CN114374214A - Transient voltage control method and device for extra-high voltage hybrid direct current transmission system - Google Patents

Transient voltage control method and device for extra-high voltage hybrid direct current transmission system Download PDF

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CN114374214A
CN114374214A CN202011104166.XA CN202011104166A CN114374214A CN 114374214 A CN114374214 A CN 114374214A CN 202011104166 A CN202011104166 A CN 202011104166A CN 114374214 A CN114374214 A CN 114374214A
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voltage
lcc
vsc
direct current
dclcc
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CN114374214B (en
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彭忠
曹森
李泰�
赵静
荆雪记
胡永昌
苏进国
李艳梅
张艳浩
肖龙
申帅华
鲁庆华
孙攀磊
程晓磊
李玉龙
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Xuji Group Co Ltd
XJ Electric Co Ltd
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Xuji Group Co Ltd
XJ Electric Co Ltd
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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
    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • 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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  • Power Engineering (AREA)
  • Inverter Devices (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

A transient voltage control method and a device for an extra-high voltage hybrid direct current power transmission system are disclosed, wherein the method comprises the following steps: LCC direct current voltage reference value U for outputting superior controldcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting a final LCC direct current voltage reference value; actual value U of DC voltagedcLCCInputting the difference with the final LCC direct current voltage reference value into a PI controller for regulation, and outputting a trigger angle cosine value; and outputting the trigger angle of the inverter station through inverse cosine calculation. According to the method, after the alternating current system fault is cleared, the LCC transient voltage controller properly reduces the voltage reference value according to the VSC overvoltage condition and the direct current line voltage drop, so that the LCC of the inverter station runs at low voltage in the system recovery process, and the system pole bus overvoltage is limited.

Description

Transient voltage control method and device for extra-high voltage hybrid direct current transmission system
Technical Field
The invention relates to the technical field of extra-high voltage direct current transmission, in particular to a transient voltage control method and device for an extra-high voltage hybrid direct current transmission system.
Background
A conventional extra-high voltage direct current transmission system uses a power grid commutation type converter LCC, and the defect that the transmission power of the system is interrupted due to the fact that the commutation of an inverter side fails exists. For an extra-high voltage hybrid direct current transmission system, an inverter station generally uses a voltage source type converter (VSC) or a combined topology of a low-voltage capacitor (LCC) and the VSC. The voltage source type converter has the advantages of no commutation failure, independent control of active power and reactive power, no need of configuring an alternating current filter and the like. The inverter station LCC and VSC hybrid cascade topological structure can prevent the system power interruption caused by commutation failure and suppression commutation failure to a certain extent, but in the fault process of an inverter side alternating current system, the power surplus of a VSC direct current side causes overvoltage of VSC, and overvoltage occurs to a pole bus in the system recovery process. How to limit the overvoltage of the pole bus in the fault recovery process of the inverter side alternating current system becomes a difficult problem.
The existing inversion side pole control system is provided with an LCC (capacitor control circuit) direct-current voltage controller and a VSC (voltage source converter) direct-current voltage controller, and under the steady-state working condition, the voltage of a pole bus of a rectification station is controlled together. For the inverter station LCC and VSC hybrid cascade topology structure, the LCC and the VSC operate in voltage balance, and therefore the LCC is equal to the VSC direct-current voltage reference value. Under the fault working condition, the LCC and VSC direct-current voltage reference values are basically maintained at the level before the fault.
For the mixed topological structure that cascades of LCC and VSC to the contravariant station, when contravariant side AC system trouble, VSC output active power is restricted, and VSC direct current side power surplus leads to VSC direct current voltage to rise. In the contravariant side alternating current system fault process, LCC is the commutation failure very likely, and direct current increases, and VSC direct current side power surplus is more, has increased VSC direct current overvoltage, probably reaches 1.3 times overvoltage (typical benchmark is 400kV), and is even higher. When the fault is cleared, the conventional LCC fixed dc voltage control method rapidly controls the LCC dc voltage to 400kV (typical value), resulting in an overvoltage of 1.15 times (reference value 800kV, typical value) in the pole bus voltage. In the process of quickly increasing the power of the system, the voltage of a pole bus of the rectifier station can reach 1.25 times (the reference value is 800kV and is a typical value) or even higher due to the inductive reactance of a line, and the insulation safety of equipment is damaged.
