CN111007360A - Extra-high voltage direct current transmission system commutation failure judgment method considering current change - Google Patents

Extra-high voltage direct current transmission system commutation failure judgment method considering current change Download PDF

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CN111007360A
CN111007360A CN201911375442.3A CN201911375442A CN111007360A CN 111007360 A CN111007360 A CN 111007360A CN 201911375442 A CN201911375442 A CN 201911375442A CN 111007360 A CN111007360 A CN 111007360A
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current
voltage
inverter
angle
commutation
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CN111007360B (en
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李凤婷
尹纯亚
赵新立
李弘昌
周博昊
樊艳芳
田易之
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Xinjiang University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing
    • 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
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Abstract

本发明公开了一种考虑电流变化的特高压直流输电系统换相失败判别方法，该方法通过对直流输电线路进行精确建模，能够在逆变侧交流系统发生对称短路故障与不对称短路故障导致逆变侧直流电压降低时，有效对逆变侧的直流电流进行计算，得出考虑直流电流动态变化的逆变器关断角计算方法，当计算得到的关断角小于逆变器换相失败的最小关断角时，判定为逆变器发生换相失败。本发明提供的考虑电流变化的特高压直流输电系统换相失败判别方法，在考虑逆变侧交流系统故障后直流电流的动态变化的前提下，实现了对换相失败的有效判别，可有效提高交直流混联系统运行风险评估结果，为保障电力系统的安全稳定运行提供依据。

Figure 201911375442

The invention discloses a method for judging the commutation failure of an ultra-high voltage direct current transmission system considering current changes. The method can accurately model the direct current transmission line, and can cause symmetrical short-circuit faults and asymmetrical short-circuit faults in the AC system on the inverter side. When the DC voltage of the inverter side decreases, the DC current of the inverter side is effectively calculated, and the calculation method of the inverter turn-off angle considering the dynamic change of the DC current is obtained. When the calculated turn-off angle is smaller than the inverter commutation failure When the minimum turn-off angle is reached, it is determined that the inverter has failed commutation. The method for judging the commutation failure of the UHVDC transmission system considering the current change provided by the present invention realizes the effective judgment on the commutation failure under the premise of considering the dynamic change of the DC current after the fault of the AC system on the inverter side, and can effectively improve the The results of the operation risk assessment of the AC-DC hybrid system provide a basis for ensuring the safe and stable operation of the power system.

Figure 201911375442

Description

Extra-high voltage direct current transmission system commutation failure judgment method considering current change
Technical Field
The invention relates to the technical field of direct current transmission, in particular to a method for judging commutation failure of an extra-high voltage direct current transmission system by considering current change.
Background
With the rapid development of an extra-high voltage direct-current transmission system and the rapid promotion of the voltage class (+/-800 kV to +/-1100 kV) and the transmission capacity (6400MW to 12000MW), more and more extra-high voltage projects are in a commissioning state and a construction state, so that the power system increasingly presents a 'strong weak cross' characteristic. This grid layout is such that: (1) the dynamic disturbance amount under the direct current fault is very strong; (2) the ac system has a weak ability to carry faults.
The core device of extra-high voltage direct current transmission is a current converter, generally a thyristor is used as a phase-change device, but the thyristor only has the capability of unidirectional conduction, namely when the voltage applied to a thyristor valve is positive, if the given thyristor triggers pulse to control the conduction of the thyristor, the thyristor can be turned off only when the voltage on the thyristor valve is negative (the line voltage naturally crosses zero). Therefore, when the voltage of the alternating current system is reduced, the inverter has the risk of phase commutation failure, once the phase commutation failure occurs in the direct current system, short-time power transmission interruption of the direct current system can cause impact on the voltage and frequency of the alternating current system at the transmitting end and the receiving end, and the safe and stable operation of the power system is seriously threatened.
At present, a commutation failure judgment method adopted by an extra-high voltage direct current transmission system is as follows: and detecting the effective value of the voltage of the alternating current system on the assumption that the direct current is unchanged, calculating the turn-off angle of the inverter, and considering that the inverter has phase commutation failure when the calculated turn-off angle is smaller than the minimum turn-off angle required by phase commutation. However, when the voltage of the ac system on the inverter side is reduced, the dc current will also rise due to the delay lag characteristic of the dc control system, and the rise of the dc current will further reduce the turn-off angle, so that the conventional determination method cannot correctly characterize the operating state of the inverter, and cannot accurately determine the commutation failure.
Disclosure of Invention
The invention aims to provide a phase change failure judgment method of an extra-high voltage direct current transmission system considering current change, which realizes effective judgment of phase change failure on the premise of considering dynamic change of direct current after an alternating current system on an inversion side fails, can effectively improve an operation risk evaluation result of an alternating current-direct current hybrid system, and provides a basis for ensuring safe and stable operation of a power system.
