JP2006014456A - Dc multitermial distribution system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a DC multiterminal distribution system in which a fault point is disconnected using a disconnector or a load-break switch of small interruption capacity by discharging the smoothing capacitor of a DC/DC converter quickly. <P>SOLUTION: The DC multiterminal distribution system comprises a plurality of power converters 7 and 10 connected with a DC distribution line 1A through disconnectors 6A, 8A and 9A or a load-break switch, and a DC power supply 3 and a load 11 connected with each power converter. The power converter 7, 10 comprises a smoothing capacitor 29 connected with the DC section on the DC distribution line side, and a control circuit 31 for discharging the smoothing capacitor to the DC power supply side or the load side based on a fault detection signal of the DC distribution line. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a DC multi-terminal distribution system, and more particularly to protection of a DC distribution line in the event of an accident.

  Along with the spread of DC distributed power sources such as fuel cells and solar power generation systems, the amount of DC power used in IT-related facilities is constantly increasing with the progress of the information society. From such a background, it has been studied to adopt a DC multi-terminal distribution system that directly distributes DC power from a DC power source and supplies power to a DC load.

  In other words, conventionally, the output of a DC power source is converted into a three-phase AC by a DC / AC converter, distributed by an AC distribution line, and returned to DC power by an AC / DC converter on the load side to supply power to the DC load. Was common. According to such a conventional AC distribution system, not only three distribution lines are required in accordance with the three phases, but there is a power loss due to stray capacitance. On the other hand, direct current distribution can transmit power with two positive and negative distribution lines, and therefore has the advantage of simplifying the distribution line and reducing power loss due to stray capacitance.

  On the other hand, in addition to the disadvantage that the voltage cannot be changed freely as in the case of alternating current, there is no point where the direct current becomes zero as in the case of alternating current. Cannot be blocked. Therefore, there is a problem that a DC circuit breaker for interrupting a DC current at the time of an accident becomes large, or it is necessary to develop a new DC circuit breaker having a large breaking capacity.

  In order to effectively cut off the DC current at the time of such an accident, it is not a DC multi-terminal distribution system, but an AC / DC converter is configured for a feeder short circuit accident in a DC electric railway power supply system. It has been proposed to control a semiconductor element to cut off an accident current (Patent Document 1). According to this, since it can interrupt before the accident current becomes an excessive value, it is not necessary to increase the breaking capacity of the DC breaker.

JP-A-4-29525

  However, in the prior art described in Patent Document 1, no consideration is given to a problem when a DC / DC converter is connected to a DC distribution line. That is, when configuring a DC multi-terminal distribution system, generally a DC power supply or a DC load is connected to a DC distribution line via a DC / DC converter. This DC / DC converter is generally a voltage type converter having a smoothing capacitor at the input / output end. Therefore, even if the current is reduced by controlling the semiconductor element of the DC / DC converter, the accumulated charge of the smoothing capacitor connected to the DC distribution line flows to the fault point. The capacity cannot be reduced.

  It is an object of the present invention to quickly discharge accumulated charges of a smoothing capacitor of a DC / DC converter so that an accident point can be isolated by a disconnector or a load switch having a small breaking capacity.

  In order to solve the above problems, a DC multi-terminal distribution system according to the present invention includes a plurality of power converters connected to a DC distribution line via a disconnector or a load switch, and a DC connected to each of the power converters. A power source and a load; and the power converter includes a smoothing capacitor connected to a direct current portion on the direct current distribution line side, and based on an accident detection signal of the direct current distribution line, stores the accumulated charge of the smoothing capacitor in the direct current line. A control circuit for discharging to the power supply side or the load side is provided.

  That is, based on the accident detection signal, by operating an inverter of a power converter having a smoothing capacitor connected to the DC section on the DC distribution line side, the electric charge accumulated in the smoothing capacitor is changed to the DC power supply side or the load side. Release promptly. As a result, the current flowing into the accident point from the smoothing capacitor connected to the DC distribution line side can be suppressed, and the current flowing into the accident point starts to decrease. If the current starts to decrease, the power converter can be disconnected from the accident point by a disconnector or a load switch having a small breaking capacity.

  In this case, a voltage type DC / DC converter in which two sets of converters capable of inverter / converter operation are connected via a transformer can be applied to the DC power supply or DC load power converter. In this case, based on the accident detection signal, an inverter / converter operable converter having a smoothing capacitor connected to the DC distribution line side is inverter-operated, and the inverter / converter is connected to the DC power supply side or DC load side Operate converters that can be operated. As a result, the charging current from the DC power supply is cut off, and the charge accumulated in the smoothing capacitor connected to the DC distribution line side is quickly released or absorbed to the DC power supply side or DC load side and attenuates. Thereby, the DC / DC converter can be separated from the accident point by the disconnector or the load switch having a small breaking capacity.

