Power interchange device, DC power distribution system, and control method for power interchange device

Abstract

To provide a power interchange device, a DC power distribution system, and a method of the controlling power interchange device that can flexibly execute system change, such as addition of a power interchange device, in a DC power distribution system.SOLUTION: When a self device functions as a master, a control device (25) controls a bidirectional DC-DC converter (21) to apply a predetermined modulation to the magnitude of a line voltage, thus executing an inquiry to another machine on whether it requires power interchange. When the self device functions as a slave, the control device controls the bidirectional DC-DC converter (21) upon receiving an inquiry via a voltmeter (20V), and provides an answer to the inquiry by outputting an output current with its magnitude modulated with a frequency uniquely defined for a request of the self device or not outputting the same to a DC line according to which one of requests is executed: whether the self device performs provision of power, receives supply of power, or does not perform provision / reception of power.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a power interchange device, a DC power distribution system, and a method for controlling a power interchange device. [Background technology]

[0002] A DC power distribution system includes a DC line and a plurality of power interchange devices connected to the DC line. Each of the plurality of power interchange devices includes a bidirectional DC-DC converter connected to the DC line, a power generation device, a power storage device, and a load connected to the DC-DC converter, and a control device that controls each part of the power interchange device. Known DC power distribution systems include a controller that is connected to the plurality of power interchange devices and that centrally manages power interchange between the power interchange devices using communications (see Patent Document 1 below).

[0003] Furthermore, in DC power distribution systems, instead of centralized management by the controller, there is also known a system in which each power interchange device individually performs droop control of the output voltage and output current of the DC-DC converter. It has been proposed that such droop control can be used to prevent interruptions in power interchange due to a system failure of the controller (see Patent Document 2 below). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-288162 [Patent Document 2] Patent No. 6458891 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the DC power distribution system described above has a problem in that it is not possible to flexibly implement system modifications such as the addition of a power interchange device.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a power interchange device, a DC distribution system, and a control method for a power interchange device that can flexibly implement system changes, such as adding a power interchange device, in a DC distribution system. [Means for solving the problem]

[0007] In order to solve the above problem, a power interchange device according to one aspect of the present disclosure is a power interchange device capable of exchanging power with another device that is another power interchange device connected to a DC line, and includes a DC bus, a power generation device, a load, and a power storage device each connected to the DC bus, a DC-DC converter connected to the DC bus and the DC line, a voltage detection device that detects the line voltage of the DC line, and a control device, and when the power interchange device that is itself functions as a master, the control device controls the DC-DC converter to detect a line voltage corresponding to the magnitude of the line voltage. By applying a certain modulation to the voltage detection device, the device executes an inquiry as to whether the other device requires power interchange, and when the device itself functions as a slave, when the inquiry is received through the voltage detection device, the device controls the DC-DC converter to respond to the inquiry by outputting an output current whose magnitude is modulated at a frequency uniquely determined for the request to the DC line, or by not outputting an output current, depending on whether the device itself is requesting to provide power, to receive power, or not to exchange power.

[0008] Furthermore, a DC power distribution system according to one aspect of the present disclosure comprises a DC line and a plurality of power interchange devices connected to the DC line, and is a DC power distribution system capable of exchanging power between the plurality of power interchange devices, and each of the plurality of power interchange devices uses any of the power interchange devices described above.

[0009] Furthermore, a control method for a power interchange device according to one aspect of the present disclosure is a control method for a power interchange device capable of exchanging power with another device that is another power interchange device connected to a DC line, wherein the power interchange device comprises a DC bus, a power generation device, a load, and a power storage device each connected to the DC bus, a DC-DC converter connected to the DC bus and the DC line, a voltage detection device that detects the line voltage of the DC line, and a control device, and includes a step of controlling the DC-DC converter to apply a predetermined modulation to the magnitude of the line voltage, thereby executing an inquiry to the other device as to whether or not power interchange is required.

[0010] Furthermore, a control method for a power interchange device according to another aspect of the present disclosure is a control method for a power interchange device capable of exchanging power with another device that is another power interchange device connected to a DC line, wherein the power interchange device comprises a DC bus, a power generation device, a load, and a power storage device each connected to the DC bus, a DC-DC converter connected to the DC bus and the DC line, a voltage detection device for detecting the line voltage of the DC line, and a control device, and when the inquiry is received through the voltage detection device, the method controls the DC-DC converter to respond to the inquiry by outputting an output current whose magnitude is modulated at a frequency uniquely determined for the request of the own device, or by not outputting an output current, depending on whether the own device requests to provide power, receive power, or not exchange power. [Effects of the Invention]

[0011] According to one aspect of the present disclosure, it is possible to provide a power interchange device, a DC distribution system, and a control method for a power interchange device that can flexibly implement system changes, such as adding a power interchange device, in a DC distribution system. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram illustrating a configuration example of a DC power distribution system according to a first embodiment of the present disclosure. [Figure 2] 2 is a diagram illustrating an example of the configuration of the power interchange device illustrated in FIG. 1. FIG. [Figure 3] FIG. 1 is a diagram illustrating a basic periodic operation of a DC power distribution system. [Figure 4] 4 is a graph showing an example of the waveform of the output voltage or output current of each power interchange device. [Figure 5] 5 is a diagram illustrating the operation of each power interchange device from time t0 to time t1 in FIG. 4. FIG. [Figure 6] 5 is a diagram illustrating the operation of each power interchange device from time t1 to time t2 in FIG. 4. FIG. [Figure 7] 5 is a diagram illustrating the operation of each power interchange device from time t2 to time t3 in FIG. 4. FIG. [Figure 8] 5 is a diagram illustrating the operation of each power interchange device from time t3 to time t4 in FIG. 4. FIG. [Figure 9] 5 is a diagram illustrating the operation of each power interchange device from time t4 to time t5 in FIG. 4. FIG. [Figure 10] 10 is a flowchart showing a specific example of the operation of the master power interchange device. [Figure 11] 10 is a flowchart showing a specific example of the operation of the slave power interchange device. [Figure 12] 10 is a diagram illustrating a specific example of the operation of each power interchange device in Modification 1. FIG. [Figure 13] 10 is a flowchart showing a specific example of the operation of the slave power interchange device of the first modification. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Embodiment 1] A first embodiment of the present disclosure will be described in detail below with reference to Fig. 1 and Fig. 2. Fig. 1 is a diagram illustrating a configuration example of a DC power distribution system 1 according to the first embodiment of the present disclosure. Fig. 2 is a diagram illustrating a configuration example of a power interchange device 2 shown in Fig. 1. Note that the following description will be given of a case where the present disclosure is applied to a DC power distribution system 1 in which a plurality of power interchange devices 2 share a common DC line 3 and interchange power between the power interchange devices 2 via the DC line 3.

[0014] <DC Distribution System 1> As shown in FIG. 1, the DC distribution system 1 of this embodiment includes a plurality of, for example, N (N is an integer greater than or equal to 2) power interchange devices 2A to 2N (hereinafter collectively referred to as "2"), and a DC line 3 to which each of the plurality of power interchange devices 2 is connected.

[0015] Furthermore, in the DC power distribution system 1 of this embodiment, one of the multiple power interchange devices 2, for example, power interchange device 2A, functions as the master power interchange device 2. Furthermore, the other power interchange devices 2B to 2N function as slave power interchange devices 2 controlled by the master power interchange device 2.

[0016] Furthermore, in the DC power distribution system 1 of this embodiment, the power interchange device 2 that functions as the master is alternated in a predetermined order, for example, using a round robin. As a result, in the DC power distribution system 1 of this embodiment, one power interchange device 2 among the multiple power interchange devices 2 takes turns functioning as the master. As a result, in the DC power distribution system 1 of this embodiment, it is possible to reliably prevent the occurrence of malfunctions such as system shutdown of the DC power distribution system 1 caused by a failure or the like in the master power interchange device 2. Furthermore, in the DC power distribution system 1 of this embodiment, it is possible to avoid the load from being concentrated on a power storage device (described below) of a specific power interchange device 2.

[0017] <Power interchange device 2> 2, the power interchange device 2 of this embodiment includes a voltmeter 20V, an ammeter 20I, a bidirectional DC-DC converter 21, a power generation device 22, a power storage device 23, and a load 24. The voltmeter 20V is a voltage detection device that detects the line voltage of the DC line 3. The ammeter 20I is a current detection device that detects the input / output current flowing in and out of the power interchange device 2 from the DC line 3.

