CN112165245A - MMC converter starting method and system - Google Patents
MMC converter starting method and system Download PDFInfo
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- CN112165245A CN112165245A CN202010758196.6A CN202010758196A CN112165245A CN 112165245 A CN112165245 A CN 112165245A CN 202010758196 A CN202010758196 A CN 202010758196A CN 112165245 A CN112165245 A CN 112165245A
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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
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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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- 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
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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
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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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
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
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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
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
- H02M7/53873—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with digital control
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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]
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Charge And Discharge Circuits For Batteries Or The Like (AREA)
- Dc-Dc Converters (AREA)
Abstract
The invention discloses a starting method of an MMC converter, which comprises the following steps: carrying out alternating current uncontrolled charging on the MMC converter, and judging that the capacitor voltage of each half bridge submodule enters a stable state after the direct current side voltage reaches an uncontrolled charging threshold value and the charging current is smaller than a preset value; AC active charging is carried out on the MMC converter, a switch tube T2 in a submodule of the MMC converter is unlocked, the number of submodules of each bridge arm working in a charging mode is gradually reduced, the voltage of the submodules is approximately equal to the rated voltage of the unlocked submodules, and the number of the submodules of each bridge arm working in the charging mode at the moment is kept constant; and (5) putting into closed-loop control to unlock the MMC current converter. According to the invention, the active charging control is carried out on the basis of the uncontrolled AC charging, so that the voltage of the sub-module capacitor can be further raised and is equal to the rated value of the voltage of the unlocked sub-module as much as possible, thereby reducing the impact current in the unlocking process of the converter and ensuring the safe and stable operation of the MMC converter.
Description
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a starting method and a starting system of an MMC (modular multilevel converter).
Background
The Modular Multilevel (MMC) converter is a cascaded extensible voltage source type converter, is particularly suitable for application in occasions of high-voltage large-capacity power systems, is widely applied in the field of high-voltage direct-current transmission in recent years, and is gradually expanded to the application of an AC/DC hybrid power distribution network system.
Contain a large amount of electric capacities among the MMC transverter valves, all submodule piece electric capacities all do not have initial voltage, before getting into the steady operation operating mode, need charge submodule piece electric capacity earlier, and this process is MMC's precharge starting process promptly. And after the pre-charging process is finished, the direct-current voltage of the sub-module of the valve group is different from the designed rated steady-state operation value of the direct-current voltage of the sub-module of the converter unlocked. The equivalent capacitance of the direct-current circuit and the capacitance of the bridge arm sub-module are large, if the converter is unlocked directly after the alternating-current uncontrolled charging or direct-current uncontrolled charging process is finished, each electric quantity of the system can pass through a series of transient processes due to the closed-loop control, the bridge arm can generate large impact current, and the power device can be damaged in serious cases.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a method and a system for starting an MMC converter, which can be stably and safely put into the MMC converter.
The technical scheme for realizing the invention is as follows:
in a first aspect, a method for starting an MMC converter is provided, including:
carrying out alternating current uncontrolled charging on the MMC converter, and judging that the capacitance voltage of each half bridge submodule enters a stable state after the direct current side voltage reaches an uncontrolled charging threshold value and the charging current is smaller than a preset value;
AC active charging is carried out on the MMC converter, a switch tube T2 in a submodule of the MMC converter is unlocked, the number of submodules of each bridge arm working in a charging mode is gradually reduced, so that the capacitance voltage of the submodules is approximately equal to the capacitance rated voltage of the unlocked submodules, and the number of the submodules of each bridge arm working in the charging mode at the moment is kept constant;
and (5) putting into closed-loop control to unlock the MMC current converter.
With reference to the first aspect, further, the dc uncontrolled charging threshold value is 65% of the dc side rated voltage.
With reference to the first aspect, further, the preset value of the charging current is 0.05-0.1 times of the rated value of the main loop current.
In combination with the first aspect, further, the number of the submodules of each bridge arm working in the charging mode is gradually reduced through a bridge arm submodule voltage-sharing algorithm, so that the capacitance voltage approximation value of the submodules is equal to the capacitance rated voltage of the unlocked submodules.
