CN110289774B - High-voltage direct-current transmission converter unit and control method and control device thereof - Google Patents

High-voltage direct-current transmission converter unit and control method and control device thereof Download PDF

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Publication number
CN110289774B
CN110289774B CN201910596850.5A CN201910596850A CN110289774B CN 110289774 B CN110289774 B CN 110289774B CN 201910596850 A CN201910596850 A CN 201910596850A CN 110289774 B CN110289774 B CN 110289774B
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China
Prior art keywords
voltage
current
type valve
valve bank
source type
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CN201910596850.5A
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Chinese (zh)
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CN110289774A (en
Inventor
卢东斌
李海英
陈松林
李九虎
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NR Electric Co Ltd
NR Engineering Co Ltd
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NR Electric Co Ltd
NR Engineering Co Ltd
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Priority to CN201910596850.5A priority Critical patent/CN110289774B/en
Publication of CN110289774A publication Critical patent/CN110289774A/en
Priority to PCT/CN2020/083883 priority patent/WO2021000620A1/en
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Classifications

    • 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
    • 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
    • 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
    • H02M7/145—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 thyratron or thyristor type requiring extinguishing means
    • H02M7/155—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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only
    • H02M7/162—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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration
    • H02M7/1623—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 thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration with control circuit
    • 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
    • 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
    • H02M1/325—Means for protecting converters other than automatic disconnection with means for allowing continuous operation despite a fault, i.e. fault tolerant converters
    • 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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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Rectifiers (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a high-voltage direct-current transmission converter unit which comprises a current source type valve bank, a converter transformer without a voltage regulating function, a voltage source type valve bank and a connecting transformer, wherein the current source type valve bank is connected with an alternating current system through the converter transformer without the voltage regulating function, the voltage source type valve bank is connected with the alternating current system through the connecting transformer, and the current source type valve bank is connected with the voltage source type valve bank in series on a direct current side. The direct-current voltage is regulated by adopting the voltage source type valve bank to regulate direct-current side voltage instead of regulating a tap of the converter transformer, so that the converter unit has the function of quickly and frequently regulating the voltage, is easy to protect after the voltage source type valve bank fails, and can not influence the continuous operation of the current source type valve bank. The invention also discloses a main loop of the HVDC transmission system, a control method and a control device of the HVDC transmission converter unit.

Description

High-voltage direct-current transmission converter unit and control method and control device thereof
Technical Field
The invention belongs to the field of high-voltage direct-current transmission, and particularly relates to a high-voltage direct-current transmission converter unit for regulating direct-current voltage by adopting a voltage source type valve bank, a control method and a control device for realizing control, and a main loop structure of a high-voltage direct-current transmission system.
Background
The high-voltage direct-current transmission system generally comprises a converter unit consisting of a power grid converter and a converter transformer with a voltage regulating function, so that alternating current is converted into direct current, and long-distance transmission is performed. The rectifying side generally maintains the triggering angle of the grid converter within a reference value range, and the inverting side generally maintains the turn-off angle of the grid converter within a reference value range. The hvdc transmission system can regulate power in a large range, and in order to maintain the dc voltage on the rectifying side constant, both the rectifying side and the inverting side need a converter transformer with a voltage regulating function to regulate the ac voltage. The voltage regulating function of the converter transformer is realized by connecting different converter transformer taps through a tap changer.
The tapping switch adopts mechanical structures such as an electric mechanism, a selector switch, a change-over switch and the like, and has a certain service life; the tap switch is difficult to protect after failure, and the accident is easily expanded to a converter transformer; the tap switch adjusts voltage in a grading way, and has poor voltage adjusting precision and low adjusting speed. Along with the access of new energy sources such as photovoltaic, wind power and the like, the high-voltage direct-current transmission system needs to frequently adjust power, the fluctuation range of alternating voltage is also enlarged, frequent actions of the tapping switch can be caused, and the tapping switch is easy to damage.
In view of the above-mentioned drawbacks of tap changers and new needs for hvdc transmission, there is a need for an hvdc transmission converter unit which enables fast, frequent voltage regulation and easy protection.
Disclosure of Invention
The invention aims to provide a high-voltage direct-current transmission converter unit, which replaces the alternating-current voltage regulating function of a converter transformer with the direct-current voltage regulating function of a voltage source converter, can realize quick and accurate voltage regulation by connecting the voltage source converter in series on the direct-current side, and can quickly isolate faults by throwing a bypass circuit of the voltage source converter and tripping an alternating-current inlet switch of the voltage source converter when the voltage source converter fails, so that the damage to a grid converter and the converter transformer can be avoided.
In order to achieve the above purpose, the invention adopts the following technical scheme:
The high-voltage direct-current transmission converter unit comprises a current source type valve bank, a converter transformer without voltage regulation function, a voltage source type valve bank and a connecting transformer, wherein the current source type valve bank is connected with an alternating current system through the converter transformer without voltage regulation function, the voltage source type valve bank is connected with the alternating current system through the connecting transformer, and the current source type valve bank is connected with the voltage source type valve bank in series on the direct current side.
In the scheme, the method comprises the following steps: the converter transformer without the voltage regulating function is a converter transformer without a tap or a tapping switch, and does not have the function of regulating the transformation ratio of windings on the network side and the valve side of the converter transformer.
The connecting transformer adopts a transformer without a tap or a tap changer and does not have the function of adjusting the transformation ratio of windings at the network side and the valve side of the transformer; or the connecting transformer adopts a transformer with a tap and a tap switch, and has the function of adjusting the transformation ratio of windings at the network side and the valve side of the transformer.
And a charging resistor is further connected between the voltage source type valve bank and the connecting transformer, and the charging resistor is connected with a switch or a disconnecting link in parallel.
The current source type valve bank adopts any one of the following three schemes: firstly, a power grid commutation converter is adopted; secondly, a grid commutation converter and a bypass switch which are connected in parallel are adopted; and thirdly, the bypass switch comprises a power grid commutation converter, a bypass switch and two connecting switches, wherein the power grid commutation converter is connected with the bypass switch in parallel, two ends after being connected in parallel are respectively connected with one ends of the two connecting switches, and two ends of the bypass switch are respectively connected with the other ends of the two connecting switches.
The power grid commutation converter is a six-ripple bridge circuit, a twelve-ripple bridge circuit or a circuit formed by connecting a plurality of six-ripple bridge circuits in series, and consists of a semi-controllable power semiconductor which can not be turned off.
The non-turn-off semi-controlled power semiconductor is a thyristor.
The voltage source type valve group adopts any one of the following three schemes: first, a voltage source converter is adopted; secondly, a voltage source converter and a bypass switch which are connected in parallel are adopted; and thirdly, the bypass switch comprises a voltage source converter, a bypass switch and two connection switches, wherein the voltage source converter is connected with the bypass switch in parallel, two ends after being connected in parallel are respectively connected with one ends of the two connection switches, and two ends of the bypass switch are respectively connected with the other ends of the two connection switches.
In the three schemes, the voltage source converter is a single voltage source converter or two or more voltage source converters are connected in parallel; in the second and third schemes, the method further comprises an inductor, wherein the inductor is connected in series with the voltage source converter or connected in series with the bypass switch.
The bypass switch is a mechanical switch or a power electronic switch; the power electronic switch is a valve bank formed by serially connecting thyristors or a valve bank formed by serially connecting turnoff full-control power semiconductors.
The voltage source converter is any one or more of the following: a two-level converter, a diode clamped multilevel converter, a modular multilevel converter MMC, a hybrid multilevel converter HMC, a two-level cascade converter CSL or a stacked two-level converter CTL; the modular multilevel converter MMC is a modular multilevel converter formed by half-bridge submodules, or a modular multilevel converter formed by full-bridge submodules, or a modular multilevel converter formed by mixing half-bridge submodules and full-bridge submodules.
The voltage source converter consists of a turnoff full-control power semiconductor; the turnoff full-control power semiconductor is any one or more of the following: insulated Gate Bipolar Transistor (IGBT), integrated Gate Commutated Thyristor (IGCT), turn-off thyristor (GTO), power field effect transistor (Power MOSFET), electron Injection Enhanced Gate Transistor (IEGT), gate Commutated Thyristor (GCT) or silicon carbide enhanced junction field effect transistor (SiC-JFET).
The half-bridge submodule or the full-bridge submodule of the modular multilevel converter MMC is provided with a bypass switch or a thyristor, and the bypass switch or the thyristor is connected in parallel with two ends of the half-bridge submodule or the full-bridge submodule and used for bypassing the half-bridge submodule or the full-bridge submodule.
