JP7658915B2 - Power device and control method thereof - Google Patents

Description

The present invention relates to a power device having at least three power storage units and a control method thereof.

A power device in which multiple batteries (energy storage units) are connected in parallel to each other via a voltage converter is disclosed, for example, in JP 2016-25791 A.

When multiple storage units with different voltages or SOCs (state of charge) are connected in parallel, charging and discharging are performed in which a current flows in proportion to the voltage difference between the storage units so that the voltages or SOCs are equalized between the storage units. In this case, if the voltage difference between the storage units is negligibly small when the storage units are simply wired, there is no problem in directly connecting the storage units in parallel.

However, in the case of removable batteries (energy storage units) that are not fixed batteries, if the battery conditions, such as voltage, temperature, internal resistance, SOC, degree of deterioration, and chargeable capacity, are different from one another, if a large voltage difference occurs between multiple energy storage units connected in parallel after a battery replacement, a large current (overcurrent) that exceeds the allowable current due to the voltage difference will flow.

One way to prevent such overcurrents is to connect multiple storage units in parallel via an equalization circuit and electrically control the equalization circuit to reduce the voltage difference between the multiple storage units. However, adding such an equalization circuit is costly.

The present invention has been made in consideration of these problems, and aims to provide a power device and a control method thereof that can minimize the impact of costs by connecting a storage unit through electrical control alone, without adding any circuits, and suppressing the occurrence of overcurrent.

A first aspect of the present invention is a power device having at least three storage units, the power device having a voltage acquisition unit that acquires the voltage values of each of the storage units, and a connection unit that connects two of the storage units whose voltage values are adjacent to each other based on the voltage values of the storage units acquired by the voltage acquisition unit.

A second aspect of the present invention is a method for controlling an electric power device having at least three storage units, comprising the steps of acquiring the voltage values of each of the storage units by a voltage acquisition unit, and connecting two of the storage units whose voltage values are adjacent to each other based on the voltage values of the storage units acquired by the voltage acquisition unit.

According to the present invention, two storage units with adjacent voltage values are selected from among at least three storage units and connected to each other. This makes it possible to connect the storage units with only electrical control without adding any circuitry, and suppress the occurrence of overcurrent. As a result, the impact of costs can be minimized. Therefore, compared to connecting all storage units simultaneously or connecting two or more storage units with voltage values that are distant from each other (not adjacent), it is possible to suppress the flow of overcurrent to the storage units while reducing the voltage difference.

FIG. 1 is a configuration diagram of a power device according to an embodiment of the present invention. FIG. 2 is a configuration diagram of the power storage unit in FIG. 1 . 2 is a flow chart illustrating the operation of the power device of FIG. 1 . FIG. 1 is an explanatory diagram of a first embodiment. FIG. 1 is an explanatory diagram of a first embodiment. FIG. 1 is an explanatory diagram of a first embodiment. FIG. 1 is an explanatory diagram of a first embodiment. FIG. 11 is an explanatory diagram of another connection example of the first embodiment. FIG. 11 is an explanatory diagram of a second embodiment. FIG. 11 is an explanatory diagram of a second embodiment. FIG. 11 is an explanatory diagram of a second embodiment. FIG. 11 is an explanatory diagram of a second embodiment. FIG. 13 is an explanatory diagram of another connection example according to the second embodiment. FIG. 13 is a configuration diagram of a power device according to a modified example.

Below, preferred embodiments of the power device and its control method according to the present invention are illustrated and explained with reference to the attached drawings.

[1. Schematic configuration of the present embodiment]
As shown in Fig. 1, the power device 10 according to this embodiment has at least three power storage units 12, an ECU 14 (voltage acquisition unit, connection unit), a notification unit 16, an internal battery 18 (another power storage unit), and a plurality of switches 20 and 22. Note that Fig. 1 illustrates a case in which four power storage units 12 (hereinafter sometimes referred to as first to fourth power storage units 12a to 12d) are arranged.

The power device 10 is also applied to the power supply system of various electric vehicles such as unicycles, two-wheelers, three-wheelers, and four-wheelers. The power device 10 is not limited to application to electric vehicles. The power device 10 can also be applied to (1) moving bodies other than vehicles such as aircraft and ships, (2) various charging equipment such as home chargers, (3) various dischargers that output power from the storage unit 12, (4) various working machines such as general-purpose working machines, lawnmowers, and tillers, and (5) power supply systems (Energy Storage Systems) that supply power to various electrical devices installed or disposed inside or outside buildings such as houses. In the following description, the case where the power device 10 is applied to an electric vehicle will be mainly described.

Each power storage unit 12 is a power storage device that is detachable from the power device 10 and can be charged and discharged. For example, a detachable lithium-ion battery pack is suitable as the power storage unit 12. Each power storage unit 12 is connected in parallel to a load 24 such as a motor and PDU of an electric vehicle. That is, the positive terminal on the output side of each power storage unit 12 is connected to the positive terminal of the load 24. The negative terminal on the output side of each power storage unit 12 is connected to the negative terminal of the load 24.

