Bidirectional power supply system and power storage system

Abstract

To obtain a bidirectional power supply system capable of achieving a simple configuration.SOLUTION: A plurality of DC / DC converters each having a first power terminal and a second power terminal, the first power terminal including first and second terminals, the second power terminal including third and fourth terminals, A second terminal of the first DC / DC converter is connected to a first terminal of the second DC / DC converter, a third terminal of the first DC / DC converter is connected to a third terminal of the second DC / DC converter, a fourth terminal of the first DC / DC converter is connected to a fourth terminal of the second DC / DC converter, and the first DC / DC converter is capable of controlling a voltage between the third and fourth terminals based on a first voltage command value, each of the one or more DC / DC converters other than the first DC / DC converter is capable of controlling a voltage between the first and second terminals based on the second voltage command value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bidirectional power supply system capable of transmitting power in both directions, and to a power storage system including such a bidirectional power supply system. [Background technology]

[0002] Some DC / DC converters are capable of transmitting power bidirectionally. For example, Patent Document 1 discloses a power supply system that includes multiple DC / DC converters, with one power terminal of each of the DC / DC converters connected in series and the other power terminals connected in parallel. In this power supply system, the multiple DC / DC converters communicate with each other to control the voltage balance at the series-connected power terminals. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-82722 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, a simple system configuration is desirable, and a simple configuration is also expected for a bidirectional power supply system.

[0005] It is desirable to provide a bidirectional power supply system and a power storage system that can achieve a simple configuration. [Means for solving the problem]

[0006] A bidirectional power supply system according to one embodiment of the present invention includes a plurality of DC / DC converters. Each of the plurality of DC / DC converters has a first power terminal including a first terminal and a second terminal, and a second power terminal including a third terminal and a fourth terminal, and is capable of transmitting power bidirectionally between the first power terminal and the second power terminal. The plurality of DC / DC converters includes a first DC / DC converter and a second DC / DC converter. The second terminal of the first DC / DC converter is connected to the first terminal of the second DC / DC converter. The third terminal of the first DC / DC converter is connected to the third terminal of the second DC / DC converter. The fourth terminal of the first DC / DC converter is connected to the fourth terminal of the second DC / DC converter. The first DC / DC converter is capable of controlling a first voltage between the third terminal and the fourth terminal of the second power terminal of the first DC / DC converter based on a first voltage command value supplied from a control device. Among the multiple DC / DC converters, each of one or more DC / DC converters other than the first DC / DC converter is capable of controlling a second voltage between a first terminal and a second terminal at a first power terminal of the DC / DC converter based on a second voltage command value supplied from the control device.

[0007] A power storage system according to one embodiment of the present invention includes the above-described bidirectional power supply system and a battery connected to the first power terminals of the plurality of DC / DC converters. [Effects of the Invention]

[0008] According to the bidirectional power supply system and the power storage system according to an embodiment of the present invention, a simple configuration can be achieved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of a power storage system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a sequence diagram illustrating an example of an operation of the power storage system shown in FIG. [Figure 3] FIG. 3 is an explanatory diagram illustrating one operating state of the power storage system shown in FIG. [Figure 4] FIG. 4 is an explanatory diagram showing another operating state of the power storage system shown in FIG. [Figure 5] FIG. 5 is an explanatory diagram illustrating an example of a correction process for a current threshold value in the power storage system shown in FIG. [Figure 6] FIG. 6 is an explanatory diagram showing another example of the correction process of the current threshold value in the power storage system shown in FIG. [Figure 7A] FIG. 7A is a flowchart illustrating an example of a process for correcting a current threshold value in the power storage system shown in FIG. [Figure 7B] FIG. 7B is another flowchart illustrating an example of the correction process of the current threshold value in the power storage system shown in FIG. [Figure 8] FIG. 8 is a block diagram illustrating an example of the configuration of a power storage system according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] <Embodiment> [Configuration example] 1 shows an example of the configuration of a power storage system 1 equipped with a bidirectional power supply system according to an embodiment of the present invention. The power storage system 1 is connected to a DC grid 100.

[0012] The DC grid 100 is a power distribution network that transmits DC power. The DC grid 100 is connected to, for example, power supply devices that convert DC power supplied from power generation facilities such as solar power generation and wind power generation, and power supply devices that convert AC power supplied from a system power supply such as a commercial power supply into DC power, and DC power is supplied from these power supply devices. The DC grid 100 then supplies power to various electronic devices that can operate based on DC power. The DC grid 100 also supplies power to various electronic devices via power supply devices that convert DC power into AC power.

[0013] The power storage system 1 is configured to store power supplied from the DC grid 100. Specifically, when the power supply to the DC grid 100 is large, the power storage system 1 stores the power by charging a battery 12 (described later) of the power storage system 1, and when the load power of the DC grid 100 is large, the battery 12 is discharged to supply power to the DC grid 100.

[0014] The power storage system 1 includes a battery management system 11, a control device 13, and a bidirectional power supply system .

[0015] The battery management system 11 has a battery 12, stores power, and monitors the operating state of the battery 12. The positive terminal TP of the battery 12 is connected to a power line L11, and the negative terminal TN is connected to a power line L12. The battery 12 is configured using, for example, a lithium-ion secondary battery. The battery management system 11 monitors, for example, the voltage of each of the multiple battery cells included in the battery 12, the voltage Vbat between the positive terminal TP and the negative terminal TN of the battery 12, the current flowing through the battery 12, the temperature of the battery 12, and the like. The battery management system 11 then supplies data on the operating state of the battery 12 to the control device 13.

[0016] The control device 13 is configured using, for example, a personal computer, and is configured to control the operation of the power storage system 1. The control device 13 controls the operation of the power storage system 1 by supplying control data to the bidirectional power supply system 14 based on data on the operating state of the battery 12 supplied from the battery management system 11.

[0017] The bidirectional power supply system 14 is configured to transmit power bidirectionally between the DC grid 100 and the battery management system 11. The bidirectional power supply system 14 has two DC / DC converters 20 (DC / DC converters 20L and 20F). The DC / DC converter 20L is also called a leader device, and the DC / DC converter 20F is also called a follower device.

[0018] Each of the DC / DC converters 20L and 20F is a bidirectional DC / DC converter capable of transmitting power in both directions. Each of the DC / DC converters 20L and 20F has power terminals T11 and T12, power terminals T21 and T22, a transformer 21, and a control circuit 22.

