CN114123286A - Flexible voltage control method for flexible direct current system - Google Patents

Flexible voltage control method for flexible direct current system Download PDF

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Publication number
CN114123286A
CN114123286A CN202111422428.1A CN202111422428A CN114123286A CN 114123286 A CN114123286 A CN 114123286A CN 202111422428 A CN202111422428 A CN 202111422428A CN 114123286 A CN114123286 A CN 114123286A
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voltage
direct current
flexible
cmr
rate
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CN114123286B (en
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杨张斌
李钢
彭代晓
王仙荣
罗代军
蒋伟
胡宗邱
张斯翔
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NR Electric Co Ltd
China Three Gorges Construction Engineering Co Ltd
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NR Electric Co Ltd
China Three Gorges Construction Engineering Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02J2003/365—Reducing harmonics or oscillations in HVDC
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • 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)
  • Control Of Electrical Variables (AREA)

Abstract

The invention discloses a flexible voltage control method of a flexible direct current system, which properly reduces the direct current voltage of a flexible direct current transmission system when the transmission power of the direct current system is less, thereby reducing the time of primary equipment bearing high voltage and reducing the transient overvoltage tolerance of the equipment. When the transmission power of the direct current system is larger, the direct current voltage of the flexible direct current transmission system is quickly recovered to a rated value, and the full-power operation of the system is ensured. The control method of the invention combines power judgment and power prediction judgment, and can reduce the problem of frequent switching of system operation voltage caused by power fluctuation.