[0018] The bidirectional DC-DC converter 21 is connected to the DC line 3 via a voltmeter 20V and an ammeter 20I. The bidirectional DC-DC converter 21 is connected between the DC line 3 and a DC bus 20L of the power interchange device 2. A power generation device 22, a power storage device 23, and a load 24 are connected to the DC bus 20L. The bidirectional DC-DC converter 21 is a DC-DC converter that transmits DC power to the DC line 3 in both directions.

[0019] The power generation device 22 includes a solar cell, and generates DC power by photoelectrically converting solar energy using the solar cell. The power generation device 22 has a DC-DC converter, and outputs the generated DC power to the DC bus 20L via the DC-DC converter. Note that, in addition to the solar cell, the power generation device 22 may also be one that uses natural energy other than solar energy, such as a wind power generator, or one that uses non-natural energy, such as a cogeneration system or an electric motor.

[0020] The power storage device 23 includes a storage battery such as a secondary battery. The power storage device 23 has a DC-DC converter and charges the storage battery with DC power supplied from the DC bus 20L. The power storage device 23 also discharges the power stored in the storage battery to the DC bus 20L. The power storage device 23 also notifies the control device 25 of the remaining battery capacity (SOC: State of Charge) as a charging rate.

[0021] The load 24 is, for example, a DC load such as an electrical device that operates on DC power. The load 24 may have a PCS (Power Conditioner System), and after DC power from the bidirectional DC-DC converter 21, the power generation device 22, or the power storage device 23 is converted by the PCS into DC power suitable for the load 24, the DC power may be supplied from the PCS.

[0022] The control device 25 controls each part of the power interchange device 2. For example, the control device 25 controls the operation of the bidirectional DC-DC converter 21.

[0023] The control device 25 is configured to handle both the case where the power interchange device 2 (its own device) functions as a master and the case where it functions as a slave. That is, when the power interchange device 2 functions as a master, the control device 25 inquires of the power interchange device 2 (other device) as a slave as to whether or not power interchange is necessary, as will be described in detail later. Furthermore, the control device 25 uses the response to the inquiry to determine whether or not power interchange is possible in the DC power distribution system 1.

[0024] Furthermore, when the power interchange device 2 functions as a slave, the control device 25 responds to an inquiry from the power interchange device 2 acting as a master. This response includes a discharge request or a charge request. A discharge request here is a request to discharge DC power from the DC line 3. A charge request here is a request to charge DC power from the DC line 3. The response also includes a request without a power interchange request, which does not involve the exchange of power.

[0025] <Example of operation> The operation of the DC power distribution system 1 of this embodiment will be specifically described below.

[0026] <Basic periodic operation of power interchange in DC distribution system 1> First, the basic periodic operation of power interchange in the DC power distribution system 1 of this embodiment will be specifically described with reference to Fig. 3. Fig. 3 is a diagram illustrating the basic periodic operation of the DC power distribution system 1.

[0027] As shown in FIG. 3, in the DC power distribution system 1 of this embodiment, a request confirmation period (time t0 to time t3) is set in which the master power interchange apparatus 2A confirms a request for power interchange with each of the slave power interchange apparatuses 2B to 2N.

[0028] Furthermore, in the DC power distribution system 1 of this embodiment, following the request confirmation period, a power interchange period (time t3 to time t5) is set in all power interchange devices 2, including the power interchange device 2A, during which power is interchanged within the DC power distribution system 1 in accordance with the power interchange determined by the power interchange device 2A.

[0029] <Example of operation of power interchange device 2 from time t0 to time t1> Next, an example of the operation of the power interchange device 2 from time t0 to time t1 in the DC power distribution system 1 of this embodiment will be specifically described with reference to Figures 4 and 5. Figure 4 is a graph showing an example of the waveform of the output voltage or output current of each power interchange device 2. Figure 5 is a diagram explaining the operation of each power interchange device 2 from time t0 to time t1 in Figure 4.

[0030] In the DC power distribution system 1 of this embodiment, before time t0, only the control device 25 of the master power interchange apparatus 2A controls the bidirectional DC-DC converter 21 to output a constant DC voltage with a waveform Vm0 as the output voltage VA. On the other hand, the control devices 25 of the slave power interchange apparatuses 2B to 2N stop the bidirectional DC-DC converter 21 and are on standby before time t0.

[0031] Then, at time t0, in the power interchange device 2A, the control device 25 controls the output voltage VA output from the bidirectional DC-DC converter 21 to the DC line 3 so that it becomes a waveform Vm1. The waveform Vm1 is a waveform obtained by voltage-modulating a constant DC voltage, which is a waveform Vm0, by superimposing a frequency fm as a first frequency on the DC voltage.

[0032] That is, the power interchange unit 2A outputs the output voltage VA having the waveform Vm1. In this manner, only the master power interchange unit 2A controls the voltage of the DC line 3 from time t0 to time t2.

[0033] Furthermore, in the DC distribution system 1 of this embodiment, from time t0 to time t1, the control devices 25 of the power interchange devices 2B to 2N each stop the bidirectional DC-DC converter 21. The power interchange devices 2B to 2N monitor the line voltage of the DC line 3 with a voltmeter 20V. When the control device 25 of the power interchange devices 2B to 2N detects that the voltage detected by the voltmeter 20V has taken on the above-mentioned modulated waveform at time t0, the control device 25 determines that a request confirmation (the above-mentioned inquiry) from the power interchange device 2A has started. Then, each of the power interchange devices 2B to 2N determines a request (answer) for the above-mentioned request confirmation based on the remaining battery capacity of the power storage device 23.

[0034] <Example of operation of power interchange device 2 from time t1 to time t2> Next, an example of the operation of the power interchange device 2 from time t1 to time t2 in the DC power distribution system 1 of this embodiment will be specifically described with reference to Figures 4 and 6. Figure 6 is a diagram illustrating the operation of each power interchange device from time t1 to time t2 in Figure 4.

[0035] In the DC power distribution system 1 of this embodiment, as described above, the power interchange device 2A outputs the output voltage VA having the waveform Vm1 during the first predetermined time T1 from time t0 to time t2. Furthermore, as shown in Fig. 4, in the DC power distribution system 1 of this embodiment, the power interchange devices 2B to 2N respond to the inquiry from the power interchange device 2A at the same timing at time t1, when a predetermined time has elapsed since time t0.

[0036] As shown in Fig. 6, for example, in the power interchange units 2B and 2N, if the control device 25 determines to make a discharge request as the response, the control device 25 controls the output current output from the bidirectional DC-DC converter 21 to the DC line 3 at time t1 to have a waveform I1. As a result, the output currents IB and IN from the power interchange units 2B and 2N have waveforms obtained by current-modulating the DC current by superimposing a frequency fs1 as a second frequency on a constant DC current having a waveform Is, as shown by waveforms 52 and 55 in Fig. 4 and waveforms i1, in in Fig. 6, respectively.

[0037] The magnitude I1(t) of the output current indicating the discharge request is expressed by the following equation (1), where Isac is the amplitude of the AC component.

[0038] I1(t) = Is+Isac×sin(2πfs1*t)―――(1)

[0039] 6, for example, in the power interchange device 2C, if the control device 25 determines to make a charge request as the response, the control device 25 controls the output current output from the bidirectional DC-DC converter 21 to the DC line 3 at time t1 to have a waveform I2. As a result, the output current IC from the power interchange device 2C becomes a waveform obtained by current-modulating the DC current by superimposing a frequency fs2 as a third frequency on a constant DC current having a waveform Is, as shown by waveform 53 in FIG. 4 and waveform i2 in FIG. 6.

[0040] The magnitude I2(t) of the output current indicating the charge request is expressed by the following equation (2), where Isac is the amplitude of the AC component.

[0041] I1(t) = Is+Isac×sin(2πfs2*t)―――(2)

[0042] As shown by waveforms 52 and 53, the power interchange device 2 making a discharge request and the power interchange device 2 making a charge request output currents at frequencies fs1 and fs2, which are different from each other. Note that frequencies fm, fs1, and fs2 are set to sufficiently low values ​​in consideration of the wiring impedance of the DC line 3.

[0043] 6, for example, in the power interchange device 2D, if the control device 25 determines that there is no request for power interchange as the response, the control device 25 keeps the bidirectional DC-DC converter 21 stopped at time t1. As a result, the output current ID from the power interchange device 2D becomes 0, as shown by the waveform 54 in FIG.

