CN106936303B - Bridge arm circuit and method for inhibiting fault current of large-capacity MMC sub-module - Google Patents

Bridge arm circuit and method for inhibiting fault current of large-capacity MMC sub-module Download PDF

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CN106936303B
CN106936303B CN201710279403.8A CN201710279403A CN106936303B CN 106936303 B CN106936303 B CN 106936303B CN 201710279403 A CN201710279403 A CN 201710279403A CN 106936303 B CN106936303 B CN 106936303B
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bridge arm
reactor
bridge
mmc
direct current
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CN106936303A (en
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张军
吴金龙
王先为
胡丁文
李道洋
姚为正
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Xian XJ Power Electronics Technology Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • 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
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0038—Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control

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Abstract

A bridge arm circuit and a method for inhibiting fault current of a large-capacity MMC sub-module mainly aim at inhibiting the fault current of the large-capacity MMC sub-module. In the design scheme of the large-capacity MMC bridge arm, each bridge arm (phase unit) in the converter is designed as a whole, a mode of dispersing bridge arm reactors is adopted, and reactors are arranged on the direct current side and the alternating current side of each bridge arm. The total inductance value of the reactor in each bridge arm is kept unchanged, and the weight coefficient of the bridge arm reactance occupied by the AC-DC side reactance is checked according to system parameters. And each bridge arm is connected with the outside of the bridge arm at the AC side and the DC connection outlet through the reactor. The bridge arm design scheme provided by the invention can effectively reduce the fault current peak value of the sub-module and inhibit the fault current rise rate, thereby improving the utilization rate of power devices in equipment, not increasing the cost of primary equipment and having better economy.

