CN111371099A - UPFC fault transition device and method based on thyristor transfer resistance circuit - Google Patents
UPFC fault transition device and method based on thyristor transfer resistance circuit Download PDFInfo
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- CN111371099A CN111371099A CN202010140164.XA CN202010140164A CN111371099A CN 111371099 A CN111371099 A CN 111371099A CN 202010140164 A CN202010140164 A CN 202010140164A CN 111371099 A CN111371099 A CN 111371099A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
- H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/10—Flexible AC transmission systems [FACTS]
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Abstract
The invention discloses a UPFC fault transition device and method based on a thyristor transfer resistance circuit. If the transmission direction of active power between the UPFC normally operating current converters is from the serial side to the parallel side, when a serious short-circuit fault occurs in a system circuit, the short-circuit energy of the serial-side MMC is absorbed by quickly switching into a transfer resistance circuit, and the parallel-side MMC is isolated from the serial-side MMC; if the transmission direction of active power between the UPFC normally-operated current converters is that the active power flows from the parallel side to the serial side, when a serious short-circuit fault occurs to a system circuit, the anti-parallel double-thyristor group can automatically cut off reverse fault current of a direct-current bus, and the MMC at the parallel side is automatically isolated from the MMC at the serial side; the UPFC is switched to the STATCOM mode, reactive power support is provided for system bus voltage after faults, and safe operation of a power system after the faults is facilitated.
Description
Technical Field
The invention relates to the technical field of alternating current transmission, in particular to a UPFC fault transition device and method based on a thyristor transfer resistor circuit.
Background
A UPFC (Unified Power Flow Controller) is a typical representative of a FACTS (flexible alternating Current Transmission Systems) device, and can flexibly implement functions such as parallel compensation, series compensation, phase shift, voltage adjustment, and line Power Flow control. The MMC (modular multilevel Converter) has the advantages of high modularization degree, low harmonic content, strong fault handling capability and the like, and is increasingly widely applied to actual engineering. When short-circuit fault occurs in an alternating current system, fault current is coupled to a serial side MMC through a serial transformer, flows through a direct current bus and forms a loop with a parallel side MMC, and normally overcurrent locking of the serial side MMC and the parallel side MMC is caused, and UPFC completely exits from operation. If the MMC at the parallel side can not be locked at the moment, the reactive power support is continuously provided for the system bus voltage, and the safe operation of the power system after the fault is more facilitated. It is therefore necessary to study the fault transition scheme of MMC-UPFC when the ac system is short circuited.
Disclosure of Invention
The invention aims to provide a UPFC fault transition device and method based on a thyristor transfer resistor circuit, and aims to solve the problems that an MMC (modular multilevel converter) on a serial side and a parallel side is always subjected to overcurrent locking and the UPFC cannot run when an alternating current system of the existing UPFC is subjected to a short-circuit fault.
In order to achieve the purpose, the invention provides the following scheme:
a thyristor transfer resistor circuit based UPFC fault transition apparatus, the apparatus comprising: the system comprises a parallel transformer, a parallel side MMC, a series transformer, a series side MMC and a thyristor transfer resistor combined circuit arranged on a direct current bus;
the MMC at the parallel side is connected into an alternating current bus through the parallel transformer; the serial side MMC is connected into an alternating current circuit in series through the serial transformer; the parallel-side MMC is connected with the serial-side MMC back to back through a direct-current bus; each bridge arm of the MMC at the parallel side consists of n half-bridge sub-modules; each bridge arm of the serial side MMC is composed of n half-bridge sub-modules;
the thyristor transfer resistor combination circuit comprises an anti-parallel double-thyristor group and a transfer resistor circuit; the anti-parallel double-crystal brake tube is connected in series at the direct-current positive electrode outlet of the parallel-side MMC; the anti-parallel double-thyristor group is formed by connecting a first thyristor and a second thyristor in an anti-parallel mode; the transfer resistance circuit is connected in parallel between the direct-current positive bus and the direct-current negative bus; the transfer resistance circuit is formed by connecting an IGBT and a damping resistor in series.
Optionally, the resistance value of the transfer resistor is 100 ohms.
Optionally, the apparatus further comprises a thyristor bypass switch; the thyristor bypass switch is connected in series at an alternating current inlet of the serial side MMC and used for bypassing the serial side MMC in emergency.