Disclosure of Invention
The invention aims to provide a transient voltage control method and device for an extra-high voltage hybrid direct current transmission system, aiming at the defects of the prior art, and the transient voltage control method and device can reduce the LCC direct current voltage reference value of an inverter station according to the overvoltage condition of a VSC and the voltage drop of a direct current line in the process that the fault of an alternating current system at the inverter side is cleared and the power of the system is rapidly recovered, so that the overvoltage of a pole bus of the system is limited.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a transient voltage control method for an extra-high voltage hybrid direct current transmission system, the extra-high voltage hybrid direct current transmission system comprises a rectification station and an inversion station, the inversion station comprises a power grid commutation converter (LCC) of a high-end valve group and a Voltage Source Converter (VSC) of a low-end valve group, and the transient voltage control method controls the direct current voltage of the LCC of the inversion station and comprises the following steps:
LCC direct current voltage reference value U for outputting superior controldcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting a final LCC direct current voltage reference value;
actual value U of DC voltagedcLCCInputting the difference with the final LCC direct current voltage reference value into a PI controller for regulation, and outputting a trigger angle cosine value;
and outputting the trigger angle of the inverter station through inverse cosine calculation.
Further, the LCC direct current voltage reference value U which is output by the upper controldcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting the final LCC dc voltage reference comprises:
collecting the AC bus voltage of the converter operated by the inverter station in real time, and calculating to obtain the minimum value U of the positive sequence component of the AC bus voltageacposmin(ii) a Passing and voltage threshold Uset1Comparing, and judging whether the alternating current system fault occurs:
if U is presentacposmin＜Uset1If the voltage regulation quantity is larger than the preset value, indicating that the alternating current system is in fault and detecting that the LCC has failed in phase commutation, outputting a voltage regulation quantity delta U by the transient voltage controllerdcLCC＝0；
If U is presentacposmin＞Uset1If the voltage is larger than the set value, the transient voltage controller outputs a voltage regulation delta U according to the VSC overvoltage condition when the alternating current system fault is cleared or the LCC phase commutation failure is not detecteddcLCC。
Further, the transient voltage controller outputs a voltage regulation delta U according to the VSC overvoltage conditiondcLCCThe method comprises the following steps:
when the inverter side alternating current system has ground fault, the VSC direct current voltage UdcVSC(ii) is increased;
when the AC system fault is cleared or the LCC phase change is normal, if U is normaldcVSCGreater than the VSC DC voltage reference value UdcrefVSCAnd VSC overvoltage dead zone value UdeadbandSum, then Δ UdcLCCIs a VSC voltage deviation component and an additional voltage limiting component UexcSum, Δ UdcLCC< 0 where the VSC voltage deviation component is in UminTo the interval 0, UminIs the VSC overvoltage minimum amplitude limit value;
when U is turnedacposmin＜Uset1And when LCC commutation fails, the additional voltage limiting component UexcSmoothly change from 0 to Uc1，Uc1For limiting the voltage parameter, Uc1＜0；
When the AC system fault is cleared or LCC phase change is normal, after a period of time delay, UexcBy Uc1Smoothly changes to 0.
Further, the PI controller regulates the output trigger angle cosine value to be limited to cos alphaminAnd cos alphamaxWhen cos α > cos αmaxWhen the output is cos alphamax(ii) a When cos alpha is less than cos alphaminWhen the output is cos alphamin(ii) a When cos alphamin≤cosα≤cosαmaxThen, the output is cos α; wherein alpha is a trigger angle, cos alphamaxIs the maximum value of the cosine of the flip angle, cos αminIs the cosine minimum of the flip angle.
