CN117706195A - Actual frequency measurement method and system of variable frequency motor - Google Patents

Actual frequency measurement method and system of variable frequency motor Download PDF

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Publication number
CN117706195A
CN117706195A CN202311634060.4A CN202311634060A CN117706195A CN 117706195 A CN117706195 A CN 117706195A CN 202311634060 A CN202311634060 A CN 202311634060A CN 117706195 A CN117706195 A CN 117706195A
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frequency
current
measurement
set time
time interval
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冯广杰
李旭
姜自强
孔晓民
赵彪
许云龙
赵呈轩
朱若松
王莉
侯思祯
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Henan Xujijibao Electric Automation Co ltd
Xuji Group Co Ltd
XJ Electric Co Ltd
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Henan Xujijibao Electric Automation Co ltd
Xuji Group Co Ltd
XJ Electric Co Ltd
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Priority to CN202311634060.4A priority Critical patent/CN117706195A/en
Publication of CN117706195A publication Critical patent/CN117706195A/en
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Abstract

The invention belongs to the field of variable frequency motors, and particularly relates to an actual frequency measurement method and system of a variable frequency motor. The invention judges the frequency range of the frequency according to the rated frequency corresponding to measurement, and determines the values of a first set time interval and a second set time interval according to the frequency range; obtaining the actual frequency of the variable frequency motor corresponding to the current measurement at least according to the current vector corresponding to the current measurement time, the first set time interval of the forward pushing of the current measurement time and the second set time interval of the forward pushing of the current measurement time; the smaller the upper threshold value of the frequency range where the rated frequency is located is, the larger the corresponding first and second set time intervals are; namely, selecting a forward pushing moment with a longer distance for a working condition with a lower frequency to calculate the actual frequency of the variable frequency motor; the working condition with higher frequency selects the forward pushing moment with a shorter distance; the excessive or insufficient interval between the corresponding moments of the selected current for calculating the actual frequency is avoided, and the accuracy of the actual frequency measurement of the variable frequency motor is improved.

Description

Actual frequency measurement method and system of variable frequency motor
Technical Field
The invention belongs to the field of variable frequency motors, and particularly relates to an actual frequency measurement method and system of a variable frequency motor.
Background
Currently, in the background of developing a novel power system, a frequency converter is commonly added to a large-sized motor by a power plant so as to reduce the station power consumption and improve the motor efficiency. After the frequency converter is added, the working frequency of the motor is not the system frequency, and the motor protection device for broadband measurement is also widely applied. In practical applications, the motor protection device for broadband measurement must rely on the acquired real-time operating frequency of the motor to accurately perform the protection measures in time.
The frequency measurement method of the variable frequency motor in the prior art usually resamples the working current of the motor, selects at least 3 point values from resampling points in a waveform of a complete period (which can be called as a cycle), and calculates the current actual frequency of the variable frequency motor as a measurement value; however, the interval between the selected points in the resampling points may affect the accuracy of the calculated actual frequency of the variable frequency motor, for example, if the interval between the selected points is large, the selected points may include points in waveforms with more than two periods, that is, the selected points include points of other cycles besides the points in a single cycle, so that the calculation result of the frequency of the variable frequency motor is wrong; the intervals between the selected points are too small and the distances are too close, so that the corresponding information of the acquired waveforms in one period is possibly incomplete, the actual frequency value of the variable frequency motor calculated according to the selected points is dithered, and the error is larger; it is difficult to obtain a more accurate actual frequency value of the variable frequency motor.
Disclosure of Invention
The invention aims to provide an actual frequency measurement method and an actual frequency measurement system of a variable frequency motor, which are used for solving the problem that the actual frequency value of the variable frequency motor is difficult to obtain by the existing frequency measurement method of the variable frequency motor.
In order to achieve the above-mentioned purpose, the present invention provides a method for measuring actual frequency of a variable frequency motor, after a variable frequency device starts to operate, determining a frequency range in which the variable frequency device is located according to a rated frequency corresponding to measurement at a certain measurement interval, and determining values of a first set time interval and a second set time interval according to the frequency range in which the rated frequency is located, wherein the first set time interval is smaller than the second set time interval; obtaining the actual frequency of the variable frequency motor corresponding to the current measurement at least according to the current vector corresponding to the current measurement time, the first set time interval of the forward pushing of the current measurement time and the second set time interval of the forward pushing of the current measurement time;
the frequency ranges are divided according to the frequency sizes, rated frequencies in different frequency ranges correspond to different first and second set time intervals respectively, and the smaller the upper threshold value of the frequency range where the rated frequency is located is, the larger the corresponding first and second set time intervals are.
