DC power distribution system

Abstract

A DC power distribution system that can appropriately deal with short-circuit faults is provided. [Solution] The DC distribution system (100, 100A) comprises an AC / DC converter (2), a DC bus (3), a plurality of DC branch lines (4), a capacitor (5) connected to a node (N1) between the AC / DC converter and the DC bus, and a first reactor (8) connected between the node and the DC bus.

Description

[Technical Field]

[0001] The present invention relates to a DC power distribution system. [Background technology]

[0002] Patent Document 1 discloses a DC power distribution system that includes an AC circuit breaker connected to the input side of a transformer, a first DC circuit breaker connected between a rectifier and a DC bus (DC busbar), and a plurality of second DC circuit breakers provided on a plurality of DC branch lines, respectively.

[0003] In this DC power distribution system, the interruption operation time of the second DC circuit breaking unit is set shorter than the interruption operation time of the AC circuit breaking unit and the interruption operation time of the first DC circuit breaking unit. As a result, when a short-circuit fault occurs, the second DC circuit breaking unit performs the interruption operation first, so that only the branch line where the short-circuit fault has occurred can be interrupted.

[0004] In addition, in this DC power distribution system, the inductance value of the short-circuit impedance of the transformer is set to a value that limits the current flowing through the rectifier when a short-circuit current flows in the DC power distribution system to a maximum current value that the rectifier can tolerate, thereby allowing the rectifier to continue supplying the short-circuit current without breaking down even when a short-circuit fault occurs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7203236 specification Summary of the Invention [Problem to be solved by the invention]

[0006] To maintain a stable DC bus voltage under normal conditions, a capacitor must be connected to the DC bus. However, if a capacitor is connected to the DC bus, a large current will flow from the capacitor to the short-circuit point immediately after a short-circuit fault occurs. This could cause the current flowing through the DC circuit breaker to exceed its allowable current, resulting in a DC circuit breaker failure. Patent Document 1 does not anticipate connecting a capacitor to the DC bus.

[0007] One aspect of the present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a DC power distribution system that can appropriately deal with short-circuit faults. [Means for solving the problem]

[0008] In order to solve the above problems, a DC power distribution system according to a first aspect of the present invention includes a converter that converts AC power from an AC system into DC power, a DC bus through which the DC power supplied from the converter flows, a plurality of DC branch lines connected to the DC bus and each having a DC circuit breaker, a capacitor connected to a node between the converter and the DC bus, and a first reactor connected between the node and the DC bus.

[0009] A DC power distribution system according to a second aspect of the present invention may be the DC power distribution system of the first aspect, further comprising a first diode connected in parallel to the first reactor with an anode facing the DC bus.

[0010] A DC power distribution system according to a third aspect of the present invention may be the DC power distribution system according to the first or second aspect, further comprising a second reactor connected between the node and the converter.

[0011] A DC power distribution system according to a fourth aspect of the present invention may be the DC power distribution system of the third aspect, further comprising a second diode connected in parallel to the second reactor with an anode facing the node.

[0012] A DC distribution system according to a fifth aspect of the present invention may be, in addition to the above-mentioned first to fourth aspects, further include an AC circuit breaker connected between the AC system and the converter, wherein when a current equal to or greater than a first threshold current flows through the AC circuit breaker for a first predetermined time or longer, the AC circuit breaker cuts off the current, and when a current equal to or greater than a second threshold current flows through the DC circuit breaker for a second predetermined time or longer, the DC circuit breaker cuts off the current, and the first threshold current and the second threshold current may be set so that the power supplied through the DC circuit breaker when the second threshold current flows through the DC circuit breaker is smaller than the power supplied through the AC circuit breaker when the first threshold current flows through the AC circuit breaker.