[0044] The power interchange device 2A monitors the input current from the DC line 3 with an ammeter 20I. As shown in FIG. 6 by the waveform i1+i2+i3+---+in, a superimposed current obtained by superimposing the output currents IB to IN of the power interchange devices 2B to 2N is input to the power interchange device 2A as an input current. The power interchange device 2A detects the input current with the ammeter 20I of the power interchange device 2A. Furthermore, as shown in FIG. 4, the power interchange devices 2B to 2N continue to perform the above response from the power interchange device 2A until time t3.

[0045] Then, before time t2, which is when a first predetermined time T1 has elapsed from time t0, the control device 25 of the power interchange device 2A performs frequency analysis, for example, FET analysis, on the input current (the input current superimposed on the bidirectional DC-DC converter 21) to detect the magnitude of the modulation component of the frequency uniquely determined for the request.

[0046] Specifically, the control device 25 detects the magnitude of the current component modulated to frequency fs1 and determines the number of slave power interchange devices 2 that have requested discharging. Furthermore, the control device 25 detects the magnitude of the current component modulated to frequency fs2 and determines the number of slave power interchange devices 2 that have requested charging. Thereafter, the control device 25 determines whether or not power interchange is possible based on the number of devices that have requested discharging and the number of devices that have requested charging that have been determined up to time t2.

[0047] In this way, in this embodiment, the control device 25 of the power interchange apparatus 2A performs frequency analysis of the input current (input current) to the power interchange apparatus 2A to detect the presence or absence of a frequency modulation component, thereby being able to determine the content of each response from each of the power interchange apparatuses 2B to 2N. As a result, in this embodiment, the power interchange apparatus 2A can operate the DC power distribution system 1 more appropriately.

[0048] <Example of operation of power interchange device 2 from time t2 to time t3> Next, an example of the operation of the power interchange device 2 from time t2 to time t3 in the DC power distribution system 1 of this embodiment will be specifically described with reference to Figures 4 and 7. Figure 7 is a diagram illustrating the operation of each power interchange device 2 from time t2 to time t3 in Figure 4.

[0049] If the control device 25 of the power interchange device 2A determines that power interchange is possible within a first predetermined time T1 from time t0 to time t2, the control device 25 controls the output voltage VA to have a waveform Vm0 at time t2. As a result, the output voltage VA from the power interchange device 2A becomes a constant DC voltage with the waveform Vm0, as shown by the waveform 50 in Fig. 4 and the waveform Vm0 in Fig. 7. As a result, the control device 25 transmits a first determination result indicating that power interchange will be performed to each of the slave power interchange devices 2B to 2N.

[0050] Furthermore, each control device 25 of the power interchange devices 2B to 2N detects the output voltage VA having the waveform Vm0 within time t2 and determines that it has been notified by the power interchange device 2A that power interchange will be performed. Then, as shown in Fig. 4, each control device 25 continues to output an output current according to the response from time t2 until time t3, after a predetermined time has elapsed.

[0051] On the other hand, if the control device 25 of the power interchange device 2A determines that power interchange is impossible based on the number of devices requesting discharge and the number of devices requesting charge that have been grasped up to time t2, then after a certain time has passed since time t2, the control device 25 controls the bidirectional DC-DC converter 21 so that the output voltage VA has waveform Vm0. That is, the control device 25 continues to output the output voltage VA having waveform Vm1 for a certain time since time t2 has passed. As a result, the control device 25 transmits a second determination result indicating that power interchange will not be performed to each of the slave power interchange devices 2B to 2N.

[0052] Furthermore, the power interchange units 2B to 2N monitor the line voltage of the DC line 3 using the voltmeter 20V, and therefore each control device 25 of the power interchange units 2B to 2N detects a constant DC voltage with the waveform Vm0 after time point t2.

[0053] As a result, each control device 25 of the power interchange devices 2B to 2N determines that the line voltage of the DC line 3 remains the modulated waveform Vm1 after time point t2, and therefore receives notification from the power interchange device 2A that power interchange will not be carried out, and stops the bidirectional DC-DC converter 21.

[0054] In addition to the above description, the power interchange devices 2B to 2N may be configured so that the output timing for responding to a discharge request and the output timing for responding to a charge request are divided into two timings between time t1 and time t2, which are different from each other.

[0055] <Example of operation of power interchange device 2 from time t3 to time t4> Next, an example of the operation of the power interchange device 2 from time t3 to time t4 in the DC power distribution system 1 of this embodiment will be specifically described with reference to Figures 4 and 8. Figure 8 is a diagram illustrating the operation of each power interchange device 2 from time t3 to time t4 in Figure 4.

[0056] The control device 25 of the power interchange device 2A outputs an output voltage VA having a waveform Vm0, as shown by the waveform 50 in FIG. 4 and the waveform Vm0 in FIG. 8, during a second predetermined time T2 from time t3 to time t4.

[0057] <Example of operation when power interchange is performed> The control device 25 of the power interchange device 2B determines that the discharge request has been accepted at time t2. As a result, the control device 25 controls the output current IB so that it has a predetermined discharge current waveform Id for the second predetermined time T2, as shown by waveform 52 in Fig. 4 and waveform Id in Fig. 8.

[0058] The control device 25 of the power interchange device 2C determines that the charge request has been accepted at time t2. As a result, the control device 25 controls the output voltage VC from the bidirectional DC-DC converter 21 to have a waveform Vm0 for the second predetermined time T2, similar to the output voltage VA of the power interchange device 2A. An input current having a constant current value Id' is then input to this power interchange device 2C, as shown by waveform 53 in Fig. 4.

[0059] The control device 25 of the power interchange device 2D determines that no request has been made at time t2. As a result, the control device 25 stops the bidirectional DC-DC converter 21 for the second predetermined time T2, as shown by the waveform 54 in Fig. 4, and maintains the output current ID at 0.

[0060] <Example of operation when power interchange is not implemented> Furthermore, each control device 25 of the power interchange devices 2B to 2N determines that power interchange will not be carried out after a certain time has elapsed after time point t2, and therefore each control device 25 stops the bidirectional DC-DC converter 21 and maintains its output current at 0 for the second predetermined time T2.

[0061] As described above, during the second predetermined time T2 from time t3 to time t4, the power interchange devices 2B to 2N operate appropriately depending on whether or not power interchange is being implemented and the content of the implementation, thereby allowing the DC distribution system 1 to also operate appropriately.

[0062] <Example of operation of power interchange device 2 from time t4 to time t5> Next, an example of the operation of the power interchange device 2 from time t3 to time t4 in the DC power distribution system 1 of this embodiment will be specifically described with reference to Figures 4 and 9. Figure 9 is a diagram illustrating the operation of each power interchange device 2 from time t4 to time t5 in Figure 4.

[0063] When the control device 25 of the power interchange device 2A detects the end of the second predetermined time T2 at time t4, it determines that the power interchange period has ended. Then, from time t4 to time t5 after the predetermined time has elapsed, the control device 25 outputs an output voltage VA with a waveform Vm0, as shown by waveform 50 in Fig. 4 and waveform Vm0 in Fig. 9.

[0064] Like the control device 25 of the power interchange device 2A, the control device 25 of each of the power interchange devices 2B to 2N determines that the power interchange period has ended at time t4. Then, as shown in Fig. 4, each of the control devices 25 of the power interchange devices 2B to 2N stops the bidirectional DC-DC converter 21 and sets the corresponding output currents IB to IN to 0.

[0065] Thereafter, in the DC power distribution system 1 of this embodiment, at time t5, the control devices 25 of all the power interchange devices 2 detect that the output current of all the power interchange devices 2 has become 0. Then, each control device 25 sets time t5 as time t0 and starts a new power interchange with one power interchange device 2 as the master power interchange device 2.

[0066] Next, the operation of each of the master and slave power interchange devices 2 of this embodiment will be specifically described with reference to Fig. 10 and Fig. 11. Fig. 10 is a flowchart showing a specific example of the operation of the master power interchange device. Fig. 11 is a flowchart showing a specific example of the operation of the slave power interchange device. In the following description, an example will be given in which the power interchange device 2A and the power interchange devices 2B to 2N function as the master power interchange device 2 and the slave power interchange device 2, respectively.

