WO2019043777A1

WO2019043777A1 - Dc power transmission system

Info

Publication number: WO2019043777A1
Application number: PCT/JP2017/030896
Authority: WO
Inventors: 崇裕石黒; 卓郎新井
Original assignee: 株式会社東芝
Priority date: 2017-08-29
Filing date: 2017-08-29
Publication date: 2019-03-07

Abstract

According to the present invention, a first converter converts input power into DC power of a prescribed voltage. A second converter has a power storage device, and converts, into AC power, the DC power supplied from the first converter via a DC link which is connected to the DC side of the first converter. A protection device, which is connected between the second converter and an AC system, has a switching unit that sets the connection between the second converter and the AC system to be in a connected state or in a disconnected state, and a load that consumes the AC power from the second converter when the switching unit achieves the disconnected state.

Description

DC power transmission system

The present invention relates to a direct current transmission system.

BACKGROUND ART In recent years, power generation methods using renewable energy, such as wind power generation and solar power generation, are widely used from the viewpoint of reducing the load on the environment associated with power generation and diversifying power sources. High-voltage direct current transmission (HVDC: High-Voltage Direct Current Transmission) is known as a system for supplying power thus generated to a power receiving facility of a consumer. HVDC is put into practical use all over the world as a method suitable for large capacity and long distance transmission. The conventional HVDC converts the transmitted DC power into AC power by the converter, and supplies the AC power to the power reception facility of the AC system. When power can not be supplied to the power receiving facility due to a ground fault or the like in the AC system, the DC power supplied from the power generation apparatus to the converter and the AC power output from the converter can not be balanced. was there. In particular, when the HVDC is connected to a generator based on a power generation system using renewable energy, it is difficult to immediately stop power generation. In this case, an overvoltage may be applied to the power storage device of the converter, which may cause the converter to stop.

JP-A-2015-515425

The problem to be solved by the present invention is to provide a DC power transmission system that can maintain high reliability at lower cost.

The DC power transmission system of the embodiment has a first converter, a second converter, and a protection device. The first converter converts input power into DC power of a predetermined voltage. The second converter has a storage device, and converts DC power supplied from the first converter into AC power via a DC link connected to the DC side of the first converter. 2 converter, having a storage device. The protection device is a protection device connected between the second converter and an alternating current system, which opens and closes a connection between the second converter and the alternating current system. And a load that consumes AC power from the second converter when the open / close unit is turned off.

The figure which shows the example to which the DC power transmission system 100 of 1st Embodiment is applied. The figure which shows an example of a structure of AC / DC converter 120 of 1st Embodiment. The figure which shows the other example of a structure of AC / DC converter 120 of 1st Embodiment. The figure which shows the normal state which the accident has not generate | occur | produced in the power transmission system. The figure which shows the initial state which the accident generate | occur | produced in the power transmission system. The figure which shows the state of the middle period where the accident generate | occur | produced in the power transmission system. The figure which shows the state of the second half in which the accident generate | occur | produced in the power transmission system. The timing chart explaining operation of direct-current power transmission system 100 of a 1st embodiment. The figure which shows the example to which DC power transmission system 100A of 3rd Embodiment is applied.

Hereinafter, a DC power transmission system according to an embodiment will be described with reference to the drawings.

First Embodiment
First, the first embodiment will be described. FIG. 1 is a diagram illustrating an example to which the DC power transmission system 100 according to the first embodiment is applied. The DC power transmission system 100 is applied to, for example, a power transmission system that transmits large-scale renewable energy such as offshore wind power generation, desert photovoltaic power generation, solar thermal power generation, etc. to a large city. The power transmission system includes, for example, a power generation device 10, a transformer 20, an AC grid 30, and a DC power transmission system 100. The DC power transmission system 100 includes an AC / DC converter 110, an AC / DC converter 120, a protection circuit 130, and a control unit 140.

Here, the protection circuit 130 is an example of the “protection device”. In addition, power generated by wind power, sunlight, or solar heat is an example of “renewable energy”.

The power generation device 10 is, for example, a generator such as a wind power generator. The power generation device 10 generates, for example, AC power with a voltage of about several hundred kilovolts, and outputs the generated power to the DC power transmission system 100. The AC power generated by the power generation device 10 is an example of “input power”.

