CN107332260B - Three-phase commutation system for improving stability of power system - Google Patents
Three-phase commutation system for improving stability of power system Download PDFInfo
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- CN107332260B CN107332260B CN201710661040.4A CN201710661040A CN107332260B CN 107332260 B CN107332260 B CN 107332260B CN 201710661040 A CN201710661040 A CN 201710661040A CN 107332260 B CN107332260 B CN 107332260B
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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
- H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
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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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
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Abstract
The invention belongs to the technical field of power electronics, and particularly relates to a three-phase commutation system for improving the stability of a power system, which comprises: the system comprises a sending end three phase and a receiving end three phase, wherein each phase of the sending end is respectively connected with an upper bridge arm and a lower bridge arm, and each phase of the receiving end is respectively connected with an upper bridge arm and a lower bridge arm; the three upper bridge arms of the sending end are connected with the three upper bridge arms of the receiving end through upper pole lines, and the three lower bridge arms of the sending end are connected with the three lower bridge arms of the receiving end through lower pole lines; the three phases of the sending end are respectively connected with respective bidirectional thyristors, and the three bidirectional thyristors are connected with any one of the three phases of the receiving end through a central line. The receiving end three-phase commutation is realized by controlling the on-off of each upper bridge arm, each lower bridge arm and each bidirectional thyristor. The output voltage and power of the three phases of the receiving end are changed by controlling the input quantity of the sub-modules. The phase change process can not generate cutoff or short circuit, and the phase change is not influenced by the direction of the damp current.
Description
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a three-phase commutation system for improving the stability of a power system.
Background
The stability problem of the power system is that whether the system returns to the original operation state or transits to a new stable operation state after a certain time after being disturbed in a certain normal operation state. The power system stability problem is generally divided into static stability and transient stability.
Fig. 1 is a schematic diagram of a generator connected to an infinite capacity system via a transformer, lines and the like. Neglecting the resistance and line admittance of each element, there is x∑＝xG+xT+xL. In normal operation, the generator and the infinite capacity system are synchronized. The power angle relation of the system is as follows:
wherein δ is phasor
And
is also called power angle.
As shown in fig. 2, the system may have two operating points a and b, and considering that the system is constantly subjected to various small disturbances, only a is a stable operating point, and b is unstable. When δ is less than 90 °, the operation of the system is stable.
At present, measures for improving the static stability of a power system include: the automatic adjusting excitation device is adopted, the reactance of the element is reduced (such as split conductors are adopted, the line voltage grade is improved, series compensation is adopted), the system structure is improved, and the like. The measures for improving the dynamic stability are as follows: the application of rapid fault removal and automatic reclosing improves the electromagnetic power output by the generator and reduces the mechanical power output by the prime motor.
The invention provides a three-phase commutation system for improving the stability of a power system. The key point is to design a power electronic system, and when the voltage phase angle difference between two ends of the line is increased by an angle larger than 120 degrees, the phase sequence between two ends of the alternating current line is converted, for example: the A, B, C three phases are converted into B, C, A, so that the angle can be reduced by 120 degrees, the power angle difference is reduced, and the system is stable.
Some existing phase-changing devices change the phase of a low-voltage load in a single phase, and instantaneous power failure or interphase instantaneous short circuit can be caused during phase change. The method provided by the invention enables the three phases to normally transmit power through alternating current respectively in the conventional state of the system, and when the phase is changed, the system is switched into a direct current transmission mode to transmit power, then phase conversion is carried out, and the three-phase alternating current transmission is recovered.
Disclosure of Invention
In view of the above technical problem, the present invention provides a three-phase commutation system for improving stability of an electric power system, including: the system comprises a sending end three phase and a receiving end three phase, wherein each phase of the sending end is respectively connected with an upper bridge arm and a lower bridge arm, and each phase of the receiving end is respectively connected with an upper bridge arm and a lower bridge arm; the three upper bridge arms of the sending end are connected with the three upper bridge arms of the receiving end through upper pole lines, and the three lower bridge arms of the sending end are connected with the three lower bridge arms of the receiving end through lower pole lines; the three phases of the sending end are respectively connected with respective bidirectional thyristors, and the three bidirectional thyristors are connected with any one of the three phases of the receiving end through a central line.