In order to achieve the purpose, the invention provides the following scheme:
a method for judging commutation failure of an extra-high voltage direct current transmission system considering current change comprises the following steps:
s1: obtaining an expression of an inverter turn-off angle, and modeling the ultra-high voltage direct current transmission line based on the equivalent inductance, the equivalent capacitance and the smoothing reactor of the direct current transmission line to obtain an equivalent circuit;
s2: respectively carrying out linearization processing and Laplace transformation on the relationship between the rectification side commutation bus voltage and the rectification side direct current voltage and the relationship between the inversion side commutation bus voltage and the inversion side direct current voltage on the basis of an equivalent circuit;
s3: modeling constant current control at the rectifying side to obtain a transfer function of a constant current controller;
s4: calculating voltage after the voltage fault of the inversion side current conversion bus, and performing Laplace transformation;
s5: calculating a direct current instruction value according to the low-voltage current-limiting control action characteristic and an inversion side direct current voltage calculation method;
s6: combining the processing results of S1-S5 to obtain a direct current expression, and performing Laplace inverse transformation on the direct current expression under a direct current standard test system to obtain an analytic expression of the direct current;
s7: determining the maximum value of the direct current according to the analytical expression of the direct current, substituting the maximum value of the direct current into the inverter turn-off angle expression, and respectively obtaining a turn-off angle expression under the single-phase earth fault and a turn-off angle expression under the three-phase short-circuit fault;
s8: judging whether only one phase voltage changes after the fault occurs, turning to S9, and if all three phase voltages change after the fault occurs, turning to S10;
s9: comparing the turn-off angle under the single-phase earth fault with the minimum turn-off angle of the inverter with the phase commutation failure, and judging that the phase commutation failure occurs when the turn-off angle under the single-phase earth fault is less than or equal to the minimum turn-off angle of the inverter with the phase commutation failure; when the turn-off angle under the single-phase earth fault is larger than the minimum turn-off angle of the inverter with the phase commutation failure, judging that the phase commutation is successful;
s10: comparing the turn-off angle under the three-phase short-circuit fault with the minimum turn-off angle of the inverter for the phase commutation failure, and judging the phase commutation failure when the turn-off angle under the three-phase short-circuit fault is less than or equal to the minimum turn-off angle of the inverter for the phase commutation failure; and when the turn-off angle under the three-phase short circuit fault is larger than the minimum turn-off angle of the inverter with the phase commutation failure, judging that the phase commutation is successful.
Optionally, in S1, the expression of the inverter turn-off angle is:
Figure BDA0002340819550000021
in the formula of ULIFor inverting the side current-converting bus voltage, XCIFor inverting side commutation reactance, IdIFor inverting side direct current, TIThe secondary side to primary side transformation ratio of the inverter side converter transformer is β is the trigger advance angle of the inverter,
Figure BDA0002340819550000022
zero crossing point offset angle for the inversion commutation busbar line voltage;
the voltage and current equations of the equivalent circuit are as follows:
Figure BDA0002340819550000031
in the formula (2), UdRFor rectifying the side DC voltage, LRIn order to consider the equivalent value of the smoothing reactor on the rectifying side and the direct current inductor, I (0) is the direct current value at the fault moment, u (0) is the direct current voltage value at the midpoint of the direct current line at the fault moment, C is the equivalent ground capacitance of the direct current transmission line, ICIs the value of the current at the capacitor C during a fault, IdIFor inverting side direct current, RdIs an equivalent resistance of a direct current transmission line, LIFor considering the equivalent inductance of the smoothing reactor on the inverter side and the direct current inductance, UdIIs the direct current voltage on the inversion side.
Optionally, in S2, based on the equivalent circuit, the linearization and the laplace transform are respectively performed on the relationship between the rectifier-side converter bus voltage and the rectifier-side dc voltage and the relationship between the inverter-side converter bus voltage and the inverter-side dc voltage, and the method specifically includes:
s201, performing linearization on the relationship between the rectifier side converter bus voltage and the rectifier side dc voltage, so that the relationship between the rectifier side dc no-load dc voltage and the rectifier side dc voltage is:
Figure BDA0002340819550000032
wherein α is a commutation side trigger angle, UdR0For rectifying side DC no-load DC voltage, XCRThe number of the commutation reactances at the rectification side is N, and the number of the ripple current converters is N;
linearizing cos α in equation (3), discretizing cos α data, and then linearly fitting the discretized data to obtain a fitting equation:
cosα＝-0.01326α+1.26231 (4)
then, the equation of the rectified side converter bus voltage and the rectified side direct current voltage after linearization processing can be obtained according to equations (3) and (4), and the laplace change is as follows:
Figure BDA0002340819550000033
in the formula dRIs defined as:
Figure BDA0002340819550000034
s202, synchronizing step 201 with the derivation principle, and performing linearization and laplace transform on the relationship between the inversion-side converter bus voltage and the inversion-side dc voltage, where the derivation principle can be expressed as:
Figure BDA0002340819550000035
in the formula dIIs defined as:
Figure BDA0002340819550000041
optionally, in S3, the modeling of the constant current control at the rectifying side to obtain a transfer function of the constant current controller specifically includes: the constant current controller measures the direct current instruction value I of the rectification side in real timedrefAnd a rectified side direct current IdIThe deviation of (2) is output through a proportional-integral link to a trigger angle of a rectification side, and a transfer function of the constant current controller is as follows:
Figure BDA0002340819550000042
in the formula IdNFor the DC rated value of the extra-high voltage DC system, KpIs a constant of proportionality, TiIs the integration time constant.