A second aspect of the present invention provides a transient voltage control apparatus for an ultra-high voltage hybrid dc power transmission system, where the ultra-high voltage hybrid dc power transmission system includes a rectification station and an inversion station, the inversion station includes a grid commutation converter LCC of a high-end valve set and a voltage source converter VSC of a low-end valve set, and the transient voltage control apparatus includes:
a transient voltage controller: LCC direct current voltage reference value U for outputting superior controldcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting a final LCC direct current voltage reference value;
a difference calculator: the actual value U of the direct current voltage is measureddcLCCPerforming difference calculation with the final LCC direct current voltage reference value;
a PI controller: inputting the result of the difference calculation into a PI controller for regulation, and outputting a trigger angle cosine value;
an inverse cosine calculator: and (4) performing inverse cosine calculation on the cosine value of the output trigger angle, and outputting the trigger angle of the inverter station.
Further, the transient voltage controller performs the following control to obtain the output voltage adjustment amount Δ UdcLCC：
Collecting the AC bus voltage of the converter operated by the inverter station in real time, and calculating to obtain the minimum value U of the positive sequence component of the AC bus voltageacposmin(ii) a Passing and voltage threshold Uset1Comparing, and judging whether the alternating current system fault occurs:
if U is presentacposmin＜Uset1If the voltage regulation quantity is larger than the preset value, indicating that the alternating current system is in fault and detecting that the LCC has failed in phase commutation, outputting a voltage regulation quantity delta U by the transient voltage controllerdcLCC＝0；
If U is presentacposmin＞Uset1If the voltage is larger than the set value, the transient voltage controller outputs a voltage regulation delta U according to the VSC overvoltage condition when the alternating current system fault is cleared or the LCC phase commutation failure is not detecteddcLCC。
Further, the transient voltage controller outputs a voltage regulation delta U according to the VSC overvoltage conditiondcLCCThe method comprises the following steps:
when the inverter side alternating current system has ground fault, the VSC direct current voltage UdcVSC(ii) is increased;
when the AC system fault is cleared or the LCC phase change is normal, if U is normaldcVSCGreater than the VSC DC voltage reference value UdcrefVSCAnd VSC overvoltage dead zone value UdeadbandSum, then Δ UdcLCCIs a VSC voltage deviation component and an additional voltage limiting component UexcSum, Δ UdcLCC< 0 where the VSC voltage deviation component is in UminTo the interval 0, UminIs the VSC overvoltage minimum amplitude limit value;
when U is turnedacposmin＜Uset1And when LCC commutation fails, the additional voltage limiting component UexcSmoothly change from 0 to Uc1，Uc1For limiting the voltage parameter, Uc1＜0；
When the AC system fault is cleared or LCC phase change is normal, after a period of time delay, UexcBy Uc1Smoothly changes to 0.
Further, the PI controller limits the output firing angle cosine value to cos alphaminAnd cos alphamaxWhen cos α > cos αmaxWhen the output is cos alphamax(ii) a When cos alpha is less than cos alphaminWhen the output is cos alphamin(ii) a When cos alphamin≤cosα≤cosαmaxThen, the output is cos α; wherein alpha is a trigger angle, cos alphamaxIs the maximum value of the cosine of the flip angle, cos αminIs the cosine minimum of the flip angle.
In summary, the present invention provides a method and an apparatus for controlling transient voltage of an ultra-high voltage hybrid dc power transmission system, the method includes: LCC direct current voltage reference value U for outputting superior controldcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting a final LCC direct current voltage reference value; actual value U of DC voltagedcLCCInputting the difference with the final LCC direct current voltage reference value into a PI controller for regulation, and outputting a trigger angle cosine value; and outputting the trigger angle of the inverter station through inverse cosine calculation. According to the method, after the alternating current system fault is cleared, the LCC transient voltage controller properly reduces the voltage reference value according to the VSC overvoltage condition and the direct current line voltage drop, so that the LCC of the inverter station runs at low voltage in the system recovery process, and the system pole bus overvoltage is limited.
Drawings
FIG. 1 is a schematic topological diagram of an ultra-high voltage hybrid direct current transmission system according to an embodiment of the invention;
fig. 2 is a schematic flow chart of a transient voltage control method of an ultra-high voltage hybrid direct current transmission system according to an embodiment of the invention;
fig. 3 is a block diagram of an LCC voltage controller of an inversion station of an ultra-high voltage hybrid direct current transmission system according to an embodiment of the invention;
fig. 4 is a block diagram of transient voltage control of the ultra-high voltage hybrid dc power transmission system according to an embodiment of the present invention.
