Power conversion device and DC power supply system

Abstract

A power conversion device for boosting, boosting, boosting, or reducing DC power input from a DC power source and outputting the DC power, the power conversion device being connected in parallel to another power conversion device and a load, the power conversion device comprising: an output current value acquisition unit for acquiring an output current value; an output voltage value acquisition unit that acquires an output voltage value; and a control unit that controls the output voltage, the control unit having: a correction value generation unit that generates an output current correction value that corrects the output current value on the basis of the output current target value and the output current value; the target value of the output current is calculated by distributing the sum of the output current value and another output current value output from the other power conversion device or the load current value input to the load to the power conversion device and the other power conversion device according to a predetermined distribution method; and a droop control unit that droops the output voltage target value on the basis of the corrected output current value corrected in accordance with the output current correction value, and the power conversion device controls the output voltage on the basis of the droop output voltage target value and the output voltage value.

Description

Technical Field

[0001] The present invention relates to a power conversion device and a DC power supply system. Background Art

[0002] Conventionally, as one of the parallel operation controls of a DC power supply system that supplies DC power using multiple converters with a storage battery as a power source, a droop control method has been used.

[0003] In the droop control method, by making the output voltage of each converter have a droop characteristic based on the output current, it becomes a highly reliable system that can be controlled without information exchange between the converters. However, it is impossible to control the output current to an appropriate value based on the load current. Therefore, when there are deviations in the droop characteristics of the converters connected in parallel, the output voltages of the converters are the same, but an imbalance in the output current occurs. As a result, the DC connection may become unstable.

[0004] Regarding such an imbalance in the output current, in the power conversion system described in Patent Document 1, by detecting the load current, the target current of a part of the converters is set, and the output current is controlled to an appropriate value, thereby eliminating the current imbalance. However, in such a method, since constant current control is required, it cannot be applied to the droop control method.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2020-120465 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] The present invention has been completed in view of the above problems, and an object thereof is to provide a technique capable of appropriately controlling an output current.

[0010] Means for Solving the Problems

[0011] The present invention for solving the above problems is a power conversion device that boosts, buck-boosts, or buck-converts the DC power input from a DC power supply and outputs it. The power conversion device is connected to a load in parallel with other power conversion devices. The other power conversion devices boost, buck-boost, or buck-convert the DC power input from other DC power supplies and output it. The power conversion device is characterized by having: an output current value acquisition unit that acquires the output current value output from the power conversion device; an output voltage value acquisition unit that acquires the output voltage value output from the power conversion device; and a control unit that controls the output voltage output from the power conversion device. The control unit has: a correction value generation unit that generates an output current correction value for correcting the output current value based on the target value of the output current output from the power conversion device, i.e., the output current target value, and the output current value. The output current target value is calculated by distributing the sum of the output current value output from the other power conversion device and the other output current value output from the other power conversion device, or the load current value input to the load, according to a prescribed distribution method in the power conversion device and the other power conversion device; and a droop control unit that droops the target value of the output voltage output from the power conversion device, i.e., the output voltage target value, based on the corrected output current value, i.e., the corrected output current value, after correction according to the output current correction value. The power conversion device controls the output voltage based on the drooped output voltage target value and the output voltage value.

[0012] Thus, by controlling the output voltage using the target value of the output current output from the power conversion device, i.e., the output current target value, and the droop control of the output current, the output current target value is calculated by distributing the sum of the other output current value output from the other power conversion device and the other output current value output from the other power conversion device, or the load current value input to the load, according to a prescribed distribution method in the power conversion device and the other power conversion device. Therefore, even when multiple power conversion devices are operating in parallel, the output current can be appropriately controlled regardless of load variations.

[0013] In addition, in the present invention, it may be that the power conversion device has: a communication unit that receives at least the output current value of the other power conversion device or the load current value; and an output current target value calculation unit that calculates at least the output current target value by distributing the sum of the output current value and the other output current value, or the load current value, according to the distribution method in the power conversion device and the other power conversion device.

[0014] In addition, in the present invention, it may also be that the power conversion device has a communication unit that transmits the output current value to the other power conversion device or an external device having an output current target value calculation unit, and receives the output current target value calculated by the output current target value calculation unit from the other power conversion device or the external device. The output current target value calculation unit calculates at least the output current target value by distributing the sum of the output current value and the other output current value, or the load current value, between the power conversion device and the other power conversion device according to the distribution method.

[0015] In addition, in the present invention, it may also be that the correction value generation unit adjusts the output current correction value based on the difference between the output current target value and the output current value.

[0016] Accordingly, based on the difference between the output current target value and the output current value, the magnitude of the current output from its own power conversion device to the load is judged, and the current correction value is adjusted accordingly. Thus, more appropriate control of the output current can be achieved.

[0017] In addition, in the present invention, it may also be that the correction value generation unit increases or decreases the output current correction value according to the relationship between the output voltage value and a specified voltage value range and the relationship between the output current value and a specified current value range.

[0018] Accordingly, the output current correction value is increased or decreased according to the relationship between the output voltage value and the specified voltage value range and the relationship between the output current value and the specified current value range. Thus, a balanced state that is different from but approximate to the output current target value can be achieved.

[0019] In addition, the present invention is a DC power supply system in which a plurality of power conversion devices that output DC power to a load are connected in parallel with respect to the load. The power conversion device boosts, step-up / down converts, or steps down the DC power input from a DC power source and outputs it. The power conversion device includes: an output current value acquisition unit that acquires an output current value output from the power conversion device; an output voltage value acquisition unit that acquires an output voltage value output from the power conversion device; and a control unit that controls the output voltage output from the power conversion device. The control unit includes: a correction value generation unit that generates an output current correction value for correcting the output current value based on a target value of the output current output from the power conversion device, i.e., an output current target value, and the output current value; and a droop control unit that droops a target value of the output voltage output from the power conversion device, i.e., an output voltage target value, based on the corrected output current value obtained by correcting the output current value according to the output current correction value. The power conversion device controls the output voltage based on the drooped output voltage target value and the output voltage value. The DC power supply system includes an output current target value calculation unit that calculates the output current target value of the power conversion device included in the DC power supply system by distributing the total value of the output current values output from the plurality of power conversion devices included in the DC power supply system or the load current value input to the load according to a specified distribution method.

[0020] Accordingly, by distributing the sum of the output current values output from the plurality of power conversion devices included in the DC power supply system or the load current value input to the load according to a specified distribution method, and by controlling the output voltage using the output current target value and the droop control of the output current of the power conversion device included in the DC power supply system, it is possible to appropriately control the output current regardless of load variations.

[0021] In addition, in the present invention, the correction value generation unit may adjust the output current correction value based on the difference between the output current target value and the output current value.

[0022] Accordingly, based on the difference between the output current target value and the output current value, the magnitude of the current output from its own power conversion device to the load is determined, and the current correction value is adjusted accordingly. Thus, more appropriate control of the output current can be performed.

[0023] In addition, in the present invention, the output current correction value may be increased or decreased according to the relationship between the output voltage value and a specified voltage value range and the relationship between the output current value and a specified current value range.

[0024] Accordingly, based on the relationship between the output voltage value and the specified voltage value range, and the output current value and the specified current value range, the output current correction value is increased or decreased, whereby a balanced state that is different from but approximate to the output current target value can be achieved.

[0025] In addition, in the present invention, it may also be that when the power supplied to the load is an amount of power that can be supplied by a part of the plurality of power conversion devices, the output current target value calculation unit performs the allocation in such a way as to reduce the operation rate of the power conversion devices included in the plurality of power conversion devices.

[0026] Accordingly, when the power supplied to the load is an amount of power that can be supplied by a part of the plurality of power conversion devices, the allocation is performed in such a way as to reduce the operation rate of the power conversion devices included in the DC power supply system, whereby the efficiency can be improved and power can be saved. When calculating the output current target value by performing the allocation in such a way as to reduce the operation rate of the power conversion devices included in the DC power supply system, for example, the following ways of allocation can be cited: starting from the power conversion device with the largest power capacity among the power conversion devices included in the DC power supply system and operating them in sequence, and in addition, when the power capacities of the power conversion devices are equal, starting from the power conversion device with the highest efficiency and operating them in sequence, and in addition, when the DC power source is a storage battery, starting from the power conversion device with the largest charge amount of the connected storage battery and operating them in sequence, but it is not limited thereto. Here, a part of the power conversion devices may be one power conversion device, or may be two or more power conversion devices depending on the amount of power supplied to the load.

[0027] In addition, the present invention is a DC power supply system, which includes a first power conversion device and a second power conversion device. The DC power supply system connects a plurality of the first power conversion devices and one or more of the second power conversion devices in parallel to supply DC power to a load. The first power conversion device steps up, steps up and down, or steps down the DC power input from a first DC power source and outputs it. The first power conversion device has: a first output current value acquisition unit that acquires a first output current value output from the first power conversion device; a first output voltage value acquisition unit that acquires a first output voltage value output from the first power conversion device; and a first control unit that controls the first output voltage output from the first power conversion device. The first control unit has: a correction value generation unit that generates a first output current correction value for correcting the first output current value based on a target value of the first output current output from the first power conversion device, i.e., a first output current target value, and the first output current value; and a first droop control unit that droops a target value of the first output voltage output from the first power conversion device, i.e., a first output voltage target value, based on the first output current value corrected according to the first output current correction value, i.e., a first corrected output current value. The first power conversion device controls the first output voltage based on the drooped first output voltage target value and the first output voltage value. The second power conversion device steps up, steps up and down, or steps down the DC power input from a second DC power source and outputs it. The second power conversion device has: a second output current value acquisition unit that acquires a second output current value output from the second power conversion device; a second output voltage value acquisition unit that acquires a second output voltage value output from the second power conversion device; and a second control unit that controls the second output voltage output from the second power conversion device. The second control unit has a second droop control unit that droops a target value of the second output voltage output from the second power conversion device, i.e., a second output voltage target value, based on the second output current value. The second power conversion device controls the second output voltage based on the drooped second output voltage target value and the second output voltage value. It is characterized in that the DC power supply system has an output current target value calculation unit that calculates the first output current target value of the first power conversion device included in the DC power supply system by distributing the total value of the first output current value and the second output current value or the load current value input to the load between the first power conversion device and the second power conversion device according to a specified distribution method.

[0028] Thus, the output voltage is controlled by using the droop control of the first output current target value and the output current of the first power conversion device. The first output current target value of the first power conversion device is calculated by distributing the sum of the output current values output from multiple first power conversion devices and at least one or more second power conversion devices included in the DC power supply system or the load current value input to the load according to a specified distribution method. Therefore, it is possible to appropriately control the output currents of the first power conversion device and the second power conversion device included in the DC power supply system regardless of load variations.

[0029] In addition, in the present invention, the second power conversion device may also be set based on the amount of electric power that can be supplied to the load.

[0030] In this way, in a DC power supply system including multiple power conversion devices connected in parallel to supply power to a load, a power conversion device operating as the second power conversion device is set based on the amount of electric power that can be supplied to the load. Thus, even in a DC power supply system in which the first power conversion device and the second power conversion device coexist, it is possible to appropriately control the output currents of the first power conversion device and the second power conversion device regardless of load variations. When setting the second power conversion device based on the amount of electric power that can be supplied to the load, for example, the following cases can be cited: setting the power conversion device with the largest power capacity among the power conversion devices included in the DC power supply system as the second power conversion device; in addition, when the power capacities of the power conversion devices are equal, setting the power conversion device with the highest efficiency as the second power conversion device; in addition, when the DC power source is a storage battery, setting the power conversion device connected to the storage battery with the largest charge amount as the second power conversion device, but it is not limited thereto.