The built-in battery 18 is a fixed type power storage device provided in the power device 10. The built-in battery 18 is connected in parallel to the load 24 via the switch 20. That is, the positive terminal of the built-in battery 18 is connected to the positive terminal of the load 24 via the switch 20. The negative terminal of the built-in battery 18 is connected to the negative terminal of the load 24. A voltage conversion circuit (not shown), such as a DC/DC converter, may be interposed between the built-in battery 18 and the load 24. As a result, when power is supplied to the load 24 from both the storage units 12 and the built-in battery 18, the voltage of the built-in battery 18 can be adjusted by the voltage conversion circuit and the adjusted voltage can be output to the load 24. In addition, when the built-in battery 18 alone supplies power to the load 24 or when power is supplied to the load 24 from each storage unit 12, the voltage conversion circuit may not be required.

The built-in battery 18 is the main power source for the power device 10 and also the startup power source for starting up each storage unit 12. Therefore, the built-in battery 18 is also connected to each storage unit 12 via each switch 22. That is, the positive terminal of the built-in battery 18 is connected to the positive power supply terminal of each storage unit 12 via each switch 22. The negative terminal of the built-in battery 18 is connected to the negative power supply terminal of each storage unit 12.

The ECU 14 is an electronic control device for the electric vehicle, and realizes various functions such as connection control for each switch 26 (see FIG. 2) described later by reading and executing a program stored in a non-transitory storage medium (not shown). The notification unit 16 is an output device such as a display device or speaker provided in the electric vehicle, and notifies the processing result of the ECU 14 to the outside.

The ECU 14 can transmit and receive signals or information to and from each of the power storage units 12, each of the switches 20, 22, and the load 24 via a communication line 28 of a Controller Area Network (CAN). Therefore, the ECU 14 controls and turns on each of the switches 20, 22 to electrically connect the built-in battery 18 to the load 24, or electrically connect the built-in battery 18 to each of the power storage units 12.

Figure 2 is a diagram showing the internal configuration of each power storage unit 12. Each power storage unit 12 has the same configuration, and only one power storage unit 12 is shown in Figure 2. As shown in Figure 2, each power storage unit 12 is a battery pack that houses a switch 26 (two-way connection circuit), a battery 30, a battery management system (BMU) 32, a resistor 34, a temperature sensor 36, and a communication unit 38.

The positive electrode of the battery 30 is connected to the positive terminal of the load 24 via the switch 26 and the positive terminal of the power storage unit 12. The negative electrode of the battery 30 is connected to the negative terminal of the load 24 via the resistor 34 and the negative terminal of the power storage unit 12. The communication unit 38 also transmits and receives signals or information to and from the ECU 14 via the communication line 28.

The BMU 32 is started when the switch 22 is turned on under the control of the ECU 14 and power is supplied from the built-in battery 18. The BMU 32 monitors the battery 30. Specifically, the BMU 32 electrically connects the battery 30 and the load 24 by turning on the switch 26 based on a control signal received from the ECU 14 to the communication unit 38 via the communication line 28. The BMU 32 also sequentially detects the voltage values across the resistor 34, and sequentially calculates the current value of the current (discharge current or charge current) flowing through the battery 30 based on the detected voltage value and the resistance value of the resistor 34. The BMU 32 also sequentially detects the voltage value of the battery 30, and sequentially calculates the SOC of the battery 30 based on the detected voltage value and the calculated current value. Furthermore, the BMU 32 also sequentially acquires the temperature of the battery 30 detected by a temperature sensor 36 such as a thermistor. The BMU 32 sequentially transmits information including the voltage value, the current value, the SOC, and the temperature from the communication unit 38 to the ECU 14 via the communication line 28 .

Therefore, the ECU 14 sequentially acquires the above information and, based on the acquired information, determines (judges) whether each switch 26 needs to be turned on (connected) or off (disconnected). The ECU 14 also transmits a control signal based on this judgment result to each communication unit 38 via the communication line 28, thereby turning on or off the switch 26 of each power storage unit 12. The ECU 14 also transmits a control signal to each switch 20, 22 via the communication line 28, thereby turning on or off each switch 20, 22.

2. Operation of the Present Embodiment
The operation of the power device 10 according to the present embodiment configured as above (a control method for the power device 10) will be described with reference to Fig. 3. This operation involves connecting each of the power storage units 12 (see Figs. 1 and 2) in parallel with each other or with the load 24 in stages, and electrically controlling the voltage difference between each of the power storage units 12, thereby preventing a large current (overcurrent) exceeding the allowable current from flowing within the power device 10, including between each of the power storage units 12.