An AC / DC converter 110 of the DC power transmission system 100 converts input power supplied from the power generation device 10 into DC power of a predetermined voltage. The AC / DC converter 110 converts, for example, AC power of a voltage of about several hundred kilovolts supplied from the power generation device 10 into a DC voltage of about several hundred kilovolts.

The AC / DC converter 120 converts the DC voltage supplied from the AC / DC converter 110 into AC power. In the present embodiment, the transmission path L between the AC / DC converter 120 and the AC / DC converter 110 is a DC side of the DC power transmission system 100 that handles DC power and an AC side that handles AC power. And functions as a connection unit. That is, the transmission line L is an example of the “DC link”.

Further, the AC / DC converter 120 has a capacitor inside, and adjusts the voltage of AC power output from the AC / DC converter 120 by storing and discharging electric charge in the capacitor. The configuration of AC / DC converter 120 will be described later. The capacitor is an example of the "power storage device".

Protection circuit 130 is connected between AC / DC converter 120 and AC system 30. Although the protection circuit 130 is connected to the AC system 30 via the transformer 20 in the example of FIG. 1, the transformer 20 may not be provided in the present embodiment. In this case, the protection circuit 130 and the AC system 30 are connected without the transformer 20. The protection circuit 130 includes an open / close unit 132, an open / close unit control unit 134, and a resistor unit 136. The resistance unit 136 is an example of the “load”.

The switching unit 132 is connected between the AC / DC converter 120 and the transformer 20, and connects or disconnects the AC / DC converter 120 and the transformer 20. The switch 132 may be a mechanical circuit breaker, or may be a gas circuit breaker or a vacuum circuit breaker. Moreover, the switch part 132 may be comprised by one switch, and may be comprised by several switch.

For example, when a specific electrical condition is satisfied in the switching unit 132, the switching unit control unit 134 controls the switching unit 132 to cut off between the AC / DC converter 120 and the transformer 20. Here, the specific electrical condition means, for example, that a current (short circuit current) equal to or more than a predetermined threshold flows due to a system fault such as a ground fault in the AC system 30 or the like. For example, switching control section 134 controls switching section 132 by utilizing the magnetic force generated when a short circuit current flows in the conductor through which the internal load current flows, and between AC / DC converter 120 and transformer 20. Is shut off.

In addition, the switching unit control unit 134 monitors the voltage of the relevant part via the instrument transformer provided at the desired location in the AC system 30, and the switching part 132 is performed when a specific electrical condition is satisfied in the relevant part. Between the AC / DC converter 120 and the transformer 20 may be shut off.
When the switching unit control unit 134 disconnects between the AC / DC converter 120 and the transformer 20, the switching unit control unit 134 notifies the control unit 140 to that effect.

By the way, in a state in which AC power is output from AC / DC converter 120 to transformer 20, switch control section 134 controls switch 132 so that there is no gap between AC / DC converter 120 and transformer 20. Even if not physically connected, if the voltage of the AC power output from the AC / DC converter 120 is high, an arc current may flow from the AC / DC converter 120 to the transformer 20. In this case, the electrical connection between the AC / DC converter 120 and the transformer 20 is not cut off even when the switching unit 132 is turned off. When an arc current flows from the AC / DC converter 120 to the transformer 20 after the switching part 132 is turned off, the AC current output from the AC / DC converter 120 needs to be stopped to stop the arc current. There is.

Resistor unit 136 is configured such that switching unit 132 shuts off between AC / DC converter 120 and transformer 20, and the AC current output from AC / DC converter 120 is stopped, thereby When the AC power is output again from AC / DC converter 120 after the electrical connection between DC converter 120 and transformer 20 is cut off, AC supplied from AC / DC converter 120 Consume power. In the example of FIG. 1, the resistance unit 136 is provided in parallel with the switching unit 132 in parallel with the AC / DC converter 120, but the resistance unit 136 is supplied from the AC / DC converter 120. It is sufficient if AC power can be consumed. Moreover, the resistance part 136 may be comprised by one resistor, and may be comprised by several resistors. In each embodiment, the configuration including the resistance portion 136 is illustrated, but in place of the resistance portion 136, it is possible to at least temporarily consume the AC power supplied from the AC / DC converter 120. It is sufficient to have an optional "load". Examples of the load may include both a resistor and an alternating current load, or may be an electric device, a charging device, or the like.

