CN110011283B - Direct-current power distribution system fault isolation method based on improved half-bridge submodule - Google Patents
Direct-current power distribution system fault isolation method based on improved half-bridge submodule Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
- H02H7/262—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of switching or blocking orders
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations
- H02H7/263—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured involving signal transmission between at least two stations involving transmissions of measured values
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- 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]
Abstract
The invention relates to a fault isolation method of a direct current distribution system based on an improved half-bridge submodule, which adopts the following structure: an anti-parallel structure composed of an IGBT VT1 and a diode VD1 is connected in series with a sub-module capacitor C, and then is connected in parallel with an anti-parallel structure composed of a reverse resistance type IGBT VT2 and a thyristor T2, an emitter of the VT1 is connected with a collector of the VT2, and a collector and an emitter of the VT2 are respectively connected with an input end and an output end of the sub-module; the fault isolation method comprises the following steps: when the protection system detects that a direct current side fault or any bridge arm of the MMC has an overcurrent, a fault signal is immediately sent to the control system; and after the control system receives the fault signal, all the IGBTs are immediately turned off.
Description
Technical Field
The invention relates to the fields of power electronics, relay protection, flexible direct current power distribution networks and the like, in particular to an improved half-bridge submodule structure and a direct current fault isolation and system recovery strategy based on the improved submodule.
Background
The obvious changes in the aspects of energy structures, grid structures and load types of the power system bring certain challenges to the existing power distribution system, and the large access of distributed power supplies enables a centralized power supply form to be changed to a multi-source multi-direction distributed structure; the power load is increasing day by day, and the requirement to electric energy quality, power supply reliability and electric energy diversification is increasing more and more. With the development of power electronic semiconductor devices and modern control, direct current transmission and distribution are receiving more and more extensive attention in the industry. The Modular Multilevel Converter (MMC) has been widely applied to the field of flexible direct-current transmission due to superior performances of good electric energy quality, high reliability and the like, and has good application prospect in the field of medium-voltage direct-current distribution.
However, a fault of a dc system (especially a two-pole short circuit fault) has the characteristics of large fault current, rapid fault development, wide fault influence range, and the like, and thus becomes a technical difficulty influencing the development and application of dc power transmission and distribution. To solve the problem, scholars at home and abroad propose various solutions, which can be classified into the following three categories according to a direct current fault isolation mode:
1) the ac side system is used to isolate fault points, mainly including single-thyristor method and double-thyristor method. The method has the advantages of low cost, no additional loss and wide application in engineering practice. Although the fault isolation methods in the methods are different, the fault current clearing is naturally attenuated by a fault loop, and the fault clearing time is longer;
2) a dc breaker is utilized. The hybrid direct-current circuit breaker can isolate direct-current faults within 5ms at the fastest speed, and the all-solid-state direct-current circuit breaker can isolate direct-current faults within 1ms at the fastest speed, and can complete fault current clearing quickly. However, the dc circuit breaker is expensive and has a large loss, and needs to be matched with a current limiting device;
3) sub-modules with fault isolation capability are utilized. Since the full-bridge submodule is proposed, a plurality of submodules with fault isolation capability are proposed in sequence, such as a clamping bimodule, a series bimodule and the like. After the fault, the IGBT is locked, so that the bridge arm capacitors are reversely connected in series to the fault loop, the fault can be quickly isolated, and the fault current can be eliminated. However, sub-modules with fault isolation capability are costly and have large operating losses;
in summary, the existing fault isolation method for the direct current transmission and distribution system generally has the contradiction between the fault isolation speed and the economical efficiency and loss. In view of the current situation, an improved half-bridge sub-module structure with fast fault isolation and system recovery capability is provided, and a system fault isolation method based on the sub-module structure is designed.