Reference numerals: LCC is a power grid commutation converter; VSC is a voltage source type converter; ACF is an AC filter; DCF is a DC filter; u shapedcrefLCC direct current voltage reference value calculated by the upper control function;
UdcLCCdirect current voltage of LCC; u shapedcVSCrefA DC voltage reference value of the VSC; u shapedcVSCThe DC voltage of the VSC; u shapeacposminThe minimum value of the positive sequence voltage of each converter AC bus of the inverter station; delta UdcLCCVoltage regulating quantity output by the transient voltage controller; cos alphamaxThe maximum value of the cosine of the trigger angle; cos alphaminTriggering the minimum value of the angle cosine; u shapedcVSCrefA DC voltage reference value of the VSC; u shapedcVSCThe DC voltage of the VSC; u shapedeadbandVSC overvoltage dead zone value; u shapeminVSC overvoltage minimum amplitude limiting value; u shapeset1Exchange the system failure decision threshold value; u shapeexcAn additional voltage limiting component; u shapec1A voltage limiting parameter; delta UdcLCCThe voltage regulating quantity output by the transient voltage controller.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
Fig. 1 is a topological structure diagram of an extra-high voltage hybrid direct-current transmission system provided by the invention. The rectifying station (sending end) of the extra-high voltage hybrid direct-current transmission system is the same as the conventional extra-high voltage, and comprises a power grid commutation converter (LCC), a direct-current filter (DCF) is connected in parallel with an LCC valve bank, and an alternating-current filter (ACF) which is grounded is arranged at the alternating-current input end. The high-end valve bank of the inversion station (receiving end) is a power grid phase-change type current converter (LCC), the LCC valve bank is connected with a Direct Current Filter (DCF) in parallel, and the alternating current output end is provided with an Alternating Current Filter (ACF) which is grounded; the low end valves are three voltage source type converters VSC (VSC 1, VSC2 and VSC3) connected in parallel, and controllable arresters are connected in parallel on the direct current side of the VSC valves.
The invention provides a transient voltage control method for an extra-high voltage hybrid direct current transmission system, the extra-high voltage hybrid direct current transmission system comprises a rectification station and an inversion station, the inversion station comprises a power grid commutation converter (LCC) of a high-end valve group and a Voltage Source Converter (VSC) of a low-end valve group, the transient voltage control method controls the direct current voltage of the LCC of the inversion station, and as shown in figure 2, the transient voltage control method comprises the following steps:
step S100, outputting LCC direct current voltage reference value U of superior control outputdcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting a final LCC direct current voltage reference value;
step S200, the actual value U of the direct current voltagedcLCCInputting the difference with the final LCC direct current voltage reference value into a PI controller for regulation, and outputting a trigger angle cosine value;
and step S300, outputting the trigger angle of the inversion station through inverse cosine calculation.
Specifically, as shown in fig. 3, fig. 3 is a direct-current voltage control block diagram of an inversion station LCC of the extra-high voltage hybrid direct-current transmission system provided by the invention. LCC direct current voltage reference value U calculated by upper control functiondcrefVoltage regulation delta U calculated by superimposed transient voltage controllerdcrefLCCAnd obtaining a final LCC direct current voltage reference value. And after the difference is made between the actual value of the direct current voltage of the LCC and the reference value, the trigger angle is output through the adjustment of a PI controller and the calculation of the inverse cosine. Compared with the conventional ultrahigh voltage control, the invention adds the transient voltage controller, and after the fault is cleared, the LCC direct current voltage reference value is reduced according to the VSC overvoltage condition and the direct current line voltage drop, so that the overvoltage impact of the pole bus in the system recovery process is limited.
