WO2020232714A1

WO2020232714A1 - Combined switch device for overvoltage protection

Info

Publication number: WO2020232714A1
Application number: PCT/CN2019/088184
Authority: WO
Inventors: Mats Andersson; Lidong ZHANG; Hailian XIE
Original assignee: Abb Power Grids Switzerland Ag
Priority date: 2019-05-23
Filing date: 2019-05-23
Publication date: 2020-11-26
Also published as: CN113875141A

Abstract

Embodiments of present disclosure relates to a combined switch device for overvoltage protection. The combined switch device comprises a first branch and a second branch. The first branch includes a semi-controlled device and a first arrester coupled to the semi-controlled device, and configured to flow a current caused by an overvoltage of a DC link. The second branch includes a full-controlled device and coupled in parallel to the first branch, the second branch configured to commutate the current from the first branch to the second branch in response to turning on the full-controlled device. By providing the combined switch device of the present disclosure, the electrical system may be protected from overvoltage with a low cost, a small footprint and a relatively simple controlling complexity.

Description

COMBINED SWITCH DEVICE FOR OVERVOLTAGE PROTECTION

TECHNICAL FIELD

Example embodiments of the present disclosure generally relate to high voltage direct current (HVDC) transmission and more particularly, to a combined switch device for overvoltage protection.

BACKGROUND

HVDC and ultra-high voltage direct current (UHVDC) transmissions operating at 800 kV are now widely under construction. In HVDC or UHVDC transmission, long lines and high DC current are used. As such, a lot of energy may be stored in the DC link itself.

Due to the fact that energy is stored in the DC line, the converter may rapidly build up a very high voltage (overvoltage) during faults, because the energy may be transmitted to the capacitor of the converter which builds up the voltage. This kind of overvoltage will cause the converter to block semi-permanently.

A combination of arresters and insulated gate bipolar transistors (IGBTs) are employed to protect the DC link from overvoltage. Chinese patent CN102484419B describes such an approach. However, IGBTs are fairly limited in maximum allowable turn-on and operating current. In this case, numerous parallel branches of IGBTs would be necessary for HVDC or UHVDC transmission. This would drive up cost, footprint and overall system complexity.

SUMMARY

Example embodiments of the present disclosure propose a solution for protect an electrical device from overvoltage.

In a first aspect, it is provided a combined switch device for overvoltage protection. The combined switch device comprises a first branch and a second branch. The first branch includes a semi-controlled device and a first arrester coupled to the semi-controlled device, and configured to flow a current caused by an overvoltage of a DC link. The second branch includes a full-controlled device and coupled in parallel to the first branch, the second branch configured to commutate the current from the first branch to the second branch in response to turning on the full-controlled device.

In a second aspect, it is provided an electrical system. The electrical system comprises a converter and a combined switch device of the first aspect. The converter is configured to convert an alternative current (AC) voltage of an AC source into a direct current (DC) voltage transmitted on a DC link. The combined switch device is configured to protect the DC link from an overvoltage.

In a third aspect, it is provided a method for manufacturing a combined switch device. The method comprises providing a first branch including a semi-controlled device and a first arrester coupled to the semi-controlled device, and configured to flow a current caused by an overvoltage of a DC link; and providing a second branch including a full-controlled device and coupled in parallel to the first branch. The second branch is configured to commutate the current from the first branch to the second branch in response to turning on the full-controlled device.

According to the embodiments of the present disclosure, the combined switch device and the electrical network system may be easily configured, and the cost, footprint and overall system complexity can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the following detailed descriptions with reference to the accompanying drawings, the above and other objectives, features and advantages of the example embodiments disclosed herein will become more comprehensible. In the drawings, several example embodiments disclosed herein will be illustrated in an example and in a non-limiting manner, wherein:

Fig. 1 illustrates an electric system in accordance with some example embodiments of the present disclosure;

Fig. 2 illustrates an example of a combined switch device in accordance with some example embodiments of the present disclosure;

Fig. 3 illustrates another example of a combined switch device in accordance with some example embodiments of the present disclosure;

Fig. 4 illustrates a further example of a combined switch device in accordance with some example embodiments of the present disclosure; and

Fig. 5 illustrates a method for manufacturing a combined switch device in accordance with some example embodiments of the present disclosure.