The beneficial effects of the technical scheme are as follows: by dividing different frequency ranges, for working conditions with lower frequency and longer period, selecting current corresponding to forward pushing time with longer distance and larger interval for calculating the actual frequency of the variable frequency motor, thereby avoiding the situation that the calculated actual frequency value of the variable frequency motor shakes to cause larger calculated actual frequency error of the variable frequency motor as much as possible; for the working conditions of higher frequency and shorter period, selecting current corresponding to forward pushing moments with shorter distance and smaller interval for calculating the actual frequency of the variable frequency motor, so that the situation that the calculation result for calculating the frequency of the variable frequency motor is wrong because the selected points comprise other cyclic waves besides the point in a single cyclic wave can be avoided; therefore, the excessive or insufficient interval between the corresponding moments of the selected current for calculating the actual frequency can be avoided, and the accuracy of the actual frequency calculation result of the variable frequency motor is improved.
Further, the second set time interval has a value twice the first set time interval.
Further, the first measurement after the frequency converter starts to operate takes the initial value of the set frequency as the rated frequency corresponding to measurement, and then each measurement determines the rated frequency corresponding to measurement according to the actual frequency of the variable frequency motor corresponding to the last measurement.
The beneficial effects of the technical scheme are as follows: and updating the rated frequency according to the actual frequency result of the variable frequency motor which is obtained by the previous test and is closer to the actual working condition, so that the obtained actual frequency of the variable frequency motor corresponding to the current test is more accurate.
Further, the current vector is a vector of three-phase current corresponding to the variable frequency motor, and the method for obtaining the actual frequency of the variable frequency motor corresponding to the current measurement at least according to the current vector corresponding to the current measurement time, the time of the current measurement time forward pushing the first set time interval and the time of the current measurement time forward pushing the second set time interval comprises the following steps:
if the current vector meets the set current condition, respectively obtaining a real part and an imaginary part of a current positive sequence component of the three-phase current vector according to the three-phase current vector corresponding to the current measurement time, the forward pushing first set time interval and the forward pushing second set time interval; obtaining a frequency value of the corresponding variable frequency motor as an intermediate value according to the real part and the imaginary part; and obtaining the actual frequency of the variable frequency motor corresponding to the current measurement according to the intermediate value.
The beneficial effects of the technical scheme are as follows: the actual frequency of the variable frequency motor corresponding to the current test is obtained only through current vector calculation at three moments, namely the current test moment, the current measurement moment, the forward pushing of the first set time interval and the forward pushing of the current measurement moment of the second set time interval, calculation is simplified, an intermediate value is set, and the calculated frequency value of the variable frequency motor is convenient to process so as to obtain the actual frequency of the variable frequency motor corresponding to the current test.
Further, the method for obtaining the actual frequency of the variable frequency motor corresponding to the measurement according to the intermediate value comprises the following steps:
if the obtained intermediate value is larger than the upper threshold value of the frequency range of the rated frequency corresponding to measurement, determining new values of the first and second set time intervals according to the frequency range of the intermediate value, and updating the intermediate value according to the current vector corresponding to the current measurement time, the first set time interval of the current measurement time and the second set time interval of the current measurement time.
The beneficial effects of the technical scheme are as follows: the method can be used for timely adjusting the values of the first and second set time intervals according to the situation that the first and second set time intervals corresponding to the frequency range where the rated frequency is located are not suitable for the actual frequency value of the motor after mutation, and guaranteeing the accuracy of the actual frequency value of the variable frequency motor calculated by the new first and second set time intervals which are more in line with the actual frequency value of the motor.
