CN114221318A - MMC sub-module circuit topology structure, fault ride-through method and application thereof - Google Patents
MMC sub-module circuit topology structure, fault ride-through method and application thereof Download PDFInfo
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- CN114221318A CN114221318A CN202111560443.2A CN202111560443A CN114221318A CN 114221318 A CN114221318 A CN 114221318A CN 202111560443 A CN202111560443 A CN 202111560443A CN 114221318 A CN114221318 A CN 114221318A
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- 238000000034 method Methods 0.000 title claims abstract description 49
- 239000004065 semiconductor Substances 0.000 claims abstract description 90
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 claims abstract description 30
- 239000011787 zinc oxide Substances 0.000 claims abstract description 15
- 238000011217 control strategy Methods 0.000 claims abstract description 11
- 230000008569 process Effects 0.000 claims description 23
- 239000003990 capacitor Substances 0.000 claims description 22
- 230000009471 action Effects 0.000 claims description 13
- 230000015556 catabolic process Effects 0.000 claims description 8
- 230000003071 parasitic effect Effects 0.000 claims description 8
- 238000009413 insulation Methods 0.000 claims description 7
- 238000007599 discharging Methods 0.000 claims description 2
- 230000001052 transient effect Effects 0.000 claims description 2
- QEIQEORTEYHSJH-UHFFFAOYSA-N Armin Natural products C1=CC(=O)OC2=C(O)C(OCC(CCO)C)=CC=C21 QEIQEORTEYHSJH-UHFFFAOYSA-N 0.000 claims 1
- 238000005265 energy consumption Methods 0.000 abstract description 23
- 238000010586 diagram Methods 0.000 description 9
- 230000005540 biological transmission Effects 0.000 description 7
- 230000017525 heat dissipation Effects 0.000 description 4
- 238000010276 construction Methods 0.000 description 3
- 230000008859 change Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 230000001360 synchronised effect Effects 0.000 description 2
- 238000004891 communication Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage
- H02H9/06—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage using spark-gap arresters
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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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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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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- 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
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
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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
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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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
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/76—Power conversion electric or electronic aspects
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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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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Abstract
The fault ride-through method of the MMC submodule circuit topological structure and the application thereof, wherein the input end of the MMC submodule is connected with the collector electrode of a switching device, and the output end of the MMC submodule is connected with the emitter electrode of the switching device; the anode of the anti-parallel diode is connected with the emitter of the power semiconductor switching device, and the cathode of the anti-parallel diode is connected with the collector of the switching device; a protection gap is connected in series with the MOV and then connected in parallel with the switching device; a voltage grading resistor is connected in parallel with the protection gap and the MOV, respectively. According to the characteristic phenomenon that the voltage of a direct current line is improved in a short time when a low-voltage fault occurs on the alternating current side of the receiving end of the offshore wind power VSC-HVDC system, the MMC sub-module structure integrating the series gap zinc oxide arrester is adopted, when the low-voltage fault occurs, the short-time rise of the voltage of the direct current line can be restrained under the condition that an MMC basic control strategy and an MMC sub-module switching strategy are not changed, and a direct current energy consumption device does not need to be additionally arranged.
Description
Technical Field
The invention relates to the technical field of flexible direct current transmission, in particular to an MMC submodule circuit topological structure based on an MMC current converter, a fault ride-through method and application thereof.
Background
The flexible direct current transmission technology can be directly connected with a weak alternating current system, has no transmission distance limitation, and does not need to be additionally provided with a reactive power compensation device, so that wide application requirements are generated in a power system. When a low-voltage fault occurs on the alternating current side of the receiving end, the voltage drop of an alternating current power grid causes the power output capacity of a receiving end converter station to be reduced, if no measures are taken, surplus power can cause overvoltage of a direct current system within tens of milliseconds, the safe operation of the system is threatened, and the offshore wind turbine can be disconnected under severe conditions.
The existing solutions mainly include two types, one is to adjust transmission power through a control strategy, and the other is to utilize an energy consumption device to absorb power generated by a fan.
