CN113937995B - Soft start method and storage medium of low-frequency power transmission system - Google Patents
Soft start method and storage medium of low-frequency power transmission system Download PDFInfo
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- CN113937995B CN113937995B CN202111096726.6A CN202111096726A CN113937995B CN 113937995 B CN113937995 B CN 113937995B CN 202111096726 A CN202111096726 A CN 202111096726A CN 113937995 B CN113937995 B CN 113937995B
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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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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- 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)
- Inverter Devices (AREA)
Abstract
The invention discloses a soft start method of a low-frequency power transmission system, which comprises the following steps: disconnecting the low frequency line switch of each converter station; the power frequency charging switch of each converter station is switched on to charge the module uncontrollably; after the voltage of the uncontrollably charged capacitor is stable, unlocking after each converter station is switched to a first operation mode; after the voltage average value of each bridge arm capacitor reaches the rated value, closing the line switch of each converter station at zero voltage; switching a certain converter station to a second operation mode and controlling a low-frequency side zero voltage; switching other converter stations to a third operation mode and controlling low-frequency side zero power; establishing the voltage of the low-frequency power transmission network to a rated value; after the alternating voltage of the low-frequency power transmission network reaches the rated value, the power is increased according to the instruction, and the starting is finished. After the invention is adopted, the line switch is switched on in the state of zero voltage and zero current at the low-frequency line side in the starting process, the synchronous detection of the switch is not needed, the cost and the complexity of the system are reduced, and no voltage and current impact is caused to the low-frequency power transmission system.
Description
Technical Field
The invention relates to the field of low-frequency power transmission, in particular to a soft start method and a storage medium of a low-frequency power transmission system.
Background
The low-frequency power transmission system based on the full-bridge modularized multi-level matrix converter (modular multilevel matrix converter, M3C) is a brand new power transmission mode, and the power frequency alternating current is converted into the low-frequency alternating current for transmission through M3C alternating current conversion, so that the power transmission efficiency is improved. In the mid-open sea wind power delivery scheme, the method is very competitive because of no need of constructing an offshore converter station with high cost and complex operation and maintenance. Although the application potential of the low-frequency power transmission system is huge, practical engineering input operation based on the M3C low-frequency power transmission technology is not reported at home and abroad, and the application of the low-frequency power transmission system still needs to be subjected to concrete and refined research. At present, researches on low-frequency power transmission systems focus on a steady-state operation control strategy and a fault ride-through control strategy under transient operation. For the starting strategy of the complete low-frequency power transmission system, the related patent literature research is not mentioned yet. In the low-frequency power transmission system engineering application, a starting strategy is indispensable, and a reasonable starting strategy can ensure the safety of system equipment and reduce the complexity of system starting.
For a low-frequency power transmission system, like the running mode of direct-current power transmission, one converter station controls the voltage of a stable low-frequency power transmission network, and the other converter stations control the power transmitted by each converter station. Under the control strategy, the low-frequency power transmission system can realize stable power transmission. However, the low-frequency power transmission system is started differently from the direct-current power transmission system, the low-frequency system power after alternating-current conversion of the low-frequency power transmission system M3C converter is alternating-current, and when the low-frequency power transmission system is started, like the direct-current power transmission system, the direct-current side switch can not be directly switched on to connect two stations for power transmission, the line switch synchronization is needed to be detected to connect a low-frequency line between the two stations, the system cost and the control complexity are increased, as in the patent of 'a wiring structure (patent grant number: CN 213879281U) for line change type synchronous switching on of a photovoltaic power generation station', overvoltage and overcurrent problems are easy to generate, and the safety and stability operation of equipment are influenced.
Disclosure of Invention
The invention aims to provide a soft start method of a low-frequency power transmission system, which has no voltage and current impact on the low-frequency power transmission system while no synchronization detection is needed, and ensures the equipment safety of the low-frequency power transmission system.