In this operational description, a case will be described in which power is supplied from each power storage unit 12 to the load 24 when the connection between the built-in battery 18 and the load 24 is cut off by turning off the switch 20. Note that when the built-in battery 18 and the load 24 are connected by turning on the switch 20, the built-in battery 18 supplies power to the load 24 via a voltage conversion circuit (not shown).

In step S1, the ECU 14 switches each switch 22 from off to on by supplying a control signal to each switch 22. This electrically connects the built-in battery 18 and the BMU 32 of each power storage unit 12, and power supply from the built-in battery 18 to each power storage unit 12 (BMU 32) begins. This starts up each BMU 32. Also, each communication unit 38 reaches a state in which it can communicate with the ECU 14 via the communication line 28 (step S1: YES). Note that in step S1, the ECU 14 and each power storage unit 12 may perform a numbering process to assign an ID number or the like to each power storage unit 12 via the communication line 28.

In step S2, the BMU 32 of each power storage unit 12 detects the voltage value of the battery 30. In this case, each BMU 32 simultaneously obtains the temperature of the battery 30, calculates the current value of the current flowing through the battery 30, and calculates the SOC of the battery 30. Therefore, each BMU 32 transmits this information from the communication unit 38 via the communication line 28 to the ECU 14. Therefore, the ECU 14 can obtain information such as the voltage value of the battery 30 from each power storage unit 12.

In step S3, the ECU 14 compares the voltage values of the batteries 30 of each storage unit 12 and determines whether the voltage difference between the highest voltage value (maximum voltage value) and the lowest voltage value (minimum voltage value) is within a voltage threshold. Here, the voltage threshold is a threshold for determining whether a large current (overcurrent) will flow between each storage unit 12 due to the voltage difference, and refers to the value of the voltage difference according to the allowable current. Therefore, if the voltage difference is within the voltage threshold, the occurrence of an overcurrent is suppressed. On the other hand, if the voltage difference exceeds the voltage threshold, there is a possibility that an overcurrent will occur.

Here, if the voltage difference between the maximum voltage value and the minimum voltage value is within the voltage threshold value (step S3: YES), in step S4, the ECU 14 determines that no overcurrent will occur even if all the power storage units 12 are connected in parallel to the load 24. Next, based on this determination result, the ECU 14 transmits a control signal to the communication unit 38 of each power storage unit 12 via the communication line 28 to instruct it to turn on the switch 26.

The BMU 32 of each power storage unit 12 switches the switch 26 from off to on based on the control signal received by the communication unit 38. This connects each power storage unit 12 (battery 30) in parallel to the load 24. As a result, power can be supplied to the load 24 and each power storage unit 12 can be charged and discharged while keeping the voltage difference between each power storage unit 12 within the voltage threshold. This allows the voltage values of the batteries 30 of each power storage unit 12 to be averaged.

On the other hand, if the voltage difference between the maximum voltage value and the minimum voltage value exceeds the voltage threshold in step S3 (step S3: NO), the ECU 14 determines that there is a possibility of an overcurrent occurring when all the power storage units 12 are connected, and proceeds to step S5. In step S5, the ECU 14 compares the voltage values of the batteries 30 of the power storage units 12, and selects a connection combination of at least two power storage units 12 that results in a voltage difference within the voltage threshold. In other words, in the case of the selected connection combination, the voltage values are close to each other (adjacent), so it is considered that an overcurrent will not occur if at least two power storage units 12 are connected in parallel.

Next, the ECU 14 transmits a control signal to the communication unit 38 of the at least two power storage units 12 via the communication line 28 to instruct the communication unit 38 of the at least two power storage units 12 to turn on the switch 26. As a result, the BMU 32 of the at least two power storage units 12 switches the switch 26 from off to on based on the control signal received by the communication unit 38. As a result, the at least two power storage units 12 (batteries 30) are connected in parallel to the load 24. This makes it possible to supply power to the load 24 and charge and discharge between the two power storage units 12 while keeping the voltage difference between the two power storage units 12 within the voltage threshold.

The BMU 32 sequentially acquires the voltage values, etc., of each battery 30. In the next step S6, the ECU 14 acquires information, such as the voltage values, of the batteries 30 from at least two power storage units 12, and determines, from the voltage values included in the acquired information, whether the voltage values of the batteries 30 have been averaged between the at least two power storage units 12 through charging and discharging.

If the voltage values of the batteries 30 are averaged (step S6: YES), the ECU 14 returns to step S2 and repeats the processing of steps S2, S3, S5, and S6. Therefore, in the power device 10 according to this embodiment, until the voltage difference between the maximum voltage value and the minimum voltage value falls within the voltage threshold (step S3: YES), the ECU 14 repeatedly acquires the voltage value of the battery 30 of each storage unit 12, determines the connection of each storage unit 12, and connects each storage unit 12 by each switch 26. In other words, in this embodiment, the storage units 12 are connected in parallel in stages, and charging and discharging are performed between the storage units 12, thereby averaging the voltage difference between the storage units 12.

