CN106921157B - Alternating-current side single-phase earth fault control method of flexible ring network controller - Google Patents

Alternating-current side single-phase earth fault control method of flexible ring network controller Download PDF

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Publication number
CN106921157B
CN106921157B CN201511001470.0A CN201511001470A CN106921157B CN 106921157 B CN106921157 B CN 106921157B CN 201511001470 A CN201511001470 A CN 201511001470A CN 106921157 B CN106921157 B CN 106921157B
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phase
alternating
current
voltage
current system
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CN106921157A (en
Inventor
阳岳希
高凯
庞辉
李强
邵宝珠
别晓玉
马巍巍
李胜辉
李洪志
许韦华
张潇桐
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Liaoning Electric Power Co Ltd
Smart Grid Research Institute of SGCC
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Liaoning Electric Power Co Ltd
Smart Grid Research Institute of SGCC
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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
    • 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]

Abstract

The invention provides a method for controlling a single-phase earth fault at an alternating current side of a flexible ring network controller, which comprises the following steps of 1: detecting the three-phase voltage of an alternating current system in real time; step 2: judging whether the alternating current system has single-phase earth fault; and step 3: acquiring the maximum value of the voltage peak value of the non-fault phase; and 4, step 4: re-determining a direct-current voltage command value of the alternating-current system; and 5: starting negative sequence current control and zero sequence current control; step 6: and judging whether the single-phase earth fault is cleared, and if so, restoring the direct-current voltage command value to the direct-current voltage command value when the alternating-current system normally operates. Compared with the prior art, the alternating-current side single-phase ground fault control method of the flexible looped network controller provided by the invention has the advantages that the direct-current voltage is reduced for a short time during the period that the single-phase ground fault occurs on the alternating-current side, the alternating-current still keeps a three-phase symmetrical sine waveform by utilizing the negative voltage output capability of the hybrid submodule structure, and the reliability of the flexible looped network controller is improved.