[0031] In addition, in the present invention, it may also be that the correction value generation unit adjusts the first output current correction value based on the difference between the first output current target value and the first output current value.

[0032] Thus, the first power conversion device included in the DC power supply system determines the magnitude of the current output from its own power conversion device to the load based on the difference between the first output current target value and the first output current value, and accordingly adjusts the first current correction value. Thereby, it is possible to perform more appropriate control of the output currents of the first power conversion device and the second power conversion device included in the DC power supply system.

[0033] In addition, in the present invention, the output current correction value can also be increased or decreased according to the relationship between the first output voltage value and a specified voltage value range and the relationship between the first output current value and a specified current value range.

[0034] Thus, according to the relationship between the first output voltage value and the specified voltage value range and the relationship between the first output current value and the specified current value range, the output current correction value is increased or decreased, whereby a balanced state that is different from but approximate to the output current target value can be achieved.

[0035] Advantages of the Invention

[0036] According to the present invention, a technique capable of appropriately controlling the output current can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 FIG. is a diagram showing a schematic configuration of a DC power supply system according to Embodiment 1 of the present invention.

[0038] Figure 2 FIG. is a flowchart showing steps of output current target value calculation and lateral current target value calculation processing according to Embodiment 1 of the present invention.

[0039] Figure 3 FIG. is a diagram explaining the principle of droop control according to Embodiment 1 of the present invention.

[0040] Figure 4 FIG. is a diagram showing simulation results in a comparative example of the DC power supply system according to Embodiment 1 of the present invention.

[0041] Figure 5 FIG. is a diagram showing simulation results in the DC power supply system according to Embodiment 1 of the present invention.

[0042] Figure 6 FIG. is a diagram showing other simulation results in a comparative example of the DC power supply system according to Embodiment 1 of the present invention.

[0043] Figure 7 FIG. is a diagram showing other simulation results in the DC power supply system according to Embodiment 1 of the present invention.

[0044] Figure 8 FIG. is a flowchart showing steps of lateral current target value adjustment processing in the DC power supply system according to Embodiment 1 of the present invention.

[0045] Figure 9 FIG. is a diagram showing a schematic configuration of a DC power supply system according to Modification 1 of Embodiment 1 of the present invention.

[0046] Figure 10This is a diagram showing the schematic structure of the DC power supply system according to the second variant of the first embodiment of the present invention.

[0047] Figure 11 This is a diagram showing the schematic structure of the DC power supply system according to the second embodiment of the present invention.

[0048] Figure 12 This is a diagram showing the simulation results in the comparative example of the DC power supply system according to the second embodiment of the present invention.

[0049] Figure 13 This is a diagram showing the simulation results in the DC power supply system according to the second embodiment of the present invention.

[0050] Figure 14 This is a diagram showing other simulation results in the comparative example of the DC power supply system according to the second embodiment of the present invention.

[0051] Figure 15 This is a diagram showing other simulation results in the DC power supply system according to the second embodiment of the present invention.

[0052] Figure 16 This is a diagram showing the schematic structure of the DC power supply system according to the first variant of the second embodiment of the present invention.

[0053] Figure 17 This is a diagram showing the schematic structure of the DC power supply system according to the second variant of the second embodiment of the present invention.

[0054] Figure 18 This is a diagram showing the schematic structure of the DC power supply system according to another variant of the present invention. Detailed implementation mode

[0055] (Application example)

[0056] Hereinafter, the application example of the present invention will be described with reference to the drawings.

[0057] Figure 1 This is a diagram showing the schematic structure of the DC power supply system 100-1 according to the application example of the present invention. The DC power supply system 100-1 includes: a first DC-DC converter 11 that boosts, buck-boosts, or buck-converts the voltage of the DC power discharged from the storage battery 13 and outputs it; a second DC-DC converter 21 that boosts, buck-boosts, or buck-converts the voltage of the DC power discharged from the storage battery 23 and outputs it; and a third DC-DC converter 31 that boosts, buck-boosts, or buck-converts the voltage of the DC power discharged from the storage battery 33 and outputs it, and causes the first DC-DC converter 11, the second DC-DC converter 21, and the third DC-DC converter 31 connected in parallel with respect to the load 3 to operate in parallel and supply DC power to the load 3.

[0058] The third DC-DC converter 31 includes an output voltage detection circuit 35, a third DC-DC converter output current detection circuit 34, a third DC-DC converter communication unit 36, and a control unit 32. The control unit 32 includes an output current target value calculation unit 320-1, a third DC-DC converter transverse current target value generator 323, a droop gain (kd3) multiplier 324, a compensator 325, and summing points 326, 327, and 328. The third DC-DC converter 31 will be described below. However, the first DC-DC converter 11 and the second DC-DC converter 21 also have the same structure.

[0059] The output current target value calculation unit 320-1 calculates the output current target value Io3ref of the third DC-DC converter 31 based on the output current values io1, io2, and io3. The output current value io3 is obtained from the third DC-DC converter output current detection circuit 34, and the output current values io1 and io2 are obtained from the first DC-DC converter 11 and the second DC-DC converter 21 respectively via the third DC-DC converter communication unit 36.

[0060] The output current values io1, io2, and io3 are averaged in the averaging processing units 320a, 320b, and 320c, and then summed in the sum value calculation unit 320d. The sum value of the output current values is distributed according to the distribution method determined or preset in the distribution method determination unit 320e to obtain the output current target value (hereinafter, simply referred to as "output current target value") Io3ref. For example, when the power capacities of the DC-DC converters 11, 21, and 31 are set to P1, P2, and P3 respectively, in the calculation execution unit 320h, the coefficient k3 calculated as k3 = P3 / (P1 + P2 + P3) is multiplied by the sum value of the output current to calculate the output current target value Io3ref. Although omitted in Figure 1 , the first DC-DC converter 11 and the second DC-DC converter 21 also have output current target value calculation units, and these output current target value calculation units have the same structure as the output current target value calculation unit 320. Then, in the output current target value calculation unit of the first DC-DC converter 11, the coefficient k1 calculated as k1 = P1 / (P1 + P2 + P3) is multiplied by the sum value of the output current in the calculation execution unit to calculate the output current target value Io1ref. In addition, in the output current target value calculation unit of the second DC-DC converter 21, the coefficient k2 calculated as k2 = P2 / (P1 + P2 + P3) is also multiplied by the sum value of the output current in the calculation execution unit to calculate the output current target value Io2ref.

[0061] The output voltage value vo is input from the output voltage detection circuit 35 to the third DC-DC converter lateral current target value generator 323, and the output current value of the second DC-DC converter (hereinafter, simply referred to as "output current value" unless otherwise specified) io3 is input from the third DC-DC converter output current detection circuit 34 to the third DC-DC converter lateral current target value generator 323. In addition, the output current target value Io3ref of the third DC-DC converter 31 is also input from the output current target value calculation unit 320-1 to the third DC-DC converter lateral current target value generator 323. The third DC-DC converter lateral current target value generator 323 generates a third DC-DC converter lateral current target value (hereinafter, simply referred to as "lateral current target value") Icr3ref based on at least the output voltage value vo, the output current value io3, and the output current target value Io3ref.

[0062] The value obtained by multiplying the value obtained by subtracting the lateral current target value Icr3ref from the output current value io3 by the droop gain kd3 is subtracted from the output voltage target value vo3ref of the third DC-DC converter, and the value obtained is subtracted from the output voltage value vo and input to the compensator 325. Based on the command value output from the compensator 325, the output voltage vo3 of the third DC-DC converter 31 is controlled.

[0063] Figure 3 A diagram showing the principle of droop control performed in the control unit 32 of the third DC-DC converter 31. Figure 3 It is a graph with the output current value io3 on the horizontal axis and the output voltage value vo3 on the vertical axis. The straight line with a slope kd3 that slopes downward to the right from the intersection with the vertical axis, i.e., the output voltage target value Vo3ref, is the characteristic line PL of the droop control. The output current value io3 detected by the third DC-DC converter output current detection circuit 34 is indicated by the thin line arrow Ar1 parallel to the horizontal axis. The output voltage target value Vo3ref1 corresponds to the intersection point P1 of the arrow Ar1 and the characteristic line PL. In Figure 1 In the control system shown, the value obtained by subtracting the lateral current target value Icr3ref indicated by the arrow Ar0 of the dash-dot line from the output current value io3 is multiplied by the droop gain kd3. This means that in Figure 3In this case, the droop characteristic is applied to the value indicated by the thick-line arrow Ar2 parallel to the horizontal axis, which is equal to the value obtained by subtracting the lateral current target value Icr3ref indicated by the arrow Ar0 of the single-dot chain line from the output current value io3, with respect to the output current value (imaginary output current value) io3im. At this time, the output voltage target value Vo3ref is lowered to the output voltage target value Vo3ref2 corresponding to the intersection point P2 of the arrow Ar2 and the characteristic line PL. Thus, in this droop control, the output voltage target value Vo3ref is not lowered to the output voltage target value Vo3ref1 under the droop control based on the output current Io3, but is lowered to the output voltage target value Vo3ref2 under the droop control based on the imaginary output current value io3im.

[0064] Thus, by this droop control based on the output current target values Io1ref, Io2ref, and Io3ref, the output currents io1, io2, and io3 can be appropriately controlled. The output current target values Io1ref, Io2ref, and Io3ref are calculated by allocating the output current total value obtained by summing the output currents of the respective DC-DC converters 11, 21, and 31 according to a predetermined allocation method.

[0065] (Embodiment 1)

[0066] Hereinafter, the DC power supply system 100-1 according to Embodiment 1 of the present invention will be described in more detail with reference to the drawings. However, the structures of the devices and systems described in this embodiment should be appropriately changed according to various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

[0067] Figure 1 FIG. is a diagram showing a schematic structure of a first DC-DC converter 11, a second DC-DC converter 21, a third DC-DC converter 31, and a control unit 32 that constitute the DC power supply system 100-1 according to Embodiment 1 of the present invention. The control units of the first DC-DC converter 11 and the second DC-DC converter 21 have the same structure as the control unit 32 of the third DC-DC converter 31, but the description thereof is omitted. In Figure 1In the following description, for the sake of illustration, the third DC-DC converter 31 and the control unit 32 are described separately. However, as a specific device, the control unit 32 is housed in the housing of the third DC-DC converter 31 (the same applies to the DC-DC converters described below). Here, the DC power supply system 100-1 corresponds to the DC power supply system of the present invention, the first DC-DC converter 11, the second DC-DC converter 21, and the third DC-DC converter 31 correspond to the multiple power conversion devices of the present invention, and each corresponds to the power conversion device of the present invention. In addition, when the third DC-DC converter 31 corresponds to the power conversion device of the present invention, the first DC-DC converter 11 and the second DC-DC converter 21 correspond to the other power conversion devices of the present invention.

[0068] The DC power supply system 100-1 includes: a first DC-DC converter 11 that boosts, buck-boosts, or buck-converts the voltage of the DC power discharged from the battery 13 and outputs it; a second DC-DC converter 21 that boosts, buck-boosts, or buck-converts the voltage of the DC power discharged from the battery 23 and outputs it; and a third DC-DC converter 31 that boosts, buck-boosts, or buck-converts the voltage of the DC power discharged from the battery 33 and outputs it. In the DC power supply system 100-1, the three DC-DC converters, namely, the first DC-DC converter 11, the second DC-DC converter 21, and the third DC-DC converter 31, are connected in parallel with respect to the load 3 and operate in parallel, thereby supplying DC power to the load 3. In Figure 1 Figure, a DC power supply system 100-1 including the first DC-DC converter 11, the second DC-DC converter 21, and the third DC-DC converter 31 respectively connected to the three batteries 13, 23, and 33 is shown. However, the DC power supply system 100-1 may also include four or more batteries and DC-DC converters connected in parallel. As a DC power source, various distributed power sources can be used, not limited to batteries. Here, the batteries 13, 23, and 33 correspond to the DC power sources of the present invention.