[0019] The power terminals T11, T12 and the power terminals T21, T22 are configured to input or output electric power. Each of the DC / DC converters 20L, 20F is configured to transmit electric power bidirectionally between the power terminals T11, T12 and the power terminals T21, T22.

[0020] The power terminal T11 of DC / DC converter 20L is connected to the power line L11, and the power terminal T12 of DC / DC converter 20L is connected to the power terminal T11 of DC / DC converter 20F. The power terminal T11 of DC / DC converter 20F is connected to the power terminal T12 of DC / DC converter 20L, and the power terminal T12 of DC / DC converter 20F is connected to the power line L12. That is, from the viewpoint of the power terminals T11 and T12, DC / DC converter 20L and DC / DC converter 20F are connected in series with each other. Voltage Vbat, which is the voltage of power line L11 with respect to power line L12, is the sum of voltages VL and VF. Here, voltage VL is the voltage of power terminal T11 of DC / DC converter 20L with respect to power terminal T12 of DC / DC converter 20L. Voltage VF is the voltage at power terminal T11 of DC / DC converter 20F relative to power terminal T12 of DC / DC converter 20F.

[0021] The power terminal T21 of DC / DC converter 20L is connected to the power line L21, and the power terminal T22 of DC / DC converter 20L is connected to the power line L22. The power terminal T21 of DC / DC converter 20F is connected to the power line L21, and the power terminal T22 of DC / DC converter 20F is connected to the power line L22. That is, from the viewpoint of the power terminals T21 and T22, DC / DC converter 20L and DC / DC converter 20F are connected in parallel to each other. The power lines L21 and L22 are connected to the DC grid 100. The voltage Vgrid of the DC grid 100 is the voltage of the power line L21 relative to the power line L22.

[0022] The transformer 21 is configured to provide DC insulation and AC connection between a plurality of circuits connected to a plurality of windings of the transformer 21. Each of the DC / DC converters 20L, 20F transmits power bidirectionally between the power terminals T11, T12 and the power terminals T21, T22 via the transformer 21. In other words, each of the DC / DC converters 20L, 20F is a so-called isolated DC / DC converter.

[0023] The control circuit 22 of the DC / DC converter 20L, which is the leader device, is configured to control the operation of the DC / DC converter 20L based on control data supplied from the control device 13. Specifically, the control circuit 22 controls the operation of the DC / DC converter 20L based on a voltage command value Vgrid1 supplied from the control device 13 so that the voltage (voltage Vgrid) at the power terminal T21 of the DC / DC converter 20L relative to the power terminal T22 of the DC / DC converter 20L becomes the voltage indicated by the voltage command value Vgrid1. The control circuit 22 also controls the operation of the DC / DC converter 20L based on a current threshold value Ith supplied from the control device 13 so that the current flowing through the power terminal T21 of the DC / DC converter 20L does not exceed the current threshold value Ith. The control circuit 22 also has a function of correcting the current threshold value Ith, as will be described later. When the control circuit 22 corrects this current threshold Ith, it controls the operation of the DC / DC converter 20L so that the current flowing through the power terminal T21 of the DC / DC converter 20L does not exceed this corrected current threshold Ith.

[0024] Control circuit 22 of DC / DC converter 20F, which is a follower device, is configured to control the operation of DC / DC converter 20F based on control data supplied from control device 13. Specifically, control circuit 22 controls the operation of DC / DC converter 20F based on voltage command value VF1 supplied from control device 13 so that the voltage (voltage VF) at power terminal T11 of DC / DC converter 20F relative to power terminal T12 of DC / DC converter 20F becomes the voltage indicated by that voltage command value VF1.

[0025] Like the control circuit 22 of DC / DC converter 20L, control circuit 22 of DC / DC converter 20F has the function of controlling the operation of DC / DC converter 20F so that the current flowing through power terminal T21 of DC / DC converter 20F does not exceed the current threshold value. However, as described above, DC / DC converter 20L limits the current flowing through power terminal T21 of DC / DC converter 20L so that it does not exceed current threshold value Ith, and as a result, the current flowing through power terminal T21 of DC / DC converter 20F is also controlled. In other words, when the current flowing through power terminal T21 of DC / DC converter 20L is limited, the current flowing through power terminal T11 of DC / DC converter 20L is limited. From the perspective of power terminals T11 and T12, DC / DC converter 20L and DC / DC converter 20F are connected in series, and therefore, limiting the current flowing through power terminal T11 of DC / DC converter 20L limits the current flowing through power terminal T11 of DC / DC converter 20F. As a result, the current flowing through the power terminal T21 of the DC / DC converter 20F is also limited. Thus, when the current flowing through the power terminal T21 of the DC / DC converter 20L is limited, the current flowing through the power terminal T21 of the DC / DC converter 20F is also limited. Therefore, the DC / DC converter 20F does not need to limit the current flowing through the power terminal T21 of the DC / DC converter 20F. Therefore, in this example, the current threshold value of the DC / DC converter 20F is set to a value sufficiently larger than the current threshold value Ith of the DC / DC converter 20L. In this example, the current threshold value of the DC / DC converter 20F is stored in advance in a nonvolatile memory included in the DC / DC converter 20F. In the bidirectional power supply system 14, by setting this current threshold value to a sufficiently large value, it is possible to prevent the current flowing through the power terminal T21 of the DC / DC converter 20F from reaching this current threshold value. In this case, the DC / DC converter 20F does not limit the current. In this way, in the bidirectional power supply system 14, the DC / DC converter 20L limits the current.