Throughout the drawings, the same or corresponding reference symbols refer to the same or corresponding parts.

DETAILED DESCRIPTION

The subject matter described herein will now be discussed with reference to several example embodiments. These embodiments are discussed only for the purpose of enabling those skilled persons in the art to better understand and thus implement the subject matter described herein, rather than suggesting any limitations on the scope of the subject matter.

The term “comprises” or “includes” and its variants are to be read as open terms that mean “includes, but is not limited to. ” The term “or” is to be read as “and/or” unless the context clearly indicates otherwise. The term “based on” is to be read as “based at least in part on. ” The term “being operable to” is to mean a function, an action, a motion or a state can be achieved by an operation induced by a user or an external mechanism. The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment. ” The term “another embodiment” is to be read as “at least one other embodiment. ”

Unless specified or limited otherwise, the terms “mounted, ” “connected, ” “supported, ” and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Furthermore, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. In the description below, like reference numerals and labels are used to describe the same, similar or corresponding parts in the Figures. Other definitions, explicit and implicit, may be included below.

In the present disclosure, the term “commutate” , “commutated” and “commutation” from a first branch to a second branch refers to the fact that the current flows in the first branch, and then it changes to flow in the second branch without flowing in the first branch. The term “withstand” and “withstanding” refers to a property of a component indicating the maximum operation condition of the component. For example, a device can withstand a current of 100 A. It indicates that the maximum current can flow through the device is 100 A. Beyond that, the device may fail or breakdown.

In the present disclosure, the term “semi-controlled device” refers to a switch that can be controlled to turn on current, but cannot be controlled to turn off current, and the term “full-controlled device” refers to a switch that can be controlled to turn on and turn off current.

Unless specified or limited otherwise, the terms “resistor” , “capacitor” , “inductor” , “switch” , “thyristor” , “IGBT” and other electrical element may include one or more element that has the same function and operates together to achieve the function. For example, a resistor may refer to two or more resistors connected in serial to function as one resistor.

As mentioned above, overvoltage on a DC link will cause the converter to block semi-permanently. Conventional approaches employ a plurality of IGBTs coupled in parallel to cooperatively flow the huge current caused by the overvoltage, since a single IGBT cannot withstand such a huge current. The plurality of IGBTs may include up to dozens or hundreds of IGBTs, and they may not be controlled to turn on and off simultaneously. Thus, the conventional approach may increase cost, footprint and design complexity.

Fig. 1 illustrates an electric system 100 in accordance with some example embodiments of the present disclosure. The electric system 100 includes an AC source 12, a first converter 14 for converting an AC current into a DC current, and a second converter 16 for converting a DC current into an AC current. Although the second converter 16 is illustrated, this is only for illustration without suggesting any limitations as to the scope of the subject matter described here. For example, a load may be provided to replace the second converter 16. The load may include a motor in an example.

A DC link including a positive line V _DC and a negative line -V _DC is provided between the first and

second converters

14 and 16. This is only for illustration without suggesting any limitations as to the scope of the subject matter described here. In an example, a single terminal DC link including a positive line and a ground line can be provided to replace the differential configuration.

The electric system 100 may include a first voltage sensor 13 and a second voltage sensor 17 to periodically or continuously measure or monitor the voltage on the positive line V _DC and the negative line -V _DC, respectively. Although the first and

second voltage sensors

13 and 17 are illustrated, this is only for illustration without suggesting any limitations as to the scope of the subject matter described here. For example, a single voltage sensing device may be provided to measure both the positive line V _DC and the negative line -V _DC.