A UPFC fault transition method based on a thyristor transfer resistor circuit, the method is based on the UPFC fault transition device based on the thyristor transfer resistor circuit, the method comprises the following steps:
if the active power transmission direction between the normally operated MMCs of the UPFC is from the serial side to the parallel side, when a serious short-circuit fault occurs in a system circuit, short-circuit energy fed into the MMC at the serial side is absorbed through input of a transfer resistor, meanwhile, an anti-parallel double-thyristor group is switched off, and the MMC at the parallel side is isolated from the MMC at the serial side; the UPFC is switched to a STATCOM mode, reactive power support is provided for a parallel side access bus after a fault, and UPFC fault transition is realized;
if the active power transmission direction between the UPFC normal operation MMC is from the parallel side to the serial side, when a serious short-circuit fault occurs to a system line, the anti-parallel double-thyristor group automatically cuts off the reverse fault current of the direct current bus, and the parallel side MMC and the serial side MMC automatically realize isolation; and the UPFC is switched to the STATCOM mode, and reactive power support is provided for the system bus voltage after the fault.
Optionally, if the active power transmission direction between the UPFC normally operating MMCs is a serial side and a parallel side, the method specifically includes:
when the anti-parallel double-thyristor group normally operates, a first thyristor of the anti-parallel double-thyristor group is cut off, a second thyristor is conducted, and a trigger pulse of the second thyristor is cancelled after the second thyristor is conducted;
when the alternating current system is short-circuited, the serial side MMC locks and then sends a conducting signal to the IGBT of the transfer resistance circuit, and the transfer resistance is put into the transfer resistance circuit to absorb short-circuit energy fed into the serial side MMC; meanwhile, the current flowing through the second thyristor which is in one-way conduction is reduced to zero, the second thyristor bears back pressure and is automatically turned off, the serial side MMC and the parallel side MMC are isolated, and the UPFC is switched to the STATCOM mode.
Optionally, if the active power transmission direction between the UPFC normally operating MMCs is a parallel side flowing to a series side, the method specifically includes:
when the anti-parallel double-thyristor group normally operates, a first thyristor of the anti-parallel double-thyristor group is switched on, a second thyristor of the anti-parallel double-thyristor group is switched off, and a trigger pulse of the first thyristor is cancelled after the first thyristor is switched on;
after the short circuit takes place for alternating current system, because the first thyristor unidirectional conduction in the anti-parallelly connected double thyristor group of series connection on the direct current bus, the fault current that series side MMC fed into direct current bus can't flow in parallel side MMC through unidirectional conduction's first thyristor, and parallel side MMC and series side MMC are automatic to be kept apart, and UPFC switches to STATCOM mode, provides reactive power for the system bus voltage after the trouble and supports.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides a UPFC fault transition device and method based on a thyristor transfer resistance circuit. If the transmission direction of active power between the UPFC normally operating current converters is from the serial side to the parallel side, when a serious short-circuit fault occurs in a system circuit, the short-circuit energy of the serial-side MMC is absorbed by quickly switching into a transfer resistance circuit, and the parallel-side MMC is isolated from the serial-side MMC; if the transmission direction of active power between the UPFC normally-operated current converters is that the active power flows from the parallel side to the serial side, when a serious short-circuit fault occurs to a system circuit, the anti-parallel double-thyristor group can automatically cut off reverse fault current of a direct-current bus, and the MMC at the parallel side is automatically isolated from the MMC at the serial side; and the UPFC is switched to the STATCOM mode, and reactive power support is provided for the system bus voltage after the fault. According to the invention, through the anti-parallel double-thyristor group and the transfer resistance circuit arranged on the direct current bus, when a serious short circuit fault occurs in a system circuit, the serial side MMC and the parallel side MMC are isolated, overcurrent locking cannot occur on the parallel side MMC, the UPFC can be switched to the STATCOM mode, reactive support is continuously provided for the system bus voltage after the fault, and the safe operation of the power system after the fault is facilitated.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a schematic structural diagram of a UPFC fault transition device based on a thyristor transfer resistor circuit according to the present invention;