[0026] Here, DC / DC converter 20L corresponds to a specific example of a "first DC / DC converter" in an embodiment of the present disclosure. DC / DC converter 20F corresponds to a specific example of a "second DC / DC converter" in an embodiment of the present disclosure. Power terminals T11 and T12 correspond to a specific example of a "first power terminal" in an embodiment of the present disclosure. Power terminal T11 corresponds to a specific example of a "first terminal" in an embodiment of the present disclosure. Power terminal T12 corresponds to a specific example of a "second terminal" in an embodiment of the present disclosure. Power terminals T21 and T22 correspond to a specific example of a "second power terminal" in an embodiment of the present disclosure. Power terminal T21 corresponds to a specific example of a "third terminal" in an embodiment of the present disclosure. Power terminal T22 corresponds to a specific example of a "fourth terminal" in an embodiment of the present disclosure. Transformer 21 corresponds to a specific example of a "transformer" in an embodiment of the present disclosure. The voltage command value Vgrid1 corresponds to a specific example of a "first voltage command value" in an embodiment of the present disclosure. The voltage Vgrid corresponds to a specific example of a "first voltage" in an embodiment of the present disclosure. The voltage command value VF1 corresponds to a specific example of a "second voltage command value" in an embodiment of the present disclosure. The voltage VF corresponds to a specific example of a "second voltage" in an embodiment of the present disclosure. The voltage VL corresponds to a specific example of a "third voltage" in an embodiment of the present disclosure. The current threshold Ith corresponds to a specific example of a "first current threshold" in an embodiment of the present disclosure. The current threshold of DC / DC converter 20F corresponds to a specific example of a "second current threshold" in an embodiment of the present disclosure. The control device 13 corresponds to a specific example of a "control device" in an embodiment of the present disclosure. The battery 12 corresponds to a specific example of a "battery" in an embodiment of the present disclosure.

[0027] [Actions and Actions] Next, the operation and function of the power storage system 1 of this embodiment will be described.

[0028] (Overview of overall operation) The battery management system 11 stores power and monitors the operating state of the battery 12. The control device 13 controls the operation of the power storage system 1 by supplying control data to the bidirectional power supply system 14 based on data on the operating state of the battery 12 supplied from the battery management system 11. The bidirectional power supply system 14 transmits power bidirectionally between the DC grid 100 and the battery management system 11.

[0029] (Detailed operation) FIG. 2 shows an example of the operation of the power storage system 1.

[0030] When the power storage system 1 is started up, the control device 13 first issues a leader setting instruction to the DC / DC converter 20L, instructing the DC / DC converter 20L to operate as a leader device, and supplies control data including data on a voltage command value Vgrid1 for the voltage Vgrid, a voltage command value VF1 for the voltage VF, and a current threshold value Ith (step S101). In this example, the voltage indicated by the voltage command value Vgrid1 is 380V. The voltage indicated by the voltage command value VF1 is half the voltage Vbat. In this example, the voltage Vbat is 480V, and the voltage indicated by the voltage command value VF1 is 240V. The control circuit 22 of the DC / DC converter 20L receives this leader setting instruction and control data.

[0031] Furthermore, control device 13 issues a follower setting instruction to DC / DC converter 20F to instruct DC / DC converter 20F to operate as a follower device, and supplies control data including data on voltage command value VF1 for voltage VF (step S102). Control circuit 22 of DC / DC converter 20F receives this follower setting instruction and control data.

[0032] Based on the leader setting instruction received in step S101, the control circuit 22 of the DC / DC converter 20L sets the operation mode to a mode in which the voltage Vgrid is controlled and the current flowing through the power terminal T21 is controlled (step S103). That is, the control circuit 22 sets the operation mode so that the DC / DC converter 20L operates as a leader device. As a result, the control circuit 22 controls the operation of the DC / DC converter 20L based on the voltage command value Vgrid1 supplied from the control device 13 so that the voltage Vgrid becomes the voltage indicated by that voltage command value Vgrid1. Furthermore, based on the current threshold value Ith supplied from the control device 13, the control circuit 22 controls the operation of the DC / DC converter 20L so that the current flowing through the power terminal T21 of the DC / DC converter 20L does not exceed the current threshold value Ith or a corrected current threshold value Ith. The correction process for the current threshold value Ith will be described in detail later.

[0033] Control circuit 22 of DC / DC converter 20F sets the operation mode to a mode for controlling voltage VF based on the follower setting instruction received in step S102 (step S104). That is, control circuit 22 sets the operation mode so that DC / DC converter 20F operates as a follower device. As a result, control circuit 22 thereafter controls the operation of DC / DC converter 20F based on voltage command value VF1 supplied from control device 13 so that voltage VF becomes the voltage indicated by that voltage command value VF1.

[0034] Then, when the start-up operation is completed (step S110), the power storage system 1 starts normal operation. In this normal operation, the power storage system 1 performs charging and discharging of the battery 12.

[0035] Fig. 3 shows one operating state of the power storage system 1 after the start-up operation is completed. For the sake of convenience of explanation, Fig. 3 shows the power storage system 1 in a simplified form.

[0036] Control circuit 22 of DC / DC converter 20L controls the operation of DC / DC converter 20L based on voltage command value Vgrid1 so that voltage Vgrid becomes 380V.

[0037] Furthermore, the control circuit 22 of the DC / DC converter 20F controls the operation of the DC / DC converter 20F based on the voltage command value VF1 so that the voltage VF is 240 V. Since the voltage Vbat of the battery 12 is 480 V and the voltage VF at the DC / DC converter 20F, which is the follower device, is 240 V, the voltage VL at the DC / DC converter 20L, which is the leader device, is 240 V. In this way, in the bidirectional power supply system 14, the voltage VL at the DC / DC converter 20L, which is the leader device, and the voltage VF at the DC / DC converter 20F, which is the follower device, are the same voltage.

[0038] As described above, in the power storage system 1, the control device 13 sets the voltage command value VF1 by calculating half the voltage (240 V) of the voltage Vbat of the battery 12 based on the voltage Vbat (480 V). Then, the control circuit 22 of the DC / DC converter 20F controls the operation of the DC / DC converter 20F based on this voltage command value VF1 so that the voltage VF becomes 240 V. This adjusts the balance between the voltage VL of the DC / DC converter 20L, which is the leader device, and the voltage VF of the DC / DC converter 20F, which is the follower device, in the power storage system 1. As a result, the power storage system 1 can reduce the possibility of the amount of power transmission of one of the DC / DC converters 20F, 20L becoming excessive, causing damage to the DC / DC converter 20.

[0039] That is, for example, during discharging, if voltage VF is greater than voltage VL, the power supplied from battery 12 to DC / DC converter 20F is greater than the power supplied from battery 12 to DC / DC converter 20L, and therefore the amount of power transmitted by DC / DC converter 20L increases. The same is true during charging. If the amount of power transmitted by one of DC / DC converters 20L, 20F becomes excessive, that DC / DC converter 20 may be damaged.

[0040] On the other hand, in the power storage system 1, the voltages VL and VF are adjusted to be the same, so that the amounts of power transmitted by the DC / DC converters 20L and 20F can be made almost the same. As a result, in the power storage system 1, the possibility of damage to the DC / DC converter 20 can be reduced.