The half-bridge submodule of the modular multilevel converter MMC is also provided with a protection thyristor, wherein the protection thyristor is connected in parallel with two ends of the half-bridge submodule to protect a reverse diode of the turnoff full-control power semiconductor connected in parallel with the protection thyristor.
The current source type valve bank or the voltage source type valve bank is provided with a bridge arm lightning arrester, a direct current side lightning arrester and a bridge arm reactor.
The current source type valve bank is connected with the voltage source type valve bank in series on the direct current side, so that the anode of the current source type valve bank is connected with the anode of the voltage source type valve bank, or the cathode of the current source type valve bank is connected with the cathode of the voltage source type valve bank; for the inversion side, the current source type valve bank is connected with the voltage source type valve bank in series on the direct current side, so that the cathode of the current source type valve bank is connected with the anode of the voltage source type valve bank, or the anode of the current source type valve bank is connected with the cathode of the voltage source type valve bank.
The anode of the current source type valve bank is the anode of the grid converter, and the cathode of the current source type valve bank is the cathode of the grid converter; the positive electrode of the voltage source type valve bank is the positive electrode of the voltage source converter, and the negative electrode of the voltage source type valve bank is the negative electrode of the voltage source converter.
The invention also provides a main loop of the high-voltage direct-current transmission system, wherein the rectifying side of the main loop of the high-voltage direct-current transmission system at least comprises a direct-current pole formed by the high-voltage direct-current transmission converter unit, the inverting side comprises a converter unit formed by a current source valve group and a converter transformer with a voltage regulating function, or comprises a converter unit formed by a voltage source valve group and a coupling transformer, or comprises a converter unit formed by a current source valve group, a converter transformer with a voltage regulating function, a voltage source valve group and a coupling transformer, or at least comprises a corresponding direct-current pole formed by the high-voltage direct-current transmission converter unit; or the inversion side of the main loop of the HVDC transmission system at least comprises a DC pole formed by the HVDC transmission converter units, the rectification side comprises a converter unit formed by a current source valve bank and a converter transformer with a voltage regulating function, or comprises a converter unit formed by a voltage source valve bank and a coupling transformer, or comprises a converter unit formed by a current source valve bank, a converter transformer with a voltage regulating function, a voltage source valve bank and a coupling transformer, or at least comprises a corresponding DC pole formed by the HVDC transmission converter units.
The invention also provides a control method suitable for the HVDC power transmission converter unit, which is divided into two cases according to the running condition of the HVDC power transmission converter unit:
When the high-voltage direct-current power transmission converter unit performs rectifying operation, the first control method is that a reference value of a control trigger angle of the current source type valve bank is unchanged, the voltage source type valve bank regulates voltage to control direct-current power or direct-current as a command value, the second control method is that the current source type valve bank controls direct-current power or direct-current as the command value, and when the trigger angle of the current source type valve bank exceeds a reference value range considering a dead zone of the trigger angle, the voltage source type valve bank regulates voltage to enable the trigger angle of the current source type valve bank to return to the reference value range considering the dead zone of the trigger angle;
When the high-voltage direct-current transmission converter unit performs inversion operation, the first control method is that the reference value of the closing angle of the current source valve bank is unchanged, the voltage source valve bank adjusts the voltage to control the direct-current voltage at the rectifying side to be a command value or a command value range considering a voltage dead zone, the second control method is that the direct-current voltage at the rectifying side of the current source valve bank is controlled to be a command value, and when the closing angle of the current source valve bank exceeds the reference value range considering the closing angle dead zone, the voltage source valve bank adjusts the voltage to enable the closing angle of the current source valve bank to return to the reference value range considering the closing angle dead zone.
In the first control method, when the current source valve bank detects that the difference between the direct current command value and the actual direct current exceeds the current margin, the current source valve bank is switched to control the direct current power or the direct current.
In the first control method and the second control method, when the current source valve bank detects that the difference between the direct current command value and the actual direct current exceeds the current margin, the current source valve bank controls the direct current.
The current margin is 0.02 times rated DC to 0.3 times rated DC.
The triggering angle of the current source type valve bank is the triggering angle of the grid converter, the voltage source type valve bank adjusts the voltage through the voltage source converter, and the closing angle of the current source type valve bank is the closing angle or the arc extinguishing angle of the grid converter.
The dead zone of the triggering angle is any value between 0 and 15 degrees, the dead zone of the turning-off angle is any value between 0 and 15 degrees, and the dead zone of the voltage is within 5% of the rated voltage of the high-voltage direct-current transmission converter unit; the reference value range of the considered trigger angle dead zone is between the reference value minus the trigger angle dead zone and the reference value plus the trigger angle dead zone, the reference value range of the considered off angle dead zone is between the reference value minus the off angle dead zone and the reference value plus the off angle dead zone, and the instruction value range of the considered voltage dead zone is between the instruction value minus the voltage dead zone and the instruction value plus the voltage dead zone.
The voltage source type valve bank regulating voltage is used for controlling the direct current voltage at the rectifying side to be a command value or a command value range considering a voltage dead zone, the direct current voltage command value at the inverting side or the command value range considering the voltage dead zone is calculated according to the direct current voltage command value at the rectifying side or the command value range considering the voltage dead zone minus a line voltage drop, the direct current voltage command value at the inverting side or the command value range considering the voltage dead zone minus the actual voltage of the current source type valve bank at the inverting side is obtained by subtracting the actual voltage of the voltage source type valve bank at the inverting side, and the voltage source type valve bank at the inverting side is regulated to the command value; the direct current voltage of the current source type valve bank control rectifying side is a command value, the direct current voltage command value of the inverting side is calculated according to the direct current voltage command value of the rectifying side minus the line voltage drop, the actual voltage of the voltage source type valve bank of the inverting side is subtracted from the direct current voltage command value of the inverting side to obtain the direct current voltage command value of the current source type valve bank of the inverting side, and the voltage of the current source type valve bank of the inverting side is regulated to the direct current voltage command value of the current source type valve bank of the inverting side.
When the voltage source converter in the voltage source type valve bank is over-voltage or fails, the bypass switch of the input voltage source converter is used for isolating the failure.
The invention also provides a control device of the HVDC transmission converter unit, which is used for controlling the HVDC transmission converter unit, and comprises a detection unit and a control unit, wherein:
The detection unit is used for detecting the triggering angle or the closing angle, the direct-current voltage and the direct-current of the current source type valve group; detecting direct current voltage and direct current of the voltage source type valve bank; detecting direct current voltage and direct current of a direct current electrode;
the control unit is used for controlling the direct current power or the direct current power of the current source type valve bank as an instruction value by the first control unit when the high-voltage direct current power transmission converter unit is in rectifying operation, and controlling the trigger angle reference value of the current source type valve bank to be unchanged by the voltage source type valve bank; when the high-voltage direct-current transmission converter unit performs inversion operation, the first control unit is used for controlling the reference value of the turn-off angle of the current source valve bank to be unchanged, the voltage source valve bank is used for adjusting the voltage to control the direct-current voltage of the rectifying side to be the command value or the command value range considering the voltage dead zone, the second control unit is used for controlling the direct-current voltage of the rectifying side of the current source valve bank to be the command value, and when the turn-off angle of the current source valve bank exceeds the reference value range considering the turn-off angle dead zone, the voltage source valve bank is used for adjusting the voltage to enable the turn-off angle of the current source valve bank to return to the reference value range considering the turn-off angle dead zone.
In the scheme, the method comprises the following steps: in the first control method, when the current source valve group detects that the difference between the direct current command value and the actual direct current exceeds the current margin, the current source valve group is switched to control the direct current power or the direct current.
In the first control method and the second control method, when the current source type valve bank detects that the difference value between the direct current command value and the actual direct current exceeds the current margin, the current source type valve bank controls the direct current.
The current margin is 0.02 times rated DC to 0.3 times rated DC.
The triggering angle of the current source type valve bank is the triggering angle of the grid converter, the voltage source type valve bank adjusts the voltage through the voltage source converter, and the closing angle of the current source type valve bank is the closing angle or the arc extinguishing angle of the grid converter.
The triggering angle dead zone is smaller than 15 degrees, the turn-off angle dead zone is smaller than 15 degrees, and the voltage dead zone is within 5% of the rated voltage of the high-voltage direct-current transmission converter unit; the instruction value range of the considered trigger angle dead zone is between the instruction value minus the trigger angle dead zone and the instruction value plus the trigger angle dead zone, the instruction value range of the considered off angle dead zone is between the instruction value minus the off angle dead zone and the instruction value plus the off angle dead zone, and the instruction value range of the considered voltage dead zone is between the instruction value minus the voltage dead zone and the instruction value plus the voltage dead zone.