Disclosure of Invention
Aiming at the problem that the existing direct current fault isolation method cannot realize the balance of fault isolation speed, economy and loss, the current transformer investment cost is reduced and the system operation loss is reduced while the direct current system is rapidly fault isolated, the improved half-bridge submodule structure with rapid fault isolation and restart capability is provided, the investment cost and the operation loss can be effectively reduced, and the direct current distribution system fault isolation method is based on the improved half-bridge submodule structure. The technical scheme is as follows:
a fault isolation method for a direct current power distribution system based on an improved half-bridge submodule adopts the following structure: the reverse parallel structure composed of an IGBT VT1 and a diode VD1 is connected with a sub-module capacitor C in series, and then is connected with a reverse parallel structure composed of an IGBT VT2 and a thyristor T2 in parallel, an emitter of the VT1 is connected with a collector of the VT2, and a collector and an emitter of the VT2 are respectively connected with an input end and an output end of the sub-module, and the reverse parallel structure is characterized in that the IGBT VT2 adopts an IGBT with a reverse resistance function, namely an RB-IGBT, or adopts a mode of connecting the IGBT and a diode in series in the same direction; after a fault occurs, the improved sub-module sends a turn-off command to the sub-module to turn off all IGBTs and cancel the turn-on signals of the thyristors, so that the bridge arm can be turned off when the current of the bridge arm crosses zero, and meanwhile, the reverse voltage blocking function can be realized; according to different system states, the improved half-bridge submodule has three working modes: (1) under the normal operation state of the system, the system continuously sends a conduction signal to the submodule thyristor; (2) after a direct current side fault occurs, once the fault is detected, a locking signal is immediately sent to the submodule, the submodule IGBT is immediately locked, a submodule capacitor discharge channel is cut off, at the moment, only the thyristor T2 in the submodule is conducted, and the converter is equivalent to a power grid commutation converter LCC; (3) in a system reclosing stage, a conducting signal is sent to all thyristors, at the moment, the bridge arm IGBT is still in a turn-off state, and the converter is equivalent to a six-pulse wave uncontrolled rectifier converter; the fault isolation method comprises the following steps: when the protection system detects that a direct current side fault or any bridge arm of the MMC has an overcurrent, a fault signal is immediately sent to the control system; after the control system receives the fault signal, all the IGBTs are immediately turned off, and at the moment, a sub-module capacitor discharge path is blocked; after short time delay, the conduction signal of the thyristor T2 is cancelled after the fault current is transferred from the submodule capacitor branch circuit to the thyristor branch circuit; then, bridge arm current is equivalent to two parts of alternating current side current feedback and naturally attenuated direct current fault current components, alternating current side current feedback and direct current fault current components are overlapped to cause bridge arm current of the sub-modules to sequentially zero, and once the bridge arm current zero-crosses, the bridge arm is immediately switched off; and finally, all bridge arms of the MMC are switched off, so that the self-clearing of the direct current fault current and the isolation of fault points are realized.
The fault isolation strategy based on the improved half-bridge submodule MMC is suitable for a flexible direct-current power distribution network, in particular to a medium-low voltage direct-current power distribution network. Compared with a single thyristor method, a method for breaking current by using a direct current breaker and a method for utilizing a submodule with fault self-clearing capability, the method realizes the balance between the fault isolation speed and the economy and the loss, and is beneficial to the quick restart of the system. The method has the following advantages:
1) when the modular multilevel converter is in normal operation, the improved half-bridge submodule has the same working mode as the half-bridge submodule, and the MMC operation control method based on the half-bridge submodule can be directly applied to an MMC based on the improved half-bridge submodule;
2) compared with a half-bridge submodule, the improved half-bridge submodule only increases the investment of one thyristor, has great advantages in the aspects of investment cost and operation loss, and can further reduce the operation loss of the converter by adopting the IGBT with the reverse resistance function;
3) the direct-current side fault of the direct-current power distribution network can be quickly isolated within 20ms, and the isolation speed is high;
4) due to the fault current clearing period, the alternating current side can continuously feed current to the fault point, and time is provided for fault location and distance measurement.
Drawings
FIG. 1 shows an improved half-bridge sub-module configuration proposed by the present invention
FIG. 2 shows a flow chart of DC side fault isolation and system reclosing based on the improved half-bridge sub-module MMC provided by the invention
FIG. 3 shows a schematic diagram of a direct-current side two-pole short-circuit fault and a schematic diagram of a fault circulation path based on an improved half-bridge submodule MMC of the invention
Fig. 4 shows the dc-side two-pole short-circuit fault isolation process based on the improved half-bridge sub-module MMC of the present invention, where (a) is the dc line fault current; graph (b) is a graph of bridge arm current during fault isolation; fig. c is a diagram of the ac-side power supply voltage.
