Control device, DC power distribution system, and control method

Abstract

To realize a control device that can improve instantaneous low compensation capability.SOLUTION: A control device includes: an AC-side current detector (91) for detecting an AC-side current; a DC-side voltage detector (82) for detecting a DC-side voltage; and a converter control device (70) for operating an AC-DC converter to bring the DC-side voltage closer to a target voltage or to maintain the DC-side voltage at the target voltage in a range in which the AC-side current does not exceed a rated current at an instantaneous low time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a control device, a DC power distribution system, and a control method. [Background technology]

[0002] Patent Document 1 discloses a power conditioner that converts DC power from a solar cell into AC power using a DCAC converter and connects it to an AC system, and also outputs the DC power from the solar cell to an external DC load. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-110830 Summary of the Invention [Problem to be solved by the invention]

[0004] In Patent Document 1, the DC / AC converter performs gate blocking when it detects a voltage sag in the grid. Therefore, in Patent Document 1, even if the voltage drop during the voltage sag is small, it is necessary to cut off the power supply from the grid and suppress power consumption. Alternatively, to avoid suppressing power consumption in this way, it is necessary to increase the capacity of the storage battery. In other words, the technology disclosed in Patent Document 1 leaves room for improvement in terms of voltage sag compensation capability.

[0005] An object of one aspect of the present invention is to realize a control device that can improve the voltage sag compensation capability. [Means for solving the problem]

[0006] In order to solve the above problems, a control device according to a first aspect of the present invention includes a current detection unit that detects the AC side current or the DC side current of an AC-CDC converter that connects an AC system and a DC bus to which a DC load is connected, a voltage detection unit that detects the DC side voltage of the AC-CDC converter, and an operation control unit that operates the AC-CDC converter to bring the DC side voltage close to a target voltage or maintain the DC side voltage at the target voltage during a momentary sag of the AC system, within a range in which the AC side current or the DC side current does not exceed the rated current of the AC-CDC converter.

[0007] In the control device according to aspect 2 of the present invention, in the above aspect 1, the operation control unit may change the operation of the AC / DC converter so that the AC side current or the DC side current is equal to or less than the rated current if the AC side current or the DC side current is greater than the rated current.

[0008] In the control device according to aspect 3 of the present invention, in the above aspect 2, the operation control unit may output a command value for output power or output current to the AC / DC converter, and if the AC side current or the DC side current is larger than the rated current, decrease the command value, and if the AC side current or the DC side current is smaller than the rated current and the DC side voltage is lower than a target voltage, increase the command value.

[0009] The control device according to aspect 4 of the present invention may be in any one of aspects 1 to 3 above, further comprising a power consumption limiting unit that limits the power consumption of the DC load connected to the DC bus if the AC side current or the DC side current is greater than the rated current.

[0010] The control device according to aspect 5 of the present invention, in any of aspects 1 to 3 above, may further include a power consumption limiting unit that limits the power consumption of the DC load connected to the DC bus if the DC side voltage is lower than a first threshold voltage that is lower than the target voltage.

[0011] The control device according to aspect 6 of the present invention may further include, in any of aspects 1 to 5 above, a charge / discharge control unit that causes a storage battery connected to the DC bus to supply power to the DC bus if the AC side current or the DC side current is greater than the rated current.

[0012] The control device according to aspect 7 of the present invention may further include, in any of aspects 1 to 5 above, a charge / discharge control unit that causes a storage battery connected to the DC bus to supply power to the DC bus if the DC side voltage is lower than a second threshold voltage that is lower than the target voltage.

[0013] In order to solve the above problems, a DC power distribution system according to an eighth aspect of the present invention includes the control device according to any one of the first to seventh aspects and the AC / DC converter.