3. Specific examples of the operation of this embodiment
Next, specific examples (first and second embodiments) of the above-mentioned operation will be described with reference to FIGS.

The first embodiment, as shown in Figures 4 to 8, illustrates a case in which the voltage values decrease in the order of the first to fourth storage units 12a to 12d (see Figures 1 and 2), and the parallel connection to the load 24 is repeated in stages, with the first storage unit 12a having the maximum voltage value as the reference, so that all of the storage units 12a to 12d are finally connected in parallel. On the other hand, the second embodiment, as shown in Figures 9 to 13, illustrates a case in which the parallel connection to the load 24 is repeated in stages, with the fourth storage unit 12d having the minimum voltage value as the reference, so that all of the storage units 12a to 12d are finally connected in parallel.

In the first and second embodiments, as shown in Figures 4 and 9, the voltage values before connection of the first to fourth power storage units 12a to 12d are V1 to V4, and the voltage threshold is Vthr. In Figures 4 to 13, the first to fourth power storage units 12a to 12d are represented as No. 1 to No. 4.

<3.1 First Example>
The first embodiment will be described with reference to FIGS. 4 to 7. As shown in FIG. 4, |V1-V4|>Vthr (step S3 in FIG. 3: NO). Therefore, when the first to fourth power storage units 12a to 12d are connected in parallel to the load 24 (see FIGS. 1 and 2), an overcurrent may flow (connection indicated by "NG" in FIG. 4). On the other hand, in the connection of the first to third power storage units 12a to 12c, the connection of the second to fourth power storage units 12b to 12d, the connection of the first power storage unit 12a and the second power storage unit 12b, the connection of the second power storage unit 12b and the third power storage unit 12c, and the connection of the third power storage unit 12c and the fourth power storage unit 12d, the voltage values of the power storage units 12 to be connected are close to each other (adjacent to each other), so that the voltage difference is within the voltage threshold Vthr and no overcurrent occurs (connection indicated by "OK" in FIG. 4).

Therefore, in the case of Figure 4, the ECU 14 alternatively selects the connection between the first storage unit 12a and the second storage unit 12b (connection A), or the connection between the first to third storage units 12a to 12c (connection B), based on the first storage unit 12a having the maximum voltage value (voltage value V1).

Here, when the ECU 14 selects connection A, the ECU 14 transmits a control signal for turning on the switch 26 to the communication unit 38 of the first power storage unit 12a and the second power storage unit 12b via the communication line 28. As a result, the BMUs 32 of the first power storage unit 12a and the second power storage unit 12b switch the switch 26 from OFF to ON based on the control signal received by the communication unit 38. As a result, the first power storage unit 12a and the second power storage unit 12b are connected in parallel to the load 24, and charging and discharging are performed between the first power storage unit 12a and the second power storage unit 12b (step S5 in FIG. 3).

As a result of charging and discharging, as shown in Fig. 5, the voltage value of the first storage unit 12a decreases from V1 to V12, while the voltage value of the second storage unit 12b increases from V2 to V12. That is, the voltage values of the first storage unit 12a and the second storage unit 12b are averaged to V12 (step S6 in Fig. 3: YES). As a result, the maximum voltage value decreases from V1 to V12.

However, as shown in FIG. 5, |V12-V4|>Vthr (step S3 in FIG. 3: NO), there is a possibility that an overcurrent will flow if the first to fourth power storage units 12a-12d are connected in parallel to the load 24 (connection marked "NG" in FIG. 5). On the other hand, in the connection of the first to third power storage units 12a-12c and the connection of the third power storage unit 12c and the fourth power storage unit 12d, the voltage values of the power storage units 12 to be connected are close to each other (adjacent), so the voltage difference is within the voltage threshold Vthr and no overcurrent will occur (connection marked "OK" in FIG. 5).

5, the ECU 14 selectively selects the connection of the first to third storage units 12a to 12c based on the first and second storage units 12a to 12b having the maximum voltage value (voltage value V12). Next, the ECU 14 transmits a control signal for turning on the switch 26 to the communication unit 38 of the first to third storage units 12a to 12c via the communication line 28. As a result, the BMU 32 of the first to third storage units 12a to 12c turns on the switch 26 based on the control signal received by the communication unit 38. As a result, the first to third storage units 12a to 12c are connected in parallel to the load 24, and charging and discharging are performed between the first to third storage units 12a to 12c (step S5 in FIG. 3).

As a result of charging and discharging, as shown in Figure 6, the voltage values of the first storage unit 12a and the second storage unit 12b decrease from V12 to V123, while the voltage value of the third storage unit 12c increases from V3 to V123. That is, the voltage values of the first to third storage units 12a to 12c are averaged to V123 (Step S6 in Figure 3: YES). As a result, the maximum voltage value decreases from V12 to V123.