fig. 2 is a simulation waveform diagram when a three-phase fault occurs at point k in fig. 1 when the active power transmission direction between converters in normal operation of UPFC is from the serial side to the parallel side without using the UPFC fault transition method provided by the present invention; fig. 2(a) is a schematic diagram of a dc current curve at an outlet of an MMC at a parallel side when the UPFC fault transition method provided by the present invention is not employed; fig. 2(b) is a schematic diagram of three-phase currents of an upper bridge arm of an MMC on a parallel side when the UPFC fault transition method provided by the present invention is not adopted; fig. 2(c) is a schematic diagram of three-phase currents of a parallel-side MMC lower bridge arm when the UPFC fault transition method provided by the present invention is not used;
fig. 3 is a simulation waveform diagram of a three-phase fault occurring at point k in fig. 1 when the active power transmission direction between converters in normal operation of UPFC is from the serial side to the parallel side when the fault transition method provided by the present invention is adopted; fig. 3(a) is a schematic diagram of a dc current curve at an outlet of an MMC at a parallel side when the UPFC fault transition method provided by the present invention is adopted; fig. 3(b) is a schematic diagram of three-phase currents of an upper bridge arm of an MMC on a parallel side when the UPFC fault transition method provided by the present invention is adopted; fig. 3(c) is a schematic diagram of three-phase currents of an MMC lower bridge arm on a parallel side when the UPFC fault transition method provided by the present invention is adopted;
fig. 4 is a simulation waveform diagram when a three-phase fault occurs at point k in fig. 1 when the transmission direction of active power between converters in normal operation of UPFC is from the parallel side to the series side without using the fault transition scheme proposed by the present invention; fig. 4(a) is a schematic diagram of a dc current curve at an outlet of an MMC at a parallel side when the UPFC fault transition method provided by the present invention is not employed; fig. 4(b) is a schematic diagram of a dc current curve at an outlet of an MMC at a series side when the UPFC fault transition method provided by the present invention is not employed; fig. 4(c) is a schematic diagram of three-phase currents of an upper bridge arm of an MMC on a parallel side when the UPFC fault transition method provided by the present invention is not adopted; fig. 4(d) is a schematic diagram of three-phase currents of a parallel-side MMC lower bridge arm when the UPFC fault transition method provided by the present invention is not used; fig. 4(e) is a schematic diagram of reactive power absorbed by the MMC on the parallel side when the UPFC fault transit method provided by the present invention is not employed;
fig. 5 is a simulation waveform diagram when a three-phase fault occurs at point k in fig. 1 when the active power transmission direction between the UPFC normally operating converters is from the parallel side to the series side when the fault transition scheme proposed by the present invention is adopted; fig. 5(a) is a schematic diagram of a dc current curve at an outlet of an MMC at a parallel side when the UPFC fault transition method provided by the present invention is adopted; fig. 5(b) is a schematic diagram of three-phase currents of an upper bridge arm of an MMC on a parallel side when the UPFC fault transition method provided by the present invention is adopted; fig. 5(c) is a schematic diagram of three-phase currents of an MMC lower bridge arm on a parallel side when the UPFC fault transition method provided by the present invention is adopted; fig. 5(d) is a schematic diagram of reactive power absorbed by the MMC on the parallel side when the UPFC fault transition method provided by the present invention is adopted.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a UPFC fault transition device and method based on a thyristor transfer resistor circuit, and aims to solve the problems that an MMC (modular multilevel converter) on a serial side and a parallel side is always subjected to overcurrent locking and the UPFC cannot run when an alternating current system of the existing UPFC is subjected to a short-circuit fault.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 1 is a schematic structural diagram of a UPFC fault transit apparatus based on a thyristor transfer resistor circuit according to the present invention. The conventional UPFC (unified power flow Controller) generally includes: parallel transformer, parallel side MMC, series transformer and series side MMC. As shown in fig. 1, the MMC on the parallel side of the UPFC is connected to the ac bus through the parallel transformer; and the serial side MMC is connected into an alternating current circuit in series through the serial transformer. The parallel side MMC is connected with the series side MMC back to back through a direct current bus. TBS is thyristor bypass switch for bypass series side MMC under emergency. Each bridge arm of the parallel side MMC is composed of n half-bridge sub-modules, such as parallel side SM in figure 11To SMnAs shown. Each bridge arm of the serial side MMC is also composed of n half-bridge sub-modules, such as serial side SM in figure 11To SMnAs shown.