[0014] In order to solve the above problems, a control method according to a ninth aspect of the present invention includes a current detection step of detecting an AC side current or a DC side current of an AC-CDC converter connecting an AC system and a DC bus to which a DC load is connected, a voltage detection step of detecting a DC side voltage of the AC-CDC converter, and an operation control step of operating the AC-CDC converter so as to bring the DC side voltage close to a target voltage or maintain the DC side voltage at the target voltage, within a range in which the AC side current or the DC side current does not exceed the rated current of the AC-CDC converter, during a momentary sag of the AC system. [Effects of the Invention]

[0015] According to one aspect of the present invention, it is possible to improve the voltage sag compensation capability. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram showing a configuration of a DC power distribution system according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing a circuit configuration of an AC / DC converter in the DC power distribution system. [Figure 3]10 is a graph showing changes over time in DC side voltage and output power during a sag in the prior art. [Figure 4] 4 is a graph showing changes over time in the DC side voltage and the output power during a sag in the first embodiment. [Figure 5] 10 is a graph showing the time variation of the DC side voltage and the output power during a momentary sag in a severe case in the prior art. [Figure 6] 6 is a graph showing changes over time in the DC side voltage and the output power during a voltage sag in a severe case in the first embodiment. [Figure 7] 10 is a graph showing time variations in output power and output power command value during a momentary sag in a severe case, and a graph showing switching operation in an AC / DC converter during a momentary sag in a severe case in the first embodiment; [Figure 8] 4 is a flowchart illustrating an example of a process executed by a converter control device of the DC power distribution system. [Figure 9] FIG. 10 is a diagram showing the configuration of a DC power distribution system according to a second embodiment. [Figure 10] 10 is a graph showing changes over time in the DC side voltage and various types of power during a momentary sag in a severe case in the second embodiment. [Figure 11] 4 is a flowchart showing an example of processing executed by a converter control device and a load control device of the DC power distribution system. [Figure 12] FIG. 10 is a diagram showing the configuration of a DC power distribution system according to a third embodiment. [Figure 13] 11 is a graph showing the time variations of the DC side voltage and various powers during a momentary sag in a severe case in the third embodiment. [Figure 14] 4 is a flowchart showing an example of processing executed by a converter control device and a storage battery control device of the DC power distribution system. DETAILED DESCRIPTION OF THE INVENTION

[0017] (Definition of terms) In this specification, the term "voltage sag" refers to an instantaneous voltage drop in a grid voltage. A voltage sag lasts until a power line fault caused by a lightning strike or the like is removed from the power grid. Generally, a voltage sag lasts for about 0.1 seconds. Unless otherwise specified, this specification assumes that a voltage drop of about 50% occurs in the grid during a voltage sag.

[0018] [Embodiment 1] (Schematic configuration of DC power distribution system) Fig. 1 is a diagram showing the configuration of a DC power distribution system 1 according to a first embodiment. As shown in Fig. 1, the DC power distribution system 1 includes an AC system 10 (power system), a transformer 20, an AC-DC converter 30, a DC bus 40, a DC load 50, a DC capacitor 60, and a converter control device 70 (operation control unit). The DC power distribution system 1 also includes a DC-side voltage detector 82 (voltage detection unit) that detects a DC-side voltage Vdc of the AC-DC converter 30. The DC power distribution system 1 also includes an AC-side current detector 91 (current detection unit) and a DC-side current detector 92 (current detection unit) that detect an AC-side current Iac and a DC-side current Idc of the AC-DC converter 30, respectively.

[0019] The AC system 10 supplies AC power to the DC bus 40. The AC system 10 is connected to the DC bus 40 via a transformer 20 and an AC-DC converter 30. The transformer 20 transforms the AC voltage input from the AC system 10. The AC-DC converter 30 converts the AC voltage input from the transformer 20 into a DC voltage and outputs it.

[0020] The DC bus 40 is a power line that supplies power from the AC system 10 to a DC load 50. The DC load 50 is at least one load device. A DC capacitor 60 is connected to the DC bus 40 to maintain the DC side voltage Vdc. A power generation device (e.g., a solar panel), a power storage system, an EV charger / discharger, etc. may also be connected to the DC bus 40.

