JP2016134996A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device capable of surely protecting against failure of a cell converter or DC short circuit accident and capable of continuing operation as a system.SOLUTION: A power conversion device includes: bypass means 5 that can short-circuit between a pair of external terminals X1 and X2 of a main circuit 20 composed of switching elements 1a and 1b and a capacitor 2; a gate drive device 4 that performs power conversion between the pair of external terminals X1 and X2 and the capacitor 2 by on-off controlling the switching elements 1a and 1b; and a self-powered device 3 that inputs a voltage of the capacitor 2 and supplies electric power to the gate drive device 4, and further includes non-contact power supply devices 7 and 8 that supply driving power to the bypass means 5 of each cell converter 100 from ground potential by a non-contact power transmission method.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a power conversion device including a plurality of cell converters connected in series with each other, and more particularly to a technique for bypassing the cell converter in the event of a failure of the cell converter.

  A modular multi-level converter (MMC) connects the output terminals of cell converters composed of switching elements, such as IGBTs, which can be turned on and off, and DC capacitors in series with each other. It is a circuit system that can output a voltage, and is a circuit system that is expected to be applied to a direct current power transmission system (HVDC), a reactive power compensator (STATCOM), and the like.

  For example, according to Patent Document 1, the MMC is configured by connecting a plurality of cell converters in series (cascade). Each cell converter includes a main circuit composed of a switching element and a DC capacitor, an external terminal for cascading with other cell converters, bypass means connected to both ends of the external terminal, and a DC capacitor for the main circuit. A self-powered power source that obtains energy from and drives the bypass means and the like.

  Then, by controlling on / off of the switching element, the voltage between the external terminals can be controlled to the voltage of the DC capacitor of the cell converter or zero. The bypass means is a normally-on short-circuit switch that can short-circuit the output of the cell converter when the cell converter fails, and the output of the failed cell converter is short-circuited by the short-circuit switch. It is also possible to continue operation as a system even if the device breaks down.

  With respect to a ground potential such as a grounding point on the ground, for example, a cell converter that may have a high potential difference of several hundreds kV at the maximum, a bypass means or a switching device driving device or a cell control device from a ground power supply Direct power supply to electrical devices in cell converters such as power converters with a dielectric strength of several hundred kV is required for each cell converter, which is very difficult in terms of cost and size. It is. Therefore, in the cell converter, the system for continuing the operation of the system by short-circuiting the failed cell converter by the bypass means operated by the drive power supply from the self-supplied power supply also simplifies the insulation design and is a general power supply in the MMC. It's a method.

  Further, for example, according to Patent Document 2, when a DC short-circuit accident in which a positive potential line and a negative potential line are short-circuited due to lightning or the like in a DC power transmission system, the cell converter is connected to the DC short-circuit circulation current. Means to protect are disclosed. Each cell converter includes a main circuit composed of a switching element and a DC capacitor, an external terminal for cascading with other cell converters, a free wheel diode connected in reverse parallel to the switching element, and the free converter. Bypass means connected in parallel with the wheel diode. The bypass means is a semiconductor element that causes a DC short-circuit current to flow in place of the freewheel diode when a DC short-circuit accident occurs, and the semiconductor element has a large current capacity with respect to the DC short-circuit current. For example, it is possible to protect the cell converter from a DC short circuit circulating current.

Japanese Patent No. 5378274 Japanese Patent No. 5318774

  In the case of Patent Document 1, specifically, a normally-on short-circuit switch 209 is connected in parallel to the output terminal as a bypass means for each cell converter 105. The self-power supply 208 is connected in parallel with the DC capacitor 203 and supplies drive power for the short-circuit switch 209 from the self-power supply 208. Accordingly, when the cell converter 105 is stopped, the driving power is not supplied from the self-supply power source 208. Therefore, the output of the cell converter 105 is short-circuited by the short-circuit switch 209 being turned on, and one cell converter 105 fails. Even in this case, it is possible to continue operation as a power conversion device.

  As described above, when the short-circuit switch 209 is in a self-ON state, no current flows through the DC capacitor 203, that is, no energy is stored in the DC capacitor 203, so that no driving power is supplied from the self-supply power source 208 to the short-circuit switch 209. For this reason, the short-circuit switch 209 cannot be turned off again by itself. To turn it off again, it is necessary to use a power supply means other than the self-power supply 208 in a state where the system is stopped.