The voltage source type valve bank regulating voltage is used for controlling the direct current voltage at the rectifying side to be a command value or a command value range considering a voltage dead zone, the direct current voltage command value at the inverting side or the command value range considering the voltage dead zone is calculated according to the direct current voltage command value at the rectifying side or the command value range considering the voltage dead zone minus a line voltage drop, the direct current voltage command value at the inverting side or the command value range considering the voltage dead zone minus the actual voltage of the current source type valve bank at the inverting side is obtained, and the voltage source type valve bank regulating voltage at the inverting side is up to the direct current voltage command value at the inverting side or the command value range considering the voltage dead zone; the direct current voltage of the current source type valve bank control rectifying side is a command value, the direct current voltage command value of the inverting side is calculated according to the direct current voltage command value of the rectifying side minus the line voltage drop, the actual voltage of the voltage source type valve bank of the inverting side is subtracted from the direct current voltage command value of the inverting side to obtain the direct current voltage command value of the current source type valve bank of the inverting side, and the voltage of the current source type valve bank of the inverting side is regulated to the direct current voltage command value of the current source type valve bank of the inverting side.
When a voltage source converter in a voltage source valve bank is over-voltage or fails, the fault may be isolated by a bypass circuit that is put into the voltage source converter.
After the scheme is adopted, the tap voltage regulating function of the converter transformer is replaced by connecting the voltage source converter in series on the direct current side, so that the voltage regulating device has the advantages of quick and accurate voltage regulation, easiness in protection and no influence on normal operation of a converter unit consisting of the power grid converter and the converter transformer after the voltage source converter fails.
Drawings
Fig. 1 is a first hvdc transmission converter unit according to the present invention;
Fig. 2 is a second hvdc transmission converter unit according to the present invention;
fig. 3 is a third hvdc transmission converter unit in accordance with the present invention;
fig. 4 is a fourth hvdc transmission converter unit in accordance with the present invention;
fig. 5 is a grid commutated converter structure of the present invention;
fig. 6 is a voltage source converter structure of the present invention;
FIG. 7 is a full bridge sub-module structure of the present invention;
FIG. 8 is a half-bridge submodule and full-bridge submodule series configuration of the present invention;
fig. 9 is a main circuit of a hvdc transmission system according to the present invention;
fig. 10 is a control method of the present invention during rectifying operation of the hvdc transmission converter unit;
fig. 11 is a control method of the present invention during inverter operation of the hvdc transmission converter unit;
fig. 12 is a control device of the hvdc transmission converter unit in accordance with the present invention;
Fig. 13 is a main circuit of an uhv dc power transmission system employing the hvdc transmission converter unit of the present invention at both stations;
Fig. 14 is a schematic diagram of a primary circuit of an uhv dc power transmission system employing a hvdc transmission converter unit in accordance with the present invention;
Fig. 15 shows a main circuit of an extra-high voltage dc power transmission system employing the hvdc transmission converter unit according to the present invention at station two.
Detailed Description
Embodiments of the present invention will be described with the aid of the following drawings, in which like components are given like reference numerals.
Fig. 1 is a schematic diagram of a first hvdc power transmission converter unit according to the present invention, which at least includes a current source type valve block 1, a converter transformer 4 without voltage regulation, a voltage source type valve block 2, and a coupling transformer 8, wherein the connection mode is that an anode X2 of the current source type valve block 1 is connected with a cathode X3 of the voltage source type valve block 2. The current source type valve bank 1 is connected with a valve side of a converter transformer 4 without voltage regulation function through a connecting wire 3, and a network side of the converter transformer 4 without voltage regulation function is connected with an alternating current system through a connecting wire 5. If the power grid commutation converter in the current source type valve bank is a six-pulse bridge type circuit, the commutation transformer 4 without the voltage regulating function is a three-phase transformer, and the connecting wires 3 and 5 are three-phase wires; if the grid converter in the current source type valve bank is a twelve-pulse bridge circuit, the converter transformer 4 without voltage regulating function is a star-star three-phase transformer and a star-angle three-phase transformer, and the connecting lines 3 and 5 are two groups of three-phase lines. The voltage source type valve bank 2 is connected with the valve side of a connecting transformer 8 through a parallel branch of a switch or a disconnecting link 6 and a charging resistor 7, and the network side of the connecting transformer 8 is connected with an alternating current system through a connecting wire 9. The connecting transformer 8 is a three-phase transformer, the parallel branch of the switch or knife 6 and the charging resistor 7 is a three-phase parallel branch, and the connecting wire 9 is a three-phase wire.
Fig. 2 is a schematic diagram of a second hvth power transmission converter unit according to the present invention, which at least includes a current source type valve block 1, a converter transformer 4 without voltage regulation, a voltage source type valve block 2, and a coupling transformer 8, wherein the connection mode is that a cathode X1 of the current source type valve block 1 is connected with a cathode X4 of the voltage source type valve block 2. The current source type valve bank 1 is connected with a valve side of a converter transformer 4 without voltage regulation function through a connecting wire 3, and a network side of the converter transformer 4 without voltage regulation function is connected with an alternating current system through a connecting wire 5. If the power grid commutation converter in the current source type valve bank is a six-pulse bridge type circuit, the commutation transformer 4 without the voltage regulating function is a three-phase transformer, and the connecting wires 3 and 5 are three-phase wires; if the grid converter in the current source type valve bank is a twelve-pulse bridge circuit, the converter transformer 4 without voltage regulating function is a star-star three-phase transformer and a star-angle three-phase transformer, and the connecting lines 3 and 5 are two groups of three-phase lines. The voltage source type valve bank 2 is connected with the valve side of a connecting transformer 8 through a parallel branch of a switch or a disconnecting link 6 and a charging resistor 7, and the network side of the connecting transformer 8 is connected with an alternating current system through a connecting wire 9. The connecting transformer 8 is a three-phase transformer, the parallel branch of the switch or knife 6 and the charging resistor 7 is a three-phase parallel branch, and the connecting wire 9 is a three-phase wire.
Fig. 3 is a schematic diagram of a third hvdc transmission converter unit according to the present invention, which at least includes a current source type valve block 1, a converter transformer 4 without voltage regulation, a voltage source type valve block 2, and a coupling transformer 8, wherein the connection mode is that a cathode X1 of the current source type valve block 1 is connected with an anode X3 of the voltage source type valve block 2. The current source type valve bank 1 is connected with a valve side of a converter transformer 4 without voltage regulation function through a connecting wire 3, and a network side of the converter transformer 4 without voltage regulation function is connected with an alternating current system through a connecting wire 5. If the power grid commutation converter in the current source type valve bank is a six-pulse bridge type circuit, the commutation transformer 4 without the voltage regulating function is a three-phase transformer, and the connecting wires 3 and 5 are three-phase wires; if the grid converter in the current source type valve bank is a twelve-pulse bridge circuit, the converter transformer 4 without voltage regulating function is a star-star three-phase transformer and a star-angle three-phase transformer, and the connecting lines 3 and 5 are two groups of three-phase lines. The voltage source type valve bank 2 is connected with the valve side of a connecting transformer 8 through a parallel branch of a switch or a disconnecting link 6 and a charging resistor 7, and the network side of the connecting transformer 8 is connected with an alternating current system through a connecting wire 9. The connecting transformer 8 is a three-phase transformer, the parallel branch of the switch or knife 6 and the charging resistor 7 is a three-phase parallel branch, and the connecting wire 9 is a three-phase wire.
Fig. 4 is a diagram of a fourth hvdc transmission converter unit according to the present invention, which at least comprises a current source type valve block 1, a converter transformer 4 without voltage regulation, a voltage source type valve block 2 and a coupling transformer 8, wherein the connection mode is that an anode X2 of the current source type valve block 1 is connected with a cathode X4 of the voltage source type valve block 2. The current source type valve bank 1 is connected with a valve side of a converter transformer 4 without voltage regulation function through a connecting wire 3, and a network side of the converter transformer 4 without voltage regulation function is connected with an alternating current system through a connecting wire 5. If the power grid commutation converter in the current source type valve bank is a six-pulse bridge type circuit, the commutation transformer 4 without the voltage regulating function is a three-phase transformer, and the connecting wires 3 and 5 are three-phase wires; if the grid converter in the current source type valve bank is a twelve-pulse bridge circuit, the converter transformer 4 without voltage regulating function is a star-star three-phase transformer and a star-angle three-phase transformer, and the connecting lines 3 and 5 are two groups of three-phase lines. The voltage source type valve bank 2 is connected with the valve side of a connecting transformer 8 through a parallel branch of a switch or a disconnecting link 6 and a charging resistor 7, and the network side of the connecting transformer 8 is connected with an alternating current system through a connecting wire 9. The connecting transformer 8 is a three-phase transformer, the parallel branch of the switch or knife 6 and the charging resistor 7 is a three-phase parallel branch, and the connecting wire 9 is a three-phase wire.