Description

Bridge arm circuit and method for inhibiting fault current of large-capacity MMC sub-module
Technical Field
The invention belongs to the field of new energy and power engineering, relates to a converter flexible direct current transmission technology, and particularly relates to a bridge arm circuit and a method for inhibiting fault current of a large-capacity MMC sub-module.
Background
Modularized multi-level voltage source type converter (MMC) based on full-control type power electronic devices has all advantages of voltage source type converter (VSC) based on the second generation flexible direct current transmission technology, including active power and reactive power which can be independently controlled, no commutation failure exists, power can be supplied to a passive island, and the like, so that the modularized multi-level voltage source type converter has the favor of academic circles and industrial circles. Meanwhile, the MMC system also has the characteristics of lower switching frequency, small switching loss, no need of an alternating current filter bank, strong expansibility and the like, so that the MMC system can be applied to occasions with high direct current voltage and high-power transmission. Based on the advantages, future high-capacity MMC can be widely applied to the consumption and grid connection of new energy sources such as large-scale wind power, photovoltaic and energy storage, and in addition, in a direct-current multi-feed-in area, the receiving-end inverter is transformed or designed into the high-capacity MMC to be developed.
In the MMC system, the sub-modules are expensive, and the current capacity and the voltage withstanding level of the fully-controlled power electronic device are very limited under the current technical conditions, so that the adoption of a symmetrical bipolar topology is the main scheme of the current high-capacity MMC. In a symmetric bipolar MMC system, if a serious fault occurs in a converter station, overcurrent of a fully-controlled power electronic device in a submodule can be caused, and a power device can be damaged in a serious condition.
Aiming at the problem, the current industry mainly solves the problems of increasing the steady-state margin of device model selection, reducing the protection setting value in a control protection system or increasing primary equipment, but the solution has limited improvement effect on the overcurrent of the sub-module and lower device utilization rate on one hand, and increases equipment cost on the other hand, so that the economy is poor.
Disclosure of Invention
The invention aims to solve the problems in the prior art, and provides a bridge arm circuit and a method for inhibiting fault current of a large-capacity MMC sub-module, which can effectively reduce the fault current of the MMC sub-module, are simple in wiring in engineering practice, simple in implementation process, free from increasing technical cost and good in economical efficiency.
In order to achieve the purpose, the bridge arm circuit comprises a system anode and a system cathode which are symmetrically formed by two independent MMCs, wherein each MMC consists of six bridge arms, the six bridge arms are divided into three groups of bridge arms consisting of an upper bridge arm and a lower bridge arm, and the three groups of bridge arms are respectively connected with a three-phase bus at the valve side of a converter transformer at the alternating current side; the six bridge arms are converged at a direct current side to form a neutral bus and a positive bus or a negative bus; the MMC of the system anode and the system cathode are independently controlled, a lower bridge arm direct current bus or a neutral bus of the system anode MMC is correspondingly connected with an upper bridge arm direct current bus or a neutral bus of the system cathode MMC and is grounded to form a direct current side reference zero potential; and the plurality of MMC series-connected bridge arm reactors form a converter transformer valve tower bridge arm unit, and the bridge arm reactors comprise direct-current side bridge arm reactors and alternating-current side bridge arm reactors.
The MMC adopts a full-bridge type, a half-bridge type or a full-bridge-half-bridge mixed type circuit consisting of a full-control type power electronic device and a capacitor.
Inductance value L of the bridge arm reactorarmInductance L with DC side bridge arm reactorauDInductance L of AC side bridge arm reactorauASatisfy Larm＝LauD+LauA(ii) a DC side bridge arm reactor LauD＝dLarm(ii) a d is a direct current side weight coefficient of the bridge arm reactor, and the larger the direct current reactance value or the line reactance value in the direct current field is, the smaller the d value is; AC side bridge arm reactor LauA＝aLarm(ii) a and a is the weight coefficient of the alternating current side of the bridge arm reactor, and the larger the direct current reactance value or the line reactance value in the direct current field is, the larger the value of a is.
And the d value and the a value are verified according to the parameter configuration in the primary wiring system of the converter station.
And the direct current side bridge arm reactor and the alternating current side bridge arm reactor are arranged at the wire outlet ends of the MMC serial circuits.