In order to achieve the above object, the solution of the present invention is:
in one aspect, the application provides a soft start method of a low-frequency power transmission system, wherein the low-frequency power transmission system comprises at least 2 converter stations, the low-frequency sides of the converter stations are connected in parallel to a common low-frequency power transmission network through low-frequency line switches, and the power frequency sides of the converter stations are connected to respective power frequency power transmission networks through power frequency charging switches; the converter station comprises a power frequency charging switch, a power frequency transformer, a matrix converter, a low-frequency transformer and a low-frequency line switch which are sequentially connected in series; the matrix converter is based on a full-bridge modularized multi-level matrix converter M3C; the soft start method comprises the following steps:
disconnecting the low frequency line switch of each converter station;
switching on the power frequency charging switch of each converter station to charge the bridge arm capacitor in an uncontrolled manner;
after the bridge arm capacitor voltages of all the converter stations are stable, each converter station is unlocked after being switched to a first operation mode; the first operation mode is used for controlling the bridge arm capacitor to be charged to a rated value;
after the voltage average value of each bridge arm capacitor reaches the rated value, the low-frequency line switch of each converter station is closed with zero voltage;
switching a certain converter station to a second operation mode and controlling a low-frequency side zero voltage; the second operation mode is used for controlling the voltage of the bridge arm capacitor to be stabilized at a rated value and controlling the matrix converter to self-produce low-frequency side voltage;
switching other converter stations to a third operation mode and controlling low-frequency side zero power; the third operation mode is used for controlling the voltage of the bridge arm capacitor to be stabilized at a rated value and controlling the low-frequency side power;
establishing the voltage of the low-frequency power transmission network to a rated value;
after the voltage of the low-frequency power transmission network reaches the rated value, the power is increased according to the instruction, and the starting is finished.
In a preferred scheme, the matrix converter comprises 9 bridge arms, wherein each three bridge arms are in one group and are divided into three groups; one end of each of the three bridge arms in the same group is connected with a three-phase power frequency port, the other ends of the three bridge arms are commonly connected to one phase of the low-frequency port, and the three bridge arms are respectively connected to different phases of the low-frequency port; the bridge arm comprises a reactor and a plurality of full-bridge sub-modules which are connected in series.
In a preferred scheme, the criterion of bridge arm capacitor voltage stabilization of the converter station is that the average value of the capacitor voltages of all bridge arm sub-modules is larger than a first capacitor voltage threshold value, and the first capacitor voltage threshold value is the power frequency side line voltage value of the converter divided by twice the number of sub-modules.
In a preferred embodiment, the first operation mode includes: and controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network, and continuously charging the capacitor of each bridge arm to rated voltage.
In a preferred embodiment, the second operation mode includes:
controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network to stabilize the capacitance voltage of each bridge arm at a rated value;
the matrix converter M3Cn is controlled to self-produce low-frequency side voltage, and the self-produce low-frequency side voltage comprises adjustable frequency and amplitude.
In a preferred embodiment, the third operation mode includes:
controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network to stabilize the capacitance voltage of each bridge arm at a rated value;
the low frequency side power level is controlled in accordance with the power target command.
In a preferred embodiment, the establishment of the voltage of the low-frequency power transmission network to the rated value is specifically: the converter station switched to the second operating mode establishes a low frequency power transmission network voltage at a rate of the order of seconds or minutes, and controls the low frequency power transmission network voltage from zero to a nominal value.
In a preferred scheme, after the voltage of the low-frequency power transmission network reaches a rated value, the method specifically comprises the following steps of: after the voltage of the low-frequency power transmission network reaches the rated value, the power is increased by the converter station switched to the third operation mode according to the instruction; and simultaneously switching to a converter station in a second operation mode, and controlling the amplitude and the frequency of the low-frequency power transmission network voltage to be in rated values.
In another aspect, the present application provides a computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements the steps of the above described soft start method of a low frequency power transmission system.
The beneficial effects of the invention are as follows:
1. the line switch can be switched on without detecting the synchronization of the switch in the starting process, and the low-frequency side of each converter station is connected, so that the cost and the complexity of the system are reduced;
2. the line switch is switched on in a state of zero voltage and zero current at the low-frequency line side, so that no voltage and current impact is caused to the low-frequency power transmission system, and the equipment safety of the low-frequency power transmission system is ensured;
3. only the control strategy of the low-frequency power transmission system is changed when the low-frequency power transmission system is started, a new hardware structure is not added, and the engineering site availability is high;
4. the method is suitable for low-frequency or frequency division power transmission engineering, and is suitable for two-end and multi-end engineering, and high in adaptability.