Transformer 20 converts the voltage of the AC power supplied from AC / DC converter 120 via protection circuit 130 into a predetermined voltage. Transformer 20 regulates the potential difference between AC / DC converter 120 and AC system 30. For example, when the transformer 20 is an insulating transformer, the protection circuit 130 and the AC system 30 can be electrically isolated.

The AC system 30 is hardware for exchanging commercial power by converting AC power and DC power mutually by the AC / DC converter 120. The AC system 30 is, for example, an AC power supply that supplies AC power, an AC load that consumes AC power, a power transmission network for transmitting AC power to an AC load, or the like.

When a system fault such as a ground fault occurs in AC system 30, control unit 140 controls AC / DC converter 120 and protection circuit 130 so that the capacitor included in AC / DC converter 120 is not overcharged. Let's do it. In the example of FIG. 1, the control unit 140 is provided outside the AC / DC converter 120. In this case, in the DC power transmission system 100 according to the embodiment, the distributed control unit 140 and the control unit (not shown) of the AC / DC converter 120 can be operated, so extension is easy. Cost and operating costs can be reduced. In the embodiment, although the case where control unit 140 is provided outside AC / DC converter 120 will be described as an example, the present invention is not limited to this, and control unit 140 may use AC / DC converter 120. It may be provided inside the

The control unit 140 monitors, for example, the AC power voltage and current at the predetermined place via an instrument transformer (not shown) provided at a predetermined place of the AC system 30. Then, for example, when a current equal to or greater than a predetermined threshold flows in the transmission line between transformer 20 and AC grid 30 due to a ground fault or the like, control unit 140 determines that a system fault such as a ground fault has occurred. judge. When it is determined that a system fault such as a ground fault has occurred, control unit 140 controls the alternating current output from alternating current / direct current converter 120 to be in the vicinity of 0 (zero). In the following description, making the alternating current output from the AC / DC converter 120 close to 0 (zero) is referred to as “stopping the AC / DC converter 120” or the like.

When a ground fault occurs in AC system 30, control unit 140 stops AC / DC converter 120. As a result, the control unit 140 can suppress damage to the internal circuit of the AC / DC converter 120 by continuing the excessive current flow to the AC / DC converter 120.
Further, the control unit 140 causes the voltage output from the AC / DC converter 120 to decrease to a value close to 0 (zero) by the excess current continuing to flow in the AC / DC converter 120, and the capacitor 140 It becomes possible to suppress falling into a state in which AC power can not be output from AC / DC converter 120 because control can not be performed so that charge is stored.
In addition, when a ground fault occurs in AC system 30, control section 140 stops AC current / DC converter 120 to stop the arc current that may be flowing to open / close section 132, thereby causing AC current / The electrical connection between DC converter 120 and transformer 20 is cut off.

The timing when the AC / DC converter 120 is stopped by the control unit 140 and the timing when the opening / closing unit 132 is turned off by the opening / closing unit control unit 134 may be earlier than either. When the switch unit 132 is put in the cut off state after the AC / DC converter 120 is stopped by the control unit 140, no arc current flows, and the AC / DC converter 120 and the switch unit 132 are put in the cut off state. The electrical connection between the transformer 20 is also cut off.

When the AC / DC converter 120 is stopped by the control unit 140, the AC / DC converter 120 does not output AC power, but DC power is supplied from the AC / DC converter 110. If this state continues, charges may continue to be accumulated in the capacitor of the AC / DC converter 120, and the voltage of the capacitor may be damaged beyond the withstand voltage. In order to avoid such damage to the capacitor, control unit 140 is notified that switching on / off unit 132 has been shut off from switching unit control unit 134 and that AC / DC converter 120 is stopped. After both conditions are satisfied, the controller 120 controls the state 120 to return to the state before the AC / DC converter 120 is stopped, that is, the state where the AC / DC converter 120 outputs AC power. In this state, since the AC power output from the AC / DC converter 120 flows not through the switching unit 132 but through the resistor unit 136, the voltage output from the AC / DC converter 120 decreases to a value close to 0 (zero). The capacitor overcharge of the AC / DC converter 120 can be prevented.

Here, an example of the AC / DC converter 120 will be described with reference to FIGS. 2 and 3. FIG. 2 is a diagram showing an example of the configuration of the AC / DC converter 120 according to the first embodiment. FIG. 2A is a diagram showing an example of a modular multilevel converter 120A (MMC). FIG. 2 (b) is a diagram showing an example of the chopper cell C provided in the modular multilevel converter 120 </ b> A.