[0013] A DC distribution system according to a sixth aspect of the present invention is, in the above-mentioned first to fifth aspects, further comprising an AC circuit breaker connected between the AC system and the converter, wherein when a current equal to or greater than a first threshold current flows through the AC circuit breaker for a first predetermined time or longer, the AC circuit breaker interrupts the current, and when a current equal to or greater than a second threshold current flows through the DC circuit breaker for a second predetermined time or longer, the DC circuit breaker interrupts the current, and the second predetermined time may be shorter than the first predetermined time. [Effects of the Invention]

[0014] According to one aspect of the present invention, it is possible to appropriately deal with a short circuit fault. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing a configuration of a DC power distribution system according to a first embodiment. [Figure 2] FIG. 1 is a diagram illustrating the state of a DC power distribution system immediately after a short-circuit fault occurs. [Figure 3] FIG. 1 is a diagram illustrating the state of a DC power distribution system from the occurrence of a short-circuit fault until a DC circuit breaker is tripped. [Figure 4] FIG. 1 is a diagram illustrating a state of a DC power distribution system immediately after a DC circuit breaker is tripped. [Figure 5]FIG. 1 is a diagram illustrating a state of a DC power distribution system from when a DC circuit breaker is tripped until when power supply to a DC branch line where no short-circuit fault occurs is started. [Figure 6] FIG. 10 is a diagram illustrating a state in which the DC power distribution system continues to supply power to a DC branch line where no short-circuit fault has occurred. [Figure 7] FIG. 10 is a diagram showing the configuration of a DC power distribution system according to a second embodiment. [Figure 8] FIG. 8 is a diagram showing experimental results of the interruption operation in the DC power distribution system shown in FIG. [Figure 9] FIG. 10 is a diagram showing the configuration of a DC power distribution system according to a comparative example. [Figure 10] FIG. 10 is a diagram showing experimental results of the interruption operation in the DC power distribution system shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Embodiment 1] (Schematic configuration of DC power distribution system) Fig. 1 is a diagram showing the configuration of a DC power distribution system 100 according to embodiment 1. As shown in Fig. 1, the DC power distribution system 100 includes an AC system 1, an AC-DC converter 2 (converter), a DC bus 3, a plurality of DC branch lines 4 (DC branch lines 4A, 4B, 4C, etc.), a capacitor 5, an AC circuit breaker 6, a plurality of DC circuit breakers 7 (DC circuit breakers 7A, 7B, 7C, etc.), a first reactor 8, and a first diode 9.

[0017] The AC system 1 supplies power to the DC bus 3. The AC-DC converter 2 converts AC power from the AC system 1 into DC power. Instead of the AC-DC converter 2, a device that irreversibly converts AC power to DC power (for example, a rectifier) ​​may be used. A transformer may be provided between the AC system 1 and the AC-DC converter 2.

[0018] The DC bus 3 is a power line through which DC power supplied from the AC / DC converter 2 flows. Multiple DC branch lines 4 branch off from the DC bus 3 and are power lines to which connected devices such as load devices, power storage systems, or power generation systems are connected. Each of the multiple DC branch lines 4 has a DC circuit breaker 7. Hereinafter, the voltage (potential) on the DC bus 3 is referred to as a DC bus voltage Vdc. Also, the current flowing through the DC bus 3 is referred to as a DC bus current Idc_bus. Also, the current flowing through the multiple DC branch lines 4 (DC branch lines 4A, 4B, 4C, etc.) is referred to as a DC branch current Idc (Idc_A, Idc_B, ​​Idc_C, etc.).

[0019] The capacitor 5 is connected to a node N1 between the AC / DC converter 2 and the DC bus 3. The capacitor 5 serves to maintain the DC bus voltage Vdc. In particular, the capacitor 5 suppresses fluctuations in the DC bus voltage Vdc that may occur when a power generation source or a variable load connected to the DC branch line 4 operates.

[0020] The AC circuit breaker 6 is connected between the AC system 1 and the AC-DC converter 2. A plurality of DC circuit breakers 7 are provided on the DC branch lines 4. The AC circuit breaker 6 and the plurality of DC circuit breakers 7 are semiconductor circuit breakers, mechanical circuit breakers, fuses, etc. Hereinafter, the voltage at the AC circuit breaker 6 is referred to as Vac.

[0021] The AC circuit breaker 6 cuts off a current when a current equal to or greater than an AC threshold current Iac_th (first threshold current) flows through the AC circuit breaker 6 for a first predetermined time Tac or longer. The DC circuit breaker 7 cuts off a current when a current equal to or greater than a DC threshold current Idc_th (second threshold current) flows through the DC circuit breaker 7 for a second predetermined time Tdc or longer.

