CN114362232B - Method for defending commutation failure in double-loop same-tower system and control system - Google Patents
Method for defending commutation failure in double-loop same-tower system and control system Download PDFInfo
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- CN114362232B CN114362232B CN202111610224.0A CN202111610224A CN114362232B CN 114362232 B CN114362232 B CN 114362232B CN 202111610224 A CN202111610224 A CN 202111610224A CN 114362232 B CN114362232 B CN 114362232B
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- 230000008569 process Effects 0.000 claims description 4
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- 230000009977 dual effect Effects 0.000 claims 1
- 230000001808 coupling effect Effects 0.000 abstract description 16
- 230000008878 coupling Effects 0.000 description 7
- 238000010168 coupling process Methods 0.000 description 7
- 238000005859 coupling reaction Methods 0.000 description 7
- 230000007123 defense Effects 0.000 description 7
- 230000008859 change Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 3
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- 230000002265 prevention Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
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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
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- 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 discloses a defending method and a control system for commutation failure in a double-loop same-tower system. The method is simple to control, can be applied to a multi-circuit same-tower direct current transmission system, effectively prevents sound pole commutation failure caused by a line coupling effect, and ensures safe and stable operation and power transmission of the direct current system.
Description
Technical Field
The invention relates to the field of direct current transmission, in particular to a method for defending commutation failure in a double-loop co-tower system and a control system.
Background
The power grid commutation converter type high-voltage direct current transmission becomes an important component means for long-distance large-capacity transmission and regional power grid interconnection by virtue of the advantages of large power transmission capacity, low transmission loss, strong asynchronous connection capability, low long-distance transmission cost and the like.
FIG. 1 is a block diagram of a dual-loop co-tower DC system. The direct current system comprises two direct current lines (namely two direct current transmission units), each direct current line is provided with two direct current transmission lines, and the total of four direct current transmission lines of the double-circuit same-tower direct current system. Each direct current transmission line comprises a rectifying station, an inversion station and a direct current transmission line, and each direct current system comprises a positive electrode and a negative electrode (positive electrode line and a negative electrode line). The input end of the rectifying station is connected with the sending end alternating current system, and the output end of the inverting station is connected with the receiving end alternating current system; the output end of the rectifying station is connected with the input end of the inverting station.
Referring to fig. 2, two dc transmission lines are all erected on the same tower, and mutual inductance and mutual capacitance exist between the lines, and each dc transmission line is typically formed by combining split conductors.
The direct current circuit model in the double-circuit same-tower direct current transmission system is as follows:
wherein u is 1 、u 2 、u 3 、u 4 Respectively representing the voltage at a certain position on each direct current transmission line; i.e 1 、i 2 、i 3 、i 4 Respectively representing the direct current on each direct current transmission line; l, R, C and G are coefficient matrices of inductance, resistance, capacitance and conductance, respectively, specifically:
wherein L is 1 、L 2 、L 3 、L 4 Respectively represent each straight lineSelf-inductance of current transmission line, R 1 、R 2 、R 3 、R 4 Respectively represent the resistance of each transmission line, G 1 、G 2 、G 3 、G 4 Respectively represent the conductance of each transmission line, C 1 、C 2 、C 3 、C 4 Respectively representing the capacitance to ground of each direct current transmission line, C 1∑ 、C 2∑ 、C 3∑ 、C 4∑ Respectively representing the equivalent coupling capacitance of each direct current transmission line; c (C) ij (i=1, 2,3,4, j=1, 2,3, 4) represents the mutual capacitance between line i and line j. The direct current transmission lines erected on the same tower are closer in distance and compact in distribution, mutual inductance and mutual capacitance between the lines are not negligible, and the line coupling effect is obvious.