When a serious short-circuit fault occurs in an alternating current system, the fault characteristics of the conventional MMC (Modular Multilevel Converter, the invention is called Converter for short) -UPFC serial and parallel side converters are as follows:
the fault current of the alternating current system is coupled to the valve side through the series transformer, the serial side MMC is subjected to overcurrent locking rapidly, and the serial side MMC is in an uncontrolled charging state after being locked;
for the UPFC in which the active power transmission direction between the converters in the normal operation state is from the serial side to the parallel side, the fault current of the direct current bus is rapidly increased, the MMC bridge arm at the parallel side locks the overcurrent, and the UPFC quits the operation;
for the UPFC in which the active power transmission direction among the converters in the normal operation state is parallel side to serial side, the current of the direct current bus is reversed, the fault current flows into the parallel side MMC through the direct current bus, the bridge arm of the parallel side MMC is subjected to overcurrent locking, and the UPFC exits the operation.
In order to avoid the overcurrent locking of the MMC at the parallel side under the condition of the fault of the existing UPFC, the invention provides a UPFC fault transition device based on a thyristor transfer resistor circuit. Referring to fig. 1, the device of the invention is provided with a thyristor transfer resistor combined circuit on an MMC-UPFC direct current bus; the thyristor transfer resistor combination circuit comprises an anti-parallel double-thyristor group and a transfer resistor circuit.
The anti-parallel double-crystal brake tube is connected in series at the direct-current positive electrode outlet of the parallel-side MMC; the anti-parallel double-thyristor group consists of a first thyristor T1And a second thyristor T2And are connected in reverse parallel. The transfer resistance circuit is connected in parallel between the positive pole and the negative pole of the direct current bus between the parallel-side MMC and the serial-side MMC; the transfer resistance circuit is formed by connecting an IGBT and a damping resistor in series. In fig. 1, S denotes an IGBT (Insulated Gate bipolar transistor) and R denotes a damping resistor.
In the device of the present invention, the transfer resistor has a resistance of 100ohm (ohm).
The apparatus further comprises a thyristor bypass switch TBS; and the thyristor bypass switch TBS is connected in series at an alternating current inlet of the series side MMC and is used for bypassing the series side MMC in emergency.
If the transmission direction of active power between the UPFC normally operating current converters is from the serial side to the parallel side, the short-circuit energy fed into the MMC at the serial side is absorbed by quickly inputting a transfer resistor, meanwhile, the anti-parallel double-thyristor group is switched off, and the MMC at the parallel side is isolated from the MMC at the serial side; and the UPFC is switched to the STATCOM mode, reactive power support is provided for a parallel side access bus after the fault, and the fault transition of the UPFC is realized.
If the transmission direction of active power between the UPFC normal operation converters is parallel side to serial side, the anti-parallel double-thyristor group can automatically cut off the reverse fault current of the direct current bus, the parallel side MMC and the serial side MMC automatically realize isolation, and the UPFC is switched to the STATCOM mode to provide reactive support for the system bus voltage after the fault.
Therefore, according to the UPFC fault transition device based on the thyristor transfer resistance circuit, when an alternating current system has a short-circuit fault, the MMC at the parallel side cannot be subjected to overcurrent locking, the UPFC can be switched to a STATCOM (STATic synchronous compensator) mode, reactive power support is continuously provided for the voltage of the bus connected to the parallel side, and safe operation of a power system after the fault is facilitated.
Based on the UPFC fault transition device based on the thyristor transfer resistance circuit, the invention also provides a UPFC fault transition method based on the thyristor transfer resistance circuit. The device is characterized in that a thyristor transfer resistor combined circuit is arranged on an MMC-UPFC direct current bus, the thyristor transfer resistor combined circuit is composed of an anti-parallel double-thyristor group and a transfer resistor circuit, the anti-parallel double-thyristor group is connected with the direct current bus in series, the transfer resistor circuit is connected between the positive pole and the negative pole of the direct current bus in parallel, and the method comprises the following steps:
if the transmission direction of active power between the UPFC normal operation converters is from the serial side to the parallel side, during normal operation, the first thyristor T of the anti-parallel double-thyristor group1Cut-off and second thyristor T2Conducting the second thyristor T2The trigger pulse is cancelled after the switch-on; when the alternating current system is short-circuited, the serial side MMC locks and then sends a conducting signal to the IGBT of the transfer resistance circuit, the transfer resistance is put into, and short-circuit energy fed into the serial side MMC is absorbed; simultaneously flows through the second thyristor T which is in one-way conduction2The current of the converter is reduced to zero, the converter bears back pressure and is automatically turned off, the MMC on the serial side and the parallel side is isolated, and the UPFC is switched to the STATCOM mode.