Description

Alternating-current side single-phase earth fault control method of flexible ring network controller
Technical Field
The invention relates to the technical field of power electronics, in particular to a method for controlling a single-phase earth fault at an alternating current side of a flexible ring network controller.
Background
With the continuous increase of transmission load, the development of power grid is established, and the electromagnetic ring network is continuously formed. The existing general method for disconnecting the electromagnetic ring network is to add an alternating current breaker at a disconnecting point or implement the partitioned operation of the power grid, but the precondition of the method is that the power grid has the basic condition of the open-loop operation. When the electromagnetic ring network is difficult to operate in an open loop mode and meets the condition of safety constraint, technologies such as a unified power flow controller, a phase shifter, an interphase power controller, a controllable series compensation and the like can be adopted, and voltage phase angles are adjusted through an FACTS device, so that circulation currents in the electromagnetic ring network are eliminated, short-circuit currents are limited, power distribution between high/low voltage networks is optimized, and the operation reliability and economy of a system are improved. The flexible ring network controller is back-to-back flexible direct current, and can realize the rapid independent control of active power and reactive power; when the alternating current system breaks down, the flexible direct current does not provide short-circuit current, the fault can be isolated rapidly, and the device has a black start function, and provides a choice for solving the problem of the electromagnetic looped network.
However, when the converter-less transformer is adopted to construct the flexible ring network controller system scheme of the converter based on the hybrid submodule, when the alternating current system has a ground short circuit fault, the fault voltage can directly act on the converter due to the fact that the converter transformer is not isolated, so that large fault voltage stress and current stress are caused, and equipment damage is easily caused. Therefore, it is necessary to provide a fault control method capable of reducing the dc voltage for a short time during a single-phase ground fault on the ac side, and preventing the fault from being transmitted to the other ac system.
Disclosure of Invention
In order to meet the needs of the prior art, the present invention provides a method for controlling an ac-side single-phase ground fault of a flexible looped network controller.
The technical scheme of the invention is as follows:
the method comprises the following steps:
step 1: detecting the three-phase voltage of an alternating current system in real time;
step 2: judging whether the alternating current system has a single-phase earth fault;
and step 3: obtaining the maximum value U of the voltage peak value of a non-fault phase after the single-phase earth fault of the alternating current system occurss_max；
And 4, step 4: redetermining direct-current voltage command value U 'of alternating-current system'd；
And 5: starting negative sequence current control and zero sequence current control;
step 6: judging whether the single-phase earth fault is cleared or not, and if so, judging that the direct-current voltage instruction value U'dRestoring the direct current voltage instruction value U to the normal operation of the alternating current systemd。
Preferably, in step 2, when the voltage of one phase of the ac system is reduced to 0 and the voltages of the other two phases are rapidly increased, a single-phase ground fault occurs in the ac system.
Preferably, the DC voltage command value U 'in step 4'dThe value range is as follows: u'd＜3Ud-2Us_max；
Wherein, UdThe direct current voltage instruction value is the direct current voltage instruction value when the alternating current system normally operates.
Preferably, the topology of the flexible ring network controller comprises a first converter and a second converter; the first converter and the second converter are both directly connected to an alternating current system;
each phase of half-bridge arm of the first converter is formed by connecting a full-bridge sub-module and at least one half-bridge sub-module in series;
each phase half bridge arm of the second converter is also formed by connecting a full-bridge submodule and at least one half-bridge submodule in series.
Compared with the closest prior art, the excellent effects of the invention are as follows:
1. the alternating-current side single-phase earth fault control method of the flexible ring network controller can completely inhibit overvoltage and overcurrent at the alternating-current side, prevent a current converter from bearing overhigh fault voltage and current, and improve the service life of equipment and the reliability of a system;
2. according to the alternating current side single-phase earth fault control method of the flexible ring network controller, the fluctuation of direct current voltage does not exceed +/-1%, the fluctuation of direct current is suppressed within +/-20%, and power electronic devices in a converter can be prevented from being damaged due to overcurrent;
3. according to the alternating current side single-phase earth fault control method of the flexible ring network controller, during the period that the single-phase earth fault occurs on the alternating current side, the direct current voltage is reduced for a short time, the negative voltage output capability of the hybrid submodule structure is utilized, the alternating current output by the converter station still keeps a three-phase symmetrical sine waveform, the fault component can be restrained, the fault is prevented from being transmitted to an alternating current system on the other side, and the reliability of the flexible ring network controller is improved.
Drawings
The invention is further described below with reference to the accompanying drawings.
FIG. 1: the topological structure schematic diagram of the flexible ring network controller in the embodiment of the invention;
FIG. 2: the response oscillogram of the half-bridge submodule in the normal operation of the alternating current system in the embodiment of the invention;
FIG. 3: the response waveform diagram of the half-bridge submodule in the embodiment of the invention when the single-phase earth fault occurs in the alternating current system;
FIG. 4: in the embodiment of the invention, the response oscillogram of the mixing submodule during the normal operation of the alternating current system is shown;
FIG. 5: the response oscillogram of the hybrid submodule in the embodiment of the invention when the single-phase earth fault occurs in the alternating-current system;
FIG. 6: the invention discloses a flow chart of an alternating-current side single-phase earth fault control method of a flexible ring network controller;
FIG. 7: the embodiment of the invention provides an alternating voltage oscillogram during fault-free control;
FIG. 8: the embodiment of the invention provides an alternating current oscillogram during fault-free control;
FIG. 9: the direct-current voltage oscillogram during the fault-free control in the embodiment of the invention;
FIG. 10: in the embodiment of the invention, a direct current waveform diagram is used during fault-free control;
FIG. 11: in the embodiment of the invention, an alternating voltage oscillogram during fault control is added;
FIG. 12: in the embodiment of the invention, an alternating current waveform diagram during fault control is added;
FIG. 13: in the embodiment of the invention, a direct-current voltage oscillogram during fault control is added;
FIG. 14: in the embodiment of the invention, a direct current waveform diagram during fault control is added.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
An embodiment of a method for controlling a single-phase ground fault on an ac side of a flexible ring network controller according to the present invention is shown in fig. 6, and specifically includes:
1. and detecting the three-phase voltage of the alternating current system in real time.
2. And judging whether the alternating current system has single-phase earth fault.
In this embodiment, when it is detected that the voltage of one phase of the ac system is reduced to 0 and the voltages of the other two phases are rapidly increased, a single-phase ground fault occurs in the ac system.
3. Obtaining the maximum value U of the voltage peak value of a non-fault phase after a single-phase earth fault occurs in an alternating-current systems_max。
4. Redetermining DC voltage command value U 'of AC system'd。
DC Voltage instruction value U 'in this embodiment'dThe value range is as follows: u'd＜3Ud-2Us_max；
Wherein, UdThe direct current voltage instruction value is the direct current voltage instruction value when the alternating current system normally operates.
5. And starting negative sequence current control and zero sequence current control.
6. Judging whether the single-phase earth fault is cleared or not, and if so, obtaining a direct-current voltage instruction value U'dRestoring the direct current voltage instruction value U to the normal operation of the alternating current systemd。
The topological structure of the flexible ring network controller adopting the alternating-current side single-phase ground fault control method is shown in fig. 1, and comprises a first converter and a second converter; and the first converter and the second converter are directly connected to an alternating current system. Wherein the content of the first and second substances,
each phase of half bridge arm of the first current converter is formed by connecting a full bridge submodule and at least one half bridge submodule in series, and each phase of half bridge arm of the second current converter is formed by connecting a full bridge submodule and at least one half bridge submodule in series. That is, in this embodiment, the first converter and the second converter are both converters formed by hybrid submodules.
In the embodiment, the response waveform diagrams of the half-bridge sub-module and the hybrid sub-module in normal operation of the alternating current system are respectively shown in fig. 2 and 4, and the response waveform diagrams of the half-bridge sub-module and the hybrid sub-module in single-phase ground fault of the alternating current system are respectively shown in fig. 3 and 5.
In this embodiment, when the ac-side single-phase ground fault control method is not adopted, the ac voltage waveform, the ac current waveform, the dc voltage waveform, and the dc current waveform of the flexible ring network controller are respectively shown in fig. 7, 8, 9, and 10; the ac voltage waveform, the ac current waveform, the dc voltage waveform and the dc current waveform of the flexible ring network controller after the ac side single-phase ground fault control method are shown in fig. 11, 12, 13 and 14, respectively.
As can be seen from fig. 7 to 14, when the control method is not used, overvoltage and overcurrent of about 1.35 times are generated on the ac side after a fault occurs, and when the control method is used, overvoltage and overcurrent on the ac side can be completely suppressed, so that the inverter is prevented from being subjected to excessive fault voltage and current, and the service life of the equipment and the reliability of the system are improved. Meanwhile, when the control method is not adopted, the common mode oscillation fluctuation generated by the direct current voltage after the fault occurs is about +/-20%, the fluctuation generated by the direct current is about +/-130%, the fluctuation of the direct current voltage after the control method is adopted does not exceed +/-1%, the fluctuation of the direct current is restrained within +/-20%, and the power electronic devices in the converter can be prevented from being damaged due to overcurrent.
Finally, it should be noted that: the described embodiments are only some embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Claims (2)