Aiming at the scheme of realizing fault ride-through by adjusting transmission power through a control strategy, the communication reliability between a transmitting end converter station and a receiving end converter station is greatly depended on, and the existing research shows that the problem of 2-class surplus power of a direct current power grid cannot be simultaneously solved by adopting a control method on the premise of not limiting steady-state operation power. (scheme I is detailed in a mechanism analysis and control method of excess power problem of Guxiansha, Mei Mian, Li Ying, Li Gao Wang, Wei Yu, Yubin Zhang Bei flexible direct current power grid [ J ] power grid technology, 2019,43(01):157-164.DOI:10.13335/j.1000-3673.pst.2018.1643.)
Aiming at the scheme of realizing fault ride-through by adopting a direct current energy consumption device, when the voltage of a receiving end alternating current side of an offshore wind power VSC-HVDC system is reduced to be below 0.9p.u., a wind turbine generator is started in low voltage ride-through mode, when the alternating current voltage of a wind power plant is reduced to be 0.2p.u., a receiving end grid side converter does not output active power, surplus power needs to be absorbed by an unloading circuit in the wind turbine generator, and the low voltage ride-through time is 100-150 ms. The internal unloading circuit usually adopts a direct current energy consumption device, the energy consumption resistor generates heat seriously during working, so the energy consumption resistor needs to be independently installed outdoors for heat dissipation, the energy consumption resistor has insulation breakdown risk because the voltage at two ends of the resistor is very high, and leads at two ends need to be connected into a wall bushing under the insulation requirement, so the cost is high. (scheme II is detailed in: xu Bin, high impact, Zhang, novel direct current energy consumption device topology [ J ] applied to main network side alternating current fault ride-through of VSC-HVDC system for offshore wind power access, China Motor engineering newspaper 2021,41(01):88-97+400, DOI:10.13334/j.0258-8013, pcsee.191984.).
The direct current energy consumption device disclosed in patent CN111162559A can stabilize the voltage of the direct current bus when the direct current energy consumption device is switched, so as to ensure the overall fault ride-through performance of the direct current energy consumption device; the high-power energy consumption device disclosed in patent CN111224421A is used for consuming surplus power on the direct current side of the flexible direct current power transmission system; the patent CN111224421A designs a main loop with fault ride-through capability, which is composed of mature equipment elements such as metal oxide voltage limiters, GAPs, GAP spark discharge devices, etc.; the above patents need to additionally add power equipment on the basis of the existing flexible direct current transmission system to realize fault ride-through, and need to control the input and exit of the power equipment according to the state of the direct current system, which is not only high in cost, but also unfavorable for the reliability of the system.
Disclosure of Invention
In order to solve the defects in the prior art, the invention discloses an offshore wind power flexible direct current system fault ride-through method based on an MMC converter, which has the technical scheme as follows:
the circuit topology structure of the MMC submodule of the integrated series gap zinc oxide arrester comprises a power semiconductor switch device, an anti-parallel diode, a protection gap, an MOV and a voltage-sharing resistor; it is characterized in that:
the input end of the MMC sub-module is connected with the collector of the power semiconductor switching device, and the output end of the MMC sub-module is connected with the emitter of the power semiconductor switching device;
the anode of the anti-parallel diode is connected with the emitter of the power semiconductor switching device, and the cathode of the anti-parallel diode is connected with the collector of the power semiconductor switching device;
the protection gap is connected with the MOV in series and then connected with the power semiconductor switching device in parallel;
the voltage equalizing resistor is respectively connected with the protection gap and the MOV in parallel;
the invention also discloses a fault ride-through method, which is characterized by comprising the following steps:
the method comprises the following steps: when the offshore wind power VSC-HVDC system normally operates, the bus voltage of the direct current system is kept within a rated range, the MMC converter operates according to a basic control strategy, the MMC sub-module is in a normal switching process, the overvoltage caused by the turn-off of the power semiconductor device does not cause the breakdown of a protection gap, and the MMC sub-module is in a normal working state at the moment.