Optionally, in S4, the calculating a voltage after the voltage fault of the inverter-side converter bus, and performing laplace transform specifically include: if the inverter side AC system is short-circuited, the voltage at the inverter side current conversion bus is reduced by delta ULIThe voltage after laplace transformation is:
Figure BDA0002340819550000043
in the formula of ULINFor the inverter-side commutation busThe operating voltage.
Optionally, in S5, calculating the dc current command value according to the low-voltage current-limiting control operation characteristic and the inverter-side dc voltage calculation method specifically includes:
the DC current command value may be calculated as:
Figure BDA0002340819550000044
optionally, the processing result of S1-S5 is combined in S6 to obtain a dc current expression, and the dc current expression is subjected to inverse laplace transform in a dc standard test system to obtain an analytic expression of the dc current, which specifically includes:
s601, combining the equations (1) to (11) of the steps S1 to S5, the dc current is calculated as:
Figure BDA0002340819550000045
in the formula:
Figure BDA0002340819550000051
and S602, substituting the parameters (table 1) of the alternating current and direct current system into the formula (13), and performing inverse Laplace transform on the formula (12) to obtain an analytic expression of the direct current, wherein the analytic expression is as follows:
IdI(t)＝K1d-K2de-79.878tcos(93.2832t+K3d) (14)
in the formula: k1d、K2d、K3dComprises the following steps:
Figure BDA0002340819550000052
optionally, in S7, determining a maximum value of the direct current according to an analytic expression of the direct current, and substituting the maximum value of the direct current into an inverter turn-off angle expression to obtain a turn-off angle expression under a single-phase ground fault and a turn-off angle expression under a three-phase short-circuit fault, specifically including:
s701, maximum value I of direct currentdImaxIs composed of
Figure BDA0002340819550000053
S702, the obtained maximum value of the direct current is taken into a formula (1), and a turn-off angle expression under the single-phase earth fault is obtained:
Figure BDA0002340819550000061
the turn-off angle expression under three-phase short-circuit fault:
Figure BDA0002340819550000062
compared with the prior art, the technology has the following beneficial effects:
the invention provides a commutation failure judging method of an extra-high voltage direct current transmission system considering current change, which is characterized in that a high-voltage direct current transmission line is accurately modeled, the relation between the commutation bus voltage at the rectifying side and the direct current voltage at the rectifying side is linearized, a linear circuit after linearization is analyzed and calculated, when an alternating current system at the inverting side fails, accurate analysis and calculation of direct current are realized, the influence of the direct current on a turn-off angle is taken into consideration, and the commutation failure judging method is provided. On the premise of accurately calculating the direct current, the method realizes effective judgment of inverter commutation failure, can effectively improve the operation risk evaluation result of the alternating current-direct current hybrid system, and provides a basis for ensuring safe and stable operation of the power system.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is an equivalent circuit diagram of an extra-high voltage DC transmission line according to an embodiment of the invention;
FIG. 2 is a linear equation curve of a cosine function according to an embodiment of the present invention;
FIG. 3 is a block diagram of a DC control system according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating low voltage current limiting control characteristics according to an embodiment of the present invention;
FIG. 5 is a comparison graph of theoretical calculation and simulation results of DC current according to the embodiment of the present invention;
fig. 6 is a graph comparing the turn-off angle and the voltage drop for different faults according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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 invention.
The invention aims to provide a phase change failure judgment method of an extra-high voltage direct current transmission system considering current change, which realizes effective judgment of phase change failure on the premise of considering dynamic change of direct current after an alternating current system on an inversion side fails, can effectively improve an operation risk evaluation result of an alternating current-direct current hybrid system, and provides a basis for ensuring safe and stable operation of a power system. .
