CN111884210A - Commutation failure control method and system under direct current layered access based on harmonic analysis - Google Patents

Commutation failure control method and system under direct current layered access based on harmonic analysis Download PDF

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CN111884210A
CN111884210A CN202010712985.6A CN202010712985A CN111884210A CN 111884210 A CN111884210 A CN 111884210A CN 202010712985 A CN202010712985 A CN 202010712985A CN 111884210 A CN111884210 A CN 111884210A
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CN111884210B (en
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姚伟
王凌娆
高东学
李程昊
艾小猛
文劲宇
张景超
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Huazhong University of Science and Technology
Electric Power Research Institute of State Grid Henan Electric Power Co Ltd
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Huazhong University of Science and Technology
Electric Power Research Institute of State Grid Henan Electric Power Co Ltd
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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
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • 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
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics
    • 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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Abstract

The invention discloses a method and a system for controlling commutation failure under direct current layered access based on harmonic analysis, and belongs to the field of power system control. The invention detects the current rising condition of the inversion side and the harmonic amplitude change in the commutation voltage in real time in a direct current layered access system, when the current or the harmonic amplitude is higher than a steady-state operation threshold value, a compensation quantity for advancing the trigger angle is generated according to the current rising quantity and the harmonic amplitude respectively, after an alternating current fault occurs, the CFPREV of the fault layer is started to output but the CFPREV of the non-fault layer is not output, the trigger angle is controlled in advance at the stage of the turn-off angle reduction of the converter of the non-fault layer, and the probability of commutation failure caused by fault disturbance of the non-fault layer is reduced.

Description

Commutation failure control method and system under direct current layered access based on harmonic analysis
Technical Field
The invention belongs to the field of power system control, and particularly relates to a commutation failure control method and system under direct current layered access based on harmonic analysis.
Background
In recent years, with the major breakthrough of the ultra-high voltage direct current transmission technology in China, a plurality of ultra-high voltage direct current transmission projects are built and put into operation one after another, direct current drop points are more and more intensive, and the voltage supporting capability of a receiving-end power grid with multi-feed-in direct current is severely challenged. In order to solve the problems, the engineering industry provides a structure for hierarchically connecting an extra-high voltage direct current inverter station into a receiving end alternating current power grid, so that the system has a large multi-feed short circuit ratio and a large voltage supporting capacity on the whole.
Due to the particularity of the topology structure in the layered access mode, the converters of different layers of the inverter station have complex coupling characteristics, including direct current coupling caused by series direct current paths and alternating current coupling caused by power exchange on connecting lines among buses. Valve bank control generally adopted by the inversion side of the conventional extra-high voltage direct current layered access system comprises fixed extinction angle control, fixed voltage control and Commutation failure prevention Control (CFPREV) as a Commutation failure auxiliary response. When an alternating current fault occurs near one layer of the converter buses, due to different electrical distances from the fault, the response of a fault layer is inconsistent with that of a CFPREV of a non-fault layer valve bank, and the response of the fault layer is generally faster, while the response of the non-fault layer is slower. However, due to the existence of the coupling relationship, the working state of the non-fault layer converter is affected by the fault layer converter, the turn-off angle rapidly drops, and the CFPREV does not output timely to regulate and control the firing angle, which may finally cause the commutation failure of the non-fault layer converter. The traditional commutation failure prevention control can not meet the operation requirement of a layered access system, so that the practical engineering value is realized on how to carry out coordination control in the layered access system and prevent the non-fault layer converter from generating commutation failure when the fault layer converter is disturbed.
At present, researches on prevention and control in an extra-high voltage layered access system are all based on fundamental voltage and fundamental current, and the threat of harmonic wave transmission in a layered system to non-fault layer commutation is not concerned yet. Tan Yan Gem et al propose that when commutation failure prevention control of a fault layer is started, commutation failure prevention control of a non-fault layer is synchronously started to realize coordination control under layered access. However, the strategy is only to simply synchronize the control of the fault layer with the control of the non-fault layer, and the control output process has difficulty in following response to the change of the converter working state in the non-fault layer.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to solve the technical problems that in the process of phase commutation failure prevention and control of an extra-high voltage layered access system, a non-fault layer is far away from a fault point, the voltage drop degree is small, the CFPREV starting time is late, and the phase commutation failure cannot be effectively prevented in time.