Fig. 5 shows a typical grid converter, which uses twelve pulsating bridge circuits, and has twelve bridge arms 10, each bridge arm 10 is connected in parallel with a lightning arrester 11, and the anodes, cathodes and midpoints of the grid converter are respectively configured with the lightning arrester.
Fig. 6 shows a typical voltage source converter, which adopts a modularized multi-level converter, and includes six bridge arms, each bridge arm is formed by connecting N sub-modules 12 and a reactor 13 in series, each reactor 13 is connected in parallel with a lightning arrester 14, and the positive pole and the negative pole of the modularized multi-level converter are respectively configured with the lightning arrester. Fig. 7 shows a sub-module with a full-bridge structure, which is composed of four IGBT devices 15 and one capacitor 16. Fig. 8 shows a sub-module with a hybrid half-bridge and full-bridge structure, which is formed by connecting a sub-module with a half-bridge structure and a sub-module with a full-bridge structure in series, wherein the sub-module with a half-bridge structure is formed by two IGBT devices 17 and a capacitor 18.
Fig. 9 is a schematic diagram of a main circuit of the hvdc transmission system according to the present invention, which is shown in fig. 1, fig. 2, fig. 3 and fig. 4. Pole I of station one 19 is constituted by fig. 1, pole II of station one 19 is constituted by fig. 2, pole I of station two 20 is constituted by fig. 3, and pole II of station two 20 is constituted by fig. 4. The first station 19 is connected to the dc line 22 through the smoothing reactor 21, and the second station 20 is connected to the dc line 22 through the smoothing reactor 21. The first station 19 is connected to the ground via a ground line 23 and the second station 20 is connected to the ground via a ground line 24. During power forward, the alternating current system 25 of the first station 19 converts alternating current into direct current through the current source type valve bank 1 and the voltage source type valve bank 2, the direct current is transmitted to the second station 20 through the direct current line 22, and the second station 20 converts the direct current into alternating current through the current source type valve bank 1 and the voltage source type valve bank 2 and transmits the alternating current to the alternating current system 26, so that direct current power forward is realized; in the power feedback process, the alternating current system 26 of the second station 20 converts alternating current into direct current through the current source type valve bank 1 and the voltage source type valve bank 2, the direct current is transmitted to the first station 19 through the direct current line 22, and the first station 19 converts the direct current into alternating current through the current source type valve bank 1 and the voltage source type valve bank 2 and transmits the alternating current to the alternating current system 25, so that direct current power feedback is realized. The main loop of the high-voltage direct-current transmission system is provided with a direct-current measuring point Id, a direct-current bus voltage measuring point Udl, a voltage source type valve group bus voltage measuring point Udm and a direct-current neutral bus voltage measuring point Udn, wherein the direct-current voltage Ud= | Udl-Udn|, and the voltage source type valve group voltage Udv = | Udm-Udn|.
Fig. 10 is a schematic diagram illustrating a control method for rectifying an hvdc converter unit according to the present invention, wherein the control method controls the hvdc converter unit shown in fig. 1, fig. 2, fig. 3 or fig. 4. Firstly, judging that a current source type valve bank, a converter transformer without a voltage regulating function, a voltage source type valve bank and a converter unit connected with the transformer are in rectifying operation or inversion operation; when the converter unit is in rectifying operation, the current source valve bank selects a fixed trigger angle control strategy (a first control method of rectifying operation) or a fixed current control strategy (a second control method of rectifying operation), if the current source valve bank is the fixed trigger angle control strategy, the trigger angle alpha of the current source valve bank is equal to the trigger angle reference value alpha ord, and the adjusting process of the current source valve bank is finished; meanwhile, the voltage source type valve bank judges whether the direct current command value Io of the voltage source type valve bank is equal to the actual direct current Id, if Io=Id, the voltage source type valve bank does not regulate the voltage, and the regulation process of the voltage source type valve bank is finished; if Io > Id, the voltage source valve bank increases its dc voltage Udv, and if Io < Id, the voltage source valve bank decreases its dc voltage Udv until io=id. If the current source type valve bank is a constant current control strategy, the current source type valve bank judges whether the direct current command value Io of the current source type valve bank is equal to the actual direct current Id, if Io=Id, the triggering angle alpha is not regulated by the current source type valve bank, and the regulation process of the current source type valve bank is finished; if Io > Id, the current source valve group decreases its firing angle α, and if Io < Id, the current source valve group increases its firing angle α until io=id; meanwhile, when the trigger angle of the current source type valve group is larger than or equal to the lower limit value alpha ord -delta alpha of the dead zone delta alpha of the considered trigger angle and smaller than or equal to the upper limit value alpha ord +delta alpha of the dead zone delta alpha of the considered trigger angle, the adjusting process of the voltage source type valve group is finished; when the trigger angle of the current source valve group is larger than the upper limit value alpha ord +delta alpha of the dead zone delta alpha of the trigger angle, the voltage source valve group reduces the direct current voltage Udv, and when the trigger angle of the current source valve group is smaller than the lower limit value alpha ord -delta alpha of the dead zone delta alpha of the trigger angle, the voltage source valve group increases the direct current voltage Udv until alpha is larger than or equal to alpha ord -delta alpha and alpha is smaller than or equal to alpha ord +delta alpha.
Fig. 11 is a schematic diagram illustrating a control method for inverter operation of a hvdc converter unit according to the present invention, wherein the hvdc converter unit is controlled according to fig. 1, fig. 2, fig. 3 or fig. 4. Firstly, judging that a current source type valve bank, a converter transformer without a voltage regulating function, a voltage source type valve bank and a converter unit connected with the transformer are in rectifying operation or inversion operation; when the converter unit is in the inversion operation, the current source type valve bank selects a constant turn-off angle control strategy (a first control method of the inversion operation) or a constant rectification side direct current voltage control strategy (a second control method of the inversion operation), if the current source type valve bank is the constant turn-off angle control strategy, the turn-off angle gamma of the current source type valve bank is equal to a turn-off angle reference value gamma ord, and the adjustment process of the current source type valve bank is finished; meanwhile, the voltage source type valve bank judges whether a direct-current voltage command value Uo at the rectifying side is equal to an actual direct-current voltage Ud, if uo=ud, the voltage source type valve bank does not regulate the voltage, and the regulation process of the voltage source type valve bank is finished; if Uo > Ud, the voltage source valve bank increases its dc voltage Udv, and if Uo < Ud, the voltage source valve bank decreases its dc voltage Udv until uo=ud. If the current source type valve bank is a constant voltage control strategy, the current source type valve bank judges whether a direct current voltage command value Uo of a rectifying side is equal to an actual direct current voltage Ud, if Uo=Ud, the current source type valve bank does not adjust a closing angle gamma, and the adjustment process of the current source type valve bank is finished; if Uo > Ud, the current source valve bank decreases its turn-off angle γ, and if Uo < Ud, the current source valve bank increases its turn-off angle γ until uo=ud; meanwhile, when the turn-off angle of the current source valve group is larger than or equal to the lower limit value gamma ord -delta gamma of the dead zone delta gamma of the considered trigger angle and smaller than or equal to the upper limit value gamma ord +delta gamma of the dead zone delta gamma of the considered trigger angle, the adjusting process of the voltage source valve group is finished; when the turn-off angle of the current source valve group is larger than the upper limit value gamma ord +delta gamma of the dead zone delta gamma of the considered trigger angle, the voltage source valve group reduces the direct current voltage Udv, and when the turn-off angle of the current source valve group is smaller than the lower limit value gamma ord -delta gamma of the dead zone delta gamma of the considered trigger angle, the voltage source valve group increases the direct current voltage Udv until gamma is larger than or equal to gamma ord -delta gamma and gamma is smaller than or equal to gamma ord +delta gamma. In the running process of the high-voltage direct-current transmission, the adjusting process is repeatedly executed, the triggering angle and the turn-off angle are adjusted to reference values, and the direct-current voltage is adjusted to command values.