Fig. 5 shows a schematic diagram of a fault current path in the MMC direct-current side two-pole short-circuit fault isolation process of the present invention.
FIG. 6 shows t of the present invention0～t1The bridge arm current is equivalent in the period.
Fig. 7 shows the dc line fault current signature during reclosing of the improved half-bridge submodule based system of the present invention, illustrating (a) the current path of the two pole short fault reclosing process; graph (b) current path for single pole ground fault reclosing process.
Detailed Description
The invention provides an improved half-bridge submodule structure with direct-current side fault self-clearing capability and quick reclosing capability, which mainly has the following characteristics:
the submodule structure is similar to a half-bridge submodule structure, wherein a group of anti-parallel structures consisting of an IGBT VT1 and a diode VD1 are connected in series with a submodule capacitor C, the branch is connected in parallel with an anti-parallel structure consisting of a reverse resistance type IGBT VT2 and a thyristor T2, an emitter of the VT1 is connected with a collector of the VT2, and a collector and an emitter of the VT2 are respectively connected with an input end and an output end of the submodule. Rated voltage withstanding values of all power electronic devices of the improved sub-module are UCNWherein U isCNIs the sub-module capacitance voltage rating.
The improved submodule is characterized in that VT1 and VD1 are the same as a half-bridge submodule, and VT2 adopts an IGBT with a Reverse resistance function, namely a Reverse-Blocking IGBT (RB-IGBT), or adopts a structure with a Reverse voltage Blocking function, for example, the IGBT and a diode are connected in series in the same direction; while T2 uses thyristors to replace the diodes in the half-bridge submodules. Therefore, after the fault occurs, the improved sub-module sends a turn-off command to the sub-module to turn off all the IGBTs and cancel the turn-on signal of the thyristor, and the turn-off of the bridge arm can be realized when the current of the bridge arm crosses zero. Meanwhile, due to the adoption of a reverse resistance type structure, the improved sub-module can realize a reverse voltage blocking function, namely, after the fault current is clear, the current feed of an alternating current power supply to a fault point can be blocked.
MMC based on improved half-bridge submodule has three operating states: normal operation state, fault clearing state and system reclosing state. During normal operation, the thyristor in the improved half-bridge submodule is continuously in a conducting state to replace the function of a freewheeling diode in the half-bridge submodule, so that the working mode of the improved half-bridge submodule is the same as that of the half-bridge submodule in the normal operation state; after receiving the fault signal, the MMC immediately sends a locking signal to all the IGBTs, simultaneously cancels the conduction signal of the thyristor, and switches the submodule to a fault clearing state; and in a reclosing stage of the system, the MMC sends a conducting signal to all thyristors, so that the MMC works in a six-pulse-wave uncontrolled rectification mode.
Based on this improved generation submodule piece, MMC can realize direct current fault's quick isolation and the system restart recovery fast:
the method comprises the following steps of quickly isolating the direct current fault: after the MMC is switched to a fault clearing state, the IGBT immediately occurs, and a discharging loop of the bridge arm submodule capacitor is cut off; at this time, the MMC bridge arm current can be equivalent to the feed current of an ac power supply and the attenuated dc component of the dc fault current, and since the dc component of the fault current at the initial stage is greater than the ac side feed current, and the thyristor does not have the self-turn-off capability, the six bridge arms of the MMC are all in the on state. And because the clamping action of the voltage of the bridge arm capacitor is not used, the current fed from the alternating current side is gradually increased. Alternating current side current feeding and attenuation direct current components are superposed to cause bridge arm current to sequentially pass zero. When the bridge arm current passes through zero, the bridge arm thyristor is locked, and the bridge arm passage is cut off. When all bridge arms are turned off, the MMC finishes clearing and fault isolation of direct-current fault current.
