JP6844352B2 - DC cutoff device - Google Patents

Description

The present invention relates to a direct current cutoff device capable of cutting off bidirectional direct current with small power loss during steady operation.

In a DC distribution system with two DC systems, when an accident occurs in one DC system, a DC circuit breaker provided between the two systems disconnects the system in which the accident occurred, thereby loading from the other normal system. It is possible to distribute power to.

The DC circuit breaker shown in FIG. 10 is composed of only the mechanical circuit breaker 4, and when an accident occurs at any of the first and second DC systems 1 and 2, the mechanical contact opens the pole and an accident occurs. Disconnect the DC system.

Further, the mechanical circuit breaker 4 is connected to the first DC system 1 and the second DC system 2, and can open the pole with respect to the bidirectional current. In a networked DC power transmission and distribution system, such as the utilization of renewable energy and the stable supply and demand of electric power, there may be cases where bidirectional current flows in one path, so this bidirectional current cutoff technology is necessary. Become.

Here, an alternating current cutoff method will be described. The AC circuit breaker is energized because it functions as a conductor when the mechanical contacts are closed (stationary), and opens the mechanical contacts when an accident occurs. An arc is generated when the mechanical contacts are opened, but the arc can be extinguished at the current zero point, so that the current can be cut off.

Moreover, since the cutoff state functions as an insulator, no current flows. Gas circuit breakers and vacuum circuit breakers are mainly used for this AC circuit breaker, and although the medium for extinguishing the arc is different, both adopt a method of extinguishing the arc at the current zero point.

However, in the case of direct current interruption, unlike an alternating current, a zero point does not occur. Therefore, in the configuration shown in FIG. 10, the arc generated when the mechanical contact is opened cannot be extinguished, resulting in contact damage or interruption failure.

Therefore, the DC cutoff device requires an auxiliary circuit or the like that generates a current zero point. Patent Document 1 and Patent Document 2 (Example 2) are disclosed as a breaking method provided with such an auxiliary circuit. FIG. 11 shows the DC current switchgear of Patent Document 1, and FIG. 12 shows the DC current switchgear of Example 2 of Patent Document 2.

Japanese Unexamined Patent Publication No. 2016-28378 Japanese Unexamined Patent Publication No. 2016-126920

As described above, bidirectional current cutoff is required in a networked DC distribution system. However, since Patent Document 1 and Example 2 of Patent Document 2 are not intended to cut off bidirectional current, there is a problem that bidirectional current cannot be cut off.

Further, in the second embodiment of Patent Document 2, a plurality of stages of a bridge circuit 5 including two semiconductor switches (IGBTs), two diodes and one capacitor are connected in series. Further, the energizing contact 6 (vacuum circuit breaker or the like) is connected in parallel to the bridge circuit 5 connected in series. In this configuration, there is a problem that the switchgear becomes large and costly.

Further, in the second embodiment of Patent Document 2, a current flows through the semiconductor switch (IGBT) of each bridge circuit 5 connected in series during the cutoff operation. A semiconductor switch causes a steady-state on-loss when a current is flowing. Further, a switching loss occurs when the semiconductor switch is turned off. Therefore, it is not preferable to use the semiconductor switch as the DC cutoff device as shown in FIG. 12 from the viewpoint of the efficiency of the entire DC distribution system.

From the above, it is an issue to provide a DC cutoff device capable of bidirectional current cutoff and suppressing an arc at the time of opening a mechanical contact without using a semiconductor switch.

The present invention has been devised in view of the above-mentioned conventional problems, and one aspect thereof is a first diode having a cathode connected to the + terminal of the first direct current system, the first direct current system, and the first direct current system. A first mechanical breaker having one end connected to a common connection point of a diode, a capacitor connected between the other end of the first mechanical breaker and the anode of the first diode, the capacitor and the first A second diode having an anode connected to a common connection point of the diode, a second mechanical breaker connected between the common connection point of the capacitor and the first mechanical breaker and the cathode of the second diode, and the like. The common connection point between the cathode of the second diode and the second mechanical breaker is connected to the + terminal of the second DC system.