Description

Flexible voltage control method for flexible direct current system
Technical Field
The invention relates to a flexible direct current transmission system of a power system, in particular to a flexible voltage control method of a flexible direct current system.
Background
The large-scale long-distance new energy access system generally adopts a flexible direct system to access an alternating current power grid. However, new energy systems, especially wind energy, vary greatly with the season and period of the wind resource. In strong wind seasons, the flexible direct system delivers more power, and in weak wind seasons, there will be a longer period of time to operate in the low power delivery mode. The dc system now delivers a smaller current at the nominal voltage. Dc cables operate at high dc voltages throughout the year. Although sufficient margin is reserved for systems such as cable dc cables at the beginning of the design, a large margin means high cost. In order to prolong the service life of the dc cable and reduce the transient voltage tolerance during the fault, it is necessary to explore a flexible dc voltage control method in high power operation and low power operation, so as to dynamically adjust the dc voltage tolerance in the subsequent engineering according to the transmission characteristics of the new energy power and reduce the voltage tolerance of the cable in normal operation.
In actual engineering, the rated voltage of the flexible direct current system is fixed, and no precedent of flexible voltage operation such as voltage reduction operation exists. Different from the conventional direct current engineering that the direct current voltage can be controlled to operate only by adjusting the control angle of the thyristor, the flexible current transmission needs to meet a certain modulation ratio margin due to the control condition. Therefore, the flexible direct current transmission operates in a voltage reduction state, and the voltage reduction amplitude is not too large.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a flexible voltage control method of a flexible direct current system for reducing overvoltage and overcurrent in a transient process.
The technical scheme is as follows: the control method of the invention comprises the following steps:
when the DC transmission power is less than or equal to kp1PrExceeds at1When the DC operating voltage is kudUr；
When the DC transmission power is greater than or equal to kp2PrExceeds at2When the DC operating voltage is Ur；
Changing a direct current voltage control instruction, and adjusting the voltage of the sub-modules according to the direct current voltage according to the same ratio:
when the DC voltage of the flexible direct current system is UrThe average voltage of the sub-modules is Ucmr；
When the flexible direct current system operates, the direct current voltage is controlled by UrSwitch to kudUrThe average voltage of the submodules is measured by UcmrSwitch to kudUcmr；
When the flexible direct current system operates, the direct current voltage is controlled by kudUrIs switched to UrThe average voltage of the submodules is kudUcmrIs switched to Ucmr；
Wherein, PrRated power supply, U, for DC systemsrRating the DC operating voltage for the DC system; k is a radical ofp1,kp2,kudIs a coefficient of less than 1, kp3≥kp2≥kp1；Δt11s to 24h, delta t2Is 20ms to 24 hours.
Further, kp10.2 to 0.9, kp20.5 to 1.0, kp30.5 to 1.0, kud0.7 to 1.0.
Further, the voltage control switching strategy adopted for changing the direct current voltage control instruction is as follows:
s1, when the transmission power is larger than kp3PrAnd lasts for deltat3After the time, a full-voltage operation instruction is sent out and the voltage regulation rate is k3；
S2, when the transmission power is larger than kp2PrAnd lasts for deltat2After the time, sending a full-pressure operation instructionAnd the voltage regulation rate is k2；
S3, full-voltage operation instruction from power prediction and voltage regulation rate k2pre；
S4, when the transmission power is less than kp1PrAnd lasts for deltat1After the time, a voltage reduction operation instruction is sent out and the voltage regulation rate is k1；
S5, step-down operation instruction from power prediction, and voltage regulation rate k1pre；
The priority of the DC voltage control commands S1-S5 is from high to low, which represents an actual DC voltage regulation rate of kU when the regulated voltage rate k is applied to the DC voltage operation raterWhen applied to the sub-module to adjust the average voltage adjustment rate, it represents that the actual voltage adjustment rate of the sub-module average voltage is kUcmr(ii) a Wherein k is k1、k2、k3、k1pre,k2preAre all less than 0.05 pu/s; Δ t3Is 20ms to 24 hours.
Further, after the control system sends a voltage reduction operation instruction, if the flexible direct current system is operated at full voltage at the moment, the voltage reduction operation steps of the flexible direct current system are as follows:
s11, controlling the DC voltage command value of the system to be U by controlling the DC voltage stationrSwitch to kudUrSwitching rate of k1Or k1pre；
S12, controlling the average voltage of the sub-module by a valve to be UcmrSwitch to kudUcmrSwitching rate of k1Or k1pre。
5. The flexible voltage control method of flexible DC system according to claim 3,
after the control system sends out a full-voltage operation instruction, if the flexible direct current system is in voltage reduction operation at the moment, the full-voltage operation steps of the flexible direct current system are as follows:
s21, average voltage of the sub-module is controlled by the valve control to be kudUcmrIs switched to UcmrThe switching rate being issued in response to the instruction valueK of (a)2、k3Or k2pre；
S22, controlling the system DC voltage command value by controlling the DC voltage station from kudUrIs switched to UrThe switching rate being k given as a function of the instruction value2、k3Or k2pre。