  On the other hand, when the load is an AC load, a DC / AC converter including the smoothing capacitor connected to the DC distribution line side can be used as a power converter. In the same manner, the load accumulated in the smoothing capacitor is absorbed by the load.

  Further, when a current-type AC / DC converter connected to an AC power source is connected to a DC distribution line via a disconnector or a load switch, the AC / DC converter may cause an accident in the DC distribution line. A control circuit for reducing the current flowing into the DC distribution line to zero based on the detection signal can be provided. As a result, since the current flowing from the AC power source to the accident point can be made zero, the current from the AC power source is not added in addition to the current flowing to the accident point, and when the current flowing to the accident point starts to decay, The AC / DC converter can be disconnected from the accident point by a disconnector or a load switch having a small breaking capacity.

  According to the present invention, the accumulated charge of the smoothing capacitor of the DC / DC converter is quickly discharged, and the current flowing through the accident point is turned to attenuation, so that the fault point can be obtained with the disconnector or the load switch having a small breaking capacity. Therefore, a highly efficient DC power distribution system can be realized.

  Hereinafter, the present invention will be described based on embodiments. FIG. 1 is a system configuration diagram showing a part of a DC multi-terminal distribution system according to an embodiment of the present invention. As shown in the figure, in the DC multi-terminal distribution system, two lines of DC distribution lines 1A and 1B, and an AC power source 2 and a fuel cell 3 as a distributed power source are linked to these DC distribution lines 1A and 1B. The AC power source 2 is connected to the disconnectors 6A and 6B via the transformer 4 and an AC / DC converter 5 that converts AC to DC. The disconnectors 6A and 6B are connected to the corresponding DC distribution lines 1A and 1B. The fuel cell 3 is connected to the DC distribution lines 1A and 1B via a DC / DC converter 7 and a disconnector 8A and 8B that convert direct current into direct current of different voltages.

  On the other hand, a DC / DC converter 10 is connected to the DC distribution lines 1A, 1B via disconnectors 9A, 9B, and a DC load 11 is connected to the DC / DC converter 10. Examples of the DC load 11 include a DC load such as an Internet data center. In addition, it can replace with disconnector 6A, 6B, 8A, 8B, 9A, 9B, and can also use the load switch which can interrupt | block a fixed direct current.

  The DC / DC converters 7 and 10 have basically the same configuration, and FIG. 2 shows a specific embodiment of the DC / DC converter 7. As shown in the figure, the DC / DC converter 7 is a DC / DC converter formed by connecting two voltage-type converters 21 and 22 via a transformer 23 of a high-frequency link. The transformer 23 can increase / decrease the voltage. Each of the converters 21 and 22 is configured by bridge-connecting four arms in which a self-extinguishing type semiconductor switch element 25 and a diode 26 are connected in antiparallel, and each inverter / converter can be operated. The DC terminal 27 of the converter 21 can be connected to the DC distribution lines 1A and 1B via the disconnectors 8A and 8B. The DC terminal 28 of the converter 22 is connected to the fuel cell 3. Smoothing capacitors 29 and 30 are connected in parallel to the DC terminals 27 and 28 of the converters 21 and 22, respectively. Each converter 21, 22 is controlled by a control circuit 31.

  In the DC / DC converter 7 configured as described above, when performing power conversion in the direction of the arrow 37 in the figure, the converter 22 is operated as an inverter, and the converter 21 is operated as a converter (diode rectification). Controlled by the control circuit 31. For example, the control circuit 31 performs inverter operation of the converter 22 so that the voltage of the smoothing capacitor 29 becomes a specified voltage. When power conversion is performed in the direction opposite to that of the arrow 37, the converter 21 is operated as an inverter so that the voltage of the smoothing capacitor 30 is a specified voltage. That is, when the DC terminal 27 is connected to the DC distribution line, the voltage command value of the DC / DC converter 7 is set to the voltage of the DC distribution system and controlled. In the case of the DC / DC converter 10, the DC terminal 28 is connected to a DC load, and the voltage command value of the DC / DC converter 10 is set to the rated DC voltage of the load for control.