The invention discloses a method for inhibiting fault current of a large-capacity MMC sub-module, which comprises the following steps of:
in the MMC operation process, the alternating-current phase voltage at the valve side of the converter transformer changes, and the voltage of the A-phase alternating-current bus presses uAn＝ua+0.5UdcThe offset occurs, and the voltage at the two ends of each bridge arm is Uarm＝0.5Udc-ua(ii) a In the formula uaIs a valve side voltage AC component, UdcFor each converter port voltage, uAnGrounding voltage values of each phase alternating current bus at the valve side; u shapearmThe voltage born by the two ends of the bridge arm in each converter; in the MMC operation process, the control of voltage, active and reactive targets is completed by controlling the charge-discharge process of the capacitor, and the control of the charge-discharge of the capacitor is completed by controlling the on-off and on-off of a power electronic device; when the MMC generates fault current, the fault moment bridge arm voltage is changed into UarmF＝UdcSub-module fault current in bridge armIn the formula IcShort-circuit discharge current, z, for sub-module capacitance at fault instantarmThe more submodules are put into the bridge arm at the moment of fault, z isarmThe smaller; to reduce the sub-module fault current, before the bridge arm is locked, I is reduced to the maximum extentarmF(ii) a A plurality of MMC (modular multilevel converter) series-connected bridge arm reactors form a converter transformer valve tower bridge arm unit, each bridge arm reactor comprises a direct current side bridge arm reactor and an alternating current side bridge arm reactor, and the inductance value L of each bridge arm reactorarmInductance L with DC side bridge arm reactorauDInductance L of AC side bridge arm reactorauASatisfy Larm＝LauD+LauA(ii) a The direct current side bridge arm reactor LauD＝dLarm(ii) a d is a direct current side weight coefficient of the bridge arm reactor, and the larger the direct current reactance value or the line reactance value in the direct current field is, the smaller the d value is; the AC side bridge arm reactor LauA＝aLarm(ii) a and a is the weight coefficient of the alternating current side of the bridge arm reactor, and the larger the direct current reactance value or the line reactance value in the direct current field is, the larger the value of a is.
Compared with the prior art, the invention has the following beneficial effects: each bridge arm is taken as a design unit, so that the connection mode is simple, the realization in the engineering is easy, the bridge arm reactors in each bridge arm unit are distributed, and the direct current side bridge arm reactors and the alternating current side bridge arm reactors are respectively configured on the direct current side and the alternating current side of the bridge arm, so that the fault current of the sub-modules can be effectively reduced. The inductance value of the bridge arm reactor in each bridge arm unit is consistent with the conventional design, so that primary equipment is not additionally added. The bridge arm circuit and the fault current suppression method can effectively reduce the safety margin of the power device, improve the availability of equipment, have good economy, do not provide strict requirements for a control protection system, and have high feasibility.
Compared with the prior art, the method for restraining the fault current can effectively reduce the overcurrent rise rate and the peak value of the sub-module under the working condition of serious fault, provide enough time for the protection strategy and cannot cause damage to the MMC sub-module. The method is simple to implement, has no strict requirement on a control protection system, and can effectively ensure the safety and stability of the flexible direct-current power transmission system.
Drawings
FIG. 1 is a schematic diagram of a large-capacity MMC symmetric bipolar topology;
FIG. 2 is a schematic diagram of a bridge arm circuit for suppressing sub-module fault currents in accordance with the present invention;
FIG. 3 is a schematic diagram of a valve hall layout of bridge arm reactors;
FIG. 4 is a waveform diagram of an overcurrent simulation of a valve bottom ground fault of an upper bridge arm in a conventional scheme;
FIG. 5 is a simulation waveform diagram of overcurrent of an upper bridge arm valve bottom ground fault.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Referring to fig. 1, large capacity MMC systems basically employ a symmetric bipolar topology. The positive pole and the negative pole in the symmetrical bipolar system respectively adopt two independent MMCs. Each MMC is composed of 6 bridge arms (phase units), alternating current sides of the bridge arms are respectively connected with a three-phase bus at the valve side of the converter transformer, and an upper bridge arm and a lower bridge arm are the same alternating current bus (the alternating current sides of an A-phase upper bridge arm and an A-phase lower bridge arm are both connected with an A-phase bus of the converter transformer). The direct current sides of the 6 bridge arms are converged to form a positive bus (or a negative bus) and a neutral bus. The positive pole or the negative pole MMC adopts an independent control system, and a direct current side reference zero potential is formed by connecting and grounding a lower bridge arm direct current bus (neutral bus) of the positive pole MMC and an upper bridge arm direct current bus (neutral bus) of the negative pole MMC.
