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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direct current
voltage
angle
current
turn
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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

The invention discloses a method for judging commutation failure of an extra-high voltage direct current transmission system considering current change, which can effectively calculate direct current on an inversion side to obtain a method for calculating a turn-off angle of an inverter considering dynamic change of the direct current when direct current voltage on the inversion side is reduced due to symmetric short-circuit fault and asymmetric short-circuit fault of an alternating current system on the inversion side by accurately modeling a direct current transmission line, and judges that the inverter has commutation failure when the calculated turn-off angle is smaller than the minimum turn-off angle of the commutation failure of the inverter. According to the extra-high voltage direct current transmission system commutation failure judgment method considering current change, on the premise that dynamic change of direct current after an inverter side alternating current system fault is considered, effective judgment of commutation failure is achieved, an alternating current and direct current series-parallel system operation risk evaluation result can be effectively improved, and a basis is provided for guaranteeing safe and stable operation of a power system.

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. A method for judging commutation failure of an extra-high voltage direct current transmission system considering current change is characterized by comprising 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.
2. The method for determining the commutation failure of the extra-high voltage direct current transmission system considering the current variation as claimed in claim 1, wherein in S1, the expression of the inverter turn-off angle is as follows:
Figure FDA0002340819540000011
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 FDA0002340819540000012
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 FDA0002340819540000021
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.
3. An extra-high voltage direct current transmission system commutation failure judgment method according to claim 2, wherein in S2, based on the equivalent circuit, the linearization and laplace transform are performed on the relationship between the commutation bus on the rectification side and the direct current voltage on the rectification side and the relationship between the commutation bus on the inversion side and the direct current voltage on the inversion side, respectively, and 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 FDA0002340819540000022
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 FDA0002340819540000023
in the formula dRIs defined as:
Figure FDA0002340819540000031
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 FDA0002340819540000032
in the formula dIIs defined as:
Figure FDA0002340819540000033
4. the method for judging commutation failure of an extra-high voltage direct current transmission system considering current variation according to claim 3, wherein the method is characterized in thatIn S3, the modeling of the constant current control at the rectifying side to obtain the 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 FDA0002340819540000034
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.
5. The method for determining the phase change failure of the extra-high voltage direct current transmission system considering the current variation as claimed in claim 4, wherein in step S4, the step of calculating the voltage after the voltage fault of the inverter side converter bus and performing the laplace transform specifically includes: 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 FDA0002340819540000035
in the formula of ULINThe rated operation voltage of the inversion side commutation bus is obtained.
6. An extra-high voltage direct current transmission system commutation failure judgment method considering current variation according to claim 5, wherein in step S5, the calculating the direct current command value according to the low voltage current limiting control operation characteristic and the inverter side direct current voltage calculating method specifically comprises:
the DC current command value may be calculated as:
Figure FDA0002340819540000041
7. the method for judging the phase change failure of the extra-high voltage direct current transmission system considering the current variation as claimed in claim 6, wherein the step S6 is performed by combining the processing results of S1-S5 to obtain a direct current expression, and the step S of performing inverse laplace transform on the direct current expression under a direct current standard test system to obtain an analytical expression of the direct current includes:
s601, combining the equations (1) to (11) of the steps S1 to S5, the dc current is calculated as:
Figure FDA0002340819540000042
in the formula:
Figure FDA0002340819540000043
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 FDA0002340819540000051
8. the method for judging the commutation failure of the extra-high voltage direct current transmission system considering the current variation as claimed in claim 7, wherein in S7, the maximum value of the direct current is determined according to the analytic expression of the direct current, and the maximum value of the direct current is substituted into the inverter turn-off angle expression to obtain the turn-off angle expression under the single-phase ground fault and the turn-off angle expression under the three-phase short-circuit fault respectively, which specifically includes:
s701, maximum value I of direct currentdImaxIs composed of
Figure FDA0002340819540000052
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 FDA0002340819540000053
the turn-off angle expression under three-phase short-circuit fault:
Figure FDA0002340819540000054
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