In order to achieve the above object, in a first aspect, an embodiment of the present invention provides a method for controlling commutation failure under dc hierarchical access based on harmonic analysis, in which a rectification converter station in an applied dc hierarchical access system accesses a rectification side through a converter transformer, and a converter station on an inversion side accesses the inversion side in a hierarchical access manner, where a high-side converter directly connected to positive and negative dc electrode lines accesses a 500kV ac bus, which is referred to as a 500kV layer, and a low-side converter directly connected to a neutral point accesses a 1000kV ac bus, which is referred to as a 1000kV layer, and each layer is provided with a commutation failure prevention control CFPREV, the method including the following steps:
s1, acquiring three-phase voltage signals and phase-change current signals of a current-change bus at the inversion side of the layer in real time;
s2, carrying out FFT (fast Fourier transform) on the three-phase voltage signal to respectively obtain a 2-order harmonic amplitude and a 3-order harmonic amplitude, judging whether the maximum harmonic amplitude exceeds a steady-state harmonic amplitude threshold value, if so, enabling harmonic compensation control, calculating the advance of a trigger angle aiming at harmonic change according to the maximum harmonic amplitude, otherwise, not enabling the harmonic compensation control, and enabling the advance of the trigger angle aiming at the harmonic change to be zero;
s3, judging whether the phase change current signal exceeds a steady-state current amplitude threshold value, if so, enabling current compensation control, calculating the advance of the trigger angle aiming at the current rise according to the current increment, otherwise, not enabling the current compensation control, and enabling the advance of the trigger angle aiming at the current change to be zero;
s4, judging whether the current converter is in a stage that a turn-off angle falls and phase commutation failure does not occur, if so, entering step S5, otherwise, entering step S1;
s5, judging whether the CFPREV of the current layer is started to output, if so, entering a step S1, otherwise, entering a step S6;
s6, judging whether the other layer of CFPREV is started to output, if so, entering a step S7, otherwise, entering a step S1;
and S7, adding the trigger angle lead aiming at the harmonic change and the trigger angle lead aiming at the current change, sending the sum to a trigger angle instruction link, and carrying out trigger angle lead control on the current layer (namely the non-fault layer).
The invention provides a method for controlling commutation failure under direct current hierarchical access based on harmonic analysis, which is used for controlling a trigger angle of an inverter side converter in a transient process under a hierarchical access mode, and is used for controlling the trigger angle based on harmonic detection and current detection in advance on the basis of turn-off angle instruction value calculation and CFPREV in conventional valve bank control. The commutation failure prevention optimization control method under the direct current layered access comprises two parts: firing angle compensation control for harmonic changes and firing angle compensation control for current changes; aiming at the trigger angle compensation control of harmonic change, FFT (fast Fourier transform) is carried out on three-phase voltage of an inverter side converter bus to obtain 2-order harmonic amplitude and 3-order harmonic amplitude of each phase, and the maximum Har is selectedmaxHar with steady state harmonic amplitude thresholdstableComparing, if Har is exceededstableThen flag bit H will be enabledsignal Setting 1, and combining the maximum harmonic amplitude HarmaxMultiplication byHarmonic coefficient kharmonicObtaining the trigger angle advance delta alpha aiming at harmonic wave changeharAnd to Δ αharClipping is at 15 °;
for the trigger angle compensation control of current variation, the direct current I is applieddAnd steady state current threshold Id_stBy comparison, if it exceeds Id_staThen the flag bit I will be enabledsignal Setting 1, applying a direct current IdThe difference with the steady-state current is obtained to obtain the current increase amount delta IdMultiplied by the current coefficient
Figure BDA0002597218380000031
Obtaining trigger angle lead for current change
Figure BDA0002597218380000032
And to
Figure BDA0002597218380000033
Clipping is at 15 °;
finally, the output delta alpha controlled by the two parts is outputharAnd
Figure BDA0002597218380000034
adding and limiting within 20 degrees, and using the sum as the output delta alpha of the commutation failure prevention optimization control strategyHI。
Preferably, whether the converter is in a stage that the turn-off angle drops and no commutation failure occurs refers to a stage that the turn-off angle of the inverter side converter on the non-fault layer starts to decrease after the inverter side converter is disturbed by a fault and is lower than a steady-state value but higher than a minimum turn-off angle value, and the value range is [5 degrees ], 20 degrees ].