In a symmetric bipolar MMC, the valve side ac phase voltage varies.
The voltage of the A-phase alternating-current bus is deviated:
uAn＝ua+0.5Udc；
thus, the voltage across each leg is:
Uarm＝0.5Udc-ua；
in the formula uaIs a valve side AC voltageAC component, UdcFor each converter port voltage, uAnGrounding voltage values of each phase alternating current bus at the valve side; u shapearmThe voltage that is assumed across the legs in each converter.
The MMC controls the voltage, active and reactive targets by controlling the charging and discharging processes of the capacitor in the submodule in the operation process of the MMC. The control of charging and discharging of the sub-module capacitor is mainly completed by controlling the on and off of the fully-controlled power electronic device. According to the MMC operation principle and the characteristics of a voltage source converter topology, when a serious fault occurs in a converter station, the MMC can generate a larger fault current. With the valve bottom and valve side bus ground faults being the most severe.
The instantaneous bridge arm voltage of the valve bottom earth fault becomes:
UarmF＝Udc；
the fault current expression of the sub-module in the bridge arm is as follows:
Figure BDA0001279158580000051
in the formula IarmFFor fault currents in sub-modules in the bridge arms, IcShort-circuit discharge current of sub-module capacitor at fault moment, the value is larger and the rising rate is faster, zarmFor the resistance value of the bridge arm at the moment of short circuit, the more submodules are put into the bridge arm at the moment of fault, zarmThe smaller. Before the bridge arm is locked, the fault current IarmFWill flow through the power electronics of the sub-module and may cause the device to crack. To suppress the fault current in the submodule, the maximum reduction I is requiredarmF。
Referring to fig. 2, each bridge arm of the MMC is a complete phase unit, each bridge arm is composed of a plurality of submodules and a bridge arm reactor which are connected in series, and the submodules are in a full-bridge type, a half-bridge type or a full-bridge-half-bridge mixed type composed of a full-control power electronic device and a capacitor. In order to suppress sub-module fault currents, each bridge arm reactor LarmThe present invention is described by taking two examples in the patent with the dispersion design, but the present solution is not limited to two dispersionsBridge arm reactor scheme.
The AC side and the DC side of each bridge arm are respectively provided with a bridge arm reactor, wherein the dispersed reactor meets the following requirements:
Larm＝LauD+LauA；
LauDis a bridge arm DC side bridge arm reactor, LauAThe total inductance value of the reactor in the bridge arm is a certain value, namely Larm。
When a serious fault in the station is a valve side alternating current bus, valve bottom position grounding or direct current side fault, a dispersion reactor is arranged in a fault current loop. The distributed reactor scheme suppresses sub-module fault currents mainly by the following two aspects of action.
1) The dispersion reactor can effectively inhibit the discharge current I of the capacitorcPeak and fault current rise rate
Figure BDA0001279158580000052
2) The distributed reactor in the fault loop increases the impedance z in the fault looparm。
Through the two functions, the bridge arm design scheme of the distributed reactance is adopted, so that the overcurrent rise rate and peak value of the submodule under the working condition of serious fault can be effectively inhibited, and enough time is provided for a protection strategy; and the sub-modules are guaranteed not to be damaged in the protection process. When the number of the dispersion reactors is more than two, the dispersion reactors can be arranged in the middle of the sub-modules according to specific working conditions, but the reactors on the direct current side and the alternating current side need to be arranged and are guaranteed to have certain inductance values.
The inductance value of the direct current side reactor is as follows:
LauD＝dLarm；
and d is a weight coefficient of the direct current side of the dispersion reactor, and the value is verified according to the system parameter configuration in the converter station. When the dc reactance value or the line reactance value in the dc field is large, the d value will be relatively small. Otherwise, the value of d may be larger.
The inductance value of the AC side reactor is as follows:
LauA＝aLarm；
wherein a is a weight coefficient on the AC side of the dispersion reactor. This value is checked against the system parameter configuration in the converter station. When the dc reactance value or the line reactance value in the dc field is large, the a value is relatively large. Otherwise, the value of a may be smaller.