[0069] The voltage (output voltage) of the connection point CP connecting the output line PwL1 of the first DC-DC converter 11, the output line PwL2 of the second DC-DC converter 21, and the output line PwL3 of the third DC-DC converter 31 is represented by vo, and the current (load current) supplied to the load 3 through the power line PwL0 is represented by io. The load current value io corresponds to the load current value of the present invention.

[0070] The third DC-DC converter 31 includes a control unit 32, an output voltage detection circuit 35, a third DC-DC converter output current detection circuit 34, and a third DC-DC converter communication unit 36. The control unit 32 includes an output current target value calculation unit 320-1, a third DC-DC converter lateral current target value generator 323, a droop gain (kd3) multiplier 324, a compensator 325, and superposition points 326, 327, 328. The control unit 32 can be configured as a computer including a CPU (Central Processing Unit), a memory, a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), etc. A part or all of the functions of each unit can be implemented by executing software in hardware or by dedicated hardware. The control unit 32 corresponds to the control unit of the present invention (as long as there is no special description, the corresponding relationship between the third DC-DC converter 31 and the structure of the present invention also holds for the corresponding structures of the first DC-DC converter 11 and the second DC-DC converter 21).

[0071] The output voltage detection circuit 35 detects the output voltage vo at the connection point CP. The third DC-DC converter output current detection circuit 34 detects the current (third DC-DC converter output current) io3 flowing through the output line PwL3 that connects the output terminal of the third DC-DC converter 31 and the connection point CP. The output voltage value vo is input from the output voltage detection circuit 35 to the third DC-DC converter lateral current target value generator 323, and the third DC-DC converter output current value (hereinafter, simply referred to as "output current value" unless otherwise specified) io3 is input from the third DC-DC converter output current detection circuit 34 to the third DC-DC converter lateral current target value generator 323. In addition, the output current target value (hereinafter, simply referred to as "output current target value") io3ref of the third DC-DC converter 31 is also input from the output current target value calculation unit 320-1 described later to the third DC-DC converter lateral current target value generator 323. The third DC-DC converter lateral current target value generator 323 generates a third DC-DC converter lateral current target value (hereinafter, simply referred to as "lateral current target value") Icr3ref based on at least the output voltage value vo, the output current value io3, and the output current target value Io3ref. Here, the output voltage detection circuit 35 corresponds to the output voltage value acquisition unit of the present invention, and the output voltage (value) vo corresponds to the output voltage (value) of the present invention. In addition, the third DC-DC converter output current detection circuit 34 corresponds to the output current value acquisition unit of the present invention, and the output current (value) io3 corresponds to the output current (value) of the present invention. The output current target value io3ref corresponds to the output current target value of the present invention. The third DC-DC converter lateral current target value generator 323 corresponds to the correction value generation unit of the present invention, and the lateral current target value Icr3ref corresponds to the output current correction value of the present invention. In addition, when the output current value io3 corresponds to the output current value of the present invention, the output current values io1 and io2 correspond to the other output current values of the present invention.

[0072] The third DC-DC converter communication unit 36 is a communication interface for transmitting and receiving information with an external device including at least the first DC-DC converter 11 and the second DC-DC converter 21. Similarly, the first DC-DC converter 11 has a first DC-DC converter communication unit 16, and the first DC-DC converter communication unit 16 is a communication interface for transmitting and receiving information with an external device including at least the third DC-DC converter 31. In addition, similarly, the second DC-DC converter 21 also has a second DC-DC converter communication unit 26, and the second DC-DC converter communication unit 26 is a communication interface for transmitting and receiving information with an external device including at least the third DC-DC converter 31.

[0073] The output current target value calculation unit 320-1 calculates the output current target value Io3ref of the third DC-DC converter 31 based on the output current value io1, the output current value io2, and the output current value io3. As will be described later, the first DC-DC converter 11 and the second DC-DC converter 21 also have output current target value calculation units that calculate the output current target value Io1ref and the output current target value Io2ref, respectively.

[0074] Figure 2 It is a flowchart showing the processing steps from the detection of the output current to the generation of the lateral current target value in each of the DC-DC converters 11, 21, and 31.

[0075] As described above, in the first DC-DC converter output current detection circuit 14 of the first DC-DC converter 11, the output current value io1 output from the first DC-DC converter 11 is detected. In the second DC-DC converter output current detection circuit 24 of the second DC-DC converter 21, the output current value io2 output from the second DC-DC converter 21 is detected. In the third DC-DC converter output current detection circuit 34 of the third DC-DC converter 31, the output current value io3 output from the third DC-DC converter 31 is detected (step S1).

[0076] The output current value io1 of the first DC-DC converter 11 and the output current value io2 of the second DC-DC converter 21 detected in this way are respectively transmitted from the first DC-DC converter communication unit 16 and the second DC-DC converter communication unit 26 to the third DC-DC converter communication unit 36, and are input to the output current target value calculation unit 320-1 via the third DC-DC converter communication unit 36. In addition, the output current value io3 of the third DC-DC converter 31 is input to the output current target value calculation unit 320-1 from the third DC-DC converter output current detection circuit 34.

[0077] The output current target value calculation unit 320-1 includes an averaging processing unit 320a that performs averaging processing on the output current value io1 of the first DC-DC converter 11, an averaging processing unit 320b that performs averaging processing on the output current value io2 of the second DC-DC converter 21, and an averaging processing unit 320c that performs averaging processing on the output current value io3 of the third DC-DC converter 31. As described above, for the output current value io1, the output current value io2, and the output current value io3 input to the output current target value calculation unit 320-1, averaging processing is respectively performed in the averaging processing unit 320a, the averaging processing unit 320b, and the averaging processing unit 320c (step S2).

[0078] In addition, the output current target value calculation unit 320-1 includes a total value calculation unit 320d that calculates the total output current value by summing the output current values after averaging processing. As described above, for the output current values io1, io2, and io3 after averaging processing in the averaging processing unit 320a, the averaging processing unit 320b, and the averaging processing unit 320c, the total output current value is calculated in the total value calculation unit 320d (step S3). The output current target value calculation unit 320-1 corresponds to the output current target value calculation unit of the present invention. In addition, although omitted in Figure 1 , the output current target value calculation units provided in the first DC-DC converter 11 and the second DC-DC converter 21 correspond to the output current target value calculation unit of the present invention.

[0079] In addition, the output current target value calculation unit 320-1 includes an allocation method determination unit 320e that allocates the total output current value to calculate the output current target values Io1ref, Io2ref, and Io3ref of the DC-DC converters 11, 21, and 31. As a method for allocating the total output current value to calculate the output current target values Io1ref, Io2ref, and Io3ref of the DC-DC converters 11, 21, and 31, various methods can be adopted. In the allocation method determination unit 320e, as exemplified below, coefficients k1, k2, and k3 for allocating the total output current value are determined by multiplying the total output current value respectively (step S4). Here, the output current target values Io1ref and Io2ref also correspond to the output current target values of the present invention.

[0080] (1) Based on the power capacity ratio of each converter, allocate the total output current value to determine the output current target value.

[0081] When the power capacities of the first DC-DC converter 11, the second DC-DC converter 21, and the third DC-DC converter 31 are set to P1, P2, and P3 respectively,

[0082] k1 = P1 / (P1 + P2 + P3),

[0083] k2 = P2 / (P1 + P2 + P3),

[0084] k3 = P3 / (P1 + P2 + P3).

[0085] (2) Based on the efficiency ratio of each converter, allocate the total output current value to determine the output current target value.

[0086] When the efficiencies of the first DC-DC converter 11, the second DC-DC converter 21, and the third DC-DC converter 31 are set to η1, η2, and η3 respectively,

[0087] k1 = η1 / (η1 + η2 + η3),

[0088] k2 = η2 / (η1 + η2 + η3),

[0089] k3 = η3 / (η1 + η2 + η3).

[0090] (3) Based on the charging amount ratio of the storage batteries connected to each converter, allocate the total output current value to determine the output current target value.

[0091] The charging amount of the storage battery is expressed as the capacity of the storage battery × the charging rate. Therefore, when the capacity and charging rate of the storage battery 13 connected to the first DC-DC converter 11 are set to J1 and SOC_1, the capacity and charging rate of the storage battery 23 connected to the second DC-DC converter 21 are set to J2 and SOC_2, and the capacity and charging rate of the storage battery 33 connected to the third DC-DC converter 31 are set to J3 and SOC_3,

[0092] k1 = J1 × SOC_1 / (J1 × SOC_1 + J2 × SOC_2 + J3 × SOC_3),

[0093] k2 = J2 × SOC_2 / (J1 × SOC_1 + J2 × SOC_2 + J3 × SOC_3),

[0094] k3 = J3 × SOC_3 / (J1 × SOC_1 + J2 × SOC_2 + J3 × SOC_3).

[0095] (4) Consider the load state, allocate the total output current value to determine the output current target value.

[0096] In the case of a light load, specifically, when the load is below the maximum power that can be supplied by a part of a plurality of parallel-connected DC-DC converters 11, etc. (hereinafter, the case of the power that can be supplied by one unit is described, but it also includes the case where the number becomes two or more by increasing one unit each time according to the load state), determine the output current value target in such a way that the current is supplied only from one DC-DC converter (for example, the first DC-DC converter 11).

[0097] In this case, considering efficiency and power saving, determine the output current target in such a way as to minimize the operating rate of multiple converters as much as possible.

[0098] (1) When the power capacities of multiple DC-DC converters 11 etc. are different, current is supplied only from the DC-DC converter with the largest power capacity.

[0099] That is, when the DC-DC converter with the largest power capacity is the x-th DC-DC converter (here, x = 1), kx = 1, ka = 0 (Px > Pa, the a-th DC-DC converter is all DC-DC converters other than the x-th DC-DC converter, here, a = 2, 3).

[0100] (2) When the power capacities of multiple DC-DC converters 11 etc. are equal, current is supplied only from the DC-DC converter with the highest efficiency.

[0101] That is, when the DC-DC converter with the highest efficiency is the x-th DC-DC converter (here, x = 1), kx = 1, ka = 0 (Px = Pa and ηx > ηa, the a-th DC-DC converter is all DC-DC converters other than the x-th DC-DC converter, here, a = 2, 3).

[0102] (3) When the DC power supply is a storage battery, current is supplied only from the DC-DC converter with the largest charge amount of the storage battery.

[0103] That is, when the DC-DC converter with the largest charge amount of the connected storage battery is the x-th DC-DC converter (here, x = 1), kx = 1, ka = 0 (Jx × SOC_1 > Ja × SOC_a, the a-th DC-DC converter is all DC-DC converters other than the x-th DC-DC converter, here, a = 2, 3).

[0104] The distribution method for distributing the total output current value to calculate the output current target values Io1ref, Io2ref, and Io3ref of the DC-DC converters 11, 21, and 31 is not limited to the above method. In addition, in the distribution method of (1) above, information on the power capacity or power capacity ratio of each DC-DC converter 11, 21, and 31 can also be obtained and stored in advance, so as to omit the distribution method determination unit 320e and the distribution method determination step (step S4). Similarly, in the distribution method of (2), information on the efficiency or efficiency ratio of each DC-DC converter 11, 21, and 31 can be obtained and stored in advance, so as to omit the distribution method determination unit 320e and the distribution method determination step (step S4). In the distribution method of (3) above, the capacities and charge rates of the storage batteries 13, 23, and 33 can be obtained dynamically, the coefficients k1, k2, and k3 can be calculated, and the obtained values can also be maintained, and the capacities and charge rates of the storage batteries 13, 23, and 33 can be obtained and updated dynamically according to each specified cycle of the output current target value calculation.