Compared with the prior art, the invention has the following remarkable effects: 1. according to the characteristics of new energy, the direct-current voltage operation is reduced in a low-power period, the time of high voltage of direct-current equipment is shortened, the service life is prolonged, and the cost is reduced; 2. the control strategy is combined with power judgment and power prediction judgment, so that the problem of frequent switching of system operating voltage caused by power fluctuation can be reduced; 3. compared with the traditional method of directly reducing the voltage control instruction value, the method has the advantages that the direct-current running voltage is adjusted in a mode of adjusting the average voltage of the sub-modules, and more control and safety margins can be provided; 4. the invention reduces the frequency of frequent switching of the system and reduces the loss of design margin of the voltage reduction operation by simultaneously extending the modulation wave upwards and downwards.
Drawings
FIG. 1 is a schematic overall flow diagram of the present invention;
FIG. 2 is a schematic diagram illustrating comparison of control margins in different voltage regulation modes according to the present invention;
FIG. 3 is a graph of a flexible voltage adjustment according to the present invention.
Detailed Description
The invention is described in further detail below with reference to the drawings and the detailed description.
Setting the rated DC voltage of flexible DC engineering to UrThe effective value of the rated valve side line voltage is UacrModulation ratio mr：
Figure BDA0003377939850000031
In general, there is mr＝0.85～0.9。
Full pressure operation: the DC operating voltage of the flexible and straight system is rated voltage Ur；
And (3) pressure reduction operation: the DC operating voltage of the flexible and straight system is kudUr，kud<1。
FIG. 1 shows the general flow chart of the present invention when the DC power delivered is less than or equal to kp1PrExceeds at1When the DC operating voltage is kudUr；
When the DC transmission power is greater than or equal to kp2PrExceeds at2When the DC operating voltage is Ur。
Changing a direct current voltage control instruction, and adjusting the voltage of the submodule according to the direct current voltage according to the same ratio:
when the DC voltage of the flexible direct current system is UrThe average voltage of the sub-modules is Ucmr；
When the flexible direct current system operates, the direct current voltage is controlled by UrSwitch to kudUrThe average voltage of the sub-modules is also increased by UcmrSwitch to kudUcmr；
When the flexible direct current system operates, the direct current voltage is controlled by kudUrIs switched to UrThe average voltage of the sub-modules is also kudUcmrIs switched to Ucmr。
In order to realize low-voltage operation under low power and full-voltage operation under high power, simultaneously reduce switching frequency as much as possible, ensure system stability and fully utilize the predictability of new energy power, the voltage control switching strategy adopted by the invention is as follows:
s1, when the transmission power is larger than kp3PrAnd lasts for deltat3After the time, a full-voltage operation instruction is sent out and the voltage regulation rate is k3；
S2, when the transmission power is larger than kp2PrAnd lasts for deltat2After the time, a full-voltage operation instruction is sent out and the voltage regulation rate is k2；
S3, full-voltage operation instruction from power prediction and voltage regulation rate k2pre；
S4, when the transmission power is less than kp1PrAnd lasts for deltat1After the time, a voltage reduction operation instruction is sent out and the voltage regulation rate is k1；
S5, step-down operation instruction from power prediction, and voltage regulation rate k1pre。
Wherein, PrRated power supply, U, for DC systemsrRating the DC operating voltage for the DC system; k is a radical ofp10.2 to 0.9, kp20.5 to 1.0, kp30.5 to 1.0, kud0.7 to 1.0, and kp3≥kp2≥kp1；Δt11s to 24h, delta t2Is 20ms to 24h, delta t3Is 20ms to 24 hours.
The unit of the above regulation rate is a standard value/time, and the meaning is that when the rate k (k) is regulated1,k2,k3,k1pre,k2pre) When the method is applied to the running speed of the direct current voltage, the actual regulating speed of the direct current voltage is kUrWhen applied to the sub-module to adjust the average voltage adjustment rate, it represents that the actual adjustment rate of the sub-module average voltage is kUcmr。k1,k2,k3,k1pre,k2preAre all less than 0.05 pu/s.
The priority of the above switching strategies S1-S5 is from high to low.
After the control system sends a step-down operation instruction, if the flexible-straight system is in full-pressure operation at the moment, the step-down operation steps of the flexible-straight system are as follows:
s11, controlling the DC voltage command value of the DC voltage station control system to be UrSwitch to kudUrSwitching rate of k1Or k1pre；
S12, controlling the average voltage of the sub-module by UcmrSwitch to kudUcmrSwitching rate of k1Or k1pre。
After the control system sends out a full-pressure operation instruction, if the flexible and straight system is in reduced-pressure operation, the full-pressure operation steps of the flexible and straight system are as follows:
s21, the average voltage of the valve control submodule is kudUcmrIs switched to UcmrThe switching rate being k given as a function of the instruction value2、k3Or k2pre；
S22, controlling the DC voltage command value of the DC voltage station control system to be kudUrIs switched to UrThe switching rate being k given as a function of the instruction value2、k3Or k2pre。
Fig. 2 is a schematic diagram showing comparison of control margins by different voltage regulation methods. When considering the modulation ratio margin, not only the case where the modulation wave touches the top but also the case where the modulation wave touches the bottom are considered. Since harmonic waves are introduced regardless of whether the modulated wave is initially determined or bottoming, when the margin is considered, the margin with a smaller margin is used as a margin reference. And the number of the sub-modules in the actual engineering is in redundant configuration, and compared with the contact with the top, the contact with the bottom has no convolution room.