[0041] In normal operation, as shown in Fig. 2, control device 13 periodically supplies control data including data on voltage command value VF1 for voltage VF to each of DC / DC converters 20L, 20F (step S111). Cycle T for supplying the control data is, for example, about 0.1 seconds to 1 minute. Control circuit 22 of DC / DC converter 20L and control circuit 22 of DC / DC converter 20F each receive this control data.

[0042] Control circuit 22 of DC / DC converter 20L repeatedly and continuously performs the process of correcting current threshold value Ith (step S112) based on voltage command value VF1 of voltage VF supplied from control device 13. The process of correcting current threshold value Ith will be described in detail later.

[0043] Control circuit 22 of DC / DC converter 20F resets the target voltage of voltage VF based on voltage command value VF1 for voltage VF supplied from control device 13 (step S113). As a result, control circuit 22 controls the operation of DC / DC converter 20F so that voltage VF becomes the voltage indicated by voltage command value VF1 supplied in step S111. That is, voltage Vbat of battery 12 may change over time. Therefore, control device 13 periodically supplies DC / DC converter 20F with a voltage command value VF1 corresponding to this voltage Vbat. Control circuit 22 resets the target voltage of voltage VF based on this voltage command value VF1. As a result, in power storage system 1, even if voltage Vbat of battery 12 changes, voltage VF can be set according to the change. As a result, the balance between voltage VL in DC / DC converter 20L, which is the leader device, and voltage VF in DC / DC converter 20F, which is the follower device, is adjusted.

[0044] (Regarding correction processing of current threshold Ith) The voltage Vbat of the battery 12 may change over time. The control device 13 supplies a voltage command value VF1 to the DC / DC converter 20F at a period T of, for example, about 0.1 seconds to 1 minute. In particular, the longer the period T, the greater the transient change in the voltage Vbat may be within the period T. In this case, a transient imbalance may occur between the voltage VL of the DC / DC converter 20L, which is the leader device, and the voltage VF of the DC / DC converter 20F, which is the follower device. In the power storage system 1, the control circuit 22 of the DC / DC converter 20L, which is the leader device, performs a process to correct the current threshold value Ith. This makes it possible to reduce the possibility that the discharge power of the battery 12 will become excessive or that the amount of power transmitted by the DC / DC converters 20F, 20L will become excessive.

[0045] FIG. 4 shows an example of the operation of the power storage system 1 during discharge, where (A) shows an example of normal operation of the power storage system 1, and (B) shows an example of a case where an imbalance occurs between the voltages VL and VF of the power storage system 1.

[0046] 4A, in normal operation, the voltage Vbat of the battery 12 is 480 V, and the voltages VL and VL are both 240 V. In addition, the voltage Vgrid of the DC grid 100 is 380 V.

[0047] In this example, the current threshold value Ith of the DC / DC converter 20L is set to 10 A. Therefore, the maximum value of the current that the DC / DC converter 20L can supply to the DC grid 100 (supplyable current IL) is 10 A.

[0048] In this example, since the voltages VL and VF are equal to each other, the power supplied by the battery 12 to the DC / DC converter 20L and the power supplied by the battery 12 to the DC / DC converter 20F are equal to each other. Therefore, the power that the DC / DC converter 20L can supply to the DC grid 100 and the power that the DC / DC converter 20F can supply to the DC grid 100 are equal to each other. Since the maximum value of the current that the DC / DC converter 20L can supply to the DC grid 100 (supplyable current IL) is 10 A, the maximum value of the current that the DC / DC converter 20F can supply to the DC grid 100 (supplyable current IF) is also 10 A. As a result, the maximum value of the current that the power storage system 1 can supply to the DC grid 100 (supplyable current Itotal) is 20 A. The power supplied by the DC / DC converters 20F and 20L to the DC grid 100 is approximately the same as the power supplied by the battery 12 to the DC / DC converters 20F and 20L. Therefore, when the power storage system 1 outputs the same current as this available current Itotal, the discharge power Pbat of the battery 12 is 7.6 kW (=380V×20A) and the discharge current Ibat of the battery 12 is 15.8A.

[0049] For example, as shown in FIG. 4B, when the voltage Vbat of the battery 12 transiently drops to 420 V, the voltage VL becomes 180 V. In this case, there is a transient imbalance between the voltage VL (180 V) at the DC / DC converter 20L, which is the leader device, and the voltage VF (240 V) at the DC / DC converter 20F, which is the follower device. In this example, the ratio of the voltages VL and VF is 3:4, so the ratio of the power supplied by the battery 12 to the DC / DC converter 20L to the power supplied by the battery 12 to the DC / DC converter 20F is also 3:4. Therefore, the ratio of the suppliable current IL of the DC / DC converter 20L to the suppliable current IF of the DC / DC converter 20F is 3:4, so the suppliable current IF of the DC / DC converter 20F is 13.3 A (= 10 A × 4 / 3). As a result, the supplyable current Itotal of the power storage system 1 is 23.3 A. If the power storage system 1 outputs a current equal to this supplyable current Itotal, the discharge power Pbat of the battery 12 is 8.9 kW (=380 V×23.3 A) and the discharge current Ibat of the battery 12 is 21.1 A.

[0050] In this way, when the voltage Vbat of the battery 12 transiently decreases, the voltage VL of the DC / DC converter 20L, which is the leader device, transiently decreases, which increases the suppliable current IF of the DC / DC converter 20F, increases the suppliable current Itotal of the power storage system 1, and increases the discharge power Pbat of the battery 12.

[0051] 4(B), if the discharge power Pbat of the battery 12 increases transiently, it may not satisfy the rated conditions of the battery 12. Therefore, the control circuit 22 of the DC / DC converter 20L performs a correction process for the current threshold value Ith.

[0052] FIG. 5 shows an example of operation of the power storage system 1 when correction processing for the current threshold value Ith is performed. In this example, the control circuit 22 resets the current threshold value Ith so that the suppliable current Itotal becomes the same as that in the normal operation (FIG. 4(A)). The control circuit 22 calculates the ratio between the voltage VL and the voltage VF based on the voltage command value VF1 for the voltage VF supplied from the control device 13 and the voltage VL at the DC / DC converter 20L, and calculates the current threshold value Ith of the DC / DC converter 20L based on this ratio. Since the suppliable current Itotal in the normal operation is 20 A, the control circuit 22 corrects the current threshold value Ith of the DC / DC converter 20L to 8.6 A (=20 A×3 / 7). At this time, as shown in FIG. 5, the suppliable current IL of the DC / DC converter 20L is 8.6 A, and the suppliable current IF of the DC / DC converter 20F is 11.4 A (=20 A×4 / 7). When the power storage system 1 outputs this available current Itotal, the discharge power Pbat and the discharge current Ibat of the battery 12 are the same as those in the normal operation (FIG. 4(A)).

