CN109494971B - Starting strategy under condition of short circuit of direct current bus of flexible direct current transmission system - Google Patents

Starting strategy under condition of short circuit of direct current bus of flexible direct current transmission system Download PDF

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CN109494971B
CN109494971B CN201811184565.4A CN201811184565A CN109494971B CN 109494971 B CN109494971 B CN 109494971B CN 201811184565 A CN201811184565 A CN 201811184565A CN 109494971 B CN109494971 B CN 109494971B
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module
voltage
bridge
modules
bridge arm
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CN109494971A (en
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刘汉军
林卫星
白鹏
侯丹
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TBEA Xinjiang Sunoasis Co Ltd
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TBEA Xinjiang Sunoasis 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
    • H02M1/36—Means for starting or stopping converters
    • 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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Power Engineering (AREA)
  • Charge And Discharge Circuits For Batteries Or The Like (AREA)

Abstract

The invention relates to a starting strategy under the condition of short circuit of a direct current bus of a flexible direct current transmission system, which determines whether a bridge arm is locked or a module is cut off through module voltage under the condition of short circuit of the direct current bus, so that a converter valve charges the module in a transverse comparison and longitudinal comparison mode, the problem that a half-bridge module cannot be charged under the special condition of short circuit of the direct current bus of the converter valve is solved, the difference of the module voltage between the bridge arms is controlled within a certain range, and the problem of inaccurate direction judgment caused by current measurement precision and dead zones is avoided.

Description

Starting strategy under condition of short circuit of direct current bus of flexible direct current transmission system
Technical Field
The invention relates to the field of flexible direct current transmission, in particular to a starting strategy under the condition of short circuit of a direct current bus of a flexible direct current transmission system.
Background
The flexible direct-current transmission system is very suitable for high-voltage and high-power occasions due to unique technical advantages, and has great engineering advantages in the fields of power grid interconnection, wind power plant grid connection, island power supply, capacity increasing transformation of urban power distribution networks and the like. The flexible direct current transmission system widely adopts a modular multilevel structure, and can independently and quickly control active power and reactive power, so that the stability of the system is improved, the fluctuation of the frequency and voltage of the system is inhibited, and the steady-state performance of a grid-connected alternating current system is improved.
Before unlocking and running, the flexible direct current transmission system needs to go through a starting process, the module is charged, and the energy-taking power supply is driven to work. At present, conventional starting comprises alternating current charging and direct current charging modes, wherein detection quantities are mostly bridge arm current and valve side voltage in the alternating current charging mode, when a system comprises a full-bridge module and a half-bridge module, the module voltage and direct current bus voltage are charged to a certain value by using an alternating current power supply, and the half-bridge module charging opportunity in an uncontrolled rectification charging stage is half of that of the full-bridge module; in the direct current charging mode, the alternating current system end is disconnected, the module is charged by using direct current side voltage, and the charging opportunities of a half-bridge module and a full-bridge module in a bridge arm in the uncontrolled rectification charging stage are the same. When the converter valve breaks down and is put on or off online, the converter valve needs to be put into operation again after fault maintenance, the starting condition of the converter valve under the condition of short circuit of a direct current bus exists, and the two charging modes are not suitable for charging under the condition. In order to meet the special charging requirement under the short circuit of the direct current bus, solve the problem that the half-bridge module is not charged during the charging process, and do not increase new detection amount, a new charging strategy needs to be developed.