When the existing flexible direct current system normally operates, the reference wave of an upper bridge arm of a phase is set as
Figure BDA0003377939850000051
The first term "1" in the above expression is a reference wave common mode component, and the magnitude of the reference wave common mode component represents the magnitude of the direct current operating voltage; the second term "m" is the differential mode component of the reference wave, the magnitude of which represents the magnitude of the alternating voltage.
At this time, the reference wave margin is
δ0＝1-m (3)
The flexible DC system of the invention can work when the DC voltage is from UrIs reduced to kudUrIn time, if the average voltage of the sub-modules is kept unchanged and only the direct current voltage reference instruction value is adjusted, the reference wave becomes
Figure BDA0003377939850000052
At this time, the reference wave margin is
δ1＝kud-m (5)
If the direct current voltage is reduced, the average voltage of the submodules is also changed from UcmrIs reduced to kudUcmrThen the reference wave becomes
Figure BDA0003377939850000053
At this time, the reference wave margin is
Figure BDA0003377939850000054
Due to kud<1, always has delta2>δ1It follows that the method of the invention clearly provides a higher modulation ratio margin. Meanwhile, the lower average voltage of the submodules also means lower overvoltage of the converter valve when a direct current fault or a valve is short-circuited, so that the safety margin of the converter valve is improved. A comparison of control margins resulting from two different voltage regulation strategies is shown in fig. 1.
Taking a wind power output direct current system as an example:
selecting a flexible direct current project with the rated direct current voltage of 800kV, the effective value of the rated valve side line voltage of 416kV, and the modulation ratio mr＝0.85。
Full pressure operation: the direct-current operating voltage of the flexible and direct system is 800kV of rated voltage;
and (3) pressure reduction operation: the direct-current operating voltage of the flexible and straight system is 760 kV;
rated power to be delivered: 1000 MW;
mean voltage of submodule: 2 kV.
In order to realize low-voltage operation under low power and full-voltage operation under high power, simultaneously reduce switching frequency as much as possible, ensure system stability and fully utilize the predictability of new energy power, the voltage control switching strategy adopted by the invention is as follows:
1) when the transmission power is greater than 900MW and the duration time is 10s, a full-voltage operation instruction is sent out, and the voltage regulation rate is 0.05 pu/min;
2) when the transmission power is greater than 800MW and the duration time is 30min, a full-voltage operation instruction is sent out, and the voltage regulation rate is 0.01 pu/min;
3) a full-pressure operation instruction from wind power prediction is used, and the adjusting speed is 0.01 pu/min;
4) when the transmission power is less than 600MW and lasts for 1h, a voltage reduction operation instruction is sent out, and the voltage regulation rate is 0.01 pu/min;
5) the step-down operation command from the power prediction adjusts the rate to 0.01 pu/min.
The switching strategy sequence number is smaller and higher in priority, and the switching strategy sequence number is kept after the instruction is sent until the switching strategy sequence number is covered by a new instruction.
After the control system sends a step-down operation instruction, if the flexible and straight system is in full-pressure operation at the moment, the step-down operation switching steps of the flexible and straight system are as follows:
and S11, switching the direct-current voltage command value of the control system of the direct-current voltage station from 800kV to 760 k. The switching rate is 0.05pu/min, namely 40 kV/min;
and S12, switching the average voltage of the valve control sub-module from 2kV to 1.9 kV.
Since the adjustment rate attached to all the strategy voltage reduction instructions is 0.01pu/min, the average voltage switching rate of the sub-module is 0.01pu/min, namely 0.02kV/min
After the control system sends out a full-pressure operation instruction, if the flexible and straight system is in reduced-pressure operation at the moment, the full-pressure operation switching steps of the flexible and straight system are as follows:
s21, switching the average voltage of the valve control sub-module from 1.9kV to 2kV
If the adjusting rate along with the full-voltage operation instruction is 0.01pu/min, the average voltage switching rate of the sub-modules is 0.01pu/min, namely 0.02 kV/min;
if the adjusting speed along with the full-voltage operation instruction is 0.05pu/min, the average voltage switching speed of the sub-module is 0.05pu/min, namely 0.1 kV/min.
S22, switching the direct-current voltage instruction value of the control system of the direct-current voltage station from 760kV to 800kV
If the adjusting rate of the operating instruction along with the full voltage is 0.01pu/min, the switching rate of the direct-current voltage instruction value is 8 kV/min;
if the adjusting speed of the running instruction along with the full voltage is 0.05pu/min, the switching speed of the direct-current voltage instruction value is 40 kV/min.
FIG. 3 is a schematic diagram of voltage regulation under the voltage switching strategy of the present invention. And starting a pressure reduction strategy after a period of time after the power of the wind field is reduced and the pressure reduction condition is met. And starting a boosting strategy after the power rises and meets the boosting condition. The dc current is always below the rated value throughout the regulation process.
When the low-voltage operation time of the converter station has a fault, the system operation voltage and the submodule voltage are lower than the full-voltage operation voltage, so that the transient voltage and the transient current are correspondingly reduced.