The quick restart of the system comprises the following specific processes: after the MMC is switched to a reclosing state, fault type judgment can be carried out according to the current and voltage characteristics of a direct-current line. For a permanent two-pole short circuit fault, once the converter is switched to a reclosing state, the alternating current side immediately feeds current to a fault point through the thyristor in a working mode of the six-pulse-wave uncontrolled rectifier, at the moment, a direct current side circuit generates huge direct current again, after a conduction signal of the thyristor is cancelled, bridge arm currents are sequentially turned off, and the direct current line current is cleared, and the process is the same as the direct current fault isolation process; for a permanent single-pole grounding fault, if the AC side transformer adopts a DYN connection method, the AC side feeds current to a fault point through an MMC single-side bridge arm, and a current feeding loop is a transformer grounding point → an MMC bridge arm → a direct current line → a fault grounding point. For transient faults, when the MMC is switched to a reclosing state, the voltage of a direct current line can be immediately established, meanwhile, line distributed capacitance charging current can be generated in the line, but the current value is relatively small, and the charging time is short. The nature of the direct current fault can be judged according to the characteristics of the line current and the line voltage. If the fault is a permanent fault, a conduction signal of the thyristor is cancelled, and after finishing current clearing of the direct current line and line dissociation removal, a quick isolating switch is adopted to isolate a fault point, so that the system can be restarted; if the fault is a transient fault, the system can be restarted immediately.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings.
Fig. 1 shows an improved half-bridge sub-module topology. The thyristor has the advantages of high reliability, high voltage resistance, inrush current resistance and the like. A thyristor is used for replacing a freewheeling diode in a half-bridge submodule, and an IGBT branch circuit connected in parallel is improved to enable the thyristor to have a reverse resistance function. Therefore, when the bridge arm current crosses zero, the MMC bridge arm can be smoothly turned off, and the current feed of the AC side power supply is simultaneously blocked. The improved half-bridge submodule structure provided by the invention has two structures, and the difference is mainly embodied in the structure of a fully-controlled branch circuit with a reverse resistance function. As shown in fig. 1(a), the circuit has a reverse resistance function by connecting an IGBT and a diode in series; as shown in fig. 1(b), Reverse Blocking IGBTs (RB-IGBTs) are used, which not only can make the sub-module have a Reverse Blocking function, but also can reduce the operation loss.
Fig. 2 is a flow chart of fault isolation and system restart based on modified HBSM-MMC. And in a normal working state, the thyristor is continuously sent with a conducting signal, and the action of the thyristor on the freewheeling diode in the half-bridge submodule is the same. Therefore, under the normal working state, the working principle of the improved half-bridge sub-module is the same as that of the half-bridge sub-module.
Once the protection system detects a fault, the control system immediately sends out locking signals to all IGBTs, and after the sub-module locking dead zone, the conduction signals of the thyristors are immediately cancelled. Because the thyristor does not have the autonomous turn-off capability, at the moment, the fault current carries out follow current through the bridge arm thyristor, and meanwhile, the alternating current side system rapidly increases the current to the fault point. And the superposition of AC side current feed and DC fault current leads to the sequential turn-off of the MMC bridge arm until the DC fault current is eliminated.
After the fault current is cleared, the fault loop is subjected to tour through a period of time delay, and then the fault reclosing operation can be performed. And sending a conduction signal to all thyristors of the MMC, and removing the conduction signal after a period of time. The MMC in the stage can be equivalent to a six-pulse uncontrolled rectification converter, and whether the fault is a permanent fault can be judged by detecting the current characteristics of the line. If the fault is a permanent fault, after a period of time delay, the quick isolating switch is opened to isolate the fault line, and then the system health part can be restarted. If the fault is a transient fault, the MMC restart operation may be immediately performed.
Fig. 3 is a schematic diagram illustrating a two-pole short-circuit fault on the dc side of the MMC. The direct-current side two-pole short-circuit fault is the most serious fault of a direct-current system, and therefore, a fault isolation process is explained by taking the two-pole short-circuit fault as an example. In the following analysis, the upper and lower arms are denoted by the letters p and n, respectively. The pa leg represents the a-phase upper leg, ipaAnd (4) representing the fault current of the bridge arm on the phase a, and so on.