Step two: after marine wind power VSC-HVDC system receives the end and exchanges the side and take place the low pressure trouble, surplus power appears in the system, direct current line voltage surpasses rated range, the capacitor voltage of MMC submodule piece risees, at MMC submodule piece switching in-process, can cause the shutoff peak overvoltage at the device both ends when power semiconductor switching device switches off, and then lead to the protection clearance to be punctured, MOV action afterwards and restriction power semiconductor switching device both ends overvoltage, can effectively reduce the capacitance voltage of MMC submodule piece at this in-process, can restrain direct current line voltage and rise.
Step three: if the low-voltage fault time of the receiving end of the offshore wind power VSC-HVDC system is larger than the specified low-voltage ride-through time, the fans of the source side which are operated in a grid-connected mode are allowed to be cut off, and then sub-modules of the sending end MMC current converter are all locked.
The invention also discloses an application of the fault ride-through method in the offshore wind power flexible direct current system.
Has the advantages that:
compared with the traditional scheme of realizing low-voltage fault ride-through by adopting a direct-current energy consumption device, the technical scheme provided by the invention does not need to use an energy consumption resistor, eliminates a wall bushing, avoids the heat dissipation problem of the energy consumption resistor and the insulation problem of the bushing, saves the occupied area, reduces the construction difficulty and improves the technical economy.
According to the technical scheme provided by the invention, the MMC sub-module structure integrating the series gap zinc oxide arrester is adopted, fault ride-through can be realized without changing an MMC basic control strategy and an MMC sub-module switching strategy, and meanwhile, the utilization rate of a power semiconductor switch device is improved.
According to the technical scheme provided by the invention, the MMC sub-module structure integrating the series gap zinc oxide arrester is adopted, fault ride-through can be realized without changing an MMC basic control strategy and an MMC sub-module switching strategy, and meanwhile, the utilization rate of a power semiconductor switch device is improved.
According to the characteristic phenomenon that the voltage of a direct current line is improved in a short time when a low-voltage fault occurs on the receiving end alternating current side of the offshore wind power VSC-HVDC system, the MMC sub-module structure integrating the series gap zinc oxide arrester is skillfully adopted, when the low-voltage fault occurs, the short-time rise of the voltage of the direct current line can be restrained under the condition that an MMC basic control strategy and an MMC sub-module switching strategy are not changed, and a direct current energy consumption device does not need to be additionally arranged.
Drawings
Fig. 1 is a circuit topology diagram of a dc energy consuming device in the prior art.
FIG. 2 is a circuit topology diagram of an integrated MMC sub-module adopted by the fault ride-through method of the offshore wind power flexible direct current system based on the MMC current converter provided by the invention;
wherein: 1. 2 is a power semiconductor switching device, 3, 4 are diodes, 5, 6 are protection gaps, 7, 8 are MOVs, 9, 10 are parasitic capacitances of the protection gaps, 11, 12 are parasitic capacitances of the MOVs, 13, 14 are voltage equalizing resistors connected in parallel with the protection gaps, 15, 16 are voltage equalizing resistors connected in parallel with the MOVs, and 17 is a capacitor.
Fig. 3 is an electrical structure schematic diagram of an application scenario of the flexible direct current system fault ride-through method for offshore wind power based on an MMC converter.
Fig. 4(a) is a schematic diagram of a signal path of a single MMC submodule in a fault ride-through process of the flexible offshore wind power direct current system fault ride-through method based on the MMC converter provided by the invention.
Fig. 4(b) is an action timing diagram of a single MMC submodule in the fault ride-through process of the flexible offshore wind power direct current system fault ride-through method based on the MMC current converter provided by the invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Fig. 2 is a circuit topology diagram of an MMC converter adopted in the fault ride-through method of the offshore wind power flexible direct current system based on the MMC converter provided by the invention.
