CN108896820B - Phase modulator startup protection phasor calculation method suitable for starting static frequency converter - Google Patents

Phase modulator startup protection phasor calculation method suitable for starting static frequency converter Download PDF

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CN108896820B
CN108896820B CN201810793811.XA CN201810793811A CN108896820B CN 108896820 B CN108896820 B CN 108896820B CN 201810793811 A CN201810793811 A CN 201810793811A CN 108896820 B CN108896820 B CN 108896820B
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phase
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CN108896820A (en
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桑建斌
包明磊
李玉平
李明
朱宇聪
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Guodian Nanjing Automation Co Ltd
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Abstract

The invention discloses a phase modulator startup protection phasor calculation method suitable for starting a static frequency converter, wherein zero-crossing point interpolation frequency measurement is carried out on a phase modulator by adopting low-pass filtered interphase voltage or neutral point current, and the frequency measurement response speed is higher; if three-phase short circuit occurs, so that the inter-phase voltage is lower than the amplitude threshold of the frequency measurement, the frequency measurement is carried out by adopting neutral point current, and the frequency measurement function is prevented from being influenced by the short-circuit fault condition; the fixed sampling rate is adopted, and the method is suitable for upgrading a conventional protection device; the principle error brought by the fixed sampling rate is corrected, and the precision is higher; the core calculation is optimized, and fitting functions are used for replacing a large number of used sine and cosine functions, so that the execution efficiency of the algorithm is ensured, and the method is suitable for protecting a phase modulator protection device which has more protection configurations and is sensitive to efficiency. The calculation method has the advantages of higher precision and higher response speed in a frequency conversion environment, can filter the whole harmonic, and has higher calculation efficiency.

Description

Phase modulator startup protection phasor calculation method suitable for starting static frequency converter
Technical Field
The invention belongs to the technical field of phase modulator start-up protection, and particularly relates to a phase modulator start-up protection phasor calculation method suitable for starting a static frequency converter.
Background
There are many ways to start up a phase modulator, and the starting ways used in the prior art mainly include: asynchronous start, low frequency start, coaxial motor start, etc. The 300MVar phase modulator which is put into operation is usually started by a Static Frequency Converter (SFC) due to the large capacity of the phase modulator, the mode is accurate in control and small in grid-connected impact, and soft starting can be achieved by matching with a synchronous device. In the starting process of the phase modulator, the frequency range of the secondary current and the voltage analog quantity input to the relay protection device is 0-52.5 Hz. Because the harmonic wave of the current output by the SFC during working is large, when the SFC adopts n-pulse inversion, the output current contains kn +/-1 (k is an integer more than or equal to 1) subharmonic wave, and therefore, the phase modulator started by the SFC has obvious frequency conversion characteristic and harmonic wave characteristic in the starting process. If the starting method can effectively filter the integral harmonic of the frequency of the phase modulator in the frequency conversion process, the starting overcurrent protection and the starting differential protection have better performance. In addition, the zero sequence voltage at the machine end in the starting state contains obvious third harmonic voltage which is mainly generated by a phase modulator, the amplitude of the third harmonic voltage is enough to influence the sensitivity of starting zero voltage protection in the starting process, and the filtering ratio of the third harmonic in the zero sequence voltage protection is required to be more than 100 in domestic industry under the power frequency state, but the third harmonic voltage has no similar requirement under the frequency conversion environment. If the third harmonic is filtered under the variable frequency environment, the performance of starting zero voltage protection is improved, and the setting sensitivity of the zero sequence voltage constant value can be improved. Therefore, it is urgently needed to develop a startup protection method with high precision, capable of filtering the whole harmonic wave and moderate algorithm calculation amount.