As shown in FIG. 2A, the modular multilevel converter 120A includes, for example, terminals T (terminals T-1 and T-2) and arm units U (arm units U-1 to U-3), And a transformer 20A. The terminals T-1 and T-2 are terminals connected to a DC system (for example, the power generation device 10 or the AC / DC converter 110). Each of arm units U-1 to U-3 is connected in parallel with each other between terminals T-1 and T-2.

The arm unit U includes a positive side arm 121P, a positive side buffer reactor 122P, a negative side buffer reactor 122N, a negative side arm 121N, and terminals T (T-3 to T-5) for inputting and outputting alternating current power. The arm unit U is connected in order of the positive side arm 121P, the positive side buffer reactor 122P, the negative side buffer reactor 122N, and the negative side arm 121N, as viewed from the terminal T-1. Further, in the arm unit U, the terminal T-3 on the connection line between the positive side buffer reactor 122P and the negative side buffer reactor 122N is connected to the transformer 20A.

Transformer 20A has the same function as transformer 20 described above. Transformer 20A is connected between arm unit U and an AC system (for example, AC system 30). Moreover, in the modular multi-level converter 120A, the transformer 20A may not be provided, and in this case, the modular multi-level converter 120A and the AC system are connected without the transformer 20A.

Each of the positive side arm 121P and the negative side arm 121N includes, for example, a plurality of chopper cells C. For example, the plurality of chopper cells C are connected in series between the side of the terminal T-1 in the positive side arm 121P and the side of the positive side buffer reactor 122P.

As shown in FIG. 2B, the chopper cell C includes a capacitor 123, a switching element 124 (switching

elements

124U and 124X), a diode 125 (

diodes

125U and 125X), and terminals T (T-3 and T-4). And The switching element 124 is, for example, an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). Switching element 124 can be turned on / off from the outside (for example, a control unit (not shown) of modular multi-level converter 120A), and is a switching element having a self-extinguishing ability. That is, the modular multilevel converter 120A is a self-excited power converter.

In chopper cell C, switching

elements

124U and 124X connected in series are connected in parallel with capacitor 123. Further, in the chopper cell C,

diodes

125U and 125X are connected in anti-parallel to the

switching elements

124U and 124X, respectively.

In the chopper cell C, when another chopper cell C is connected to the positive side of the chopper cell C, the terminal T-3 is connected to the terminal T-4 of the other chopper cell C. When no other chopper cell C is connected to the positive side of the chopper cell C, the terminal T-3 is connected to the terminal T-1. In the chopper cell C, when another chopper cell C is connected to the negative side of the chopper cell C, the terminal T-4 is connected to the terminal T-3 of the other chopper cell C. When the other chopper cell C is not connected to the negative side of the chopper cell C, the terminal T-4 is connected to the terminal T-2.

Chopper cell C sets the voltage at terminal T-3 by connecting or blocking

switching elements

124U and 124X under control of the control unit (not shown) of modular multi-level converter 120A. Is a predetermined unit voltage (positive side), a zero voltage, or a predetermined unit voltage (negative side).

Each of the arm units U-1 to U-3 outputs a multilevel voltage waveform by adjusting the voltage of the terminal T-3 of each of the plurality of chopper cells C which each has.

Thus, the modular multi-level converter 120A, which is an example of the AC / DC converter 120, includes a plurality of chopper cells C, and the chopper cell C includes a capacitor 123.

FIG. 3 is a diagram showing another example of the configuration of the AC / DC converter 120 according to the first embodiment. FIG. 3 is a diagram showing an example of the two-level converter 120B. As shown in FIG. 3, the two-level converter 120B includes terminals T (terminals T-8 and T-9), a capacitor 126, units V (units V-1 to V-3), and an AC filter 129. , And a transformer 20B.

The terminals T-8 and T-9 are terminals connected to a DC system (for example, the power generation device 10 or the AC / DC converter 110). Each of units V-1 to V-3 is connected in parallel with one another between terminals T-8 and T-9. The unit V includes a switching element 127 (switching

elements

127U and 127X), a diode 128 (

diodes

128U and 128X), and terminals T (T-10 to T-12) that input and output AC power.