Further, the method for obtaining the actual frequency of the variable frequency motor corresponding to the measurement according to the intermediate value further includes:
if the absolute value of the difference between the obtained intermediate value and the actual frequency of the variable frequency motor corresponding to the last measurement is smaller than a set abrupt change threshold value, immediately obtaining the actual frequency of the variable frequency motor according to the intermediate value; otherwise, delaying for a set time length, and then obtaining the actual frequency of the variable frequency motor according to the intermediate value.
The beneficial effects of the technical scheme are as follows: abnormal jitter of the measured data caused by frequency mutation or sampling abnormality can be avoided.
Further, if the maximum value of the modulus values of the three-phase current vectors corresponding to the current measurement time is larger than a set current threshold value, judging that the current vectors meet a set current condition; the method for obtaining the actual frequency of the variable frequency motor corresponding to the current measurement at least according to the current vector corresponding to the current measurement time, the first set time interval of forward pushing of the current measurement time and the second set time interval of forward pushing of the current measurement time further comprises the following steps:
and if the current vector does not meet the set current condition, obtaining the actual frequency of the variable frequency motor corresponding to the current measurement according to the actual frequency of the variable frequency motor corresponding to the last measurement.
The beneficial effects of the technical scheme are as follows: the CT no-flow condition in the working process of the variable frequency motor can be found in time through whether the current vector meets the set current condition, and the actual frequency of the variable frequency motor corresponding to the last test is adopted as the actual frequency of the variable frequency motor corresponding to the current test according to the condition, so that the influence of the actual frequency of the variable frequency motor with larger error calculated according to the current on the subsequent test is avoided.
Further, the current vector obtaining method corresponding to the measuring time, the forward pushing first set time interval and the forward pushing second set time interval comprises the following steps:
determining resampling points corresponding to the current measurement time, the number of resampling points corresponding to the first set time interval and the number of resampling points corresponding to the second set time interval; taking the current vector at the resampling point corresponding to the current measurement time as the current vector corresponding to the current measurement time; and taking the resampling points corresponding to the measuring time as a reference, and taking the current vectors at the resampling points corresponding to the first set time interval and the resampling points corresponding to the second set time interval as the current vectors corresponding to the time of forward pushing the first set time interval and the second set time interval.
The beneficial effects of the technical scheme are as follows: the corresponding current vector is obtained by pushing forward the resampling point at a set time interval, so that the method is convenient to adapt to the resampling technology commonly used in the prior art.
Further, the upper and/or lower threshold values of the frequency range for dividing the frequency range are determined according to the accuracy requirements of the actual frequency of the variable frequency motor.
The beneficial effects of the technical scheme are as follows: and when the precision requirement is low, the number of divided frequency ranges is reduced, so that the frequency calculation and the frequency division process are simplified, and the calculation efficiency is improved.
The invention also provides an actual frequency measuring system of the variable frequency motor, which comprises a processor, wherein the processor is used for executing program instructions to realize the actual frequency measuring method of the variable frequency motor.
The actual frequency measuring system of the variable frequency motor can achieve the same beneficial effects as the actual frequency measuring method of the variable frequency motor.
Drawings
FIG. 1 is a schematic diagram of a typical connection mode of a variable frequency motor to which the actual frequency measurement method of the variable frequency motor is applied in an embodiment of the actual frequency measurement method of the variable frequency motor of the present invention;
fig. 2 is a flow chart of an actual frequency measuring method of a variable frequency motor in an embodiment of the actual frequency measuring method of a variable frequency motor according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent.
Practical frequency measurement method embodiment of variable frequency motor
The embodiment provides a technical scheme of an actual frequency measurement method of a variable frequency motor, and a typical wiring mode of the variable frequency motor to which the measurement method is applicable refers to fig. 1; the measuring method specifically comprises the following steps:
when the frequency converter starts to operate, judging the frequency range of the frequency converter according to the rated frequency corresponding to measurement according to a certain measurement interval, and determining the values of a first set time interval and a second set time interval according to the frequency range of the rated frequency, wherein the first set time interval is smaller than the second set time interval; and obtaining the actual frequency of the variable frequency motor corresponding to the current measurement at least according to the current vector corresponding to the current measurement time, the first set time interval of the forward pushing of the current measurement time and the second set time interval of the forward pushing of the current measurement time. Because the first set interval is pushed forward from the current measurement time, the second set interval is also pushed forward from the current measurement time, the current measurement time is set as point A, the point of the first set interval n pushed forward by point A is set as point B, the point of the second set interval 2n pushed forward by point A is set as point C, the interval between point A and point B is set as point n, the set interval between point B and point C is also set as point n, namely the equal interval between point A and the first set interval of pushed forward, the point B of the first set interval of pushed forward and the point C of the second set interval of pushed forward is set as point B, and the setting is convenient for adapting to the conventional algorithm for calculating the frequency corresponding to the frequency by the point pushed forward at the equal interval in the frequency.