As described above, an overvoltage may occur on at least one of the DC lines of the DC link. In case of overvoltage, a device needs to be provided to flow the huge amount of current caused by the overvoltage to the ground. During the overvoltage, the current may be huge at the beginning, and shrinks to a lower current in a short time.

In an example, a combined switch device 20 is provided between the positive line V _DC and the ground to handle such current caused by the overvoltage. The combined switch device 20 may be a DC chopper, and is configured to flow the current to the ground when the overvoltage occurs on the line V _DC.

In an example, the first voltage sensor 13 detects the voltage, and transmits to an indication of the detected voltage to the driving circuit 18. The driving circuit 18 transmits a driving signal to the combined switch device 20 in response to determining that the detected voltage exceeds a first predetermined voltage value.

The first predetermined voltage value is set for the overvoltage. The driving circuit 18 may include a processing circuit or a comparison circuit to perform the comparison with the predetermined voltage value. This is only for illustration without suggesting any limitations as to the scope of the subject matter described here. For example, the processing circuit or the comparison circuit may be provided as an independent controller coupled between the driving circuit and the voltage sensor 13, and configured to perform the comparison and transmit the driving signal to the driving circuit 18.

Analogously, the second voltage sensor 17 is configured to detect the voltage of the negative line –V _DC, and there may another independent controller coupled between the driving circuit and the voltage sensor 17, and configured to perform the comparison and transmit the driving signal to the driving circuit 18.

The first combined switch device 20 is configured to flow a current caused by an overvoltage of a DC link based on the driving instruction from the driving circuit 18. The second combined switch device 30 may have a configuration similar or same as the combined switch device 20, and operates analogously.

Although the first and second

combined switch device

20 and 30 are illustrated, this is only for illustration without suggesting any limitations as to the scope of the subject matter described here. For example, a single combined switch device or other protection devices may be provided to protect both the positive line V _DC and the negative line -V _DC from overvoltage.

Although the first and second

combined switch device

20 and 30 are illustrated between the first converter 14 and the second converter 16, this is only for illustration without suggesting any limitations as to the scope of the subject matter described here. For example, the first combined switch device 20 may be provided elsewhere, such as between the AC source 12 and the converter 14 for overvoltage protection.

Although the first voltage sensor 13 and the first combined switch device 20 are illustrated to be independent from each other, this is only for illustration without suggesting any limitations as to the scope of the subject matter described here. For example, the first voltage sensor 13 may be integrated into the first combined switch device 20. In addition, at least one of the driving circuit 18 and the current sensor 11 may be integrated into the first combined switch device 20. In a further example, a combined switch device may include at least one of the combined

switch devices

20 and 30, the driving circuit 18, the current sensor 11 and the

voltage sensors

13 and 17.

Fig. 2 illustrates an example of a combined switch device in accordance with some example embodiments of the present disclosure. The combined switch device 20 may be a DC chopper. The combined switch device 20 includes, among other things, a first branch and a second branch.

The first branch includes a semi-controlled device 27 and a first arrester 24 coupled to the semi-controlled device 27. The first branch is configured to flow a current caused by an overvoltage of a DC link. The semi-controlled device 27 may be a thyristor.

Although the thyristor and the arrestor are illustrated for the first branch, this is only for illustration without suggesting any limitations as to the scope of the subject matter described here. For example, a device that has fast turn-on capability within a few milliseconds or even faster, high turn-on current capability significantly higher than an IGBT, and no ability to turn off/break current can be employed to replace the thyristor.

In case of overvoltage, the semi-controlled device 27 may be turned on based on the driving signal from the driving circuit 18. The current flows from the positive voltage V _DC to the ground GND via the arrester 22 and the first branch. The current is monitored or sensed by the current sensor 11.

The semi-controlled device 27 such as the thyristor may have a capability of flowing large turn-on current. In this event, numerous parallel branches for flowing large turn-on current in the conventional configuration can be omitted here to significantly reduce cost, footprint and complexity.