  If a DC short-circuit accident occurs when applied to a DC power transmission system, the short-circuit switch 209 can be turned on to bypass the short-circuit circulation current, but once the short-circuit switch 209 is turned on. As described above, it cannot be turned off again by itself, and even if the DC short circuit circulating current is removed, all cell converters will be held in the bypass state, and the output voltage will drop and the system will operate. Will not be able to continue.

  Further, in the configuration of Patent Document 2, when it is intended to protect the cell converter when it fails, the bypass means is configured to prevent the cell converter against a DC short circuit circulating current when a DC short circuit fault occurs in the DC power transmission system. Because it is connected in reverse parallel to the switching element so that it can protect the current, it can flow only in one direction, so even if the cell converter fails, the period in which the output of the cell converter flows in one direction In other words, since only a half cycle is short-circuited, the operation of the system cannot be continued.

As described above, in Patent Document 1, a protective operation for compensating the continuous operation of the system against a failure of the cell converter is possible, but it is necessary to stop the operation of the system when returning the failed cell converter. I wo n’t. In addition, for a DC short-circuit accident, it is impossible to perform a protection operation by continuing the operation of the system.
Further, in Patent Document 2, a protection operation in the case of a transient DC short-circuit accident such as lightning in a DC power transmission system is possible, but a reliable protection operation cannot be compensated for a failure of a cell converter.

  The present invention has been made to solve the conventional problems as described above, and is capable of reliable protection against a cell converter failure and a DC short-circuit accident. An object of the present invention is to provide a power converter capable of continuing operation.

A power conversion device according to the present invention is a power conversion device including a plurality of cell converters connected in series to each other, and each cell converter includes a main circuit including a switching element and a capacitor, A pair of external terminals for deriving the circuit to the outside, bypass means capable of short-circuiting between the pair of external terminals, and a gate for performing power conversion between the pair of external terminals and the capacitor by controlling on / off of the switching element In the power conversion device including the driving device and the self-feeding device that inputs the voltage of the capacitor to feed the gate driving device,
A non-contact power feeding device that supplies driving power from the ground potential to the bypass means of each cell converter by a non-contact power transmission system is provided.

  As described above, the power conversion device according to the present invention includes the non-contact power supply device that supplies drive power from the ground potential to the bypass means of each cell converter by the non-contact power transmission method. Therefore, it is possible to perform a reliable protection operation against a DC short-circuit accident, and it is possible to continue operation as a system.

It is a figure which shows the structure of the power converter device by Embodiment 1 of this invention. It is a figure which shows an internal structure in the case of using the mechanical switch 11 as an example of the bypass means 5 of FIG. It is a figure which shows an internal structure in the case of using the semiconductor switch 13 as an example of the bypass means 5 of FIG. 10 is a timing chart showing the operation timing of the bypass means according to the configuration of the conventional example shown in Patent Document 1. 10 is a timing chart showing the operation timing of the bypass means according to the configuration of the conventional example shown in Patent Document 2. It is a timing chart which shows the operation timing of the bypass means in the power converter device of this invention. It is a figure which shows the structure of the power converter device by Embodiment 2 of this invention. It is a figure which shows the structure of the power converter device by Embodiment 3 of this invention.

Embodiment 1 FIG.
1 is a diagram showing a configuration of a power conversion device according to Embodiment 1 of the present invention. The power conversion device includes cell converters 100a, 100b, 100c,... Connected in series (cascade) to each other. Hereinafter, as a representative, the configuration of the cell converter 100a will be described as 100.

  Switching elements 1 a and 1 b that can be controlled to be turned on and off, such as IGBTs, are connected in series to each other, and a capacitor 2 is connected to the switching elements 1 a and 1 b to constitute the main circuit 20. A diode is connected in antiparallel to each switching element 1a, 1b. The main circuit 20 is led to the outside through a pair of external terminals X1 and X2, and is connected to other cell converters 100b and 100c. The bypass means 5 is connected to the external terminals X1 and X2.