In unit V, switching

elements

127U and 127X are connected in series, and

diodes

128U and 128X are connected in anti-parallel to switching

elements

127U and 127X, respectively. Further, in each of units V-1 to V-3, a terminal T-10 on a connection line between switching

element

127U and 127X is connected to transformer 20B via AC filter 129.

The unit V sets the voltage of the terminal T-3 to the connection state or the disconnection state of each of the

switching elements

127U and 127X based on control from a control unit (not shown) of the two-level converter 120B. Or a predetermined unit voltage (positive side), a zero voltage, or a predetermined unit voltage (negative side). The AC filter 129 smoothes the voltage at the terminal T of the unit V. As a result, the AC filter 129 outputs a voltage close to a sine wave, that is, a voltage of AC power. Transformer 20B has the same function as transformer 20 described above. Transformer 20B is connected between AC filter 129 and an AC system (for example, AC system 30).

Thus, the capacitor 126 is included in the two-level converter 120 B which is an example of the AC / DC converter 120.

Next, the operation of the DC power transmission system 100 when an accident occurs will be described with reference to FIGS. 4 to 8. The accident in the DC power transmission system 100 here is, for example, a case where the power transmission line between the transformer 20 and the AC grid 30 is grounded due to lightning strike or the like.

FIG. 4 is a diagram showing a normal state where no accident has occurred in the power transmission system. In the normal state, switching unit 132 brings AC / DC converter 120 and transformer 20 into a connected state. For this reason, the current D of the AC power output from the AC / DC converter 120 flows to the transformer 20 through the switching unit 132, and the current D does not flow to the resistance unit 136.

FIG. 5 is a diagram showing an initial state in which an accident has occurred in the power transmission system. In the initial state where an accident occurs, the current D flows from the accident point (the point where the ground fault occurs) between the transformer 20 and the AC system 30 to the ground or the like. At this time, the effective voltage of the AC power output from AC / DC converter 120 to transformer 20 has a value of 0 (zero) or a value close to 0 (zero), which is smaller than the state before the accident occurs. It becomes a value. If the voltage is in the state of 0 (zero), the AC / DC converter 120 can not output AC power.

FIG. 6 is a diagram illustrating a medium-term state in which an accident has occurred in the power transmission system. In the middle state where an accident has occurred, the control unit 140 controls the AC / DC converter 120 to stop. In addition, the switching unit 132 is controlled by the switching unit control unit 134 so as to cut off the AC / DC converter 120 and the transformer 20.

Here, the power generation device 10 and the AC / DC converter 110 may continue to operate regardless of whether or not an accident has occurred. In particular, when the power generation device 10 is a power generation using renewable energy such as wind power generation or solar power generation, it is difficult to immediately stop the power generation device 10. For this reason, the power generation device 10 may generate DC power, the AC / DC converter 110 may convert DC power into DC power of a predetermined voltage, and the converted power may continue to be supplied to the AC / DC converter 120. .

Therefore, if the control as shown in FIG. 7 is not performed, the AC / DC converter 120 receives the supply of the DC power regardless of the output stop, and the balance of the exchange of the power in the AC / DC converter 120 is I can not take it. The balance of the exchange of electric power in the AC / DC converter 120 is lost, and as a result, charge is continuously accumulated in the capacitor of the AC / DC converter 120, resulting in damage to the storage function of the capacitor, causing AC / DC conversion. Device 120 may become out of control. Therefore, in the embodiment, the output of AC power by AC / DC converter 120 is restarted as described below.

FIG. 7 is a diagram illustrating a late state in which an accident has occurred in the power transmission system. In the late state where an accident occurred, the control unit 140 restarts the output of AC power by the AC / DC converter 120. When the current D of the AC power output from the AC / DC converter 120 is returned to the state before the occurrence of the accident by the control unit 140, the current D flows to the resistance unit 136, and the AC / DC converter 120 The output AC power is consumed by the resistor of the resistor unit 136. Thereby, overcharging of the capacitor of the AC / DC converter 120 can be suppressed, and the AC / DC converter 120 can be prevented from becoming uncontrollable. Further, since the AC power output from AC / DC converter 120 is consumed by the resistor of resistor unit 136, the output voltage of AC / DC converter 120 is reduced and the voltage is 0 (zero). Can be prevented.
After the accident is recovered, restoration of the entire DC power transmission system 100 is performed in accordance with a predetermined procedure determined in advance.