Referring to fig. 3, in the implementation process of the engineering, the layout scheme of the valve hall is set by taking each bridge arm as a unit. Will disperse L of bridge arm reactorauDAnd LauAAnd the direct current wiring outlet and the alternating current wiring outlet of the valve hall are respectively positioned according to the wiring mode of the converter valve. The MMC converter valve consists of a plurality of submodules, and each bridge arm is provided with a plurality of valve towers. The wiring modes of the valve towers of the bridge arms are mutually independent, namely, the wiring mode that the valve towers are directly connected does not exist between the bridge arms. The external lines at the AC and DC sides of the bridge arms use the dispersion reactors as outlets. Since the total inductance value of the dispersion reactor is constant, no additional primary equipment is added in the valve hall.
In order to verify the scheme provided by the scheme, the same simulation model and working conditions are respectively adopted, and the conventional bridge arm scheme is compared with the bridge arm design scheme provided by the invention.
Referring to fig. 4, in a conventional bridge arm design in a symmetric bipolar system, the bridge arm reactances are arranged predominantly on the ac side of the bridge arm in a concentrated manner. The converter valves between the bridge arms are directly connected to each other on the direct current side.
After a valve bottom ground fault occurs, the current of the bridge arm submodule rapidly rises, the converter starts to be locked after the bridge arm locking protection setting value is reached, and the fault current still continues to rise in the locking process. When the locking is completed after a time delay (locking time), the bridge arm current reaches a peak value and begins to fall. In conventional bridge arm designs, the peak bridge arm current value after a fault occurs is very high, about 2.0pu, which may cause damage to the power devices and thus shutdown of the converter station. At present, aiming at the problems, the main solution is to greatly increase the operation safety margin of the device, so that the rated current of the device in steady state operation is far less than the rated current of the device, and the economy is poor. In addition, the fault current has a high rise rate, so that the control protection system has high requirements.
Referring to fig. 5, the fault process is the same as that in fig. 4, when a valve bottom ground fault occurs, the bridge arm current rapidly rises, the converter starts to be locked after reaching the bridge arm locking protection setting value, and the fault current still continues to rise in the locking process. When the locking is completed after a time delay (locking time), the bridge arm current reaches a peak value and begins to fall.
In the scheme designed by the invention, the bridge arm current rising rate is effectively inhibited due to the action of the dispersion reactor. The peak value of the bridge arm current is effectively restrained to 1.6pu, and the value can generally meet the requirement of safety and stability of the system.
After the bridge arm design scheme provided by the invention is adopted, the margin in the operation process of the bridge arm sub-modules can be relatively reduced, and the utilization rate of equipment is improved. Due to the reduced rate of rise, the requirements for controlling the protection system are not stringent. And primary equipment is not added in the implementation process of the design scheme, so that the economical efficiency is better in the actual operation of the converter station.
In the design scheme of the high-capacity MMC bridge arm, each bridge arm (phase unit) in the converter is designed as a whole, a mode of dispersing bridge arm reactors is adopted, and reactors are arranged on the direct current side and the alternating current side of each bridge arm. The total inductance value of the reactor in each bridge arm is kept unchanged, and the weight coefficient of the bridge arm reactance occupied by the AC-DC side reactance is checked according to system parameters. And each bridge arm is connected with the outside of the bridge arm at the AC side and the DC connection outlet through the reactor. The bridge arm design scheme of the invention can effectively reduce the fault current peak value of the submodule and inhibit the fault current rise rate, improves the availability of the power device in the equipment, does not increase the cost of primary equipment, does not put forward additional requirements on a secondary system, and is good in economy in engineering. The large-capacity MMC generally adopts a full-bridge submodule, a half-bridge submodule or a hybrid submodule as a basic unit for commutation. Due to the current limiting capability of the device and the characteristics of the voltage source converter, the high-voltage large-capacity MMC basically adopts a symmetrical bipolar topological structure. Faults in the converter station will cause large fault currents to the MMC and in severe cases may cause loss of components and shutdown of the converter station. The invention aims to mainly carry out suppression scheme design aiming at fault current of a high-voltage large-capacity MMC sub-module, and is used for making up the technical defects at present and effectively solving the problem.
The above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the same, and the actions of various conventional modifications or changes of the present invention by referring to the above embodiments after reading the patent application document by those skilled in the art are also considered to fall within the protection scope of the claims of the present patent application.