Fig. 4 is a diagram showing a fault current at a dc side, a bridge arm current and an ac power supply voltage in a dc side two-pole short-circuit fault isolation process based on an improved half-bridge sub-module MMC. The dc fault isolation process can be divided into three phases according to fig. 4.
Fig. 5 is a schematic diagram of a fault current path in the MMC dc-side two-pole short-circuit fault isolation process. According to fig. 4 and 5, taking the two-pole short-circuit fault shown in fig. 3 as an example, the dc-side fault isolation process is specifically as follows:
stage 1: t is t0～t1Bridge arm submodule capacitor discharge stage
As shown in fig. 4(a), when a short-circuit fault occurs between the two poles on the dc side, the impedance between the two poles on the dc side is suddenly changedAnd the voltage on the direct current side is reduced to generate sudden change. Therefore, the capacitor in the on state is immediately discharged to the fault point, and the direct current fault current is rapidly increased. Therefore, the main source of the fault current is the bridge arm submodule discharge. And after the protection system detects the fault, immediately sending a fault signal to the MMC control system. And after receiving the fault signal, the control system immediately sends a locking signal to the bridge arm submodule and cancels the conduction control signal of the thyristor after delaying to leave the dead zone. After receiving the locking signal, the MMC bridge arm IGBT is at t1Latch-up occurs at all times.
And (2) stage: t is t1～t5MMC bridge arm alternate closing phase
And after the IGBT is locked, the sub-module capacitor discharge loop is cut off. At this time, because the direct current component of the fault current is greater than the alternating current side feed current, and the thyristor does not have the autonomous turn-off capability, the six bridge arms of the MMC are all in a conducting state. t is t0～t1Meanwhile, the fault current path is as shown in fig. 5 (a). According to the superposition principle, the bridge arm current in the section can be equivalent to the superposition of the alternating current side current and the bridge arm fault current component, as shown in fig. 6.
Without the clamping effect of the bridge arm capacitor voltage, the AC side feed current begins to increase. When the bridge arm current passes through zero, the bridge arm thyristor is locked, and the bridge arm is turned off. As shown in FIG. 4(c), t1The amplitude of the phase voltage of the power supply c on the AC side is larger at the moment, so that the current feed is rapidly increased, and the nc bridge arm is caused to be at t2The moment is rapidly turned off, and the fault current path after the time is as shown in fig. 5 (b). Then pb bridge arm at t3The time is off and the fault current path is as shown in fig. 5 (c).
Then, the phase a feeds to the phase b through the arm na and the arm nb, and the phase c feeds to the phase a through the arm pc and the arm pa, resulting in that the phase ipaAnd inaAre all reduced. Meanwhile, phase c feeds a current to phase b through the fault point, resulting in an increase in the dc-side fault current, as shown in fig. 5 (a). i.e. inaAt t4The moment is zero-crossing first, and the na bridge arm is switched off.
When the na bridge arm is turned off, the fault current path is as shown in FIG. 5 (d)) As shown. When the phase a is the same as the phase c, the current is fed to the phase b through a fault point, and simultaneously, the voltage difference between the phase a and the phase c is reduced. Therefore, the a-phase upper arm current and the fault current rapidly increase. When u isa>ucWhen u is turned onacForce ipcDecrease rapidly at t5Time ipcZero crossing, the pc bridge arm is turned off.
So far, the nc, pb, na and pc bridge arms are all turned off.
And (3) stage: t is t5～t6Stage of clearing fault current on DC side
In this stage, the fault current path is as shown in fig. 5 (e). As shown in FIG. 4(c), t5Time uab>0, therefore, phase a feeds phase b through the pa leg, the fault point, and the nb leg. Resulting in a continued increase in the dc side fault current. When u isab<At 0, the fault current is rapidly reduced to zero due to the reversal of the fault current with the phase-to-phase voltage. When the fault current passes through zero, the pa bridge arm and the nb bridge arm are turned off. To this end, the MMC achieves self-clearing of the dc side fault current.