Disclosure of Invention
In order to solve the problems and the defects, the invention aims to provide a starting strategy under the condition of short circuit of a direct current bus of a flexible direct current transmission system, under the condition of short circuit of the direct current bus, whether bridge arms are locked or a module is cut off is determined through module voltage, so that a converter valve charges the modules in a transverse comparison and longitudinal comparison mode (the sum of the module voltage of each bridge arm is calculated, the transverse comparison is performed on all the bridge arms, and the longitudinal comparison is performed on upper and lower bridge arms of each phase), the problem of module charging is solved, the difference of the module voltage among the bridge arms is controlled within a certain range, and the problem of inaccurate direction judgment caused by current measurement precision and dead zones is avoided.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a starting strategy under the condition of short circuit of a direct current bus of a flexible direct current transmission system comprises the following steps:
step 1, when a direct current bus is in short circuit, all modules are locked, an alternating current power supply carries out uncontrolled rectification charging on the sub-modules through a soft start resistor, the full-bridge modules carry out self-checking after the voltage of the full-bridge modules is stable, and if the self-checking is passed, successfully configured state information is uploaded, and the step 2 is entered; if the self-checking fails, uploading the state information of the configuration failure, and entering the step 5;
step 2, starting a first voltage-sharing algorithm and pre-charging, wherein the specific method of the first voltage-sharing algorithm is as follows: setting a timing period Tset1At each Tset1Is started by averaging the voltage V of all half-bridge modules in the converter valveHAnd a set value Uset1Making a comparison when VH≥Uset1If yes, entering step 3; when V isH＜Uset1When it is passing throughSetting whether the bridge arm is a locked bridge arm or a module-cut bridge arm according to the comparison result and the longitudinal comparison result, starting the controllable charging of the module after the setting is finished, starting the next timing cycle until V is reachedH≥Uset1Entering step 3;
step 3, all modules are self-checked, if the self-check fails, the state information of the configuration failure is uploaded, and the step 5 is entered; if the self-checking is passed, uploading successfully configured state information, and starting a second voltage-sharing algorithm to charge the module;
the specific method of the second voltage-sharing algorithm is as follows: setting a timing period Tset2At each Tset2Is started, the average voltage U of all modules in the converter valve is calculatedSM-aveAnd a set value Uset2Comparing when U isSM-ave≥Uset2If yes, entering the step 4; if U is presentSM-ave＜Uset2Setting whether the bridge arm is a locked bridge arm or a module-cut bridge arm according to the results of transverse comparison and longitudinal comparison, starting the controllable charging of the module after the setting is finished, starting the next timing cycle until the timing cycle expires and the next timing cycle is started until U is reachedSM-ave≥Uset2Entering step 4;
step 4, all modules are locked, and the soft start resistor is cut off to be successfully started;
step 5, locking all modules, stopping starting charging and failing to start;
in the step 2 and the step 3,
the longitudinal comparison method comprises the following steps: the sum V of the voltage of each phase upper bridge arm modulexP_sumAnd the sum V of the lower bridge arm module voltagexN_sumMaking a difference, and making the absolute value of the difference delta VyAnd limit value Ulim1Making a comparison when Δ Vy≥Ulim1When the bridge arm with the larger sum of the module voltages of the phase is locked, the bridge arm with the smaller sum of the module voltages cuts off N modules, and other modules are locked; when Δ Vy＜Ulim1When the bridge arms are locked, the upper bridge arm and the lower bridge arm of the phase are locked;
the method of transverse comparison comprises the following steps: maximum value V of sum of module voltages in all bridge armsmaxAnd a minimum value VminMaking a difference, and dividing the difference value delta VxAnd limit value Ulim2Making a comparison when Δ Vx＜Ulim2Carrying out controllable charging on the module according to the result of longitudinal comparison; when Δ Vx≥Ulim2When, VmaxThe upper bridge arm and the lower bridge arm of the phase are locked, and then the starting module is used for controllable charging;
the U islim1A limit value, U, representing the comparison of the sum of the upper bridge arm module voltages and the sum of the lower bridge arm module voltages of each phaselim2The maximum value of the sum of the module voltages in all bridge arms is represented by a comparison limit value with the minimum value of the sum of the module voltages, and x represents any one of a phase a, a phase b and a phase c;
the values of N are as follows: [ N ]tol-Vline_pk/Urate/2]＜N＜NFBIn which N istolNumber of bridge arm modules, Vline_pkIs the peak value of the valve side line voltage, UrateFor rated voltage of module, NFBIs the number of full bridge modules.
Further, in the first voltage-sharing algorithm described in step 2, when the transverse comparison and the longitudinal comparison are performed, Δ V of each phase is calculatedyAre all less than Ulim1And Δ Vx＜Ulim2Then, the system charges according to the charging mode in the last timing period; when the transverse comparison and the longitudinal comparison are performed for the first time, Δ V of each phaseyAre all less than Ulim1And Δ Vx＜Ulim2Then, the system is in a timing period T according to a preset default valueset1The modules are precharged internally.
Further, the full-bridge module self-checking is to detect whether a full-bridge module which cannot drive the energy-taking power supply to work exists, and the self-checking indicates that the full-bridge module can drive the energy-taking power supply to work and is normally started; and if the self-checking fails, the situation shows that a full-bridge module which can not drive the energy-taking power supply to work exists, and the system is not allowed to be started continuously and is shut down for maintenance.
Further, the longitudinal comparison and the transverse comparison in the step 2 and the step 3 are both dynamic comparisons, and the V isxN_sum、VxP_sum、VminAnd VmaxAre all based on the last one at the beginning of each timing cycleThe charging result of the cycle is recalculated.