FIG. 8 is a timing chart for explaining the operation of the DC power transmission system 100 according to the first embodiment. FIG. 8A shows an example in the case where the open / close unit 132 is cut off before the AC / DC converter 120 is stopped when a ground fault occurs. FIG. 8B shows an example in which the open / close unit 132 is cut off after the AC / DC converter 120 is stopped when a ground fault occurs.

The upper part of each of FIGS. 8A and 8B shows the state of the AC / DC converter 120, and the lower part shows the connection state between the AC / DC converter 120 and the converter. The horizontal axes at the top and bottom of each of FIGS. 8A and 8B indicate time. In the upper part of each of FIGS. 8A and 8B, a state in which normal AC power is output from AC / DC converter 120 is shown as a “normal state”, and AC power from AC / DC converter 120 is shown. Is indicated as "stopped" when it is stopped. Further, in the lower part of each of FIGS. 8A and 8B, a state in which the AC / DC converter 120 and the transformer 20 are connected is shown as a “connected state”, and the case where it is cut off is Shown as "blocked state".

In the example of FIG. 8A, a ground fault occurs at time T1, and first, the opening / closing unit 132 is put into the interruption state by the opening / closing unit control unit 134. Next, at time T2, the AC / DC converter 120 is stopped by the control unit 140. Then, at time T3, control unit 140 returns AC / DC converter 120 to the normal state. The arc current may continue to flow through the switching unit 132 at time T1, but the arc current is stopped at time T2. At time T3, the AC power of AC / DC converter 120 is consumed by resistance unit 136.

In the example of FIG. 8B, a ground fault occurs at time T11, and the AC / DC converter 120 is stopped by the control unit 140 first. Next, at time T12, the open / close unit 132 is put in the shutoff state by the open / close unit control unit 134. Then, at time T13, control unit 140 returns AC / DC converter 120 to the normal state. Since the current from the AC / DC converter 120 is stopped at time T11, no arc current flows in the switching part 132 at time T12. At time T3, the AC power of AC / DC converter 120 is consumed by resistance unit 136.

Note that the time during which AC / DC converter 120 is stopped, (time from time T2 to T3 in the example of FIG. 8A, and time from time T1 to T3 in the example of FIG. 8B) is restricted. Although it is not, it is desirable to be as short as possible. This is because the longer the time from time T1 to time T3 is, the more charge is accumulated in the capacitor of the AC / DC converter 120 and the possibility of being overcharged increases.

As described above, the DC power transmission system 100 according to the first embodiment includes the AC / DC converter 110, the AC / DC converter 120, and the protection circuit 130. The AC / DC converter 110 converts DC power generated by the power generation device 10 into DC power of a predetermined voltage. The AC / DC converter 120 has a capacitor, and converts DC power supplied from the AC / DC converter 110 via the transmission path L into AC power. Protection circuit 130 is connected between AC / DC converter 120 and AC system 30. The protection circuit 130 further includes an open / close unit 132 and a resistor unit 136. The switching unit 132 brings the connection between the AC / DC converter 120 and the AC system 30 into a connected state or a disconnected state. Resistor 136 consumes AC power from AC / DC converter 120 when switch 132 is turned off.

Thereby, in the DC power transmission system 100 of the first embodiment, high reliability can be maintained at lower cost. Even when a ground fault or the like occurs in AC system 30, switching unit 132 disconnects the connection between AC / DC converter 120 and AC system 30, and output from AC / DC converter 120 A reduction in voltage can be suppressed, and the resistor unit 136 can suppress the overcharging of the capacitor of the AC / DC converter 120 by consuming the AC power output from the AC / DC converter 120, This is because the AC / DC converter 120 can be prevented from falling out of control.

As a comparative example, a configuration is considered in which a protection circuit 130 is provided on the side of the DC system (for example, between the AC / DC converter 110 and the power generation device 10). In this configuration, the resistor unit 136 of the protection circuit 130 consumes the DC power output from the power generation device 10. However, when the power generation device 10 is a wind power generator, the amount of DC power output from the power generation device 10 changes in accordance with the air volume. In order to consume changing power, the resistor unit 136 needs to be configured of, for example, a large number of resistors that can be switched by a semiconductor switch. In such a configuration, many effective semiconductors must be used, which increases the cost of the apparatus.