[0021] The converter control device 70 includes an acquisition unit 71, a command generation unit 72, and a command output unit 73. During a momentary sag in the AC system 10, the converter control device 70 operates the AC-CDC converter 30 so as to bring the DC-side voltage Vdc close to or maintain the target voltage Vdc_ref within a range in which the AC-side current Iac or the DC-side current Idc does not exceed the rated current of the AC-CDC converter 30. If the AC-side current Iac or the DC-side current Idc is greater than the rated current, the converter control device 70 changes the operation of the AC-CDC converter 30 so that the AC-side current Iac or the DC-side current Idc is equal to or less than the rated current.

[0022] The acquisition unit 71 acquires the DC-side voltage Vdc detected by the DC-side voltage detector 82. The acquisition unit 71 also acquires the AC-side current Iac and the DC-side current Idc detected by the AC-side current detector 91 and the DC-side current detector 92, respectively.

[0023] The command generating unit 72 determines a command value to be output to the AC / DC converter 30 based on the DC side voltage Vdc and the AC side current Iac or the DC side current Idc acquired by the acquiring unit 71. The command value indicates the output power or output current output from the AC / DC converter 30 to the DC bus 40, or the output power or output current output from the AC / DC converter 30 to the AC system 10.

[0024] Specifically, the command generating unit 72 decreases the command value if the AC side current Iac or the DC side current Idc is greater than the rated current. Furthermore, the command generating unit 72 increases the command value if the AC side current Iac or the DC side current Idc is less than the rated current and the DC side voltage Vdc is lower than the target voltage Vdc_ref. The command generating unit 72 may determine the command value based on whether both the AC side current Iac and the DC side current Idc are greater than or less than the rated current. Instead of the rated current of the AC-DC converter 30, the command generating unit 72 may use a predetermined upper limit threshold value that is less than the rated current. For ease of explanation, the following describes a case where the output power command value is determined based on whether the AC side current Iac is greater than or less than the rated current.

[0025] The command output unit 73 outputs the command value determined by the command generation unit 72 to the AC / DC converter 30.

[0026] Fig. 2 is a diagram showing the circuit configuration of the AC-DC converter 30. As shown in Fig. 2, the AC-DC converter 30 forms a three-phase bridge circuit including six switching elements S1 to S6. The switching elements S1 to S6 are, for example, IGBTs (Insulated Gate Bipolar Transistors), which are elements for a self-excited converter. The switching elements S1 to S6 perform switching operations based on command values ​​input from a converter control device 70. Specifically, the switching elements S1 to S6 are operated using PWM (Pulse Width Modulation) control or the like so as to output an AC voltage waveform corresponding to the output power command value input from the converter control device 70.

[0027] (Time variation of DC voltage and output power during a momentary sag) Fig. 3 is a graph (reference numerals 3001 and 3002, respectively) showing the change over time of the DC side voltage and output power during a sag in the conventional technology (where gate blocking is performed during a sag). Fig. 4 is a graph (reference numerals 4001 and 4002, respectively) showing the change over time of the DC side voltage and output power during a sag in this embodiment.

[0028] As shown in Figure 3, in the conventional technology, the AC / DC converter performs gate blocking during a voltage sag, which stops the power supply from the AC / DC converter to the DC bus. As a result, the DC side voltage decreases over time.

[0029] 4, in this embodiment, even during a momentary sag, power supply from the AC / DC converter 30 to the DC bus continues. Therefore, the DC side voltage is maintained at the target voltage of 700V.

[0030] Fig. 5 is a graph (reference numerals 5001 and 5002, respectively) showing the time variation of the DC side voltage and output power during a sag in a severe case (when the load on the DC bus is larger than that in Fig. 3) in the conventional technology. Fig. 6 is a graph (reference numerals 6001 and 6002, respectively) showing the time variation of the DC side voltage and output power during a sag in a severe case in this embodiment.

[0031] As shown in Figure 5, when a voltage sag occurs in the DC bus under a larger load in the conventional technology, the impact of the power supply interruption from the AC-DC converter to the DC bus becomes greater. The DC side voltage drops more rapidly compared to Figure 3.

[0032] On the other hand, as shown in Figure 6, in this embodiment, if a voltage sag occurs when the load on the DC bus 40 is larger, the AC-DC converter 30 continues to supply power to the DC bus as long as the AC side current Iac does not exceed the rated current. That is, the AC-DC converter 30 reduces the output power during the voltage sag from the output power before the voltage sag to continue supplying power to the DC bus. Therefore, the DC side voltage decreases more gradually than in the prior art.