Further, as one aspect thereof, when a current is flowing from the first DC system to the second DC system and an accident occurs in the second DC system, the second mechanical circuit breaker is opened and then the pole is opened. When the first mechanical circuit breaker is opened after the capacitor is charged and a current is flowing from the second DC system to the first DC system and an accident occurs in the first DC system, the first DC system is used. It is characterized in that the second mechanical circuit breaker is opened after the mechanical circuit breaker is opened and the charging of the capacitor is completed.

Further, as another embodiment, the capacitor is provided with a discharge resistor connected in parallel to the capacitor and a switch connected in series with the discharge resistor.

Further, as one aspect thereof, when a current is flowing from the first DC system to the second DC system and an accident occurs in the second DC system, after opening the second mechanical circuit breaker. After the capacitor is fully charged, the first mechanical circuit breaker is opened, then the switch is closed, and after the capacitor is discharged, the switch is opened, and a current flows from the second DC system to the first DC system. If an accident occurs in the first DC system, the first mechanical circuit breaker is opened, the second mechanical circuit breaker is opened after the capacitor is fully charged, and then the switch is closed. It is characterized in that the switch is opened after the pole is discharged and the capacitor is discharged.

According to the present invention, it is possible to provide a DC cutoff device capable of bidirectional current cutoff and suppressing an arc at the time of opening a mechanical contact without using a semiconductor switch.

The figure which shows the DC cutoff device in Embodiment 1. FIG. The figure which shows the DC cutoff device in a steady state in Embodiment 1. FIG. The figure which shows the DC cutoff device at the time of cutoff in Embodiment 1. FIG. The time chart which shows the current of the 2nd DC system side in Embodiment 1. A time chart showing a voltage across the second mechanical circuit breaker according to the first embodiment. The time chart which shows the contact operation of the 1st and 2nd mechanical circuit breakers in Embodiment 1. FIG. The figure which shows the DC cutoff device in Embodiment 2. FIG. The figure which shows the DC cutoff device at the time of discharge in Embodiment 2. FIG. The time chart which shows the contact operation of the 1st and 2nd mechanical circuit breakers and a switch in Embodiment 2. The figure which shows an example of the conventional DC circuit breaker. The figure which shows the DC current switchgear of Patent Document 1. FIG. The figure which shows the DC current switchgear of Patent Document 2.

Hereinafter, embodiments 1 and 2 of the DC blocking device of the present invention will be described in detail with reference to FIGS. 1 to 9.

[Embodiment 1]
FIG. 1 shows the DC cutoff device 3 of the first embodiment. As shown in FIG. 1, the DC cutoff device 3 is connected to the first DC system 1 and the second DC system 2. The DC circuit breaker 3 is a full bridge circuit having a first mechanical circuit breaker CB1 and a second mechanical circuit breaker CB2, a first diode D1 and a second diode D2, and a capacitor C.

The cathode of the first diode D1 is connected to the + terminal of the first DC system 1. One end of the first mechanical circuit breaker CB1 is connected to a common connection point between the first DC system 1 and the first diode D1. A capacitor C is connected between the other end of the first mechanical circuit breaker CB1 and the anode of the first diode D1.

The anode of the second diode D2 is connected to the common connection point between the capacitor C and the first diode D1 (anode). The second mechanical circuit breaker CB2 is connected between the common connection point of the capacitor C and the first mechanical circuit breaker CB1 and the cathode of the second diode D2. The common connection point between the cathode of the second diode D2 and the second mechanical circuit breaker CB2 is connected to the + terminal of the second DC system 2.

The first mechanical circuit breaker CB1 and the second mechanical circuit breaker CB2 perform a closing or opening operation of the mechanical contacts. The first diode D1 and the second diode D2 are connected so as not to be conductive with respect to the currents flowing from the first DC system 1 and the second DC system 2, respectively.