With half-bridge MMC as an example, the circuit topology structure of the MMC submodule of the integrated series gap zinc oxide arrester comprises: 2 power semiconductor switching devices, 2 protection gaps, 2 MOVs and 4 voltage-sharing resistors. In the MMC submodule: the anode of the anti-parallel diode 3 is connected with the emitter of the power semiconductor switching device 1, and the cathode of the anti-parallel diode 3 is connected with the collector of the power semiconductor switching device 1; the anode of the anti-parallel diode 4 is connected with the emitter of the power semiconductor switching device 2, and the cathode of the anti-parallel diode 4 is connected with the collector of the power semiconductor switching device 2; the positive electrode of the capacitor 17 is connected with the collector of the power semiconductor switch tube 1, and the negative electrode of the capacitor 17 is connected with the emitter of the power semiconductor switch tube 2; the positive connection of the half-bridge type MMC sub-module is led out from the node of the emitting electrode of the power semiconductor switch device 1 and the collecting electrode of the power semiconductor switch device 2, and the negative connection of the half-bridge type MMC sub-module is led out from the node of the emitting electrode of the power semiconductor switch device 2. Connecting the protection gap 5 in series with the MOV7, the protection gap 6 in series with the MOV8, the protection gap 5 in parallel with the voltage equalizing resistor 13, the protection gap 6 in parallel with the voltage equalizing resistor 14, the MOV7 in parallel with the voltage equalizing resistor 15, and the MOV8 in parallel with the voltage equalizing resistor 16 to form two port elements; the terminal of the port element formed by connecting the protection gap 5 and the voltage-equalizing resistor 13 is connected to the collector of the power semiconductor switching device 1, and the terminal of the port element formed by connecting the MOV7 and the voltage-equalizing resistor 15 is connected to the emitter of the power semiconductor switching device 1; the terminal of the port element formed by connecting the guard gap 6 and the voltage equalizing resistor 14 is connected to the collector of the power semiconductor switching device 2, and the terminal of the port element formed by connecting the MOV8 and the voltage equalizing resistor 16 is connected to the emitter of the power semiconductor switching device 2.
The receiving end MMC of the offshore wind power VSC-HVDC system has 6 bridge arms, and each bridge arm is provided with 1 bridge arm reactor L0And the bridge arms of each phase are combined together to form a phase unit, and the three-phase bridge arms are connected in parallel. The power semiconductor switch device is IGBT, IGCT or IEGT.
Fig. 3 is an electrical structure schematic diagram of an application scenario of the flexible direct current system fault ride-through method for offshore wind power based on an MMC converter. To further illustrate the fault ride-through method proposed by the present invention, the electrical structure diagram of the application scenario described in fig. 3 is described in detail, and the overall working process is as follows:
the method comprises the following steps: when the offshore wind power VSC-HVDC system normally operates, the bus voltage of the direct current system is kept within a rated range, the MMC converter operates according to a basic control strategy, the MMC sub-module is in a normal switching process, peak overvoltage caused by turn-off of a power semiconductor device does not cause breakdown of a protection gap, and the MMC sub-module is in a normal working state at the moment.
Step two: after low voltage fault takes place for marine wind power VSC-HVDC system receiving end interchange side, the energy that receiving end MMC consumed reduces, make receiving end alternating current electric network's power consumption ability reduce, but the wind turbine generator system that send end MMC connects is because unable synchronous acceptance receiving end MMC connects the alternating current electric network's voltage, frequency, electric quantity such as wave form, the operating condition of wind turbine generator system can not change in the short time, lead to surplus power to get into the MMC transverter and charge to the condenser of MMC submodule piece, and then lead to the electric capacity voltage short-term improvement. At this moment, the MMC current converter continues to operate according to an original control strategy, in the switching process of the MMC sub-module, switching-off peak overvoltage can be caused at two ends of the power semiconductor switching device when the power semiconductor switching device is switched off, and then a protection gap is broken down, then MOV acts and limits the overvoltage at two ends of the power semiconductor switching device, the capacitance voltage of the MMC sub-module can be effectively reduced in the process, and the voltage rise of a direct current circuit can be restrained.
Step three: if the low-voltage fault time of the receiving end of the offshore wind power VSC-HVDC system is larger than the specified low-voltage ride-through time, the fans of the source side which are operated in a grid-connected mode are allowed to be cut off, and then sub-modules of the sending end MMC current converter are all locked.
In the second step, the MMC sub-module is integrated with the series gap zinc oxide arrester.