In order to solve the above technical problems, chinese patent publication No. CN105277781A discloses an electrical phasor measurement method and apparatus adapted to a frequency conversion process, which includes: (1) the protection device uses a fixed sampling frequency to collect secondary side voltage and current of a voltage transformer and/or a current transformer, and uses a frequency measurement algorithm to detect the frequency of a voltage and current signal; (2) determining the length of a data window according to the sampling frequency and the current voltage and current frequency, and calculating to obtain new N data values in the current data window by an interpolation method; (3) and carrying out phasor calculation on the N data values by using a phasor algorithm so as to obtain the phasor of the voltage and the current. Although the technical scheme in the patent can solve the problem that the conventional method cannot measure or has large measurement errors under the condition of rapid frequency change, a large amount of interpolation needs to be carried out on the sampled data, and the problem of large calculation amount exists.
Disclosure of Invention
In order to filter out the third harmonic voltage generated by a phase modulator and the kn +/-1 (k is an integer larger than or equal to 1) subharmonic current output by an SFC in a starting frequency conversion environment, accurately measure the fundamental wave of the electrical quantity of the phase modulator in the frequency conversion process, improve the starting protection performance and reduce the calculated quantity, the invention provides the phase modulator starting protection phasor calculation method suitable for starting a static frequency converter, which does not need to carry out a large amount of interpolation on sampled data, only needs to carry out one-time compensation on each piece of frequency data and has small calculated quantity.
The technical purpose is achieved, the technical effect is achieved, and the invention is realized through the following technical scheme:
a phase modulator start-up protection phasor calculation method suitable for starting a static frequency converter comprises the following steps:
sampling the relevant parameters of the phase modulator, and calculating to obtain the working frequency f of the phase modulator0；
According to the sampling frequency f of the protection devicesAnd the measured working frequency f of the phase modulator in real time0Calculating to obtain the number of sampling points N of each cycleallCounting the number N of the sampling pointsallPerforming snapshot processing on the data to obtain the number of points actually participating in calculation of each cycle after snapshot, wherein the number of points actually participating in calculation of each cycle comprises an integer part N and a decimal part delta N;
determining the data window length of the zero sequence voltage at the generator end according to the integer part N of the points actually participating in calculation of each cycle wave, and calculating the phasor of k harmonics of the zero sequence voltage at the generator end by using discrete Fourier transform;
according to the decimal part delta N in the points actually participating in calculation of each cycle wave, the zero sequence voltage k harmonic phasor at the machine end is compensated, and phasor calculation of startup protection of the phase modulator is completed.
Further, sampling related parameters of the phase modulator, and calculating to obtain the working frequency f of the phase modulator0The method specifically comprises the following steps:
sampling terminal phase-to-phase voltage or neutral point current of the camera, and simultaneously sampling the analog quantity X to be detected to obtain sampling instantaneous values of all parameters;
measuring frequency by using terminal interphase voltage sampling value data window or neutral point current sampling value data window to obtain working frequency f of phase modulator0。
Further, the machine end interphase voltage or the neutral point current of the camera is sampled, and frequency measurement is performed by using a machine end interphase voltage sampling value data window or a neutral point current sampling value data window, specifically:
firstly, the interphase voltage at the machine end of the phase modulator is sampled, and if the interphase voltage is lower than the amplitude threshold of frequency measurement due to the three-phase short circuit at the machine end of the phase modulator, the protection device adopts a neutral point current sampling value data window to measure the frequency.
Furthermore, the frequency measurement is carried out by adopting a zero-crossing point interpolation method, in the processing process, data is subjected to low-pass filtering processing, the filter requires that 0-60Hz signals are not attenuated, and the attenuation can be reduced to be less than 0.1 time when the frequency is more than 100 Hz.
Further, the number of sampling points per cycle is NallComprises the following steps:
Figure GDA0002440512520000021
the number of the sampling points is NallIn the data extraction processing, the extraction interval is:
Figure GDA0002440512520000031
m is an integer and represents a threshold value for judging whether a cycle sampling point is subjected to snapshot processing, and the value range of m is more than or equal to 12 and less than or equal to 24;
the number of points actually participating in calculation per cycle after snapshot is as follows:
Figure GDA0002440512520000032
in the formula, N represents an integer part, and Δ N represents a fractional part.