Preferably, whether CFPREV has enabled output means that output Δ α of CFPREV is to be outputCFPREVWhen higher than this value, CFPREV is considered to have enabled output, otherwise CFPREV is considered to have not enabled output, as compared to a minimum value of 0.001.
In a second aspect, the present invention provides a harmonic analysis-based commutation failure control system under dc hierarchical access, including:
the signal acquisition unit is used for acquiring three-phase voltage signals and phase-change current signals of the current-changing bus at the inversion side of the layer in real time;
the harmonic detection and compensation unit is used for performing FFT (fast Fourier transform) on the three-phase voltage signal to respectively obtain a 2-order harmonic amplitude and a 3-order harmonic amplitude, and calculating trigger angle compensation quantity aiming at harmonic change according to the 2-order harmonic amplitude and the 3-order harmonic amplitude;
the current detection and compensation unit is used for calculating trigger angle compensation amount aiming at current change according to the phase change current signal increase amount;
the converter turn-off angle detection unit is used for detecting the turn-off angle of the converter to judge the working state of the converter and ensure that the trigger angle compensation is output only in the process of reducing the turn-off angle of the non-fault layer after the fault occurs;
and the CFPREV detection unit is used for detecting the starting state of each layer of CFPREV in the system and ensuring that the trigger angle compensation of the non-fault layer is output only when the CFPREV of the fault layer is started but not when the CFPREV of the non-fault layer is not started after the fault occurs.
Preferably, the turn-off angle of the inverter-side converter on the non-fault layer starts to decrease after the inverter-side converter is subjected to fault disturbance, is lower than a steady-state value but higher than a minimum turn-off angle value, and is in a stage that the turn-off angle of the converter with the value range of [5 degrees and 20 degrees ] falls and no commutation failure occurs.
Preferably, the output Δ α of CFPREVCFPREVWhen higher than this value, CFPREV is considered to have enabled output, otherwise CFPREV is considered to have not enabled output, as compared to a minimum value of 0.001.
In a third aspect, the present invention provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the commutation failure control method under the dc hierarchical access based on harmonic analysis according to the first aspect.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
the method for controlling commutation failure under direct current layered access based on harmonic analysis comprises two aspects of harmonic detection and compensation control and current detection and compensation control. Due to the complex alternating current-direct current coupling relationship among layers in the layered access system, the current of a fault layer is increased and a large amount of harmonic waves are generated after an alternating current fault occurs, and the alternating current-direct current coupling relationship is a main reason for the phase change failure of a non-fault layer. The method can detect the change of current rise and harmonic content increase in the fault development stage, quickly advance the trigger angle of the non-fault layer, reserve sufficient margin for commutation, and make up the defect that the CFPREV cannot be started in time and commutation failure is easy to occur in the non-fault layer due to slight voltage drop.
Drawings
Fig. 1 is a schematic flowchart of a commutation failure control method under dc hierarchical access based on harmonic analysis according to an embodiment of the present invention;
fig. 2 is a topology structure diagram of a dc power transmission system with an inverting side being hierarchically connected to a receiving end according to an embodiment of the present invention;
fig. 3 is a control block diagram of a commutation failure control method under the dc hierarchical access based on harmonic analysis according to an embodiment of the present invention;
fig. 4(a) is a comparison graph of a non-fault layer turn-off angle γ varying with time before and after a commutation failure control method under a direct current hierarchical access based on harmonic analysis according to an embodiment of the present invention;
fig. 4(b) is a trigger angle command α before and after the commutation failure control method under the dc hierarchical access based on harmonic analysis according to the embodiment of the present inventionorderGraph over time.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1, a method for controlling commutation failure under dc hierarchical access based on harmonic analysis includes the following steps:
s1, acquiring three-phase voltage signals and phase-change current signals of a current-change bus at the inversion side of the layer in real time;
s2, carrying out FFT (fast Fourier transform) on the three-phase voltage signal to respectively obtain a 2-order harmonic amplitude and a 3-order harmonic amplitude, judging whether the maximum harmonic amplitude exceeds a steady-state harmonic amplitude threshold value, if so, enabling harmonic compensation control, calculating the advance of a trigger angle aiming at harmonic change according to the maximum harmonic amplitude, otherwise, not enabling the harmonic compensation control, and enabling the advance of the trigger angle aiming at the harmonic change to be zero;
s3, judging whether the phase change current signal exceeds a steady-state current amplitude threshold value, if so, enabling current compensation control, calculating the advance of the trigger angle aiming at the current rise according to the current increment, otherwise, not enabling the current compensation control, and enabling the advance of the trigger angle aiming at the current change to be zero;
s4, judging whether the current converter is in a stage that a turn-off angle falls and phase commutation failure does not occur, if so, entering step S5, otherwise, entering step S1;
s5, judging whether the CFPREV of the current layer is started to output, if so, entering a step S1, otherwise, entering a step S6;
s6, judging whether the other layer of CFPREV is started to output, if so, entering a step S7, otherwise, entering a step S1;
and S7, adding the trigger angle lead aiming at the harmonic change and the trigger angle lead aiming at the current change, sending the sum to a trigger angle instruction link, and carrying out trigger angle lead control on the current layer (namely the non-fault layer).