Fig. 4 is an action timing diagram of a single MMC submodule in a low-voltage fault ride-through process of the method for fault ride-through of the offshore wind power flexible direct-current system based on the MMC current converter provided by the invention. Referring to fig. 4, the detailed operation logic of each element of the MMC sub-module in step two will now be described in detail according to the timing sequence:
assuming that the direction of the bridge arm current in the MMC sub-module is the direction identified in fig. 2, the MMC sub-module is normally switched according to the basic valve control instruction all the time.
Before T0 moment, when the offshore wind power VSC-HVDC system normally operates, neither the integrated protection gap in the MMC sub-module nor the MOV act.
And at the time T0, a low-voltage fault occurs on the receiving end alternating current side of the offshore wind power VSC-HVDC system.
And in the period from T0 to T1, the lower bridge arm power semiconductor switching device of the MMC sub-module is just in an off state at the moment. After low voltage fault takes place for marine wind power VSC-HVDC system receiving end interchange side, the energy that receiving end MMC consumed reduces, make receiving end alternating current electric network's power consumption ability reduce, but the wind turbine generator system that send end MMC connects is because unable synchronous acceptance receiving end MMC connects the alternating current electric network's voltage, frequency, electric quantity such as wave form, the operating condition of wind turbine generator system can not change in the short time, lead to surplus power to get into the MMC transverter and charge to the condenser of MMC submodule piece, and then lead to the electric capacity voltage short-term improvement.
And at the moment of T1, according to the basic valve control instruction, the upper bridge arm power semiconductor switching device of the MMC sub-module is turned off, and the lower bridge arm power semiconductor switching device of the MMC sub-module is turned on.
In the time period from T1 to T2, the lower bridge arm power semiconductor switching device is conducted, and the lower bridge arm power semiconductor switching device and the protection gap parasitic capacitor and the MOV parasitic capacitor form a short-circuit charging and discharging loop. Since a pure capacitance loop is formed before and after the circuit is switched, the capacitance voltage jumps, and the charges on all capacitor plates on the node which is not connected with the voltage source are instantly conserved in the circuit switching, so that the voltage division conditions of the protection gap and the MOV in the current stage can be deduced according to the principle, and the voltage of the protection gap is shown in figure 4. The capacitance voltage of the MMC sub-module is continuously increased in the phase.
And at the moment of T2, according to the basic valve control instruction, the upper bridge arm power semiconductor switching device of the MMC sub-module is switched on, and the lower bridge arm power semiconductor switching device of the MMC sub-module is switched off.
In the time period from T2 to T3, when the power semiconductor switching device is turned off, the current flowing through the device suddenly changes in a very short time, and a turn-off peak overvoltage is formed under the action of stray inductance inside the device, and the formula of the turn-off peak overvoltage is as follows: vpeak＝L0Ddti, wherein: vpeakFor turn-off peak overvoltage across the device, L0I is the stray inductance inside the device and i is the current flowing through the device. In the turn-off process of the lower bridge arm power semiconductor switching device, the voltages at the two ends of the lower bridge arm power semiconductor switching device gradually rise, and the voltages at the two ends of the device are redistributed in the protection gap and the MOV according to a circuit topology structure, an electromagnetic transient process and kirchhoff law.
At time T3, the voltage across the protection gap reaches a breakdown value, and the protection gap is broken down to a conducting state.
In the period from T3 to T4, the overvoltage generated by the turn-off of the lower bridge arm power semiconductor switching device of the MMC sub-module reaches the MOV action value, the overvoltage peak value is suppressed to the MOV residual voltage value, the MOV residual voltage value is higher than the voltage of the capacitor of the MMC sub-module at the moment, the current flowing through the series gap zinc oxide arrester rapidly crosses zero, the self insulation strength recovers, and then the voltages of the switching device and the MOV rapidly drop to the capacitor voltage. In the process, energy is consumed in the breakdown process of the protection gap, and the capacitance voltage of the MMC sub-module is effectively reduced.
At the time of T4, the voltage at the two ends of the lower bridge arm power semiconductor switching device, the voltage at the two ends of the MOV and the voltage of the MMC sub-module capacitor are all equal.