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
As shown in fig. 1 to 4, the method for judging commutation failure of an extra-high voltage direct current transmission system considering current change, provided by the invention, is based on CIGRE HVDC high-voltage direct current standard test system model parameters, and comprises the following steps:
s1: obtaining an expression of an inverter turn-off angle, and modeling the ultra-high voltage direct current transmission line based on the equivalent inductance, the equivalent capacitance and the smoothing reactor of the direct current transmission line to obtain an equivalent circuit;
s2: respectively carrying out linearization processing and Laplace transformation on the relationship between the rectification side commutation bus voltage and the rectification side direct current voltage and the relationship between the inversion side commutation bus voltage and the inversion side direct current voltage on the basis of an equivalent circuit;
s3: modeling constant current control at the rectifying side to obtain a transfer function of a constant current controller;
s4: calculating voltage after the voltage fault of the inversion side current conversion bus, and performing Laplace transformation;
s5: calculating a direct current instruction value according to the low-voltage current-limiting control action characteristic and an inversion side direct current voltage calculation method;
s6: combining the processing results of S1-S5 to obtain a direct current expression, and performing Laplace inverse transformation on the direct current expression under a direct current standard test system to obtain an analytic expression of the direct current;
s7: determining the maximum value of the direct current according to the analytical expression of the direct current, substituting the maximum value of the direct current into the inverter turn-off angle expression, and respectively obtaining a turn-off angle expression under the single-phase earth fault and a turn-off angle expression under the three-phase short-circuit fault;
s8: judging whether only one phase voltage changes after the fault occurs, turning to S9, and if all three phase voltages change after the fault occurs, turning to S10;
s9: comparing the turn-off angle under the single-phase earth fault with the minimum turn-off angle of the inverter with the phase commutation failure, and judging that the phase commutation failure occurs when the turn-off angle under the single-phase earth fault is less than or equal to the minimum turn-off angle of the inverter with the phase commutation failure; when the turn-off angle under the single-phase earth fault is larger than the minimum turn-off angle of the inverter with the phase commutation failure, judging that the phase commutation is successful;
s10: comparing the turn-off angle under the three-phase short-circuit fault with the minimum turn-off angle of the inverter for the phase commutation failure, and judging the phase commutation failure when the turn-off angle under the three-phase short-circuit fault is less than or equal to the minimum turn-off angle of the inverter for the phase commutation failure; and when the turn-off angle under the three-phase short circuit fault is larger than the minimum turn-off angle of the inverter with the phase commutation failure, judging that the phase commutation is successful.
In S1, the expression of the inverter turn-off angle is:
Figure BDA0002340819550000081
in the formula of ULIFor inverting the side current-converting bus voltage, XCIFor inverting side commutation reactance, IdIFor inverting side direct current, TIThe secondary side to primary side transformation ratio of the inverter side converter transformer is β is the trigger advance angle of the inverter,
Figure BDA0002340819550000082
zero crossing point offset angle for the inversion commutation busbar line voltage;
the voltage and current equations of the equivalent circuit are as follows:
Figure BDA0002340819550000083
in the formula (2), UdRFor rectifying the side DC voltage, LRIn order to consider the equivalent value of the smoothing reactor on the rectifying side and the direct current inductor, I (0) is the direct current value at the fault moment, u (0) is the direct current voltage value at the midpoint of the direct current line at the fault moment, C is the equivalent ground capacitance of the direct current transmission line, ICIs the value of the current at the capacitor C during a fault, IdIFor inverting side direct current, RdIs an equivalent resistance of a direct current transmission line, LIFor considering the equivalent inductance of the smoothing reactor on the inverter side and the direct current inductance, UdIIs the direct current voltage on the inversion side.
In S2, based on the equivalent circuit, the linearization and laplace transform are respectively performed on the relationship between the rectifier-side converter bus voltage and the rectifier-side dc voltage and the relationship between the inverter-side converter bus voltage and the inverter-side dc voltage, and the method specifically includes:
s201, performing linearization on the relationship between the rectifier side converter bus voltage and the rectifier side dc voltage, so that the relationship between the rectifier side dc no-load dc voltage and the rectifier side dc voltage is:
Figure BDA0002340819550000084
wherein α is a commutation side trigger angle, UdR0For rectifying side DC no-load DC voltage, XCRThe number of the commutation reactances at the rectification side is N, and the number of the ripple current converters is N;
linearizing cos α in equation (3), as shown in fig. 2, by discretizing cos α data and then linearly fitting the discretized data, the fitting equation is obtained:
cosα＝-0.01326α+1.26231 (4)
then, the equation of the rectified side converter bus voltage and the rectified side direct current voltage after linearization processing can be obtained according to equations (3) and (4), and the laplace change is as follows:
Figure BDA0002340819550000091
in the formula dRIs defined as:
Figure BDA0002340819550000092
s202, synchronizing step 201 with the derivation principle, and performing linearization and laplace transform on the relationship between the inversion-side converter bus voltage and the inversion-side dc voltage, where the derivation principle can be expressed as:
Figure BDA0002340819550000093
in the formula dIIs defined as：
Figure BDA0002340819550000094
In S3, the modeling of the rectifier-side constant current control to obtain the transfer function of the constant current controller specifically includes: FIG. 3 is a block diagram of a DC control system, in which a constant current controller measures a DC command value I of a rectifier side in real timedrefAnd a rectified side direct current IdIThe deviation of (2) is output through a proportional-integral link to a trigger angle of a rectification side, and a transfer function of the constant current controller is as follows:
Figure BDA0002340819550000095
in the formula IdNFor the DC rated value of the extra-high voltage DC system, KpIs a constant of proportionality, TiIs the integration time constant.