[0067] <Example of operation of master power interchange unit 2A (own unit)> First, the operation of the power interchange device 2A will be specifically described using Fig. 10. In the power interchange device 2A, the control device 25 controls the output voltage output from the bidirectional DC-DC converter 21 to the power interchange devices 2B to 2N via the DC line 3 at time t0 so that it has a waveform Vm1 (step S1). Specifically, the power interchange device 2A controls the bidirectional DC-DC converter 21 to apply a predetermined modulation to the magnitude of the line voltage, thereby inquiring of the power interchange devices 2B to 2N (other devices) as to whether or not power interchange is necessary.

[0068] Next, in the power interchange apparatus 2A, the control device 25 receives the output current from the power interchange apparatuses 2B to 2N, thereby receiving a response to the inquiry. That is, the control device 25 receives the input current (the input current to the power interchange apparatus 2A) to the bidirectional DC-DC converter 21 from the DC line 3. Then, based on the input current, the control device 25 calculates the number of power interchange apparatuses 2 that have made discharge requests and the number of power interchange apparatuses 2 that have made charge requests, which are indicated in the responses from the power interchange apparatuses 2B to 2N (step S2).

[0069] Furthermore, in the DC power distribution system 1, the above response to the power interchange device 2A is made simultaneously at the same timing from all slave power interchange devices 2B to 2N, for example, at time t1, a predetermined time after time t0, when the power interchange device 2A made the inquiry.

[0070] Next, in the power interchange device 2A, the control device 25 detects the number of power interchange devices 2 that have made the above-mentioned discharge request and the number of power interchange devices 2 that have made the above-mentioned charge request within a first predetermined time T1 from time t0 when the above-mentioned inquiry is made (i.e., until time t2).The control device 25 then determines whether or not the conditions for starting power interchange are met based on the detected numbers (step S3).

[0071] Specifically, the control device 25 calculates the magnitude of the total interchange power in the DC power distribution system 1 (i.e., the magnitude of the interchange power interchanged through the DC line 3) from, for example, the number of power interchange devices 2 that have made a discharge request or the number of power interchange devices 2 that have made a charge request. Then, the control device 25 determines whether the calculated magnitude of the interchange power exceeds the capacity of the DC line 3 (e.g., rated power).

[0072] Then, when the control device 25 determines that the magnitude of the interchanged power does not exceed the capacity within the first predetermined time T1 from time t0, the control device 25 determines that the numbers calculated in step S2 satisfy the conditions for starting power interchange (YES in step S3). In other words, the control device 25 determines that power interchange is possible, and controls the output voltage output from the bidirectional DC-DC converter 21 to the power interchange devices 2B to 2N via the DC line 3 at time t2 to have a waveform Vm0 (step S4).

[0073] In other words, when the control device 25 determines that power interchange will be performed, it stops applying the predetermined modulation to the magnitude of the line voltage within a first predetermined time T1 from the time t0 when the above-mentioned inquiry is made. As a result, the control device 25 transmits a first determination result indicating that power interchange will be performed to the power interchange devices 2B to 2N. As a result, in the DC power distribution system 1, the power interchange device 2A notifies the power interchange devices 2B to 2N of the end of the above-mentioned inquiry period, and at time t3 when the predetermined time has elapsed, the power interchange devices 2A to 2N start power interchange.

[0074] Next, in the power interchange device 2A, the control device 25 determines whether or not a second predetermined time T2 has elapsed since time t3 when power interchange was started. Furthermore, the control device 25 determines whether or not the output current from the bidirectional DC-DC converter 21 to the DC line 3 is 0 A (step S5). Then, if the control device 25 does not determine that the second predetermined time T2 has elapsed since time t3 or that the output current is 0 A (NO in step S5), the control device 25 enters a standby state.

[0075] On the other hand, when the control device 25 determines that the second predetermined time T2 has elapsed since time t3 and that the output current is 0 A (YES in step S5), the control device 25 determines that the power interchange period in the DC distribution system 1 has ended and stops operation at time t4.

[0076] Furthermore, if the control device 25 determines that the magnitude of the interchanged power exceeds the above-mentioned capacity within the first predetermined time T1 from time t0, the control device 25 determines that the numbers of units calculated in step S2 do not satisfy the conditions for starting power interchange (NO in step S3). In other words, the control device 25 determines that the conditions for starting power interchange are not satisfied even after the first predetermined time T1 has elapsed, and determines that power interchange is not possible.

[0077] Furthermore, in step S3, the control device 25 of the power interchange device 2A determines whether or not power interchange is possible using the magnitude of the interchanged power interchanged over the DC line 3 and the capacity of the DC line 3, so the power interchange device 2A can appropriately determine whether or not power interchange is possible. As a result, the DC distribution system 1 of this embodiment can be operated appropriately.

[0078] Then, after a certain time has passed after the first predetermined time T1 has elapsed, the control device 25 controls the output voltage output from the bidirectional DC-DC converter 21 to the power interchange devices 2B to 2N via the DC line 3 so that it has a waveform Vm0 (step S6).

[0079] In other words, when the control device 25 determines that power interchange will not be performed, it continues to apply a predetermined modulation to the magnitude of the line voltage even after time t2, which is the elapse of the first predetermined time T1 from time t0. As a result, the control device 25 transmits a second determination result indicating that power interchange will not be performed to the power interchange devices 2B-2N. As a result, in the DC power distribution system 1, the power interchange device 2A notifies the power interchange devices 2B-2N of the end of the inquiry period after time t2, which is the elapse of the first predetermined time T1 from time t0, and the power interchange devices 2A-2N stop operating.

[0080] In the above description, a case has been described in which it is determined in step S3 that power interchange is impossible when the magnitude of the interchanged power is greater than the capacity of the DC line 3. However, this embodiment is not limited to this. For example, it is also possible to calculate the difference between the number of power interchange devices 2 that have responded with a discharge request and the number of power interchange devices 2 that have responded with a charge request, and determine that power interchange is impossible when the calculated difference is equal to or greater than a predetermined number.

[0081] In this case, in the power interchange device 2A, the control device 25 can determine whether the ratio of the circuit loss in the DC line 3 to the interchanged power will become large. As a result, the power interchange device 2A can appropriately determine whether or not to interchange power in the DC distribution system 1, and can operate the DC distribution system 1 appropriately.

[0082] <Example of operation of slave power interchange units 2B to 2N (other devices)> Next, the operation of the power interchange devices 2B to 2N will be specifically described with reference to Fig. 11. As shown in Fig. 11, in the power interchange devices 2B to 2N, the control device 25 determines whether the voltage of the DC line 3 is a voltage controlled to have a modulated waveform Vm1 (step S11). In other words, the control device 25 determines whether the input voltage input from the power interchange device 2A to the bidirectional DC-DC converter 21 via the DC line 3 has the waveform Vm1. When the control device 25 determines that the input voltage does not have the waveform Vm1 (NO in step S11), the control device 25 enters a standby state.

[0083] On the other hand, when the control device 25 determines that the input voltage has the waveform Vm1 (YES in step S11), the control device 25 determines whether or not to issue the discharge request as the response by time t1 based on the remaining battery capacity of the power storage device 23 (step S12). Specifically, the control device 25 determines whether or not the remaining battery capacity is equal to or greater than a first threshold value (for example, 70%).

[0084] Then, when the control device 25 determines to respond to the discharge request by confirming that the remaining battery charge is equal to or greater than the first threshold value (YES in step S12), the control device 25 controls the output current output from the bidirectional DC-DC converter 21 to the DC line 3 at time point t1 to have a waveform I1 (step S13). As a result, in the power interchange device 2A, the output current controlled to have the waveform I1 is input from the DC line 3 to the bidirectional DC-DC converter 21 as the input current.

[0085] Next, in the power interchange units 2B to 2N, the control unit 25 determines whether or not the AC component of frequency fm has disappeared from the line voltage within a first predetermined time T1 from the time t0 when the inquiry from the power interchange unit 2A is received (step S14).

[0086] Specifically, the control device 25 determines whether the input voltage input to the bidirectional DC-DC converter 21 has the waveform Vm0 within a first predetermined time T1 from time t0. When the control device 25 determines that the input voltage has the waveform Vm0 within the first predetermined time T1 from time t0 (YES in step S14), the control device 25 determines that it has been notified by the power interchange device 2A of the end of the inquiry period and that the discharge request has been accepted.