If the transmission direction of active power between the UPFC normal operation converters is parallel side flow to series sideIn normal operation, the first thyristor T of the anti-parallel double-thyristor group1Conducting, second thyristor T2Cut-off, first thyristor T1The trigger pulse is cancelled after the switch-on; when the AC system is short-circuited, the first thyristor T in the anti-parallel double-thyristor group connected in series on the DC bus1Unidirectional conduction, fault current fed into direct current bus by MMC on series side can not pass through unidirectional conduction first thyristor T1Flow into parallel side MMC, parallel side MMC and series connection side MMC are automatic to be kept apart, and UPFC switches to STATCOM mode, provides reactive power for the system bus voltage after the trouble and supports.
Therefore, the invention isolates the serial-parallel side MMC through the anti-parallel double-thyristor group and the transfer resistance circuit arranged on the direct current bus when the system line has serious short circuit fault, the parallel side MMC can not have overcurrent locking, the UPFC is switched to the STATCOM mode, reactive support is provided for the system bus voltage after the fault, and the safe operation of the power system after the fault is facilitated.
In order to illustrate the effect of the apparatus and method for UPFC fault transition based on thyristor transfer resistor circuit according to the present invention, the following verification is performed.
Fig. 2 is a simulation waveform diagram of a three-phase fault occurring at point k in fig. 1 when the active power transmission direction between converters in normal operation of UPFC is from the serial side to the parallel side without using the UPFC fault transition method provided by the present invention. Fig. 2(a) is a schematic diagram of a dc current curve at an outlet of an MMC at a parallel side when the UPFC fault transition method provided by the present invention is not used. FIG. 2(a) shows the abscissa as time t in seconds(s); the ordinate is the direct current magnitude fed into the parallel side MMC outlet, and the unit is kA. Fig. 2(b) is a schematic diagram of three-phase currents of an upper bridge arm of the MMC on the parallel side when the UPFC fault transition method provided by the present invention is not adopted, and fig. 2(c) is a schematic diagram of three-phase currents of a lower bridge arm of the MMC on the parallel side when the UPFC fault transition method provided by the present invention is not adopted.
Fig. 3 is a simulation waveform diagram of a three-phase fault occurring at point k in fig. 1 when the active power transmission direction between converters in normal operation of UPFC is from the serial side to the parallel side when the fault transition method provided by the present invention is adopted. Fig. 3(a) is a schematic diagram of a dc current curve at an outlet of an MMC at a parallel side when the UPFC fault transition method provided by the present invention is adopted. FIG. 3(a) shows the abscissa as time t in seconds(s); the ordinate is the direct current magnitude fed into the parallel side MMC outlet, and the unit is kA. Fig. 3(b) is a schematic diagram of three-phase currents of an upper bridge arm of an MMC on a parallel side when the UPFC fault transition method provided by the present invention is adopted, and fig. 3(c) is a schematic diagram of three-phase currents of a lower bridge arm of the MMC on the parallel side when the UPFC fault transition method provided by the present invention is adopted.
If the transmission direction of active power between the converters in normal operation of the UPFC is from the serial side to the parallel side, a three-phase fault is set at a k point at the head end of an outlet of an UPFC access circuit in the graph 1, the fault occurrence time is 1.5s, and the fault duration is 0.5 s. When the fault transition scheme provided by the invention is not adopted, the simulation waveform is shown in fig. 2, and it can be seen that after a fault occurs, before TBS is conducted, the direct current bus current is continuously increased, and the MMC bridge arm on the parallel side is subjected to overcurrent locking; when the fault transition scheme provided by the invention is adopted, the simulation waveform is shown in figure 3, and it can be seen that the direct current bus current at the outlet of the parallel-side MMC becomes zero after the transfer resistance circuit is put into use, the parallel-side MMC bridge arm cannot be subjected to overcurrent locking, and the parallel-side MMC after the fault can provide reactive power support for the system bus. The experimental result shows that when a system line has a serious short-circuit fault, the fault transition scheme provided by the invention can isolate the serial-parallel side MMC, and the parallel side MMC can not be subjected to overcurrent locking.