In S4, calculating the voltage after the inverter-side converter bus voltage fault, and performing laplace transform, specifically including: if the inverter side AC system is short-circuited, the voltage at the inverter side current conversion bus is reduced by delta ULIThe voltage after laplace transformation is:
Figure BDA0002340819550000096
in the formula of ULINThe rated operation voltage of the inversion side commutation bus is obtained.
In S5, calculating a dc current command value according to the low-voltage current-limiting control operation characteristic and the inverter-side dc voltage calculation method, specifically including:
the DC current command value may be calculated as:
Figure BDA0002340819550000101
combining the processing results of S1-S5 in S6 to obtain a dc current expression, and performing inverse laplace transform on the dc current expression in a dc standard test system to obtain an analytic expression of the dc current, which specifically includes:
s601, combining the equations (1) to (11) of the steps S1 to S5, the dc current is calculated as:
Figure BDA0002340819550000102
in the formula:
Figure BDA0002340819550000103
s602, taking the AC/DC system parameters (see Table 1) into formula (13), and performing inverse Laplace transform on formula (12) to obtain an analytic expression of the DC, wherein the analytic expression is as follows:
IdI(t)＝K1d-K2de-79.878tcos(93.2832t+K3d) (14)
in the formula: k1d、K2d、K3dComprises the following steps:
Figure BDA0002340819550000111
when the voltage drop value of the inversion side conversion bus is 0.1 due to the inversion side alternating current system fault, the direct current analytic expression is as follows:
IdI(t)＝0.2464e-79.878t[cos(93.2832t)+3.5463sin(93.2832t)]+2 (16)
considering the delay action time of the system control system as t0Then, the expression of the dc current is:
Figure BDA0002340819550000112
consider t0At 3ms, the simulation result and the theoretical result when the inverter side commutation bus voltage drops to 0.1pu are shown in fig. 5.
TABLE 1 CIGRE HVDC DC Standard test System parameters
Figure BDA0002340819550000113
In S7, determining a maximum value of the dc current according to the analytic expression of the dc current, and substituting the maximum value of the dc current into the shutdown angle expression of the inverter to obtain a shutdown angle expression under a single-phase ground fault and a shutdown angle expression under a three-phase short-circuit fault, respectively, specifically including:
s701, obtaining a point with a derivative of 0 by differentiating the direct current expression obtained in the step S6, and finally obtaining a maximum value I of the direct currentdImaxIs composed of
Figure BDA0002340819550000114
S702, the obtained maximum value of the direct current is taken into a formula (1), and a turn-off angle expression under the single-phase earth fault is obtained:
Figure BDA0002340819550000121
the turn-off angle expression under three-phase short-circuit fault:
Figure BDA0002340819550000122
the method is mainly characterized in that the maximum value of the direct current after the fault of the alternating current system on the inversion side is solved, and under the condition that the parameters of the alternating current and direct current system are known, the expression of the direct current can be obtained by solving through the formulas (14) and (15), and then the maximum value I of the direct current can be obtained by solvingdImaxThen, the commutation failure can be accurately determined by the equations (19) and (20) according to the different types of the failure.