Furthermore, a self-power feeding device 3 is provided that inputs the voltage of the capacitor 2 of the main circuit 20 and feeds power to a gate driving device 4 and other devices in the cell converter 100 described later.
The self-feeding device 3 is usually constituted by a DC / DC converter that converts the high voltage of the capacitor 2 that fluctuates by the operation of the main circuit 20 into a constant low voltage.

  The gate drive device 4 is controlled between the pair of external terminals X1 and X2 and the capacitor 2 by performing on / off control of the switching elements 1a and 1b based on the power supplied from the self-feed device 3 through the first feed line 6. The power conversion is performed, and the voltage of the capacitor 2 or the zero voltage is output between the external terminals X1 and X2.

  The bypass means 5 is in an open state when it is normal, and when a failure of the cell converter 100 or a DC short-circuit accident occurs, it is detected and short-circuited to short-circuit between the external terminals X1 and X2. The bypass means 5 operates by receiving drive power from the ground potential by a non-contact power feeding device including the power transmission side power feeding device 7 and the power receiving side power feeding device 8.

By securing a necessary space insulation distance between the power transmission side power supply device 7 and the power reception side power supply device 8, while satisfying the insulation specifications, the power transmission side power supply device 7 is connected to the power reception side power supply device 8 by a non-contact power transmission method. Non-contact driving power 9 is transmitted.
This non-contact power transmission system is said to have been developed from the beginning of the 20th century, but its transmission energy was very low. Since then, developments for increasing transmission efficiency, transmission energy, and separation distance have been promoted, and practical examples have expanded in the 21st century.

The present invention solves the conventional problems by creatively applying this non-contact power transmission system to the drive system of the bypass means responsible for the protective operation in this type of power converter of high voltage specification. .
Specific methods for contactless power transmission include electromagnetic induction using electromagnetic induction through magnetic flux, electromagnetic resonance using electromagnetic resonance, and converting power into electromagnetic waves via an antenna. There are a radio system for transmission, and a laser system using a laser beam.
However, in both cases, there is an unavoidable limit to the transmission power, and it is important to reduce the transmission power when applied to the device of the present application. For convenience of explanation, the transmission power reduction measures required for the non-contact power feeding devices 7 and 8 Will mainly be described in the second and subsequent embodiments, and hereinafter, returning to the bypass means 5 in FIG. 1, a specific example thereof will be described.

FIG. 2 shows an internal configuration when a mechanical switch 11 as an example of the bypass means 5 is used.
The one using the mechanical switch 11 has a metal contact, and includes a vacuum switch and an electromagnetic switch, and can pass a current in both directions. The mechanical switch 11 can be short-circuited or opened by applying drive energy from the power-receiving-side power supply device 8 to the mechanical switch drive device 12 configured by an excitation coil or the like through the second power supply line 10.

FIG. 3 shows an internal configuration when using the semiconductor switch 13 as an example of the bypass means 5.
The semiconductor switch 13 can flow current in both directions by configuring switching elements 13a and 13b, such as thyristors and IGBTs, that can be switched at high speeds in reverse parallel to each other. The semiconductor switch 13 can be short-circuited or opened by applying driving energy from the power-receiving-side power feeding device 8 to the semiconductor switch driving device 14 formed of an electronic circuit through the second power feeding line 10.

  Next, the protection operation by the bypass unit 5 in the power conversion device will be described. In order to facilitate the understanding of the present invention, the above-described problem is briefly described. First, the protection operation in the conventional case will be described with reference to FIGS.

FIG. 4 is a timing chart showing the operation timing of the bypass means according to the configuration of the conventional example shown in Patent Document 1.
When the cell converter in FIG. 5A fails, as described above, drive power is not supplied from the self-supplied power supply due to the cell converter failure, and the output of the cell converter is short-circuited when the bypass means is turned on. Then, the current is attenuated by circulating to the bypass means, and the failure ends at that time. Thus, even if one cell converter fails, the operation as a power converter can be continued.

  The figure (b) assumes the occurrence of a DC short-circuit accident. By the occurrence of a DC short-circuit accident, the bypass means of each cell converter can be turned on to bypass the short-circuit circulation current. It cannot be turned off again. Therefore, even if the DC short-circuit accident is removed, since all the cell converters are held in the bypass state, the output voltage is lowered and the operation as the power converter cannot be continued.