[0105] The output current target value calculation unit 320-1 includes a calculation execution unit 320h that calculates the output current target value Io3ref of the third DC-DC converter 31 according to the determined allocation method. In the calculation execution unit 320h, the output current target value Io3ref of the third DC-DC converter 31 is calculated according to the determined allocation method (step S5). Specifically, in the calculation execution unit 320h, the output current target value Io3ref is calculated by multiplying the total output current value by the coefficient k3.

[0106] The first DC-DC converter 11 has the same output current target value calculation unit as the output current target value calculation unit 320-1. In the output current target value calculation unit of the first DC-DC converter 11, in the averaging processing unit, the output current io1 output from the output current detection circuit 14 of the first DC-DC converter, the output current io2 output from the output current detection circuit 24 of the second DC-DC converter and obtained via the second DC-DC converter communication unit 26 and the first DC-DC converter communication unit 16, and the output current io3 output from the output current detection circuit 34 of the third DC-DC converter and obtained via the third DC-DC converter communication unit 36 and the first DC-DC converter communication unit 16 are respectively averaged. In the total value calculation unit, the total output current value is calculated. In the allocation method determination unit, the coefficient k1 for allocating the total output current value is determined. In the calculation execution unit, the total output current value is multiplied by the coefficient k1 to calculate the output current target value Io1ref (step S5), and is output to the first DC-DC converter lateral current target value generator.

[0107] The second DC-DC converter 21 also has an output current target value calculation unit that is the same as the output current target value calculation unit 320-1. In the output current target value calculation unit of the second DC-DC converter 21, in the averaging unit, the output current io1 output from the output current detection circuit 14 of the first DC-DC converter and obtained via the first DC-DC converter communication unit 16 and the second DC-DC converter communication unit 26, the output current io2 output from the output current detection circuit 24 of the second DC-DC converter, and the output current io3 output from the output current detection circuit 34 of the third DC-DC converter and obtained via the third DC-DC converter communication unit 36 and the second DC-DC converter communication unit 26 are respectively averaged. In the total value calculation unit, the total output current value is calculated. In the distribution method determination unit, the coefficient k2 for distributing the total output current value is determined. In the calculation execution unit, the total output current value is multiplied by the coefficient k2 to calculate the output current target value Io2ref (step S5), which is output to the lateral current target value generator of the second DC-DC converter.

[0108] Based on the output current target value Io3ref, the output voltage value vo, and the output current value io3 calculated in the output current target value calculation unit 320-1, the lateral current target value Icr3ref is generated in the lateral current target value generator 323 of the third DC-DC converter (step S6). Although it is omitted in Figure 1 similarly, in the lateral current target value generator of the first DC-DC converter 11, based on the output current target value Io1ref, the output voltage value vo, and the output current value io1, the lateral current target value Icr1ref of the first DC-DC converter 11 is generated (step S6). In the lateral current target value generation unit of the second DC-DC converter, based on the output current target value Io2ref, the output voltage value vo, and the output current value io2, the lateral current target value Icr2ref of the second DC-DC converter 21 is generated (step S6).

[0109] Based on Figure 2 the flowchart description, the output current target values of each converter are repeated at the communication cycle to update the output current target values of each converter. The generation process and update process of the lateral current target value of each converter are not limited to being repeated at the communication cycle, and the update cycle can be appropriately set and adjusted.

[0110] At the summing point 326, the lateral current target value Icr3ref generated in the third DC-DC converter lateral current target value generator 323 is subtracted from the output current value io3 and input to the droop gain multiplier 324. After being multiplied by the droop gain kd3 in the droop gain multiplier 324, it is subtracted from the output voltage target value vo3ref of the third DC-DC converter at the summing point 327. In this way, the value obtained by subtracting the value obtained by multiplying the value obtained by subtracting the lateral current target value Icr3ref from the output current value io3 by the droop gain kd3 from the output voltage target value vo3ref of the third DC-DC converter is subtracted from the output voltage value vo at the summing point 328 and input to the compensator 325. Then, the output voltage vo3 of the third DC-DC converter 31 is controlled based on the command value output from the compensator 325. The value obtained by subtracting the lateral current target value Icr3ref from the output current value io3 (the imaginary output current value described later) io3im corresponds to the corrected output current value of the present invention. The output voltage target value vo3ref of the third DC-DC converter corresponds to the output voltage target value of the present invention. The droop gain multiplier 324 and the summing point 327 correspond to the droop control section of the present invention.

[0111] The third DC-DC converter 31 performs a droop operation to droop the output voltage according to the output current io3. However, the control section 32 of the third DC-DC converter 31 does not multiply the output current value io3 by the droop gain kd3, but as described above, multiplies the value obtained by subtracting the lateral current target value Icr3ref from the output current value io3 by the droop gain kd3. Figure 3 It is a diagram for explaining the principle of the droop control (hereinafter, also referred to as "this droop control") implemented in the control section 32 of the third DC-DC converter 31. Figure 3 It is a graph with the output current value io3 on the horizontal axis and the output voltage value vo on the vertical axis. The straight line with a slope kd3 that slopes downward to the right from the intersection with the vertical axis, i.e., the output voltage target value Vo3ref, is the characteristic line PL of the droop control ( Figure 3 The principle of which holds in common in this droop control. Therefore, in the reference numerals, the "3" indicating the third DC-DC converter 31 is omitted. The output current value io3 detected by the third DC-DC converter output current detection circuit 322 is indicated by the thin line arrow Ar1 parallel to the horizontal axis. The output voltage target value Vo3ref1 corresponds to the intersection point P1 of this arrow Ar1 and the characteristic line PL. In Figure 1 the control system shown, the value obtained by subtracting the lateral current target value Icr3ref indicated by the arrow Ar0 with a single dotted line from the output current value io3 is multiplied by the droop gain kd3. This means that in Figure 3In this case, the value indicated by the thick-line arrow Ar2 parallel to the horizontal axis, which is equal to the value obtained by subtracting the lateral current target value Icr3ref indicated by the arrow Ar0 of the single-dot chain line from the output current value io3, is applied with a droop characteristic to the output current value (imaginary output current value) io3im. At this time, the output voltage target value Vo3ref drops to the output voltage target value Vo3ref2 corresponding to the intersection point P2 of the arrow Ar2 and the characteristic line PL. In this way, in this droop control, the output voltage target value Vo3ref does not droop to the output voltage target value Vo3ref1 under the droop control based on the output current value io3, but droops to the output voltage target value Vo3ref2 under the droop control based on the imaginary output current value io3im. Here, the lateral current target value Icr3ref corresponds to the output current correction value of the present invention, and the imaginary output current value io3im corresponds to the corrected output current value of the present invention.

[0112] Here, an explanation is given for the basis for controlling the output current io3 based on the lateral current target value Icr3ref. Three DC-DC converters are called the n-th unit (n = 1, 2, 3) (in Figure 1 the example, the first DC-DC converter 11 is the 1st unit, the second DC-DC converter 21 is the 2nd unit, and the third DC-DC converter 31 is the 3rd unit). The output voltage target value is set as Voref, the output current of the n-th unit is set as ion, the lateral current target value of the n-th unit is set as Icrnref, the droop gain of the n-th unit is set as kdn, the output voltage detection ratio of the n-th unit is set as αsn, the output current detection ratio of the n-th unit is set as βsn, and the load resistance is set as Ro.

[0113] At this time, in the steady state of the three DC-DC converters, the following equations hold.

[0114] [Equation 1]

[0115]

[0116] [Equation 2]

[0117] V o =R o ·(i o1 +i o2 +i o3 )

[0118] From the above equation, it can be seen that the output current ion can be controlled by the lateral current target value Icrnref. In addition, the description here holds not limited to the case of n = 3.

[0119] By means of such droop control of the present invention, it is possible to appropriately control the output currents of the DC-DC converters 11, 21, and 31 operating in parallel.

[0120] As described with reference to Figure 1 the control system of the third DC-DC converter 31, a lateral current target value Icr3ref is generated based on the output voltage value vo, the output current value io3, and the output current target value Io3ref. The lateral current target value Icr3ref is not limited to this information and may also be generated based on the charge amount (the amount of electric power that can be discharged) of the storage battery 33, the charging rate, and the like. In the case of droop control based on the output current value io3, the output voltage target value droops to Vo2ref1 according to the characteristic line PL, and the third DC-DC converter 31 is subjected to constant voltage control to become this output voltage target value. However, in the present droop control, by using the lateral current target value Icr3ref generated based on the output current target value Io3ref or the like, it is possible to achieve droop control and a control with higher degrees of freedom. The lateral current target value Icr3ref is determined such that the output current io3 increases when the charge amount of the storage battery 33 is large and the output current io3 decreases when the charge amount of the storage battery 33 is small. Thereby, it is possible to evenly distribute the discharge current among the storage batteries and prevent the discharge of a specific storage battery from progressing. In addition, in the case where the PV module is connected to the third DC-DC converter 31 as a DC power source, the lateral current target value Icr3ref can also be determined such that the output current of the third DC-DC converter 31 increases when the generated power of the PV module is large. In this way, by determining the lateral current target value Icr3ref according to the state of the DC power source connected to the third DC-DC converter 31, it is possible to perform droop control on the third DC-DC converter 31 so as to obtain a desired output current io3.

[0121] The simulation results of the output current control of the DC-DC converters 11, 21, and 31 in the DC power supply system 100-1 according to the present embodiment will be described. Figure 4 The simulation results of the comparative example are shown, Figure 5 The simulation results of the present embodiment are shown.

[0122] Here, it is assumed that the capacitances of all the DC-DC converters 11, 21, and 31 are equal, and only the output voltage detection deviation of the first DC-DC converter 11 is -1%, and the load current value io is 30 A. In the comparative example, the case where no output current target value is set for all the DC-DC converters 11, 21, and 31 is shown. In the present embodiment, output current target values Io1ref, Io2ref, and Io3ref obtained by distributing the total output current value based on the above power capacity ratio are set for all the DC-DC converters 11, 21, and 31.Figure 4 and Figure 5 Both have time (seconds) on the horizontal axis. The upper graph shows the output voltage values with voltage (V) on the vertical axis, and the lower graph shows the output current values with current (A) on the vertical axis.

[0123] In Figure 4 the simulation results of the comparative example shown, as shown in the following figure, each of the DC-DC converters 11, 21, and 31 should output 10 A, which is 1 / 3 of the load current value io, as the output current values io1, io2, and io3. However, due to the influence of the output voltage detection deviation of the first DC-DC converter 11, the output current value io1 exceeds 10 A, and the output current values io2 and io3 are less than 10 A. The output currents of the DC-DC converters 11, 21, and 31 are unbalanced. Additionally, in Figure 4 the output current value io2 and the output current value io3 overlap.

[0124] In contrast, in Figure 5 the DC power supply system 100-1 of the present embodiment shown, the imbalance of the output current values io1, io2, and io3 is eliminated, and all the DC-DC converters 11, 21, and 31 output 10 A as the output current values io1, io2, and io3. Furthermore, in Figure 5 the output current value io2 and the output current value io3 overlap.