With reference to the first aspect, further, the step of gradually reducing the number of the sub-modules of each bridge arm operating in the charging mode by using a bridge arm sub-module voltage-sharing algorithm so that the capacitance voltage of the sub-modules is approximately equal to the capacitance rated voltage of the unlocked sub-modules specifically includes: monitoring all sub-module capacitor voltage values of a bridge arm of the MMC converter in real time and sequencing according to the magnitude; and simultaneously monitoring the current direction of the bridge arm, judging that the submodules are charged when the current direction of the bridge arm is positive, and then according to the number N of the submodules in the charging stateonSelecting N according to the sequence of the capacitor voltage values of the sub-modules from low to highonKeeping the charge state of the submodule with the lowest voltage and unlocking the rest N-NonAnd the submodule sends a pulse to the switching tube T2 to enable the submodule to enter a cutting state until the approximate value of the capacitor voltage of the submodule is equal to the rated capacitor voltage of the unlocked submodule.
With reference to the first aspect, further, the step of enabling the capacitor voltage of the sub-module to be approximately equal to the capacitor rated voltage of the unlocked sub-module specifically includes: and the capacitor voltage of the sub-module is positioned between the upper limit and the lower limit of the capacitor rated voltage of the unlocked sub-module, and the upper limit and the lower limit of the capacitor rated voltage of the unlocked sub-module are set according to empirical values.
In a second aspect, an MMC converter starting system is provided, including:
the AC uncontrolled charging module: carrying out alternating current uncontrolled charging on the MMC converter, and judging that the voltage of each half bridge module enters a stable state after the voltage of the direct current side reaches an uncontrolled charging threshold value and the charging current is smaller than a preset value;
AC active charging module: the system is used for AC active charging of the MMC converter, unlocking a switch tube T2 in a submodule of the MMC converter, gradually reducing the number of submodules of each bridge arm working in a charging mode, enabling the capacitance voltage of the submodules to be approximately equal to the capacitance rated voltage of the unlocked submodules, and keeping the number of the submodules of each bridge arm working in the charging mode constant at the moment;
the MMC transverter drops into the module: for putting into closed-loop control and unlocking the MMC converter.
Has the advantages that: compared with the prior art, the active charging control method and the device have the advantages that the active charging control is carried out on the basis of the uncontrolled alternating current charging, the voltage of the sub-module capacitor can be further raised and is equal to the rated value of the capacitor voltage of the sub-module after unlocking as far as possible, so that the impact current in the unlocking process of the converter is reduced, and the safe and stable operation of the MMC converter is guaranteed.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a graph comparing voltage waveforms of DC side with active charging in the present invention and without active charging in the prior art;
FIG. 3 is a comparison graph of voltage waveforms of submodules of bridge arms in a conventional non-active charging mode and in an active charging mode according to the present invention;
FIG. 4 is a comparison graph of RTDS test waveforms before and after the active charging control strategy is added to the pre-charging process;
FIG. 5 is a schematic diagram of a topological structure of an MMC converter in the present invention;
FIG. 6 is a schematic diagram of the main wiring of the dual-port MMC converter station system of the present invention.
Detailed Description
The invention is further described with reference to the accompanying drawings.
The half-bridge MMC converter topology in the invention is shown in figure 5, wherein the half-bridge sub-modules are shown as SM 1-SMn.
As shown in fig. 1 to 6, a method for starting an MMC converter includes the following steps: wherein: u. ofx(x is A, B, C) is the AC side voltage of the outlet of the converter; u. ofxP、uxN、ixP、ixNThe voltage and the current of the upper bridge arm and the lower bridge arm are respectively; i.e. ixIs the net side current; u. ofdc、idcDirect current side voltage and current respectively; l is bridge arm inductance ucIs the sub-module capacitance voltage; neglecting the bridge arm internal resistance.