FIG. 5 is a timing chart showing the operation timing of the bypass means according to the configuration of the conventional example shown in Patent Document 2.
FIG. 6A assumes a cell converter failure. Since the bypass means is connected in reverse parallel to the switching element and can flow only one-way current, as described above, the cell converter Even if a failure occurs, only a period corresponding to a half cycle of the applied voltage is short-circuited, and the failure of the cell converter continues and the operation as a power conversion device cannot be continued.

  When the DC short-circuit accident shown in FIG. 5B occurs, if the DC short-circuit accident is removed within the period corresponding to the half cycle after the bypass means is turned on due to the occurrence of the DC short-circuit accident, Is turned off, and the operation as a power conversion device can be continued.

  As described above, in both the cell converter failure and the DC short-circuit accident occurrence, the protective operation by the bypass means, which is based on the continuation of the operation as the power conversion device, is realized in any of the conventional cases of FIGS. Can not do it. Further, in the former one of FIG. 4 of FIG. 4, there is a problem that the bypass means once turned on cannot be returned to the OFF state unless another power source is prepared and driving power is supplied.

The power conversion device according to Embodiment 1 of the present invention enables this realization, and will be described below with reference to the timing chart of FIG.
FIG. 4A shows the operation of the bypass means 5 when the cell converter is faulty. When the cell converter 100 breaks down, a detector (not shown) detects this, and the non-contact driving power 9 transmitted from the power transmission side power supply device 7 provided separately from the self power supply device 3 is received by the power reception side power supply device 8. Then, the bypass means 5 is short-circuited through the second feeder 10.

Since the drive power of the bypass means 5 is not obtained from the self-power feeding device 3, the bypass means 5 can be opened when the failure of the cell converter 100 is completed, as shown in FIG.
Therefore, at this time, the power conversion device can continue operation in the state of the original power capacity.

Next, FIG. 4B shows the operation of the bypass means 5 when a DC short-circuit accident occurs. When a DC short circuit circulating current flows through the free wheel diode of the switching element 1b due to an accident, the switching element 1b is damaged. The bypass means 5 is short-circuited through the second power supply line 10 and the DC short circuit circulating current is also shunted to the bypass means 5 to prevent the switching element 1b from being damaged.
When the DC short circuit circulating current is removed, the power converter can be safely operated continuously by opening the bypass means 5.

  As described above, in the power conversion device according to Embodiment 1 of the present invention, the power transmission side power supply device 7 that supplies driving power from the ground potential to the bypass means 5 of each cell converter 100 by the non-contact power transmission method; Since the non-contact power feeding device including the power receiving side power feeding device 8 is provided, a reliable protection operation can be performed against a failure of the cell converter and a DC short-circuit accident. Operation as a system can be continued.

Embodiment 2. FIG.
In the second and subsequent embodiments, as described above, in the non-contact power transmission method, the power that can be transmitted is still limited at this stage regardless of the type of the method. , 8 is intended to reduce the transmission power required.

FIG. 7 is a diagram showing a configuration of a power conversion device according to Embodiment 2 of the present invention. The only difference from the case of the first embodiment is that the newly provided power supply device changeover switch 16 and the configuration related thereto are different. Therefore, these will be mainly described below.
The power feeding device changeover switch 16 is inserted between the bypass means 5 and the power receiving side power feeding device 8. The power feeding device changeover switch 16 includes an output from the power receiving side power feeding device 8 via the second power feeding line 10, and an output from the self power feeding device 3 via the first power feeding line 6 in addition to this. Can be input.

  Further, a state signal 15 indicating whether the bypass unit 5 is in a short-circuited state or an open state is taken into the power feeding device changeover switch 16 from a sensor such as a micro switch provided in the contact movable part of the bypass unit 5. Then, according to the state signal 15, the supply source of the driving power to the bypass means 5 is changed to the non-contact power feeding devices 7 and 8 via the second power feeding line 10 or the self power feeding device 3 via the first power feeding line 6. Switch to.