Further, the method comprises the steps of determining the data window length of the zero sequence voltage at the generator end according to the integer part N of the number of points actually participating in calculation of each cycle, and calculating the phasor of k-th harmonic of the zero sequence voltage at the generator end by using discrete Fourier transform, and specifically comprises the following steps:
t in the analog X (t) to be measured1Phasor of k-th harmonic of time
Figure GDA0002440512520000033
Expressed as:
Figure GDA0002440512520000034
at [ t ]1-T，t1]Real part R of k harmonic phasor of zero sequence voltage at internal counterpoint terminalkThe approximation according to the trapezoidal rule yields:
Figure GDA0002440512520000035
the imaginary part is obtained by the same method:
Figure GDA0002440512520000036
wherein X (N) is the zero sequence voltage sampling value at the terminal of the current time, and X (N-N) is the first N/fsThe sampling value at the moment, Delta S is the number N of sampling points actually participating in the calculation of each cyclefThe fractional part of (a) corresponds to the trapezoidal area.
Further, according to a decimal part delta N in the number of points actually participating in calculation of each cycle wave, the k-th harmonic phasor of the zero sequence voltage at the machine end is compensated, and the method specifically comprises the following steps:
solving for Δ S:
Figure GDA0002440512520000037
in the formula, X (N)f) Is t1A theoretical value of time;
and (5) and (6) are arranged according to the formula (7) to obtain the real part and the imaginary part of the compensated k-th harmonic phasor.
Further, with t1X (n-K) around timen) Obtaining t by interpolating the sampling values at two points X (n)1Theoretical value of time X (N)f) The approximate expression is:
X(Nf)≈X(n-Kn)+[X(n)-X(n-Kn)]ΔN (8)。
further, the real part of the compensated k-th harmonic phasor is:
Figure GDA0002440512520000041
the real part of the compensated k-th harmonic phasor is as follows:
Figure GDA0002440512520000042
further, cos (t), sin (t) in the formulas (9) and (10) are subjected to a fitting function sin (x)f、cos(x)fAlternatively, the real and imaginary components of the final compensated k harmonic phasor are calculated, and the fitting function sin (x)f、cos(x)fRespectively as follows:
Figure GDA0002440512520000043
Figure GDA0002440512520000044
compared with the prior art, the invention has the beneficial effects that:
the phase modifier startup protection phasor calculation method suitable for starting the static frequency converter provided by the invention has the advantages of higher precision and higher response speed in a frequency conversion environment, can filter the whole harmonic wave, has higher calculation efficiency, and is specifically represented by the following aspects:
(1) and the interphase voltage or neutral point current after low-pass filtering is adopted to carry out zero crossing point interpolation frequency measurement on the camera, so that the frequency measurement response speed is higher.
(2) If three-phase short circuit occurs, so that the inter-phase voltage is lower than the amplitude threshold of frequency measurement, the frequency measurement is carried out by adopting neutral point current, and the influence of short circuit fault conditions on the frequency measurement function is avoided.
(3) The fixed sampling rate is adopted, and the method is suitable for upgrading a conventional protection device; and the principle error caused by the fixed sampling rate is corrected, so that the precision is higher.
(4) The core calculation part is optimized, when the number of calculation points is large, the point extraction processing is carried out in a self-adaptive mode, a fitting function is used for replacing a large number of used sine and cosine functions, the execution efficiency of the algorithm is guaranteed, and the method is suitable for protecting a phase modulator protection device which is large in protection configuration and sensitive to efficiency.
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FIG. 1 is a schematic diagram of the amplitude-frequency characteristics of a low-pass filter for frequency measurement;
FIG. 2 shows a schematic representation of the processing of the real part of the phasor;
FIG. 3 shows a schematic of the calculation when the input is a step voltage;
fig. 4 shows a schematic diagram of the calculation when the third harmonic voltage is superimposed.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The following detailed description of the principles of the invention is provided in connection with the accompanying drawings.