[0125] Next, the simulation results when the capacitances of all the DC-DC converters 11, 21, and 31 are equal, the output voltage detection deviation of only the first DC-DC converter 11 is -1%, and the load current value io varies between 30 A and 60 A at a period of 0.25 seconds are described. Figure 6 represents the simulation results of the comparative example, Figure 7 represents the simulation results of the present embodiment. Here, the comparative example also represents the case where there is no output current target value for all the DC-DC converters 11, 21, and 31, and the present embodiment represents the case where output current target values io1ref, io2ref, and io3ref are set for all the DC-DC converters 11, 21, and 31 by allocating the total output current value based on the above power capacity ratio. In Figure 6 and Figure 7 both have time (seconds) on the horizontal axis. The upper graph shows the output voltage values with voltage (V) on the vertical axis, and the lower graph shows the output current values with current (A) on the vertical axis.

[0126] In Figure 6In the simulation results shown, as shown in the following figure, regarding the output current that varies due to load changes, the output current values io1 exceed 20 A and 10 A respectively, and the output current values io2 and io3 are lower than 20 A and 10 A respectively, resulting in an imbalance in the output currents of the respective DC-DC converters 11, 21, and 31. In addition, in Figure 6 the output current value io2 and the output current value io3 coincide.

[0127] In contrast, in Figure 7 the present embodiment shown, the imbalance in the output current values io1, io2, and io3 is eliminated, and all the DC-DC converters 11, 21, and 31 output 20 A or 10 A as the output current values io1, io2, and io3 according to load changes. In addition, in Figure 7 the output current value io2 and the output current value io3 coincide.

[0128] In this way, in the DC power supply system 100-1 including a plurality of DC-DC converters 11, 21, and 31 that perform the present droop control for setting the output current target value, the lateral current target value can be adjusted so that the output voltage converges within the set range. Figure 8 is a flowchart showing the steps of the lateral current target value adjustment process. Here, each of the DC-DC converters 11, 21, and 31 executes the process shown in the flowchart shown in Figure 8 When taking the third DC-DC converter 31 as an example, the process is performed when the third DC-DC converter lateral current target value generator 323 in the control unit 32 generates the lateral current target value Icr3ref. In this lateral current target value adjustment process, each of the DC-DC converters 11, 21, and 31 performs processing based on the output voltage and output current that can be measured by itself. The set range of the output voltage (including the minimum voltage value) and the set range of the output current (including the maximum current value and the minimum current value) described later are determined according to the specifications of the DC-DC converters 11, 21, and 31 respectively connected to the storage batteries 13, 23, and 33. Hereinafter, the lateral current target value adjustment process in the control unit 32 will be described as an example. In addition, this lateral current target value adjustment process can also be applied in the same way in the following modification examples 1 and 2, embodiment 2, modification examples 1 and 2 of embodiment 2, and other modification examples.

[0129] First, the control unit 32 determines whether the detected output voltage value vo is within the set range (step S11). Here, the set range of the output voltage value vo corresponds to the specified output voltage range of the present invention, and whether the output voltage value vo is within the set range and whether it is less than the minimum voltage described later correspond to the relationship between the output voltage value of the present invention and the specified voltage value range.

[0130] When it is determined in step S11 that the output voltage value vo is within the set range, the control unit 32 determines whether the detected output current value io3 is within the set range (step S12). The set range of the output current value io3 corresponds to the specified output current range of the present invention. Whether the output current value io3 described later is within the set range, whether it is greater than the maximum current value described later, and whether it is less than the minimum current value correspond to the relationship between the output current value and the specified current value range of the present invention.

[0131] When it is determined in step S11 that the output voltage value vo is not within the set range, the control unit 32 determines whether the output voltage value vo is less than the minimum voltage value (step S13).

[0132] When it is determined in step S12 that the output current value io3 is within the set range, the control unit 32 determines whether the output current value io3 is greater than the output current target value Io3ref (step S14).

[0133] When it is determined in step S14 that the output current value io3 is greater than the output current target value Io3ref, the control unit 32 increases the lateral current target value Icr3ref (step S15) and ends the process.

[0134] When it is determined in step S14 that the output current value io3 is less than or equal to the output current target value Io3ref, the control unit 32 decreases the lateral current target value Icr3ref (step S16) and ends the process.

[0135] When it is determined in step S13 that the output voltage value vo is less than the minimum voltage value, the control unit 32 determines whether the output current value io3 is greater than the maximum current value (step S17).

[0136] When it is determined in step S17 that the output current value io3 is greater than the maximum current value, the control unit 32 increases the lateral current target value Icr3ref (step S18) and ends the process.

[0137] When it is determined in step S17 that the output current value io3 is less than or equal to the maximum current value, the control unit 32 decreases the lateral current target value Icr3ref (step S19) and ends the process.

[0138] When it is determined in step S13 that the output voltage value vo is greater than or equal to the minimum voltage value, the control unit 32 determines whether the output current value io3 is less than the minimum current value (step S20).

[0139] When it is determined in step S20 that the output current value io3 is less than the minimum current value, the control unit 32 decreases the lateral current target value Icr3ref (step S21) and ends the process.

[0140] When it is determined in step S20 that the output current value io3 is equal to or greater than the minimum current value, the control unit 32 increases the lateral current target value Icr3ref (step S22) and ends the process.

[0141] According to the above algorithm, by giving play to the characteristics of droop control, when the output voltage is at the upper limit value or the lower limit value of the set range, it is determined that the current supply is too small or too large. By adjusting the lateral current target value, a balanced state that is different from but approximate to the output current target value can be achieved.

[0142] In this way, in the DC power supply system 100-1 of this embodiment, according to the lateral current target values generated based on the output current target values Io1ref, Io2ref, and Io3ref, droop control is performed in each of the DC-DC converters 11, 21, and 31. Thus, the output currents io1, io2, and io3 of the respective DC-DC converters 11, 21, and 31 can be appropriately controlled, and the imbalance of the output currents can be suppressed. The output current target values Io1ref, Io2ref, and Io3ref are calculated by distributing the total output current corresponding to the load current value io according to a specified distribution method.

[0143] In the above-described Embodiment 1, in each of the DC-DC converters 11, 21, and 31, the total output current value is calculated after averaging the detected output current values io1, io2, and io3, respectively. However, a load current detection circuit for detecting the load current io may be provided, and the load current value io may be distributed according to the same distribution method in place of the total output current value, and the output current target values Io1ref, Io2ref, and Io3ref may be calculated. In this case, the output current target value calculation unit 320-1 has a load current acquisition unit that acquires the load current value from the load current detection circuit in place of the averaging processing units 320a, 320b, 320c, and the total value calculation unit 320d (the same modification can also be made to Embodiment 2 described below).

[0144] (Modification Example 1)

[0145] Hereinafter, with reference to Figure 9 , a DC power supply system 100-2 according to Modification Example 1 of Embodiment 1 will be described. The same reference numerals are given to the same structures as those of the DC power supply system 100-1 of Embodiment 1, and the description thereof is omitted.

[0146] In the DC power supply system 100-1 of the above-described Embodiment 1, the output current target value calculation unit 320 is provided in the control units of the first DC-DC converter 11, the second DC-DC converter 21, and the third DC-DC converter 31. However, the output current target value calculation unit 320 may be provided outside each control unit. Figure 9 Fig. shows a schematic configuration of a DC power supply system 100-2 according to Modification 1 of Embodiment 1. The DC power supply system 100-2 is the same as the DC power supply system 100-1 of Embodiment 1, except that output current target values Io1ref, Io2ref, and Io3ref are provided from an external device 400-1. The same reference numerals are given to the structures common to the DC power supply system 100-1, and the description thereof is omitted.

[0147] As Figure 9 shown, in the DC power supply system 100-2 according to Modification 1 of Embodiment 1, the output current target value calculation unit 420-1 is provided not in the control units of the respective DC-DC converters but in the external device 400-1. In Figure 9 , only the structure related to the output current target value calculation in the external device 400-1 is shown. The external device 400-1 may be any device that is communicably connected to the first DC-DC converter 11-2, the second DC-DC converter 21-2, and the third DC-DC converter 31-2 via the external communication unit 46, and its structure and function are not particularly limited. Here, the DC power supply system 100-2 corresponds to the DC power supply system of the present invention, the first DC-DC converter 11-2, the second DC-DC converter 21-2, and the third DC-DC converter 31-2 correspond to the plurality of power conversion devices of the present invention, and each corresponds to the power conversion device of the present invention. In addition, when the third DC-DC converter 31-2 corresponds to the power conversion device of the present invention, the first DC-DC converter 11-2 and the second DC-DC converter 21-2 correspond to the other power conversion devices of the present invention. The control unit 32-2 corresponds to the control unit of the present invention. The control units of the first DC-DC converter 11-2 and the second DC-DC converter 21-2 also correspond to the control unit of the present invention. In addition, the output current target value calculation unit 420-1 corresponds to the output current target value calculation unit of the present invention.

[0148] In the external device 400-1, the output current io1 output from the output current detection circuit 14 of the first DC-DC converter is obtained via the first DC-DC converter communication unit 16 and the external communication unit 46, the output current io2 output from the output current detection circuit 24 of the second DC-DC converter is obtained via the second DC-DC converter communication unit 26 and the external communication unit 46, and the output current io3 output from the output current detection circuit 34 of the third DC-DC converter is obtained via the third DC-DC converter communication unit 36 and the external communication unit 46. The functions of the average processing unit 420a, the average processing unit 420b, the average processing unit 420c, the total value calculation unit 420d, the allocation method determination unit 420e, and the calculation execution unit 420h of the output current target value calculation unit 420-1 are the same as those of the average processing unit 320a, the average processing unit 320b, the average processing unit 320c, the total value calculation unit 320d, the allocation method determination unit 320e, and the calculation execution unit 320h of the output current target value calculation unit 320-1 in the first embodiment. Here, the output current total value is multiplied by the coefficient k1 and the coefficient k2 determined by the allocation method determination unit 420e in the calculation execution unit 420f and the calculation execution unit 420g respectively, and the output current target value Io1ref and the output current target value Io2ref are calculated respectively.

[0149] The output current target value Io1ref, the output current target value Io2ref, and the output current target value Io3ref calculated by the output current target value calculation unit 420-1 are input to the first DC-DC converter lateral current target value generator, the second DC-DC converter lateral current target value generator, and the third DC-DC converter lateral current target value generator 323 via the external communication unit 46, the first DC-DC converter communication unit 16, the second DC-DC converter communication unit 26, and the third DC-DC converter communication unit 36 respectively.

[0150] In this way, in the DC power supply system 100-2 of the first modified example, according to the lateral current target values generated based on the output current target values Io1ref, Io2ref, and Io3ref, droop control is performed in each of the DC-DC converters 11-2, 21-2, and 31-2. Thus, the output currents io1, io2, and io3 of the respective DC-DC converters 11-2, 21-2, and 31-2 can be appropriately controlled, and the imbalance of the output currents can be suppressed. The output current target values Io1ref, Io2ref, and Io3ref are calculated by allocating the output current total value corresponding to the load current value io according to a specified allocation method.

[0151] (Second Modified Example)

[0152] Hereinafter, referring toFigure 10 This section describes the DC power supply system 100-3, which is a modified example 2 of Example 1. For the same structures as those in the DC power supply system 100-1 of Example 1, the same reference numerals are used and the descriptions are omitted. In the DC power supply system 100-1 of the above Example 1, the output current target value calculation unit 320 is provided in the control units of the first DC-DC converter 11, the second DC-DC converter 21, and the third DC-DC converter 31. However, the output current target value calculation unit 320 can also be provided in the control unit of any DC-DC converter. Here, an example in which the output current target value calculation unit 320-2 is provided in the control unit 32-3 of the third DC-DC converter 31-3 is described. However, the output current target value calculation unit can also be provided in either the first DC-DC converter 11-3 or the second DC-DC converter 21-3.