The upper bridge arm or the lower bridge arm is formed by connecting a plurality of sub-modules with the same structure and controllable on-off in series.
The sub-modules are sub-modules of the modular multilevel converter.
The receiving end three-phase commutation is realized by controlling the on-off of each upper bridge arm, each lower bridge arm and each bidirectional thyristor.
The output voltage and power of the three phases of the receiving end are changed by controlling the input quantity of the sub-modules.
And the system before the phase change is in an alternating current transmission state, the system is in a modularized multi-level flexible direct current transmission state during the phase change, and the alternating current transmission state is recovered after the phase change, so that the phase change is completed.
The invention has the beneficial effects that: and in a conventional state, the three phases normally transmit power through alternating current respectively, when the phases are changed, the system is switched to a direct current transmission mode to transmit power, then phase conversion is carried out, and the three-phase alternating current transmission is recovered. By the phase transformation method, the power angle of the power system is changed, and the stability of the power system is improved. And no current interruption or short circuit occurs in the process of phase change, thereby causing no great fluctuation of the transmission power. The phase transformation of the present invention is not affected by the direction of the tidal current.
Drawings
FIG. 1 is a schematic diagram of a stand-alone infinity system.
Fig. 2 shows the power-angle characteristics of a single-machine infinite system.
Fig. 3 is a main circuit of the commutation system of the power system.
Fig. 4 is a sub-module circuit.
FIG. 5 is a current loop before phase change
FIG. 6 shows sub-module operating state 1: v1 ON, V2 OFF
FIG. 7 shows submodule working state 2: v1 OFF, V2 ON
Fig. 8 shows the current loop after commutation.
Detailed Description
The embodiments are described in detail below with reference to the accompanying drawings.
As shown in fig. 3. Each phase is composed of a plurality of submodules with the same structure in series connection. TRA, TRB and TRC are bidirectional thyristors. Fig. 4 shows the internal structure of the submodule, wherein V1 and V2 are IGBTs, and VT1 and VT2 are thyristors.
(1) An alternating current transmission state:
in an initial state, V2 and VT2 of all submodules of an A-phase upper bridge arm are turned on, V1 and VT1 are turned off, the submodules are in a short-circuit state, an A-phase lower bridge arm and a TRA switching device are both in a turn-off state, and at the moment, an A-phase of a sending end is connected with an A-phase of a receiving end through an upper pole line. V2 and VT2 of all sub-modules of the B-phase lower bridge arm are switched on, V1 and VT1 are switched off, the sub-modules are in a short-circuit state, switch devices in the B-phase upper bridge arm and a TRB are in a switching-off state, and at the moment, the B-phase of a sending end is connected with the B-phase of a receiving end through a down-pole wire. And C-phase upper and lower bridge arms are switched off, C-phase TRC is switched on, and at the moment, the C-phase of the sending end and the C-phase of the receiving end are connected through a middle polar line. The three phases of the sending end alternating current A, B, C are then connected through the commutation loop and the receiving end A, B, C, respectively, as shown in fig. 5.
(2) The direct current transmission state:
when phase conversion is needed, VT1 and VT2 of all sub-modules are in normally open states, TRA, TRB and TRC are turned off, V1 and V2 are turned on and off according to a modular multi-level flexible direct current control mode, at the moment, the phase conversion system is similar to a back-to-back flexible direct current transmission system, and power is transmitted through direct current.