In practical direct current transmission engineering, a plurality of direct current transmission lines are usually erected with a tower, the distance between the direct current lines is relatively short, electromagnetic coupling exists between the lines, and the coupling effect and influence of the lines are more obvious along with the improvement of the transmission distance and the transmission grade. Because the conventional direct current system adopts the thyristor as the commutation element, the commutation failure is an inherent problem, and the severe change of the electric quantity of a certain circuit caused by the fault can cause the severe fluctuation of the electric quantity of a sound circuit caused by the electromagnetic coupling between the circuits, so that the commutation failure of the certain sound circuit is caused. However, the existing commutation failure prevention control based on the detection of the ac voltage at the inversion side is difficult to effectively suppress the commutation failure of this type, and therefore, it is necessary to study an effective prevention method for the commutation failure caused by the line coupling effect (the commutation failure caused by the line coupling effect includes the dc line ground fault condition, the dc fault line restart condition, and the dc current flowing condition at the inversion side).
The existing defense methods mainly comprise the following steps:
1. based on the commutation voltage time area theory, the judgment of commutation failure caused by the coupling effect of the same-tower parallel-rack multi-circuit direct current line is realized in an online real-time calculation mode, but the calculation is complex, and the system is not beneficial to quickly triggering corresponding defensive measures.
2. Aiming at the monopole ground fault working condition, the commutation failure defense method based on real-time emergency trigger angle calculation is slow in corresponding speed, limited in applicable working condition and still needs to be improved in the aspects of response speed and multi-working condition application range.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a defense method and a control system for commutation failure in a double-loop co-tower system, aiming at the defects of the prior art, and effectively avoiding the successive commutation failure of other sound polar lines caused by line coupling of fault polar lines in the double-loop system.
In order to solve the technical problems, the invention adopts the following technical scheme: a defending method of commutation failure in a double-loop same-tower system comprises two direct-current power transmission units, wherein each direct-current power transmission unit comprises two direct-current power transmission lines; comprising the following steps:
when a certain direct current transmission line of the double-circuit same-tower system fails, judging whether the commutation failure risk of other direct current transmission lines is increased;
when the commutation failure risk of the other direct current transmission lines is increased, triggering the inversion side valve bank of the direct current transmission line with the increased commutation failure risk in advance.
According to the invention, after judging the sound pole with the increased commutation risk caused by the coupling effect of the fault line, the inversion side valve bank of the sound pole is triggered in advance, so that the problem that the fault line in the double-circuit system causes the successive commutation failure of other sound lines through the line coupling is effectively avoided, and the stable operation capability of the system is improved.
The specific implementation process for judging whether the commutation failure risk of other direct current transmission lines is increased comprises the following steps:
collecting fault signals of a double-circuit same-tower system and direct current of an inversion side of each direct current transmission unit;
analyzing the fault signal, and if the fault type is that the direct current on the direct current fault line restarts or the direct current on the inversion side flows through and the direct current on the inversion side of the direct current transmission unit with the fault increases, increasing the risk of commutation failure of the valve bank on the inversion side of the direct current transmission line, which is opposite to the direct current direction of the direct current transmission line with the fault, in other direct current transmission lines; if the fault type is a direct current line grounding fault and the direct current of the inversion side of the failed direct current transmission unit is reduced, the risk of phase inversion failure of the inversion side valve group of the direct current transmission line in the same direction as the direct current of the failed direct current transmission line in other direct current transmission lines is increased.
The commutation failure risk judging method is based on Lenz's law, does not need complex data sampling and calculation, has short control delay and quick system response, and is beneficial to the commutation failure defense of the direct current transmission system.
The specific implementation process for triggering the inversion side valve bank of the direct current transmission line in advance comprises the following steps: controlling the trigger angle instruction of the inversion side valve bank of the direct current transmission line to be alpha inv ：
α inv ＝α inv0 -Δα CFP -Δα；
Wherein alpha is inv0 For the generated inversion-side firing angle command, Δα CFP As the trigger angle advance in voltage drop, delta alpha max For the upper limit value of the trigger angle advance, P N Is the rated transmission power of the direct current transmission line, I dNmax For maximum allowable DC current, X s For equivalent commutation reactance, U ac Rated AC bus voltage at inversion side of DC transmission line, gamma N Is the rated arc extinguishing angle.