And in the period from T4 to T5, the lower bridge arm power semiconductor switching device of the MMC sub-module keeps an off state, and the voltage of the lower bridge arm power semiconductor switching device is equal to the voltage of the capacitor of the MMC sub-module. At the moment, the time constant in the circuit topology loop is large, and the switching frequency of the power semiconductor switching device in the MMC sub-module is high, so that the voltage at two ends of the protection gap is not suddenly changed under the action of the parasitic capacitance of the protection gap.
And after the T5 moment, the MMC sub-module continues switching according to the valve control instruction. If the overvoltage generated when the power semiconductor switching device is turned off is enough to break down the protection gap, the process from T0 to T5 is repeated; if the capacitance voltage of the MMC sub-module is reduced to a desired value, the action process of the time period from T0 to T5 is not repeated.
According to the characteristic phenomenon that the voltage of a direct current line is improved in a short time when a low-voltage fault occurs on the receiving end alternating current side of the offshore wind power VSC-HVDC system, the MMC sub-module structure integrating the series gap zinc oxide arrester is skillfully adopted, when the low-voltage fault occurs, the short-time rise of the voltage of the direct current line can be restrained under the condition that an MMC basic control strategy and an MMC sub-module switching strategy are not changed, and a direct current energy consumption device does not need to be additionally arranged. Compared with the similar existing scheme, the scheme of the patent has the advantages of lower cost, higher integration degree and higher utilization rate of the power semiconductor switch device.
The technical scheme provided by the invention ingeniously utilizes the characteristic phenomenon that the voltage of the direct-current line is improved in a short time when the low-voltage fault occurs on the receiving end alternating-current side of the offshore wind power VSC-HVDC system, adopts the mode of the cooperation action of the protection gap and the MOV to inhibit the voltage rise of the direct-current line, and compared with the traditional scheme of realizing low-voltage fault ride-through by adopting a direct-current energy consumption device, the invention does not need to use an energy consumption resistor, eliminates a wall bushing, avoids the heat dissipation problem of the energy consumption resistor and the insulation problem of the bushing, saves the floor area, reduces the construction difficulty and improves the technical economy.
The technical scheme provided by the invention ingeniously utilizes the characteristic phenomenon that the voltage of the direct-current line is improved in a short time when the low-voltage fault occurs on the receiving end alternating-current side of the offshore wind power VSC-HVDC system, adopts the mode of the cooperation action of the protection gap and the MOV to inhibit the voltage rise of the direct-current line, and compared with the traditional scheme of realizing low-voltage fault ride-through by adopting a direct-current energy consumption device, the invention does not need to use an energy consumption resistor, eliminates a wall bushing, avoids the heat dissipation problem of the energy consumption resistor and the insulation problem of the bushing, saves the floor area, reduces the construction difficulty and improves the technical economy.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, but that various changes and modifications may be made without departing from the spirit and scope of the invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (8)
1. The circuit topology structure of the MMC submodule of the integrated series gap zinc oxide arrester comprises a power semiconductor switch device, an anti-parallel diode, a protection gap, an MOV and a voltage-sharing resistor; it is characterized in that:
the input end of the MMC sub-module is connected with the collector of the power semiconductor switching device, and the output end of the MMC sub-module is connected with the emitter of the power semiconductor switching device;
the anode of the anti-parallel diode is connected with the emitter of the power semiconductor switching device, and the cathode of the anti-parallel diode is connected with the collector of the power semiconductor switching device;
the protection gap is connected with the MOV in series and then connected with the power semiconductor switching device in parallel;
the voltage equalizing resistor is connected in parallel with the protection gap and the MOV respectively.
