CN111025023A - Disturbance energy limit value selection method for injection type harmonic impedance measurement - Google Patents

Disturbance energy limit value selection method for injection type harmonic impedance measurement Download PDF

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CN111025023A
CN111025023A CN201911315327.7A CN201911315327A CN111025023A CN 111025023 A CN111025023 A CN 111025023A CN 201911315327 A CN201911315327 A CN 201911315327A CN 111025023 A CN111025023 A CN 111025023A
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disturbance
injection
noise interference
limit value
impedance
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CN111025023B (en
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何正友
宋依桐
胡海涛
潘鹏宇
肖冬华
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Southwest Jiaotong University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/16—Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/08—Measuring resistance by measuring both voltage and current

Abstract

The invention discloses a disturbance energy limit value selection method for injection type harmonic impedance measurement, which comprises the following steps: determining the relative error of the measuring frequency containing background harmonic component and noise interference quantity; and solving the disturbance injection current at the common coupling point to obtain the injection disturbance current limit value of the measurement frequency including background harmonic component and noise interference quantity. The method has the advantages that the index selection is carried out based on the relative error formula of the impedance measured value and the theoretical value, and the method is high in accuracy; according to the corresponding requirements of the actual system to be measured, the definite and effective injection disturbance limit judgment is made before the impedance measurement is carried out, and the method has strong applicability; the method has the advantages that the influence of noise and background harmonic waves on the measurement accuracy is focused, the purpose of ensuring the safe and stable operation of the system to be measured while the cost is saved is achieved, and the method is high in practicability.