The submodule has two working states at this time: (1) IGBT V1 is on, and V2 is off. At the moment, the current can flow in two directions, and the output voltage is the sub-module capacitor voltage. As shown in fig. 6. (2) IGBT V1 is turned off, and V2 is turned on. At the moment, the current can flow in two directions, and the output voltage is zero voltage. As shown in fig. 7. The output voltage and power of the converter can be flexibly changed by controlling and changing the number of the sub-modules.
(3) And (3) restoring alternating current transmission and simultaneously carrying out phase commutation:
v2 and VT2 of all sub-modules of an upper bridge arm of a sending end A phase are switched on, V1 and VT1 are switched off, a lower bridge arm of the sending end A phase and a TRA switching device are in a switched-off state, V2 and VT2 of all sub-modules of an upper bridge arm of a receiving end B phase are switched on, V1 and VT1 are switched off, switching devices of all sub-modules of a lower bridge arm of the receiving end B phase are switched off, and the A phase of the sending end and the B phase of the receiving end are connected through an upper pole line. And the switching devices of all the sub-modules of the upper bridge arm and the lower bridge arm of the sending end B phase are turned off, the TRB is turned on, the switching devices of all the sub-modules of the upper bridge arm and the lower bridge arm of the receiving end C phase are turned off, and the B phase of the sending end and the C phase of the receiving end are connected through a middle polar line. V2 and VT2 of all sub-modules of the sending end C-phase lower bridge arm are turned on, V1 and VT1 are turned off, the sending end C-phase upper bridge arm and the TRA switching devices are in an off state, V2 and VT2 of all sub-modules of the receiving end A-phase lower bridge arm are turned on, V1 and VT1 are turned off, the switching devices of all sub-modules of the receiving end A-phase upper bridge arm are turned off, and at the moment, the sending end C-phase and the receiving end A-phase are connected through a down pole line. Therefore, the three phases of the sending end alternating current A, B, C are respectively connected with the three phases of the receiving end B, C, A through a phase change loop, so that the phase change is realized. As shown in fig. 8.
When the direction of the tide is reverse, the phase change mode is the same.
The above embodiments are only preferred embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (3)
1. A three-phase commutation system for improving the stability of an electrical power system, comprising: the system comprises a sending end three phase and a receiving end three phase, wherein each phase of the sending end is respectively connected with an upper bridge arm and a lower bridge arm, and each phase of the receiving end is respectively connected with an upper bridge arm and a lower bridge arm; the three upper bridge arms of the sending end are connected with the three upper bridge arms of the receiving end through upper pole lines, and the three lower bridge arms of the sending end are connected with the three lower bridge arms of the receiving end through lower pole lines; the three phases of the transmitting end are respectively connected with respective bidirectional thyristors TRA, TRB and TRC, and the three bidirectional thyristors are connected with any one of the three phases of the receiving end through a central line;
the upper bridge arm or the lower bridge arm is formed by connecting a plurality of sub-modules with the same structure and controllable on-off in series; the sub-modules are sub-modules of the modular multilevel converter;
1) an alternating current transmission state:
in an initial state, the IGBTs V2 and the thyristors VT2 of all the submodules of the phase A upper bridge arm are switched on, the IGBTs V1 and the thyristors VT1 are switched off, the submodules are in a short-circuit state, the phase A lower bridge arm and a bidirectional thyristor TRA switch device are both in a switching-off state, and at the moment, the phase A of a transmitting end is connected with the phase A of a receiving end through an upper pole line; the IGBT V2 and the thyristor VT2 of all the submodules of the B-phase lower bridge arm are switched on, the IGBT V1 and the thyristor VT1 are switched off, the submodules are in a short-circuit state, the switching devices in the B-phase upper bridge arm and the bidirectional thyristor TRB are in a switching-off state, and at the moment, the B-phase of a sending end and the B-phase of a receiving end are connected through a down-pole wire; the upper bridge arm and the lower bridge arm of the C phase are turned off, the bidirectional thyristor TRC of the C phase is turned on, and the C phase of the sending end and the C phase of the receiving end are connected through a middle polar line; then the three phases of the sending end alternating current A, B, C are respectively connected with the three phases of the receiving end A, B, C through the phase change loop;