In this case, |V123-V4|≦Vthr (step S3 in FIG. 3: YES), so even if the first to fourth power storage units 12a to 12d are connected in parallel to the load 24, no overcurrent will occur (connection "OK" in FIG. 6). Therefore, the ECU 14 alternatively selects the connection of the first to fourth power storage units 12a to 12d based on the first to third power storage units 12a to 12c with the maximum voltage value (voltage value V123). Next, the ECU 14 transmits a control signal for turning on the switch 26 to the communication unit 38 of the first to fourth power storage units 12a to 12d via the communication line 28. As a result, the BMU 32 of the first to fourth power storage units 12a to 12d turns on the switch 26 based on the control signal received by the communication unit 38. As a result, first to fourth power storage units 12a to 12d are connected in parallel to load 24, and charging and discharging are performed among first to fourth power storage units 12a to 12d (step S4 in FIG. 3).

As a result of charging and discharging, the voltage values of the first to third storage units 12a to 12c decrease from V123 to V1234, while the voltage value of the fourth storage unit 12d increases from V4 to V1234, as shown in Figure 7. In other words, the voltage values of the first to fourth storage units 12a to 12d are averaged to V1234.

In the above description, the case where connection A in Fig. 4 is alternatively selected has been described. When ECU 14 alternatively selects connection B, ECU 14 transmits a control signal for turning on switch 26 to communication unit 38 of first to third power storage units 12a to 12c via communication line 28. As a result, BMU 32 of first to third power storage units 12a to 12c switches switch 26 from OFF to ON based on the control signal received by communication unit 38. As a result, first to third power storage units 12a to 12c are connected in parallel to load 24, and charging and discharging are performed between first to third power storage units 12a to 12c (step S5 in Fig. 3).

As a result of charging and discharging, as shown in Figure 8, the voltage value of the first storage unit 12a decreases from V1 to V123, the voltage value of the second storage unit 12b remains at V2 (=V123), and the voltage value of the third storage unit 12c increases from V3 to V123. That is, the voltage values of the first to third storage units 12a to 12c are averaged to V123 (Step S6 in Figure 3: YES). As a result, the maximum voltage value decreases from V1 to V123.

In this case, |V123-V4|≦Vthr (step S3 in FIG. 3: YES), and therefore, as in the case of FIG. 6, even if the first to fourth storage units 12a to 12d are connected in parallel to the load 24, no overcurrent occurs (connection "OK" in FIG. 8). Therefore, the ECU 14 selectively selects the connection of the first to fourth storage units 12a to 12d based on the first to third storage units 12a to 12c with the maximum voltage value (voltage value V123). Next, the ECU 14 transmits a control signal for turning on the switch 26 to the communication unit 38 of the first to fourth storage units 12a to 12d via the communication line 28. As a result, the BMU 32 of the first to fourth storage units 12a to 12d turns on the switch 26 based on the control signal received by the communication unit 38. As a result, first to fourth power storage units 12a to 12d are connected in parallel to load 24, and charging and discharging are performed among first to fourth power storage units 12a to 12d (step S4 in FIG. 3).

In this case as well, as a result of charging and discharging, the voltage values of the first to third storage units 12a to 12c decrease from V123 to V1234, while the voltage value of the fourth storage unit 12d increases from V4 to V1234, as shown in Figure 7. When connection B is selected, the voltage values of the first to fourth storage units 12a to 12d can be averaged to V1234 more quickly than in the case of connection A.

<3.2 Second Example>
The second embodiment will be described with reference to FIGS. 9 to 12. As shown in FIG. 9, |V1-V4|>Vthr (step S3 in FIG. 3: NO). Therefore, when the first to fourth power storage units 12a to 12d are connected in parallel to the load 24, an overcurrent may flow (connection indicated by "NG" in FIG. 9). On the other hand, in the connection of the first to third power storage units 12a to 12c, the connection of the second to fourth power storage units 12b to 12d, the connection of the first power storage unit 12a and the second power storage unit 12b, the connection of the second power storage unit 12b and the third power storage unit 12c, and the connection of the third power storage unit 12c and the fourth power storage unit 12d, the voltage values of the power storage units 12 to be connected are close to each other (adjacent to each other) and the voltage difference is within the voltage threshold value Vthr, so no overcurrent occurs (connection indicated by "OK" in FIG. 9).

Therefore, in the case of Figure 9, the ECU 14 alternatively selects between the connection between the third storage unit 12c and the fourth storage unit 12d (connection C), or the connection between the second to fourth storage units 12b to 12d (connection D), based on the fourth storage unit 12d having the minimum voltage value (voltage value V4).

Here, when the ECU 14 selects connection C, the ECU 14 transmits a control signal for turning on the switch 26 to the communication unit 38 of the third and fourth storage units 12c and 12d via the communication line 28. As a result, the BMUs 32 of the third and fourth storage units 12c and 12d switch the switch 26 from OFF to ON based on the control signal received by the communication unit 38. As a result, the third and fourth storage units 12c and 12d are connected in parallel to the load 24, and charging and discharging are performed between the third and fourth storage units 12c and 12d (step S5 in FIG. 3).