The first measurement after the frequency converter starts to operate takes the initial value of the set frequency as the rated frequency corresponding to measurement, and then the rated frequency corresponding to measurement is determined according to the actual frequency of the variable frequency motor corresponding to the last measurement in each measurement, namely, the rated frequency is updated in real time according to the actual frequency result of the variable frequency motor which is more similar to the actual working condition and is obtained by the previous measurement, so that the obtained actual frequency of the variable frequency motor corresponding to the current measurement is more accurate. For example, in this embodiment, the initial frequency value is set to be 50Hz, and the rated frequency corresponding to each subsequent measurement is updated according to the actual frequency of the variable frequency motor corresponding to the last measurement.
Since the resampling interval in the prior art is usually a fixed value, it is difficult to directly realize the time interval set by forward pushing to obtain the corresponding current vector, so the current vector obtaining modes corresponding to the current measurement time, the first set time interval of the current measurement time forward pushing and the time of the current measurement time forward pushing the second set time interval include:
determining resampling points corresponding to the current measurement time, the number of resampling points corresponding to the first set time interval and the number of resampling points corresponding to the second set time interval; taking the current vector at the resampling point corresponding to the current measurement time as the current vector corresponding to the current measurement time; and taking the resampling points corresponding to the measuring time as a reference, and taking the current vectors at the resampling points corresponding to the first set time interval and the resampling points corresponding to the second set time interval as the current vectors corresponding to the moments of the first set time interval and the second set time interval of the measuring time. The corresponding current vector is obtained by pushing forward the resampling point for a set time interval, so that the method is convenient to adapt to the resampling technology commonly used in the prior art.
The frequency range is divided according to the frequency size, the rated frequencies in different frequency ranges correspond to different first and second set time intervals respectively, and the smaller the upper threshold value of the frequency range where the rated frequency is located is, the larger the corresponding first and second set time intervals are; the upper threshold value of the frequency range for dividing the frequency range is determined according to the accuracy requirement of the actual frequency of the variable frequency motor, so that the number of the divided frequency ranges can be reduced when the accuracy requirement is not high, the frequency calculation and the frequency division process are simplified, and the calculation efficiency is improved.
In this embodiment, in order to avoid the problem of low calculation efficiency caused by excessive frequency range division, two frequency ranges are divided, which are called a short window frequency measurement frequency range and a long window frequency measurement frequency range; specifically, the upper threshold value for dividing the long-window frequency measurement frequency range (i.e., the lower threshold value for dividing the short-window frequency measurement frequency range) is 25Hz, and when the range of about 0-70Hz of the working frequency of the variable-frequency motor is combined, the short-window frequency measurement frequency range (greater than 25 Hz) is adapted to the 25-71 Hz operation condition, and the long-window frequency measurement frequency range (less than or equal to 25 Hz) is adapted to the 9-25 Hz operation condition. The time interval set by forward pushing is realized by means of forward pushing resampling points, specifically, the number of resampling points corresponding to a first set time interval and a second set time interval corresponding to a short window frequency measurement range is k and 2k respectively, wherein k is a set positive integer; the number of resampling points corresponding to the first set time interval and the second set time interval corresponding to the long window frequency measurement frequency range is 3k and 6k respectively; it can be seen that, on the basis that the resampling interval is a fixed value, the number of resampling points corresponding to the first and second set time intervals corresponding to the long window frequency measurement frequency range is obviously greater than the number of resampling points corresponding to the first and second set time intervals corresponding to the short window frequency measurement frequency range, that is, the first and second set time intervals corresponding to the long window frequency measurement frequency range are respectively greater than the first and second set time intervals corresponding to the short window frequency measurement frequency range.