FIG. 2 shows the DC cutoff device in the steady state of the first embodiment. In the steady state, the first mechanical circuit breaker CB1 and the second mechanical circuit breaker CB2 are in the closed pole state, and a bidirectional energization path as shown in FIG. 2 is obtained.

At this time, no current flows through the first diode D1 and the second diode D2, and the capacitor C is not charged. Further, in the steady-state energization path, since the current flows through the first mechanical circuit breaker CB1 and the second mechanical circuit breaker CB2, there is almost no power loss.

FIG. 3 shows a DC cutoff device 3 when an accident occurs on the second DC system 2 side. When an accident occurs on the second DC system 2 side, the second mechanical circuit breaker CB2 opens, and as shown in FIG. 3, the first mechanical circuit breaker CB1 → capacitor C → second diode D2 from the first DC system 1 side. Current flows through the path of.

Further, the voltage across the second mechanical circuit breaker CB2 (≈ the voltage across the capacitor C) gradually rises due to the charging operation of the capacitor C. (See FIG. 5 described later) The time change of this voltage is determined by the capacitance value of the capacitor C and the resistance component of the load connected to the second DC system 2 side (not shown). Since the voltage across the second mechanical circuit breaker CB2 gradually rises in this way, no arc is generated when the second mechanical circuit breaker CB2 is opened.

When the capacitor C is fully charged, the current on the second DC system 2 side becomes substantially zero. After that, as shown in FIG. 1, the first mechanical circuit breaker CB1 is opened while the second mechanical circuit breaker CB2 is open and the current of the first mechanical circuit breaker CB1 is substantially zero. As a result, the current can be safely cut off without generating an arc even when the first mechanical circuit breaker CB1 is opened.

The direction of current flow and the current value at the time of an accident are monitored by using a host controller, and by operating the contacts of the first machine circuit breaker CB1 and the second machine circuit breaker CB2, the first machine circuit breaker CB1 and The second mechanical circuit breaker CB2 is opened and closed.

FIG. 4 shows the second DC system 2 side current from the steady state to the completion of interruption in the first embodiment. FIG. 5 shows the voltage across the second mechanical circuit breaker CB2. Here, time t0 indicates a steady state, time t1 indicates an accident, time t2 indicates an opening time of the second mechanical circuit breaker CB2, time t3 indicates an approximately zero current, and time t4 indicates an opening time of the first mechanical circuit breaker CB1. ing.

Further, FIG. 6 shows the closing and opening operations of the first mechanical circuit breaker CB1 and the second mechanical circuit breaker CB2 at that time. The closed pole state is on and the open pole state is off.

When the time t0 is steady, the first and second mechanical circuit breakers CB1 and CB2 are closed as shown in FIG. 6, and the current on the second DC system 2 side is in a normal state as shown in FIG. 5, FIG. As shown in, the voltage across the second mechanical circuit breaker CB2 is 0.

When an accident occurs in the second DC system 2 at time t1, the current on the second DC system 2 side starts to increase as shown in FIG.

At time t2, when the second mechanical circuit breaker CB2 is opened as shown in FIG. 6, the capacitor C is charged as shown in FIG. 5, and the voltage across the second mechanical circuit breaker CB2 begins to rise. As shown, the current on the second DC system 2 side begins to decrease.

At time t3, the charging of the capacitor C is completed as shown in FIG. 5, the voltage across the second mechanical circuit breaker CB2 becomes constant, and the current on the second DC system 2 side becomes substantially zero as shown in FIG. ..

At time t4, the first mechanical circuit breaker CB1 is opened as shown in FIG.

In the first embodiment, the shutoff method when an accident occurs on the second DC system 2 side has been described, but even when an accident occurs on the first DC system 1 side, it is possible to shut off by the same principle and the target operation. Is. In this case, at time t2, the first mechanical circuit breaker CB1 is opened instead of the second mechanical circuit breaker CB2.