[0087] Thereafter, in the power interchange devices 2B to 2N, the control device 25 determines time t3, which is a predetermined period of time that has elapsed since time t2 when it was determined that the discharge request was accepted. Then, from time t3, the control device 25 continues to control the output current from the bidirectional DC-DC converter 21 to the DC line 3 so that the output current has a predetermined discharge current waveform Id, for a second predetermined time T2 (step S15).

[0088] Then, in the power interchange units 2B to 2N, the control unit 25 determines that the power interchange period has ended at time t4, when the second predetermined time T2 has elapsed since time t3, and stops its operation (step S16).

[0089] On the other hand, in the power interchange devices 2B to 2N, when the control device 25 does not determine that the input voltage has the waveform Vm0 within the first predetermined time T1 from the time t0 (NO in step S14), the control device 25 determines that the discharge request from the power interchange device 2A has not been acknowledged. Then, in the power interchange devices 2B to 2N, the control device 25 proceeds to step S16 and stops its operation.

[0090] Furthermore, in the power interchange devices 2B to 2N, when the control device 25 determines not to respond to the discharge request (NO in step S12), the control device 25 determines whether or not to respond by issuing the charge request based on the remaining battery capacity of the power storage device 23 (step S17). Specifically, the control device 25 determines whether or not the remaining battery capacity is less than a second threshold value (for example, 50%).

[0091] Then, when the control device 25 determines to respond to the charge request by confirming that the remaining battery charge is less than the second threshold value (YES in step S17), the control device 25 controls the output current output from the bidirectional DC-DC converter 21 to the DC line 3 at time point t2 so that it has a waveform I2 (step S18). As a result, in the power interchange device 2A, the output current controlled to have the waveform I2 is input from the DC line 3 to the bidirectional DC-DC converter 21 as the input current.

[0092] Next, in the power interchange units 2B to 2N, the control unit 25 determines whether or not the AC component of frequency fm has disappeared from the line voltage within a first predetermined time T1 from the time t0 when the inquiry from the power interchange unit 2A is received (step S19).

[0093] Specifically, the control device 25 determines whether the input voltage input to the bidirectional DC-DC converter 21 has the waveform Vm0 within a first predetermined time T1 from time t0. When the control device 25 determines that the input voltage has the waveform Vm0 within the first predetermined time T1 from time t0 (YES in step S19), the control device 25 determines that it has been notified by the power interchange device 2A that the inquiry period has ended and that the charging request has been acknowledged.

[0094] Thereafter, in the power interchange devices 2B to 2N, the control device 25 determines time t3, which is a predetermined period of time that has elapsed since time t2, when it was determined that the charging request was accepted. Then, from time t3, the control device 25 continues to control the output voltage from the bidirectional DC-DC converter 21 to the DC line 3 so that the output voltage has a waveform Vm0, for a second predetermined time T2 (step S20).

[0095] Then, in the power interchange units 2B to 2N, the control unit 25 determines that the power interchange period has ended at time t4, when the second predetermined time T2 has elapsed since time t3, and stops its operation (step S21).

[0096] On the other hand, in the power interchange devices 2B to 2N, when the control device 25 does not determine that the input voltage has the waveform Vm0 within the first predetermined time T1 from the time t0 (NO in step S19), the control device 25 determines that the charge request from the power interchange device 2A has not been acknowledged. Then, in the power interchange devices 2B to 2N, the control device 25 proceeds to step S21 and stops its operation.

[0097] Furthermore, when the control device 25 of the power interchange devices 2B to 2N determines that it will not respond to the charge request (NO in step S17), it determines that it will not request power interchange as a response to the power interchange device 2A. Specifically, when the control device 25 confirms that the remaining battery charge of the power storage device 23 is equal to or greater than the second threshold and less than the first threshold, the control device 25 determines that it will not request power interchange from the power interchange device 2A. Then, the control device 25 stops the bidirectional DC-DC converter 21 at time point t1, thereby notifying the power interchange device 2A that it will not request power interchange as a response.

[0098] In addition, in the power interchange units 2B to 2N, the control unit 25 determines whether or not the AC component of frequency fm has disappeared from the line voltage within a first predetermined time T1 from the time t0 when the inquiry from the power interchange unit 2A is received (step S22).

[0099] Specifically, the control device 25 determines whether or not the input voltage input to the bidirectional DC-DC converter 21 has the waveform Vm0 within a first predetermined time T1 from time t0. Then, when the control device 25 determines that the input voltage has the waveform Vm0 within the first predetermined time T1 from time t0 (YES in step S22), the control device 25 determines that it has been notified by the power interchange device 2A of the end of the inquiry period and that no request for power interchange has been made.

[0100] Thereafter, in the power interchange devices 2B to 2N, at time t3, a predetermined period of time has elapsed since time t2, when the control device 25 determines that no request for power interchange has been recognized, the bidirectional DC-DC converter 21 continues to be stopped and waits in a stopped state for a second predetermined time T2 (step S23).

[0101] On the other hand, in the power interchange devices 2B to 2N, when the control device 25 does not determine that the input voltage has the waveform Vm0 within the first predetermined time T1 from time t0 (NO in step S22), the control device 25 determines that no request for power interchange has been acknowledged by the power interchange device 2A. Then, in the power interchange devices 2B to 2N, the control device 25 stops its operation without waiting in a stopped state for the second predetermined time T2.

[0102] As described above, the DC power distribution system 1 of this embodiment includes a DC line 3 and a plurality of power interchange devices 2 connected to the DC line 3. The power interchange device 2 includes a DC bus 20L, and a power generation device 22, a load 24, and a power storage device 23, each connected to the DC bus 20L. The power interchange device 2 also includes a bidirectional DC-DC converter 21 connected to the DC bus 20L and the DC line 3, a voltmeter 20V that detects the line voltage of the DC line 3, an ammeter 20I that detects input / output currents flowing in and out of the DC line 3, and a control device 25.

[0103] When the control device 25 functions as the master power interchange device 2, it controls the bidirectional DC-DC converter 21 to apply a predetermined modulation to the magnitude of the line voltage, thereby querying the power interchange devices 2B to 2N as to whether or not power interchange is required.

[0104] Furthermore, when the control device 25 functions as a slave, it controls the bidirectional DC-DC converter 21 upon receiving the inquiry via the voltmeter 20V. The control device 25 then determines which of the following requests the control device 25 will make: provide power, receive power, or not exchange power. Furthermore, the control device 25 responds to the inquiry by outputting, to the DC line 3, an output current whose magnitude is modulated at a frequency uniquely determined for the request of the control device 2, or by not outputting any output current, in accordance with the determined request. As a result, in this embodiment, system modifications, such as the addition of a power interchange device 2, can be flexibly implemented in the DC distribution system 1.

[0105] Specifically, in a DC power distribution system, the electric wires used in the DC lines are usually selected based on the sum of the rated current values ​​of the power interchange devices included in the DC power distribution system (i.e., the capacity of the DC line 3). For this reason, for example, when adding a new power interchange device, it may be necessary to carry out work to change the electric wires in order to increase the capacity of the DC line.

[0106] In contrast, in the DC power distribution system 1 of the present embodiment, one of the multiple power interchange devices 2 functions as a master, and the remaining power interchange devices 2 function as slaves. In the DC power distribution system 1 of the present embodiment, the master power interchange device 2 monitors the operating states of the slave power interchange devices 2 and the total amount of power interchanged across the entire DC line 3, as described above, to determine whether or not power interchange can be performed. As a result, in the DC power distribution system 1 of the present embodiment, even when a new power interchange device 2 is added, system modifications to the DC power distribution system 1 can be flexibly implemented without having to perform work to change the electric wires.

[0107] Furthermore, in this embodiment, when the control device 25 functions as the master and receives the response via the ammeter 20I, the control device 25 uses the received response to determine whether or not to perform power interchange. Furthermore, if the control device 25 determines to perform power interchange, it stops applying a predetermined modulation to the magnitude of the line voltage within a first predetermined time T1 from the time t0 at which the inquiry was made. As a result, the control device 25 transmits a first determination result indicating that power interchange will be performed to the slave power interchange device 2. Furthermore, if the control device 25 determines not to perform power interchange, it continues applying a predetermined modulation to the magnitude of the line voltage even after time t2, which is the elapse of the first predetermined time T1. As a result, the control device 25 transmits a second determination result indicating that power interchange will not be performed to the slave power interchange device 2. As a result, the DC power distribution system 1 of this embodiment can appropriately perform power interchange without centralized management using communications. Furthermore, the DC power distribution system 1 of this embodiment can reliably and flexibly implement system modifications, such as the addition of a power interchange device 2.