Further, the set value Uset1The working voltage of the energy taking power supply is greater than or equal to the working voltage of the energy taking power supply and is less than the rated voltage of the module; the set value Uset2The module rated voltage.
Further, the U islim1And Ulim2And carrying out adaptive adjustment according to the system voltage level.
Further, Ulim1Taking the rated voltage of a single module to be 2% -4%, Ulim2Taking 2% of the product of the module rated voltage and the module number.
Further, said Tset1And Tset2The values are the same.
Further, said Tset1And Tset2The value is 100 mus.
Compared with the prior art, the invention has at least the following beneficial effects: the starting strategy of the invention is reasonable in design, the related detection quantity is the module voltage, no new detection quantity is added, and the problem of inaccurate direction judgment caused by current detection precision and dead zone is avoided; in the starting strategy of the invention, the module division number N determines the voltage-sharing effect of the bridge arm half-bridge module and the full-bridge module, the module number division number N is too small, the full-bridge module has more charging opportunities, and the voltage of the half-bridge module cannot be charged to the state of consistent voltage of the full-bridge module; when the module cut-off value N exceeds the number of full-bridge modules, the voltage of the full-bridge modules is cut off first in the sequencing result, and the current flows through a bridge arm of a half-bridge without being charged, so that the full-bridge and the half-bridge are not charged, and therefore, a proper module cut-off value needs to be selected]The formula that < N < NFB, the number of bridge arm full bridge modules NFB needs to be more than [ Ntol-Vline _ pk/Urate/2%]Considering the reliability and safety of charging, if NFB is sufficient, the number of cut-off modules required by 1.1-1.2 times of rated voltage can be selected, that is, the number of cut-off modules is selected
Figure GDA0002659168040000041
If NFB is not sufficientThe divisor N may be selected as NFB.
In addition, by adjusting Ulim1And Ulim2The difference of module voltages among the bridge arms can be improved, the difference between the upper bridge arm and the lower bridge arm of each phase can be improved by adjusting Ulim1, and the smaller Ulim1 is, the higher the switching charging frequency of the upper bridge arm and the lower bridge arm is, and the smaller the difference is; by adjusting Ulim2Can improve the difference of module voltages among phases, theoretically Ulim2The difference of modules among phases is smaller, but the difference between the maximum value of the sum of the module voltages and the minimum value of the sum of the module voltages frequently exceeds Ulim2The limit value is that the frequency of single-phase locking is increased, the charging speed of the module is slowed down, and the voltage equalization of the module is not facilitated, so that when a debugging strategy is adopted, a proper U needs to be selected according to specific system parameterslim1And Ulim2。
The invention does not depend on the detection of alternating current system voltage, alternating current and bridge arm current to determine the charging path, but sets the charging path by detecting the module voltage.
Drawings
FIG. 1 is a start-up flow diagram of the present invention;
FIG. 2 is a converter valve topology of a flexible DC power transmission system of the present invention;
FIG. 3 illustrates a charging path under the strategy of the present invention;
FIG. 4 is another charging path under the strategy of the present invention;
FIG. 5 is another charging path under the strategy of the present invention;
FIG. 6 is another charging path under the strategy of the present invention;
FIG. 7 is a diagram of a module capacitor voltage waveform of the present invention.
Detailed Description
The following detailed description of embodiments of the invention is provided in connection with the accompanying drawings and the examples.
Fig. 2 is a converter valve topological diagram of the flexible dc power transmission system according to the embodiment of the present invention, in which an ac power source is connected to the converter valve through a soft start resistor and a transformer, the converter valve includes six bridge arms, each bridge arm is composed of a plurality of half-bridges and a full-bridge module, and a dc bus end of the converter valve is short-circuited.
Fig. 1 is a starting flow chart of the present invention, wherein the starting flow includes the following implementation steps:
setting a timing period Tset1At each Tset1Is started by averaging the voltage V of all half-bridge modules in the converter valveHAnd a set value Uset1The comparison is carried out until the average voltage V of all the modulesHAre all greater than a set value Uset1Completing the pre-charging;
after the completion of the precharge, a timer period T is setset2At each Tset2Is started, the average voltage U of all modules in the converter valve is calculatedSM-aveAnd a set value Uset2The comparison is carried out until the average voltage U of all modulesSM-aveAre all greater than a set value Uset2And the charging is completed. In a preferred embodiment of the invention, Tset1And Tset2All are 100 mus.