[0153] In the output current target value calculation unit 320-2, the output current target value Io1ref of the first DC-DC converter 11, the output current target value Io2ref of the second DC-DC converter 21, and the output current target value Io3ref of the third DC-DC converter 31 are calculated based on the output current value io1, the output current value io2, and the output current value io3. The output current target value calculation unit 320-2 corresponds to the output current target value calculation unit of the present invention.

[0154] The structures of the average processing unit 320a, the average processing unit 320b, the average processing unit 320c, the total value calculation unit 320d, the distribution method determination unit 320e, and the calculation execution unit 320h of the output current target value calculation unit 320-2 are the same as those in Example 1. The output current target value calculation unit 320-2 also multiplies the output current total value by the coefficient k1 and the coefficient k2 determined by the distribution method determination unit 320e in the calculation execution unit 320f and the calculation execution unit 320g, respectively, to calculate the output current target value Io1ref and the output current target value Io2ref, respectively.

[0155] The output current target values Io1ref and Io2ref calculated by the output current target value calculation unit 320-2 are respectively input to the first DC-DC converter lateral current target value generator and the second DC-DC converter lateral current target value generator via the third DC-DC converter communication unit 36, the first DC-DC converter communication unit 16, and the second DC-DC converter communication unit 26. The output current target value Io3ref calculated by the output current target value calculation unit 320-2 is input to the third DC-DC converter lateral current target value generator 323. The processing of the input output current target values Io1ref, Io2ref, and Io3ref is the same as that in the first embodiment, and thus the description thereof is omitted. Here, the DC power supply system 100-3 corresponds to the DC power supply system of the present invention, the first DC-DC converter 11-3, the second DC-DC converter 21-3, and the third DC-DC converter 31-3 correspond to the plurality of power conversion devices of the present invention, and each corresponds to the power conversion device of the present invention. In addition, when the third DC-DC converter 31-3 is considered to correspond to the power conversion device of the present invention, the first DC-DC converter 11-3 and the second DC-DC converter 21-3 correspond to the other power conversion devices of the present invention. The control unit 32-3 corresponds to the control unit of the present invention. In addition, the control units of the first DC-DC converter 11-2 and the second DC-DC converter 21-2 also correspond to the control unit of the present invention. In addition, the output current target value calculation unit 320-3 corresponds to the output current target value calculation unit of the present invention.

[0156] Thus, in the DC power supply system 100-3 of this modification 2, droop control is performed in each of the DC-DC converters 11-3, 21-3, and 31-3 according to the lateral current target values generated based on the output current target values Io1ref, Io2ref, and Io3ref. As a result, the output currents io1, io2, and io3 of the respective DC-DC converters 11-3, 21-3, and 31-3 can be appropriately controlled, and the imbalance of the output currents can be suppressed. The output current target values Io1ref, Io2ref, and Io3ref are calculated by distributing the total output current corresponding to the load current value io according to a specified distribution method.

[0157] (Second Embodiment)

[0158] Hereinafter, the DC power supply system 200-1 of the second embodiment of the present invention will be described. Figure 11FIG. 0 is a diagram showing a schematic configuration of a first DC-DC converter 11-4, a second DC-DC converter 21-4, a third DC-DC converter 31-4, and a control unit 32-4 of the DC power supply system 200-1 according to Embodiment 2 of the present invention. For the structures common to Embodiment 1, the same reference numerals are used and detailed descriptions thereof are omitted.

[0159] Similar to the DC power supply system 100-1 of Embodiment 1, the DC power supply system 200-1 sets output current target values Io2ref and Io3ref for the second DC-DC converter 21-4 and the third DC-DC converter 31-4, and does not set an output current target value Io1ref for the first DC-DC converter 11-4.

[0160] Therefore, the block structure of the output current target value calculation unit 320-4 is also different from that of the output current target value calculation unit 320-1. In the output current target value calculation unit 320-4, output current values io1, io2, and io3 are obtained from the respective DC-DC converters 11-4, 21-4, and 31-4, average processing is performed in the average processing units 320a, 320b, and 320c, and they are totaled in the total value calculation unit 320d, which is the same as the output current target value calculation unit 320-1 of Embodiment 1. In the output current target value calculation unit 320-4, only the coefficient for calculating the output current target value Io3ref is determined by the allocation method determined in the allocation method determination unit 320e. For example, k3 = P3 / (P1 + P2 + P3) is calculated by the method of allocating the total output current value according to the power capacity ratio of the respective DC-DC converters 11, 21, and 31 described for Embodiment 1. Then, the total output current value is multiplied by the coefficient k3 in the calculation execution unit 320h to calculate the output current target value Io3ref. Although omitted in Figure 11 the second DC-DC converter 21 also has an output current target value calculation unit, which has the same structure as the output current target value calculation unit 320-4 except for the calculation execution unit 320h. In the output current target value calculation unit of the second DC-DC converter 21, only the coefficient for calculating the output current target value Io2ref is determined by the allocation method determined in the allocation method determination unit 320e. For example, k2 = P2 / (P1 + P2 + P3) is calculated by the method of allocating the total output current value according to the power capacity ratio of the respective DC-DC converters 11, 21, and 31 described for Embodiment 1. Then, the total output current value is multiplied by the coefficient k2 in the calculation execution unit 320g to calculate the output current target value Io2ref.

[0161] Here, the first DC-DC converter 11-4 corresponds to the second power conversion device of the present invention, and the second DC-DC converter 21-4 and the third DC-DC converter 31-4 correspond to multiple first power conversion devices of the present invention. Additionally, the storage batteries 23 and 33 correspond to the first DC power source of the present invention, and the storage battery 13 corresponds to one or more second DC power sources of the present invention. Moreover, the output current detection circuit 24 of the second DC-DC converter and the output current detection circuit 34 of the third DC-DC converter correspond to the first output current value acquisition unit of the present invention, and the output current detection circuit 14 of the first DC-DC converter corresponds to the second output current value acquisition unit of the present invention. Also, the output currents (values) io2 and io3 correspond to the first output current (value) of the present invention, and the output current value io1 corresponds to the second output current value (value) of the present invention. Further, the output voltage detection circuit 35 and the corresponding structure of the second DC-DC converter 21-4 correspond to the first output voltage value acquisition unit of the present invention, and the structure of the first DC-DC converter 11-4 that is equivalent to the output voltage detection circuit 35 corresponds to the second output voltage value acquisition unit of the present invention. Additionally, the output voltage value vo corresponds to the first output voltage value and the second output voltage value of the present invention. Also, the control unit 32 and the corresponding structure of the second DC-DC converter 21-4 correspond to the first control unit of the present invention, and the structure of the first DC-DC converter 11-4 that is equivalent to the control unit corresponds to the second control unit of the present invention. Moreover, the output current target values Io2ref and Io3ref correspond to the first output current target value of the present invention. Additionally, the droop gain multiplier 324, the summing point 327, and the corresponding structures of the second DC-DC converter 21-4 correspond to the first droop control unit of the present invention, and the structures of the first DC-DC converter 11-4 that are corresponding to the droop gain multiplier 324 and the summing point 327 correspond to the second droop control unit of the present invention. The cross-current target values Icr3ref and Icr2ref correspond to the first output current correction value of the present invention. The value obtained by subtracting the cross-current target value Icr3ref from the output current value io3 (imaginary output current value io3im) and the value obtained by subtracting the cross-current target value Icr2ref from the output current value io2 (imaginary output current value io2im) correspond to the first corrected output current value of the present invention. Furthermore, the output voltage target values vo2ref and vo3ref correspond to the first output voltage target value of the present invention, and the output voltage target value vo1ref corresponds to the second output voltage target value of the present invention.

[0162] The output current target value Io3ref calculated in the output current target value calculation unit 320-4 is input to the third DC-DC converter lateral current target value generator 323. Similarly, the output current target value Io2ref calculated in the output current target value calculation unit of the second DC-DC converter 21 is input to the lateral current target value generator of the second DC-DC converter 21. In the second DC-DC converter 21-4 and the third DC-DC converter 31-4, the same droop control as in Embodiment 1 is performed.

[0163] When referring to Figure 11 the structure of the first DC-DC converter 11-4 that does not set the output current target value Io1ref in the structure description of the third DC-DC converter 31-4 in, the first DC-DC converter 11-4 does not include structures equivalent to the third DC-DC converter lateral current target value generator 323 and the superimposition point 236 (nor does it include a structure equivalent to the output current target value calculation unit 320-4). The output voltage value vo output from the structure equivalent to the output voltage detection circuit 35 is only input to the structure equivalent to the superimposition point 328. In addition, the output current value io1 output from the structure equivalent to the third DC-DC converter output current detection circuit 34 (the first DC-DC converter output current detection circuit 14) is directly multiplied by the droop gain kd1 and input to the structure equivalent to the superimposition point 327 without passing through the structure equivalent to the superimposition point 326. The first DC-DC converter 11-4 has the same structure for the structures equivalent to the superimposition points 327, 328, and the compensator 325.

[0164] The simulation results of the output current control of each DC-DC converter 11-4, 21-4, and 31-4 in the DC power supply system 200-1 of Embodiment 2 will be described. Figure 12 The simulation results of the comparative example are shown, Figure 11 The simulation results of this Embodiment 2 are shown. The structure of the chart showing the simulation results is the same as that of Embodiment 1, so the description is omitted.

[0165] Here, it is assumed that the capacitances of all the DC-DC converters 11-4, 21-4, and 31-4 are equal, the output voltage detection deviation of only the first DC-DC converter 11-4 is -1%, and the load current value io is 30 A. The comparative example shows the case where no output current target value is set for all the DC-DC converters 11-4, 21-4, and 31-4. This embodiment shows the following case: for the first DC-DC converter 11-4, no output current target value is set, and for the second DC-DC converter 21-4 and the third DC-DC converter 31-4, output current target values Io1ref, Io2ref, and Io3ref are set by allocating the total output current value based on the above power capacity ratio.

[0166] In Figure 12 the simulation results of the comparative example shown in the figure below, as shown in the following figure, each of the DC-DC converters 11-4, 21-4, and 31-4 should output 1 / 3 of the load current value io, that is, 10 A, as the output current values io1, io2, and io3. However, due to the influence of the output voltage detection deviation of the first DC-DC converter 11-4, the output current value io1 exceeds 10 A, and the output current values io2 and io3 are less than 10 A, and the output current values io1, io2, and io3 of each of the DC-DC converters 11-4, 21-4, and 31-4 become unbalanced. In addition, in Figure 12 the output current value io2 and the output current value io3 overlap.

[0167] In contrast, in Figure 11 the DC power supply system 200-2 of Embodiment 2 shown in the figure below, initially, an imbalance occurs in the output current values io1, io2, and io3, but after a certain period of time, the imbalance in the output current values io1, io2, and io3 is eliminated, and all the DC-DC converters 11-4, 21-4, and 31-4 output 10 A as the output current values io1, io2, and io3. In addition, in Figure 11 the output current value io2 and the output current value io3 overlap.

[0168] Next, the simulation results when the capacitances of all the DC-DC converters 11-4, 21-4, and 31-4 are equal, the output voltage detection deviation of only the first DC-DC converter 11 is -1%, and the load current value io changes between 30 A and 60 A at a period of 0.25 seconds are described. Figure 12 The simulation results representing the comparative example Figure 15Shows the simulation results of the DC power supply system 200 of Embodiment 2. Here, the comparative example also shows the case where there is no output current target value for all the DC-DC converters 11-4, 21-4, and 31-4. This embodiment shows the following situation: for the first DC-DC converter 11-4, no output current target value is set, and for the second DC-DC converter 21-4 and the third DC-DC converter 31-4, output current target values io2ref and io3ref are set, which are obtained by allocating the total output current value based on the above power capacity ratio.