Step one, carrying out AC uncontrolled charging on the MMC current converter, and when the DC side voltage reaches an uncontrolled charging threshold value and the charging current is smaller than a preset value (according to the characteristics of an AC uncontrolled charging circuit, if the charging current is not controlled)After the charging control process is finished, the amplitude of the voltage of the valve arm of the MMC main circuit is equal to the amplitude of the voltage of the alternating current bus line, the theoretical value of the charging current of the main circuit is zero, the zero-current threshold of the charging current of the main circuit is set, the zero-current threshold can be 0.05-0.1 time of the rated current and can form a criterion of finishing the alternating current uncontrolled charging of the MMC with the uncontrolled charging threshold value), the capacitor voltage of each half bridge submodule is judged to enter a stable state, and the voltage U of the bridge arm is judged to enter a stablearmEqual to the DC side voltage udc(ii) a Here, the threshold value of the uncontrolled charging voltage on the dc side is determined according to the total dc voltage output characteristic of the MMC current converter during the ac uncontrolled charging phase, where 65% of the rated voltage (rated voltage of the dc bus) on the dc side is taken, and the detailed analysis is as follows:
and after the AC uncontrolled charging process is finished, the maximum charging voltage value of the DC voltage is equal to the peak value of the voltage of the AC side bus. In MMC main loop parameter design, the effective value of the alternating-current side bus voltage is UdcN1.00 to 1.05 times of/2, UdcNThe rated voltage of the direct current bus is obtained. Therefore, the maximum charging rate of the direct-current voltage in the uncontrolled alternating-current charging stage is as follows:
namely the maximum charging value of the total direct current voltage under the AC uncontrolled charging mode can reach 71% -74% of the rated direct current voltage, the invention sets a per unit value threshold of the direct current voltage of 0.65pu according to the electrical characteristics of the charging process and considering the voltage drop of a charging current-limiting resistance loop, when the per unit value of the total direct current voltage is greater than the threshold value, the master control system judges that the MMC AC uncontrolled charging process is finished, wherein U is the maximum charging value of the total direct current voltage under the AC uncontrolled charging model_rmsRepresenting the effective value of the alternating line voltage.
Step two, closing a charging resistance bypass switch (MMC converter charging loop is composed of a charging current limiting resistor R shown in the attached figure 5)limAnd a bypass switch CB 2. Charging current-limiting resistor is connected in series in the MMC main loop for limiting charging current in the MMC starting process, after the charging process is completed by the MMC valve arm submodule capacitor, the charging current-limiting resistor is withdrawn through a bypass switch), AC active charging is carried out on the MMC converter, and the MMC converter is unlockedThe switching tube T2 in the submodule of the device gradually reduces the number of submodules of each bridge arm working in a charging mode through a bridge arm submodule voltage-sharing algorithm, so that the capacitance voltage of the submodules is approximately equal to the capacitance rated voltage of the unlocked submodules, and the method specifically comprises the following steps:
monitoring all sub-module capacitor voltage values of a bridge arm of the MMC converter in real time and sequencing according to the magnitude; and simultaneously monitoring the current direction of the bridge arm, judging that the submodules are charged when the current direction of the bridge arm is positive, and then according to the number N of the submodules in the charging stateonSelecting N according to the sequence of the capacitor voltage values of the sub-modules from low to highonKeeping the charging state of the submodule with the lowest voltage, and unlocking the rest N-N by the master control systemonThe submodule sends a pulse to the switch tube T2 to enable the submodule to enter a conducting state, so that the submodule where the submodule is located enters a cutting-off state until the voltage of the submodule is approximately equal to the rated voltage of the unlocked submodule, and the rated voltage value u of the capacitor of the submodule iscNA group of upper voltage limits U is set nearbyCN maxAnd lower limit UCN minRespectively take UCN max＝1.05ucNAnd UCN min＝0.95ucN(set according to experience value), when the capacitor voltage of the bridge arm submodule reaches the set upper and lower limit ranges, namely UCN min<uc<UCN maxAnd judging that the alternating current active charging process is completed, wherein at the moment, the capacitor voltages of all the sub-modules of the bridge arm of the MMC converter reach the range of the designed rated value upper limit and lower limit, at the moment, part of the sub-modules in the bridge arm are in a charging working mode, and the rest of the sub-modules are in a cutting working mode, wherein N represents the number of the sub-modules of each bridge arm.