Further, the LCC direct current voltage reference value U which is output by the upper controldcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCAnd outputs the final LCC direct currentThe reference values include:
collecting the AC bus voltage of the converter operated by the inverter station in real time, and calculating to obtain the minimum value U of the positive sequence component of the AC bus voltageacposmin(ii) a Passing and voltage threshold Uset1Comparing, and judging whether the alternating current system fault occurs:
if U is presentacposmin＜Uset1If the voltage regulation quantity is larger than the preset value, indicating that the alternating current system is in fault and detecting that the LCC has failed in phase commutation, outputting a voltage regulation quantity delta U by the transient voltage controllerdcLCC＝0；
If U is presentacposmin＞Uset1If the voltage is larger than the set value, the transient voltage controller outputs a voltage regulation delta U according to the VSC overvoltage condition when the alternating current system fault is cleared or the LCC phase commutation failure is not detecteddcLCC。
Further, the transient voltage controller outputs a voltage regulation delta U according to the VSC overvoltage conditiondcLCCThe method comprises the following steps:
when the inverter side alternating current system has ground fault, the VSC direct current voltage UdcVSC(ii) is increased;
when the AC system fault is cleared or the LCC phase change is normal, if U is normaldcVSCGreater than the VSC DC voltage reference value UdcrefVSCAnd VSC overvoltage dead zone value UdeadbandSum, then Δ UdcLCCIs a VSC voltage deviation component and an additional voltage limiting component UexcSum, Δ UdcLCC< 0 where the VSC voltage deviation component is in UminTo the interval 0, UminIs the VSC overvoltage minimum amplitude limit value;
when U is turnedacposmin＜Uset1And when LCC commutation fails, the additional voltage limiting component UexcSmoothly change from 0 to Uc1，Uc1For limiting the voltage parameter, Uc1＜0；
When the AC system fault is cleared or LCC phase change is normal, after a period of time delay, UexcBy Uc1Smoothly changes to 0.
Specifically, as shown in fig. 4, fig. 4 is a block diagram of a transient voltage controller of the ultra-high voltage hybrid direct current transmission system provided by the present invention. Inversion station control system acquisition and commissioning switchCalculating the AC bus voltage of the current transformer to obtain the minimum value U of the positive sequence component of the AC bus voltageacposmin. Passing and voltage threshold Uset1And comparing to judge whether the AC system fault occurs. If U is presentacposmin<Uset1Indicating AC system fault, detecting LCC phase change failure, and outputting voltage regulation delta U by transient voltage controllerdcLCCEqual to 0. If U is presentacposmin>Uset1Indicating that the AC system fault is cleared or the LCC commutation failure is not detected, the transient voltage controller outputs a voltage regulation delta U according to the VSC overvoltage conditiondcLCC. When the inverter side alternating current system has ground fault, the VSC direct current voltage UdcVSCAnd (4) rising. If the U is in normal phase change after the AC system fault is cleared or the LCC is in normal phase changedcVSCGreater than the VSC DC voltage reference value UdcrefVSCWith overvoltage dead band value UdeadbandSum, Δ UdcLCCWill contain a VSC voltage deviation component (at U)minTo the interval 0) and an additional voltage limiting component Uexc，ΔUdcLCC<0. When U is turnedacposmin<Uset1And when LCC commutation fails, the additional voltage limiting component UexcSmoothly change from 0 to Uc1(Uc1<0). When the AC system fault is cleared or LCC phase change is normal, after a period of time delay, UexcBy Uc1Smoothly changes to 0. U shapeexcThe method is used for limiting overvoltage of a pole bus of the rectifier station caused by line inductive reactance in the quick recovery process of the system. After the alternating current system fault is cleared, the LCC transient voltage controller properly reduces the voltage reference value, so that in the system recovery process, the LCC of the inverter station runs at low voltage, and the overvoltage of a system pole bus is limited.
Further, the PI controller regulates the output trigger angle cosine value to be limited to cos alphaminAnd cos alphamaxWhen cos α > cos αmaxWhen the output is cos alphamax(ii) a When cos alpha is less than cos alphaminWhen the output is cos alphamin(ii) a When cos alphamin≤cosα≤cosαmaxThen, the output is cos α; wherein alpha is a trigger angle, cos alphamaxIs the maximum value of the cosine of the flip angle, cos αminIs touched byThe cosine minimum of the angle.