[0053] In the energy storage system 1, even if the voltage VL at the DC / DC converter 20L, which is the leader device, drops transiently, the discharge power Pbat of the battery 12 can be made to satisfy the rated conditions by performing the correction process for the current threshold Ith in this manner.

[0054] 4(B), if the supplyable current I of DC / DC converter 20F increases transiently, it may no longer satisfy the rated conditions of DC / DC converter 20F. Therefore, control circuit 22 of DC / DC converter 20L performs a correction process for current threshold Ith.

[0055] FIG. 6 shows another example of operation of the power storage system 1 when the correction process for the current threshold value Ith is performed. The control circuit 22 calculates the ratio between the voltage VL and the voltage VF based on the voltage command value VF1 for the voltage VF supplied from the control device 13 and the voltage VL at the DC / DC converter 20L, and calculates the current threshold value Ith based on this ratio so that the supplyable current IF of the DC / DC converter 20F does not exceed the maximum rated value for the output current of the DC / DC converter 20F. For example, if the maximum rated value for the output current of the DC / DC converter 20F is 11 A, the control circuit 22 sets the supplyable current IF of the DC / DC converter 20F to 11 A. In this case, as shown in FIG. 6, the supplyable current IL of the DC / DC converter 20L is 8.25 A (=11 A × 3 / 4). Therefore, the control circuit 22 corrects the current threshold value Ith to 8.25 A.

[0056] In the energy storage system 1, even if the voltage VL of the DC / DC converter 20L, which is the leader device, drops transiently, the output current of the DC / DC converter 20F can satisfy the rated conditions by performing the correction process of the current threshold value Ith in this manner.

[0057] In the above example, as shown in Fig. 4(B), a case has been described in which the voltage Vbat of the battery 12 transiently decreases. However, there may also be a case in which the voltage Vbat of the battery 12 transiently increases. In this case, the voltage VL of the DC / DC converter 20L, which is the leader device, transiently increases, and the voltage VL becomes greater than the voltage VF. Even in this case, the power storage system 1 similarly performs a correction process for the current threshold value Ith, thereby making it possible to make the discharge power Pbat of the battery 12 satisfy the rated conditions and to make the output current of the DC / DC converter 20L satisfy the rated conditions.

[0058] 7 shows an example of the correction process for the current threshold value Ith. In step S112 shown in FIG. 2, control circuit 22 of DC / DC converter 20L repeatedly and continuously performs the following process.

[0059] Control circuit 22 of DC / DC converter 20L checks whether voltage VL is equal to voltage command value VF1 for voltage VF supplied from control device 13 in step S111 (step S201). Specifically, DC / DC converter 20L detects voltage VL and compares the detected voltage VL with voltage command value VF1 for voltage VF supplied from control device 13 in step S111. Because DC / DC converter 20F controls voltage VF based on voltage command value VF1, control circuit 22 can compare voltage VL with voltage VF by comparing voltage VL with voltage command value VF1.

[0060] If voltage VL is equal to voltage command value VF1 ("Y" in step S201), control circuit 22 uses current threshold value Ith supplied from control device 13 in step S101 as a control parameter (step S202). Then, this processing ends. As a result, control circuit 22 controls the operation of DC / DC converter 20L so that the current flowing through power terminal T21 of DC / DC converter 20L does not exceed current threshold value Ith supplied from control device 13 in step S101.

[0061] If the voltage VL is different from the voltage command value VF1 ("N" in step S201), the control circuit 22 of the DC / DC converter 20L checks whether the voltage VL is smaller than the voltage command value VF1 of the voltage VF supplied from the control device 13 in step S111 (step S203).

[0062] If voltage VL is smaller than voltage command value VF1 ("Y" in step S203), control circuit 22 of DC / DC converter 20L calculates current threshold value Ith of DC / DC converter 20L and calculates supplyable current IF of DC / DC converter 20F based on voltage command value VF1 for voltage VF supplied from control device 13 in step S111 and voltage VL detected by DC / DC converter 20L (step S204). Specifically, control circuit 22 calculates the ratio between voltage VL and voltage VF (voltage command value VF1), as described using Fig. 5, and calculates current threshold value Ith and supplyable current IF based on this ratio.

[0063] Next, control circuit 22 checks whether or not the supplyable current IF calculated in step S204 satisfies the rating conditions of DC / DC converter 20F (step S205). Specifically, control circuit 22 stores the maximum rated value of the output current at power terminal T21 of DC / DC converter 20F, and checks whether or not the calculated supplyable current IF is equal to or less than this maximum rated value.

[0064] If the suppliable current IF satisfies the rated conditions of DC / DC converter 20F ("Y" in step S205), control circuit 22 uses current threshold value Ith calculated in step S204 as a control parameter (step S206). Then, this processing ends. As a result, control circuit 22 controls the operation of DC / DC converter 20L so that the current flowing through power terminal T21 of DC / DC converter 20L does not exceed current threshold value Ith calculated in step S204.

[0065] If the supplyable current IF does not satisfy the rated conditions of DC / DC converter 20F ("N" in step S205), a current threshold value Ith is calculated so that the supplyable current IF satisfies the rated conditions of DC / DC converter 20F (step S207). Specifically, as described using Fig. 6, control circuit 22 calculates the ratio between voltage VL and voltage VF (voltage command value VF1), and calculates current threshold value Ith based on this ratio so that the supplyable current IF of DC / DC converter 20F does not exceed the maximum rated value for the output current of DC / DC converter 20F.

[0066] Control circuit 22 then uses current threshold value Ith calculated in step S207 as a control parameter (step S208). Then, this process ends. Control circuit 22 thereby controls the operation of DC / DC converter 20L so that the current flowing through power terminal T21 of DC / DC converter 20L does not exceed current threshold value Ith calculated in step S207.