[0022] Also, the AC threshold current Iac_th and the DC threshold current Idc_th are set such that the DC threshold power Pdc_th is smaller than the AC threshold power Pac_th. Here, the AC threshold power Pac_th is the power supplied downstream through the AC circuit breaker 6 when the AC threshold current Iac_th flows through the AC circuit breaker 6. Also, the DC threshold power Pdc_th is the power supplied downstream through the DC circuit breaker 7 when the DC threshold current Idc_th flows through the DC circuit breaker 7. That is, the AC threshold current Iac_th and the DC threshold current Idc_th are set so that the following equations (1) to (3) hold. ·Iac_th = Pac_th ÷ Vac ··· (Equation 1) ·Idc_th = Pdc_th ÷ Vdc ··· (Equation 2) ·Pdc_th < Pac_th ··· (Equation 3) As a result, when a short-circuit fault occurs, the DC circuit breaker 7 of the DC branch line 4 where the short-circuit fault has occurred is more likely to perform a cutoff operation earlier than the AC circuit breaker 6.

[0023] Also, the second predetermined time Tdc may be shorter than the first predetermined time Tac. As a result, when a short-circuit fault occurs, the DC circuit breaker 7 of the DC branch line 4 where the short-circuit fault has occurred is more likely to perform a cutoff operation earlier than the AC circuit breaker 6. Note that the cutoff conditions of the AC circuit breaker 6 and the DC circuit breaker 7 may be set to satisfy both Pdc_th < Pac_th and Tdc < Tac.

[0024] The first reactor 8 is connected between the node N1 and the DC bus 3. The first reactor 8 has a role of suppressing a rapid increase in Idc due to a large current flowing from the capacitor 5 to the DC branch line 4 immediately after a short-circuit fault occurs in any of the DC branch lines 4.

[0025] The first diode 9 is connected in parallel to the first reactor 8 such that the anode faces the DC bus 3 side. The first diode 9 refluxes the current flowing through the first reactor 8 immediately after the DC circuit breaker 7 of the DC branch line 4 where the short-circuit fault has occurred is cut off. Thereby, the first diode 9 can suppress the voltage rise of the DC bus voltage Vdc immediately after the cutoff due to the first reactor 8.

[0026] (Example of DC power distribution system operation) 2 to 6 are diagrams showing the flow of processing executed by the DC power distribution system 100 when a short-circuit fault occurs. An example of the operation of the DC power distribution system 100 will be described below with reference to FIGS.

[0027] Fig. 2 is a diagram showing the state of the DC power distribution system 100 immediately after a short-circuit fault occurs. As shown in Fig. 2, immediately after a short-circuit fault occurs in one of the DC branch lines 4 (assumed to be the DC branch line 4C), a large current flows from the capacitor 5 to the DC branch line 4C. At this time, the first reactor 8 suppresses a sudden increase in the DC branch current Idc_C due to the large current flowing from the capacitor 5 to the DC branch line 4C. Note that, because a reactor component (not shown) is included between the AC system 1 and the AC-DC converter 2, the rise of the current flowing from the AC system 1 to the DC branch line 4C is slower than the rise of the current flowing from the capacitor 5 to the DC branch line 4C.

[0028] Fig. 3 is a diagram showing the state of the DC power distribution system 100 from when a short-circuit fault occurs until when the DC circuit breaker 7 is tripped. As shown in Fig. 3, even after the current has completely flowed from the capacitor 5 to the DC branch line 4C, the short-circuit current continues to be supplied from the AC system 1 to the DC branch line 4C.

[0029] 4 is a diagram showing the state of the DC power distribution system 100 immediately after the DC circuit breaker 7 is tripped. As shown in FIG. 4, when the DC branch current Idc_C is equal to or greater than the DC threshold current Idc_th for a period equal to or greater than the second predetermined time Tdc, the DC circuit breaker 7C is tripped. As a result, the DC branch line 4C is disconnected from the DC power distribution system 100.