The direct current layered access system aimed at by the method simultaneously meets the following conditions:
1) the rectifying side is connected with the direct current converter station through a converter transformer;
2) the inversion side converter station is accessed to the inversion side in a layered access mode, wherein a high-end converter directly connected with positive and negative direct current polar lines is accessed to a 500kV alternating current bus, namely a 500kV layer, and a low-end converter directly connected with a neutral point is accessed to a 1000kV alternating current bus, namely a 1000kV layer;
3) the inverter side converters are all provided with a commutation failure prevention control CFPREV.
As shown in fig. 2, the dc power transmission system with the inverting side connected to the receiving end in a layered manner includes: rectifying side, direct current transmission line and contravariant side.
The rectification side comprises: a rectification side AC system, an AC filter, a rectification side converter station (including four 12-pulse converters, which are a positive high-end converter, a positive low-end converter, a negative high-end converter, and a positive low-end converter). The alternating current filter is directly connected with a rectifying side alternating current system bus, and the rectifying side alternating current system is connected with the direct current transmission line through the rectifying side converter station.
The DC transmission line includes: line equivalent resistance RdAnd a dc filter. Wherein, the direct current circuit is directly connected with the rectifying side converter station and the inversion side converter station.
The inverter side includes: inverting side AC systems 1, 2; the inverter side converter station comprises four 12-pulse wave converters, namely a positive electrode high-end converter, a positive electrode low-end converter, a negative electrode high-end converter and a positive electrode low-end converter, and an alternating current filter. The inverter-side alternating current systems 1 and 2 are connected to the equivalent reactance of the tie line through the tie transformer.
S1, acquiring three-phase voltage signals and phase-change current signals of an inversion side current-change bus in real time.
In the layered access system, the main reason that the non-fault layer is disturbed by the fault layer under the action of AC-DC coupling to cause commutation failure is commutation voltage waveform distortion caused by current rise and harmonic content increase, so that the two parameters are detected.
And S2, carrying out FFT (fast Fourier transform) on the phase-to-phase voltage signal to respectively obtain a 2-order harmonic amplitude and a 3-order harmonic amplitude, judging whether the maximum harmonic amplitude exceeds a steady-state harmonic amplitude threshold value, if so, enabling harmonic compensation control, calculating the advance of the trigger angle aiming at harmonic change according to the maximum harmonic amplitude, otherwise, not enabling the harmonic compensation control, and enabling the advance of the trigger angle aiming at the harmonic change to be zero.
When the alternating current system fails, low-frequency non-characteristic harmonics can be generated due to the fact that voltage is no longer three-phase symmetrical balance positive voltage, converter transformer saturation is caused by rising of direct current, abnormal operation of power electronic components and the like, and 2-order and 3-order harmonic amplitudes are the highest, so that only 2-order harmonic amplitudes and 3-order harmonic amplitudes of three-phase voltage are calculated. After the alternating current fault occurs in a half period, the harmonic content can rise to a high value, the trigger angle compensation quantity cannot rise all the time along with the harmonic amplitude, otherwise, the reactive power consumption is too much, the phase change is not facilitated, and therefore the amplitude limit of the trigger angle compensation quantity calculated in the step is within 15 degrees.
And S3, judging whether the current value exceeds a steady-state current amplitude threshold value, if so, enabling current compensation control, and calculating the advance of the trigger angle aiming at the current rise according to the current increment, otherwise, not enabling the current compensation control, and enabling the advance of the trigger angle aiming at the current change to be zero.