[0108] Furthermore, in this embodiment, when the control device 25 of the slave power interchange device 2 receives an inquiry from the master power interchange device 2, it selects the request and responds based on the power storage rate (remaining battery capacity) of the power storage device 23. As a result, in this embodiment, the master power interchange device 2 can appropriately determine the amount of power to be exchanged with the slave power interchange device 2, and the DC power distribution system 1 can be operated appropriately.

[0109] Furthermore, in this embodiment, when the control device 25 of the slave power interchange device 2 responds to a discharge request or a charge request, it starts responding at time t1, a predetermined time after time t0 when the inquiry was started. This allows the master power interchange device 2 to receive responses from the slave power interchange devices 2 at the same time. As a result, in this embodiment, the master power interchange device 2 can immediately determine whether or not to interchange power. Therefore, in this embodiment, the DC power distribution system 1 can be operated more appropriately.

[0110] [Variation 1] Modification 1 of the present disclosure will be specifically described with reference to Fig. 12. Fig. 12 is a diagram illustrating a specific example of the operation of each power interchange device in Modification 1. For ease of explanation, members having the same functions as those described in the above embodiment will be denoted by the same reference numerals, and their description will not be repeated.

[0111] The main difference between this modified example 1 and the above-described embodiment 1 is that the slave power interchange device 2 determines a delay time from the time t0 when it receives an inquiry from the master power interchange device 2 to the time when it makes a reply based on the magnitude of the remaining battery charge (charging rate), and then makes the reply when the determined delay time has elapsed.

[0112] In other words, in the slave power interchange device 2 of this variant example 1, the control device 25 determines the urgency of the request depending on the charging rate, and the higher the urgency, the shorter the time it takes to start providing the response from the time t0 when the inquiry is received.

[0113] 12, in this first modification, each control device 25 of the slave power interchange devices 2B to 2G determines the standby time as the delay time based on the remaining battery capacity (SOC) of the power storage device 23. Furthermore, each control device 25 determines a shorter value for the standby time as the remaining battery capacity approaches the full charge value or the end-of-discharge value.

[0114] 12, when the control devices 25 of the power interchange devices 2B to 2D detect SOC values ​​of 90%, 80%, and 70%, respectively, they determine standby times of, for example, 1 s, 2 s, and 3 s. When the control devices 25 of the power interchange devices 2E to 2G detect SOC values ​​of 40%, 30%, and 20%, respectively, they determine standby times of, for example, 3 s, 2 s, and 1 s.

[0115] In this first modification, when the control device 25 of the master power interchange device 2 receives a discharge request and a charge request as a response from a slave power interchange device 2, the control device 25 calculates the sum of the number of discharge requests and the number of charge requests. Then, when the control device 25 detects that the calculated sum has reached a predetermined number or more, it stops making inquiries to the slave power interchange device 2. As a result, in this first modification, acceptance of responses from other slave power interchange devices 2 is terminated.

[0116] 12, the control device 25 of the master power interchange device 2 receives the discharge request and the charge request from the power interchange devices 2B and 2G after a one-second wait time from time t0 when request confirmation is started. Furthermore, after the one-second wait time has elapsed, the control device 25 receives the discharge request and the charge request from the power interchange devices 2C and 2F.

[0117] The control device 25 then calculates the sum of the number of discharge requests and the number of charge requests, and when it detects that the calculated sum has reached a predetermined number or more, it stops accepting responses from the remaining power interchange devices 2D and 2E. As a result, in the DC power distribution system 1, the control devices 25 of the power interchange devices 2D and 2E are maintained in a stopped state by stopping the bidirectional DC-DC converters 21 without the lapse of the one-second standby time. Meanwhile, power interchange is carried out between the power interchange devices 2B, 2C, 2F, and 2G.

[0118] <Operation example of modified example 1> Next, an example of operation in Modification 1 will be specifically described with reference to Fig. 13. Fig. 13 is a flowchart showing a specific example of operation of the slave power interchange device 2 in Modification 1. Note that the following description will mainly focus on operations that are different from those of the slave power interchange device 2 in the above-described first embodiment.

[0119] As shown in step S31 of FIG. 13, after deciding to make a discharge request, the control device 25 determines the standby time TD as described above, and does not make a response to the master power interchange device 2 during the standby time TD.

[0120] Thereafter, the control device 25 determines whether or not the AC component of frequency fm has disappeared from the line voltage (step S32). Then, the control device 25 determines that the AC component of frequency fm has disappeared by detecting that the input voltage to the bidirectional DC-DC converter 21 has a waveform Vm0 (YES in step S32). Then, the control device 25 is notified by the power interchange device 2A that the inquiry period has ended, and determines that the discharge request has been acknowledged. Then, the control device 25 proceeds to step S13, as in the first embodiment.

[0121] On the other hand, when the control device 25 does not determine that the AC component of frequency fm has disappeared (NO in step S32), the control device 25 determines that the discharge request from the power interchange device 2A has not been acknowledged. Then, the control device 25 stops the bidirectional DC-DC converter 21 and proceeds to step S23.

[0122] As shown in step S33 of FIG. 13, after deciding to make a charge request, the control device 25 determines the standby time TD as described above, and does not make a response to the master power interchange device 2 during the standby time TD.

[0123] Thereafter, the control device 25 determines whether or not the AC component of frequency fm has disappeared from the line voltage (step S34). Then, the control device 25 determines that the AC component of frequency fm has disappeared by detecting that the input voltage to the bidirectional DC-DC converter 21 has a waveform Vm0 (YES in step S32). Then, the control device 25 is notified by the power interchange device 2A that the inquiry period has ended, and determines that the charging request has been acknowledged. Then, the control device 25 proceeds to step S13, as in the first embodiment.

[0124] On the other hand, when the control device 25 does not determine that the AC component of frequency fm has disappeared (NO in step S32), the control device 25 determines that the charge request from the power interchange device 2A has not been acknowledged. Then, the control device 25 stops the bidirectional DC-DC converter 21 and proceeds to step S23.

[0125] As described above, in the present modified example 1, in the slave power interchange device 2, the control device 25 determines the urgency of the request depending on the magnitude of the charging rate, and the higher the urgency, the shorter the time it starts to respond from the time t0 when the inquiry is received. This allows the master power interchange device 2 to preferentially interchange power with slave power interchange devices 2 that have a high risk of surplus or depletion in terms of the charging rate, and allows the DC power distribution system 1 to operate more appropriately.

[0126] Furthermore, in this modification 1, the control device 25 calculates the sum of the number of discharge requests and the number of charge requests. Then, when the control device 25 detects that the calculated sum has reached a predetermined number or more, it stops the inquiry and stops accepting responses from the remaining power interchange devices 2. As a result, in this modification 1, even if the urgency of the request is determined in the slave power interchange device 2, the master power interchange device 2 can more appropriately determine whether or not to interchange power, and the DC power distribution system 1 can be operated more appropriately.

[0127] In addition to the above explanation, in the master power interchange device 2, the control device 25 determines the amount of interchange power to be interchanged over the DC line 3 based on the multiple received replies. Then, when the control device 25 detects that the determined amount of interchange power has reached the capacity of the DC line 3, it may stop the inquiry and stop accepting replies from the remaining power interchange devices 2. Furthermore, the control device 25 determines the difference between the number of slave power interchange devices 2 that have requested to provide power and the number of slave power interchange devices 2 that have requested to receive power based on the multiple received replies. Then, when the determined difference is equal to or greater than a predetermined number, the control device 25 may stop the inquiry and stop accepting replies from the remaining power interchange devices 2.

[0128] [Variation 2] Modification 2 of the present disclosure will be specifically described. For ease of explanation, the same reference numerals will be used to designate members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0129] The main difference between this variant example 2 and the above embodiment 1 is that in the slave power interchange device 2, the control device 25 determines the magnitude of the output current depending on the magnitude of the requested power requested in the discharge request or charge request, and executes the response.

[0130] In the present second modification, the slave power interchange device 2 is configured to change the output current in accordance with the interchanged power when executing a discharge request or a charge request to the master power interchange device 2.

[0131] Specifically, a case will be described in which the reference power of the interchanged power of the slave power interchange device 2 is, for example, 1 kW. In this case, when the power interchange device 2 executes a discharge request of 2 kW, the control device 25 controls the output current from the bidirectional DC-DC converter 21 to have a waveform 2I1 that is twice the waveform I1.