Drawings
Fig. 1 is a schematic diagram of a matrix converter structure;
fig. 2 is a low frequency power transmission system start-up flow chart;
figure 3 is a diagram of an embodiment of a low frequency power transmission system of three converter stations.
Detailed Description
The following describes specific embodiments of the present invention in detail with reference to the drawings.
The application is applicable to low frequency or divisionThe frequency transmission project is simultaneously suitable for two-end and multi-end projects. The low-frequency power transmission system comprises N converter stations, wherein N is more than or equal to 2, N is the number of the converter stations, (n=1, 2, … …, N), and the low-frequency side of the nth converter station passes through a low-frequency line switch QL n Parallel connection is connected to a common low-frequency power transmission network, and the power frequency side of the converter station passes through a power frequency charging switch QC n Accessing respective power frequency power transmission networks; the converter station comprises a power frequency charging switch QC which is sequentially connected in series n TG of power frequency transformer n Matrix converter M3C n TL (Low frequency Transformer) with low frequency n Low frequency line switch QL n . As shown in fig. 1, the matrix converter M3C n Consists of 9 bridge arms; every three bridge arms are divided into three groups; one end of each of the three bridge arms in the same group is connected with a three-phase power frequency port, the other ends of the three bridge arms are commonly connected to one phase of the low-frequency port, and the three bridge arms are respectively connected to different phases of the low-frequency port; each bridge arm is formed by connecting a reactor with a plurality of full-bridge submodules in series, and each full-bridge submodule comprises four switching devices and a capacitor.
Fig. 2 shows a soft start method of a low frequency power transmission system according to an embodiment of the present application, which is characterized in that the steps are:
s100: low-frequency line switch QL for switching off individual converter stations n The converter stations exit the low frequency power transmission network and are electrically isolated from each other.
S200: power frequency charging switch QC for switching on each converter station n And carrying out uncontrolled charging on the bridge arm capacitance.
S300: after the bridge arm capacitor voltages of all the converter stations are stable, each converter station is unlocked after being switched to a first operation mode; the first operation mode is used for controlling the bridge arm capacitor to be charged to a rated value.
S400: after the voltage average value of each bridge arm capacitor reaches the rated value, the low-frequency line switch QL of each converter station is closed by zero voltage n . Because the M3C low-frequency side keeps zero voltage in the first operation mode, the low-frequency side line switch can be directly switched on without detecting the same period of the switch, and the cost and the complexity of the system are reduced; at the position ofThe switch of the closing line is in a state of zero voltage and zero current at the low-frequency line side, so that no voltage and current impact is caused to the low-frequency power transmission system, and the equipment safety of the low-frequency power transmission system is ensured.
S500: switching a certain converter station to a second operation mode and controlling a low-frequency side zero voltage; the second operation mode is used for controlling the bridge arm capacitor voltage to be stabilized at a rated value and controlling the matrix converter to self-produce low-frequency side voltage.
S600: switching other converter stations to a third operation mode and controlling low-frequency side zero power; the third operation mode is used for controlling the voltage of the bridge arm capacitor to be stabilized at a rated value and controlling the low-frequency side power.
S700: the voltage of the low-frequency power transmission network is set to a rated value. In particular, the low frequency power transmission network voltage is established by the converter station switched to the second operation mode at a rate of seconds or minutes, and the low frequency power transmission network voltage is controlled from zero to the nominal value.
S800: after the voltage of the low-frequency power transmission network reaches the rated value, the power is increased according to the instruction, and the starting is finished. Specifically, after the voltage of the low-frequency power transmission network reaches a rated value, the power is increased by a converter station switched to a third operation mode according to instructions; and simultaneously switching to a converter station in a second operation mode, and controlling the amplitude and the frequency of the low-frequency power transmission network voltage to be in rated values.