In the first embodiment, it is possible to perform a direct current cutoff that does not generate an arc for a bidirectional direct current. Further, since the first mechanical circuit breaker CB1 and the second mechanical circuit breaker CB2 are always energized in the steady state, there is almost no power loss.

Further, the present embodiment 1 has the following effects as compared with Patent Document 1 (Example 2).
-It can be composed of a bridge circuit consisting of two mechanical circuit breakers, two diodes, and one capacitor.
-Compared with Patent Document 2 (Example 2) in which a plurality of bridge circuits including semiconductor switches are used, the number of parts is small, and the size and cost can be reduced.
-Since a semiconductor switch such as an IGBT is not used, no loss of the semiconductor switch occurs not only at the steady state but also at the time of interruption. The first embodiment is superior in terms of the efficiency of the entire power distribution system.

[Embodiment 2]
FIG. 7 shows the DC cutoff device of the second embodiment. The same parts as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. In the DC cutoff device of the second embodiment, in addition to the configuration of the first embodiment, a discharge resistor R is connected in parallel with the capacitor C. Further, a switch SW is connected in series with the discharge resistor R. The switch SW opens and closes.

As the switch SW, a mechanical circuit breaker is used as in the case of the first mechanical circuit breaker CB1 and the second mechanical circuit breaker CB2. However, since a current flows through the switch SW only for a short time only when the capacitor C is discharged, the mechanical cutoff of the switch SW may have a small current capacity.

Further, the switch SW may be replaced with a semiconductor switch instead of the mechanical circuit breaker. When replaced with a semiconductor switch, the loss generated in the semiconductor switch is not related to the efficiency of the entire system because it occurs only when the first mechanical circuit breaker CB1 and the second mechanical circuit breaker CB2 are opened.

The operation / operation of the second embodiment is as follows. Differences from the first embodiment will be described.

FIG. 7 is a configuration diagram of the DC circuit breaker of the second embodiment, and shows a state in which the current cutoff as in the first embodiment is completed and the first mechanical circuit breaker CB1 and the second mechanical circuit breaker CB2 are opened. Shown. In the second embodiment as well, a case where a current is flowing from the first DC system 1 to the second DC system 2 and an accident occurs on the second DC system 2 side will be described.

In the second embodiment, when the DC system is re-introduced after the interruption of the DC system in which the accident has occurred, that is, when the continuity and interruption functions of the repeated DC interruption device 3 are used, the capacitor C is connected after the interruption is completed. It is necessary to discharge the charged voltage. In this case, as shown in FIG. 7, a discharge resistor R may be attached in parallel with the capacitor C. Further, since it is necessary to switch between charging and discharging the capacitor C, the switch SW is connected in series with the discharging resistor R.

FIG. 8 shows the DC cutoff device 3 at the time of discharge in the second embodiment. Since it takes a period to charge the capacitor C from the fixed time to the completion of shutoff, the switch SW keeps the pole open state as shown in FIG. 7. Since it takes a period to discharge the capacitor C from the completion of the shutoff to the re-turning on, the switch SW is closed as shown in FIG.

After the current is cut off, in the closed state of the switch SW, a current flows and discharge is performed in the discharge resistor R as shown by the broken line in FIG. Whether or not the discharge is completed is determined by detecting the voltage Vc across the capacitor C and determining that the discharge is complete when the voltage Vc ≈ 0 across the capacitor C. When the discharge is completed, the switch SW is opened so that no current flows through the discharge resistor R when the switch SW is turned on again. After that, the second mechanical circuit breaker CB2 and the first mechanical circuit breaker CB1 are closed in this order, and the DC system is turned on again.

FIG. 9 shows the contact operation of the first mechanical circuit breaker CB1, the second mechanical circuit breaker CB2, and the switch SW from the steady state to the shutoff and re-entry. The closed pole state is on and the open pole state is off.

Time t0, time t2, and time t4 in FIG. 9 are the same as those in the first embodiment. Time t5 is when the switch SW is closed, time t6 is when the switch SW is open, time t7 is when the second mechanical circuit breaker CB2 is closed, time t8 is when the first mechanical circuit breaker CB1 is closed, and time t9 is after re-insertion. Shows the steady time of.