[0067] In step S203, if voltage VL is greater than voltage command value VF1 ("N" in step S203), control circuit 22 of DC / DC converter 20L calculates current threshold value Ith of DC / DC converter 20L based on voltage command value VF1 for voltage VF supplied from control device 13 in step S111 and voltage VL detected by DC / DC converter 20L (step S209). Specifically, control circuit 22 calculates the ratio between voltage VL and voltage VF (voltage command value VF1), as in the case of Fig. 5, and calculates current threshold value Ith based on this ratio. Supplyable current IL is the same as current threshold value Ith.

[0068] Next, control circuit 22 checks whether or not the supplyable current IL calculated in step S209 satisfies the rating conditions of DC / DC converter 20L (step S210). Specifically, control circuit 22 stores the maximum rated value of the output current at power terminal T21 of DC / DC converter 20L, and checks whether or not the calculated supplyable current IL is equal to or less than this maximum rated value.

[0069] If the suppliable current IL satisfies the rated conditions of DC / DC converter 20L ("Y" in step S210), control circuit 22 uses current threshold value Ith calculated in step S209 as a control parameter (step S211). Then, this processing ends. As a result, control circuit 22 controls the operation of DC / DC converter 20L so that the current flowing through power terminal T21 of DC / DC converter 20L does not exceed current threshold value Ith calculated in step S209.

[0070] If the supplyable current IL does not satisfy the rated conditions of the DC / DC converter 20L ("N" in step S210), the control circuit 22 sets the current threshold Ith to a value equal to the maximum rated value of the output current of the DC / DC converter 20L (step S212).

[0071] Then, control circuit 22 uses current threshold value Ith set in step S212 as a control parameter (step S213). Then, this process ends. As a result, control circuit 22 controls the operation of DC / DC converter 20L so that the current flowing through power terminal T21 of DC / DC converter 20L does not exceed current threshold value Ith calculated in step S212.

[0072] This is the end of this process. Control circuit 22 of DC / DC converter 20L continues to repeatedly perform this process in step S112 shown in FIG.

[0073] Thus, the bidirectional power supply system 14 includes a plurality of DC / DC converters, including a first DC / DC converter (DC / DC converter 20L) and a second DC / DC converter (DC / DC converter 20F), each having a first power terminal (power terminal T11) and a second terminal (power terminal T12) and a second power terminal (power terminal T21) and a third terminal (power terminal T21) and a fourth terminal (power terminal T22), and capable of transmitting power bidirectionally between the first and second power terminals. The second terminal (power terminal T12) of the first DC / DC converter (DC / DC converter 20L) is connected to the first terminal (power terminal T11) of the second DC / DC converter (DC / DC converter 20F). The third terminal (power terminal T21) of the first DC / DC converter (DC / DC converter 20L) is connected to the third terminal (power terminal T21) of the second DC / DC converter (DC / DC converter 20F), and the fourth terminal (power terminal T22) of the first DC / DC converter (DC / DC converter 20L) is connected to the fourth terminal (power terminal T22) of the second DC / DC converter (DC / DC converter 20F). The first DC / DC converter (DC / DC converter 20L) is capable of controlling a first voltage (voltage Vgrid) between the third terminal (power terminal T21) and the fourth terminal (power terminal T22) of the second power terminals (power terminals T21, T22) of the first DC / DC converter (DC / DC converter 20L) based on a first voltage command value (voltage command value Vgrid1) supplied from the control device 13. Of the multiple DC / DC converters, each of the one or more DC / DC converters (DC / DC converter 20F) other than the first DC / DC converter (DC / DC converter 20L) is capable of controlling a second voltage (voltage VF) between a first terminal (power terminal T11) and a second terminal (power terminal T12) at the first power terminals (power terminals T11, T12) of that DC / DC converter, based on a second voltage command value (voltage command value VF1) supplied from control device 13. This makes it possible to achieve a simple configuration in bidirectional power supply system 14.

[0074] For example, as in the technology described in Patent Document 1, when multiple DC / DC converters communicate with each other to control the voltage balance at series-connected power terminals, the system becomes complicated. In other words, in this system, each of the multiple DC / DC converters must communicate with the other DC / DC converters, resulting in a complex circuit configuration. Furthermore, a communication path must be provided for the multiple DC / DC converters to communicate with each other. As a result, the system becomes complicated. Meanwhile, in the bidirectional power supply system 14, the DC / DC converter 20F controls the voltage VF based on the voltage command value VF1 supplied from the control device 13. When the voltage indicated by the voltage command value VF1 is half the voltage Vbat of the battery 12, the voltage VL of the DC / DC converter 20L and the voltage VF of the DC / DC converter 20F become the same voltage. In this way, the bidirectional power supply system 14 can control the voltage balance. Since the bidirectional power supply system 14 does not require communication between the DC / DC converter 20L and the DC / DC converter 20F, a simple configuration can be achieved.

[0075] In the bidirectional power supply system 14, the first DC / DC converter (DC / DC converter 20L) is capable of controlling a first current flowing through the second power terminals (power terminals T21, T22) of the first DC / DC converter so that the first current does not exceed a first current threshold (current threshold Ith). In the bidirectional power supply system 14, from the perspective of the power terminals T11, T12, the DC / DC converter 20L and the DC / DC converter 20F are connected in series. Therefore, when the current flowing through the power terminal T21 of the DC / DC converter 20L is limited, the current flowing through the power terminal T21 of the DC / DC converter 20F is also limited. Therefore, the DC / DC converter 20F does not need to control the current. In this way, in the bidirectional power supply system 14, only the DC / DC converter 20L controls the current, making it possible to achieve a simple configuration.

[0076] In the bidirectional power supply system 14, each of the one or more DC / DC converters (DC / DC converter 20F) can control the second current flowing through the second power terminal (power terminals T21, T22) of that DC / DC converter so that it does not exceed a second current threshold, and the second current threshold is set to be greater than the first current threshold (current threshold Ith). This prevents the current flowing through the power terminal T21 of the DC / DC converter 20F from reaching the second current threshold. In this case, the DC / DC converter 20F does not limit the current. Therefore, in the bidirectional power supply system 14, only the DC / DC converter 20L controls the current, making it possible to achieve a simple configuration.