In the starting method of the embodiment, each station converter is charged and unlocked from the power frequency side respectively, low-frequency voltage is not generated, and after all the station low-frequency line switches are connected to the low-frequency power transmission network in the zero-voltage state, the low-frequency voltage is built.
For step S300, in some embodiments, the method for determining the bridge arm capacitor voltage stabilization of the converter station is: and when the average value of the capacitance voltages of all the bridge arm sub-modules is larger than the first capacitance voltage threshold value, the bridge arm capacitance voltage of the current station is considered to be stable. The first capacitor voltage threshold is the power frequency side line voltage value of the converter divided by twice the number of the submodules.
For step S300, in some embodiments, the first mode of operation is set to: controlling positive and negative sequence current components flowing into matrix converter by power frequency power transmission network, and continuing to supply eachThe capacitance of each bridge arm is charged to the rated voltage. The power frequency positive sequence current component is used for continuously charging capacitance voltage average values of all bridge arms to rated values; the power frequency negative sequence current component is used for balancing M3C n The capacitance voltage average value of each bridge arm. The low frequency side voltage characteristic of the matrix converter in the first operation mode is to maintain zero voltage and no additional control is needed to make the low frequency side zero voltage.
For step S500, in some embodiments, the second mode of operation is set to: controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network to stabilize the capacitance voltage of each bridge arm at a rated value; the matrix converter M3Cn is controlled to self-generate low-frequency side voltage. The self-generated low-frequency side voltage comprises adjustable frequency and amplitude, the frequency can be changed from zero to power frequency, the amplitude can be changed from zero to rated value, and the rated frequency and the amplitude are usually defaulted. The power frequency positive sequence current component is used for maintaining the capacitance voltage average value of the bridge arm to be near the rated value; the power frequency negative sequence current component is used for balancing M3C n The capacitance voltage average value of each bridge arm.
For step S600, in some embodiments, the third operation mode is set as follows: controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network to stabilize the capacitance voltage of each bridge arm at a rated value; the low frequency side power level is controlled in accordance with the power target command. The power frequency positive sequence current component is used for maintaining the capacitance voltage average value of the bridge arm to be near the rated value; the power frequency negative sequence current component is used for balancing M3C n The capacitance voltage average value of each bridge arm.
The method will be described below with reference to fig. 3, taking a low frequency power transmission system consisting of three converter stations as an example.
Fig. 3 shows a low frequency power transmission system consisting of three converter stations. The converter station 1 is powered by a power frequency charging switch QC 1 TG of power frequency transformer 1 Matrix converter M3C 1 TL (Low frequency Transformer) with low frequency 1 Low frequency line switch QL 1 Sequentially connected in series; low frequency side of converter station 1 is switched QL by low frequency line 1 Parallel connection to common low-frequency power transmission network, 1 power frequency of converter stationSide-pass power frequency charging switch QC 1 And accessing to a power frequency power transmission network S1. The converter station 2 is powered by a power frequency charging switch QC 2 TG of power frequency transformer 2 Matrix converter M3C 2 TL (Low frequency Transformer) with low frequency 2 Low frequency line switch QL 2 Sequentially connected in series; low frequency side of converter station 2 is switched QL by low frequency line 2 The parallel connection is connected with a common low-frequency power transmission network, and the power frequency side of the converter station 2 passes through a power frequency charging switch QC 2 And accessing to a power frequency power transmission network S2. The converter station 3 is powered by a power frequency charging switch QC 3 TG of power frequency transformer 3 Matrix converter M3C 3 TL (Low frequency Transformer) with low frequency 3 Low frequency line switch QL 3 Sequentially connected in series; low frequency side of the converter station 3 is switched QL by a low frequency line 3 The parallel connection is connected with a common low-frequency power transmission network, and the power frequency side of the converter station 3 passes through a power frequency charging switch QC 3 And accessing to a power frequency power transmission network S3. The soft start method comprises the following steps:
low-frequency line switch QL for switching off individual converter stations 1 、QL 2 And QL 3 The method comprises the steps of carrying out a first treatment on the surface of the Each converter station exits the low-frequency power transmission network and is electrically isolated from each other;
power frequency charging switch QC for switching on each converter station 1 、QC 2 And QC 3 Uncontrolled charging is carried out on bridge arm capacitance;
after the capacitor voltage is stable, unlocking after each converter station is switched to a first operation mode; the first operation mode is set as: and controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network, and continuously charging the capacitor of each bridge arm to rated voltage. The control station 1 power frequency power transmission network S1 flows positive and negative sequence current components to the matrix converter M3C 1 Continuing to give M3C 1 The capacitor of each bridge arm is charged to rated voltage; the control station 2 power frequency power transmission network S12 flows positive and negative sequence current components to the matrix converter M3C 2 Continuing to give M3C 2 The capacitor of each bridge arm is charged to rated voltage; the control station 3 power frequency power transmission network S3 flows positive and negative sequence current components to the matrix converter M3C 3 Continuing to give M3C 3 The capacitance of each bridge arm is charged to the rated voltage.