[0030] Fig. 5 is a diagram showing the state of the DC power distribution system 100 from when the DC circuit breaker 7 is tripped until power supply to a (healthy) DC branch line 4 where no short-circuit fault has occurred starts. As shown in Fig. 5, after the DC circuit breaker 7 is tripped, the current from the AC system 1 flows to the capacitor 5. This suppresses a voltage rise in the DC bus voltage Vdc immediately after the DC circuit breaker 7C is tripped. In addition, the current flowing through the first reactor 8 flows to the capacitor 5 through the first diode 9. This suppresses a voltage rise in the DC bus voltage Vdc caused by the first reactor 8 immediately after the DC circuit breaker 7C is tripped.

[0031] Fig. 6 is a diagram showing a state in which the DC power distribution system 100 continues to supply power to the DC branch lines 4 in which no short-circuit fault has occurred. As shown in Fig. 6, when the DC circuit breaker 7C is tripped, the supply of power from the AC system 1 to the DC branch lines 4 in which no short-circuit fault has occurred (such as the DC branch lines 4A and 4B) is resumed.

[0032] (Action and effect) According to the above configuration, the capacitor 5 is connected to the node N1 between the AC-DC converter 2 and the DC bus 3. This suppresses fluctuations in the DC bus voltage Vdc caused by a power generation source or a variable load. It also suppresses a voltage rise in the DC bus voltage Vdc when a short-circuit current is interrupted. This prevents a failure of connected devices or a complete shutdown of the DC power distribution system 100 due to an overvoltage of the DC bus voltage Vdc when a short-circuit current is interrupted.

[0033] Furthermore, the first reactor 8 is connected between the node N1 and the DC bus 3. This makes it possible to suppress a sudden increase in the DC branch current Idc caused by a large current flowing from the capacitor 5 to the DC branch line 4 where the short-circuit fault has occurred immediately after the occurrence of a short-circuit fault. This prevents the DC branch current Idc from exceeding the allowable current of the DC circuit breaker, causing the DC circuit breaker to break down. In other words, by providing the first reactor 8, the DC distribution system 100 can appropriately deal with short-circuit faults.

[0034] Also, the first diode 9 is connected in parallel with the first reactor 8. Thereby, the voltage rise of the DC bus voltage Vdc immediately after interruption due to the first reactor 8 can be suppressed. Also, the resonance generated between the first reactor 8 and the capacitor 5 can be suppressed.

[0035] Also, the interruption conditions of the AC breaker 6 and the DC breaker 7 are set to satisfy Pdc_th < Pac_th and / or Tdc < Tac. Thereby, the DC breaker 7 of the DC branch line 4 where a short-circuit fault has occurred is more likely to perform an interruption operation than the AC breaker 6.

[0036] 〔Embodiment 2〕 Other embodiments of the present invention will be described below. For convenience of explanation, members having the same functions as those described in the above embodiments are denoted by the same reference numerals, and the description thereof will not be repeated.

[0037] FIG. 7 is a diagram showing the configuration of the DC power distribution system 100A according to Embodiment 2. As shown in FIG. 7, the DC power distribution system 100A is different from the DC power distribution system 100 according to Embodiment 1 in that it further includes a second reactor 10 and a second diode 11.

[0038] The second reactor 10 is connected between the node N1 and the ACDC converter 2. The second reactor 10 has a role of suppressing the harmonic components of the current supplied from the AC system 1.

[0039] The second diode 11 is connected in parallel with the second reactor 10 such that the anode faces the node N1 side. The second diode 11 refluxes the current flowing through the second reactor 10 immediately after the DC breaker 7 of the DC branch line 4 where a short-circuit fault has occurred is interrupted. Thereby, the second diode 11 can suppress the voltage rise of the DC bus voltage Vdc immediately after interruption due to the second reactor 10.

[0040] (Example) Fig. 8 is a diagram showing experimental results (hereinafter referred to as an example) of the interruption operation in the DC power distribution system 100A shown in Fig. 7. Reference numerals 8001 to 8005 in Fig. 8 respectively denote waveforms showing time changes of the DC bus voltage Vdc, the DC bus current Idc_bus, the DC branch current Idc_A, the DC branch current Idc_B, ​​and the DC branch current Idc_C according to the example.