Keeping the quantity of the submodules of each bridge arm of the MMC current converter working in the charging mode constant at the moment, and thus finishing the pre-charging process of the MMC current converter.
And step three, unlocking the MMC current converter, putting the MMC current converter into closed-loop control, and finishing the starting process of the MMC current converter.
In the second step, the working mode of the submodule is greatly different from the working mode of the submodule after the converter is unlocked, the switching tube T1 is always in the off state in the active charging stage, the state of the submodule is only related to the switching tube T2, and the working mode of the active charging is shown in the following table 1:
TABLE 1
Compared with the prior art, the active charging control method and the device have the advantages that the active charging control is carried out on the basis of the uncontrolled alternating current charging, the voltage of the sub-module capacitor can be further increased and is equal to the rated value of the voltage of the sub-module after unlocking as far as possible, so that the impact current in the unlocking process of the converter is reduced, and the safe and stable operation of the MMC converter is guaranteed.
The MMC converter starting system provided by the embodiment of the invention comprises:
the AC uncontrolled charging module: carrying out alternating current uncontrolled charging on the MMC converter, and judging that the capacitor voltage of each half bridge submodule enters a stable state after the direct current side voltage reaches an uncontrolled charging threshold value and the charging current is smaller than a preset value;
AC active charging module: the system is used for AC active charging of the MMC converter, unlocking a switch tube T2 in a submodule of the MMC converter, gradually reducing the number of submodules of each bridge arm working in a charging mode, enabling the capacitance voltage of the submodules to be approximately equal to the capacitance rated voltage of the unlocked submodules, and keeping the number of the submodules of each bridge arm working in the charging mode constant at the moment;
the MMC transverter drops into the module: for putting into closed-loop control and unlocking the MMC converter.
In order to verify the effectiveness of the active pre-charging control strategy, the pre-charging control strategy provided by the invention is realized by software and hardware in an MMC converter controller prototype, a dual-port converter station System hardware-in-loop Real-Time simulation platform is established by applying the MMC converter controller prototype and an RTDS (Real Time Digital simulation System), and the active pre-charging control strategy is tested and verified.
The MMC converter controller prototype consists of a main control device and a valve control device. The main control device collects analog quantity information such as alternating current system voltage and current, direct current system voltage and current, MMC converter bridge arm current and the like, and information such as switch on-off state and the like, so that the system-level control function of the converter is realized; the valve control device collects information such as capacitance voltage and valve bank state of a submodule (half-bridge arm submodule) of the MMC converter valve bank, and the control function inside the MMC converter valve bank is achieved.
According to the active pre-charging control strategy flow shown in the attached figure 1, after the AC uncontrolled charging process of the MMC converter is completed, the main control device sends out a signal for starting the active pre-charging control and instructs N the number of sub-modules of the upper bridge arm and the lower bridge arm of each phase valve group to be conductedxP、NxNAnd gradually reducing from N and sending to a valve control device. The valve control device receives the number instruction of the conducting submodules of the upper bridge arm and the lower bridge arm of the main control device, and selects N by using a sorting voltage-sharing algorithm according to the current direction of the valve armsxP、NxNAnd enabling the submodule to enter a cut-off mode, and keeping the other submodules in a charging mode until the direct current capacitor voltage of all the submodules is stable and approaches to the designed rated voltage value. After the pre-charging process is finished, the main control device sends out a valve group unlocking instruction, and the valve control device generates a corresponding trigger pulse according to a closed-loop control target value sent by the main control device.
The hardware-in-the-loop real-time simulation platform of the dual-port MMC converter station system is composed of an RTDS digital model, RTDS simulation equipment and an MMC converter controller prototype. According to the accompanying drawing 6, a dual-port MMC system RTDS digital model is built, each bridge arm of a dual-port MMC converter valve group comprises 22 sub-modules, rated direct current voltage is 20kV, rated alternating current voltage is 10kV, bridge arm reactors are 0.5pu, rated power is 10MW, and sub-module capacitors are 3000 uF.