The invention provides a commutation failure judging method of an extra-high voltage direct current transmission system considering current change, which is characterized in that a high-voltage direct current transmission line is accurately modeled, the relation between the commutation bus voltage at the rectifying side and the direct current voltage at the rectifying side is linearized, a linear circuit after linearization is analyzed and calculated, when an alternating current system at the inverting side fails, accurate analysis and calculation of direct current are realized, the influence of the direct current on a turn-off angle is taken into consideration, and the commutation failure judging method is provided. On the premise of accurately calculating the direct current, the method realizes effective judgment of inverter commutation failure, can effectively improve the operation risk evaluation result of the alternating current-direct current hybrid system, and provides a basis for ensuring safe and stable operation of the power system.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (8)

1.一种考虑电流变化的特高压直流输电系统换相失败判别方法，其特征在于，包括以下步骤：1. a method for judging the commutation failure of a UHV DC transmission system considering current changes, is characterized in that, comprises the following steps: S1：获取逆变器关断角的表达式，并基于直流输电线路等效电感、电容以及平波电抗器，对特高压直流输电线路进行建模，得到等效电路；S1: Obtain the expression of the turn-off angle of the inverter, and model the UHV DC transmission line based on the equivalent inductance, capacitance and smoothing reactor of the DC transmission line to obtain the equivalent circuit; S2：基于等效电路，分别对整流侧换流母线电与整流侧直流电压间的关系、逆变侧换流母线电压与逆变侧直流电压间的关系进行线性化处理和拉普拉斯变换；S2: Based on the equivalent circuit, the relationship between the rectifier side commutation bus power and the rectifier side DC voltage, and the relationship between the inverter side commutation bus voltage and the inverter side DC voltage are linearized and Laplace transform. ; S3：整流侧定电流控制建模，获得定电流控制器的传递函数；S3: Model the constant current control of the rectifier side to obtain the transfer function of the constant current controller; S4：计算逆变侧换流母线电压故障后电压，并进行拉普拉斯变换；S4: Calculate the voltage after the inverter side commutation bus voltage fault, and perform Laplace transform; S5：根据低压限流控制动作特性与逆变侧直流电压计算方法，计算直流电流指令值；S5: Calculate the DC current command value according to the action characteristics of the low-voltage current-limiting control and the calculation method of the DC voltage at the inverter side; S6：结合S1-S5的处理结果，获得直流电流表达式，在直流标准测试系统下，对直流电流表达式进行拉普拉斯反变换，得到直流电流的解析表达式；S6: Combine the processing results of S1-S5 to obtain the DC current expression, and under the DC standard test system, perform inverse Laplace transform on the DC current expression to obtain the analytical expression of the DC current; S7：根据直流电流的解析表达式确定直流电流最大值，将直流电流最大值代入逆变器关断角表达式中，分别获得单相接地故障下的关断角表达式和三相短路故障下的关断角表达式；S7: Determine the maximum value of the DC current according to the analytical expression of the DC current, substitute the maximum value of the DC current into the expression of the turn-off angle of the inverter, and obtain the expression of the turn-off angle under the single-phase ground fault and under the three-phase short-circuit fault respectively. The turn-off angle expression of ; S8：判断如果发生故障后只有一个相电压发生变化，则转向S9，如果发生故障后有三个相电压均发生变化，则转向S10；S8: Judging that if only one phase voltage changes after the fault occurs, go to S9, and if all three phase voltages change after the fault occurs, go to S10; S9：将单相接地故障下的关断角与逆变器发生换相失败的最小关断角进行比较，当单相接地故障下的关断角小于等于逆变器发生换相失败的最小关断角时，则判断为换相失败；当单相接地故障下的关断角大于逆变器发生换相失败的最小关断角时，则判断为换相成功；S9: Compare the turn-off angle under the single-phase ground fault with the minimum turn-off angle at which the inverter fails to commutate. When the turn-off angle under the single-phase ground fault is less than or equal to the minimum turn-off angle for the inverter failure When the commutation angle is broken, it is judged as commutation failure; when the turn-off angle under single-phase ground fault is greater than the minimum turn-off angle at which the inverter fails commutation, it is judged as commutation success; S10：将三相短路故障下的关断角与逆变器发生换相失败的最小关断角进行比较，当三相短路故障下的关断角小于等于逆变器发生换相失败的最小关断角时，则判断为换相失败；当三相短路故障下的关断角大于逆变器发生换相失败的最小关断角时，则判断为换相成功。S10: Compare the turn-off angle under the three-phase short-circuit fault with the minimum turn-off angle at which the inverter fails commutation. When the turn-off angle under the three-phase short-circuit fault is less than or equal to the minimum turn-off angle at which the inverter fails commutation When the angle is broken, it is judged that the commutation fails; when the turn-off angle under the three-phase short-circuit fault is greater than the minimum turn-off angle of the inverter for the commutation failure, it is judged that the commutation is successful. 2.根据权利要求1所述的考虑电流变化的特高压直流输电系统换相失败判别方法，其特征在于，所述S1中，所述逆变器关断角的表达式为：2. The method for judging the commutation failure of the UHVDC transmission system considering current changes according to claim 1, wherein in the S1, the expression of the inverter turn-off angle is:
Figure FDA0002340819540000011
Figure FDA0002340819540000011
 式中，ULI为逆变侧换流母线电压，XCI为逆变侧换相电抗，IdI为逆变侧直流电流，TI为逆变侧换流变压器二次侧与一次侧变比为，β为逆变器触发超前角，
Figure FDA0002340819540000012
为逆变换流母线线电压过零点偏移角度；In the formula, U LI is the inverter-side commutation bus voltage, X CI is the inverter-side commutation reactance, I dI is the inverter-side DC current, and T I is the transformation ratio between the secondary side and the primary side of the inverter-side converter transformer is, β is the triggering lead angle of the inverter,
Figure FDA0002340819540000012
is the offset angle of the zero-crossing point of the inverter-converted busbar voltage; 所述等效电路的电压、电流方程为：The voltage and current equations of the equivalent circuit are:
Figure FDA0002340819540000021
Figure FDA0002340819540000021
 式(2)中，UdR为整流侧直流电压，LR为考虑整流侧平波电抗器与直流电感的等效值，i(0_)为故障时刻的直流电流值，u(0_)为故障时刻直流线路中点直流电压值，C为直流输电线路等效对地电容，IC为故障期间电容C处的电流值，IdI为逆变侧直流电流，Rd为直流输电线路等效电阻，LI为考虑逆变侧平波电抗器与直流电感的等效电感，UdI为逆变侧直流电压。In formula (2), U dR is the DC voltage on the rectifier side, LR is the equivalent value considering the smoothing reactor on the rectifier side and the DC inductance, i(0_) is the DC current value at the time of the fault, and u(0_) is the fault The DC voltage value at the midpoint of the DC line at time, C is the equivalent ground capacitance of the DC transmission line, I C is the current value at the capacitor C during the fault, I dI is the DC current on the inverter side, and R d is the equivalent resistance of the DC transmission line , L I is the equivalent inductance considering the smoothing reactor on the inverter side and the DC inductor, and U dI is the DC voltage on the inverter side. 3.根据权利要求2所述的考虑电流变化的特高压直流输电系统换相失败判别方法，其特征在于，所述S2中，基于等效电路，分别对整流侧换流母线电与整流侧直流电压间的关系、逆变侧换流母线电压与逆变侧直流电压间的关系进行线性化处理和拉普拉斯变换，具体包括：3. The method for judging the commutation failure of the UHVDC transmission system considering current changes according to claim 2, wherein in the S2, based on the equivalent circuit, the commutation busbar power on the rectifier side and the DC on the rectifier side are respectively The relationship between the voltages, the relationship between the inverter side commutation bus voltage and the inverter side DC voltage is linearized and Laplace transform, including: S201，整流侧换流母线电压与整流侧直流电压间的关系进行线性化处理，则整流侧直流空载直流电压与整流侧直流电压之间的关系为：S201, the relationship between the commutation bus voltage on the rectifier side and the DC voltage on the rectifier side is linearized, and the relationship between the DC no-load DC voltage on the rectifier side and the DC voltage on the rectifier side is:
Figure FDA0002340819540000022
Figure FDA0002340819540000022
 式中，α为整流侧触发角，UdR0为整流侧直流空载直流电压，XCR为整流侧换相电抗，N为脉动换流器的个数；In the formula, α is the firing angle of the rectifier side, U dR0 is the no-load DC voltage of the rectifier side, X CR is the commutation reactance of the rectifier side, and N is the number of pulsating converters; 对式(3)中的cosα进行线性化，通过对cosα数据进行离散化，其次对离散数据进行线性拟合，得到拟合方程为：Linearize cosα in formula (3), by discretizing the cosα data, and then performing linear fitting on the discrete data, the fitting equation is obtained as: cosα＝-0.01326α+1.26231 (4)cosα=-0.01326α+1.26231 (4) 则根据式(3)与(4)可得整流侧换流母线电压与整流侧直流电压经过线性化处理后的方程，并进行拉普拉斯变化后为：Then according to equations (3) and (4), the linearized equations of the commutation bus voltage on the rectifier side and the DC voltage on the rectifier side can be obtained, and after the Laplace change is:
Figure FDA0002340819540000023
Figure FDA0002340819540000023
 式中dR定义为：where d R is defined as:
Figure FDA0002340819540000031
Figure FDA0002340819540000031
 S202，同步骤201推导原理，对逆变侧换流母线电压与逆变侧直流电压间关系进行线性化处理和拉普拉斯变换，可表示为：S202, the same as the deduction principle of step 201, the linearization processing and Laplace transform are performed on the relationship between the commutation bus voltage on the inverter side and the DC voltage on the inverter side, which can be expressed as:
Figure FDA0002340819540000032
Figure FDA0002340819540000032
 式中dI定义为：where dI is defined as:
Figure FDA0002340819540000033
Figure FDA0002340819540000033