2. The circuit topology of the MMC submodule of an integrated series gap zinc oxide arrester of claim 1, characterized by: the MMC submodule is a half-bridge MMC submodule, and a specific topological structure is as follows: the anode of the anti-parallel diode 3 is connected with the emitter of the power semiconductor switching device 1, and the cathode of the anti-parallel diode 3 is connected with the collector of the power semiconductor switching device 1; the anode of the anti-parallel diode 4 is connected with the emitter of the power semiconductor switching device 2, and the cathode of the anti-parallel diode 4 is connected with the collector of the power semiconductor switching device 2; the positive electrode of the capacitor 17 is connected with the collector of the power semiconductor switch tube 1, and the negative electrode of the capacitor 17 is connected with the emitter of the power semiconductor switch tube 2; the positive connection of the half-bridge type MMC sub-module is led out from the node of the emitting electrode of the power semiconductor switch device 1 and the collecting electrode of the power semiconductor switch device 2, and the negative connection of the half-bridge type MMC sub-module is led out from the node of the emitting electrode of the power semiconductor switch device 2.
3. The circuit topology of the MMC submodule of an integrated series gap zinc oxide arrester of claim 2, characterized by: connecting a protection gap 5 and an MOV7 in series, connecting a protection gap 6 and an MOV8 in series, connecting the protection gap 5 and a voltage-sharing resistor 13 in parallel, connecting the protection gap 6 and a voltage-sharing resistor 14 in parallel, connecting an MOV7 and a voltage-sharing resistor 15 in parallel, and connecting an MOV8 and a voltage-sharing resistor 16 in parallel to form two port elements; the terminal of the port element formed by connecting the protection gap 5 and the voltage-equalizing resistor 13 is connected to the collector of the power semiconductor switching device 1, and the terminal of the port element formed by connecting the MOV7 and the voltage-equalizing resistor 15 is connected to the emitter of the power semiconductor switching device 1; the terminal of the port element formed by connecting the guard gap 6 and the voltage equalizing resistor 14 is connected to the collector of the power semiconductor switching device 2, and the terminal of the port element formed by connecting the MOV8 and the voltage equalizing resistor 16 is connected to the emitter of the power semiconductor switching device 2.
4. The circuit topology of the MMC submodule of an integrated series gap zinc oxide arrester of claim 1, characterized by: the power semiconductor switch device is an IGBT, an IGCT or an IEGT.
5. A fault ride-through method comprising the circuit topology of the MMC submodule of the integrated series gap zinc oxide arrester of claim 1, characterized by comprising the steps of:
the method comprises the following steps: when the offshore wind power VSC-HVDC system normally operates, the bus voltage of the direct current system is kept within a rated range, the MMC converter operates according to a basic control strategy, and the MMC sub-module does not cause breakdown of a protection gap due to overvoltage caused by turn-off of a power semiconductor device in the normal switching process, and is in a normal working state;
step two: after a low-voltage fault occurs on the alternating current side of the receiving end of the offshore wind power VSC-HVDC system, surplus power occurs in the system, the voltage of a direct current line exceeds a rated range, the voltage of a capacitor of an MMC sub-module rises, in the switching process of the MMC sub-module, switching-off peak overvoltage can be caused at two ends of a power semiconductor switching device when the power semiconductor switching device is switched off, a protection gap is further punctured, then MOV acts and limits the overvoltage at two ends of the power semiconductor switching device, in the process, the capacitance voltage of the MMC sub-module can be effectively reduced, and the voltage rise of the direct current line can be restrained;
step three: if the low-voltage fault time of the receiving end of the offshore wind power VSC-HVDC system is larger than the specified low-voltage ride-through time, the fans of the source side which are operated in a grid-connected mode are allowed to be cut off, and then sub-modules of the sending end MMC current converter are all locked.
6. The fault ride-through method of claim 5, wherein: the first step further comprises the following steps:
when the offshore wind power VSC-HVDC system normally operates, the MMC sub-module is normally switched according to a basic valve control instruction all the time, and a protection gap and an MOV integrated in the MMC sub-module do not act.