However, the semi-controlled device 27 cannot be controlled to turn off current. For example, the semi-controlled device 27 cannot be turned off by applying a certain voltage at its control terminal. The semi-controlled device 27 can be turned off when the current flowing through the semi-controlled device 27 approaches to zero. As such, the second branch is provided to help to turn off the semi-controlled device 27 by commutating the current from the first branch to the second branch.

The current sensor 11 transmits a signal indicative of the sensed current to the driving circuit 18 or an independent controller. If the signal is below a predetermined current value, the driving circuit 18 or the independent controller may send an instruction to turn on the second branch, such that the current commutates from the first branch to the second branch in response to turning on the full-controlled device 29. In an example, the predetermined current value may be below the maximum current for the full-controlled device 29 such as the IGBT under normal operation.

At this moment, the configuration of the arrester 24 is equivalent to provide a reverse voltage to the semi-controlled device 27 to cause the current to commutate from the first branch to the second branch naturally. After the commutation, the current is mainly flows through the second branch, and the current in the first branch approaches to zero such that the semi-controlled device 27 is turned off at last. In this case, the current flowing in the first branch before commutation is larger than the current flowing in the second branch.

Although the semi-controlled device 27 and the arrester 24 are illustrated for the first branch, this is only for illustration without suggesting any limitations as to the scope of the subject matter described here. For example, a resistor may be coupled in series with the semi-controlled device 27 and the arrester 24 to dissipate heat generated by the current.

The second branch including a full-controlled device 29 is coupled in parallel to the first branch. The second branch is configured to commutate the current from the first branch to the second branch in response to turning on the full-controlled device 29. Although the full-controlled device 29 is illustrated for the second branch, this is only for illustration without suggesting any limitations as to the scope of the subject matter described here. For example, an inductor may be coupled in series with the full-controlled device 29 to limit the rate of current change.

The full-controlled device 29 may be an IGBT or IGBTs. Although the IGBT is illustrated, this is only for illustration without suggesting any limitations as to the scope of the subject matter described here. For example, a device that can be controlled to rapidly turn on and off current can be applied here for the full-controlled device 29. The semi-controlled device 27 may be configured to withstand more current than the full-controlled device 29.

The driving circuit 18 is configured to turn off the full-controlled device 29 in response to receiving an indication of a voltage of the DC link being below a predetermined voltage value. The indication of the voltage of the DC link may be sent by the

voltage sensor

13 or 17 to the driving circuit 18 to indicate that the voltage of the DC link is below a predetermined voltage value. At this moment, there is no overvoltage occurring on the DC link because the voltage of the DC link has fallen below the predetermined threshold for the overvoltage.

In an example, the combined switch device 20 may include a third branch including a third arrester 26 coupled in parallel to the first and second branches. The third branch and the second arrester 22 are configured to operate as a pole arrester. Although the third arrester 26 is illustrated for the third branch, this is only for illustration without suggesting any limitations as to the scope of the subject matter described here.

Fig. 3 illustrates another example of a combined switch 40 in accordance with some example embodiments of the present disclosure. The combined switch 40 may be applied in a scenario of wind power electricity. The fault such as overvoltage at the DC link may cause the electricity stored in the capacitors of the converters. The stored energy may cause a semi or permanent fault to the converter. In this case, the energy needs to be transferred or dissipated.

The combined switch device 40 includes a first branch and a second branch. The first branch and the second branch are configured and operate similarly to the first and second branches of the combined switch device 20, and their configuration and operation are omitted for brevity.

The combined switch device 40 includes a resistor 42 coupled to the first and second branches. In case of overvoltage, the current flows through the resistor 42, and the resistor 42 generates heat according to Joule’s law. As such, a part of the energy caused by overvoltage may be transformed into heat and dissipated by the resistor 42, without causing damages to the converter coupled to the DC link.