Due to the series current path of the fault layer and the non-fault layer, after a fault occurs, the current of the fault layer is increased to directly cause the phase change margin requirement of the non-fault layer to be increased, and therefore compensation is carried out on the trigger angle of the non-fault layer according to the current increase to increase the phase change margin of the non-fault layer. After the alternating current fault occurs for a half period, the current can rise to a higher value, and the trigger angle compensation amount cannot be too large, so that the amplitude limit of the trigger angle compensation amount calculated in the link is within 15 degrees.
S4, judging whether the current converter is in a stage that a turn-off angle falls and phase commutation failure does not occur, if so, entering step S5, otherwise, entering step S1;
the stage of whether the converter is in a stage that the turn-off angle drops and the commutation failure does not occur yet refers to a stage that the turn-off angle of the inverter side converter on the non-fault layer starts to drop after the inverter side converter is disturbed by a fault and is lower than a steady-state value but higher than a minimum turn-off angle value. If the commutation failure occurs on a non-fault layer, the compensation of the commutation failure control method under the direct current layered access based on the harmonic analysis to the trigger angle only consumes more reactive power and is not beneficial to the system recovery, so the trigger angle compensation is stopped. Similarly, if the turn-off angle of the non-fault layer is recovered to be larger than or equal to the steady-state value, indicating that the inverter has passed the phase-change failure dangerous period, the trigger angle compensation should be stopped. The off angle value range is [5 degrees, 20 degrees ]
S5, judging whether the CFPREV of the current layer is started to output, if so, entering a step S1, otherwise, entering a step S6;
the commutation failure control under the direct current layered access based on harmonic analysis is to carry out advanced control on a trigger angle in a neutral period in which a non-fault layer commutation state is deteriorated and a CFPREV is not started after a fault occurs so as to make up for the defect that the CFPREV is not started timely. Therefore, after the CFPREV of the current layer is detected to be started, the output of the commutation failure control under the direct current layered access based on the harmonic analysis should be stopped, and the negative influence caused by excessive advance of the trigger angle due to the advance control superposition of the trigger angle is prevented.
S6, judging whether the other layer of CFPREV is started to output, if so, entering a step S7, otherwise, entering a step S1;
the commutation failure control under the direct current hierarchical access based on harmonic analysis aims at the commutation failure of a non-fault layer caused by alternating current fault, so that the commutation failure control under the direct current hierarchical access based on harmonic analysis is prevented from moving when current change and harmonic change are caused by small interference. Therefore, the commutation failure control should detect the starting condition of each layer of converter CFPREV, if another layer is started and the layer is not yet started, the other layer is a fault layer and has an alternating current fault, and the layer is a non-fault layer, so that the commutation failure control condition under the direct current layered access based on harmonic analysis is met, and the output of the trigger angle lead is carried out.
S7, adding the trigger angle lead aiming at the harmonic change and the trigger angle lead aiming at the current change, and transmitting the sum to a trigger angle instruction link to carry out trigger angle lead control on a non-fault layer;
and superposing the trigger angle advance instruction output of commutation failure control under the direct current layered access based on harmonic analysis and the trigger angle instruction obtained by valve bank control calculation to obtain a final trigger angle instruction.
As shown in fig. 3, a method for controlling commutation failure under dc hierarchical access based on harmonic analysis, trigger angle advance Δ αHIThe generation process comprises a harmonic detection and compensation link and a harmonic detection and compensation link.