As a result of charging and discharging, as shown in Fig. 10, the voltage value of the third storage unit 12c decreases from V3 to V34, while the voltage value of the fourth storage unit 12d increases from V4 to V34. That is, the voltage values of the third storage unit 12c and the fourth storage unit 12d are averaged to V34 (step S6 in Fig. 3: YES). As a result, the minimum voltage value increases from V4 to V34.

However, since |V1-V34|>Vthr (step S3 in FIG. 3: NO), there is still a possibility that an overcurrent will flow if the first to fourth power storage units 12a-12d are connected in parallel to the load 24 (connection marked "NG" in FIG. 10). On the other hand, the connection of the second to fourth power storage units 12b-12d and the connection of the first power storage unit 12a and the second power storage unit 12b will not cause an overcurrent because the voltage values of the power storage units 12 to be connected are close to each other (adjacent to each other) and the voltage difference is within the voltage threshold Vthr (connection marked "OK" in FIG. 10).

Therefore, the ECU 14 selectively selects the connection of the second to fourth storage units 12b to 12d based on the third storage unit 12c and the fourth storage unit 12d having the minimum voltage value (voltage value V34). Next, the ECU 14 transmits a control signal for turning on the switch 26 to the communication unit 38 of the second to fourth storage units 12b to 12d via the communication line 28. As a result, the BMUs 32 of the second to fourth storage units 12b to 12d turn on the switch 26 based on the control signal received by the communication unit 38. As a result, the second to fourth storage units 12b to 12d are connected in parallel to the load 24, and charging and discharging are performed between the second to fourth storage units 12b to 12d (step S5 in FIG. 3).

As a result of charging and discharging, as shown in Figure 11, the voltage value of the second storage unit 12b decreases from V2 to V234, while the voltage values of the third storage unit 12c and the fourth storage unit 12d increase from V34 to V234. That is, the voltage values of the second to fourth storage units 12b to 12d are averaged to V234 (Step S6 in Figure 3: YES). As a result, the minimum voltage value increases from V34 to V234.

In this case, |V1-V234|≦Vthr (step S3 in FIG. 3: YES), so even if the first to fourth power storage units 12a-12d are connected in parallel to the load 24, no overcurrent will occur (connection "OK" in FIG. 11). Therefore, the ECU 14 alternatively selects the connection of the first to fourth power storage units 12a-12d based on the second to fourth power storage units 12b-12d with the minimum voltage value (voltage value V234). Next, the ECU 14 transmits a control signal for turning on the switch 26 to the communication unit 38 of the first to fourth power storage units 12a-12d via the communication line 28. As a result, the BMU 32 of the first to fourth power storage units 12a-12d turns on the switch 26 based on the control signal received by the communication unit 38. As a result, first to fourth power storage units 12a to 12d are connected in parallel to load 24, and charging and discharging are performed among first to fourth power storage units 12a to 12d (step S4 in FIG. 3).

As a result of charging and discharging, as shown in Figure 12, the voltage value of the first storage unit 12a decreases from V1 to V1234, while the voltage values of the second to fourth storage units 12b to 12d increase from V234 to V1234. In other words, the voltage values of the first to fourth storage units 12a to 12d are averaged to V1234.

In the above description, the case where connection C in FIG. 9 is alternatively selected has been described. When ECU 14 alternatively selects connection D, ECU 14 transmits a control signal for turning on switch 26 to communication unit 38 of second to fourth power storage units 12b to 12d via communication line 28. As a result, BMU 32 of second to fourth power storage units 12b to 12d switches switch 26 from OFF to ON based on the control signal received by communication unit 38. As a result, second to fourth power storage units 12b to 12d are connected in parallel to load 24, and charging and discharging are performed between second to fourth power storage units 12b to 12d (step S5 in FIG. 3).

As a result of charging and discharging, as shown in Figure 13, the voltage value of the second storage unit 12b drops from V2 to V234, the voltage value of the third storage unit 12c remains at V3 (=V234), and the voltage value of the fourth storage unit 12d rises from V4 to V234. That is, the voltage values of the second to fourth storage units 12b to 12d are averaged to V234 (Step S6 in Figure 3: YES). As a result, the minimum voltage value rises from V4 to V234.

In this case, since |V1-V234|≦Vthr (step S3 in FIG. 3: YES), no overcurrent occurs even if the first to fourth storage units 12a-12d are connected in parallel to the load 24, as in the case of FIG. 11 (connection indicated by "OK" in FIG. 13). Therefore, the ECU 14 selectively selects the connection of the first to fourth storage units 12a-12d based on the second to fourth storage units 12b-12d with the minimum voltage value (voltage value V234). Next, the ECU 14 transmits a control signal for turning on the switch 26 to the communication unit 38 of the first to fourth storage units 12a-12d via the communication line 28. As a result, the BMU 32 of the first to fourth storage units 12a-12d turns on the switch 26 based on the control signal received by the communication unit 38. As a result, first to fourth power storage units 12a to 12d are connected in parallel to load 24, and charging and discharging are performed among first to fourth power storage units 12a to 12d (step S4 in FIG. 3).