[0033] 7 is a graph (reference numeral 7001) showing the time variations of the output power and the output power command value during an instantaneous sag in a severe case, and a graph (reference numeral 7002) showing the switching operation of the AC-DC converter 30 during an instantaneous sag in a severe case. In detail, reference numeral 7001 in Fig. 7 is a graph showing the time variations of the output power P, the output power command value P' such that Vdc = Vdc_ref, and the output power command value P'' such that Iac ≦ Iac_r (Iac_r: AC side rated current of the AC-DC converter).

[0034] As shown by reference numeral 7001 in FIG. 7 , if the DC side voltage Vdc can be maintained at the target voltage Vdc_ref without the AC side current Iac exceeding the rated current, the converter control device 70 generates an output power command value P′ that substantially maintains the output power before the sag. However, in a severe case, if an attempt is made to maintain the DC side voltage Vdc at the target voltage Vdc_ref, the AC side current Iac may exceed the rated current Iac_r. Therefore, the converter control device 70 generates an output power command value P″ (>0) that reduces the output power before the sag so that the AC side current Iac does not exceed the rated current. As a result, the output power P output from the AC-DC converter 30 to the DC bus 40 is maintained at an output power command value P″ that is lower than the output power before the sag and greater than 0.

[0035] As indicated by reference numeral 7002 in FIG. 7, the AC / DC converter 30 continues the switching operation of the switching elements S1 to S6 based on the command value output from the converter control device 70 even during an instantaneous sag.

[0036] (Example of operation of the control device according to the first embodiment) Fig. 8 is a flowchart showing an example of processing executed by the converter control device 70. As shown in Fig. 8, in S11, the acquisition unit 71 acquires the DC side voltage Vdc detected by the DC side voltage detector 82 and the AC side current Iac detected by the AC side current detector 91 (current detection step and voltage detection step).

[0037] In S12, the command generating unit 72 determines whether the AC side current Iac is greater than the rated current Iac_r. If the AC side current Iac is greater than the rated current Iac_r, the command generating unit 72 determines an output power command value such that Iac≦Iac_r (S13). Specifically, the command generating unit 72 reduces the output power command value. On the other hand, if the AC side current Iac is equal to or less than the rated current Iac_r, the command generating unit 72 determines an output power command value such that Vdc=Vdc_ref (S14). Specifically, if the DC side voltage Vdc is lower than the target voltage Vdc_ref, the command generating unit 72 increases the output power command value, and if the DC side voltage Vdc is higher than the target voltage Vdc_ref, the command generating unit 72 decreases the output power command value.

[0038] In S15, the command output unit 73 outputs the output power command value determined in S13 or S14 to the AC / DC converter 30 (operation control step). The AC / DC converter 30 performs the switching operation of the switching elements S1 to S6 based on the output power command value.

[0039] (Advantages of the control device according to the first embodiment) With the above configuration, the converter control device 70 can operate the AC-CDC converter 30 during a sag without gate blocking the AC-CDC converter 30 so as to continue power supply within a range in which the AC-side current Iac does not exceed the rated current. That is, the converter control device 70 can utilize the system voltage during a sag to operate the AC-CDC converter 30 so as to continue power supply to the extent possible. This can suppress a decrease in the DC-side voltage Vdc. Therefore, the sag compensation capability of the DC power distribution system 1 can be improved.

[0040] Furthermore, there is no need to add facilities such as a power storage system to deal with voltage sags, which means the cost required for voltage sag countermeasures can be reduced.Furthermore, the capacity of the DC capacitor 60 for maintaining the DC side voltage Vdc can also be reduced.

[0041] (Variation) When a voltage sag occurs, the converter control device 70 may maintain the DC side voltage Vdc at the target voltage by supplying power to the DC bus 40 from other devices (such as a power storage system or a power generation device) connected to the DC bus 40. If the DC side voltage Vdc cannot be maintained at the target voltage, the converter control device 70 may operate the AC / DC converter 30 to bring the DC side voltage Vdc close to or maintain the target voltage within a range in which the AC side current does not exceed the rated current of the AC / DC converter 30.