On the other hand, in the DC power transmission system 100 of the present embodiment, it is not necessary to use an expensive semiconductor switch for the protection circuit 130. Since the voltage value of the AC power output from the AC / DC converter 120 can be controlled by the AC / DC converter 120, for example, the protection circuit 130 is effective for the AC power output from the AC / DC converter 120. It suffices to have a resistor capable of consuming power.

Further, in the DC power transmission system 100 according to the first embodiment, the resistor unit 136 is provided in parallel to the switching unit 132 with respect to the AC / DC converter 120. As a result, in the DC power transmission system 100 according to one embodiment, the transformer 20 can be supplied with power even when the switching unit 132 is in the shutoff state, in addition to the effects described above. It is possible to restore the DC transmission system 100 more smoothly if the accident recovers.

Further, in the DC power transmission system 100 according to the first embodiment, DC power input to the AC / DC converter 110 is renewable energy. Thus, in the DC power transmission system 100 according to one embodiment, when an accident occurs on the side of the AC system 30, the DC power supplied to the AC / DC converter 120 can not be immediately stopped. Even in this case, alternating current power can be supplied from the alternating current / direct current converter 120 to the transformer 20 via the resistor portion 136.

Further, the DC power transmission system 100 according to the first embodiment further includes a control unit 140 that causes the AC / DC converter 120 to stop outputting AC power when the switching unit 132 is turned off. Thus, in the DC power transmission system 100 according to one embodiment, when the switching unit 132 is cut off due to a ground fault or the like in the AC system 30, the controller 140 controls the AC / DC converter 120. By stopping the output of the circuit, it is possible to suppress a drop in voltage output from the AC / DC converter 120 and prevent the AC / DC converter 120 from becoming uncontrollable.

Further, in the DC power transmission system 100 according to the first embodiment, the control unit 140 notifies that the output of the AC power of the AC / DC converter 120 has been stopped and that the switching unit 132 has been shut off. After both conditions of receiving (from the switch control unit 134) are satisfied, the AC / DC converter 120 is made to restart the output of AC power. Thus, in the DC power transmission system 100 according to the first embodiment, the control unit 140 outputs the output of the AC / DC converter 120 even when the arc current is generated when the switching unit 132 is turned off. The arc current can be stopped by stopping the Therefore, the output of the AC power from the AC / DC converter 120 can be consumed by the resistor unit 136 by resuming the output of the AC power while the control unit 140 does not generate the arc current. Therefore, overcharging of the capacitor of AC / DC converter 120 can be suppressed, and damage to AC / DC converter 120 can be prevented.

Second Embodiment
Next, a second embodiment will be described. The second embodiment is different from the above-described first embodiment in that the control unit 140 controls the open / close unit 132.

The control unit 140 monitors the voltage and current of AC power at a predetermined place of the AC system 30, and when the current of the AC system 30 is in a predetermined state, such as when a current equal to or greater than a predetermined threshold flows in the area And instructs the control unit of the AC / DC converter 120 to stop the AC / DC converter 120, and instructs the switch control unit 134 to switch the switch 132 off.

In the second embodiment, the open / close controller 134 may be omitted. When the open / close unit control unit 134 is omitted, the open / close unit 132 is put in the closed state under the control of the control unit 140. In this case, the control unit 140 is an example of the “control unit”.

In addition, after switch unit 132 is turned off, control unit 140 instructs the control unit of AC / DC converter 120 to resume the output of AC power from AC / DC converter 120.

As described above, in the DC power transmission system 100 of the second embodiment, the output of the current of the AC power converted by the AC / DC converter 120 is stopped, and the AC / DC converter 120 and the AC system 30 And a control unit 140 for making the connection between Thus, in the DC power transmission system 100 according to the second embodiment, the control unit 140 performs AC / DC conversion when the state of the AC system 30 is a predetermined state, such as when a short circuit accident occurs in the AC system 30. When the switch control unit 134 (or the control unit 140) shuts off the open / close unit 132 while stopping the switch 120, it is possible to prevent the voltage of the AC power from being lowered.

Further, in the DC power transmission system 100 according to the second embodiment, the control unit 140 both stops the output of the AC current of the AC / DC converter 120 and turns the switching unit 132 into the shutoff state. And causes the AC / DC converter 120 to resume output of AC power. Thus, in the DC power transmission system 100 of the second embodiment, the AC power output from the AC / DC converter 120 can be consumed by the resistor unit 136, and the capacitor of the AC / DC converter 120 is excessive. It can be prevented from being charged.