The triggering angle instruction adjustment belongs to feedforward control, is quick in control response, and can effectively avoid the problem of phase-change failure of a sound pole line caused by a coupling effect of a fault line while ensuring the transmission level of direct current power, and ensure the safe and stable operation of an alternating current-direct current system.
As an inventive concept, the present invention also provides a control system for a dual-loop co-tower system, comprising a computer device; the computer device is configured or programmed to perform the steps of the defense method of the present invention.
Compared with the prior art, the invention has the following beneficial effects: the invention provides a defending method for commutation failure caused by direct current line coupling effect in a double-loop same-tower system. The method provided by the invention can be applied to a double-loop same-tower direct current transmission system, and can effectively avoid the successive commutation failure of other sound polar lines caused by the coupling of the fault polar lines in the double-loop system, thereby improving the stable operation capability and the power transmission level of the system.
Drawings
FIG. 1 is a block diagram of a dual-loop co-tower DC system;
fig. 2 is a block diagram of a direct current transmission line of a dual-loop system;
FIG. 3 is a flow chart of a defense method according to an embodiment of the present invention;
fig. 4 is a control schematic diagram of a dc power transmission system according to an embodiment of the present invention;
FIG. 5 (a) shows the change of the DC current on the inversion side of each pole line after the earth fault of the I return positive pole line; fig. 5 (b) shows the change of the turn-off angle of the II return positive and negative lines after the I return positive line has a ground fault; FIG. 5 (c) shows the change of the DC current at the inversion side of each pole line after the earth fault of the I return positive pole line after the method of the present invention is introduced; fig. 5 (d) shows the change of the turn-off angle of the II return positive and negative wires after the earth fault of the I return positive wire after the method of the present invention is introduced.
Detailed Description
As shown in fig. 3, for the dual-loop same-tower dc transmission system, the present embodiment is improved by the control system, so as to solve the problem of robust pole commutation failure caused by the line coupling effect. Referring to fig. 3, the method according to the embodiment of the present invention specifically includes the following steps: (1) Judging a sound pole with increased commutation risk caused by the coupling effect of the fault line; (2) And triggering the inversion side valve bank with increased commutation risk in the sound pole (namely, the direct current transmission line which does not have faults) in advance to prevent commutation failure.
Specifically, the robust determination of the increased risk of commutation failure includes the steps of:
(1) Collecting fault signals Flag1, flag2, flag3 and Flag4 of double-circuit positive and negative electrode lines and direct current i at inversion side of each line I-1 、i I-2 、i II-1 、i II-2 ；
(2) Analyzing the fault signals of all the lines and the current change condition of the inversion side of the fault pole, and judging whether the risk of commutation failure of all sound pole lines is increased due to the line coupling effect.
Referring to table 1, the specific failure determination method is: if the fault type is that the direct current fault line is restarted or the direct current of the inversion side flows through and the direct current of the inversion side of the fault line is increased, the inversion side valve bank of the sound polar line opposite to the current direction is increased in the commutation failure risk; if the fault type is a direct current line ground fault and the direct current of the inversion side of the fault line is reduced, the risk of commutation failure of the inversion side valve group of the sound polar line with the same current direction is increased.
TABLE 1 Fault Condition correspondence
Further, after judging a sound pole with an increased risk of commutation failure, the corresponding control is enabled. Referring to fig. 4, the power command of the healthy return dc system is adjusted to 1.2 times the rated value, and the healthy pole inversion side valve bank with increased risk of commutation failure is enabled to trigger control in advance. Specifically, in the advanced triggering control method of the sound pole inversion side valve group, the triggering angle instruction is alpha inv ＝α inv0 -Δα CFP -Δα。
Wherein alpha is inv For the final inversion side firing angle command, α inv0 For the inversion side trigger angle instruction generated by the original control system, delta alpha is the introduced trigger angle advance, delta alpha CFP Is the trigger angle advance at the time of voltage drop (if no voltage drop occurs, Δα CFP =0). Specifically, the introduced trigger angle advance delta alpha meets the protection requirement of commutation failure, and ensures that the transmission power of a sound line is not less than rated power, so that the maximum value calculation formula of delta alpha is as follows:
wherein Δα max For the upper limit value of the trigger angle advance, P N For rated transmission of DC power, I dNmax For maximum allowable DC current, X s For equivalent commutation reactance, U ac For the rated ac busbar voltage at the inverter side, gamma N Is the rated arc extinguishing angle.