7. The fault ride-through method of claim 5, wherein: the second step further comprises:
at the time of T0, a low-voltage fault occurs on the receiving end alternating current side of the offshore wind power VSC-HVDC system;
in the period from T0 to T1, the lower bridge arm power semiconductor switching device of the MMC sub-module is just in a turn-off state at the moment; after a low-voltage fault occurs on the alternating current side of the receiving end of the offshore wind power VSC-HVDC system, the energy consumed by the MMC of the receiving end is reduced, so that the power consumption capacity of the alternating current power grid of the receiving end is reduced, but the working state of the wind power set connected with the MMC of the sending end cannot be changed due to the fact that the wind power set cannot synchronously receive the voltage, frequency and waveform parameters of the alternating current power grid connected with the MMC of the receiving end, surplus power enters an MMC transverter and charges a capacitor of the MMC submodule, and further the capacitance voltage is improved in a short time;
at the time of T1, according to the basic valve control instruction, the upper bridge arm power semiconductor switching device of the MMC sub-module is turned off, and the lower bridge arm power semiconductor switching device of the MMC sub-module is turned on;
in the period from T1 to T2, as the lower bridge arm power semiconductor switching device is conducted, a short-circuit charging and discharging loop is formed by the lower bridge arm power semiconductor switching device and the protection gap parasitic capacitor and the MOV parasitic capacitor; because a pure capacitance loop is formed before and after the circuit is switched, capacitance voltage jumps, and charges on all capacitor plates on a node which is not connected with a voltage source are instantly conserved at the circuit switching moment, so that the conditions of a protection gap and MOV voltage division in the stage are calculated, and the capacitance voltage of the MMC sub-module is continuously increased in the stage;
at the time of T2, according to a basic valve control instruction, an upper bridge arm power semiconductor switching device of the MMC sub-module is switched on, and a lower bridge arm power semiconductor switching device of the MMC sub-module is switched off;
in the time period from T2 to T3, when the power semiconductor switching device is turned off, the current flowing through the device suddenly changes in a very short time, and a turn-off peak overvoltage is formed under the action of stray inductance inside the device, and the formula of the turn-off peak overvoltage is as follows:
in the formula: vpeakFor turn-off peak overvoltage across the device, L0Is the stray inductance inside the device, i is the current flowing through the device; at the lower bridge armIn the turn-off process of the power semiconductor switch device, the voltage at the two ends of the power semiconductor switch device gradually rises, and the voltage at the two ends of the power semiconductor switch device is redistributed in a protection gap and an MOV according to a circuit topological structure, an electromagnetic transient process and kirchhoff law;
at the time of T3, the voltage at the two ends of the protection gap reaches the breakdown value, and the protection gap is broken down and converted into a conduction state;
in the period from T3 to T4, when the overvoltage generated by the turn-off of a lower bridge arm power semiconductor switching device of an MMC sub-module reaches an MOV action value, the peak value of the overvoltage is suppressed to be an MOV residual voltage value, because the MOV residual voltage value is higher than the voltage of a capacitor of the MMC sub-module at the moment, the current flowing through a series gap zinc oxide arrester quickly crosses zero, the self insulation strength is recovered, and then the voltages of the switching device and the MOV are quickly reduced to the capacitor voltage; in the process, as the breakdown process of the protection gap consumes energy, the capacitance voltage of the MMC sub-module is effectively reduced;
at the time of T4, the voltage at two ends of the lower bridge arm power semiconductor switching device, the voltage at two ends of the MOV and the voltage of the MMC sub-module capacitor are equal;
in the time period from T4 to T5, the lower bridge arm power semiconductor switching device of the MMC sub-module keeps an off state, and the voltage of the lower bridge arm power semiconductor switching device is equal to the voltage of a capacitor of the MMC sub-module; because the time constant tau in the circuit topological structure at this moment is larger, and the switching frequency of the power semiconductor switching element in the MMC sub-module is higher, the voltage at the two ends of the protection gap is not suddenly changed under the action of the parasitic capacitance of the protection gap;
after the time T5, the MMC sub-module continues switching according to the valve control instruction; if the overvoltage generated when the power semiconductor switching device is turned off is enough to break down the protection gap, the process from T0 to T5 is repeated; if the capacitance voltage of the MMC sub-module is reduced to a desired value, the action process of the time period from T0 to T5 is not repeated.
8. Use of the fault ride-through method according to any of the claims 5-7 in an offshore wind power flexible dc system.
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