Because 3-order harmonic voltage generated by a phase modulator and kn +/-1 (k is an integer larger than or equal to 1) order harmonic current output by the SFC exist in the starting frequency conversion environment, the fundamental wave of the electrical quantity of the phase modulator in the frequency conversion process cannot be accurately measured, and the starting protection performance is poor. In order to solve the above problems, a method and a device for measuring an electrical quantity phasor suitable for a frequency conversion process are proposed in the prior art, but a large amount of interpolation needs to be performed on sampled data, and a problem of large calculation amount exists. Therefore, the invention provides the phase modifier startup protection phasor calculation method suitable for the startup of the static frequency converter, which does not need to carry out a large amount of interpolation on the sampled data, only needs to carry out one-time compensation on each cycle of data, can carry out the snapshot processing in a self-adaptive manner when the number of calculation points is large, and has less calculation amount.
The invention relates to a phase modulator startup protection phasor calculation method suitable for startup of a static frequency converter, which is characterized in that the frequency of phase modulator interphase voltage or neutral point current is measured, the length of a sampling window for startup protection phasor calculation is adjusted according to the frequency of the phase modulator and the fixed sampling rate of a protection device, then a Fourier algorithm is discretized by using a trapezoidal rule on the basis of a variable data window, principle errors caused by the fixed sampling rate are corrected, and the core calculation is optimized for ensuring the execution efficiency of the algorithm while the trapezoidal rule is used, and specifically comprises the following steps:
step one, sampling relevant parameters of a phase modulator, and calculating to obtain the working frequency f of the phase modulator0；
The first step specifically comprises the following steps:
(1.1) using a protection device to adjust the terminal interphase voltage U of the cameraAB、UBCOr neutral point current INA、INB、INCSampling is carried out, and simultaneously, the analog quantity X to be measured with frequency change in starting protection is also sampled to obtain the sampling instantaneous value of each parameter, namely the sampling instantaneous value UAB(t)、UBC(t)、INA(t)、INB(t)、INC(t)、X(t)；
In a specific embodiment of the present invention, the protection device is a relay protection device; the analog quantity X to be measured of frequency change in the startup protection can be the analog quantity needed by any phase modifier protection, and the startup protection in the phase modifier protection mainly refers to the zero sequence voltage U at the machine end0Three-phase current I at terminal of generatorA、IB、ICNeutral point current INA、INB、INc；
(1.2) carrying out frequency measurement by utilizing a terminal interphase voltage sampling value data window or a neutral point current sampling value data window to obtain the working frequency of the phase modulator;
in a preferred embodiment of the present invention, the frequency measurement in step (1.2) is performed by using a zero-crossing point interpolation method, in the processing process, data is subjected to low-pass filtering, a filter requires that a signal of 0-60Hz is not attenuated, and the signal can be attenuated to less than 0.1 times at above 100 Hz.
Preferably, in the step (1.1) and the step (1.2), the protection device samples an end-to-end phase-to-phase voltage or a neutral point current of the camera, and measures a frequency by using an end-to-end phase-to-phase voltage sampling value data window or a neutral point current sampling value data window, specifically:
firstly, the inter-phase voltage at the machine end of the phase modulator is sampled, and if the inter-phase voltage is lower than the amplitude threshold of frequency measurement due to the three-phase short circuit at the machine end of the phase modulator, the protection device carries out frequency measurement on a data window adopting neutral point current sampling values.
Step two, according to the sampling frequency f of the protection devicesAnd the measured working frequency f of the phase modulator in real time0Calculating to obtain the number of sampling points N of each cycleall，NallNot necessarily an integer. To reduce the amount of calculation, the number N of the sampling pointsallPerforming snapshot processing on the data to obtain the number of points actually participating in calculation of each cycle after snapshot, wherein the number of points actually participating in calculation of each cycle comprises an integer part N and a decimal part delta N;
wherein, the number of sampling points of each cycle is as follows:
Figure GDA0002440512520000061
the number of the sampling points is NallIn the data extraction processing, the extraction interval is:
Figure GDA0002440512520000062
m is an integer and represents a threshold value for judging whether a cycle sampling point is subjected to snapshot processing, and the value range of m is more than or equal to 12 and less than or equal to 24;
the number of points actually participating in calculation per cycle after snapshot is as follows:
Figure GDA0002440512520000071
n denotes an integer part and Δ N denotes a fractional part.