Here, the characteristic requested | required by the opening / closing characteristic of the bypass means 5 used with the power converter device made into object by this application is demonstrated.
As described above, the duty that is primarily required as this type of bypass means 5 is to quickly short-circuit between the external terminals X1 and X2 that have been open until then when a failure of the cell converter 100 occurs. This is to enable continuous operation as a system. On the other hand, the operation of opening the bypass means 5 once short-circuited is for returning the cell converter 100 to the original circuit when the failure of the cell converter 100 is recovered. Compared to this, low-speed operation is sufficient.

That is, in this type of bypass means 5, the short-circuit operation requires a high speed operation, and therefore requires a relatively large drive power, and the open operation may be a low-speed operation and therefore may require a relatively small drive power. .
In this regard, a normal circuit breaker used in a normal short-circuit state in a power / distribution / transformer system is primarily responsible for opening the line in the event of an accident, and operates at high speed during open operation, and therefore requires a large amount of drive power. It is very different from what is required.

  The power conversion device according to the second embodiment of the present invention was made by creatively focusing on the characteristics of the opening / closing characteristics required for the above-described bypass means 5, and the state signal 15 indicates a short-circuit state. When the power supply device switch 16 is selected, the second power supply line 10 is selected and connected to the bypass means 5. When the bypass means 5 inputs an opening command from this state, the power supply device changeover switch 16 is contactless via the second power supply line 10. The opening operation is performed by the non-contact driving power 9 from the power feeding devices 7 and 8. Further, when the state signal 15 indicates an open state, the power feeding device changeover switch 16 performs a short-circuit operation using the driving power from the self-power feeding device 3 via the first power feeding line 6.

With the above configuration, the non-contact power feeding devices 7 and 8 drive only the opening operation that requires a relatively small driving power as compared with the case where the driving power is supplied in both the short-circuiting operation and the opening operation of the bypass unit 5. Since it suffices to supply power, the transmission power required for the non-contact power feeding devices 7 and 8 can be greatly reduced, and the application thereof is facilitated.
Further, since the self-power feeding device 3 also obtains sufficient energy from the capacitor 2 in the open state of the bypass means 5, it is possible to reliably supply the necessary drive power to the bypass means 5 at the time of a short-circuit command. Then, when the voltage of the capacitor 2 is reduced or becomes 0 and sufficient energy cannot be obtained from the capacitor 2, and the bypass means 5 is in a short circuit state, the contactless power feeding devices 7 and 8 supply driving power to the bypass means 5 instead. Since it is supplied, the bypass means 5 can execute the opening operation without any trouble at the time of opening command.

  That is, with respect to the method of supplying driving power to the bypass means 5, the non-contact power feeding devices 7 and 8 and the self-power feeding device 3 are extremely rational by making effective use of the characteristics of the opening / closing characteristics of this type of bypass means 5. It can be said that the division of roles is achieved.

  As described above, in the power conversion device according to the second embodiment of the present invention, the bypass means 5 performs a high-speed operation with a relatively large drive power in the short-circuit operation, and a low-speed operation with a relatively small drive power in the open operation. When the bypass means 5 is in a short-circuited state, driving power is supplied from the non-contact power feeding devices 7 and 8 to the bypass means 5 and the bypass means 5 is in an open state. Is a non-contact power feeding device that supplies driving power to the bypass means 5 according to a state signal 15 indicating whether the state of the bypass means 5 is short-circuited or opened so that the driving power is supplied from the self-power feeding apparatus 3 to the bypass means 5. Since the power supply device changeover switch 16 for switching to 7, 8 or the self-power supply device 3 is provided, the short-circuiting / opening operation of the bypass means 5 can be performed without any trouble. The transmit power required for the non-contact power feeding device 7, 8 can be significantly reduced, there is an effect that its application is easy.

Embodiment 3 FIG.
FIG. 8 is a diagram showing a configuration of a power conversion device according to Embodiment 3 of the present invention.
In addition to the configuration shown in FIG. 7 in the second embodiment, a non-contact power supply command device 17 shown in FIG. 8 is further added to further reduce the transmission power required for the non-contact power supply devices 7 and 8. Is intended.