Fig. 4 is a simulation waveform diagram of a three-phase fault occurring at point k in fig. 1 when the active power transmission direction between the UPFC normally operating converters is from the parallel side to the series side without using the fault transition scheme proposed by the present invention. Fig. 4(a) is a schematic diagram of a dc current curve at an outlet of an MMC at a parallel side when the UPFC fault transition method provided by the present invention is not used. FIG. 4(a) shows the abscissa as time t in seconds(s); the ordinate is the direct current magnitude fed into the parallel side MMC outlet, and the unit is kA. Fig. 4(b) is a schematic diagram of a dc current curve at an outlet of an MMC at a series side when the UPFC fault transition method provided by the present invention is not used. Fig. 4(c) is a schematic diagram of three-phase currents of an upper bridge arm of the MMC on the parallel side when the UPFC fault transition method provided by the present invention is not adopted, fig. 4(d) is a schematic diagram of three-phase currents of a lower bridge arm of the MMC on the parallel side when the UPFC fault transition method provided by the present invention is not adopted, and fig. 4(e) is a schematic diagram of reactive power absorbed by the MMC on the parallel side when the UPFC fault transition method provided by the present invention is not adopted.
Fig. 5 is a simulation waveform diagram of a three-phase fault occurring at point k in fig. 1 when the active power transmission direction between converters in normal operation of UPFC is from the parallel side to the series side when the fault transition scheme proposed by the present invention is adopted. Fig. 5(a) is a schematic diagram of a direct current curve at an outlet of an MMC at a parallel side when the UPFC fault transition method provided by the present invention is adopted, fig. 5(b) is a schematic diagram of three-phase currents of an upper bridge arm of the MMC at the parallel side when the UPFC fault transition method provided by the present invention is adopted, fig. 5(c) is a schematic diagram of three-phase currents of a lower bridge arm of the MMC at the parallel side when the UPFC fault transition method provided by the present invention is adopted, and fig. 5(d) is a schematic diagram of reactive power absorbed by the MMC at the parallel side when the UPFC fault transition method provided by the present invention is adopted.
If the transmission direction of active power between the converters in normal operation of the UPFC is parallel-side flow to serial-side, a three-phase fault is set at a k point at the head end of an outlet of an UPFC access circuit in the graph 1, the fault occurrence time is 1.5s, and the fault duration is 0.5 s. When the fault transition scheme provided by the invention is not adopted, the simulation waveform is shown in fig. 4, and it can be seen that after a fault occurs, before TBS is conducted, the direct current bus current is reversed, and the MMC bridge arm on the parallel side is subjected to overcurrent locking; when the fault transition scheme provided by the invention is adopted, the simulation waveform is shown in fig. 5, and it can be seen that the direct current bus current is cut off after the fault is carried out, the parallel side MMC bridge arm cannot be locked by overcurrent, and the parallel side MMC after the fault can provide reactive power support for the system bus. The experimental result shows that when a serious short-circuit fault occurs in a system line, the fault transition scheme provided by the invention can isolate the serial-parallel side MMC, and the parallel side MMC can not be subjected to overcurrent locking.
Verification results show that the fault transition scheme provided by the invention can quickly realize serious short-circuit fault transition of a system circuit when the MMC-UPFC operates in different working states.
The invention discloses a UPFC fault transition device and method based on a thyristor transfer resistor circuit. If the transmission direction of active power between the UPFC normally operating current converters is from the serial side to the parallel side, when a serious short-circuit fault occurs in a system circuit, the short-circuit energy of the serial-side MMC is absorbed by quickly switching into a transfer resistance circuit, and the parallel-side MMC is isolated from the serial-side MMC; if the transmission direction of active power between the UPFC normally-operated current converters is that the active power flows from the parallel side to the serial side, when a serious short-circuit fault occurs to a system circuit, the anti-parallel double-thyristor group can automatically cut off reverse fault current of a direct-current bus, and the MMC at the parallel side is automatically isolated from the MMC at the serial side; the UPFC is switched to the STATCOM mode, reactive power support is provided for system bus voltage after faults, and safe operation of a power system after the faults is facilitated.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.