[0041] Fig. 9 is a diagram showing the configuration of a DC power distribution system 100R according to a comparative embodiment. As shown in Fig. 9, the DC power distribution system 100R according to the comparative embodiment differs from the DC power distribution system 100A according to the second embodiment in that the DC power distribution system 100R does not have the first reactor 8, the first diode 9, the second reactor 10, and the second diode 11.

[0042] Fig. 10 is a diagram showing experimental results (hereinafter referred to as a comparative example) of the interruption operation in the DC power distribution system 100R shown in Fig. 9. Reference numerals 10001 to 10005 in Fig. 10 are graphs showing temporal changes of the DC bus voltage Vdc, the DC bus current Idc_bus, the DC branch current Idc_A, the DC branch current Idc_B, ​​and the DC branch current Idc_C, respectively, according to the comparative example.

[0043] The voltage and current waveforms according to the comparative example and the example will be described below with reference to FIGS.

[0044] As shown in Figures 8 and 10, in the example and comparative example, a short-circuit fault occurs at time t1, the DC circuit breaker 7 of the DC branch line 4 where the short-circuit fault occurred (DC branch line 4C) is shut off at time t2, and power supply to healthy DC branch lines 4 (DC branch lines other than DC branch line 4C) is resumed at time t3 (i.e., the DC bus voltage Vdc returns to its normal value).

[0045] In the comparative example, immediately after time t1, the DC branch current Idc_C flowing through the DC branch line 4 in which the short-circuit fault occurred exceeded the allowable current of the DC circuit breaker 7 (reference numeral 10005 in FIG. 10). On the other hand, in the example, immediately after time t1, the DC branch current Idc_C flowing through the DC branch line 4 in which the short-circuit fault occurred fell below the allowable current of the DC circuit breaker 7 (reference numeral 8005 in FIG. 8). This indicates that the first reactor 8 can suppress a sudden increase in Idc_C.

[0046] Furthermore, in the example, similarly to the comparative example, immediately after time t2, the DC bus voltage Vdc was below the overvoltage level (reference numeral 8001 in FIG. 8 ). This indicates that by circulating the current flowing through the first reactor 8 by the first diode 9, it is possible to suppress the voltage rise of the DC bus voltage Vdc immediately after interruption caused by the first reactor 8.

[0047] [Additional Notes] 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]

[0048] 1 AC system 2 AC / DC converters 3 DC bus 4 DC branch line 5. Capacitors 6 AC circuit breaker 7 DC circuit breaker 8. First reactor 9 First Diode 10 Second reactor 11 Second diode 100, 100A DC power distribution system N1 node

Claims

1. a converter that converts AC power from the AC system into DC power; a DC bus through which DC power supplied from the converter flows; a plurality of DC branch lines connected to the DC bus, each having a DC circuit breaker; a capacitor connected to a node between the converter and the DC bus; a first reactor connected between the node and the DC bus.

2. The DC power distribution system according to claim 1 , further comprising a first diode connected in parallel to the first reactor with an anode facing the DC bus.

3. The DC power distribution system according to claim 1 or 2, further comprising a second reactor connected between the node and the converter.

4. The DC power distribution system according to claim 3 , further comprising a second diode connected in parallel to the second reactor with an anode facing the node.

5. further comprising an AC breaker connected between the AC system and the converter; When a current equal to or greater than a first threshold current flows through the AC circuit breaker for a first predetermined time or longer, the AC circuit breaker interrupts the current, When a current equal to or greater than a second threshold current flows through the DC circuit breaker for a second predetermined time or longer, the DC circuit breaker interrupts the current, 3. The DC power distribution system according to claim 1, wherein the first threshold current and the second threshold current are set so that power supplied through the DC circuit breaker when the second threshold current flows through the DC circuit breaker is smaller than power supplied through the AC circuit breaker when the first threshold current flows through the AC circuit breaker.

6. further comprising an AC breaker connected between the AC system and the converter; When a current equal to or greater than a first threshold current flows through the AC circuit breaker for a first predetermined time or longer, the AC circuit breaker interrupts the current, When a current equal to or greater than a second threshold current flows through the DC circuit breaker for a second predetermined time or longer, the DC circuit breaker interrupts the current, The DC power distribution system according to claim 1 or 2, wherein the second predetermined time is shorter than the first predetermined time.

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