A second aspect of the present invention provides a transient voltage control apparatus for an ultra-high voltage hybrid dc power transmission system, where the ultra-high voltage hybrid dc power transmission system includes a rectification station and an inversion station, the inversion station includes a grid commutation converter LCC of a high-end valve set and a voltage source converter VSC of a low-end valve set, and the transient voltage control apparatus includes:
a transient voltage controller: LCC direct current voltage reference value U for outputting superior controldcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting a final LCC direct current voltage reference value;
a difference calculator: the actual value U of the direct current voltage is measureddcLCCPerforming difference calculation with the final LCC direct current voltage reference value;
a PI controller: inputting the result of the difference calculation into a PI controller for regulation, and outputting a trigger angle cosine value;
an inverse cosine calculator: and (4) performing inverse cosine calculation on the cosine value of the output trigger angle, and outputting the trigger angle of the inverter station.
In summary, the present invention provides a method and an apparatus for controlling transient voltage of an ultra-high voltage hybrid dc power transmission system, the method includes: LCC direct current voltage reference value U for outputting superior controldcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting a final LCC direct current voltage reference value; actual value U of DC voltagedcLCCInputting the difference with the final LCC direct current voltage reference value into a PI controller for regulation, and outputting a trigger angle cosine value; and outputting the trigger angle of the inverter station through inverse cosine calculation. According to the method, after the alternating current system fault is cleared, the LCC transient voltage controller properly reduces the voltage reference value according to the VSC overvoltage condition and the direct current line voltage drop, so that the LCC of the inverter station runs at low voltage in the system recovery process, and the system pole bus overvoltage is limited.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.

Claims (8)

1. A transient voltage control method for an extra-high voltage hybrid direct current transmission system comprises a rectification station and an inversion station, wherein the inversion station comprises a power grid commutation converter (LCC) of a high-end valve group and a Voltage Source Converter (VSC) of a low-end valve group, and the transient voltage control method controls the direct current voltage of the LCC of the inversion station, and is characterized by comprising the following steps:
LCC direct current voltage reference value U for outputting superior controldcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting a final LCC direct current voltage reference value;
actual value U of DC voltagedcLCCInputting the difference with the final LCC direct current voltage reference value into a PI controller for regulation, and outputting a trigger angle cosine value;
and outputting the trigger angle of the inverter station through inverse cosine calculation.
2. The method according to claim 1, wherein the LCC dc voltage reference U is a reference value of the LCC dc voltage output by the superordinate controllerdcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting the final LCC dc voltage reference comprises:
collecting the AC bus voltage of the converter operated by the inverter station in real time, and calculating to obtain the minimum value U of the positive sequence component of the AC bus voltageacposmin(ii) a Passing and voltage threshold Uset1Comparing, and judging whether the alternating current system fault occurs:
if U is presentacposmin＜Uset1If the voltage regulation quantity is larger than the preset value, indicating that the alternating current system is in fault and detecting that the LCC has failed in phase commutation, outputting a voltage regulation quantity delta U by the transient voltage controllerdcLCC＝0；
If U is presentacposmin＞Uset1If the voltage is larger than the set value, the transient voltage controller outputs a voltage regulation delta U according to the VSC overvoltage condition when the alternating current system fault is cleared or the LCC phase commutation failure is not detecteddcLCC。
3. The method of claim 2, wherein the transient voltage controller outputs the voltage adjustment Δ U based on the VSC overvoltage conditiondcLCCThe method comprises the following steps:
when the inverter side alternating current system has ground fault, the VSC direct current voltage UdcVSC(ii) is increased;
when the AC system fault is cleared or the LCC phase change is normal, if U is normaldcVSCGreater than the VSC DC voltage reference value UdcrefVSCAnd VSC overvoltage dead zone value UdeadbandSum, then Δ UdcLCCIs a VSC voltage deviation component and an additional voltage limiting component UexcSum, Δ UdcLCC< 0 where the VSC voltage deviation component is in UminTo the interval 0, UminIs the VSC overvoltage minimum amplitude limit value;
when U is turnedacposmin＜Uset1And when LCC commutation fails, the additional voltage limiting component UexcSmoothly change from 0 to Uc1，Uc1For limiting the voltage parameter, Uc1＜0；
When the AC system fault is cleared or LCC phase change is normal, after a period of time delay, UexcBy Uc1Smoothly changes to 0.