A. The converter valve alternating current circuit breaker is disconnected, the direct current bus is short-circuited, the soft start resistor is connected, and the module is locked;
B. the converter valve AC circuit breaker is closed, the AC power supply carries out uncontrolled rectification charging on the submodule through the soft start resistor, a current circulation branch is added due to the short circuit of the DC bus, in a loop formed by the AC system and the converter valve, the current flows through a branch (half-bridge non-charging branch) with lower potential of the converter valve more easily, the half-bridge module has less charging chance, and the voltage for driving the energy-taking power supply to work cannot be reached;
C. after the module voltage is stable, the full-bridge module performs self-checking, whether the configuration is successful or not is uploaded, if the configuration is unsuccessful, the system is shut down, and since the half-bridge module voltage is lower, the energy-taking power supply cannot be driven to work, the self-checking is not performed;
D. after the full-bridge module is successfully configured, self-voltage-sharing is started, and for the x-phase (any phase a/b/c), the sum V of the voltages of the bridge arm modules on the x-phase is calculatedxP_sumAnd the sum V of the lower bridge arm module voltagesxN_sumAnd finding out the maximum value V of the sum of the module voltages in six bridge arms of the converter valvemaxAnd minimum value Vmin(or all modules per phase)After voltage summation, finding out the maximum value and the minimum value in three phases, and having little effect difference); if VxP_sumDecreasing VxN_sumGreater than a set value Ulim1Time (U)lim1For controlling the difference between the upper and lower arms, the value being related to the number of modules and the rated voltage of the modules, Ulim1The smaller the voltage difference of the module is, but the higher the switching locking bridge arm frequency is, the U islim1The larger the switching locking bridge arm frequency is, the lower the switching locking bridge arm frequency is, but the module difference is larger), the x-phase upper bridge arm module is locked, and the x-phase lower bridge arm module cuts off N modules with higher voltage (N) according to the requirementtol-Vline_pk/Urate/2]＜N＜NFBIn which N istolNumber of bridge arm modules, Vline_pkIs the peak value of the valve side line voltage, UrateFor rated voltage of module, NFBFull bridge module number), the other modules of the x-phase lower bridge arm are locked, the voltage of the x-phase lower bridge arm module is increased until VxN_sumDecreasing VxP_sumGreater than a set value Ulim1When the current is switched to x-phase lower bridge arm locking, the x-phase upper bridge arm cuts off N modules with higher voltage, and other modules of the x-phase upper bridge arm are locked and sequentially circulated; if VmaxDecreasing VminGreater than a limit value Ulim2Wherein U islim2For controlling voltage difference between phases, the value is related to the number of modules and rated voltage of the modules, Ulim2Too small may cause the half-bridge to be charged too frequently, regardless of VmaxWhether the difference between the sum of the upper bridge arm module voltages and the sum of the lower bridge arm module voltages of the phase exceeds a limit value U or notlim1，VmaxThe upper bridge arm and the lower bridge arm of the phase are locked, and the modules of other bridge arms start to charge;
thus, the voltage of the half-bridge module starts to rise according to the cycle detection and comparison of the set time period, so that the voltages of the half-bridge module and the full-bridge module are charged to be in a consistent state;
E. when the average voltage of all half-bridge modules reaches the set value Uset1And locking all modules, starting self-checking of all modules, uploading a command of whether configuration is successful, and stopping the system if the configuration is unsuccessful, wherein Uset1The voltage is greater than the working voltage of the energy-taking power supply and less than the rated voltage of the module;
F. after all modules are successfully configured, repeating the step D until the average value of all module voltages reaches a set value Uset2And the module voltage sharing meets the requirement, all modules are locked, wherein Uset2Is the rated voltage of the module;
G. and cutting off the soft start resistor, finishing starting and waiting for unlocking.
By adjusting Ulim1And Ulim2The difference of module voltages among bridge arms can be improved.
The module division value N determines the voltage-sharing effect of the bridge arm half-bridge module and the bridge arm full-bridge module, the module number division value N is too small, the full-bridge module has more charging opportunities, and the voltage of the half-bridge module cannot be charged to the state that the voltage of the full-bridge module is consistent; when the module division number N exceeds the number of full-bridge modules, the voltage of the full-bridge module is cut off first due to the high voltage in the sequencing result, and the current flows through the bridge arm of the half-bridge which is not charged, so that the full-bridge and the half-bridge are not charged, and therefore, a proper module division number needs to be selected.