Description

Disturbance energy limit value selection method for injection type harmonic impedance measurement
Technical Field
The invention relates to the field of active impedance measurement in a power system, in particular to a disturbance energy limit value selection method for injection type harmonic impedance measurement.
Background
With the development and popularization of power electronic technology, important industrial systems such as new energy power generation, flexible direct current transmission, electrified railways and the like increasingly show the trend of power electronization. While the nonlinear power electronic equipment exerts the excellent performance, a series of oscillation and instability problems are brought, and the safe and stable operation of each large power grid is seriously interfered. Existing research indicates that impedance characteristic mismatch between a VSC (Voltage Source Converter) type device and a power network may cause oscillation or instability of a VSC control system. Accurate harmonic impedance measurements are currently an important means of analyzing system stability.
Harmonic impedance measurement methods can be classified into two categories, the "passive" and the "active". The active method estimates the harmonic impedance of the system side by using the additional disturbance amount generated artificially, and the disturbance mode is more accurate than the result obtained by the passive method. However, the disturbance injected by the method may be affected by various factors, for example, when the injection power is too small, the noise component, the background harmonic component, and the harmonic loss of the line and the transformer contained in the system itself will "drown" the injection signal with a high probability, which affects the accuracy of the impedance measurement result. It can be seen that the "injection" method is an important impedance measurement method, and there is a close coupling relationship between the injection signal related index and the system under test. It is therefore necessary to define the relevant parameters of the injected signal reasonably according to the actual conditions of the system under test.
Disclosure of Invention
The invention aims to provide a method for selecting a disturbance signal limit value for injection type harmonic impedance measurement, which is used for presetting a disturbance energy limit standard before measurement and providing technical support for ensuring safe and stable operation of a system.
The technical scheme for realizing the purpose of the invention comprises a disturbance energy limit value selection method considering background harmonic components and not considering the background harmonic components, and comprises the following steps:
a method for disturbance energy limit selection for injection harmonic impedance measurements, comprising:
step 1: determining relative error of measuring frequency containing background harmonic component and noise interference quantity
Figure BDA0002325690210000021
Wherein the content of the first and second substances,
Figure BDA0002325690210000022
in order to perturb the injected current at the point of common coupling,
Figure BDA0002325690210000023
for the background harmonic voltage on the side of the system to be tested,
Figure BDA0002325690210000024
respectively, the noise interference amount of the voltage signal and the current signal,
Figure BDA0002325690210000025
the system frequency domain impedance under the ideal condition;
step 2: making the engineering design precision grade of the measuring system be relative error
Figure BDA0002325690210000026
Solving for
Figure BDA0002325690210000027
Obtaining the limit value of the injection disturbance current of the measuring frequency containing background harmonic component and noise interference amount, i.e.
Figure BDA0002325690210000028
Another method for selecting the disturbance energy limit value for injection harmonic impedance measurement comprises
Step 1: determining that the measurement frequency contains no background harmonic component, only the relative error of the noise interference amount
Figure BDA0002325690210000029
Wherein the content of the first and second substances,
Figure BDA00023256902100000210
in order to perturb the injected current at the point of common coupling,
Figure BDA00023256902100000211
respectively, the noise interference amount of the voltage signal and the current signal,
Figure BDA00023256902100000212
the system frequency domain impedance under the ideal condition;
step 2: making the engineering design precision grade of the measuring system be relative error
Figure BDA00023256902100000213
Solving for
Figure BDA00023256902100000214
Obtaining the limit value of the injection disturbance current of which the measuring frequency does not contain background harmonic components and only contains noise interference quantity, namely
Figure BDA00023256902100000215
Compared with the prior art, the invention has the beneficial effects that:
the invention meets the refinement requirements required by the impedance measurement process and the research and development of the measurement device in the field of the power system, and fills the blank in the aspect of the limitation of the injection energy in the injection impedance measurement field. The invention has the following advantages:
the method carries out index selection based on the relative error formula of the impedance measured value and the theoretical value, the precision setting can be consistent with the obtained result, and the method is high in accuracy.
By using the method, the definite and effective injection disturbance limit judgment can be made before the impedance measurement is carried out according to the corresponding requirements of the actual system to be measured, and the method has strong applicability.
And thirdly, the method achieves the aim of ensuring the safe and stable operation of the system to be measured while saving cost from the aspect of avoiding the influence of noise and background harmonic waves on the measurement accuracy, and has high practicability.
Drawings
FIG. 1 is a schematic diagram of the selection of the disturbance energy limit for injection impedance measurement.
Fig. 2 is a schematic diagram of the injection impedance measurement principle.
Fig. 3 is a logic diagram of injection impedance measurement that takes noise and background harmonic interference into account.
FIG. 4 is a measurement of the system impedance at a greater than disturbance energy index. Fig. 4(a) shows impedance measurement results under the disturbance limit indexes of 500%, 200%, 150%, and 100%, and fig. 4(b) shows corresponding relative error results.
FIG. 5 is a measurement of the system impedance when less than the perturbation energy index. Fig. 5(a) shows impedance measurement results under the 75%, 50%, and 25% disturbance limit indicators, and fig. 5(b) shows corresponding relative error results.
Detailed Description
The following further describes the embodiments of the present invention with reference to the drawings.
A disturbance energy limit value selection method for injection harmonic impedance measurement considers system background harmonic and noise interference and according to a relative error formula of an impedance measured value and a theoretical value
Figure BDA0002325690210000041
Determining a measure of injected signal emission value at the point of common coupling, wherein
Figure BDA0002325690210000042
Is an index of the relative error,
Figure BDA0002325690210000043
for the system impedance obtained by injection measurement mixed with background harmonics and system noise,
Figure BDA0002325690210000044
is a system frequency domain impedance expression under an ideal condition.
The frequency domain expression of the system impedance under ideal conditions is listed:
Figure BDA0002325690210000045
wherein
Figure BDA0002325690210000046
Respectively, the voltage at PCC (Point of Common Coupling) and the disturbance injection current.
Listing the frequency domain expression of the actual value of the system impedance considering background harmonic and noise quantity:
Figure BDA0002325690210000047
wherein
Figure BDA0002325690210000048
The voltage at the PCC and the disturbance injection current respectively contain noise disturbance quantities,
Figure BDA00023256902100000418
is the system side background harmonic voltage.
Order to
Figure BDA0002325690210000049
As to the amount of voltage noise interference,
Figure BDA00023256902100000410
as a current noise interference amount, then
Figure BDA00023256902100000411
Can be rewritten as:
Figure BDA00023256902100000412
combined with relative error formula
Figure BDA00023256902100000413
Obtaining a relative error expression of the measuring frequency including background harmonic components:
Figure BDA00023256902100000414
and measuring relative error expressions that frequencies do not include background harmonic components:
Figure BDA00023256902100000415
then after selecting the engineering design accuracy grade, delta will bez1Or deltaz2Substituting and solving
Figure BDA00023256902100000416
Obtaining an expression of the limit value of the injection disturbance current of which the measurement frequency contains the background harmonic component:
Figure BDA00023256902100000417
and (3) measuring an injection disturbance current limit expression with the frequency not containing background harmonic components:
Figure BDA0002325690210000051
the two methods are respectively suitable for different frequency bands. The method including the background harmonic component is suitable for a low frequency band having a high background harmonic content, which greatly increases the complexity of the calculation and reduces the calculation rate when it is used for a medium and high frequency band. The method without the background harmonic component is suitable for medium and high frequency bands with low background harmonic content, and effectively reduces the calculation complexity and accelerates the calculation rate.
When the method is used specifically, the background harmonic voltage in the two formulas can be analyzed in the mode of national public power grid harmonic voltage limit standard, TB/T3442-2016 noise voltage limit standard and system (including power supply grid side, transmission line and transformer) harmonic impedance estimation
Figure BDA0002325690210000052
Noise voltage
Figure BDA0002325690210000053
Noise current
Figure BDA0002325690210000054
Theoretical value of system impedance
Figure BDA0002325690210000055
And the engineering design precision is limited to 0.5 level.
The harmonic impedance estimation can utilize the following calculation formula of each part of harmonic impedance: calculation formula for harmonic short-circuit impedance of each frequency of power grid
Figure BDA0002325690210000056
Wherein h represents the harmonic order, VgIndicating the voltage class, S, of the power systemdIndicating the short-circuit capacity of the high-voltage system, and the SCR indicating the short-circuit ratio;
Figure BDA0002325690210000057
represents the fundamental impedance; traction transformer harmonic impedance calculation formula
Figure BDA0002325690210000058
Figure BDA0002325690210000059
Wherein
Figure BDA00023256902100000510
Indicating fundamental leakage reactance, U, of the transformerd% of short-circuit voltage of transformer, UBCharacterization of the rated voltage, S, of the electrical power system reduced to the secondary sideTRepresenting the capacity of the transformer; approximate calculation formula of harmonic impedance of power transmission line
Figure DA00023256902154764
Figure BDA00023256902100000511
Wherein
Figure BDA00023256902100000512
f0Is the fundamental frequency, K is the correction coefficient of the stranded wire, p is the perimeter (cm) of the section of the wire, rho is the resistivity,
Figure BDA00023256902100000513
representing the phase angle, l is the length of the transmission line.
The obtained fundamental impedance parameters of each part are shown in the following table:
TABLE 1 high-voltage side-group wave short-circuit impedance of the system
Figure BDA0002325690210000061
TABLE 2 fundamental impedance of traction transformer
Figure BDA0002325690210000062
TABLE 3 transmission line fundamental wave impedance
Figure BDA0002325690210000063
And further, the conclusion that the transformer capacity has the greatest influence on the index setting is obtained by changing the network side capacity, the length of the transmission line and the transformer capacity, and further, the limiting index expression is simplified to obtain the capacity S of the transformerTAnd system voltage class
Figure BDA0002325690210000064
The relevant disturbance energy limit simplifies the formula:
Figure BDA0002325690210000065