  The control circuit 31 may have the same configuration with respect to the DC / DC converter 7 and the DC / DC converter 10, and an example of a main part thereof is shown in FIG. As shown in the figure, the DC voltage control circuit 32 generates a current command value corresponding to the DC voltage command value. The current command value output from the DC voltage control circuit 32 is input to the constant current control circuit 34 via the command value switching circuit 33. The constant current control circuit 34 generates a pulse control signal for driving the semiconductor switch element of the converter in accordance with the input current command value, and outputs the pulse control signal to the pulse generation circuit 35. The pulse generation circuit 35 generates a pulse for switching the upper and lower arms of the bridge circuit based on the input pulse control signal, and supplies the pulse to the gate of each semiconductor switch element. On the other hand, the command value switching circuit 33 is supplied with a current command value Ip1 at the time of an accident in the DC distribution line system. The command value switching circuit 33 is switched by an accident detection signal output from the accident detection circuit 36 for detecting an accident in the DC distribution line system, and selects a current command value output from the DC voltage control circuit 32 when normal. At the time of an accident, the current command value Ip1 at the time of the accident is selected. The current command value Ip1 at the time of the accident is set according to the type of the accident. For example, in the case of detecting a ground fault such as the DC distribution lines 1A and 1B, Ip1 = 0 is set. Thereby, the constant current control circuit 34 controls the output DC voltage of the converter 7 so that the DC current becomes zero. Thereby, the direct current voltage of the output of the DC / DC converter 7 is controlled so that the current flowing through the DC / DC converter 7 becomes zero. This action attenuates the accident current.

  On the other hand, an AC / DC converter 5 for converting alternating current connected to an alternating current power source 2 such as an existing alternating current distribution system into direct current is configured as shown in FIG. The three-phase alternating current input via the transformer 4 is input to the alternating current side of a thyristor converter 42 formed by connecting thyristors via a three-phase bridge via an alternating current terminal 41. The DC side of the thyristor converter is connected to a DC terminal 44 via a DC current smoothing reactor 43, and further connected to DC distribution lines 1A and 1B via disconnectors 6A and 6B. That is, the AC / DC converter 5 is configured as a current-type separately excited converter. The thyristor converter 42 is controlled by the control circuit 45.

  As shown in FIG. 5, the control circuit 45 inputs the DC current command value generated by the active power control circuit 51 to the constant current control circuit 53 via the command value switching circuit 52, and the constant current control circuit 53. Is provided with a pulse generation circuit 55 for driving and controlling the thyristor based on the ignition phase signal output from. On the other hand, the command value switching circuit 52 is supplied with a current command value Ip2 at the time of an accident in the DC distribution line system. The command value switching circuit 52 is switched by an accident detection signal output from an accident detection circuit 56 that detects an accident in the DC distribution line system, and selects a current command value output from the active power control circuit 51 when normal. At the time of an accident, the current command value Ip2 at the time of the accident is selected. When, for example, Ip2 = 0 is switched by detecting a ground fault in a DC distribution line or the like, the constant current control circuit 53 controls the output DC voltage of the separately excited converter so that the DC current becomes zero. Thereby, the output current supplied from the AC / DC converter 5 to the DC distribution line can be made zero. If a DC / AC converter is provided in parallel with the AC / DC converter 5, power can be sent from the DC distribution line system to the AC system.

  In the DC multi-terminal distribution system of the embodiment configured as described above, the operation at the time of a ground fault of the DC distribution line 1A or 1B, which is a feature of the present invention, will be described. When operating on the line of the DC distribution line 1A and a ground fault occurs at the point F of the line, the DC / DC converter 7 supplies the fuel cell 3 to the DC distribution line 1A as described above. The output current is controlled to zero by reducing the direct current. Similarly, the AC / DC converter 5 controls the DC current supplied from the AC power source 2 to the DC distribution line 1A to be zero. On the other hand, the DC / DC converter 10 increases the DC power supplied to the DC load 11 and releases the energy of the DC distribution line to the load.

  Therefore, the AC / DC converter 5 system can quickly disconnect the AC / DC converter 5 system by the disconnector 6A having a small breaking capacity because the DC power supplied to the DC distribution line 1A quickly becomes zero. it can. However, since the DC / DC converter 7 is a voltage type, it has the smoothing capacitor 29 connected to the direct current portion on the direct current transmission line side. Therefore, even if the current command value Ip2 is zero, the accumulated charge in the smoothing capacitor 29 is reduced. A current will flow until it is discharged. The DC / DC converter 10 performs an operation of fixing or increasing (not shown) the current command value Ip2 as before the accident and discharging the accumulated charge of the smoothing capacitor 29 to the DC load 11.

  That is, in the case of the DC / DC converter 10 in which the smoothing capacitor 29 is connected to the DC portion on the DC distribution line 1A side, even if the supply current or the load current is reduced, the charge accumulated in the smoothing capacitor 29 is not grounded. It will flow into accident point F. Therefore, the disconnectors 8A and 9A cannot be opened immediately after the accident is detected, and the protection of the accident is delayed.