1. An alternating-current side single-phase ground fault control method of a flexible ring network controller, the method comprising:
step 1: detecting the three-phase voltage of an alternating current system in real time;
step 2: judging whether the alternating current system has a single-phase earth fault;
and step 3: obtaining the maximum value U of the voltage peak value of a non-fault phase after the single-phase earth fault of the alternating current system occurss_max；
And 4, step 4: redetermining direct-current voltage command value U 'of alternating-current system'd；
And 5: starting negative sequence current control and zero sequence current control;
step 6: judging whether the single-phase earth fault is cleared or not, and if so, judging that the direct-current voltage instruction value U'dRestoring the direct current voltage instruction value U to the normal operation of the alternating current systemd；
In the step 2, when the voltage of one phase of the alternating current system is reduced to 0, the voltage of the other two phases is rapidly increased, and then the alternating current system has a single-phase earth fault;
in the step 4, the DC voltage command value U'dThe value range is as follows: u'd＜3Ud-2Us_max；
Wherein, UdThe direct current voltage instruction value is the direct current voltage instruction value when the alternating current system normally operates.
2. The ac-side single-phase ground fault control method of the flexible ring network controller according to claim 1, wherein the topology of the flexible ring network controller includes a first converter and a second converter; the first converter and the second converter are both directly connected to an alternating current system;
each phase of half-bridge arm of the first converter is formed by connecting a full-bridge sub-module and at least one half-bridge sub-module in series;
each phase half bridge arm of the second converter is also formed by connecting a full-bridge submodule and at least one half-bridge submodule in series.
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