[0042] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0043] (Schematic configuration of DC power distribution system) 9 is a diagram showing the configuration of a DC power distribution system 101 according to the second embodiment. The DC power distribution system 101 according to the second embodiment differs from the DC power distribution system 1 according to the first embodiment in that it further includes a load control device 170 (power consumption limiting unit). The DC power distribution system 101 also differs from the DC power distribution system 1 according to the first embodiment in that it further includes an AC-side voltage detector 81 that detects the AC-side voltage Vac of the AC-DC converter 30.

[0044] In this embodiment, the converter control device 70 cooperates with the load control device 170 to operate the AC / DC converter 30 to continue power supply during a voltage sag. In detail, when the AC side current Iac is larger than the rated current Iac_r or when the DC side voltage Vdc is smaller than a first threshold voltage VdcL that is lower than the target voltage Vdc_ref, the converter control device 70 outputs an instruction to the load control device 170 to limit the power consumption of the DC load 50 (load power consumption).

[0045] The load control device 170 includes an acquisition unit 171, a command generation unit 172, and a command output unit 173. The load control device 170 limits the power consumption of the DC load 50.

[0046] The acquisition unit 171 acquires the AC side voltage Vac via the converter control device 70. The acquisition unit 171 also receives an instruction output from the instruction output unit 73 of the converter control device 70.

[0047] If the AC-side current Iac is greater than the rated current Iac_r, the command generating unit 172 limits the power consumption of the load connected to the DC bus. That is, when the acquiring unit 171 receives an instruction to limit the load power consumption, the command generating unit 172 determines a command value (power consumption command value) to be output to the DC load 50 based on the load power consumption acquired by the acquiring unit 171 and the AC-side voltage Vac. The command value is an upper limit value for the load power consumption. Specifically, the command generating unit 172 determines the power consumption command value so that the load power consumption is smaller than the rated current Iac_r × AC-side voltage Vac. Note that the command generating unit 172 may limit the power consumption of the load connected to the DC bus when the DC-side voltage Vdc is smaller than a first threshold voltage VdcL that is equal to or smaller than the target voltage Vdc_ref.

[0048] The command output unit 173 outputs the command value determined by the command generation unit 172 to the DC load 50 .

[0049] 10 shows an example in which the converter control device 70 and the load control device 170 are spatially separated and exchange data via known wired or wireless communication. However, the configurations of the converter control device 70 and the load control device 170 are not limited to this, and for example, the functions of the converter control device 70 and the load control device 170 may be integrated into an integrated control device.

[0050] The DC power distribution system 101 may further include a load-side voltage detector 83 and a load-side current detector 93 that detect a voltage (load-side voltage Vdc') and a current (load-side current Idc'), respectively, in the vicinity of the DC load 50 on the DC bus 40. The acquisition unit 171 may acquire load power consumption based on the detected load-side voltage Vdc' and load-side current Idc'. When the AC-side current Iac is larger than the rated current Iac_r, the command generation unit 172 may determine a power consumption command value that is smaller than the load power consumption.

[0051] (Time variation of DC voltage and output power during a momentary sag) 10 is a graph (reference numerals 10001 and 10002) showing the time variations of the DC side voltage and various powers during a momentary sag in a severe case in this embodiment. Reference numeral 10002 in FIG. 10 shows a graph showing the time variations of the output power and the load power consumption.

[0052] As shown in FIG. 10 , in this embodiment, when a voltage sag occurs when the load on the DC bus 40 is large, the AC-DC converter 30 continues to supply power to the DC bus, as in the first embodiment. At this time, the DC side voltage gradually decreases. Here, when the AC side current Iac exceeds the rated current Iac_r or the DC side voltage Vdc falls below the first threshold voltage VdcL (in the example shown in FIG. 10 , 0.07 to 0.08 seconds after the voltage sag), the load power consumption is limited. This stops the decrease in the DC side voltage, and the AC-DC converter 30 continues to supply power to the DC bus as long as the AC side current Iac does not exceed the rated current.