 4.根据权利要求3所述的考虑电流变化的特高压直流输电系统换相失败判别方法，其特征在于，所述S3中，整流侧定电流控制建模，获得定电流控制器的传递函数，具体包括：定电流控制器通过实时测量整流侧直流电流指令值Idref与整流侧直流电流IdI的偏差，经过比例-积分环节输出整流侧触发角，定电流控制器的传递函数为：4. The method for judging the commutation failure of the UHVDC transmission system considering current changes according to claim 3, wherein in the S3, the constant current control model of the rectifier side is modeled, and the transfer function of the constant current controller is obtained, Specifically, the constant current controller measures the deviation of the rectifier side DC current command value I dref and the rectifier side DC current I dI in real time, and outputs the rectifier side firing angle through the proportional-integral link. The transfer function of the constant current controller is:
Figure FDA0002340819540000034
Figure FDA0002340819540000034
 式中，IdN为特高压直流系统直流电流额定值，Kp为比例常数，Ti为积分时间常数。In the formula, I dN is the rated value of the DC current of the UHVDC system, K p is the proportional constant, and T i is the integral time constant. 5.根据权利要求4所述的考虑电流变化的特高压直流输电系统换相失败判别方法，其特征在于，所述S4中，计算逆变侧换流母线电压故障后电压，并进行拉普拉斯变换，具体包括：若逆变侧交流系统短路导致逆变侧换流母线处电压降低ΔULI，经过拉普拉斯变换后的电压为：5. The method for judging the commutation failure of the UHVDC transmission system considering current changes according to claim 4, wherein in the step S4, the voltage after the voltage failure of the commutation bus on the inverter side is calculated, and the Laplacian is performed. The Laplace transform specifically includes: if the inverter side AC system is short-circuited and the voltage at the inverter side commutation bus is reduced by ΔU LI , the voltage after Laplace transform is:
Figure FDA0002340819540000035
Figure FDA0002340819540000035
 式中，ULIN为逆变侧换流母线额定运行电压。In the formula, U LIN is the rated operating voltage of the inverter-side commutation bus. 6.根据权利要求5所述的考虑电流变化的特高压直流输电系统换相失败判别方法，其特征在于，所述S5中，根据低压限流控制动作特性与逆变侧直流电压计算方法，计算直流电流指令值，具体包括：6. The method for judging the commutation failure of the UHVDC transmission system considering current changes according to claim 5, wherein in the S5, according to the low-voltage current-limiting control action characteristics and the inverter-side DC voltage calculation method, calculate DC current command value, including: 直流电流指令值可计算为：The DC current command value can be calculated as:
Figure FDA0002340819540000041
Figure FDA0002340819540000041
 7.根据权利要求6所述的考虑电流变化的特高压直流输电系统换相失败判别方法，其特征在于，所述S6中结合S1-S5的处理结果，获得直流电流表达式，在直流标准测试系统下，对直流电流表达式进行拉普拉斯反变换，得到直流电流的解析表达式，具体包括：7. The method for judging the commutation failure of an UHV DC transmission system considering current changes according to claim 6, wherein, in the S6, in combination with the processing results of S1-S5, a DC current expression is obtained, and in the DC standard test Under the system, perform inverse Laplace transform on the expression of DC current to obtain the analytical expression of DC current, including: S601，结合步骤S1至步骤S5的公式(1)至公式(11)可得直流电流计算为：S601, combining the formula (1) to the formula (11) of the step S1 to the step S5, the DC current can be calculated as:
Figure FDA0002340819540000042
Figure FDA0002340819540000042
 式中：where:
Figure FDA0002340819540000043
Figure FDA0002340819540000043
 S602，将交直流系统参数(表1)带入式(13)，并对(12)进行拉普拉斯反变换即可求解得到直流电流的解析表达式为：S602, bring the AC/DC system parameters (Table 1) into equation (13), and perform the inverse Laplace transform on (12) to solve to obtain the analytical expression of the DC current: IdI(t)＝K1d-K2de-79.878tcos(93.2832t+K3d) (14)I dI (t)=K 1d -K 2d e -79.878t cos(93.2832t+K 3d ) (14) 式中：K1d、K2d、K3d为：In the formula: K 1d , K 2d , K 3d are:
Figure FDA0002340819540000051
Figure FDA0002340819540000051
 8.根据权利要求7所述的考虑电流变化的特高压直流输电系统换相失败判别方法，其特征在于，所述S7中，根据直流电流的解析表达式确定直流电流最大值，将直流电流最大值代入逆变器关断角表达式中，分别获得单相接地故障下的关断角表达式和三相短路故障下的关断角表达式，具体包括：8. The method for judging the commutation failure of the UHVDC transmission system considering current changes according to claim 7, wherein in the S7, the maximum value of the DC current is determined according to the analytical expression of the DC current, and the maximum value of the DC current is determined as the maximum value of the DC current. The value is substituted into the inverter turn-off angle expression, and the turn-off angle expression under single-phase ground fault and the turn-off angle expression under three-phase short-circuit fault are obtained respectively, including: S701，直流电流最大值IdImax为S701, the maximum value of the DC current I dImax is
Figure FDA0002340819540000052
Figure FDA0002340819540000052
 S702，将所得出的直流电流最大值带入式(1)中，获得单相接地故障下的关断角表达式：S702, bring the obtained maximum value of DC current into formula (1) to obtain the expression of the turn-off angle under the single-phase ground fault:
Figure FDA0002340819540000053
Figure FDA0002340819540000053
 三相短路故障下的关断角表达式：Turn-off angle expression under three-phase short-circuit fault:
Figure FDA0002340819540000054
Figure FDA0002340819540000054
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