In this case, too, as a result of charging and discharging, the voltage value of the first storage unit 12a decreases from V1 to V1234, while the voltage values of the second to fourth storage units 12b to 12d increase from V234 to V1234, as shown in Figure 12. When connection D is selected, the voltage values of the first to fourth storage units 12a to 12d can be averaged to V1234 more quickly than in the case of connection C.

[4. Modifications]
The power device 10 according to the present embodiment may have a modified configuration shown in Fig. 14. In this modified configuration, each power storage unit 12 (12a to 12d) has only a battery 30 and a temperature sensor 36. A voltage sensor 40 that sequentially detects the voltage value of the battery 30 is connected in parallel to each battery 30. Furthermore, the positive terminal of each battery 30 is connected to the positive terminal of the load 24 via a current sensor 42 and a switch 26. Furthermore, the negative terminal of each battery 30 is connected to the negative terminal of the load 24. The current sensor 42 sequentially detects the current value of the current flowing through the battery 30.

The ECU 14 is connected to each temperature sensor 36, each voltage sensor 40, and each current sensor 42 via an analog signal line 44. The ECU 14 sequentially acquires the temperature of the battery 30 detected by each temperature sensor 36, the voltage value of the battery 30 detected by each voltage sensor 40, and the current value detected by each current sensor 42. Therefore, even in this modified example, the ECU 14 can execute the connection process of the switch 26 described above.

1 and 2, the ECU 14 acquires voltage values and the like from each power storage unit 12. Also, in the configuration of FIG. 14, the voltage value detected by the voltage sensor 40 is input to the ECU 14. This embodiment is not limited to these configurations, and the ECU 14 may estimate the voltage value based on information from each power storage unit 12.

5. Effects of this embodiment
As described above, the present embodiment relates to the power device 10 having at least three power storage units 12 (12a to 12d) and a control method thereof.

In this case, the power device 10 has a voltage acquisition unit that acquires the voltage values of each of the storage units 12, and an ECU 14 that functions as a connection unit that connects two of the storage units 12 that have adjacent voltage values to each other based on the acquired voltage values of the storage units 12.

The control method of the power device 10 also includes a step (step S2) in which the ECU 14 acquires the voltage values of the storage units 12, and a step (steps S4 and S5) in which two of the storage units 12 that have adjacent voltage values are connected to each other based on the acquired voltage values of the storage units 12.

In this manner, in this embodiment, two storage units 12 with adjacent voltage values are selected from among at least three storage units 12 and connected to each other. This allows the storage units 12 to be connected by electrical control alone, without adding any circuitry, and the occurrence of an overcurrent can be suppressed. As a result, the impact of costs can be minimized. Therefore, compared to connecting all storage units 12 simultaneously or connecting two or more storage units 12 with voltage values that are distant from each other (not adjacent), it is possible to suppress the flow of an overcurrent in the storage units 12 while reducing the voltage difference.

In this case, the ECU 14 connects the storage unit 12 with the maximum voltage value (e.g., V1) or the minimum voltage value (e.g., V4) to the storage unit 12 with an adjacent voltage value. This connects the two storage units 12 based on the storage unit 12 with the maximum or minimum voltage value. As a result, the maximum voltage value is lowered or the minimum voltage value is raised. Therefore, the overall voltage difference between the storage units 12 is reliably reduced, and the occurrence of overcurrent can be efficiently suppressed.

In addition, it is preferable that the ECU 14 connects the storage unit 12 with the maximum voltage value to the storage unit 12 with a voltage value adjacent to that of the storage unit 12. The higher the voltage value of the storage unit 12, the lower the internal resistance value, and the larger the current value of the current that flows during charging and discharging. Therefore, by connecting two storage units 12 based on the storage unit 12 with the maximum voltage value, it is possible to quickly average the voltage values of the connected storage units 12. In addition, since the higher the voltage value of the storage unit 12, the more likely the storage unit 12 is to deteriorate, by connecting the storage units 12 while keeping the voltage difference within the voltage threshold, it is possible to average the voltage values of the storage units 12 while suppressing the occurrence of overcurrent and deterioration of the storage units 12.

In this case, the ECU 14 repeatedly obtains the voltage value of the power storage unit 12 and connects the power storage unit 12 until the voltage difference between the maximum voltage value and the minimum voltage value falls within a predetermined voltage threshold. This makes it possible to connect all the power storage units 12 while suppressing the occurrence of overcurrent, and reliably average the voltage values.

