storage device 20 with an energy density higher than that of the first electric storage device 10 mainly output an electric current. This makes it possible to achieve a high energy density and a high power density in the electric power storage apparatus 1 which has a small size and a simplified configuration and does not need the DC/DC converter.
As to the characteristics of the electric power storage apparatus 1 which can achieve a high energy density and a high power density, test result of the electric power storage apparatus 1 in Example 2 will be described with reference to
As shown in
After that, in an interval of 30 seconds (period L2 of
Since the first electric storage device 10 was charged for the period L2, most of an electric current output, corresponding to the power (output) of 400 W, was output from the first electric storage device 10, for 10 seconds in a period L3 following the period L2.
As shown in
As described above, for the first load which requires a high power (output) for a short time, the high power (output) characteristic of the first electric storage device 10 worked. In contrast, for the second load which requires a low power (output) for a long time, the high energy characteristic of the second electric storage device 20 worked. Therefore, by utilizing a difference in the internal resistance between the first electric storage device 10 and the second electric storage device 20, it becomes possible to realize the electric power storage apparatus 1 which can achieve a high power (output) and a high energy. Since this characteristic is obtained by utilizing the difference in the internal resistance between the second electric storage device 20 and the first electric storage device 10, the DC/DC converter is not necessary, so that the size of the electric power storage apparatus 1 can be reduced, and the control for the electric power storage apparatus 1 can be simplified.
As to the characteristics of the electric power storage apparatus 1 including the electric storages cells 11 connected to each other in parallel and the electric storage cells 21 connected to each other in parallel, the test result of the electric power storage apparatus 1 in Example 3 of
By use of this electric power storage apparatus 1, the same simulation as that for the second load which requires a low power (output) for a long time in Example 2 was conducted. The internal resistance of the first electric storage device 10 of
As described above, depending on the number of the first electric storage cells 11 connected in parallel in the first electric storage device 10 and the number of the second electric storage cells 21 connected in parallel in the second electric storage device 20, the power (output) characteristics and capacities of the first electric storage device 10 and the second electric storage device 20 can be adjusted as desired to meet the demand.
Numerous modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, the description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and/or function may be varied substantially without departing from the spirit of the invention.
An electric power storage apparatus of the present invention is useful as an electric power storage apparatus or the like, which can achieve a high energy density and a high power density, while reducing its size and simplifying its configuration.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-017403 | Feb 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/003020 | 1/27/2017 | WO | 00 |