[0053] (Example of operation of the control device according to the second embodiment) Fig. 11 is a flowchart showing an example of processing executed by the converter control device 70 and the load control device 170. As shown in Fig. 11, in S21, the acquisition unit 71 of the converter control device 70 acquires the AC side voltage Vac, the DC side voltage Vdc, and the AC side current Iac.

[0054] In S22, the command generating unit 72 determines whether the AC-side current Iac is greater than the rated current Iac_r. The command generating unit 72 may also determine whether the DC-side voltage Vdc is less than the first threshold voltage VdcL. If the AC-side current Iac is greater than the rated current Iac_r (or the DC-side voltage Vdc is less than the first threshold voltage VdcL), the command output unit 73 outputs an instruction to limit the load power consumption to the load control device 170. When the acquiring unit 171 of the load control device 170 receives the instruction, the command generating unit 172 determines a power consumption command value such that Iac_r×Vac>load power consumption (S23). On the other hand, if the AC-side current Iac is less than the rated current Iac_r (or the DC-side voltage Vdc is greater than or equal to the first threshold voltage VdcL), the command generating unit 72 determines an output power command value such that Vdc=Vdc_ref (S24), as in the first embodiment.

[0055] In S25, the command output unit 173 outputs the power consumption command value determined in S23 to the DC load 50. In S26, the command output unit 73 outputs the output power command value determined in S24 to the AC / DC converter 30.

[0056] (Advantages of the control device according to the second embodiment) According to the above configuration, the converter control device 70 cooperates with the load control device 170 to further suppress the decrease in the DC-side voltage Vdc by limiting the load power consumption. Therefore, the instantaneous sag compensation capability of the DC power distribution system 101 can be further improved.

[0057] [Embodiment 3] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0058] (Schematic configuration of DC power distribution system) 12 is a diagram showing the configuration of a DC power distribution system 201 according to embodiment 3. The DC power distribution system 201 according to embodiment 3 differs from the DC power distribution system 1 according to embodiment 1 in that it includes a storage battery 250, a DC-DC converter 230, and a storage battery control device 270 (charge / discharge control unit). The DC power distribution system 201 also differs from the DC power distribution system 1 according to embodiment 1 in that it further includes an AC-side voltage detector 81 that detects the AC-side voltage Vac of the AC-DC converter 30.

[0059] The storage battery 250 is connected to the DC bus 40. The storage battery 250 stores electric power as energy inside, and supplies the stored energy to the DC-DC converter 230 as DC as needed.

[0060] The DCDC converter 230 is connected between the storage battery 250 and the DC bus 40. The DCDC converter 230 is a power conversion device that converts the DC voltage supplied from the storage battery 250 and supplies the converted voltage to the DC bus 40. In other words, the storage battery 250 supplies power to the DC bus 40 via the DCDC converter 230.

[0061] In this embodiment, the converter control device 70 operates the AC / DC converter 30 to continue power supply during a voltage sag in cooperation with the storage battery control device 270. In detail, when the AC side current Iac is larger than the rated current Iac_r or when the DC side voltage Vdc is smaller than a second threshold voltage VdcB that is lower than the target voltage Vdc_ref, the converter control device 70 outputs an instruction to the storage battery control device 270 to supply power from the storage battery 250 to the DC bus 40.

[0062] The storage battery control device 270 includes an acquisition unit 271, a command generation unit 272, and a command output unit 273. The storage battery control device 270 controls the DC-DC converter 230 to cause the storage battery 250 to perform charging and discharging operations.

[0063] The acquisition unit 271 acquires the AC side voltage Vac via the converter control device 70. The acquisition unit 271 also receives an instruction output from the command output unit 73 of the converter control device 70.