Step three, determining the data window length of the zero sequence voltage at the machine end according to the integer part N of the points actually participating in calculation of each cycle wave, and calculating the phasor of k-th harmonic of the zero sequence voltage at the machine end by using discrete Fourier transform;
the third step specifically comprises the following steps:
t in the analog X (t) to be measured1Phasor of k-th harmonic of time
Figure GDA0002440512520000072
Expressed as:
Figure GDA0002440512520000073
at [ t ]1-T，t1]Real part R of k harmonic phasor of zero sequence voltage at internal counterpoint terminalkApproximated by the trapezoidal rule to obtain (for function X (t) cos (2k π f)0t) integration over the time axis), i.e. at equal time intervals
Figure GDA0002440512520000074
Discretization, see in particular fig. 2:
Figure GDA0002440512520000075
the imaginary part is obtained by the same method:
Figure GDA0002440512520000076
wherein X (N) is the zero sequence voltage sampling value at the terminal of the current time, and X (N-N) is the first N/fsThe sampling value at the moment, Delta S is the number N of sampling points actually participating in the calculation of each cyclefThe fractional part of (a) corresponds to the trapezoidal area.
Step four, according to the decimal part delta N in the points actually participating in the calculation of each cycle wave, compensating the k harmonic phasor of the zero sequence voltage at the machine end, and completing the phasor calculation of the startup protection of the phase modulator;
the fourth step is specifically as follows:
solving for Δ S:
Figure GDA0002440512520000077
in the formula, X (N)f) Is t1A theoretical value of time;
further, said X (N)f) Preferably, t is used1X (n-K) around timen) And X (n) two-point sampling value is obtained by interpolation, and the approximate expression is as follows:
X(Nf)≈X(n-Kn)+[X(n)-X(n-Kn)]ΔN (8)
obtaining a real part and an imaginary part of the compensated k-th harmonic phasor according to the formula (7) and the formula (5) and the formula (6);
the real part of the compensated k-th harmonic phasor is as follows:
Figure GDA0002440512520000081
the imaginary part of the compensated k-th harmonic phasor is as follows:
Figure GDA0002440512520000082
preferably, to save computation, cos (t), sin (t) in equations (9) and (10) are applied to the fitting function sin (x) in calculating the real part and imaginary part of the compensated k-th harmonic phasorf、cos(x)fAlternative, fitting function sin (x)f、cos(x)fRespectively as follows:
Figure GDA0002440512520000083
Figure GDA0002440512520000084
finally, calculating according to the formulas (7) to (12) to obtain compensated terminal zero sequence voltage k harmonic phasor
Figure GDA0002440512520000085
Completing the phasor calculation.
Example 1
In this embodiment, it is set that no three-phase short circuit occurs at the phase modulator end, and the phase-to-phase voltage is higher than or equal to the amplitude threshold of the frequency measurement. The following describes the phase modulation start-up protection method suitable for starting a static frequency converter in the present invention with reference to fig. 1-4.
In this embodiment, the phase modulation start-up protection method suitable for starting a stationary frequency converter specifically includes the following steps:
step 1: firstly, sampling AB phase-to-phase voltage at the machine terminal and zero sequence voltage at the machine terminal by a relay protection device to obtain sampled instantaneous values of the AB phase-to-phase voltage and the zero sequence voltage at the machine terminal;
step 2: the sampled value of terminal AB interphase voltage is processed by low-pass filtering through a low-pass filter as shown in figure 1, and the implementation manner of the low-pass filtering in a program is as follows:
Figure GDA0002440512520000091
wherein, x (N) is the current original sampling point, h (k) is the filter coefficient, y (N) is the sampling point at the current moment after filtering, and the number of the filter coefficients is N + 1;
forming a new frequency measurement data window by the processed data according to time arrangement, judging the zero crossing point position of the new frequency measurement data window, carrying out interpolation according to sampling values at two sides of the zero crossing point when the zero crossing point position is found to obtain the accurate time of the zero crossing point, searching the next zero crossing point time by the same method, and obtaining the working frequency f of the phase modulator according to the time difference of the zero crossing point0(ii) a The data window refers to an array with a certain length used for storing analog quantity sampling values in a program, the frequency measurement data window in the invention is a sampling value array used for measuring frequency, and the data window in the invention comprises a data window used for measuring frequency and a data window used for measuring phasor.