Fig. 12 is a control device for a hvdc transmission converter unit according to the present invention, for controlling the hvdc transmission converter unit of fig. 1, 2, 3 or 4, the control device comprises a detection unit and a control unit, wherein:
The detection unit is used for detecting a triggering angle or a closing angle, a direct-current voltage and a direct-current of the current source type valve group; detecting direct current voltage and direct current of the voltage source type valve bank; detecting direct current voltage and direct current of a direct current electrode;
The control unit is used for controlling the direct current power or the direct current power of the current source type valve bank as an instruction value by the first control unit when the high-voltage direct current power transmission converter unit is in rectifying operation, and controlling the trigger angle reference value of the current source type valve bank to be unchanged by the voltage source type valve bank; when the high-voltage direct-current transmission converter unit performs inversion operation, the first control unit controls the off angle reference value of the current source type valve bank to be unchanged, the voltage source type valve bank regulates voltage to control direct-current voltage at the rectifying side to be a command value or a command value range considering a voltage dead zone, the second control unit controls the direct-current voltage at the rectifying side of the current source type valve bank to be a command value, and when the off angle of the current source type valve bank exceeds the reference value range considering the off angle dead zone, the voltage source type valve bank regulates voltage to enable the off angle of the current source type valve bank to return to the reference value range considering the off angle dead zone.
Example 1:
Fig. 13 shows an embodiment of a main circuit of an uhv dc transmission system in which both stations use the above-mentioned converter unit. The main loop of the HVDC transmission system consists of a first station 19, a second station 20, a DC circuit 22, a grounding electrode line 23 and a grounding electrode line 24. Station one 19 comprises a high-voltage direct-current power transmission converter unit, a converter transformer 28 without voltage regulation, a connecting transformer 35, a direct-current filter 32, an alternating-current filter 33, a smoothing reactor 21, an alternating-current system 25 and a grounding electrode line 24, wherein the converter transformer 28 without voltage regulation cannot regulate a tap; station two 20 comprises a high voltage direct current power transmission converter unit, a converter transformer 28 without voltage regulation, a junction transformer 35, a direct current filter 32, an alternating current filter 33, a smoothing reactor 21, an alternating current system 26 and a ground electrode line 25, wherein the converter transformer 28 without voltage regulation cannot regulate taps. The hvdc converter unit consists of a current source type valve block 39 and a voltage source type valve block 40. The current source type valve bank 39 comprises two power grid commutation converters 27 adopting twelve-pulse bridge circuits, a bypass switch 29, a connection disconnecting link 30 and a bypass disconnecting link 31, the voltage source type valve bank 40 comprises a voltage source converter 34 adopting modularized multi-level converters, a bypass switch or bypass power electronic switch 36, and the connection disconnecting link 30 and the bypass disconnecting link 31, wherein the voltage source converter 34 comprises a submodule 38 and a bridge arm reactor 37, and the submodule 38 is a full-bridge submodule or a half-bridge submodule.
The first station 19 is connected to the ground via a ground line 23 and the second station 20 is connected to the ground via a ground line 24. During power forward, the alternating current system 25 of the first station 19 converts alternating current into direct current through the current source type valve bank 39 and the voltage source type valve bank 40, the direct current is transmitted to the second station 20 through the direct current line 22, and the second station 20 converts the direct current into alternating current through the current source type valve bank 39 and the voltage source type valve bank 40 and transmits the alternating current to the alternating current system 26, so that direct current power forward is realized; in the power feedback process, the alternating current system 26 of the second station 20 converts alternating current into direct current through the current source type valve bank 39 and the voltage source type valve bank 40, the direct current is transmitted to the first station 19 through the direct current line 22, and the first station 19 converts the direct current into alternating current through the current source type valve bank 39 and the voltage source type valve bank 40 and transmits the alternating current to the alternating current system 25, so that direct current power feedback is realized.
When power is sent forward, the first station 19 is in rectifying operation, the current source valve group 39 selects a fixed trigger angle control strategy or a fixed current control strategy, if the current source valve group 39 is the fixed trigger angle control strategy, the trigger angle alpha of the current source valve group 39 is equal to the trigger angle reference value alpha ord, and the adjustment process of the current source valve group 39 is finished; meanwhile, the voltage source type valve bank 40 judges whether the direct current command value Io of the voltage source type valve bank is equal to the actual direct current Id, if Io=Id, the voltage source type valve bank 40 does not regulate the voltage, and the regulation process of the voltage source type valve bank 40 is finished; if Io > Id, the voltage source valve bank 40 increases its dc voltage Udv, and if Io < Id, the voltage source valve bank 40 decreases its dc voltage Udv until io=id. If the current source type valve bank 39 is a constant current control strategy, the current source type valve bank 39 judges whether the direct current command value Io is equal to the actual direct current Id, if io=id, the current source type valve bank 39 does not adjust the trigger angle α, and the adjustment process of the current source type valve bank 39 is finished; if Io > Id, the current source valve group 39 decreases its firing angle α, and if Io < Id, the current source valve group 39 increases its firing angle α until io=id; meanwhile, when the trigger angle of the current source type valve group 39 is greater than or equal to the lower limit value alpha ord -delta alpha of the dead zone delta alpha of the considered trigger angle and less than or equal to the upper limit value alpha ord +delta alpha of the dead zone delta alpha of the considered trigger angle, the adjusting process of the voltage source type valve group 40 is ended; when the firing angle of the current source valve block 39 is greater than the upper limit value α ord +Δα of the dead zone Δα of the firing angle considered, the voltage source valve block 40 reduces its dc voltage Udv, and when the firing angle of the current source valve block 39 is less than the lower limit value α ord - Δα of the dead zone Δα of the firing angle considered, the voltage source valve block 40 increases its dc voltage Udv until α is greater than or equal to α ord - Δα and α is less than or equal to α ord +Δα. Throughout the process, converter transformer 28 does not adjust taps to change the grid side and valve side winding ratios.
When power is sent forward, the second station 20 is in inversion operation, the current source type valve bank 39 selects a constant turn-off angle control strategy or a constant rectification side direct current voltage control strategy, if the current source type valve bank 39 is the constant turn-off angle control strategy, the turn-off angle gamma of the current source type valve bank is equal to the turn-off angle reference value gamma ord, and the adjustment process of the current source type valve bank 39 is finished; meanwhile, the voltage source type valve bank 40 judges whether the direct current voltage command value Uo at the rectifying side is equal to the actual direct current voltage Ud, if uo=ud, the voltage source type valve bank 40 does not regulate the voltage, and the regulation process of the voltage source type valve bank 40 is finished; if Uo > Ud, the voltage source valve bank 40 increases its dc voltage Udv, and if Uo < Ud, the voltage source valve bank 40 decreases its dc voltage Udv until uo=ud. If the current source type valve bank 39 is a constant voltage control strategy, the current source type valve bank 39 judges whether the direct current voltage command value Uo at the rectifying side is equal to the actual direct current voltage Ud, if uo=ud, the current source type valve bank 39 does not adjust the off angle gamma, and the adjustment process of the current source type valve bank 39 is finished; if Uo > Ud, the current source valve block 39 decreases its turn-off angle γ, and if Uo < Ud, the current source valve block 39 increases its turn-off angle γ until uo=ud; meanwhile, when the closing angle of the current source type valve group 39 is greater than or equal to the lower limit value gamma ord -delta gamma of the dead zone delta gamma of the considered triggering angle and less than or equal to the upper limit value gamma ord + delta gamma of the dead zone delta gamma of the considered triggering angle, the adjusting process of the voltage source type valve group 40 is ended; when the turn-off angle of the current source type valve group 39 is larger than the upper limit value γ ord +Δγ of the dead zone Δγ of the considered trigger angle, the voltage source type valve group 40 reduces the direct current voltage Udv thereof, and when the turn-off angle of the current source type valve group 39 is smaller than the lower limit value γ ord - Δγ of the dead zone Δγ of the considered trigger angle, the voltage source type valve group 40 increases the direct current voltage Udv thereof until γ is not smaller than γ ord - Δγ and γ is not smaller than γ ord +Δγ. Throughout the process, converter transformer 28 does not adjust taps to change the grid side and valve side winding ratios.