Third Embodiment
Next, a third embodiment will be described using FIG. FIG. 8 is a block diagram showing a configuration example of the DC power transmission system 100A of the third embodiment. The third embodiment is different from the above-described embodiment in that a transformer 20 is provided between the AC / DC converter 120 and the protection circuit 130. The third embodiment is different from the above-described embodiment in that the transformer 20 is not provided between the protection circuit 130 and the AC system 30.

The control unit 140 monitors, for example, the voltage at the relevant point via the instrument transformer provided at a desired location in the alternating current system 30, and for an unshown instrument provided between the protection circuit 130 and the alternating current system 30. The voltage and current of AC power supplied to AC system 30 are monitored via a transformer. Then, when a current equal to or greater than a predetermined threshold flows in the transmission line between transformer 20 and AC grid 30 due to a ground fault or the like, control unit 140 stops AC / DC converter 120 in a stopped state. Control to be Further, at this time, the control unit 140 controls the opening / closing unit 132 to be in the disconnection state. Then, control unit 140 resumes the output of AC power of AC / DC converter 120 after the electrical connection between AC / DC converter 120 and AC system 30 is cut off.

According to at least one embodiment described above, the transmission connected to the DC side of the AC / DC converter 110 includes the AC / DC converter 110 for converting input power into DC power of a predetermined voltage, and a capacitor. AC / DC converter 120 for converting DC power supplied from AC / DC converter 110 via path L into AC power, and protection connected between AC / DC converter 120 and AC system 30 The circuit 130 is a switching unit 132 for connecting or disconnecting the connection between the AC / DC converter 120 and the AC system 30, and the switching unit 132 using the AC / DC converter 120 and the AC system 30. High reliability can be maintained at low cost by having a protection circuit 130 having a resistor portion 136 that consumes AC power from the AC / DC converter 120 when there is an interruption state. Rukoto can. Even when a ground fault or the like occurs in AC system 30, switching unit 132 disconnects the connection between AC / DC converter 120 and AC system 30, and output from AC / DC converter 120 A reduction in voltage can be suppressed, and the resistor unit 136 can suppress the overcharging of the capacitor of the AC / DC converter 120 by consuming the AC power output from the AC / DC converter 120, This is because the AC / DC converter 120 can be prevented from falling out of control.

While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These embodiments can be implemented in other various forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the invention described in the claims and the equivalents thereof as well as included in the scope and the gist of the invention.

In the case of a system accident, damage to AC / DC converter 120 can be suppressed, and can be applied to a transmission system in HVDC.

DESCRIPTION OF SYMBOLS 10 Power generation apparatus 20 Transformer 30 AC system 100 DC power transmission system 110 AC / DC converter 120 AC / DC converter 130 protection circuit 132 switching unit 134 switching Control unit, 136 ... resistance unit, 140 ... control unit

Claims

A first converter for converting input power into DC power of a predetermined voltage;
A second converter for converting DC power supplied from the first converter into AC power via a DC link connected to a DC side of the first converter, the storage device having an electric storage device;
A protection device connected between the second converter and an alternating current system, wherein the switching unit brings the connection between the second converter and the alternating current system into a connected state or a disconnected state; A protection device having a load that consumes AC power from the second converter when the switching unit is in the shutoff state;
DC power transmission system provided with
The DC power transmission system according to claim 1, wherein the load includes a resistor provided in parallel to the switching unit with respect to the second converter.
The DC power transmission system according to claim 1, wherein the power input to the first converter is renewable energy.
The control device further includes a control unit that causes the second converter to stop the output of alternating current power when the opening / closing unit is in the disconnection state.
The direct current transmission system according to any one of claims 1 to 3.
The control unit is configured to stop the output of the alternating current power of the second converter and to receive the notification that the switching unit has been switched off. The DC power transmission system according to claim 4, wherein the converter (2) restarts the output of AC power.
The controller further includes a control unit that causes the second converter to stop the output of AC power while the switching unit is in a shutoff state when the state of the AC system is a predetermined state.
The direct current transmission system according to any one of claims 1 to 3.
The control unit controls the second converter to output alternating current power when both of stopping the output of the alternating current power of the second converter and setting the switching unit in the cutoff state are satisfied. The direct current transmission system according to claim 6, wherein the output of is resumed.