Claims (6)
1. A thyristor transfer resistor circuit based UPFC fault transition apparatus, the apparatus comprising: the system comprises a parallel transformer, a parallel side MMC, a series transformer, a series side MMC and a thyristor transfer resistor combined circuit arranged on a direct current bus;
the MMC at the parallel side is connected into an alternating current bus through the parallel transformer; the serial side MMC is connected into an alternating current circuit in series through the serial transformer; the parallel-side MMC is connected with the serial-side MMC back to back through a direct-current bus; each bridge arm of the MMC at the parallel side consists of n half-bridge sub-modules; each bridge arm of the serial side MMC is composed of n half-bridge sub-modules;
the thyristor transfer resistor combination circuit comprises an anti-parallel double-thyristor group and a transfer resistor circuit; the anti-parallel double-crystal brake tube is connected in series at the direct-current positive electrode outlet of the parallel-side MMC; the anti-parallel double-thyristor group is formed by connecting a first thyristor and a second thyristor in an anti-parallel mode; the transfer resistance circuit is connected in parallel between the direct-current positive bus and the direct-current negative bus; the transfer resistance circuit is formed by connecting an IGBT and a damping resistor in series.
2. The thyristor-transfer resistor circuit-based UPFC fault transit device of claim 1, wherein the transfer resistor has a resistance of 100 ohms.
3. The thyristor-transferred resistor circuit-based UPFC fault transition device of claim 1, further comprising a thyristor bypass switch; the thyristor bypass switch is connected in series at an alternating current inlet of the serial side MMC and used for bypassing the serial side MMC in emergency.
4. A method for transitioning a fault of a UPFC based on a thyristor-switched resistor circuit, wherein the method is based on the apparatus for transitioning a fault of a UPFC based on a thyristor-switched resistor circuit of claim 1, the method comprising:
if the active power transmission direction between the normally operated MMCs of the UPFC is from the serial side to the parallel side, when a serious short-circuit fault occurs in a system circuit, short-circuit energy fed into the MMC at the serial side is absorbed through input of a transfer resistor, meanwhile, an anti-parallel double-thyristor group is switched off, and the MMC at the parallel side is isolated from the MMC at the serial side; the UPFC is switched to a STATCOM mode, reactive power support is provided for a parallel side access bus after a fault, and UPFC fault transition is realized;
if the active power transmission direction between the UPFC normal operation MMC is from the parallel side to the serial side, when a serious short-circuit fault occurs to a system line, the anti-parallel double-thyristor group automatically cuts off the reverse fault current of the direct current bus, and the parallel side MMC and the serial side MMC automatically realize isolation; and the UPFC is switched to the STATCOM mode, and reactive power support is provided for the system bus voltage after the fault.
5. The thyristor transfer resistor circuit-based UPFC fault transition method of claim 4, wherein if the active power transmission direction between the UPFC normal operation MMCs is the serial side and the parallel side, the method specifically comprises:
when the anti-parallel double-thyristor group normally operates, a first thyristor of the anti-parallel double-thyristor group is cut off, a second thyristor is conducted, and a trigger pulse of the second thyristor is cancelled after the second thyristor is conducted;
when the alternating current system is short-circuited, the serial side MMC locks and then sends a conducting signal to the IGBT of the transfer resistance circuit, and the transfer resistance is put into the transfer resistance circuit to absorb short-circuit energy fed into the serial side MMC; meanwhile, the current flowing through the second thyristor which is in one-way conduction is reduced to zero, the second thyristor bears back pressure and is automatically turned off, the serial side MMC and the parallel side MMC are isolated, and the UPFC is switched to the STATCOM mode.
6. The thyristor transfer resistor circuit-based UPFC fault transition method of claim 4, wherein if the active power transmission direction between the UPFC normal operation MMCs is parallel side flow to serial side, the method specifically comprises:
when the anti-parallel double-thyristor group normally operates, a first thyristor of the anti-parallel double-thyristor group is switched on, a second thyristor of the anti-parallel double-thyristor group is switched off, and a trigger pulse of the first thyristor is cancelled after the first thyristor is switched on;
after the short circuit takes place for alternating current system, because the first thyristor unidirectional conduction in the anti-parallelly connected double thyristor group of series connection on the direct current bus, the fault current that series side MMC fed into direct current bus can't flow in parallel side MMC through unidirectional conduction's first thyristor, and parallel side MMC and series side MMC are automatic to be kept apart, and UPFC switches to STATCOM mode, provides reactive power for the system bus voltage after the trouble and supports.
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