Example 2:
Fig. 14 shows a main circuit embodiment of an uhv dc power transmission system employing the above converter unit at station one. The main loop of the HVDC transmission system consists of a first station 19, a second station 20, a DC circuit 22, a grounding electrode line 23 and a grounding electrode line 24. Station one 19 comprises a high-voltage direct-current power transmission converter unit, a converter transformer 28 without voltage regulation, a connecting transformer 35, a direct-current filter 32, an alternating-current filter 33, a smoothing reactor 21, an alternating-current system 25 and a grounding electrode line 24, wherein the converter transformer 28 without voltage regulation cannot regulate a tap; station two 20 comprises a current source valve block 39, a converter transformer 41 with voltage regulation, a junction transformer 35, a dc filter 32, an ac filter 33, a smoothing reactor 21, an ac system 26 and a ground line 25, wherein the converter transformer 41 with voltage regulation can regulate taps. The hvdc converter unit consists of a current source type valve block 39 and a voltage source type valve block 40. The current source type valve bank 39 comprises two power grid commutation converters 27 adopting twelve-pulse bridge circuits, a bypass switch 29, a connection disconnecting link 30 and a bypass disconnecting link 31, the voltage source type valve bank 40 comprises a voltage source converter 34 adopting modularized multi-level converters, a bypass switch or bypass power electronic switch 36, and the connection disconnecting link 30 and the bypass disconnecting link 31, wherein the voltage source converter 34 comprises a submodule 38 and a bridge arm reactor 37, and the submodule 38 is a full-bridge submodule or a half-bridge submodule.
The first station 19 is connected to the ground via a ground line 23 and the second station 20 is connected to the ground via a ground line 24. During power forward, the alternating current system 25 of the first station 19 converts alternating current into direct current through the current source type valve bank 39 and the voltage source type valve bank 40, the direct current is transmitted to the second station 20 through the direct current line 22, and the second station 20 converts the direct current into alternating current through the current source type valve bank 39 and transmits the alternating current to the alternating current system 26, so that direct current power forward is realized; in the power feedback process, the alternating current system 26 of the second station 20 converts alternating current into direct current through the current source type valve bank 39, the direct current is transmitted to the first station 19 through the direct current line 22, and the first station 19 converts the direct current into alternating current through the current source type valve bank 39 and the voltage source type valve bank 40 and transmits the alternating current to the alternating current system 25, so that direct current power feedback is realized.
When power is sent forward, the first station 19 is in rectifying operation, the current source valve group 39 selects a fixed trigger angle control strategy or a fixed current control strategy, if the current source valve group 39 is the fixed trigger angle control strategy, the trigger angle alpha of the current source valve group 39 is equal to the trigger angle reference value alpha ord, and the adjustment process of the current source valve group 39 is finished; meanwhile, the voltage source type valve bank 40 judges whether the direct current command value Io of the voltage source type valve bank is equal to the actual direct current Id, if Io=Id, the voltage source type valve bank 40 does not regulate the voltage, and the regulation process of the voltage source type valve bank 40 is finished; if Io > Id, the voltage source valve bank 40 increases its dc voltage Udv, and if Io < Id, the voltage source valve bank 40 decreases its dc voltage Udv until io=id. If the current source type valve bank 39 is a constant current control strategy, the current source type valve bank 39 judges whether the direct current command value Io is equal to the actual direct current Id, if io=id, the current source type valve bank 39 does not adjust the trigger angle α, and the adjustment process of the current source type valve bank 39 is finished; if Io > Id, the current source valve group 39 decreases its firing angle α, and if Io < Id, the current source valve group 39 increases its firing angle α until io=id; meanwhile, when the trigger angle of the current source type valve group 39 is greater than or equal to the lower limit value alpha ord -delta alpha of the dead zone delta alpha of the considered trigger angle and less than or equal to the upper limit value alpha ord +delta alpha of the dead zone delta alpha of the considered trigger angle, the adjusting process of the voltage source type valve group 40 is ended; when the firing angle of the current source valve block 39 is greater than the upper limit value α ord +Δα of the dead zone Δα of the firing angle considered, the voltage source valve block 40 reduces its dc voltage Udv, and when the firing angle of the current source valve block 39 is less than the lower limit value α ord - Δα of the dead zone Δα of the firing angle considered, the voltage source valve block 40 increases its dc voltage Udv until α is greater than or equal to α ord - Δα and α is less than or equal to α ord +Δα. Throughout the process, converter transformer 28 does not adjust taps to change the grid side and valve side winding ratios.
When power is sent forward, the second station 20 is in inversion operation, the current source type valve bank 39 selects a constant turn-off angle control strategy or a constant rectification side direct current voltage control strategy, if the current source type valve bank 39 is the constant turn-off angle control strategy, the turn-off angle gamma of the current source type valve bank is equal to the turn-off angle reference value gamma ord, and the adjustment process of the current source type valve bank 39 is finished; meanwhile, the current source type valve bank 39 judges whether the direct current voltage command value Uo at the rectifying side is in a command value range considering the voltage dead zone delta Ud with the actual direct current voltage Ud, and if the absolute value of the direct current voltage Uo-Ud is less than or equal to delta Ud, the tap is not regulated by the converter transformer 41; if Uo-Ud > Δud, the converter transformer 41 adjusts the tap to increase the no-load dc voltage of the current source valve bank 39; if Ud-Uo > DeltaUd, the converter transformer 41 adjusts the tap reduction current source valve bank 39 no-load DC voltage command value until Uo-Ud < DeltaUd. If the current source type valve bank 39 is a constant voltage control strategy, the current source type valve bank 39 judges whether the direct current voltage command value Uo at the rectifying side is equal to the actual direct current voltage Ud, if uo=ud, the current source type valve bank 39 does not adjust the off angle gamma, and the adjustment process of the current source type valve bank 39 is finished; if Uo > Ud, the current source valve block 39 decreases its turn-off angle γ, and if Uo < Ud, the current source valve block 39 increases its turn-off angle γ until uo=ud; meanwhile, when the off angle of the current source type valve group 39 is greater than or equal to the lower limit value gamma ord -delta gamma of the dead zone delta gamma of the off angle and less than or equal to the upper limit value gamma ord + delta gamma of the dead zone delta gamma of the off angle, the converter transformer 41 does not adjust the tap; when the turn-off angle of the current source type valve group 39 is larger than an upper limit value γ ord +Δγ considering the turn-off angle dead zone Δγ, the converter transformer 41 adjusts the tap to decrease the no-load direct current voltage of the current source type valve group 39, and when the turn-off angle of the current source type valve group 39 is smaller than a lower limit value γ ord - Δγ considering the turn-off angle dead zone Δγ, the converter transformer 41 adjusts the tap to increase the no-load direct current voltage of the current source type valve group 39 until γ is larger than or equal to γ ord - Δγ and γ is smaller than or equal to γ ord +Δγ. Throughout the process, the converter transformer 41 adjusts taps to change the net-side and valve-side winding ratios.
Example 3:
Fig. 15 shows a main circuit embodiment of an extra-high voltage direct current transmission system of which the converter unit is adopted by the second station. The main loop of the HVDC transmission system consists of a first station 19, a second station 20, a DC circuit 22, a grounding electrode line 23 and a grounding electrode line 24. Station one 19 comprises a current source valve group 39, a converter transformer 41 with voltage regulating function, a junction transformer 35, a direct current filter 32, an alternating current filter 33, a smoothing reactor 21, an alternating current system 25 and a grounding electrode line 24, wherein the converter transformer 28 with voltage regulating function can regulate taps; station two 20 comprises a high voltage direct current power transmission converter unit, a converter transformer 28 without voltage regulation, a junction transformer 35, a direct current filter 32, an alternating current filter 33, a smoothing reactor 21, an alternating current system 26 and a ground electrode line 25, wherein the converter transformer 28 without voltage regulation cannot regulate taps. The hvdc converter unit consists of a current source type valve block 39 and a voltage source type valve block 40. The current source type valve bank 39 comprises two power grid commutation converters 27 adopting twelve-pulse bridge circuits, a bypass switch 29, a connection disconnecting link 30 and a bypass disconnecting link 31, the voltage source type valve bank 40 comprises a voltage source converter 34 adopting modularized multi-level converters, a bypass switch or bypass power electronic switch 36, and the connection disconnecting link 30 and the bypass disconnecting link 31, wherein the voltage source converter 34 comprises a submodule 38 and a bridge arm reactor 37, and the submodule 38 is a full-bridge submodule or a half-bridge submodule.
The first station 19 is connected to the ground via a ground line 23 and the second station 20 is connected to the ground via a ground line 24. During power forward, the alternating current system 25 of the first station 19 converts alternating current into direct current through the current source type valve bank 39 of the first station, the direct current is transmitted to the second station 20 through the direct current line 22, and the second station 20 converts the direct current into alternating current through the current source type valve bank 39 and the voltage source type valve bank 40 and transmits the alternating current to the alternating current system 26, so that direct current power forward is realized; in the power feedback process, the alternating current system 26 of the second station 20 converts alternating current into direct current through the current source type valve bank 39 and the voltage source type valve bank 40, the direct current is transmitted to the first station 19 through the direct current line 22, and the first station 19 converts the direct current into alternating current through the current source type valve bank 39 and transmits the alternating current to the alternating current system 25, so that direct current power feedback is realized.