2) the direct current transmission state:
when phase conversion is needed, thyristors VT1 and VT2 of all submodules are in normally open states, a bidirectional thyristor TRA, a bidirectional thyristor TRB and a bidirectional thyristor TRC are turned off, an IGBT V1 and an IGBT V2 are turned on and off according to a modularized multi-level flexible direct current control mode, and at the moment, the power of a phase conversion system is transmitted through direct current;
the submodule has two working states at this time:
1) the IGBT V1 is switched on, and the IGBT V2 is switched off; at the moment, the current can flow in two directions, and the output voltage is the sub-module capacitor voltage;
2) the IGBT V1 is turned off, and the IGBT V2 is turned on; at the moment, the current can flow in two directions, and the output voltage is zero voltage; the output voltage and power of the converter are flexibly changed by controlling and changing the number of the sub-modules;
3) and (3) restoring alternating current transmission and simultaneously carrying out phase commutation:
switching on IGBT V2 and a thyristor VT2 of all submodules of a sending end A phase upper bridge arm, switching off IGBT V1 and a thyristor VT1, switching devices of a sending end A phase lower bridge arm and a bidirectional thyristor TRA are in a switching-off state, switching on IGBT V2 and a thyristor VT2 of all submodules of a receiving end B phase upper bridge arm, switching off IGBT V1 and a thyristor VT1, switching devices of all submodules of a receiving end B phase lower bridge arm are switched off, and at the moment, the sending end A phase and the receiving end B phase are connected through an upper polar line; the switching devices of all the submodules of the upper bridge arm and the lower bridge arm of the phase B at the sending end are turned off, the bidirectional thyristor TRB is turned on, the switching devices of all the submodules of the upper bridge arm and the lower bridge arm of the phase C at the receiving end are turned off, and the phase B at the sending end and the phase C at the receiving end are connected through a middle polar line; the IGBT V2 and the thyristor VT2 of all the submodules of the sending end C-phase lower bridge arm are switched on, the IGBT V1 and the thyristor VT1 are switched off, the sending end C-phase upper bridge arm and the bidirectional thyristor TRC switching device are both in a switching-off state, the IGBT V2 and the thyristor VT2 of all the submodules of the receiving end A-phase lower bridge arm are switched on, the IGBT V1 and the thyristor VT1 are switched off, the switching devices of all the submodules of the receiving end A-phase upper bridge arm are switched off, and at the moment, the sending end C-phase A-phase and the receiving end; therefore, three phases of the sending end alternating current A, B, C are respectively connected with three phases of the receiving end B, C, A through a phase change loop to realize phase change;
when the direction of the tide is reverse, the phase change mode is the same.
2. The system of claim 1, wherein the output voltage and power of the receiving end three phases are changed by controlling the number of inputs of the submodules.
3. The system of claim 1, wherein the system is in an AC transmission state before commutation, in a modular multilevel flexible DC transmission state during commutation, and is restored after commutation to complete commutation.
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| CN111049407B (en) * | 2020-01-03 | 2021-03-02 | 东南大学 | Series-parallel modular multilevel converter with current-breaking capability and control method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN104904109A (en) * | 2012-11-27 | 2015-09-09 | Abb技术有限公司 | Thyristor based voltage source converter |
| CN106099873A (en) * | 2016-06-30 | 2016-11-09 | 全球能源互联网研究院 | A kind of subregion interconnect device monopolar grounding fault guard method without connection transformator |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104904109A (en) * | 2012-11-27 | 2015-09-09 | Abb技术有限公司 | Thyristor based voltage source converter |
| CN106099873A (en) * | 2016-06-30 | 2016-11-09 | 全球能源互联网研究院 | A kind of subregion interconnect device monopolar grounding fault guard method without connection transformator |
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