4. The method of claim 1, wherein the PI controller regulates the voltage of the power transmission system by limiting a triggering angle cosine value of the output to cos αminAnd cos alphamaxWhen cos α > cos αmaxWhen the output is cos alphamax(ii) a When cos alpha is less than cos alphaminWhen the output is cos alphamin(ii) a When cos alphamin≤cosα≤cosαmaxThen, the output is cos α; wherein alpha isFlip angle, cos αmaxIs the maximum value of the cosine of the flip angle, cos αminIs the cosine minimum of the flip angle.
5. The utility model provides an extra-high voltage mixes direct current transmission system transient state voltage control device, extra-high voltage mixes direct current transmission system includes rectifier station and contravariant station, and the contravariant station includes the voltage source type transverter VSC of the electric wire netting commutation transverter LCC of high-end valves and low-end valves, its characterized in that includes:
a transient voltage controller: LCC direct current voltage reference value U for outputting superior controldcrefSuperimposing the voltage adjustment Δ U processed by the transient voltage controllerdcLCCOutputting a final LCC direct current voltage reference value;
a difference calculator: the actual value U of the direct current voltage is measureddcLCCPerforming difference calculation with the final LCC direct current voltage reference value;
a PI controller: inputting the result of the difference calculation into a PI controller for regulation, and outputting a trigger angle cosine value;
an inverse cosine calculator: and (4) performing inverse cosine calculation on the cosine value of the output trigger angle, and outputting the trigger angle of the inverter station.
6. The EHV-HVDC system transient voltage control device of claim 5, wherein the transient voltage controller is configured to control the output voltage adjustment Δ U to obtain the output voltage adjustment Δ UdcLCC：
Collecting the AC bus voltage of the converter operated by the inverter station in real time, and calculating to obtain the minimum value U of the positive sequence component of the AC bus voltageacposmin(ii) a Passing and voltage threshold Uset1Comparing, and judging whether the alternating current system fault occurs:
if U is presentacposmin＜Uset1If the voltage regulation quantity is larger than the preset value, indicating that the alternating current system is in fault and detecting that the LCC has failed in phase commutation, outputting a voltage regulation quantity delta U by the transient voltage controllerdcLCC＝0；
If U is presentacposmin＞Uset1If yes, it indicates that the AC system fault is cleared or no LCC is detectedWhen the commutation fails, the transient voltage controller outputs a voltage regulation delta U according to the VSC overvoltage conditiondcLCC。
7. The EHV-HVDC system transient voltage control device of claim 6, wherein the transient voltage controller outputs the voltage adjustment Δ U in response to a VSC overvoltage conditiondcLCCThe method comprises the following steps:
when the inverter side alternating current system has ground fault, the VSC direct current voltage UdcVSC(ii) is increased;
when the AC system fault is cleared or the LCC phase change is normal, if U is normaldcVSCGreater than the VSC DC voltage reference value UdcrefVSCAnd VSC overvoltage dead zone value UdeadbandSum, then Δ UdcLCCIs a VSC voltage deviation component and an additional voltage limiting component UexcSum, Δ UdcLCC< 0 where the VSC voltage deviation component is in UminTo the interval 0, UminIs the VSC overvoltage minimum amplitude limit value;
when U is turnedacposmin＜Uset1And when LCC commutation fails, the additional voltage limiting component UexcSmoothly change from 0 to Uc1，Uc1For limiting the voltage parameter, Uc1＜0；
When the AC system fault is cleared or LCC phase change is normal, after a period of time delay, UexcBy Uc1Smoothly changes to 0.
8. The device according to claim 5, wherein the PI controller limits the cosine value of the output firing angle to cos αminAnd cos alphamaxWhen cos α > cos αmaxWhen the output is cos alphamax(ii) a When cos alpha is less than cos alphaminWhen the output is cos alphamin(ii) a When cos alphamin≤cosα≤cosαmaxThen, the output is cos α; wherein alpha is a trigger angle, cos alphamaxIs the maximum value of the cosine of the flip angle, cos αminIs the cosine minimum of the flip angle.
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