That is, as shown in the figure, the non-contact power supply command device 17 receives the state signal 15 indicating whether the bypass means 5 is short-circuited or opened, and only when the state signal 15 indicates a short-circuit state, that is, the bypass means. Only when 5 is in the standby state for the opening operation, the start command is output to the power transmission side power supply device 7 of the non-contact power supply device.
Therefore, when the state signal 15 indicates the open state, that is, when the bypass unit 5 is in a standby state for the short-circuit operation, the start command is not output to the power transmission side power supply device 7. Accordingly, during this time, the non-contact power feeding devices 7 and 8 do not consume standby power, the duty required for the non-contact power feeding devices 7 and 8 is further reduced, and the application thereof is made easier. It is.

  As described above, the power conversion device according to Embodiment 3 of the present invention includes the non-contact power supply command device 17 that outputs a start command to the power transmission side power supply device 7 only when the bypass unit 5 is in a short-circuit state. The duty required for the non-contact power feeding devices 7 and 8 is further reduced, and the application is made easier.

Embodiment 4 FIG.
Although not specifically shown, when the semiconductor switch 13 is used as the bypass means 5 described with reference to FIG. 3 of the first embodiment, an optical trigger semiconductor employing optical trigger switching elements for the switching elements 13a and 13b. It is a switch.
Along with this, the non-contact power feeding apparatus is configured by an optical fiber cable that transmits an optical drive signal for driving the optical trigger semiconductor switch on and off.

  In general, it is relatively easy to design an optical fiber cable between parts where a high potential difference exists. Therefore, in the power conversion device according to the fourth embodiment, whether or not the second and third embodiments are adopted is acceptable. Regardless of this, there is an advantage that the application of the non-contact power feeding device becomes easy.

  It should be noted that the present invention can be freely combined with each other within the scope of the invention, and each embodiment can be appropriately modified or omitted.

1a, 1b switching element, 2 capacitor, 3 self-feeding device,
4 Gate drive device, 5 Bypass means, 6 First feed line, 7 Power transmission side feed device,
8 Power-receiving-side power supply device, 9 Non-contact driving power, 10 Second power supply line, 11 Mechanical switch,
12 drive device for mechanical switch, 13 semiconductor switch,
13a, 13b switching element, 14 driving device for semiconductor switch,
15 status signal, 16 power feeding device changeover switch, 17 contactless power feeding command device,
20 Main circuit, 100, 100a to 100c Cell converter, X1, X2 External terminal.

Claims (8)

A power conversion device comprising a plurality of cell converters connected in series with each other,
Each cell converter includes a main circuit composed of a switching element and a capacitor, a pair of external terminals for deriving the main circuit to the outside, bypass means capable of short-circuiting between the pair of external terminals, and the switching Electric power provided with a gate driving device that performs power conversion between the pair of external terminals and the capacitor by controlling on / off of the element, and a self-feeding device that inputs the voltage of the capacitor and supplies power to the gate driving device In the conversion device,
A power conversion device comprising a non-contact power supply device that supplies driving power from a ground potential to the bypass means of each cell converter by a non-contact power transmission method. The bypass means has an opening / closing characteristic in which a short-circuit operation performs a high-speed operation with a relatively large driving power, and an open operation performs a low-speed operation with a relatively small driving power. The power converter according to claim 1, wherein driving power is supplied from the power feeding device to the bypass unit, and driving power is supplied from the non-contact power feeding device to the bypass unit during the opening operation. . A power supply device changeover switch for switching a source of driving power to the bypass device to the non-contact power supply device or the self-power supply device according to a state signal indicating whether the state of the bypass device is short-circuited or opened. The power conversion device according to claim 2. 4. The power conversion device according to claim 2, further comprising a non-contact power supply command device that activates the non-contact power supply device only when the bypass unit is in a short-circuit state. 5. The power converter according to any one of claims 1 to 4, wherein the bypass means is a mechanical switch having a metal contact. 5. The power conversion device according to claim 1, wherein the bypass unit is a semiconductor switch that can flow in both directions. 6. 7. The power conversion device according to claim 6, wherein the semiconductor switch is an optical trigger semiconductor switch, and the non-contact power feeding device is an optical fiber cable that transmits an optical drive signal for driving the optical trigger semiconductor switch on and off. . 8. The power conversion device according to claim 1, wherein direct current outputs from the plurality of cell converters are connected in series to each other and connected to a direct current power transmission line.

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