[0064] If the AC side current Iac is larger than the rated current Iac_r, the command generating unit 272 causes power to be supplied from the storage battery 250 to the DC bus 40. That is, when the acquiring unit 271 receives an instruction to supply power from the storage battery 250 to the DC bus 40, the command generating unit 272 determines a command value (charge / discharge power command value) to be output to the DC-DC converter 230 based on the charge / discharge power, load power consumption, and AC side voltage Vac acquired by the acquiring unit 271. The command value is the charge / discharge power from the storage battery 250. Specifically, the command generating unit 272 determines the charge / discharge power command value so that the load power consumption+charge / discharge power (charge power is taken as positive) is lower than the rated current Iac_r×AC side voltage Vac. The command generating unit 272 may cause the storage battery 250 to supply power to the DC bus 40 when the DC-side voltage Vdc is lower than a second threshold voltage VdcB that is lower than the target voltage Vdc_ref.

[0065] The command output unit 273 outputs the command value determined by the command generation unit 272 to the DC-DC converter 230.

[0066] The DC power distribution system 201 may further include a DC bus side voltage detector 84 and a DC bus side current detector 94 that detect the voltage (DC bus side voltage Vdc") and current (DC bus side current Idc") on the DC bus 40 side of the DC-DC converter 230, respectively.

[0067] The acquisition unit 271 may acquire the battery charge / discharge power based on the detected DC bus side voltage Vdc" and DC bus side current Idc". When the AC side current Iac is larger than the rated current Iac_r, the command generation unit 272 may determine a charge / discharge power command value (charging power is taken as positive) that is smaller than the battery charge / discharge power.

[0068] The acquiring unit 271 may also derive the load power consumption from the difference between the output power based on the detected DC side current Idc and DC side voltage Vdc and the storage battery charge / discharge power based on the DC bus side voltage Vdc" and the DC bus side current Idc". Alternatively, the acquiring unit 271 may acquire the load power consumption from the load control device 170 shown in FIG. 10.

[0069] (Time variation of DC voltage and output power during a momentary sag) 13 is a graph (reference numerals 13001 and 13002, respectively) showing the time variations of the DC side voltage and various powers during a momentary sag in a severe case in this embodiment. Reference numeral 13002 in FIG. 13 shows a graph showing the time variations of the output power, the load power consumption, and the battery charge / discharge power.

[0070] As shown in FIG. 13, in this embodiment, when a voltage sag occurs when the load on the DC bus 40 is larger, the AC-DC converter 30 continues to supply power to the DC bus, as in the first embodiment. At this time, the DC-side voltage gradually decreases. Here, when the AC-side current Iac exceeds the rated current Iac_r or the DC-side voltage Vdc falls below the second threshold voltage VdcB (in the example shown in FIG. 13, 0.07 to 0.08 seconds after the voltage sag), the battery charging / discharging power increases to the supply side. This stops the decrease in the DC-side voltage, and the AC-DC converter 30 continues to supply power to the DC bus as long as the AC-side current Iac does not exceed the rated current.

[0071] (Example of operation of the control device according to the third embodiment) Fig. 14 is a flowchart showing an example of processing executed by the converter control device 70 and the storage battery control device 270. As shown in Fig. 14, in S31, the acquisition unit 71 of the converter control device 70 acquires the AC side voltage Vac, the DC side voltage Vdc, and the AC side current Iac.

[0072] In S32, the command generating unit 72 determines whether the AC-side current Iac is greater than the rated current Iac_r. The command generating unit 72 may also determine whether the DC-side voltage Vdc is less than a second threshold voltage VdcB. If the AC-side current Iac is greater than the rated current Iac_r (or the DC-side voltage Vdc is less than the second threshold voltage VdcB), the command output unit 73 outputs an instruction to the battery control device 270 to supply power from the storage battery 250 to the DC bus 40. When the acquiring unit 271 of the storage battery control device 270 receives the instruction, the command generating unit 272 determines a charge / discharge power command value such that Iac_r×Vac>load power consumption+storage battery charge / discharge power (charge power is taken as positive) (S33). On the other hand, when the AC side current Iac is equal to or less than the rated current Iac_r (or the DC side voltage Vdc is equal to or greater than the second threshold voltage VdcB), the command generating unit 72 determines an output power command value such that Vdc=Vdc_ref, as in the first embodiment (S34).