Aiming at the trigger angle compensation control of harmonic change, FFT conversion is carried out on the three-phase voltage of the inversion side converter bus to obtain 2-order harmonic amplitude and 3-order harmonic amplitude of each phase, and the maximum Har is selectedmaxHar with steady state harmonic amplitude thresholdstableComparing, if Har is exceededstableThen the flag bit will be enabledHsignalSetting 1, and combining the maximum harmonic amplitude HarmaxMultiplying by a harmonic coefficient kharmonicObtaining the trigger angle advance delta alpha aiming at harmonic wave changeharAnd to Δ αharClipping is at 15 °;
for the trigger angle compensation control of current variation, the direct current I is applieddAnd steady state current threshold Id_stBy comparison, if it exceeds Id_staThen the flag bit I will be enabledsignal Setting 1, applying a direct current IdThe difference with the steady-state current is obtained to obtain the current increase amount delta IdMultiplied by the current coefficient
Figure BDA0002597218380000091
Obtaining trigger angle lead for current change
Figure BDA0002597218380000092
And to
Figure BDA0002597218380000093
Clipping is at 15 °;
finally, the output delta alpha controlled by the two parts is outputharAnd
Figure BDA0002597218380000094
adding and limiting within 20 degrees as output delta alpha of the commutation failure control strategyHI。
At trigger angle advance delta alphaHIBefore output, the turn-off angle should be also set to the minimum turn-off angle gammaminAngle of closure with steady state gammastaComparing to determine whether the converter is in the stage of turn-off angle falling and no commutation failure, corresponding to gammamesThe value range is [5 degrees, 20 degrees ]]。
Output Δ α of CFPREV of another layerCFPREV1Comparing with a minimum value of 0.001, and when the value is higher than the minimum value, the CFPREV of the other layer is considered to be started to output; at the same time, the output Δ α of CFPREV of the layer is adjustedCFPREVWhen the minimum value is less than 0.001, it is considered that the output of the CFPREV of the current layer is not enabled, and the fault layer CFPREV is enabled after the AC fault but the fault layer CFPREV is not enabledA dynamic neutral period.
Delta alpha output by controlling commutation failure under direct current layered access based on harmonic analysisHIOutput of CFPREV of this layer Δ αCFPREVAdding the firing angle command alpha obtained by valve group control calculation to obtain a final firing angle command value alphaorderWherein at the same time, Δ αHIAnd Δ αCFPREVAt least one should be zero.
A commutation failure control system under direct current hierarchical access based on harmonic analysis, the system comprising:
the signal acquisition unit is used for acquiring three-phase voltage signals and phase-change current signals of the current-changing bus at the inversion side of the layer in real time;
the harmonic detection and compensation unit is used for performing FFT (fast Fourier transform) on the three-phase voltage signal to respectively obtain a 2-order harmonic amplitude and a 3-order harmonic amplitude, and calculating trigger angle compensation quantity aiming at harmonic change according to the 2-order harmonic amplitude and the 3-order harmonic amplitude;
the current detection and compensation unit is used for calculating trigger angle compensation amount aiming at current change according to the phase change current signal increase amount;
the converter turn-off angle detection unit is used for detecting the turn-off angle of the converter to judge the working state of the converter and ensure that the trigger angle compensation is output only in the process of reducing the turn-off angle of the non-fault layer after the fault occurs;
and the CFPREV detection unit is used for detecting the starting state of each layer of CFPREV in the system and ensuring that the trigger angle compensation of the non-fault layer is output only when the CFPREV of the fault layer is started but not when the CFPREV of the non-fault layer is not started after the fault occurs.
Fig. 4(a) is a graph of turn-off angles of non-fault layers before and after the commutation failure control method under the dc hierarchical access based on the harmonic analysis, and fig. 4(b) is a graph of firing angle instructions of non-fault layers before and after the commutation failure control method under the dc hierarchical access based on the harmonic analysis. It can be seen that after the direct current hierarchical access lower commutation failure control method based on harmonic analysis is adopted, after an alternating current fault occurs in 1s, the trigger angle command quickly makes a response, the trigger angle is advanced, a sufficient commutation margin is provided for a non-fault layer, the turn-off angle slightly falls and is stabilized at about 15 degrees after the fault, the turn-off angle is quickly recovered and rises, and no commutation failure occurs. When the direct current hierarchical access lower commutation failure control method based on harmonic analysis is not adopted, commutation failure response of a non-fault layer is very slow, commutation failure occurs until a turn-off angle is reduced to zero, and a trigger angle is not obviously reduced, so that the effectiveness of the direct current hierarchical access lower commutation failure control method based on harmonic analysis is verified. It should be noted that the specific control effect is related to the ac coupling strength of the layered access system, and the lower the ac coupling degree of the dc layered access system is, the better the control effect is.