Fig. 7 shows the dc line fault current signature during reclosing of the system based on the improved half-bridge submodule of the present invention, where (a) is the current path during reclosing for a permanent bipolar short circuit fault and the potential feed path during reclosing for a transient fault; and (b) is a current path of a permanent single-machine ground fault in the reclosing process and a potential feed path in the transient fault reclosing process. For the two-pole short circuit fault, if the fault is a permanent fault, after the reclosing operation, the alternating current power supply immediately feeds current to the fault point through the conducted thyristor, and the current feeding path is shown as a current path (i) in fig. 7 (a). In the case of a single-machine ground fault, if the fault is a permanent fault, after the reclosing operation, the current path of the ac power supply is as shown in (b) of fig. 7. Therefore, for a permanent fault, the ac power will feed the fault point, which is represented by a larger dc current on the dc line.
For an MMC with an active system on the ac side of the receiving end, if the fault is a transient fault, a potential current path of the ac side power supply is as shown in a current path (c) of fig. 7. At this time, if the bridge arm submodule capacitors satisfy the following relationship, no current will appear in the dc line.
Namely, it is
In the formula up1And up2Respectively representing the amplitude of the AC side power supply voltage of the MMC1 and the MMC 1; n represents the number of MMC single bridge arm sub-modules; u shapeCRepresenting the mean voltage of the sub-module capacitor, UCNRepresenting the rated voltage of the sub-module capacitor; m1And M2The modulation ratios of MMC1 and MMC2 are shown, respectively.
For the MMC with a passive system on the alternating current side of the receiving end, the potential current-feeding path is similar to the current path (ii) in fig. 7(a), and the difference is that the alternating current side of the MMC has no function of an alternating current system. At this time, only the following formula needs to be satisfied, and no current feeding will occur in the direct current line.
Obviously, the bridge arm sub-module capacitance will satisfy this condition.
In fact, after the direct current system breaks down, the protection system can complete fault diagnosis and communication in a short time (which can be completed within 1 ms), and the capacitor discharge depth of the bridge arm sub-module is limited. In addition, MMCs typically provide some redundancy. Thus, no current feed occurs in the dc line.
It should be noted that, due to the effect of the line capacitor at the initial stage of reclosing, even if the fault is a transient fault, the charging current is generated on the dc line, and the charging of the line capacitor can be generally completed within 2 ms. Therefore, this charging phase needs to be avoided upon fault type identification. In the present invention, in order to accurately identify the type of fault, it is suggested to set the reclosing time to 10ms or more.
And after the fault identification is finished, corresponding operation is carried out according to the fault type, and then the system restarting operation can be carried out.
The invention relates to a direct current power distribution system fault isolation and system recovery strategy based on an improved half-bridge submodule. The improved half-bridge submodule is mainly characterized in that an IGBT and a diode of a capacitor parallel branch in the half-bridge submodule are improved, a thyristor is used for replacing a freewheeling diode in the branch, and meanwhile, the IGBT with a reverse resistance function or a structure with the reverse resistance function is used for replacing the IGBT in the branch. Therefore, the half-bridge sub-module has the direct-current fault self-clearing capability and the quick system restarting function. Under the normal operation state of the system, the control mode of the improved half-bridge type MMC is the same as that of the half-bridge type MMC; when a direct current side fault is detected, a blocking signal is immediately sent to the MMC, the conducting signal of the pin-withdrawing thyristor is delayed, then each bridge arm is sequentially turned off by utilizing the characteristic of alternating current side current feeding, and finally the elimination of direct current fault current is realized; and in the system restarting stage, sending a conducting signal to all thyristors, quickly identifying whether the fault is a permanent fault or not by utilizing the current and voltage characteristics of a direct-current side line, and quickly restarting the system according to the fault property. The invention balances the conflict between the fault isolation speed and the investment and the loss of the flexible direct current system based on the MMC, is beneficial to the quick restart of the system and improves the power supply reliability of the system.