[0132] Furthermore, when the power interchange device 2 executes a 2 kW charge request, the control device 25 controls the output current from the bidirectional DC-DC converter 21 to have a waveform 2I2 that is twice the waveform I2. This allows the slave power interchange device 2 to respond to the master power interchange device 2 with discharge requests or charge requests for two devices.

[0133] As a result, in this variant example 2, when each slave power interchange device 2 responds to the master power interchange device 2, the output current is changed according to the requested power to be exchanged, making it possible to exchange power in accordance with the power capacity of each slave power interchange device 2.

[0134] [Software implementation example] Each functional block of the power interchange device 2 (particularly the control device 25) may be realized by a logic circuit (hardware) formed on an integrated circuit (IC chip) or the like, or may be realized by software.

[0135] In the latter case, the power interchange device 2 includes a computer that executes instructions of a program, which is software that realizes each function. This computer includes, for example, at least one processor and at least one computer-readable recording medium that stores the program. The object of the present invention is achieved by having the processor in the computer read and execute the program from the recording medium. A CPU (Central Processing Unit), for example, can be used as the processor.

[0136] The recording medium may be a "non-transitory tangible medium," such as a ROM (Read Only Memory), a tape, a disk, a card, a semiconductor memory, or a programmable logic circuit. The computer may further include a RAM (Random Access Memory) for expanding the program. The program may be supplied to the computer via any transmission medium capable of transmitting the program (such as a communications network or broadcast waves). One aspect of the present invention may also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.

[0137] 〔summary〕 In order to solve the above problem, a power interchange device according to one aspect of the present disclosure is a power interchange device capable of exchanging power with another device that is another power interchange device connected to a DC line, and includes a DC bus, a power generation device, a load, and a power storage device each connected to the DC bus, a DC-DC converter connected to the DC bus and the DC line, a voltage detection device that detects the line voltage of the DC line, and a control device, and when the power interchange device that is itself functions as a master, the control device controls the DC-DC converter to detect a line voltage corresponding to the magnitude of the line voltage. By applying a certain modulation to the voltage detection device, the device executes an inquiry as to whether the other device requires power interchange, and when the device itself functions as a slave, when the inquiry is received through the voltage detection device, the device controls the DC-DC converter to respond to the inquiry by outputting an output current whose magnitude is modulated at a frequency uniquely determined for the request to the DC line, or by not outputting an output current, depending on whether the device itself is requesting to provide power, to receive power, or not to exchange power.

[0138] According to the above configuration, it is possible to provide a power interchange device that can flexibly implement system modifications, such as the addition of a power interchange device, in a DC power distribution system.

[0139] The power interchange device according to one aspect described above may further include a current detection device that detects input / output current flowing in and out of the device itself from the DC line, and when the device itself functions as a master and receives the response through the current detection device, the control device may use the received response to determine whether or not to interchange power, and when it has determined that power interchange will be performed, it may transmit a first determination result indicating that power interchange will be performed to the other device by stopping the application of a predetermined modulation to the magnitude of the line voltage within a first predetermined time from the time the inquiry was executed, and when it has determined that power interchange will not be performed, it may transmit a second determination result indicating that power interchange will not be performed to the other device by continuing to apply a predetermined modulation to the magnitude of the line voltage even after the first predetermined time has elapsed.

[0140] According to the above configuration, when the control device functions as the master, the control device uses the response to determine whether or not to perform power interchange. Furthermore, when it determines to perform power interchange, it transmits a first determination result to the other devices, and when it determines not to perform power interchange, it transmits a second determination result to the other devices using an operation different from the first determination result. This ensures flexible implementation of system changes, such as adding a power interchange device.

[0141] In the power interchange device according to the above aspect, the control device may receive responses from each of the other devices by performing frequency analysis of the input / output currents and detecting the magnitude of a modulation component of a frequency uniquely determined for each of the requests connected to the DC line.

[0142] According to the above configuration, the control device can easily determine the content of the response from each of the other devices by performing frequency analysis of the input / output current and detecting the magnitude of the frequency modulation component, thereby enabling the master power interchange device to operate the DC power distribution system more appropriately.

[0143] In the power interchange device relating to the above-mentioned aspect, when executing the judgment, the control device may calculate the amount of interchange power to be interchanged on the DC line when power interchange is performed in accordance with a request from the other device, and when the calculated amount of interchange power is greater than the capacity of the DC line, determine that power interchange will not be performed.

[0144] According to the above configuration, the master power interchange device can appropriately determine whether or not to interchange power, and can operate the DC power distribution system appropriately.

[0145] In the power interchange device relating to one aspect described above, when executing the judgment, the control device may calculate the difference between the number of other machines that have requested to provide power and the number of other machines that have requested to receive power, determined based on the multiple responses, and may determine not to interchange power when the calculated difference is equal to or greater than a predetermined number.

[0146] According to the above configuration, the master power interchange device can determine whether the ratio of circuit loss in the DC line to the interchanged power is large. As a result, the master power interchange device can appropriately determine whether to interchange power, and can operate the DC power distribution system appropriately.

[0147] In the power interchange device according to the above aspect, when the control device receives the first judgment result through the voltage detection device when the own device functions as a slave, the control device controls the DC-DC converter to output an output current of a predetermined magnitude to the DC line for a second predetermined time when the own device requests to be supplied with power, controls the DC-DC converter to receive an input current of a predetermined magnitude from the DC line for the second predetermined time when the own device requests to be supplied with power, and stops the DC-DC converter when the own device requests not to exchange power; When the second determination result is received through the voltage detection device, the DC-DC converter may be stopped.

[0148] According to the above configuration, when a request to provide power is accepted, the slave power interchange device outputs an output current of a predetermined magnitude to the DC line for a second predetermined time. Furthermore, when a request to receive power is accepted, the slave power interchange device receives an input current of a predetermined magnitude from the DC line for a second predetermined time. Furthermore, when a request not to exchange power is accepted, the slave power interchange device stops the DC-DC converter. Furthermore, when the slave power interchange device is notified that power interchange will not be conducted, the slave power interchange device stops the DC-DC converter. This allows the slave power interchange device to operate appropriately depending on whether power interchange is being conducted and the details of the implementation, and also allows the DC distribution system to operate appropriately.

[0149] In the power interchange device according to the above aspect, when the control device functions as a slave, the control device may select the request based on a charging rate of the power storage device.

[0150] According to the above configuration, the control device selects a request and responds to the master power interchange device based on the charge rate of the storage device, so that the master power interchange device can appropriately determine the amount of power to be transferred to each of the other devices, allowing the DC power distribution system to operate appropriately.

[0151] In the power interchange device according to the above aspect, when the control device itself functions as a slave, the control device may start executing the response when a predetermined time has elapsed since the master started the inquiry.

[0152] With the above configuration, the master power interchange device receives responses from each of the other devices at the same time. As a result, the master power interchange device can immediately determine whether or not to interchange power. This allows the DC power distribution system to operate more appropriately.

[0153] In the power interchange device according to the above aspect, the control device may determine the urgency of the request depending on the magnitude of the charging rate, and the higher the urgency, the shorter the time from the time of receiving the inquiry to the start of the response.

[0154] According to the above configuration, the master power interchange device can prioritize power interchange with a slave power interchange device that has a high risk of surplus or depletion in terms of the charge rate, thereby allowing the DC power distribution system to operate more appropriately.

[0155] In the power interchange device according to one aspect described above, when the control device is functioning as a master, upon receiving the response, the control device may calculate the sum of the number of the other devices that have requested to provide power and the number of the other devices that have requested to receive power, determined based on the multiple received responses, and stop the query when it detects that the calculated sum has reached a certain number or more, or calculate the amount of interchanged power to be exchanged over the DC line based on the multiple received responses and detects that the calculated amount of interchanged power has reached the capacity of the DC line, or calculate the difference between the number of the other devices that have requested to provide power and the number of the other devices that have requested to receive power, based on the multiple received responses, and stop the query when it detects that the calculated difference has reached a certain number or more.

[0156] According to the above configuration, the master power interchange device can more appropriately determine whether or not to interchange power even when the urgency of the request is determined in each of the other devices, thereby allowing the DC distribution system to operate more appropriately.

[0157] In the power interchange device according to the above aspect, when the control device is functioning as a slave, the control device may determine the magnitude of the modulation component of the output current when executing the response in accordance with the magnitude of the requested power when requesting the provision of power, or the magnitude of the requested power when requesting the receipt of power.