The detection quantity is the module voltage, no new detection quantity is added, and the problem of inaccurate direction judgment caused by current detection precision and dead zones is avoided.
Fig. 3 shows a charging path 1 formed according to a starting strategy, where, taking phases a and b as examples, an a-phase alternating current voltage is higher than a b-phase alternating current voltage, and when lower arms of the phases a and b are locked and upper arms of the phases a and b respectively cut off N modules, an alternating current flows in from the upper arm of the phase a and flows out from the upper arm of the phase b.
Fig. 4 shows the charging path 2 formed according to the starting strategy, and taking the phases a and b as examples, if the a-phase alternating current voltage is higher than the b-phase alternating current voltage, when the upper arms of the phases a and b are locked and the lower arms of the phases a and b cut off N modules, the alternating current flows in from the lower arm of the phase a and flows out from the lower arm of the phase b.
Fig. 5 shows a charging path 3 formed according to a starting strategy, and taking phases a and b as examples, if the phase a alternating current voltage is higher than the phase b, when the phase a upper arm is locked, the phase a lower arm cuts off N modules, the phase b lower arm is locked, and the phase b upper arm cuts off N modules, then alternating current flows in from the phase a lower arm, and flows out from the phase b upper arm through a direct current bus.
Fig. 6 shows the charging path 4 formed according to the starting strategy, and taking the phases a and b as examples, if the phase a has an ac voltage higher than that of the phase b, when the phase a lower arm is locked, the phase a upper arm cuts off N modules, the phase b upper arm is locked, and the phase b lower arm cuts off N modules, then ac current flows in from the phase a upper arm, and flows out from the phase b lower arm through the dc bus.
Fig. 7 shows the half-bridge and full-bridge module capacitor voltage waveforms obtained according to the designed starting process. According to the designed starting process, the time sequence of each stage is as follows:
(1) t 0-t 1, carrying out uncontrolled rectifying charging by a soft start resistor, carrying out self-checking on the full-bridge module after the module voltage is stabilized, and carrying out configuration commands;
(2) t 1-t 2, starting the first voltage-sharing algorithm, and when the voltage of the half-bridge module rises to Uset1When the system is in use, all modules are locked;
(3) t 2-t 3, all modules self-check and concurrently configure commands;
(4) t 3-t 4, starting a second voltage-sharing algorithm, and when the average voltage of the module rises to Uset2When the system is in use, all modules are locked;
(5) t 4-t 5, self-discharge with soft start resistance;
(6) t 5-t 6, the soft start resistor is cut off, the start is finished, and the state of waiting for unlocking is entered.
Finally, it should be noted that those of ordinary skill in the art will understand that: modifications and equivalents may be made to the embodiments of the invention by those skilled in the art, which modifications and equivalents are within the scope of the claims appended hereto.

Claims (9)

1. A starting method under the condition of short circuit of a direct current bus of a flexible direct current transmission system is characterized by comprising the following steps:
step 1, when a direct current bus is in short circuit, all modules are locked, an alternating current power supply carries out uncontrolled rectification charging on the sub-modules through a soft start resistor, the full-bridge modules carry out self-checking after the voltage of the full-bridge modules is stable, and if the self-checking is passed, successfully configured state information is uploaded, and the step 2 is entered; if the self-checking fails, uploading the state information of the configuration failure, and entering the step 5;
step 2, starting a first voltage-sharing algorithm and pre-charging, wherein the specific method of the first voltage-sharing algorithm is as follows: setting a timing period Tset1At each Tset1Is started by averaging the voltage V of all half-bridge modules in the converter valveHAnd a set value Uset1Making a comparison when VH≥Uset1If yes, entering step 3; when V isH＜Uset1And then, setting whether the bridge arm is a locked bridge arm or a module-cut bridge arm according to the results of transverse comparison and longitudinal comparison, starting the controllable charging of the module after the setting is finished, starting the next timing cycle until V is reached to the end of the timing cycleH≥Uset1Entering step 3;
step 3, all modules are self-checked, if the self-check fails, the state information of the configuration failure is uploaded, and the step 5 is entered; if the self-checking is passed, uploading successfully configured state information, and starting a second voltage-sharing algorithm to charge the module;