In summary, according to the actual frequency measurement method of the variable frequency motor of the embodiment, by dividing different frequency ranges, for the working conditions of lower frequency and longer period, the current corresponding to the resampling point (i.e. forward pushing moment) with longer distance and larger interval is selected to be used for calculating the actual frequency of the variable frequency motor, so that the situation that the calculated actual frequency error of the variable frequency motor is larger due to jitter of the calculated actual frequency value of the variable frequency motor can be avoided as much as possible; for the working conditions of higher frequency and shorter period, selecting current corresponding to resampling points (namely forward pushing moments) with shorter distance and smaller interval for calculating the actual frequency of the variable frequency motor, and avoiding the situation that the calculation result for calculating the frequency of the variable frequency motor is wrong because other points except for the point in a single cycle are included in the selected points; the excessive or insufficient interval between the selected resampling points (namely, the moments corresponding to the current for calculating the actual frequency) can be avoided, so that the accuracy of the actual frequency calculation result of the variable frequency motor is improved.
Specifically, referring to fig. 2, when the measurement is performed, the operation mode of the motor is firstly determined according to the position of the 3G knife switch, that is, whether the frequency converter starts to operate is determined; when the 3G disconnecting link is in the closed position, the frequency converter is judged to be not operated, the motor works near the system frequency, frequency calculation can be carried out according to the collected bus PT voltage, namely, the actual working frequency value of the frequency conversion motor is calculated by adopting a conventional simple calculation mode of the bus PT voltage, so that the calculation efficiency is improved;
when the 3G disconnecting link is in the split state, judging that the frequency converter starts to operate, and firstly judging the frequency range of the frequency converter according to a certain measurement interval by taking a set frequency initial value (50 Hz) as the rated frequency corresponding to measurement; because the upper threshold value used for dividing the long-window frequency measurement frequency range and the lower threshold value of the short-window frequency measurement frequency range set in the embodiment are 25Hz, the rated frequency corresponding to the current measurement is judged to be in the short-window frequency measurement frequency range; in this embodiment, the values of the first set time interval and the second set time interval corresponding to the short window frequency measurement frequency range are respectively 1/n cycle and 2/n cycle corresponding to the short window frequency measurement frequency range (the short cycle may be a cycle length wave corresponding to the short window frequency measurement frequency range set in advance, the 1/n cycle is a value of 1/n of one cycle of the short window frequency measurement frequency range, and the 2/n cycle is a value of 2/n of one cycle of the short window frequency measurement frequency range), and in other embodiments, the values of the first set time interval and the second set time interval corresponding to the short window frequency measurement frequency range may be set directly in advance without being indirectly determined according to the cycle corresponding to the short window frequency measurement frequency range; the number of the resampling points corresponding to the forward pushing of the values of the first set time interval and the second set time interval corresponding to the short window frequency measurement range is k and 2k respectively, and the actual frequency of the variable frequency motor corresponding to the current measurement is obtained according to the resampling point corresponding to the current measurement time M, the time (M-k) of forward pushing k resampling points and the current vector corresponding to the time (M-2 k) of forward pushing 2k resampling points; then each measurement according to a certain measurement interval is performed, the rated frequency corresponding to measurement is determined according to the actual frequency of the variable-frequency motor corresponding to the last measurement, when the rated frequency corresponding to measurement appears in the subsequent measurement and is smaller than 25Hz, namely, the rated frequency corresponding to measurement is in the long-window frequency measurement frequency range, the values of the first set time interval and the second set time interval corresponding to the long-window frequency measurement frequency range are respectively 1/n frequency and 2/n frequency corresponding to the long-period wave (the long-period wave can be the wave with the set period length corresponding to the long-window frequency measurement frequency range set in advance, the 1/n frequency is the value of 1/n of one period of the long-period wave, and the 2/n frequency is the value of 2/n of one period of the long-period wave), in other embodiments, the values of the first set time interval and the second set time interval corresponding to the long-window frequency measurement frequency range can be directly set in advance, and the values of the first set time interval and the second set time interval can be indirectly determined without being required according to the corresponding to the frequency of the long-period wave; the number of resampling points corresponding to the forward pushing of the values of the first set time interval and the second set time interval corresponding to the long window frequency measuring range is 3k and 6k respectively; in order to ensure the measurement accuracy, n is more than or equal to 3 and less than or equal to 8; and obtaining the actual frequency of the variable frequency motor corresponding to the current measurement according to the current vector corresponding to the resampling point corresponding to the current measurement time M, the time (M-3 k) of pushing forward 3k resampling points and the time (M-6 k) of pushing forward 6k resampling points.