Referring to fig. 5 (a), after the positive line returned to I has a ground fault, the dc current on the inverter side is suddenly reduced after the ground fault, and the positive line current returned to II is increased due to the line coupling effect; referring to fig. 5 (b), the off angle of the II return positive line rapidly drops to 0, i.e., the inversion side of the II return positive line fails to commutate, in addition, the current of the II return positive line further increases after the commutation failure of the II return positive line, which results in unavoidable increase of the current of the II return negative line under the influence of line coupling, and then the phase-change failure of the II negative line occurs, i.e., the phase-change failure of the II return positive line is mainly affected by the grounding failure of the I return positive line, and the phase-change failure of the II return negative line is mainly affected by the phase-change failure of the II return positive line. It can be said that the commutation failure of the II-back negative line is a chain reaction due to the line coupling effect.
Referring to fig. 5 (c), after the defense method according to the embodiment of the present invention is introduced, the fault current of the healthy polar line is limited to a certain extent; referring to fig. 5 (d), the turn-off angle of the II return positive line is not dropped to 0 although it is reduced, i.e., no commutation failure occurs due to the line coupling effect, so that the commutation failure of the II return negative line is also effectively avoided, i.e., the occurrence of the subsequent cascading failure of the line coupling effect is avoided.
Claims (4)
1. A defending method of commutation failure in a double-loop same-tower system comprises two direct-current power transmission units, wherein each direct-current power transmission unit comprises two direct-current power transmission lines; characterized by comprising the following steps:
when a certain direct current transmission line of the double-circuit same-tower system fails, judging whether the commutation failure risk of other direct current transmission lines is increased;
when the commutation failure risk of the other direct current transmission lines is increased, triggering an inversion side valve bank of the direct current transmission line with the increased commutation failure risk in advance;
the specific implementation process for triggering the inversion side valve bank of the direct current transmission unit in advance comprises the following steps:
controlling the trigger angle instruction of the inversion side valve bank of the direct current transmission line to be alpha inv ：
α inv ＝α inv0 -Δα CFP -Δα；
Wherein alpha is inv0 For the generated inversion-side firing angle command, Δα CFP As the trigger angle advance in voltage drop, delta alpha max For the upper limit value of the trigger angle advance, P N Is the rated transmission power of the direct current transmission line, I dNmax For maximum allowable DC current, X s For equivalent commutation reactance, U ac Rated AC bus voltage at inversion side of DC transmission line, gamma N Is the rated arc extinguishing angle.
2. The method for defending commutation failure in a double-loop co-tower system according to claim 1, wherein the specific implementation process for judging whether the commutation failure risk of other direct current transmission lines is increased comprises:
collecting fault signals of a double-circuit same-tower system and direct current of an inversion side of each direct current transmission unit;
analyzing the fault signal, and if the fault type is that the direct current on the direct current fault line restarts or the direct current on the inversion side flows through and the direct current on the inversion side of the direct current transmission unit with the fault increases, increasing the risk of commutation failure of the valve bank on the inversion side of the direct current transmission line, which is opposite to the direct current direction of the direct current transmission line with the fault, in other direct current transmission lines; if the fault type is a direct current line grounding fault and the direct current of the inversion side of the failed direct current transmission unit is reduced, the risk of phase inversion failure of the inversion side valve group of the direct current transmission line in the same direction as the direct current of the failed direct current transmission line in other direct current transmission lines is increased.
3. A control system for a dual-loop co-tower system, comprising a computer device; the computer device being configured or programmed for performing the steps of the method of claim 1 or 2.
4. A dual loop co-tower system employing the control system of claim 3.
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