Waiting for each bridge arm capacitanceAfter the voltage average value reaches the rated value, the zero voltage closes the line switch QL of each converter station 1 、QL 2 And QL 3 。
Switching the converter station 2 to the second operation mode and controlling the low frequency side zero voltage, switching the converter station 1 and the converter station 3 to the third operation mode and controlling the low frequency side zero power. The second operation mode is set as: controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network to stabilize the capacitance voltage of each bridge arm at a rated value; and controlling the matrix converter to self-generate low-frequency side voltage. The third mode of operation is set to: controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network to stabilize the capacitance voltage of each bridge arm at a rated value; the low frequency side power level is controlled in accordance with the power target command. The converter station 2 switched to the second operation mode controls the power frequency power transmission network S2 to flow positive and negative sequence current components to the matrix converter so as to stabilize M3C 2 The capacitance voltage of each bridge arm is at a rated value; simultaneous matrix converter M3C 2 The self-generated low-frequency side voltage comprises adjustable frequency and amplitude, the frequency can be changed from zero to power frequency, the amplitude can be changed from zero to rated value, and the default is rated frequency and amplitude; converter station 1 and converter station 3 switched to the third operation mode control power frequency power transmission networks S1 and S3 to flow positive and negative sequence current components to matrix converter M3C, respectively 1 And M3C 3 To stabilize M3C 1 And M3C 3 The capacitance voltage of each bridge arm is at a rated value; and meanwhile, the power of the low-frequency side is controlled according to a target instruction, and the power can be changed from zero to a rated value, including active power and reactive power.
Establishing the voltage of the low-frequency power transmission network to a rated value; the converter station 2 switched to the second operating mode establishes a low frequency power transmission network voltage at a rate of the order of seconds or minutes, reaching the nominal value from zero.
After the voltage of the low-frequency power transmission network reaches the rated value, the power is increased according to the instruction, and the starting is finished. After the voltage of the low-frequency power transmission network reaches the rated value, switching to a converter station 1 and a converter station 3 in a third operation mode, and raising power according to the instruction; the converter station 2 switched to the second operating mode controls the low frequency power transmission network voltage amplitude and frequency to be at nominal values.
The embodiment of the application also provides a computer readable storage medium, wherein the computer readable storage medium is stored with a computer program, and the computer program realizes the steps of the soft start method of the low-frequency power transmission system when being executed by a processor.
It will be appreciated by those skilled in the art that 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 flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations 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 embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereto, and any modification made on the basis of the technical scheme according to the technical idea of the present invention falls within the protection scope of the present invention.
The foregoing detailed description is directed to a specific embodiment of the invention, which is not intended to limit the scope of the invention, but rather is to be accorded the full scope of the claims without departing from the true spirit and scope of the invention.