Claims (5)

1. A flexible voltage control method of a flexible direct current system is characterized in that,
when the DC transmission power is less than or equal to kp1PrExceeds at1When the DC operating voltage is kudUr；
When the DC transmission power is greater than or equal to kp2PrExceeds at2When the DC operating voltage is Ur；
Changing a direct current voltage control instruction, and adjusting the voltage of the sub-modules according to the direct current voltage according to the same ratio:
when the DC voltage of the flexible direct current system is UrThe average voltage of the sub-modules is Ucmr；
When the flexible direct current system operates, the direct current voltage is controlled by UrSwitch to kudUrThe average voltage of the submodules is measured by UcmrSwitch to kudUcmr；
When the flexible direct current system operates, the direct current voltage is controlled by kudUrIs switched to UrThe average voltage of the submodules is kudUcmrIs switched to Ucmr；
Wherein, PrRated power supply, U, for DC systemsrRating the DC operating voltage for the DC system; k is a radical ofp1,kp2,kudIs a coefficient of less than 1, kp3≥kp2≥kp1；Δt11s to 24h, delta t2Is 20ms to 24 hours.
2. The flexible voltage control method of claim 1, wherein k is kp10.2 to 0.9, kp20.5 to 1.0, kp30.5 to 1.0, kud0.7 to 1.0.
3. The flexible voltage control method of the flexible DC system according to claim 1, wherein the DC voltage control command is changed by using the following voltage control switching strategy:
s1, when the transmission power is larger than kp3PrAnd lasts for deltat3After the time, a full-voltage operation instruction is sent out and the voltage regulation rate is k3；
S2, when the transmission power is larger than kp2PrAnd lasts for deltat2After the time, a full-voltage operation instruction is sent out and the voltage regulation rate is k2；
S3, full-voltage operation instruction from power prediction and voltage regulation rate k2pre；
S4, when the transmission power is less than kp1PrAnd lasts for deltat1After the time, a voltage reduction operation instruction is sent out and the voltage regulation rate is k1；
S5, step-down operation instruction from power prediction, and voltage regulation rate k1pre；
The priority of the DC voltage control commands S1-S5 is from high to low, which represents an actual DC voltage regulation rate of kU when the regulated voltage rate k is applied to the DC voltage operation raterWhen applied to the sub-module to adjust the average voltage adjustment rate, it represents that the actual voltage adjustment rate of the sub-module average voltage is kUcmr(ii) a Wherein k is k1、k2、k3、k1pre,k2preAre all less than 0.05 pu/s; Δ t3Is 20ms to 24 hours.
4. The flexible voltage control method of flexible DC system according to claim 3,
after the control system sends a voltage reduction operation instruction, if the flexible direct current system is in full voltage operation at the moment, the voltage reduction operation steps of the flexible direct current system are as follows:
s11, controlling the DC voltage command value of the system to be U by controlling the DC voltage stationrSwitch to kudUrSwitching rate of k1Or k1pre；
S12, controlling the average voltage of the sub-module by a valve to be UcmrSwitch to kudUcmrSwitching rate of k1Or k1pre。
5. The flexible voltage control method of flexible DC system according to claim 3,
after the control system sends out a full-voltage operation instruction, if the flexible direct current system is in voltage reduction operation at the moment, the full-voltage operation steps of the flexible direct current system are as follows:
s21, average voltage of the sub-module is controlled by the valve control to be kudUcmrIs switched to UcmrThe switching rate being k given as a function of the instruction value2、k3Or k2pre；
S22, controlling the system DC voltage command value by controlling the DC voltage station from kudUrIs switched to UrThe switching rate being k given as a function of the instruction value2、k3Or k2pre。
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105140948A (en) * 2015-07-06 2015-12-09 南京南瑞继保电气有限公司 Flexible direct current transmission system power coordination control method
GB201620739D0 (en) * 2016-06-13 2017-01-18 Xj Group Corp Method and apparatus for fault prediction of sub-module in flexible direct current transmission converter valve
WO2018196830A1 (en) * 2017-04-27 2018-11-01 南京南瑞继保电气有限公司 Method for initiating flexible dc transmission system under isolated island condition
CN110932304A (en) * 2019-11-08 2020-03-27 南京南瑞继保工程技术有限公司 Control system and control method for direct current energy consumption device

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105140948A (en) * 2015-07-06 2015-12-09 南京南瑞继保电气有限公司 Flexible direct current transmission system power coordination control method
GB201620739D0 (en) * 2016-06-13 2017-01-18 Xj Group Corp Method and apparatus for fault prediction of sub-module in flexible direct current transmission converter valve
WO2018196830A1 (en) * 2017-04-27 2018-11-01 南京南瑞继保电气有限公司 Method for initiating flexible dc transmission system under isolated island condition
CN110932304A (en) * 2019-11-08 2020-03-27 南京南瑞继保工程技术有限公司 Control system and control method for direct current energy consumption device

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