Claims (1)
1. A fault isolation method for a direct current power distribution system based on an improved half-bridge submodule adopts the following structure: the reverse parallel structure composed of an IGBT VT1 and a diode VD1 is connected with a sub-module capacitor C in series, and then is connected with a reverse parallel structure composed of an IGBT VT2 and a thyristor T2 in parallel, an emitter of the VT1 is connected with a collector of the VT2, and a collector and an emitter of the VT2 are respectively connected with an input end and an output end of the sub-module, and the reverse parallel structure is characterized in that the IGBT VT2 adopts an IGBT with a reverse resistance function, namely an RB-IGBT, or adopts a mode of connecting the IGBT and a diode in series in the same direction; after a fault occurs, all IGBTs are turned off by sending a turn-off command to the submodule, and a turn-on signal of the thyristor is cancelled, so that the bridge arm can be turned off when the current of the bridge arm crosses zero, and meanwhile, the reverse voltage blocking function can be realized; according to different system states, the improved half-bridge submodule has three working modes: (1) under the normal operation state of the system, the system continuously sends a conduction signal to the submodule thyristor; (2) after a direct current side fault occurs, once the fault is detected, a locking signal is immediately sent to the submodule, the submodule IGBT is immediately locked, a submodule capacitor discharge channel is cut off, at the moment, only the thyristor T2 in the submodule is conducted, and the converter is equivalent to a power grid commutation converter LCC; (3) in a system reclosing stage, a conducting signal is sent to all thyristors, at the moment, the bridge arm IGBT is still in a turn-off state, and the converter is equivalent to a six-pulse wave uncontrolled rectifier converter; the fault isolation method comprises the following steps: when the protection system detects that a direct current side fault or any bridge arm of the MMC has an overcurrent, a fault signal is immediately sent to the control system; after the control system receives the fault signal, all the IGBTs are immediately turned off, and at the moment, a sub-module capacitor discharge path is blocked; after short time delay, the conduction signal of the thyristor T2 is cancelled after the fault current is transferred from the submodule capacitor branch circuit to the thyristor branch circuit; then, bridge arm current is equivalent to two parts of alternating current side current feedback and naturally attenuated direct current fault current components, alternating current side current feedback and direct current fault current components are overlapped to cause bridge arm current of the sub-modules to sequentially zero, and once the bridge arm current zero-crosses, the bridge arm is immediately switched off; and finally, all bridge arms of the MMC are switched off, so that the self-clearing of the direct current fault current and the isolation of fault points are realized.
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| CN110995038A (en) * | 2019-11-21 | 2020-04-10 | 中国电力科学研究院有限公司 | MMC (modular multilevel converter) and DC fault isolation method and system based on MMC |
| CN110994974B (en) * | 2019-11-25 | 2020-11-20 | 上海交通大学 | Low-loss modular multi-level direct current-direct current converter and submodule thereof |
| CN113131770A (en) * | 2021-05-27 | 2021-07-16 | 天津大学 | Two-level voltage source type converter device with fault self-clearing capability |
| CN115808646B (en) * | 2023-01-17 | 2023-05-02 | 国网山西省电力公司电力科学研究院 | Flexible direct current system line fault property identification method based on improved half-bridge MMC |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3001552A1 (en) * | 2014-09-23 | 2016-03-30 | Alstom Technology Ltd | Voltage source converter and control thereof |
| CN107370393A (en) * | 2017-06-29 | 2017-11-21 | 全球能源互联网研究院 | A kind of Modularized multi-level converter sub-module topological structure and its guard method |
| CN108448542A (en) * | 2018-02-07 | 2018-08-24 | 许继集团有限公司 | Sub-modular structure with alternating current-direct current fault clearance ability and MMC topological structures |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104767185B (en) * | 2015-03-20 | 2017-07-21 | 浙江大学 | A kind of current conversion station and its control method with DC Line Fault Scavenging activity |
-
2019
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP3001552A1 (en) * | 2014-09-23 | 2016-03-30 | Alstom Technology Ltd | Voltage source converter and control thereof |
| CN107370393A (en) * | 2017-06-29 | 2017-11-21 | 全球能源互联网研究院 | A kind of Modularized multi-level converter sub-module topological structure and its guard method |
| CN108448542A (en) * | 2018-02-07 | 2018-08-24 | 许继集团有限公司 | Sub-modular structure with alternating current-direct current fault clearance ability and MMC topological structures |
Non-Patent Citations (1)
| Title |
|---|
| 采用逆阻型子模块的新型模块化多电平换流器;杨晓峰 等;《中国电机工程学报》;20160405;第36卷(第7期);1885-1889 * |
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