And step 3: according to the operating frequency f of the phase-modifying machine0Sampling frequency f of the protection devicesMeanwhile, the calculated amount is optimized, and a cycle wave is calculated and actually usedThe number of sampling points;
the total sampling points of terminal AB interphase voltage per cycle are as follows:
Figure GDA0002440512520000092
the total sampling point number N in the data window for the variable frequency phasor calculation in the starting protectionallPerforming snapshot processing, wherein the number of interval points during snapshot is
Figure GDA0002440512520000093
The number of points actually involved in the calculation per cycle is:
Figure GDA0002440512520000101
wherein N represents an integer part and Δ N represents a fractional part;
and 4, step 4: according to the number N of sampling points actually used by a cycle wavefDetermining the data window length of the zero sequence voltage at the generator end, and calculating the phasor of k harmonics of the zero sequence voltage at the generator end by using discrete Fourier transform
Figure GDA0002440512520000102
T in original signal X (t) of terminal zero sequence voltage1Phasor of k-th harmonic of time
Figure GDA0002440512520000103
Expressed as:
Figure 1
will be provided with
Figure GDA0002440512520000105
X (t) cos (2k π f) in the solid part of (1)0t) is plotted in a coordinate system, as shown in FIG. 2;
according to FIG. 2, at [ t ]1-T,t1]Real part R of k harmonic phasor of zero sequence voltage at internal counterpoint terminalkThe approximation according to the trapezoidal rule yields:
Figure GDA0002440512520000106
the imaginary part is obtained by the same method:
Figure GDA0002440512520000107
wherein, X (N) is the zero sequence voltage sampling value at the terminal of the current time, X (N-N) is the sampling value at the previous N/fs time, and Δ S is the compensation area (shaded portion) in fig. 2.
And 5: according to the number N of sampling points actually used by a cycle wavefAnd the decimal part delta N compensates the k harmonic phasor of the zero sequence voltage at the machine end.
The Δ S trapezoidal area in fig. 2 is:
Figure GDA0002440512520000108
x (N) in the formula (7)f) Obtaining an approximate expression of X (N) by interpolationf)≈X(n-Kn)+[X(n)-X(n-Kn)]ΔN (8)
In order to save calculation amount, sine coefficients cos (t), sin (t) which are greatly used in the algorithm adopt a fitting function sin (x)f、cos(x)fAlternatively, the fitting function is:
Figure GDA0002440512520000111
Figure GDA0002440512520000112
cos (t) Using the fitting function cos (x)fAnd (4) replacing, obtaining a real part of k harmonic phasor by the arrangement formula (5) as follows:
Figure GDA0002440512520000113
the imaginary part of the k harmonic phasor is obtained by the same method
Figure GDA0002440512520000114
The program in the relay protection device calculates and obtains k harmonic phasor of zero sequence voltage at the compensated machine end according to the formulas (7) to (12)
Figure GDA0002440512520000115
Step 6: experiments were carried out according to the calculation method of the invention, the parameters involved in the experiments: the value of the threshold value m for judging whether the sampling point of the cycle is subjected to the snapshot processing is 24, and the sampling frequency of the device is 1200 Hz.
Step zero sequence voltage is input to the improved starting zero voltage protection under the frequencies of 15Hz, 25Hz and 40Hz, the initial time voltage is 2V, the voltage suddenly increases to 5V after 230ms, and the wave recording waveform of the device is shown in figure 3. The machine end zero sequence voltage amplitude (fundamental wave) in fig. 3 is calculated by the method of the invention, the voltage amplitude measured before and after the change of the machine end zero sequence voltage is accurate and stable, and the response speed of the method of the invention to the step input is about 1 electrical cycle.