Claims (2)

1. a method for selecting a disturbance energy limit for injection harmonic impedance measurement, comprising:
step 1: determining relative error of measuring frequency containing background harmonic component and noise interference quantity
Figure FDA0002325690200000011
Wherein the content of the first and second substances,
Figure FDA0002325690200000012
in order to perturb the injected current at the point of common coupling,
Figure FDA0002325690200000013
for the background harmonic voltage on the side of the system to be tested,
Figure FDA0002325690200000014
respectively, the noise interference amount of the voltage signal and the current signal,
Figure FDA0002325690200000015
the system frequency domain impedance under the ideal condition;
step 2: making the engineering design precision grade of the measuring system be relative error
Figure FDA0002325690200000016
Solving for
Figure FDA0002325690200000017
Obtaining the limit value of the injection disturbance current of the measuring frequency containing background harmonic component and noise interference amount, i.e.
Figure FDA0002325690200000018
2. A disturbance energy limit value selection method for injection type harmonic impedance measurement is characterized by comprising the following steps
Step 1: determining that the measurement frequency contains no background harmonic component, only the relative error of the noise interference amount
Figure FDA0002325690200000019
Wherein the content of the first and second substances,
Figure FDA00023256902000000110
in order to perturb the injected current at the point of common coupling,
Figure FDA00023256902000000111
respectively, the noise interference amount of the voltage signal and the current signal,
Figure FDA00023256902000000112
the system frequency domain impedance under the ideal condition;
step 2: making the engineering design precision grade of the measuring system be relative error
Figure FDA00023256902000000113
Solving for
Figure FDA00023256902000000114
Obtaining the limit value of the injection disturbance current of which the measuring frequency does not contain background harmonic components and only contains noise interference quantity, namely
Figure FDA00023256902000000115
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