the specific method of the second voltage-sharing algorithm is as follows: setting a timing period Tset2At each Tset2Is started, the average voltage U of all modules in the converter valve is calculatedSM-aveAnd a set value Uset2Comparing when U isSM-ave≥Uset2If yes, entering the step 4; if U is presentSM-ave＜Uset2Setting whether the bridge arm is a locked bridge arm or a module-cut bridge arm according to the results of transverse comparison and longitudinal comparison, starting the controllable charging of the module after the setting is finished, starting the next timing cycle until the timing cycle expires and the next timing cycle is started until U is reachedSM-ave≥Uset2Entering step 4;
step 4, all modules are locked, and the soft start resistor is cut off to be successfully started;
step 5, locking all modules, stopping starting charging and failing to start;
in the step 2 and the step 3,
the longitudinal comparison method comprises the following steps: the sum V of the voltage of each phase upper bridge arm modulexP_sumAnd the sum V of the lower bridge arm module voltagexN_sumMaking a difference, and making the absolute value of the difference delta VyAnd limit value Ulim1Ratio of performanceWhen Δ V is smaller thany≥Ulim1When the bridge arm with the larger sum of the module voltages of the phase is locked, the bridge arm with the smaller sum of the module voltages cuts off N modules, and other modules are locked; when Δ Vy＜Ulim1When the bridge arms are locked, the upper bridge arm and the lower bridge arm of the phase are locked;
the method of transverse comparison comprises the following steps: maximum value V of sum of module voltages in all bridge armsmaxAnd a minimum value VminMaking a difference, and dividing the difference value delta VxAnd limit value Ulim2Making a comparison when Δ Vx＜Ulim2Carrying out controllable charging on the module according to the result of longitudinal comparison; when Δ Vx≥Ulim2When, VmaxThe upper bridge arm and the lower bridge arm of the phase are locked, and then the starting module is used for controllable charging;
the U islim1A limit value, U, representing the comparison of the sum of the upper bridge arm module voltages and the sum of the lower bridge arm module voltages of each phaselim2The maximum value of the sum of the module voltages in all bridge arms is represented by a comparison limit value with the minimum value of the sum of the module voltages, and x represents any one of a phase a, a phase b and a phase c;
the values of N are as follows: [ N ]tol-Vline_pk/Urate/2]＜N＜NFBIn which N istolNumber of bridge arm modules, Vline_pkIs the peak value of the valve side line voltage, UrateFor rated voltage of module, NFBIs the number of full bridge modules.
2. The method according to claim 1, wherein in the first grading algorithm in step 2, the Δ ν V for each phase is compared between the transverse and longitudinal comparisons during the short circuiting of the dc busbars in the hvdc transmission systemyAre all less than Ulim1And Δ Vx＜Ulim2Then, the system charges according to the charging mode in the last timing period; when the transverse comparison and the longitudinal comparison are performed for the first time, Δ V of each phaseyAre all less than Ulim1And Δ Vx＜Ulim2Then, the system is in a timing period T according to a preset default valueset1The modules are precharged internally.
3. The starting method for the short circuit condition of the direct current bus of the flexible direct current transmission system according to claim 1, wherein the full-bridge module self-check is to detect whether there is a full-bridge module which cannot drive the energy-taking power supply to work, and the self-check indicates that the full-bridge module can drive the energy-taking power supply to work and is started normally; and if the self-checking fails, the situation shows that a full-bridge module which can not drive the energy-taking power supply to work exists, and the system is not allowed to be started continuously and is shut down for maintenance.
4. The method according to claim 1, wherein the longitudinal comparison and the transverse comparison in step 2 and step 3 are both dynamic comparisons, and the V is a value obtained by comparing the V with the V in the case of a short circuit of the dc bus of the flexible dc power transmission systemxN_sum、VxP_sum、VminAnd VmaxAre recalculated at the beginning of each timing cycle based on the charging results of the previous cycle.
5. The method of claim 1, wherein the set value U is set according to a short circuit condition of the DC bus of the flexible DC power transmission systemset1The working voltage of the energy taking power supply is greater than or equal to the working voltage of the energy taking power supply and is less than the rated voltage of the module; the set value Uset2The module rated voltage.
6. The method of claim 1, wherein the U is a number of units in a soft DC power transmission system with a short-circuited DC buslim1And Ulim2And carrying out adaptive adjustment according to the system voltage level.
7. The method of claim 6, wherein U is selected from the group consisting oflim1Taking the rated voltage of a single module to be 2% -4%, Ulim2Taking 2% of the product of the module rated voltage and the module number.
8. The flexible direct current transmission system direct current bus short circuit condition of claim 1The starting method under the condition, characterized in that, the T isset1And Tset2The values are the same.
9. The method of claim 1, wherein T is the time of starting a flexible DC power transmission system with a short-circuited DC busset1And Tset2The value is 100 mus.
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