The grounding fault occurs when the frequency of the camera is 15Hz under the simulation starting state, the fundamental voltage in the zero sequence voltage channel at the end of the fault front end is zero, the third harmonic voltage is 1V, the fundamental zero sequence voltage is increased to 4V after the fault, the third harmonic voltage keeps 1V unchanged, and the device records waves as shown in figure 4. Fig. 4 shows that the method of the present invention can accurately measure the fundamental voltage, simultaneously can filter the third harmonic voltage, and avoid the influence of the third harmonic voltage inherent in the phase modulator on the sensitivity of the startup zero-voltage protection.
In summary, the following steps:
the invention provides a phase modulator startup protection phasor calculation method suitable for starting a static frequency converter, wherein zero-crossing point interpolation frequency measurement is carried out on a phase modulator by adopting low-pass filtered interphase voltage or neutral point current, and the corresponding frequency measurement speed is higher; if three-phase short circuit occurs, so that the inter-phase voltage is lower than the amplitude threshold of frequency measurement, the frequency measurement is carried out by adopting neutral point current, and the frequency measurement function is prevented from being influenced by the short-circuit fault condition; the fixed sampling rate is adopted, and the method is suitable for upgrading a conventional protection device; the principle error brought by the fixed sampling rate is corrected, and the precision is higher; the core calculation is optimized, and fitting functions are used for replacing a large number of used sine and cosine functions, so that the execution efficiency of the algorithm is ensured, and the method is suitable for protecting a phase modulator protection device which has more protection configurations and is sensitive to efficiency. The protection algorithm has the advantages of higher precision and higher response speed in a frequency conversion environment, can filter the whole harmonic, and has higher calculation efficiency.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (10)

1. A phase modulator start-up protection phasor calculation method suitable for starting a static frequency converter is characterized by comprising the following steps:
sampling the relevant parameters of the phase modulator, and calculating to obtain the working frequency f of the phase modulator0；
According to the sampling frequency f of the protection devicesAnd the measured working frequency f of the phase modulator in real time0Calculating to obtain the number of sampling points N of each cycleallCounting the number N of the sampling pointsallPerforming snapshot processing on the data to obtain the number of points actually participating in calculation of each cycle after snapshot, wherein the number of points actually participating in calculation of each cycle comprises an integer part N and a decimal part delta N;
determining the data window length of the zero sequence voltage at the generator end according to the integer part N of the points actually participating in calculation of each cycle wave, and calculating the phasor of k harmonics of the zero sequence voltage at the generator end by using discrete Fourier transform;
according to the decimal part delta N in the points actually participating in calculation of each cycle wave, the zero sequence voltage k harmonic phasor at the machine end is compensated, and phasor calculation of startup protection of the phase modulator is completed.
2. The method for calculating the startup protection phasor of the phase modulator suitable for starting the static frequency converter according to claim 1, wherein the method comprises the following steps: sampling related parameters of the phase modulation machine, and obtaining the working frequency f of the phase modulation machine through calculation0The method specifically comprises the following steps:
sampling terminal phase-to-phase voltage or neutral point current of the camera, and simultaneously sampling the analog quantity X to be detected to obtain sampling instantaneous values of all parameters;
measuring frequency by using terminal interphase voltage sampling value data window or neutral point current sampling value data window to obtain working frequency f of phase modulator0。
3. The method for calculating the startup protection phasor of the phase modulator suitable for starting up the static frequency converter according to claim 2, wherein the method comprises the following steps:
the method comprises the following steps of sampling terminal phase-to-phase voltage or neutral point current of the camera, and measuring frequency by using a terminal phase-to-phase voltage sampling value data window or a neutral point current sampling value data window, and specifically comprises the following steps:
firstly, the interphase voltage at the machine end of the phase modulator is sampled, and if the interphase voltage is lower than the amplitude threshold of frequency measurement due to the three-phase short circuit at the machine end of the phase modulator, the protection device adopts a neutral point current sampling value data window to measure the frequency.