[0169] In Figure 12 the shown simulation results, as shown in the following figure, for the output current that varies due to load changes, the output current values io1 also exceed 20A and 10A respectively. In contrast, the output current values io2 and io3 are respectively lower than 20A and 10A, resulting in an imbalance in the output currents of the respective DC-DC converters 11-4, 21-4, and 31-4. In addition, in Figure 12 the output current value io2 and the output current value io3 coincide.

[0170] In contrast, in Figure 15 the DC power supply system 200 of Embodiment 2 shown, the imbalance in the output current values io1, io2, and io3 is eliminated, and all the DC-DC converters 11-4, 21-4, and 31-4 output 20A or 10A as the output current values io1, io2, and io3 according to the load change. In addition, in Figure 15 the output current value io2 and the output current value io3 coincide.

[0171] In this way, in the DC power supply system 200 of Embodiment 2, according to the lateral current target value generated based on the output current target values Io2ref and Io3ref, droop control is performed in the second DC-DC converter 21-4 and the third DC-DC converter 31-4. Thus, even when parallel operation is performed including the first DC-DC converter 11-4 that performs droop control without setting an output current target value, the output currents io1, io2, and io3 of the respective DC-DC converters 11-4, 21-4, and 31-4 can be appropriately controlled, and the imbalance in the output current can be suppressed. The output current target values Io2ref and Io3ref are calculated by allocating the total output current value corresponding to the load current value io according to a specified allocation method.

[0172] As a method for determining the DC-DC converter (the first DC-DC converter 11 in this Embodiment 2) that does not set an output current target value in the DC power supply system, for example, it can be determined based on the amount of electric power that can be supplied to the load as follows.

[0173] (1) When the power capacities of multiple DC-DC converters 11-4 etc. are different, the output current target value is not set for the DC-DC converter with the largest power capacity.

[0174] (2) When the power capacities of multiple DC-DC converters 11-4 etc. are equal, the output current target value is not set for the DC-DC converter with the highest efficiency.

[0175] (3) When the DC power supply is a storage battery, the output current target value is not set for the DC-DC converter with the highest charging efficiency of the storage battery capacity.

[0176] The method for determining the DC-DC converter for which the output current target value is not set is not limited to the above examples.

[0177] (Variant Example 1)

[0178] In the DC power supply system 200-1 of the above-described Embodiment 2, the output current target value calculation unit 320-4 is provided in the control unit 32-4 of the third DC-DC converter 31-4, and the output current target value calculation unit with the same structure is provided in the control unit of the second DC-DC converter 21. However, it may also be provided outside these control units. Figure 16 Schematic structure of the DC power supply system 200-2 showing Variant Example 1 of Embodiment 2. The DC power supply system 200-2 is the same as the DC power supply system 200-1 of Embodiment 2 except that the output current target values Io2ref and Io3ref are provided from the external device 400-2 respectively. For the structures common to the DC power supply system 200-1, the same reference numerals are given and the description is omitted.

[0179] As Figure 16 shown, in the DC power supply system 200-2 of Variant Example 1 of Embodiment 2, the output current target value calculation unit 420-2 is not provided in the control unit 32-6 of the third DC-DC converter 31-6 and the control unit of the second DC-DC converter 21, but is provided in the external device 400-2. In Figure 16 it, only the structure related to the output current target value calculation in the external device 400-2 is shown. The external device 400-2 may be any device that is communicably connected to the first DC-DC converter 11-3, the second DC-DC converter 21-3, and the third DC-DC converter 31-3 via the external communication unit 46, and its structure and function are not particularly limited.

[0180] In the external device 400-2, the output current io1 output from the output current detection circuit 14 of the first DC-DC converter is obtained via the first DC-DC converter communication unit 16 and the external communication unit 46, the output current io2 output from the output current detection circuit 24 of the second DC-DC converter is obtained via the second DC-DC converter communication unit 26 and the external communication unit 46, and the output current io3 output from the output current detection circuit 34 of the third DC-DC converter is obtained via the third DC-DC converter communication unit 36 and the external communication unit 46. The functions of the average processing unit 420a, the average processing unit 420b, the average processing unit 420c, the total value calculation unit 420d, the distribution method determination unit 420e, and the calculation execution unit 420h of the output current target value calculation unit 420-2 are the same as those of the average processing unit 420a, the average processing unit 420b, the average processing unit 420c, the total value calculation unit 420d, the distribution method determination unit 420e, and the calculation execution units 420g and 420h of the output current target value calculation unit 420-1 in the first modification of the first embodiment. However, the output current target value calculation unit 420-2 does not have the calculation execution unit 420f for calculating the output current target value Io1ref of the first DC-DC converter 11 and does not output the output current target value Io1ref.

[0181] Here, the first DC-DC converter 11-4 corresponds to the second power conversion device of the present invention, and the second DC-DC converter 21-6 and the third DC-DC converter 31-6 correspond to multiple first power conversion devices of the present invention. Additionally, the output current detection circuit 24 of the second DC-DC converter and the output current detection circuit 34 of the third DC-DC converter correspond to the first output current value acquisition unit of the present invention, and the output current detection circuit 14 of the first DC-DC converter corresponds to the second output current value acquisition unit of the present invention. Also, the output currents (values) io2 and io3 correspond to the first output current (value) of the present invention, and the output current value io1 corresponds to the second output current value (value) of the present invention. Further, the output voltage detection circuit 35 and the corresponding structure of the second DC-DC converter 21-6 correspond to the first output voltage value acquisition unit of the present invention, and the structure of the first DC-DC converter 11-4 that is equivalent to the output voltage detection circuit 35 corresponds to the second output voltage value acquisition unit of the present invention. Moreover, the output voltage value vo corresponds to the first output voltage value and the second output voltage value of the present invention. Additionally, the control unit 32-5 and the corresponding structure of the second DC-DC converter 21-6 correspond to the first control unit of the present invention, and the structure of the first DC-DC converter 11-4 that is equivalent to the control unit corresponds to the second control unit of the present invention. Also, the output current target values Io2ref and Io3ref correspond to the first output current target value of the present invention. Further, the droop gain multiplier 324, the summing point 327, and the corresponding structures of the second DC-DC converter 21-4 correspond to the first droop control unit of the present invention, and the structures of the first DC-DC converter 11-4 that correspond to the droop gain multiplier 324 and the summing point 327 correspond to the second droop control unit of the present invention. The lateral current target values Icr3ref and Icr2ref correspond to the first output current correction value of the present invention. The value obtained by subtracting the lateral current target value Icr3ref from the output current value io3 (imaginary output current value io3im) and the value obtained by subtracting the lateral current target value Icr2ref from the output current value io2 (imaginary output current value io2im) correspond to the first corrected output current value of the present invention. Additionally, the output voltage target values vo2ref and vo3ref correspond to the first output voltage target value of the present invention, and the output voltage target value vo1ref corresponds to the second output voltage target value of the present invention.

[0182] The output current target values Io2ref and Io3ref calculated by the output current target value calculation unit 420-2 are respectively input to the second DC-DC converter lateral current target value generator and the third DC-DC converter lateral current target value generator 323 via the external communication unit 46, the second DC-DC converter communication unit 26, and the third DC-DC converter communication unit 36.

[0183] In this way, in the DC power supply system 200-3 of the second modification example, droop control is performed in the second DC-DC converter 21-6 and the third DC-DC converter 31-6 according to the lateral current target values generated based on the output current target values Io2ref and Io3ref. Thus, even when parallel operation is performed including the first DC-DC converter 11-4 that performs droop control without setting an output current target value, the output currents io1, io2, and io3 of the respective DC-DC converters 11-4, 21-6, and 31-6 can be appropriately controlled, and the imbalance of the output currents can be suppressed. The output current target values Io2ref and Io3ref are calculated by distributing the total output current corresponding to the load current value io according to a prescribed distribution method.

[0184] (Second Modification Example)

[0185] Hereinafter, with reference to Figure 17 , the DC power supply system 200-2 of the second modification example of the second embodiment will be described. For the same structure as the DC power supply system 200-1 of the second embodiment, the same reference numerals are given and the description is omitted.

[0186] In the DC power supply system 200-1 of the second embodiment described above, the output current target value calculation unit 320-2 is provided in the third DC-DC converter 31-2, and an output current target value calculation unit having the same structure is provided in the second DC-DC converter 21.

[0187] In this way, the output current target value calculation unit can be provided only in the third DC-DC converter 31, rather than being provided in the second DC-DC converter 21 and the third DC-DC converter 31 respectively. Figure 17 The schematic structure of the DC power supply system 200-3 of the second modification example of the second embodiment is shown. The output current target value Io2ref of the second DC-DC converter 21 calculated in the output current target value calculation unit 320-6 is input to the second DC-DC converter lateral current target value generator from the third DC-DC converter communication unit 36 via the second DC-DC converter communication unit 26. Then, the output current target value Io3ref of the third DC-DC converter 31-2 is input to the third DC-DC converter lateral current target value generator 323.

[0188] In the output current target value calculation unit 320-6 of Modification 2, for the output current values io1, io2, and io3 obtained by performing averaging processing in the averaging processing unit 320c, the averaging processing unit 320b, and the averaging processing unit 320c, the output current total value is calculated in the total value calculation unit 320d. In the allocation method determination unit 320e, the coefficient k3 for allocating the output current total value is determined by multiplying it with the output current total value, and the output current target value Io3ref calculated in the calculation execution unit 320h is output to the third DC-DC converter lateral current target value generator 323. Similarly, in the allocation method determination unit 320e, the coefficient k2 for allocating the output current total value is determined by multiplying it with the output current total value, and the output current target value Io2ref calculated in the calculation execution unit 320g is output to the lateral current target value generator of the second DC-DC converter 21-6 via the third DC-DC converter communication unit 36 and the second DC-DC converter communication unit 26.

[0189] Here, the first DC-DC converter 11-4 corresponds to the second power conversion device of the present invention, and the second DC-DC converter 21-6 and the third DC-DC converter 31-6 correspond to multiple first power conversion devices of the present invention. The output current detection circuit 24 of the second DC-DC converter and the output current detection circuit 34 of the third DC-DC converter correspond to the first output current value acquisition unit of the present invention, and the output current detection circuit 14 of the first DC-DC converter corresponds to the second output current value acquisition unit of the present invention. In addition, the output currents (values) io2 and io3 correspond to the first output current (value) of the present invention, and the output current value io1 corresponds to the second output current value (value) of the present invention. In addition, the output voltage detection circuit 35 and the corresponding structure of the second DC-DC converter 21-6 correspond to the first output voltage value acquisition unit of the present invention, and the structure of the first DC-DC converter 11-4 that is equivalent to the output voltage detection circuit 35 corresponds to the second output voltage value acquisition unit of the present invention. In addition, the output voltage value vo corresponds to the first output voltage value and the second output voltage value of the present invention. In addition, the control unit 32-6 and the corresponding structure of the second DC-DC converter 21-6 correspond to the first control unit of the present invention, and the structure of the first DC-DC converter 11-4 that is equivalent to the control unit corresponds to the second control unit of the present invention. In addition, the output current target values Io2ref and Io3ref correspond to the first output current target value of the present invention. In addition, the droop gain multiplier 324, the summing point 327, and the corresponding structures of the second DC-DC converter 21-6 correspond to the first droop control unit of the present invention, and the structures of the first DC-DC converter 11-4 that correspond to the droop gain multiplier 324 and the summing point 327 correspond to the second droop control unit of the present invention. The lateral current target values Icr3ref and Icr2ref correspond to the first output current correction value of the present invention. The value obtained by subtracting the lateral current target value Icr3ref from the output current value io3 (imaginary output current value io3im) and the value obtained by subtracting the lateral current target value Icr2ref from the output current value io2 (imaginary output current value io2im) correspond to the first corrected output current value of the present invention. In addition, the output voltage target values vo2ref and vo3ref correspond to the first output voltage target value of the present invention, and the output voltage target value vo1ref corresponds to the second output voltage target value of the present invention.