  Therefore, in the present embodiment, in order to discharge the energy stored in the DC distribution line 1A (or 1B) at a high speed in the event of an accident at high speed, the converter 21 of the DC / DC converter 7 is operated as an inverter, thereby providing a smoothing capacitor. The energy stored in the DC power distribution line 1A (or 1B) such as 29 is discharged to the fuel cell 3 side or the DC load 11 side, and the current flowing through the accident point F is made zero at high speed. Since direct current cannot be sent back to the fuel cell 3, when the DC / DC converter 7 is operated as an inverter, the charge stored in the smoothing capacitor 29 is stored in the smoothing capacitor 30. Therefore, it is necessary to change the output voltage command of the converter 22 of the DC / DC converter 7 to a voltage that is transiently higher than the specified voltage.

  Note that the charge of the smoothing capacitor 29 of the DC / DC converter 7 may also be released to the load side by the DC / DC converter 10 via the DC distribution line 1A. It is preferable that the charge of the smoothing capacitor 29 of the DC converter 7 is reliably collected on the fuel cell side.

  In the above embodiment, a DC multi-terminal distribution system configuration using a disconnector or a circuit breaker with a small breaking current rating has been shown, but the present invention is not limited to this, and also in a DC multi-terminal distribution system using a load switch. By performing current control of the DC / DC converter and the AC / DC converter, there is an advantage that the current interrupting rating of the load switch can be reduced.

  Moreover, although the example of the DC load 11 was shown as a load, it cannot be overemphasized that an AC load can be included. In this case, the DC / DC converter 10 may be changed to a DC / AC converter.

  As described above, according to the present embodiment, when a ground fault occurs in the operating DC distribution line 1A or 1B, power cannot be sent to the DC load 11, but the fault section is cut off by a disconnector and is sound. Power can be reliably supplied to the load using the line. In other words, if a ground fault occurs at point F of the DC distribution line 1A, the disconnectors 6A, 8A, 9A are opened to disconnect the accident line DC distribution line 1A, and the disconnectors 6B, 8B, 9B are turned on. Electric power can be supplied to the load using the sound DC distribution line 1B.

  In addition to the fuel cell 3, a solar power generation system can be applied as the distributed power source. Further, the DC / DC converter 7 can be omitted by making the voltage of the distributed DC power source equal to the voltage of the power distribution system. In this case, since the number of the smoothing capacitors 29 can be reduced, the accumulated energy of the distribution line system that must be released in the event of an accident can be reduced.

1 is a system configuration diagram of a part of a DC multi-terminal distribution system according to an embodiment of the present invention. It is a block diagram of one Embodiment of a DC / DC converter. It is a block diagram of the control circuit of one Embodiment of a DC / DC converter. It is a block diagram of one Embodiment of an AC / DC converter. It is a block diagram of the control circuit of one Embodiment of an AC / DC converter.

Explanation of symbols

1A, 1B DC distribution line 2 AC power supply 3 Fuel cell 5 AC / DC converter 6A, 6B, 8A, 8B, 9A, 9B Disconnector 7, 10 DC / DC converter 11 DC load 21, 22 Converter 29, 30 Smoothing capacitor 31 Control circuit

Claims (6)

  A plurality of power converters connected to a DC distribution line via a disconnector or a load switch; and a DC power source and a load connected to each of the power converters, the power converter including the DC distribution line A smoothing capacitor is connected to the DC section on the side, and a control circuit is provided for discharging the accumulated charge of the smoothing capacitor to the DC power supply side or the load side based on an accident detection signal of the DC distribution line. DC multi-terminal power distribution system.   The DC power converter according to claim 1, wherein the power converter is a voltage type DC / DC converter in which two converters capable of operating an inverter / converter are connected via a transformer. Terminal power distribution system.   The load includes an AC load, and the power converter connected to the AC load is a DC / AC converter including the smoothing capacitor connected to the DC distribution line side. Item 5. A DC multi-terminal power distribution system according to item 1.   A current-type AC / DC converter connected to an AC power source is connected to the DC distribution line via a disconnector or a load switch, and the AC / DC converter detects an accident detection signal of the DC distribution line. The DC multi-terminal distribution system according to claim 1, further comprising a control circuit that restricts a current flowing into the DC distribution line to zero based on   2. The DC multi-terminal according to claim 1, wherein the control circuit blocks the gate pulse of the power converter after discharging the accumulated charge of the smoothing capacitor to the DC power supply side or the load side. Power distribution system.   5. The DC multi-terminal distribution system according to claim 4, wherein the control circuit blocks the gate pulse of the AC / DC converter after the current flowing into the DC distribution line is reduced to zero.

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