The above description is only for the preferred embodiment of the present application, but the scope of the present application 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 application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (7)

1. A direct current layered access lower commutation failure control method based on harmonic analysis is characterized in that a direct current converter station in an applied direct current layered access system is accessed to a rectifying side through a converter transformer, the inverter side converter station is accessed to an inverter side in a layered access mode, wherein a high-end converter directly connected with positive and negative direct current polar lines is accessed to a 500kV alternating current bus, the high-end converter is 500kV layer, a low-end converter directly connected with a neutral point is accessed to a 1000kV alternating current bus, the low-end converter is 1000kV layer, and each layer is provided with commutation failure prevention control CFPREV, and the method comprises the following steps:
s1, acquiring three-phase voltage signals and phase-change current signals of a current-change bus at the inversion side of the layer in real time;
s2, carrying out FFT (fast Fourier transform) on the three-phase voltage signal to respectively obtain a 2-order harmonic amplitude and a 3-order harmonic amplitude, judging whether the maximum harmonic amplitude exceeds a steady-state harmonic amplitude threshold value, if so, enabling harmonic compensation control, calculating the advance of a trigger angle aiming at harmonic change according to the maximum harmonic amplitude, otherwise, not enabling the harmonic compensation control, and enabling the advance of the trigger angle aiming at the harmonic change to be zero;
s3, judging whether the phase change current signal exceeds a steady-state current amplitude threshold value, if so, enabling current compensation control, calculating the advance of the trigger angle aiming at the current rise according to the current increment, otherwise, not enabling the current compensation control, and enabling the advance of the trigger angle aiming at the current change to be zero;
s4, judging whether the current converter is in a stage that a turn-off angle falls and phase commutation failure does not occur, if so, entering step S5, otherwise, entering step S1;
s5, judging whether the CFPREV of the current layer is started to output, if so, entering a step S1, otherwise, entering a step S6;
s6, judging whether the other layer of CFPREV is started to output, if so, entering a step S7, otherwise, entering a step S1;
and S7, adding the trigger angle lead aiming at the harmonic change and the trigger angle lead aiming at the current change, and transmitting to a trigger angle instruction link to carry out trigger angle advanced control on the current layer.
2. The method according to claim 1, wherein the phase of whether the converter is in a stage that the turn-off angle is dropped and no commutation failure has occurred means that the turn-off angle of the inverter-side converter on the non-fault layer starts to decrease after the disturbance of the fault, and the value of the turn-off angle is in the range of [5 degrees, 20 degrees ] when the turn-off angle is lower than the steady state value and higher than the minimum turn-off angle value.
3. The method of claim 1, wherein whether CFPREV enables output is that the output of CFPREV is Δ αCFPREVWhen higher than this value, CFPREV is considered to have enabled output, otherwise CFPREV is considered to have not enabled output, as compared to a minimum value of 0.001.
4. A commutation failure control system under DC hierarchical access based on harmonic analysis, the system comprising:
the signal acquisition unit is used for acquiring three-phase voltage signals and phase-change current signals of the current-changing bus at the inversion side of the layer in real time;
the harmonic detection and compensation unit is used for performing FFT (fast Fourier transform) on the three-phase voltage signal to respectively obtain a 2-order harmonic amplitude and a 3-order harmonic amplitude, and calculating trigger angle compensation quantity aiming at harmonic change according to the 2-order harmonic amplitude and the 3-order harmonic amplitude;
the current detection and compensation unit is used for calculating trigger angle compensation amount aiming at current change according to the phase change current signal increase amount;
the converter turn-off angle detection unit is used for detecting the turn-off angle of the converter to judge the working state of the converter and ensure that the trigger angle compensation is output only in the process of reducing the turn-off angle of the non-fault layer after the fault occurs;
and the CFPREV detection unit is used for detecting the starting state of each layer of CFPREV in the system and ensuring that the trigger angle compensation of the non-fault layer is output only when the CFPREV of the fault layer is started but not when the CFPREV of the non-fault layer is not started after the fault occurs.
5. The system according to claim 4, wherein the shutdown angle of the non-faulted inverter-side converter begins to decrease after a fault disturbance, is lower than a steady state value but higher than a minimum shutdown angle value, and the shutdown angle of the converter with the value range of [5 °, 20 ° ] is at a stage where the shutdown angle drops and no commutation failure has occurred.
6. The system of claim 4, wherein the output of CFPREV Δ αCFPREVWhen higher than this value, CFPREV is considered to have enabled output, otherwise CFPREV is considered to have not enabled output, as compared to a minimum value of 0.001.
7. A computer-readable storage medium, wherein a computer program is stored on the computer-readable storage medium, and when executed by a processor, the computer program implements the method for controlling commutation failure under dc hierarchical access based on harmonic analysis according to any one of claims 1 to 3.
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