Fig. 4 illustrates a further example of a combined switch 50 in accordance with some example embodiments of the present disclosure. The combined switch device 50 includes a first branch, a second branch and a third branch coupled in parallel. The first, second and third branches are configured and operate similarly to the first, second, and third branches of the combined switch device 20, and their configuration and operation are omitted for brevity.

The combined switch device 50 includes a fourth branch coupled in parallel to the first, second, and third branches. The fourth branch includes a snubber circuit 58. The snubber circuit 58 includes a diode 51, a second resistor 53 coupled to the diode 51, and a capacitor 55 coupled to the second resistor 53.

For a semi-controlled device 57 such as a thyristor, the snubber circuit 58 is only responsible for turning-on. The snubber circuit including a series of resistors and capacitors can be charged in advance. When detecting an overvoltage, the semi-controller device 57 is fired.

For a full-controlled device 59 such as an IGBT, the snubber circuit 58 is responsible for both turning-on and turning-off. After firing the semi-controlled device 57, the current will go through the first branch to ground, and the voltage drop of the first branch will be very small. If no diode 51 is provided, the charged snubber circuit of the full-controlled device 59 will release its energy to the first branch. Thus there will be no energy to fire the full-controlled device 59. By providing the diode 51 coupling between the resistor 53 and the first branch, the diode 51 will prevent the snubber circuit to release its energy since the diode 51 can only conduct in one direction.

As an alternative, a modular multilevel converter (MMC) cell may be provided for the second branch, instead of the full-controlled device 59, since MMC cells have capacitors themselves to supply the energy to gate units (GU) .

Fig. 5 illustrates a method 200 for manufacturing a combined switch in accordance with some example embodiments of the present disclosure. At 202, it is provided a first branch including a semi-controlled device and a first arrester coupled to the semi-controlled device. The first branch is configured to flow a current caused by an overvoltage of a DC link.

At 204, it is provided a second branch including a full-controlled device and coupled in parallel to the first branch, the second branch configured to commutate the current from the first branch to the second branch in response to turning on the full-controlled device.

Hereinafter, some example implementations of the subject matter described herein will be listed.

Item 1: There is provided a combined switch device for overvoltage protection. The combined switch device comprises a first branch including a semi-controlled device and a first arrester coupled to the semi-controlled device, and configured to flow a current caused by an overvoltage of a DC link; and a second branch including a full-controlled device and coupled in parallel to the first branch, the second branch configured to commutate the current from the first branch to the second branch in response to turning on the full-controlled device.

Item 2: According to the combined switch device of Item 1, the semi-controlled device includes a thyristor, and the full-controlled device includes an IGBT.

Item 3: According to the combined switch device of Item 1 or 2, the combined switch device further comprises a current sensor configured to sense the current flowing in the first branch.

Item 4: According to the combined switch device of any of Items 1-3, the combined switch device further comprises a first resistor or a second arrestor coupled to the first and second branches and configured to flow the current caused by the overvoltage of the DC link.

Item 5: According to the combined switch device of any of Items 1-4, the combined switch device further comprises a third branch including a third arrester coupled in parallel to the first and second branches. The third branch and the second arrester are configured to operate as a pole arrester.

Item 6: According to the combined switch device of any of Items 1-5, the combined switch device further comprises a fourth branch including a snubber circuit and coupled in parallel to the first and second branches.

Item 7: According to the combined switch device of any of Items 1-6, the snubber circuit includes a diode, a second resistor coupled to the diode, and a capacitor coupled to the second resistor.

Item 8: According to the combined switch device of any of Items 1-7, the current flowing in the first branch before commutation is larger than the current flowing in the second branch.

Item 9: According to the combined switch device of any of Items 1-8, the semi-controlled device is configured to withstand more current than the full-controlled device.

Item 10: According to the combined switch device of any of Items 1-9, the combined switch device further comprises a driving circuit coupled to the semi-controlled and full-controlled devices and configured to selectively turn on the semi-controlled and full-controlled devices.