And performing a pre-charging simulation test of the MMC converter station in a ring real-time simulation platform by using the system hardware of the dual-port converter station, and comparing pre-charging characteristics of a prototype of the MMC converter controller when an active charging control strategy is not adopted and an active control strategy is adopted respectively, wherein the simulation test waveform is shown in attached figures 2-4. According to simulation test results, the master control pre-charging control method provided by the invention can be used for lifting the voltage of the sub-module capacitor and effectively inhibiting starting impact current in the active charging process before the current converter is unlocked.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (7)
1. An MMC converter starting method is characterized by comprising the following steps:
carrying out alternating current uncontrolled charging on the MMC converter, and judging that the capacitance voltage of each half bridge submodule enters a stable state after the direct current side voltage reaches an uncontrolled charging threshold value and the charging current is smaller than a preset value;
AC active charging is carried out on the MMC converter, a switch tube T2 in a submodule of the MMC converter is unlocked, the number of submodules of each bridge arm working in a charging mode is gradually reduced, so that the capacitance voltage of the submodules is approximately equal to the capacitance rated voltage of the unlocked submodules, and the number of the submodules of each bridge arm working in the charging mode at the moment is kept constant;
and (5) putting into closed-loop control to unlock the MMC current converter.
2. The MMC converter starting method according to claim 1, wherein the uncontrolled charging threshold is 65% of rated.
3. The MMC converter starting method of claim 1, wherein the preset value of the charging current is 0.05-0.1 times its primary loop current rating.
4. The MMC converter starting method of claim 1, wherein the number of submodules of each bridge arm operating in a charging mode is gradually reduced by a bridge arm submodule voltage-sharing algorithm, such that the submodule voltage is approximately equal to the rated voltage of the unlocked submodule.
5. The MMC converter starting method of claim 4, wherein the step-by-step reduction of sub-modules of each bridge arm operating in a charging mode is performed by a bridge arm sub-module voltage-sharing algorithmThe number of modules, which makes the capacitor voltage of the sub-module approximately equal to the capacitor rated voltage of the unlocked sub-module, is specifically: monitoring all sub-module capacitor voltage values of a bridge arm of the MMC converter in real time and sequencing according to the magnitude; and simultaneously monitoring the current direction of the bridge arm, judging that the submodules are charged when the current direction of the bridge arm is positive, and then according to the number N of the submodules in the charging stateonSelecting N according to the sequence of the capacitor voltage values of the sub-modules from low to highonKeeping the charge state of the submodule with the lowest voltage and unlocking the rest N-NonAnd the submodule sends a pulse to the switching tube T2 to enable the submodule to enter a cutting state until the approximate value of the capacitor voltage of the submodule is equal to the rated capacitor voltage of the unlocked submodule.
6. The MMC converter starting method of claim 4, wherein the capacitor voltage of the sub-module approximately equals to the capacitor rated voltage of the unlocked sub-module is specifically: the sub-module voltage is located between the upper limit and the lower limit of the capacitor rated voltage of the sub-module after unlocking, and the upper limit and the lower limit of the capacitor rated voltage of the sub-module after unlocking are set according to empirical values.
7. An MMC converter starting system, characterized by includes:
the AC uncontrolled charging module: carrying out alternating current uncontrolled charging on the MMC converter, and judging that the capacitance voltage of each half bridge submodule enters a stable state after the direct current side voltage reaches an uncontrolled charging threshold value and the charging current is smaller than a preset value;
AC active charging module: the system is used for AC active charging of the MMC converter, unlocking a switch tube T2 in a submodule of the MMC converter, gradually reducing the number of submodules of each bridge arm working in a charging mode, enabling the capacitance voltage of the submodules to be approximately equal to the capacitance rated voltage of the unlocked submodules, and keeping the number of the submodules of each bridge arm working in the charging mode constant at the moment;
the MMC transverter drops into the module: and the method is used for unlocking the MMC current converter and putting the MMC current converter into closed-loop control.
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