In the second embodiment, the direction in which the current flows and the current value at the time of an accident are monitored by using the host controller, and the first mechanical circuit breaker CB1, the second mechanical circuit breaker CB2, and the switch SW are operated.

Further, in the second embodiment, the shutoff and re-input operations when an accident occurs on the second DC system 2 side have been described, but the same principle and target operations are also described when an accident occurs on the first DC system 1 side. It is possible to shut off and re-inject at. In this case, the first mechanical circuit breaker CB1 is opened at time t2, and the second mechanical circuit breaker CB2 is opened at time t4. Further, the first mechanical circuit breaker CB1 is closed at time t7, and the second mechanical circuit breaker CB2 is closed at time t8.

The second embodiment has the same effect as that of the first embodiment. Further, in the second embodiment, by connecting the discharge resistor R and the charge / discharge switching switch SW, it is possible to repeatedly cut off the direct current and turn it on again.

Although the above description has been made in detail only with respect to the specific examples described in the present invention, it is clear to those skilled in the art that various modifications and modifications can be made within the scope of the technical idea of the present invention. It goes without saying that such modifications and modifications fall within the scope of the claims.

For example, the bridge circuits of FIGS. 1 and 7 have a configuration in which the first mechanical circuit breaker CB1 and the first diode D1 are arranged in opposite directions, and the second mechanical circuit breaker CB2 and the second diode D2 are arranged in opposite directions. You may. In this case, the cathode terminal of the first diode D1 is connected to the + terminal of the first DC system 1. Further, the cathode terminal of the second diode D2 is connected to the + terminal of the second DC system 2.

1 ... 1st DC system 2 ... 2nd DC system 3 ... DC circuit breaker 4 ... Mechanical circuit breaker CB1 ... 1st mechanical circuit breaker CB2 ... 2nd mechanical circuit breaker D1 ... 1st diode D2 ... 2nd diode C ... Capacitor R … Discharge resistor SW… Switch

Claims (4)

The first diode whose cathode is connected to the + terminal of the first DC system,
A first mechanical circuit breaker whose one end is connected to a common connection point between the first DC system and the first diode,
A capacitor connected between the other end of the first mechanical circuit breaker and the anode of the first diode,
A second diode whose anode is connected to the common connection point between the capacitor and the first diode,
A second mechanical circuit breaker connected between the common connection point of the capacitor and the first mechanical circuit breaker and the cathode of the second diode, and
The common connection point between the cathode of the second diode and the second mechanical circuit breaker is connected to the + terminal of the second DC system, and the semiconductor switch is connected in parallel to the first diode and the second diode. A DC circuit breaker characterized by the absence. If a current is flowing from the first DC system to the second DC system and an accident occurs in the second DC system, the first is performed after the second mechanical circuit breaker is opened and the capacitor is fully charged. Open the mechanical circuit breaker,
When a current is flowing from the second DC system to the first DC system and an accident occurs in the first DC system, the first mechanical circuit breaker is opened, the capacitor is charged, and then the first DC system is charged. 2. The DC circuit breaker according to claim 1, wherein the mechanical circuit breaker is opened. A discharge resistor connected in parallel with the capacitor
A switch connected in series with the discharge resistor,
The DC cutoff device according to claim 1, further comprising. When a current is flowing from the first DC system to the second DC system and an accident occurs in the second DC system, the first DC system is opened, the second mechanical circuit breaker is opened, and the capacitor is charged. 1 The mechanical circuit breaker is opened, then the switch is closed, the capacitor is discharged, and then the switch is opened.
When a current is flowing from the second DC system to the first DC system and an accident occurs in the first DC system, the first DC circuit breaker is opened, the capacitor is charged, and then the first DC system is charged. 2. The DC circuit breaker according to claim 3, wherein the mechanical circuit breaker is opened, then the switch is closed, the capacitor is discharged, and then the switch is opened.

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