[0077] In bidirectional power supply system 14, first DC / DC converter (DC / DC converter 20L) can detect a third voltage (voltage VL) between a first terminal (power terminal T11) and a second terminal (power terminal T12) at a first power terminal of the first DC / DC converter, and can correct a first current threshold (current threshold Ith) based on the third voltage (voltage VL) and a second voltage command value (voltage command value VF1) supplied from control device 13. As a result, for example, as shown in FIGS. 4 to 6, even if voltage Vbat of battery 12 transiently drops, correcting current threshold Ith can be performed to make discharge power Pbat of battery 12 satisfy the rated conditions, and the output current of DC / DC converter 20F can satisfy the rated conditions.

[0078] In bidirectional power supply system 14, the first DC / DC converter (DC / DC converter 20L) is further capable of calculating the maximum current value of the current flowing through the second power terminal (power terminal T21) of each of the one or more DC / DC converters based on a third voltage (voltage VL) and a second voltage command value (voltage command value VF1) supplied from control device 13, and is capable of correcting the first current threshold value (current threshold value Ith) based on the third voltage (voltage VL), the second voltage command value (voltage command value VF1) supplied from control device 13, and the maximum current value. As a result, for example, even if the voltage Vbat of battery 12 transiently drops as shown in FIGS. 4 and 6, the output current of DC / DC converter 20F can satisfy the rated conditions by correcting the current threshold value Ith.

[0079] [effect] As described above, this embodiment includes a plurality of DC / DC converters, including a first DC / DC converter and a second DC / DC converter, each having a first power terminal including a first terminal and a second terminal and a second power terminal including a third terminal and a fourth terminal, and capable of transmitting power bidirectionally between the first power terminal and the second power terminal. The second terminal of the first DC / DC converter is connected to the first terminal of the second DC / DC converter. The third terminal of the first DC / DC converter is connected to the third terminal of the second DC / DC converter, and the fourth terminal of the first DC / DC converter is connected to the fourth terminal of the second DC / DC converter. The first DC / DC converter is capable of controlling a first voltage between the third terminal and the fourth terminal of the second power terminal of the first DC / DC converter based on a first voltage command value supplied from a control device. Among the multiple DC / DC converters, each of the one or more DC / DC converters other than the first DC / DC converter is capable of controlling the second voltage between the first terminal and the second terminal at the first power terminal of the DC / DC converter based on the second voltage command value supplied from the control device, thereby achieving a simple configuration.

[0080] In the present embodiment, the first DC / DC converter is capable of controlling the first current flowing through the second power terminal of the first DC / DC converter so that the first current does not exceed the first current threshold, thereby achieving a simple configuration.

[0081] In this embodiment, each of the one or more DC / DC converters is capable of controlling the second current flowing through the second power terminal of the DC / DC converter so that the second current does not exceed the second current threshold, and the second current threshold is larger than the first current threshold, making it possible to realize a simple configuration.

[0082] In this embodiment, the first DC / DC converter can detect a third voltage between the first terminal and the second terminal of the first power terminal of the first DC / DC converter, and can correct the first current threshold based on the third voltage and the second voltage command value supplied from the control device. As a result, even if the battery voltage drops transiently, the current threshold can be corrected to ensure that the battery discharge power satisfies the rated conditions, and the output current of the second DC / DC converter satisfies the rated conditions.

[0083] In this embodiment, the first DC / DC converter is further capable of calculating the maximum current value of the current flowing through the second power terminal of each of the one or more DC / DC converters based on the third voltage and the second voltage command value supplied from the control device, and is capable of correcting the first current threshold based on the third voltage, the second voltage command value supplied from the control device, and the maximum current value. As a result, even if the battery voltage drops transiently, the output current of the second DC / DC converter can satisfy the rated conditions by correcting the current threshold.

[0084] [Variations] In the above embodiment, the power storage system 1 is provided with one follower device, but is not limited to this, and instead, for example, two or more follower devices may be provided as in a power storage system 1A shown in Fig. 8. This power storage system 1A includes a control device 13A and a bidirectional power supply system 14A.

[0085] The control device 13A is configured to control the operation of the power storage system 1A, similar to the control device 13 (FIG. 1). The control device 13A controls the operation of the power storage system 1A by supplying control data to the bidirectional power supply system 14A based on data on the operating state of the battery 12 supplied from the battery management system 11.

[0086] The bidirectional power supply system 14A has three DC / DC converters 20 (DC / DC converters 20L, 20FA, and 20FB). The DC / DC converters 20FA and 20FB are follower devices.

[0087] The power terminal T11 of DC / DC converter 20L is connected to the power line L11, and the power terminal T12 of DC / DC converter 20L is connected to the power terminal T11 of DC / DC converter 20FA. The power terminal T11 of DC / DC converter 20FA is connected to the power terminal T12 of DC / DC converter 20L, and the power terminal T12 of DC / DC converter 20FA is connected to the power terminal T11 of DC / DC converter 20FB. The power terminal T11 of DC / DC converter 20FB is connected to the power terminal T12 of DC / DC converter 20FA, and the power terminal T12 of DC / DC converter 20FB is connected to the power line L12. That is, from the viewpoint of the power terminals T11 and T12, DC / DC converters 20L, 20FA, and 20FB are connected in series with each other. Voltage Vbat, which is the voltage of power line L11 relative to power line L12, is the sum of voltages VL, VFA, and VFB. Here, voltage VFA is the voltage at power terminal T11 of DC / DC converter 20FA relative to power terminal T12 of DC / DC converter 20FA, and voltage VFB is the voltage at power terminal T11 of DC / DC converter 20FB relative to power terminal T12 of DC / DC converter 20FB.

[0088] A power terminal T21 of DC / DC converter 20L is connected to power line L21, and a power terminal T22 of DC / DC converter 20L is connected to power line L22. A power terminal T21 of DC / DC converter 20FA is connected to power line L21, and a power terminal T22 of DC / DC converter 20FA is connected to power line L22. A power terminal T21 of DC / DC converter 20FB is connected to power line L21, and a power terminal T22 of DC / DC converter 20FB is connected to power line L22. That is, from the viewpoint of power terminals T21 and T22, DC / DC converters 20L, 20FA, and 20FB are connected in parallel with each other.