When power is forward fed, the first station 19 is in rectifying operation, the current source type valve bank 39 adopts a constant current control strategy, the current source type valve bank 39 judges whether the direct current command value Io of the current source type valve bank is equal to the actual direct current Id, if Io=Id, the current source type valve bank 39 does not adjust the trigger angle alpha, and the adjusting process of the current source type valve bank 39 is finished; if Io > Id, the current source valve group 39 decreases its firing angle α, and if Io < Id, the current source valve group 39 increases its firing angle α until io=id; meanwhile, when the trigger angle of the current source type valve group 39 is greater than or equal to the lower limit value alpha ord -delta alpha of the dead zone delta alpha of the considered trigger angle and less than or equal to the upper limit value alpha ord +delta alpha of the dead zone delta alpha of the considered trigger angle, the converter transformer 41 does not adjust the tap; when the firing angle of the current source type valve group 39 is larger than the upper limit value alpha ord + delta alpha of the dead zone delta alpha of the firing angle, the converter transformer 41 adjusts the tap to reduce the no-load direct current voltage of the current source type valve group 39, and when the firing angle of the current source type valve group 39 is smaller than the lower limit value alpha ord -delta alpha of the dead zone delta alpha of the firing angle, the converter transformer 41 adjusts the tap to increase the no-load direct current voltage of the current source type valve group 39 until alpha is larger than or equal to alpha ord -delta alpha and alpha is smaller than or equal to alpha ord + delta alpha. Throughout the process, the converter transformer 41 adjusts taps to change the net-side and valve-side winding ratios.
When power is sent forward, the second station 20 is in inversion operation, the current source type valve bank 39 selects a constant turn-off angle control strategy or a constant rectification side direct current voltage control strategy, if the current source type valve bank 39 is the constant turn-off angle control strategy, the turn-off angle gamma of the current source type valve bank is equal to the turn-off angle reference value gamma ord, and the adjustment process of the current source type valve bank 39 is finished; meanwhile, the voltage source type valve bank 40 judges whether the direct current voltage command value Uo at the rectifying side is equal to the actual direct current voltage Ud, if uo=ud, the voltage source type valve bank 40 does not regulate the voltage, and the regulation process of the voltage source type valve bank 40 is finished; if Uo > Ud, the voltage source valve bank 40 increases its dc voltage Udv, and if Uo < Ud, the voltage source valve bank 40 decreases its dc voltage Udv until uo=ud. If the current source type valve bank 39 is a constant voltage control strategy, the current source type valve bank 39 judges whether the direct current voltage command value Uo at the rectifying side is equal to the actual direct current voltage Ud, if uo=ud, the current source type valve bank 39 does not adjust the off angle gamma, and the adjustment process of the current source type valve bank 39 is finished; if Uo > Ud, the current source valve block 39 decreases its turn-off angle γ, and if Uo < Ud, the current source valve block 39 increases its turn-off angle γ until uo=ud; meanwhile, when the closing angle of the current source type valve group 39 is greater than or equal to the lower limit value gamma ord -delta gamma of the dead zone delta gamma of the considered triggering angle and less than or equal to the upper limit value gamma ord + delta gamma of the dead zone delta gamma of the considered triggering angle, the adjusting process of the voltage source type valve group 40 is ended; when the turn-off angle of the current source type valve group 39 is larger than the upper limit value γ ord +Δγ of the dead zone Δγ of the considered trigger angle, the voltage source type valve group 40 reduces the direct current voltage Udv thereof, and when the turn-off angle of the current source type valve group 39 is smaller than the lower limit value γ ord - Δγ of the dead zone Δγ of the considered trigger angle, the voltage source type valve group 40 increases the direct current voltage Udv thereof until γ is not smaller than γ ord - Δγ and γ is not smaller than γ ord +Δγ. Throughout the process, converter transformer 28 does not adjust taps to change the grid side and valve side winding ratios.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereto, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the present invention.

Claims (24)

1. A control method of a high-voltage direct-current transmission converter unit is characterized by comprising the following steps of: according to the running condition of the high-voltage direct-current transmission converter unit, two conditions are divided:
When the high-voltage direct-current power transmission converter unit performs rectifying operation, the first control method is that a reference value of a control trigger angle of the current source type valve bank is unchanged, the voltage source type valve bank regulates voltage to control direct-current power or direct-current as a command value, the second control method is that the current source type valve bank controls direct-current power or direct-current as the command value, and when the trigger angle of the current source type valve bank exceeds a reference value range considering a dead zone of the trigger angle, the voltage source type valve bank regulates voltage to enable the trigger angle of the current source type valve bank to return to the reference value range considering the dead zone of the trigger angle;
When the high-voltage direct-current transmission converter unit performs inversion operation, the first control method is that a reference value of a closing angle of a current source valve bank is unchanged, a voltage source valve bank adjusts voltage to control direct-current voltage at a rectifying side to be a command value or a command value range considering a voltage dead zone, the second control method is that the direct-current voltage at the rectifying side is controlled by the current source valve bank to be a command value, and when the closing angle of the current source valve bank exceeds the reference value range considering the closing angle dead zone, the voltage source valve bank adjusts the voltage to enable the closing angle of the current source valve bank to return to the reference value range considering the closing angle dead zone;
The voltage source type valve bank regulating voltage is used for controlling the direct current voltage at the rectifying side to be a command value or a command value range considering a voltage dead zone, the direct current voltage command value at the inverting side or the command value range considering the voltage dead zone is calculated according to the direct current voltage command value at the rectifying side or the command value range considering the voltage dead zone minus a line voltage drop, the direct current voltage command value at the inverting side or the command value range considering the voltage dead zone minus the actual voltage of the current source type valve bank at the inverting side is obtained by subtracting the actual voltage of the voltage source type valve bank at the inverting side, and the voltage source type valve bank at the inverting side is regulated to the command value; the direct current voltage of the rectifying side of the current source type valve bank is controlled to be a command value, the direct current voltage command value of the inverting side is calculated according to the direct current voltage command value of the rectifying side minus the line voltage drop, the actual voltage of the voltage source type valve bank of the inverting side is subtracted from the direct current voltage command value of the inverting side to obtain the direct current voltage command value of the current source type valve bank of the inverting side, and the voltage of the current source type valve bank of the inverting side is regulated to the direct current voltage command value of the current source type valve bank of the inverting side;
the high-voltage direct-current transmission converter unit comprises a current source type valve bank, a converter transformer without voltage regulation function, a voltage source type valve bank and a connecting transformer, wherein the current source type valve bank is connected with an alternating current system through the converter transformer without voltage regulation function, the voltage source type valve bank is connected with the alternating current system through the connecting transformer, and the current source type valve bank is connected with the voltage source type valve bank in series on the direct current side.
2. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: the converter transformer without the voltage regulating function is a converter transformer without a tap or a tapping switch, and does not have the function of regulating the winding transformation ratio of the network side and the valve side of the converter transformer.
3. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: the connecting transformer adopts a transformer without a tap or a tap changer and does not have the function of adjusting the transformation ratio of windings at the network side and the valve side of the transformer; or the connecting transformer adopts a transformer with a tap and a tap switch, and has the function of adjusting the transformation ratio of windings at the network side and the valve side of the transformer.
4. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: and a charging resistor is further connected between the voltage source type valve bank and the connecting transformer, and the charging resistor is connected with a switch or a disconnecting link in parallel.
5. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: the current source type valve bank adopts any one of the following three schemes: firstly, a power grid commutation converter is adopted; secondly, a grid commutation converter and a bypass switch which are connected in parallel are adopted; and thirdly, the bypass switch comprises a power grid commutation converter, a bypass switch and two connecting switches, wherein the power grid commutation converter is connected with the bypass switch in parallel, two ends after being connected in parallel are respectively connected with one ends of the two connecting switches, and two ends of the bypass switch are respectively connected with the other ends of the two connecting switches.
6. The control method of the high-voltage direct-current transmission converter unit according to claim 5, wherein: the power grid commutation converter adopts a six-pulse bridge circuit, a twelve-pulse bridge circuit or a circuit formed by connecting a plurality of six-pulse bridge circuits in series, and the circuit is composed of a semi-controlled power semiconductor which can not be turned off.
7. The control method of the high-voltage direct-current transmission converter unit according to claim 6, wherein: the non-turn-off semi-controlled power semiconductor is a thyristor.
8. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: the voltage source type valve group adopts any one of the following three schemes: first, a voltage source converter is adopted; secondly, a voltage source converter and a bypass switch which are connected in parallel are adopted; and thirdly, the bypass switch comprises a voltage source converter, a bypass switch and two connection switches, wherein the voltage source converter is connected with the bypass switch in parallel, two ends after being connected in parallel are respectively connected with one ends of the two connection switches, and two ends of the bypass switch are respectively connected with the other ends of the two connection switches.
9. The control method of a high-voltage direct-current transmission converter unit according to claim 8, wherein: in the three schemes, the voltage source converter is a single voltage source converter or two or more voltage source converters are connected in parallel; in the second and third schemes, the method further comprises an inductor, wherein the inductor is connected in series with the voltage source converter or connected in series with the bypass switch.
10. The control method of a high-voltage direct-current transmission converter unit according to claim 8, wherein: the bypass switch adopts a mechanical switch or a power electronic switch, and the power electronic switch is a valve bank formed by serially connecting thyristors or a valve bank formed by serially connecting turnoff full-control power semiconductors.
11. The control method of a high-voltage direct-current transmission converter unit according to claim 8, wherein: the voltage source converter adopts a two-level converter, a diode clamping type multi-level converter, a modularized multi-level converter MMC, a hybrid multi-level converter HMC, a two-level cascading type converter CSL or a stacking type two-level converter CTL; the modular multilevel converter MMC is a modular multilevel converter formed by half-bridge submodules, or a modular multilevel converter formed by full-bridge submodules, or a modular multilevel converter formed by mixing half-bridge submodules and full-bridge submodules.
12. The control method of a high-voltage direct-current transmission converter unit according to claim 11, wherein: the half-bridge submodule or the full-bridge submodule of the modular multilevel converter MMC is provided with a bypass switch or a thyristor, and the bypass switch or the thyristor is connected at two ends of the half-bridge submodule or the full-bridge submodule in parallel and used for bypassing the half-bridge submodule or the full-bridge submodule.
13. The control method of a high-voltage direct-current transmission converter unit according to claim 11, wherein: the half-bridge submodule of the modular multilevel converter MMC is also provided with a protection thyristor, and the protection thyristor is connected at two ends of the half-bridge submodule in parallel to protect the reverse diode of the turnoff full-control power semiconductor connected in parallel with the protection thyristor.
14. The control method of a high-voltage direct-current transmission converter unit according to claim 8, wherein: the voltage source converter is composed of a turnoff full-control type Power semiconductor, and the turnoff full-control type Power semiconductor adopts an insulated gate bipolar transistor IGBT, an integrated gate commutated thyristor IGCT, a turnoff thyristor GTO, a Power field effect transistor Power MOSFET, an electron injection enhancement gate transistor IEGT, a gate commutated thyristor GCT or a silicon carbide enhancement junction field effect transistor SiC-JFET.
15. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: each bridge arm of the current source type valve bank or the voltage source type valve bank is connected with a lightning arrester in parallel; and the direct current sides of the current source type valve bank or the voltage source type valve bank are connected with lightning arresters in parallel.
16. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: for the rectifying side, the current source type valve bank is connected with the voltage source type valve bank in series on the direct current side, so that the anode of the current source type valve bank is connected with the anode of the voltage source type valve bank, or the cathode of the current source type valve bank is connected with the cathode of the voltage source type valve bank; for the inversion side, the current source type valve bank is connected with the voltage source type valve bank in series on the direct current side, so that the cathode of the current source type valve bank is connected with the anode of the voltage source type valve bank, or the anode of the current source type valve bank is connected with the cathode of the voltage source type valve bank.
17. The control method of a hvdc transmission converter unit in accordance with claim 16, wherein: the current source type valve bank comprises a power grid converter, the anode of the current source type valve bank is the anode of the power grid converter, and the cathode of the current source type valve bank is the cathode of the power grid converter; the voltage source type valve bank comprises a voltage source converter, wherein the end of the positive electrode of the voltage source type valve bank is the end of the positive electrode of the voltage source converter, and the end of the negative electrode of the voltage source type valve bank is the end of the negative electrode of the voltage source converter.
18. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: in the first control method, when the current source valve bank detects that the difference between the direct current command value and the actual direct current exceeds the current margin, the current source valve bank is switched to control the direct current power or the direct current.
19. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: when the high-voltage direct-current transmission converter unit performs inversion operation, in the first control method and the second control method, when the current source type valve bank detects that the difference value between the direct-current command value and the actual direct-current exceeds the current margin, the current source type valve bank controls the direct-current.
20. A method of controlling a hvdc transmission converter unit in accordance with claim 18 or 19, wherein: the current margin is 0.02 times rated direct current to 0.3 times rated direct current.
21. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: the triggering angle of the current source type valve bank is the triggering angle of the grid converter, the voltage source type valve bank adjusts the voltage through the voltage source converter, and the closing angle of the current source type valve bank is the closing angle or the arc extinguishing angle of the grid converter.
22. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: the triggering angle dead zone is any value between 0 and 15 degrees, the turn-off angle dead zone is any value between 0 and 15 degrees, and the voltage dead zone is within 5% of the rated voltage of the high-voltage direct-current transmission converter unit; the reference value range of the considered trigger angle dead zone is between the reference value minus the trigger angle dead zone and the reference value plus the trigger angle dead zone, the reference value range of the considered off angle dead zone is between the reference value minus the off angle dead zone and the reference value plus the off angle dead zone, and the instruction value range of the considered voltage dead zone is between the instruction value minus the voltage dead zone and the instruction value plus the voltage dead zone.
23. A control method of a high voltage direct current transmission converter unit according to claim 1, characterized in that: and when the voltage source converter in the voltage source type valve bank is overvoltage or fails, isolating the failure by a bypass switch of the input voltage source converter.
24. The utility model provides a controlling means suitable for HVDC conversion unit which characterized in that: comprises a detection unit and a control unit, wherein:
The detection unit is used for detecting the triggering angle or the closing angle, the direct-current voltage and the direct-current of the current source type valve group; detecting direct current voltage and direct current of the voltage source type valve bank; detecting direct current voltage and direct current of a direct current electrode;
The control unit is used for controlling the direct current power or the direct current power of the current source type valve bank as an instruction value by the first control unit when the high-voltage direct current power transmission converter unit is in rectifying operation, and controlling the trigger angle reference value of the current source type valve bank to be unchanged by the voltage source type valve bank; when the high-voltage direct-current transmission converter unit performs inversion operation, a first control unit controls a cut-off angle reference value for a current source type valve bank to be unchanged, a voltage source type valve bank regulates voltage to control direct-current voltage at a rectifying side to be a command value or a command value range considering a voltage dead zone, a second control unit controls direct-current voltage at the rectifying side for the current source type valve bank to be a command value, and when the cut-off angle of the current source type valve bank exceeds the reference value range considering the cut-off angle dead zone, the voltage source type valve bank regulates voltage to enable the cut-off angle of the current source type valve bank to return to the reference value range considering the cut-off angle dead zone;
The high-voltage direct-current transmission converter unit comprises a current source type valve bank, a converter transformer without voltage regulation function, a voltage source type valve bank and a connecting transformer, wherein the current source type valve bank is connected with an alternating current system through the converter transformer without voltage regulation function, the voltage source type valve bank is connected with the alternating current system through the connecting transformer, and the current source type valve bank is connected with the voltage source type valve bank in series on the direct current side;
the voltage source type valve bank regulating voltage is used for controlling the direct current voltage at the rectifying side to be a command value or a command value range considering a voltage dead zone, the direct current voltage command value at the inverting side or the command value range considering the voltage dead zone is calculated according to the direct current voltage command value at the rectifying side or the command value range considering the voltage dead zone minus a line voltage drop, the direct current voltage command value at the inverting side or the command value range considering the voltage dead zone minus the actual voltage of the current source type valve bank at the inverting side is obtained by subtracting the actual voltage of the voltage source type valve bank at the inverting side, and the voltage source type valve bank at the inverting side is regulated to the command value; the direct current voltage of the current source type valve bank control rectifying side is a command value, the direct current voltage command value of the inverting side is calculated according to the direct current voltage command value of the rectifying side minus the line voltage drop, the actual voltage of the voltage source type valve bank of the inverting side is subtracted from the direct current voltage command value of the inverting side to obtain the direct current voltage command value of the current source type valve bank of the inverting side, and the voltage of the current source type valve bank of the inverting side is regulated to the direct current voltage command value of the current source type valve bank of the inverting side.
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