Claims (9)
1. The soft start method of the low-frequency power transmission system comprises at least 2 converter stations, wherein the low-frequency sides of the converter stations are connected in parallel to a common low-frequency power transmission network through low-frequency line switches, and the power frequency sides of the converter stations are connected to respective power frequency power transmission networks through power frequency charging switches; the converter station comprises a power frequency charging switch, a power frequency transformer, a matrix converter, a low-frequency transformer and a low-frequency line switch which are sequentially connected in series; the matrix converter is based on a full-bridge modularized multi-level matrix converter M3C; the soft start method is characterized by comprising the following steps:
disconnecting the low frequency line switch of each converter station;
switching on the power frequency charging switch of each converter station to charge the bridge arm capacitor in an uncontrolled manner;
after the bridge arm capacitor voltages of all the converter stations are stable, each converter station is unlocked after being switched to a first operation mode; the first operation mode is used for controlling the bridge arm capacitor to be charged to a rated value;
after the voltage average value of each bridge arm capacitor reaches the rated value, the low-frequency line switch of each converter station is closed with zero voltage;
switching a certain converter station to a second operation mode and controlling a low-frequency side zero voltage; the second operation mode is used for controlling the voltage of the bridge arm capacitor to be stabilized at a rated value and controlling the matrix converter to self-produce low-frequency side voltage;
switching other converter stations to a third operation mode and controlling low-frequency side zero power; the third operation mode is used for controlling the voltage of the bridge arm capacitor to be stabilized at a rated value and controlling the low-frequency side power;
establishing the voltage of the low-frequency power transmission network to a rated value;
after the voltage of the low-frequency power transmission network reaches the rated value, the power is increased according to the instruction, and the starting is finished.
2. A soft start method of a low frequency power transmission system according to claim 1, wherein: the matrix converter comprises 9 bridge arms, wherein each three bridge arms are in one group and are divided into three groups; one end of each of the three bridge arms in the same group is connected with a three-phase power frequency port, the other ends of the three bridge arms are commonly connected to one phase of the low-frequency port, and the three bridge arms are respectively connected to different phases of the low-frequency port; the bridge arm comprises a reactor and a plurality of full-bridge sub-modules which are connected in series.
3. A soft start method of a low frequency power transmission system according to claim 1, wherein:
the criterion of the bridge arm capacitor voltage stability of the converter station is that the average value of the capacitor voltages of all bridge arm submodules is larger than a first capacitor voltage threshold value, and the first capacitor voltage threshold value is the power frequency side line voltage value of the matrix converter divided by twice the number of submodules.
4. A soft start method of a low frequency power transmission system according to claim 1, wherein: the first operation mode includes: and controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network, and continuously charging the capacitor of each bridge arm to rated voltage.
5. A soft start method of a low frequency power transmission system according to claim 1, wherein: the second operation mode includes:
controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network to stabilize the capacitance voltage of each bridge arm at a rated value;
and controlling the self-generated low-frequency side voltage of the matrix converter, wherein the self-generated low-frequency side voltage comprises adjustable frequency and amplitude.
6. A soft start method of a low frequency power transmission system according to claim 1, wherein: the third operation mode includes:
controlling positive and negative sequence current components flowing into the matrix converter by the power frequency power transmission network to stabilize the capacitance voltage of each bridge arm at a rated value;
the low frequency side power level is controlled in accordance with the power target command.
7. A method of soft start of a low frequency power transmission system according to claim 1, wherein said establishing a voltage to rating of the low frequency power transmission network is specifically: the converter station switched to the second operating mode establishes a low frequency power transmission network voltage at a rate of the order of seconds or minutes, and controls the low frequency power transmission network voltage from zero to a nominal value.
8. The soft start method of a low frequency power transmission system according to claim 1, wherein after the voltage of the low frequency power transmission network reaches a rated value, the method specifically comprises: after the voltage of the low-frequency power transmission network reaches the rated value, the power is increased by the converter station switched to the third operation mode according to the instruction; and simultaneously switching to a converter station in a second operation mode, and controlling the amplitude and the frequency of the low-frequency power transmission network voltage to be in rated values.
9. A computer readable storage medium, characterized in that the computer readable storage medium has stored thereon a computer program which, when executed by a processor, implements the steps of the soft start method of a low frequency power transmission system according to any of claims 1 to 8.
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