[0073] In S35, the command output unit 273 outputs the charge / discharge power command value determined in S33 to the DC-DC converter 230. In S36, the command output unit 73 outputs the output power command value determined in S34 to the DC-DC converter 230.

[0074] (Advantages of the control device according to the third embodiment) According to the above configuration, the converter control device 70 cooperates with the storage battery control device 270, thereby further suppressing a decrease in the DC side voltage Vdc due to discharge of the storage battery 250. Therefore, the instantaneous sag compensation capability of the DC power distribution system 201 can be further improved.

[0075] [Software implementation example] The functions of the control device (hereinafter referred to as the "device") can be realized by a program that causes a computer to function as the device, and a program that causes a computer to function as each control block of the device (particularly each part included in the converter control device 70, the load control device 170, and the battery control device 270).

[0076] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The control device and storage device execute the program, thereby realizing the functions described in each of the above embodiments.

[0077] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0078] Furthermore, some or all of the functions of the control blocks can be realized by logic circuits. For example, an integrated circuit in which a logic circuit that functions as each of the control blocks is formed is also included in the scope of the present invention. In addition, the functions of the control blocks can also be realized by, for example, a quantum computer.

[0079] Furthermore, each process described in each of the above embodiments may be executed by AI (Artificial Intelligence). In this case, the AI ​​may run on the control device or on another device (for example, an edge computer or a cloud server).

[0080] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0081] 1, 101, 201 DC power distribution system 10 AC system 30 AC / DC converter 40 DC bus 50 DC load 70 Converter control device (operation control unit) 82 DC side voltage detector (voltage detection section) 91 AC side current detector (current detection section) 92 DC side current detector (current detection section) 170 Load control device (power consumption limiting unit) 250 storage battery 270 Battery control device (charge / discharge control unit)

Claims

1. a current detection unit that detects an AC side current or a DC side current of an AC-DC converter that connects an AC system and a DC bus to which a DC load is connected; a voltage detection unit that detects a DC side voltage of the AC-DC converter; an operation control unit that operates the AC-DC converter to bring the DC side voltage close to a target voltage or maintain the DC side voltage at the target voltage, within a range in which the AC side current or the DC side current does not exceed a rated current of the AC-DC converter, during a momentary sag of the AC system.

2. 2. The control device according to claim 1, wherein, if the AC side current or the DC side current is greater than the rated current, the operation control unit changes the operation of the AC-DC converter so that the AC side current or the DC side current is equal to or less than the rated current.

3. The operation control unit outputting a command value for output power or output current to the AC-DC converter; 3. The control device according to claim 2, wherein the control device decreases the command value if the AC side current or the DC side current is greater than the rated current, and increases the command value if the AC side current or the DC side current is smaller than the rated current and the DC side voltage is lower than a target voltage.

4. The control device according to claim 1 , further comprising a power consumption limiting unit that limits power consumption of the DC load connected to the DC bus if the AC side current or the DC side current is greater than the rated current.

5. The control device according to claim 1 , further comprising a power consumption limiting unit that limits power consumption of the DC load connected to the DC bus when the DC side voltage is lower than a first threshold voltage that is equal to or lower than the target voltage.

6. 2. The control device according to claim 1, further comprising a charge / discharge control unit that causes a storage battery connected to the DC bus to supply power to the DC bus if the AC side current or the DC side current is greater than the rated current.

7. 2. The control device according to claim 1, further comprising a charge / discharge control unit that causes a storage battery connected to the DC bus to supply power to the DC bus when the DC side voltage is lower than a second threshold voltage that is lower than the target voltage.

8. A DC power distribution system comprising the control device according to any one of claims 1 to 7 and the AC-DC converter.

9. a current detection step of detecting an AC side current or a DC side current of an AC-DC converter connecting an AC system and a DC bus to which a DC load is connected; a voltage detection step of detecting a DC side voltage of the AC-DC converter; and an operation control step of operating the AC-DC converter so as to bring the DC side voltage close to a target voltage or maintain the DC side voltage at the target voltage, within a range in which the AC side current or the DC side current does not exceed a rated current of the AC-DC converter, during a momentary sag of the AC system.

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