The above mentioned current vectors are all vectors of three-phase currents corresponding to the variable frequency motor, in this embodiment, three-phase currents at the motor end (CT 2) or the neutral point (CT 3) of the variable frequency motor; in this embodiment, the method for obtaining the actual frequency of the variable frequency motor corresponding to the current measurement according to at least the current vector corresponding to the current measurement time, the first set time interval of the forward pushing of the current measurement time, and the second set time interval of the forward pushing of the current measurement time includes:
if the current vector meets the set current condition, respectively obtaining a real part and an imaginary part of a current positive sequence component of the three-phase current vector according to the current measurement time, the three-phase current vector corresponding to the time of forward pushing the first set time interval and the second set time interval; according to the obtained real part and imaginary part, a frequency value of a corresponding variable frequency motor is obtained by combining a positive sequence frequency measurement method to serve as an intermediate value; obtaining the actual frequency of the variable frequency motor corresponding to the measurement according to the intermediate value; the actual frequency of the variable frequency motor corresponding to the current test is obtained only through current vector calculation at three moments, namely the current test moment, the moment of the current measurement moment, the moment of the forward pushing of the first set time interval and the moment of the forward pushing of the second set time interval, so that calculation can be simplified; and the intermediate value is set, so that the calculated frequency value of the variable frequency motor is conveniently processed to obtain the actual frequency of the variable frequency motor corresponding to the test.
The CT no-flow condition exists in the working process of the variable frequency motor, the actual frequency of the variable frequency motor calculated according to the current is meaningless, and larger errors can exist; therefore, the embodiment sets a set current condition, and if the maximum value of the modulus values of the three-phase current vectors corresponding to the current measurement time is greater than the set current threshold value, the current vector is judged to meet the set current condition; if the current vector does not meet the set current condition, the actual frequency of the variable frequency motor corresponding to the current measurement is obtained according to the actual frequency of the variable frequency motor corresponding to the last measurement (in the embodiment, the actual frequency of the variable frequency motor corresponding to the last measurement is directly used as the actual frequency of the variable frequency motor corresponding to the current measurement); therefore, whether the current vector meets the set current condition or not can be timely found out that CT is not flowing in the working process of the variable frequency motor, the actual frequency of the variable frequency motor corresponding to the last test is adopted as the actual frequency of the variable frequency motor corresponding to the current test according to the condition, and the influence of the actual frequency of the variable frequency motor with larger error calculated according to the current on the subsequent test is avoided.
The mode of measuring the actual frequency of the corresponding variable frequency motor according to the intermediate value further comprises the following steps:
if the absolute value of the difference between the obtained intermediate value and the actual frequency of the variable frequency motor corresponding to the last measurement is smaller than a set abrupt change threshold value, immediately obtaining the actual frequency of the variable frequency motor according to the intermediate value; otherwise, delaying for a set time length, and then obtaining the actual frequency of the variable frequency motor according to the intermediate value; thereby, abnormal jitter of the measured data caused by frequency mutation or sampling abnormality can be avoided.