[0190] Thus, in the DC power supply system 200-3 of this second modification example, droop control is performed in the second DC-DC converter 21-6 and the third DC-DC converter 31-6 according to the lateral current target value generated based on the output current target values Io2ref and Io3ref. Thereby, even when parallel operation is performed including the first DC-DC converter 11-4 that performs droop control with an un-set output current target value, the output currents io1, io2, and io3 of the respective DC-DC converters 11-4, 21-6, and 31-6 can be appropriately controlled, and the imbalance of the output currents can be suppressed. The output current target values Io2ref and Io3ref are calculated by distributing the total output current corresponding to the load current value io according to a prescribed distribution method.

[0191] (Other modification examples)

[0192] Hereinafter, a DC power supply system 300 according to another modification example of the present invention will be described. Figure 18 FIG. is a diagram showing a schematic configuration of a first DC-DC converter 11-7, a second DC-DC converter 21-7, a third DC-DC converter 31-7, and a control unit 32-7 that constitute the DC power supply system 300 according to the modification example of the present invention. For the structures common to those in the first embodiment, the same reference numerals are used and detailed descriptions thereof are omitted. This modification example can be applied not only to the first embodiment but also to the first and second modification examples of the first embodiment, the second embodiment, and the first and second modification examples of the second embodiment in the same manner.

[0193] In the DC power supply system 300, the first DC-DC converter 11-7, the second DC-DC converter 21-7, and the third DC-DC converter 31-7 are connected in parallel with respect to the connection point CP, and loads such as the first load 3-1, the second load 3-2, and the third load 3-3 are connected in a distributed manner. The first load 3-1 is connected to the output line PwL1, the second load 3-2 is connected to the output line PwL2, and the third load 3-3 is connected to the output line PwL3. Moreover, the output line PwL1, the output line PwL2, and the output line PwL3 are respectively connected to the connection point CP. In the DC power supply system 300 to which such distributed first load 3-1, second load 3-2, and third load 3-3 are connected, the first DC-DC converter 11-7, the second DC-DC converter 21-7, and the third DC-DC converter 31-7 are configured in the same manner as the first DC-DC converter 11, the second DC-DC converter 21, and the third DC-DC converter 31 of the first embodiment, and droop control with an output current target value set is performed. Thus, the output currents io1, io2, and io3 of the respective DC-DC converters 11-7, 21-7, and 31-7 can be appropriately controlled, and the imbalance of the output currents can be suppressed. Here, the first load 3-1, the second load 3-2, and the third load 3-3 correspond to the loads of the present invention.

[0194] In addition, the structures of the above embodiments can be combined as much as possible without departing from the problems and technical ideas of the present invention. For example, in the above embodiments, an example applied to a DC power supply system having a storage battery as a distributed power source has been described. However, the present invention can also be applied to a DC power supply system having a solar power generation module as a distributed power source. Further, the present invention can also be applied to a DC power supply system using an energy source such as a fuel cell module, a gas engine module, a wind power generation module, a tidal power generation module, a hydraulic power generation module, a geothermal power generation module, or a combination thereof instead of the solar power generation module.

[0195] <Appendix 1>

[0196] A power conversion device (31) that boosts, buck-boosts, or buck-converts DC power input from a DC power source (33) and outputs it. The power conversion device (31) is connected in parallel with other power conversion devices (11, 21) to a load (3). The other power conversion devices (11, 21) boost, buck-boost, or buck-convert DC power input from other DC power sources (13, 23) and output it. The power conversion device (31) includes:

[0197] An output current value acquisition unit (34) that acquires an output current value (io3) output from the power conversion device (31);

[0198] An output voltage value acquisition unit (35) that acquires an output voltage value (vo) output from the power conversion device (31); and

[0199] A control unit (32) that controls the output voltage output from the power conversion device (31),

[0200] The control unit (32) generates an output current correction value (io3im) for correcting the output current value (io3) based on a target value of the output current (io3) output from the power conversion device (31), i.e., an output current target value (io3ref), and the output current value (io3). The output current target value (io3ref) is calculated by distributing, according to a prescribed distribution method, the sum of other output current values (io1, io2) output from the other power conversion devices (11, 21) or the load current value (io) input to the load (3) between the power conversion device (31) and the other power conversion devices (11, 21).

[0201] The power conversion device (31) includes droop control units (324, 327) that droop a target value of the output voltage (vo) output from the power conversion device (31), i.e., an output voltage target value (Vo3ref), based on the corrected output current value, i.e., a corrected output current value (io3im), corrected by the output current correction value (Icr3ref).

[0202] The power conversion device (31) controls the output voltage based on the drooped output voltage target value (Vo3ref) and the output voltage value (vo).

[0203] Reference Numeral Explanation

[0204] 3: Load; 11: First DC-DC converter; 21: Second DC-DC converter; 31: Third DC-DC converter; 32: Control unit; 323: Third DC-DC converter lateral current target value generator; 324: Droop gain multiplication unit; 326, 327: Superposition points; 100: DC power supply system.

Claims

1. A power conversion device that boosts, buck-boosts, or buck-converts the DC power input from a DC power supply and outputs it. The power conversion device is connected to a load in parallel with other power conversion devices. The other power conversion devices boost, buck-boost, or buck-convert the DC power input from other DC power supplies and output it. It is characterized in that, The power conversion device has: an output current value acquisition unit that acquires an output current value output from the power conversion device; an output voltage value acquisition unit that acquires an output voltage value output from the power conversion device; and a control unit that controls the output voltage output from the power conversion device, wherein the control unit has: a correction value generation unit that generates an output current correction value for correcting the output current value based on a target value of the output current output from the power conversion device, i.e., an output current target value, and the output current value, and the output current target value is calculated by distributing the sum of the output current value and another output current value output from another power conversion device, or a load current value input to the load, between the power conversion device and the other power conversion device according to a prescribed distribution method; and a droop control unit that droops a target value of the output voltage output from the power conversion device, i.e., an output voltage target value, based on the corrected output current value, i.e., the corrected output current value, obtained by correcting according to the output current correction value, and the power conversion device controls the output voltage based on the drooped output voltage target value and the output voltage value.

2. The power conversion device according to claim 1, wherein the power conversion device has: a communication unit that receives at least the output current value of the other power conversion device or the load current value; and an output current target value calculation unit that calculates at least the output current target value by distributing the sum of the output current value and the other output current value, or the load current value, between the power conversion device and the other power conversion device according to the distribution method.

3. The power conversion device according to claim 1, wherein the power conversion device has a communication unit that transmits the output current value to the other power conversion device or an external device having an output current target value calculation unit, and receives the output current target value calculated by the output current target value calculation unit from the other power conversion device or the external device, and the output current target value calculation unit calculates at least the output current target value by distributing the sum of the output current value and the other output current value, or the load current value, between the power conversion device and the other power conversion device according to the distribution method.

4. The power conversion device according to claim 1, wherein the correction value generation unit adjusts the output current correction value based on the difference between the output current target value and the output current value.

5. The power conversion device according to claim 1, wherein the correction value generation unit increases or decreases the output current correction value according to the relationship between the output voltage value and a prescribed voltage value range and the relationship between the output current value and a prescribed current value range.

6. A DC power supply system formed by connecting in parallel a plurality of power conversion devices that output DC power to a load with respect to the load, characterized in that The power conversion device boosts, boosts and buck-boosts, or buck-boosts the DC power input from a DC power source and outputs it. The power conversion device includes: an output current value acquisition unit that acquires an output current value output from the power conversion device; an output voltage value acquisition unit that acquires an output voltage value output from the power conversion device; and a control unit that controls the output voltage output from the power conversion device, wherein the control unit includes: a correction value generation unit that generates an output current correction value for correcting the output current value based on a target value of the output current output from the power conversion device, i.e., an output current target value, and the output current value; and a droop control unit that droops a target value of the output voltage output from the power conversion device, i.e., an output voltage target value, based on the corrected output current value obtained by correcting the output current value according to the output current correction value, and the power conversion device controls the output voltage based on the drooped output voltage target value and the output voltage value, the DC power supply system includes an output current target value calculation unit that calculates the output current target value of the power conversion device included in the DC power supply system by distributing the total value of the output current values output from the plurality of power conversion devices included in the DC power supply system or the load current value input to the load according to a prescribed distribution method.

7. The DC power supply system according to claim 6, wherein the correction value generation unit adjusts the output current correction value based on the difference between the output current target value and the output current value.

8. The DC power supply system according to claim 6, wherein the correction value generation unit increases or decreases the output current correction value according to the relationship between the output voltage value and a prescribed voltage value range and the relationship between the output current value and a prescribed current value range.

9. The DC power supply system according to claim 6, wherein when the power supplied to the load is an amount of power that can be supplied by a part of the plurality of power conversion devices, the output current target value calculation unit performs the distribution in such a way as to reduce the operation rate of the power conversion devices included in the plurality of power conversion devices.

10. A DC power supply system includes a first type of power conversion device and a second type of power conversion device. The DC power supply system supplies DC power to a load by connecting a plurality of the first type of power conversion devices and one or more of the second type of power conversion devices in parallel. The first type of power conversion device boosts, boosts and buck-boosts, or buck-boosts the DC power input from a first type of DC power source and outputs it. The first type of power conversion device includes: a first type of output current value acquisition unit that acquires a first type of output current value output from the first type of power conversion device; a first type of output voltage value acquisition unit that acquires a first type of output voltage value output from the first type of power conversion device; and The first control unit controls a first output voltage output from the first power conversion device. The first control unit includes: A correction value generation unit that generates a first output current correction value for correcting the first output current value based on a target value of a first output current, i.e., a first output current target value, and the first output current value output from the first power conversion device; and A first droop control unit that droops a target value of the first output voltage, i.e., a first output voltage target value, output from the first power conversion device based on a first corrected output current value obtained by correcting the first output current value according to the first output current correction value. The first power conversion device controls the first output voltage based on the drooped first output voltage target value and the first output voltage value. The second power conversion device boosts, buck-boosts, or buck-converts DC power input from a second DC power source and outputs it. The second power conversion device includes: A second output current value acquisition unit that acquires a second output current value output from the second power conversion device; A second output voltage value acquisition unit that acquires a second output voltage value output from the second power conversion device; and A second control unit that controls a second output voltage output from the second power conversion device. The second control unit includes a second droop control unit that droops a target value of the second output voltage, i.e., a second output voltage target value, output from the second power conversion device based on the second output current value. The second power conversion device controls the second output voltage based on the drooped second output voltage target value and the second output voltage value. The DC power supply system is characterized in that The DC power supply system includes an output current target value calculation unit that calculates the first output current target value of the first power conversion device included in the DC power supply system by distributing the sum of the first output current value and the second output current value or the load current value input to the load between the first power conversion device and the second power conversion device according to a specified distribution method.

11. The DC power supply system according to claim 10, characterized in that The DC power supply system sets the second power conversion device based on the amount of electric power that can be supplied to the load.

12. The DC power supply system according to claim 10 or 11, characterized in that The correction value generation unit adjusts the first output current correction value based on the difference between the first output current target value and the first output current value.

13. The DC power supply system according to claim 10 or 11, characterized in that The correction value generation unit increases or decreases the first output current correction value according to the relationship between the first output voltage value and a specified voltage value range and the relationship between the first output current value and a specified current value range.

Images