Item 11: According to the combined switch device of any of Items 1-10, the driving circuit is configured to turn on the semi-controlled device in response to receiving an indication of overvoltage.

Item 12: According to the combined switch device of any of Items 1-11, the driving circuit is further configured to turn on the full-controlled device in response to receiving an indication of the current being below a predetermined current value.

Item 13: According to the combined switch device of any of Items 1-12, the driving circuit is further configured to turn off the full-controlled device in response to receiving an indication of a voltage of the DC link being below a predetermined voltage value.

Item 14: There is provided an electrical system. The electrical system comprises a converter configured to convert an AC voltage of an AC source into a DC voltage transmitted on a DC link; and a combined switch device of any of Items 1-14 configured to protect the DC link from an overvoltage.

Item 15: There is provided a method for manufacturing a combined switch device. The method comprises providing a first branch including a semi-controlled device and a first arrester coupled to the semi-controlled device, and configured to flow a current caused by an overvoltage of a DC link; and providing a second branch including a full-controlled device and coupled in parallel to the first branch, the second branch configured to commutate the current from the first branch to the second branch in response to turning on the full-controlled device.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. On the other hand, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A combined switch device (20) for overvoltage protection, comprising:

a first branch including a semi-controlled device (27) and a first arrester (24) coupled to the semi-controlled device (27) , and configured to flow a current caused by an overvoltage of a DC link; and

a second branch including a full-controlled device (29) and coupled in parallel to the first branch, the second branch configured to commutate the current from the first branch to the second branch in response to turning on the full-controlled device (29) .
The combined switch device of Claim 1, wherein the semi-controlled device includes a thyristor, and the full-controlled device includes an IGBT.
The combined switch device of Claim 1, further comprising a current sensor (11) configured to sense the current flowing in the first branch.
The combined switch device of Claim 1, further comprising a first resistor (42) or a second arrestor (22) coupled to the first and second branches and configured to flow the current caused by the overvoltage of the DC link.
The combined switch device of Claim 4, further comprising a third branch including a third arrester (26) coupled in parallel to the first and second branches;

wherein the third branch and the second arrester (22) are configured to operate as a pole arrester.
The combined switch device of Claim 1, further comprising a fourth branch including a snubber circuit (58) and coupled in parallel to the first and second branches.
The combined switch device of Claim 6, wherein the snubber circuit includes a diode (51) , a second resistor (53) coupled to the diode (51) , and a capacitor (55) coupled to the second resistor (53) .
The combined switch device of Claim 1, wherein the current flowing in the first branch before commutation is larger than the current flowing in the second branch.
The combined switch device of Claim 1, wherein the semi-controlled device (27) is configured to withstand more current than the full-controlled device (29) .
The combined switch device of Claim 1, further comprising a driving circuit (18) coupled to the semi-controlled and full-controlled devices and configured to selectively turn on the semi-controlled and full-controlled devices.
The combined switch device of claim 10, wherein the driving circuit (18) is configured to turn on the semi-controlled device in response to receiving an indication of overvoltage.
The combined switch device of claim 11, wherein the driving circuit (18) is further configured to turn on the full-controlled device in response to receiving an indication of the current being below a predetermined current value.
The combined switch device of claim 12, wherein the driving circuit is further configured to turn off the full-controlled device in response to receiving an indication of a voltage of the DC link being below a predetermined voltage value.
An electrical system (100) comprising:

a converter (14) configured to convert an alternative current (AC) voltage of an AC source into a direct current (DC) voltage transmitted on a DC link; and

a combined switch device of any of claims 1-13 configured to protect the DC link from an overvoltage.
A method (200) for manufacturing a combined switch device, comprising:

providing (202) a first branch including a semi-controlled device and a first arrester coupled to the semi-controlled device, and configured to flow a current caused by an overvoltage of a DC link; and

providing (204) a second branch including a full-controlled device and coupled in parallel to the first branch, the second branch configured to commutate the current from the first branch to the second branch in response to turning on the full-controlled device.