4. The method for calculating the startup protection phasor of the phase modulator suitable for starting up the static frequency converter according to claim 1 or 3, wherein the method comprises the following steps: the frequency measurement is carried out by adopting a zero crossing point interpolation method, in the processing process, data is subjected to low-pass filtering processing, a filter requires that 0-60Hz signals are not attenuated, and the attenuation of more than 100Hz can be reduced to be less than 0.1 time.
5. The method for calculating the startup protection phasor of the phase modulator suitable for starting the static frequency converter according to claim 1, wherein the method comprises the following steps: the number of sampling points per cycle is NallComprises the following steps:
Figure FDA0002440512510000011
the number of the sampling points is NallIn the data extraction processing, the extraction interval is:
Figure FDA0002440512510000021
m is an integer and represents a threshold value for judging whether a cycle sampling point is subjected to snapshot processing, and the value range of m is more than or equal to 12 and less than or equal to 24;
the number of points actually participating in calculation per cycle after snapshot is as follows:
Figure FDA0002440512510000022
in the formula, N represents an integer part, and Δ N represents a fractional part.
6. The method for calculating the startup protection phasor of the phase modulator suitable for starting up the static frequency converter according to claim 5, wherein the method comprises the following steps: the method comprises the following steps of determining the data window length of the zero sequence voltage at the generator end according to the integer part N of the number of points actually participating in calculation of each cycle wave, and calculating the phasor of k-th harmonic of the zero sequence voltage at the generator end by using discrete Fourier transform, and specifically comprises the following steps:
t in the analog X (t) to be measured1Phasor of k-th harmonic of time
Figure FDA0002440512510000023
Expressed as:
Figure FDA0002440512510000024
at [ t ]1-T，t1]Real part R of k harmonic phasor of zero sequence voltage at internal counterpoint terminalkThe approximation according to the trapezoidal rule yields:
Figure FDA0002440512510000025
the imaginary part is obtained by the same method:
Figure FDA0002440512510000026
wherein X (N) is the zero sequence voltage sampling value at the terminal of the current time, and X (N-N) is the first N/fsThe sampling value at the moment, Delta S is the number N of sampling points actually participating in the calculation of each cyclefThe fractional part of (a) corresponds to the trapezoidal area.
7. The method for calculating the startup protection phasor of the phase modulator suitable for starting up the static frequency converter according to claim 5, wherein the method comprises the following steps: according to the decimal part delta N in the points actually participating in calculation of each cycle wave, the k-th harmonic phasor of the zero sequence voltage at the machine end is compensated, and the method specifically comprises the following steps:
solving for Δ S:
Figure FDA0002440512510000027
in the formula, X (N)f) Is t1A theoretical value of time;
and (5) and (6) are arranged according to the formula (7) to obtain the real part and the imaginary part of the compensated k-th harmonic phasor.
8. The method for calculating the startup protection phasor of the phase modulator suitable for starting up the static frequency converter according to claim 7, wherein the method comprises the following steps: by t1X (n-K) around timen) Obtaining t by interpolating the sampling values at two points X (n)1Theoretical value of time of day
X(Nf) The approximate expression is:
X(Nf)≈X(n-Kn)+[X(n)-X(n-Kn)]ΔN (8)。
9. the method for calculating the startup protection phasor of the phase modulator suitable for starting up a static frequency converter according to claim 7 or 8, wherein the method comprises the following steps: the real part of the compensated k-th harmonic phasor is as follows:
Figure FDA0002440512510000031
the imaginary part of the compensated k-th harmonic phasor is as follows:
Figure FDA0002440512510000032
10. the method for calculating the startup protection phasor of the phase modulator suitable for starting up the static frequency converter according to claim 9, wherein the method comprises the following steps: applying the fitting function sin (x) to cos (t), sin (t) in the formulas (9) and (10)f、cos(x)fAlternatively, the real and imaginary components of the final compensated k harmonic phasor are calculated, and the fitting function sin (x)f、cos(x)fRespectively as follows:
Figure FDA0002440512510000033
Figure FDA0002440512510000041
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