Claims (6)

1. The utility model provides a restrain bridge arm circuit of large capacity MMC submodule piece fault current which characterized in that: the system comprises a system anode and a system cathode which are symmetrically composed of two independent MMCs, wherein each MMC consists of six bridge arms, the six bridge arms are divided into three groups of bridge arms composed of an upper bridge arm and a lower bridge arm, and the three groups of bridge arms are respectively connected with a three-phase bus at the valve side of a converter transformer at the alternating current side; the six bridge arms are converged at a direct current side to form a neutral bus and a positive bus or a negative bus; the MMC of the system anode and the system cathode are independently controlled, a lower bridge arm direct current bus or a neutral bus of the system anode MMC is correspondingly connected with an upper bridge arm direct current bus or a neutral bus of the system cathode MMC and is grounded to form a direct current side reference zero potential; the converter transformer valve tower bridge arm unit is formed by connecting a plurality of MMC (modular multilevel converter) bridge arm reactors in series, wherein each bridge arm reactor comprises a direct current side bridge arm reactor and an alternating current side bridge arm reactor;
the bridge arm reactors in each bridge arm unit are distributed, and a direct current side bridge arm reactor and an alternating current side bridge arm reactor are respectively configured on the direct current side and the alternating current side of the bridge arm; on one hand, bridge arm reactor is used for inhibiting discharge current I of capacitorcPeak and fault current rise rate
Figure FDA0002035182330000011
On the other hand, the bridge arm reactors increase the impedance z in the fault looparm。
2. The bridge arm circuit for suppressing the fault current of the large-capacity MMC sub-module according to claim 1, characterized in that: the MMC adopts a full-bridge type, a half-bridge type or a full-bridge-half-bridge mixed type circuit consisting of a full-control type power electronic device and a capacitor.
3. The bridge arm circuit for suppressing the fault current of the large-capacity MMC sub-module according to claim 1, characterized in that: inductance value L of the bridge arm reactorarmInductance L with DC side bridge arm reactorauDInductance L of AC side bridge arm reactorauASatisfy Larm＝LauD+LauA(ii) a DC side bridge arm reactor LauD＝dLarm(ii) a d is a direct current side weight coefficient of the bridge arm reactor, and the larger the direct current reactance value or the line reactance value in the direct current field is, the smaller the d value is; AC side bridge arm reactor LauA＝aLarm(ii) a and a is the weight coefficient of the alternating current side of the bridge arm reactor, and the larger the direct current reactance value or the line reactance value in the direct current field is, the larger the value of a is.
4. The bridge arm circuit for suppressing the fault current of the large-capacity MMC sub-module according to claim 3, characterized in that: and the d value and the a value are verified according to the parameter configuration in the primary wiring system of the converter station.
5. The bridge arm circuit for suppressing the fault current of the large-capacity MMC sub-module according to claim 1 or 3, characterized in that: and the direct current side bridge arm reactor and the alternating current side bridge arm reactor are arranged at the wire outlet ends of the MMC serial circuits.
6. A method for suppressing a bridge arm circuit for suppressing a fault current of a large-capacity MMC submodule according to claim 1, comprising: in the MMC operation process, the AC phase voltage at the valve side of the converter transformer occursVariation, A-phase AC bus voltage pressing uAn＝ua+0.5UdcThe offset occurs, and the voltage at the two ends of each bridge arm is Uarm＝0.5Udc-ua(ii) a In the formula uaIs a valve side voltage AC component, UdcFor each converter port voltage, uAnGrounding voltage values of each phase alternating current bus at the valve side; u shapearmThe voltage born by the two ends of the bridge arm in each converter; in the MMC operation process, the control of voltage, active and reactive targets is completed by controlling the charge-discharge process of the capacitor, and the control of the charge-discharge of the capacitor is completed by controlling the on-off and on-off of a power electronic device; when the MMC generates fault current, the fault moment bridge arm voltage is changed into UarmF＝UdcSub-module fault current in bridge arm
Figure FDA0002035182330000021
In the formula IcShort-circuit discharge current, z, for sub-module capacitance at fault instantarmThe more submodules are put into the bridge arm at the moment of fault, z isarmThe smaller; to reduce the sub-module fault current, before the bridge arm is locked, I is reduced to the maximum extentarmF(ii) a A plurality of MMC (modular multilevel converter) series-connected bridge arm reactors form a converter transformer valve tower bridge arm unit, each bridge arm reactor comprises a direct current side bridge arm reactor and an alternating current side bridge arm reactor, and the inductance value L of each bridge arm reactorarmInductance L with DC side bridge arm reactorauDInductance L of AC side bridge arm reactorauASatisfy Larm＝LauD+LauA(ii) a The direct current side bridge arm reactor LauD＝dLarm(ii) a d is a direct current side weight coefficient of the bridge arm reactor, and the larger the direct current reactance value or the line reactance value in the direct current field is, the smaller the d value is; the AC side bridge arm reactor LauA＝aLarm(ii) a and a is the weight coefficient of the alternating current side of the bridge arm reactor, and the larger the direct current reactance value or the line reactance value in the direct current field is, the larger the value of a is.
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CN107968413B (en) * 2017-11-06 2019-12-03 东南大学 A kind of THE UPFC structure having failure current limit ability
CN109302058A (en) * 2018-10-11 2019-02-01 昆明理工大学 A kind of direct current-direct current Modular multilevel converter and its control method with the output of three level of class
CN111181186B (en) * 2018-11-09 2024-03-15 许继电气股份有限公司 Modularized multi-level hybrid topology valve tower for flexible direct-current transmission
CN113489360A (en) * 2021-08-16 2021-10-08 华北电力大学 Energy storage type MMC accurate analysis modeling method based on modal division

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CN102938560A (en) * 2012-10-19 2013-02-20 浙江大学 Direct-current converter station based on bipolar structure
CN103117666A (en) * 2013-02-26 2013-05-22 南京南瑞继保电气有限公司 Flexible direct current (DC) transmission bipolar topological structure based on modular multi-level converter

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CN102938560A (en) * 2012-10-19 2013-02-20 浙江大学 Direct-current converter station based on bipolar structure
CN103117666A (en) * 2013-02-26 2013-05-22 南京南瑞继保电气有限公司 Flexible direct current (DC) transmission bipolar topological structure based on modular multi-level converter

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