Furthermore, when the ECU 14 includes two power storage units 12 with approximately the same voltage value, the ECU 14 interconnects the two power storage units 12 and the power storage unit 12 whose voltage value is adjacent to the two power storage units 12, resulting in three power storage units 12. This allows the voltage values of the power storage units 12 to be averaged quickly and efficiently.

In this case, the three storage units 12 are connected in parallel to the load 24, making it possible to supply power from each storage unit 12 to the load 24.

In addition, a built-in battery 18 (another power storage unit) different from the three power storage units 12 is connected in parallel to the load 24 together with the power storage units 12. This makes it possible to supply power from the built-in battery 18 to the load 24, and to supply power from the built-in battery 18 to each power storage unit 12 to start up the respective power storage units 12.

Furthermore, when the voltage difference between two adjacent power storage units 12 exceeds a voltage threshold, the ECU 14 prohibits the two power storage units 12 from being connected to each other. This makes it possible to reliably suppress the occurrence of overcurrent.

The power device 10 also includes three switches 26 (two-way connection circuits) that connect any two of the three power storage units 12 to each other. This allows the ECU 14 to electrically control each of the switches 26.

In this case, the ECU 14 can connect the power storage units 12 to each other by selecting one of the switches 26.

Of course, the present invention is not limited to the above-described embodiments, and various configurations can be adopted based on the contents of this specification.

Claims (9)

In a power device (10) having at least three power storage units (12, 12a to 12d),
a voltage acquisition unit (14) that acquires a voltage value of each of the at least three power storage units;
a connection unit (14) that connects two of the at least three power storage units, the two power storage units having adjacent voltage values, to each other based on the voltage values of the at least three power storage units acquired by the voltage acquisition unit;
Another power storage unit (18) different from at least three of the power storage units;
having
the other power storage unit is a startup power source for starting up the at least three power storage units,
The power device includes two-way connection circuits (26) that connect any two of the at least three power storage units to each other, the number of which is the same as the number of the power storage units ;
Each of the at least three power storage units includes the two-way connection circuit, a battery (30), and a control unit (32) that controls the two-way connection circuit,
the two-way connection circuit is a switch capable of connecting the battery to an outside of the power storage unit,
Each of the at least three power storage units is started up by starting up the control unit in response to power being supplied from the other power storage units;
When the control unit receives an instruction from the connection unit to select the two-way connection circuit while the power storage unit is activated, the control unit switches the switch from off to on, thereby causing charging and discharging to occur between the battery and the outside of the power storage unit. 2. The power device according to claim 1,
The connection portion connects the power storage unit having a maximum voltage value where the voltage value is maximum, or a minimum voltage value where the voltage value is minimum, to the power storage unit having an adjacent voltage value. 3. The power device according to claim 2,
The connection unit connects the power storage unit having the maximum voltage value to the power storage unit having an adjacent voltage value. 4. The power device according to claim 2,
The power device repeatedly acquires the voltage value of the power storage unit by the voltage acquisition unit and connects the power storage unit by the connection unit until a voltage difference between the maximum voltage value and the minimum voltage value becomes within a predetermined threshold value. In the power device according to any one of claims 1 to 4,
The connection unit of the power device is configured to, when there are two or more storage units having approximately the same voltage value , interconnect the two or more storage units and the storage units whose voltage values are adjacent to the two or more storage units. In the power device according to any one of claims 1 to 5,
The at least three power storage units and the other power storage unit are connected in parallel to a load (24). In the power device according to any one of claims 1 to 6,
The connection unit prohibits mutual connection of the two power storage units when a voltage difference between the two power storage units whose voltage values are adjacent to each other exceeds a predetermined threshold value. In the power device according to any one of claims 1 to 7,
A power device, wherein the connection unit connects the power storage units to each other by selecting one of the two-way connection circuits. A method for controlling a power device (10) having at least three power storage units (12, 12a to 12d), comprising:
supplying power from another power storage unit (18) to the at least three power storage units, thereby starting up the at least three power storage units;
acquiring a voltage value of each of the at least three power storage units by a voltage acquisition unit (14);
a step of connecting two of the at least three power storage units, the two power storage units having adjacent voltage values, to each other by a connection unit (14) based on the voltage values of the at least three power storage units acquired by the voltage acquisition unit;
having
The power device includes two-way connection circuits (26) that connect any two of the at least three power storage units to each other, the number of which is the same as the number of the power storage units ;
Each of the at least three power storage units includes the two-way connection circuit, a battery (30), and a control unit (32) that controls the two-way connection circuit,
the two-way connection circuit is a switch capable of connecting the battery to an outside of the power storage unit,
Each of the at least three power storage units is started up by starting up the control unit in response to power being supplied from the other power storage units;
A method for controlling a power device, in which, when the control unit receives an instruction from the connection unit to select the two-way connection circuit while the storage unit is activated, the control unit switches the switch from off to on, thereby causing charging and discharging to occur between the battery and the outside of the storage unit.

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