[0158] According to the above configuration, when each other device responds to the master power interchange device, the output current is changed according to the requested power that is requested for interchange, making it possible to interchange power according to the power capacity of each other device.

[0159] Furthermore, a DC power distribution system according to one aspect of the present disclosure comprises a DC line and a plurality of power interchange devices connected to the DC line, and is a DC power distribution system capable of exchanging power between the plurality of power interchange devices, and each of the plurality of power interchange devices uses any of the power interchange devices described above.

[0160] According to the above configuration, it is possible to provide a DC power distribution system that allows for flexible system modifications such as the addition of a power interchange device.

[0161] Furthermore, a control method for a power interchange device according to one aspect of the present disclosure is a control method for a power interchange device capable of exchanging power with another device that is another power interchange device connected to a DC line, wherein the power interchange device comprises a DC bus, a power generation device, a load, and a power storage device each connected to the DC bus, a DC-DC converter connected to the DC bus and the DC line, a voltage detection device that detects the line voltage of the DC line, and a control device, and includes a step of controlling the DC-DC converter to apply a predetermined modulation to the magnitude of the line voltage, thereby executing an inquiry to the other device as to whether or not power interchange is required.

[0162] According to the above configuration, it is possible to provide a method for controlling a power interchange device in a DC power distribution system that allows for flexible system modifications, such as the addition of a power interchange device.

[0163] Furthermore, a control method for a power interchange device according to one aspect of the present disclosure is a control method for a power interchange device capable of exchanging power with another device that is another power interchange device connected to a DC line, wherein the power interchange device comprises a DC bus, a power generation device, a load, and a power storage device each connected to the DC bus, a DC-DC converter connected to the DC bus and the DC line, a voltage detection device for detecting the line voltage of the DC line, and a control device, and when the inquiry is received through the voltage detection device, the method controls the DC-DC converter to respond to the inquiry by outputting an output current whose magnitude is modulated at a frequency uniquely determined for the request of the own device to the DC line, or by not outputting an output current, depending on whether the own device requests to provide power, receive power, or not exchange power.

[0164] According to the above configuration, it is possible to provide a method for controlling a power interchange device in a DC power distribution system that allows for flexible system modifications, such as the addition of a power interchange device.

[0165] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the embodiments are also included in the technical scope of the present disclosure. [Explanation of symbols]

[0166] 1 DC power distribution system 2, 2A~2N power interchange device 3 DC lines 20V voltmeter (voltage detection device) 20I ammeter (current detection device) 20L DC busbar 21 Bidirectional DC-DC converter 22 Power generating equipment 23 Energy storage device 24 Load 25 Control device

Claims

1. A power interchange device that can interchange power with another device that is another power interchange device connected to a DC line, A DC busbar, a power generation device, a load, and a power storage device, each connected to the DC bus; a DC-DC converter connected to the DC bus and the DC line; a voltage detection device for detecting a line voltage of the DC line; a control device; The control device When the power interchange device itself functions as a master, controlling the DC-DC converter to apply a predetermined modulation to the magnitude of the line voltage, thereby inquiring of the other device as to whether or not power interchange is required; When the own device functions as a slave, When the inquiry is received through the voltage detection device, the power interchange device controls the DC-DC converter to respond to the inquiry by outputting an output current whose magnitude is modulated at a frequency uniquely determined for the request to the DC line, or by not outputting an output current, depending on whether the device is requesting to provide power, receive power, or not to exchange power.

2. a current detection device that detects an input / output current flowing into and out of the device from the DC line; When the control device itself functions as a master, When the response is received through the current detection device, the received response is used to determine whether or not to provide power interchange; and when it is determined that power interchange will be performed, transmitting a first determination result indicating that power interchange will be performed to the other device by stopping the application of a predetermined modulation to the magnitude of the line voltage within a first predetermined time from the time when the inquiry is executed; 2. The power interchange device according to claim 1, wherein, when it is determined that power interchange will not be performed, a second determination result indicating that power interchange will not be performed is transmitted to the other device by continuing to apply a predetermined modulation to the magnitude of the line voltage even after the first predetermined time has elapsed.

3. The control device 3. The power interchange device according to claim 2, wherein a response from each of the other devices is received by performing a frequency analysis of the input / output current and detecting the magnitude of a modulation component of a frequency uniquely determined for each of the requests connected to the DC line.

4. The control device 4. The power interchange device according to claim 2 or 3, wherein when the determination is made, the amount of interchange power to be interchanged on the DC line when power interchange is performed in accordance with a request from the other device is calculated, and when the amount of interchange power calculated is greater than the capacity of the DC line, the power interchange device determines not to perform power interchange.

5. The control device 4. The power interchange device according to claim 2 or 3, wherein when making the judgment, the device calculates a difference between the number of other devices that have requested to provide power and the number of other devices that have requested to receive power, determined based on a plurality of the responses, and when the calculated difference is equal to or greater than a predetermined number, the device determines not to interchange power.

6. When the control device functions as a slave, When the first determination result is received through the voltage detection device, When the device itself requests the provision of power, the device controls the DC-DC converter to output an output current of a predetermined magnitude to the DC line for a second predetermined time period; When the device itself requests power supply, the device controls the DC-DC converter to receive an input current of a predetermined magnitude from the DC line for the second predetermined time period; When the device itself requests not to exchange power, the DC-DC converter is stopped. When the second determination result is received through the voltage detection device, The power interchange device according to any one of claims 2 to 5, wherein the DC-DC converter is stopped.

7. When the control device functions as a slave, The power interchange device according to claim 1 , wherein the request is selected based on a charging rate of the power storage device.

8. When the control device functions as a slave, The power interchange device according to claim 1 , wherein the execution of the response is started when a predetermined time has elapsed since the master started the inquiry.

9. The control device 8. The power interchange device according to claim 7, wherein the urgency of the request is determined according to the magnitude of the charging rate, and the higher the urgency, the shorter the time from the time of receiving the inquiry to start the response.

10. When the control device itself functions as a master, 10. The power interchange device according to claim 9, wherein, upon receiving the response, the device calculates the sum of the number of the other devices that have requested to provide power and the number of the other devices that have requested to receive power, determined based on the multiple received responses, and stops the inquiry when it detects that the calculated sum has reached a certain number or more, or calculates the amount of interchanged power to be exchanged over the DC line based on the multiple received responses and detects that the calculated amount of interchanged power has reached the capacity of the DC line, or calculates the difference between the number of the other devices that have requested to provide power and the number of the other devices that have requested to receive power, based on the multiple received responses, and stops the inquiry when it detects that the calculated difference has reached a predetermined number or more.

11. When the control device functions as a slave, 11. The power interchange device according to claim 1, wherein when executing the response, the magnitude of the modulation component of the output current is determined according to the magnitude of the requested power when requesting the provision of power, or the magnitude of the requested power when requesting the receipt of power.

12. A DC power distribution system comprising a DC line and a plurality of power interchange devices connected to the DC line, capable of interchange of power between the plurality of power interchange devices, A DC power distribution system, wherein the power interchange device according to any one of claims 1 to 11 is used for each of the plurality of power interchange devices.

13. A control method for a power interchange device that can interchange power with another device that is another power interchange device connected to a DC line, comprising: the power interchange device comprises a DC bus, a power generation device, a load, and a power storage device each connected to the DC bus, a DC-DC converter connected to the DC bus and the DC line, a voltage detection device that detects a line voltage of the DC line, and a control device; A control method for a power interchange device, comprising: a step of controlling the DC-DC converter to apply a predetermined modulation to the magnitude of the line voltage, thereby executing an inquiry to the other device as to whether or not power interchange is required.

14. A control method for a power interchange device that can interchange power with another device that is another power interchange device connected to a DC line, comprising: the power interchange device comprises a DC bus, a power generation device, a load, and a power storage device each connected to the DC bus, a DC-DC converter connected to the DC bus and the DC line, a voltage detection device that detects a line voltage of the DC line, and a control device; A control method for a power interchange device, comprising: when an inquiry as to whether or not power interchange is required is received from the other device through the voltage detection device, controlling the DC-DC converter to respond to the inquiry by outputting an output current whose magnitude is modulated at a frequency uniquely determined for the request of the own device, or by not outputting an output current, depending on whether the own device requests to provide power, receive power, or not exchange power.

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