[0089] Control circuit 22 of DC / DC converter 20FA, which is a follower device, controls the operation of DC / DC converter 20FA based on a voltage command value supplied from control device 13 so that the voltage (voltage VFA) at power terminal T11 of DC / DC converter 20FA, relative to power terminal T12, becomes the voltage indicated by the voltage command value. Similarly, control circuit 22 of DC / DC converter 20FB, which is a follower device, controls the operation of DC / DC converter 20FB based on a voltage command value supplied from control device 13 so that the voltage (voltage VFB) at power terminal T11 of DC / DC converter 20FB, relative to power terminal T12, becomes the voltage indicated by the voltage command value. In this example, bidirectional power supply system 14A has three DC / DC converters 20, and therefore the voltage indicated by the voltage command value for voltage VFA and the voltage indicated by the voltage command value for voltage VFB are ⅓ of voltage Vbat of battery 12.

[0090] Although the present invention has been described above by way of embodiments and modifications, the present invention is not limited to these embodiments and can be modified in various ways.

[0091] For example, the voltage Vbat of the battery 12, the voltage Vgrid of the DC grid 100, the suppliable currents IL, IF, Itotal, and the current threshold Ith exemplified in the above embodiment are merely examples and can be set as appropriate.

[0092] The effects described in this specification are merely examples, and the effects of the present disclosure are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present disclosure.

[0093] Furthermore, the present disclosure may take the following aspects.

[0094] (1) a plurality of DC / DC converters including a first DC / DC converter and a second DC / DC converter, each of which has a first power terminal including a first terminal and a second terminal, and a second power terminal including a third terminal and a fourth terminal, and which are capable of transmitting power bidirectionally between the first power terminal and the second power terminal; the second terminal of the first DC / DC converter is connected to the first terminal of the second DC / DC converter; the third terminal of the first DC / DC converter is connected to the third terminal of the second DC / DC converter; the fourth terminal of the first DC / DC converter is connected to the fourth terminal of the second DC / DC converter; the first DC / DC converter is capable of controlling a first voltage between the third terminal and the fourth terminal at the second power terminal of the first DC / DC converter based on a first voltage command value supplied from a control device; Among the plurality of DC / DC converters, each of the one or more DC / DC converters other than the first DC / DC converter is capable of controlling a second voltage between the first terminal and the second terminal at the first power terminal of the DC / DC converter based on a second voltage command value supplied from the control device. Two-way power system. (2) The first DC / DC converter is capable of controlling a first current flowing into the second power terminal of the first DC / DC converter so that the first current does not exceed a first current threshold. The bidirectional power supply system according to (1) above. (3) each of the one or more DC / DC converters is capable of controlling a second current flowing into the second power terminal of that DC / DC converter such that the second current does not exceed a second current threshold; The second current threshold is greater than the first current threshold. The bidirectional power supply system according to (2) above. (4) The first DC / DC converter a third voltage between the first terminal and the second terminal at the first power terminal of the first DC / DC converter is detectable; The first current threshold value can be corrected based on the third voltage and the second voltage command value supplied from the control device. The bidirectional power supply system according to (2) or (3). (5) The first DC / DC converter further comprises: a maximum current value of a current flowing through the second power terminal of each of the one or more DC / DC converters can be calculated based on the third voltage, the second voltage command value supplied from the control device, and the first current threshold value; The first current threshold value can be corrected based on the third voltage, the second voltage command value supplied from the control device, and the maximum current value. The bidirectional power supply system according to (4) above. (6) Each of the plurality of DC / DC converters has a transformer and is capable of transmitting power bidirectionally between the first power terminal and the second power terminal via the transformer. The bidirectional power supply system according to any one of (1) to (5). (7) The bidirectional power supply system according to any one of claims 1 to 6; a battery connected to the first power terminals of the plurality of DC / DC converters; A power storage system equipped with [Explanation of symbols]

[0095] 1,1A...energy storage system, 11...battery management system, 12...battery, 13,13A...control device, 14,14A...bidirectional power supply system, 20,20F,20FA,20FB,20L...DC / DC converter, 21...transformer, 22...control circuit, Ith...current threshold, L11, L12, L21, L22...power line, T11, T12, T21, T22, TN...negative terminal, TP...positive terminal, VF, VFA, VFB...voltage, VF1...voltage command value, VL...voltage, Vgrid...voltage, Vgrid1...voltage command value.

Claims

1. a plurality of DC / DC converters including a first DC / DC converter and a second DC / DC converter, each having a first power terminal including a first terminal and a second terminal, and a second power terminal including a third terminal and a fourth terminal, and capable of transmitting power bidirectionally between the first power terminal and the second power terminal; the second terminal of the first DC / DC converter is connected to the first terminal of the second DC / DC converter; the third terminal of the first DC / DC converter is connected to the third terminal of the second DC / DC converter; the fourth terminal of the first DC / DC converter is connected to the fourth terminal of the second DC / DC converter; the first DC / DC converter is capable of controlling a first voltage between the third terminal and the fourth terminal at the second power terminal of the first DC / DC converter based on a first voltage command value supplied from a control device; Among the plurality of DC / DC converters, each of the one or more DC / DC converters other than the first DC / DC converter is capable of controlling a second voltage between the first terminal and the second terminal at the first power terminal of the DC / DC converter based on a second voltage command value supplied from the control device. Two-way power system.

2. The first DC / DC converter is capable of controlling a first current flowing into the second power terminal of the first DC / DC converter so that the first current does not exceed a first current threshold. The bidirectional power supply system of claim 1 .

3. each of the one or more DC / DC converters is capable of controlling a second current flowing into the second power terminal of that DC / DC converter such that the second current does not exceed a second current threshold; The second current threshold is greater than the first current threshold. The bidirectional power supply system of claim 2 .

4. The first DC / DC converter comprises: a third voltage between the first terminal and the second terminal at the first power terminal of the first DC / DC converter is detectable; The first current threshold value can be corrected based on the third voltage and the second voltage command value supplied from the control device. The bidirectional power supply system of claim 2 .

5. The first DC / DC converter further comprises: a maximum current value of a current flowing through the second power terminal of each of the one or more DC / DC converters can be calculated based on the third voltage, the second voltage command value supplied from the control device, and the first current threshold value; The first current threshold value can be corrected based on the third voltage, the second voltage command value supplied from the control device, and the maximum current value. The bidirectional power supply system of claim 4 .

6. Each of the plurality of DC / DC converters has a transformer and is capable of transmitting power bidirectionally between the first power terminal and the second power terminal via the transformer. The bidirectional power supply system of claim 1 .

7. The bidirectional power supply system according to any one of claims 1 to 6, a battery connected to the first power terminals of the plurality of DC / DC converters; A power storage system equipped with

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