Specifically, if it is determined that the rated frequency corresponding to the current measurement is within the short window frequency measurement frequency range, calculating a vector value of the current moment (i.e., the current test moment) of the CT three-phase current of the variable frequency motor end through fourier transform according to the rated frequency corresponding to the measurementVector value of the three-phase current at a time k resampling points before (i.e. the time of the first set time interval is advanced by the time of the current measurement)>And a vector value of the three-phase current 2k times before the resampling point (i.e. the time of the second set time interval is advanced)>Then according to the vector values of the 3 moments, correspondingly calculating the real part R of the positive sequence component of the current vector value corresponding to the current test moment ms And imaginary part I ms The current measurement time advances by a first set time interval to the real part R of the positive sequence component of the current flow value m-k And imaginary part I m-k And advancing the real part R of the positive sequence component of the current magnitude corresponding to the moment of the second set time interval m-2k And imaginary part I m-2k The three groups of real part and imaginary part data are applied to a positive sequence frequency measurement method to obtain the frequency value of the corresponding variable frequency motor as an intermediate value f temp The method comprises the steps of carrying out a first treatment on the surface of the Obtaining the actual frequency of the variable frequency motor corresponding to the measurement according to the intermediate value; under the condition that the rated frequency is in a short window frequency measuring frequency range, the frequency calculation mode according to the positive sequence frequency measuring method is as follows:
wherein f s In order to obtain the frequency value of the corresponding variable frequency motor by a positive sequence frequency measurement method, T s Resampling fixed interval, kT s The first set time interval corresponding to the rated frequency in the short window frequency measuring frequency range is obtained. If the obtained intermediate value f temp Is larger than the upper threshold value of the frequency range in which the corresponding rated frequency is measured, namely, the frequency value of the corresponding variable-frequency motor obtained by a positive sequence frequency measurement method is larger than the upper threshold value 25Hz of the short window frequency measurement frequency range, and then the method is pressed againTaking the intermediate value f temp The value of the new first and second set time intervals is determined in the frequency range of the corresponding variable frequency motor (namely, the frequency value obtained by the positive sequence frequency measurement method), and then the intermediate value is updated according to the current vector corresponding to the current measurement time, the new first set time interval forward from the current measurement time and the new second set time interval forward from the current measurement time.
Meanwhile, when step mutation occurs in the frequency or abnormal points occur in sampling, the situation of calculating frequency distortion can be caused, so that a set mutation threshold value delta t is set in the embodiment, and when the absolute value of the difference value between the intermediate value and the actual frequency of the variable frequency motor corresponding to the last measurement is smaller than delta t, the measurement frequency is immediately updated, namely the actual frequency of the variable frequency motor is immediately obtained according to the intermediate value; otherwise, after the time delay is set to a time length (the set time length of the embodiment is 2/n cycle time, namely, the time delay is set to a second set time interval, such as 2k sampling points in a short window and 6k sampling points in a long window), the actual frequency of the variable frequency motor is further calculated according to the intermediate value, so that the rapid and accurate frequency measurement can be performed when the frequency of the system is suddenly changed or when the sampling is abnormal. Specifically, if the absolute value of the difference between the intermediate value and the actual frequency of the variable frequency motor corresponding to the last measurement is smaller than Δt, the fact that no frequency step mutation and no abnormal sampling point exist is indicated, the actual frequency of the variable frequency motor can be directly calculated, and the protection action mobility is ensured; if the absolute value of the difference between the intermediate value and the actual frequency of the variable frequency motor corresponding to the last measurement is more than or equal to deltat, the occurrence of frequency step mutation or abnormal sampling point is indicated, the influence is eliminated by delay, and the normal operation is more than one cycle of delay; in this case, in order to protect the activity and the accuracy of the actual frequency calculation of the variable frequency motor, the present embodiment does not delay more than one cycle, but delays 2/n cycles (n is a constant greater than 2 and is usually 3 n.ltoreq.8), that is, the second set time interval is set above, during this delay, the frequency measurement is performed for multiple frequency corrections according to the latest sampling value, so that the actual frequency of the variable frequency motor approaches, the error is within the acceptable range of the protection device, and can be corrected to the correct value successively in the subsequent real-time calculation of the actual frequency of the variable frequency motor.
And the corresponding set current condition isWherein I is n T is a secondary rated value, and the value range of t is 0.005-0.02, t is multiplied by I n I.e. the set flow threshold value. Then whenWhen the current vector is judged to meet the set current condition, namely CT has current, the corresponding frequency value f of the variable frequency motor can be obtained by a positive sequence frequency measurement method s As an intermediate value, measuring the actual frequency of the corresponding variable frequency motor according to the intermediate value; otherwise, judging that the CT is not flowing, and taking the actual frequency of the variable frequency motor corresponding to the last measurement as the actual frequency of the variable frequency motor corresponding to the current measurement;
in this embodiment, before calculating the time of the first set time interval before the time of the measurement, the vector value corresponding to the time of the second set time interval before the time of the measurement, or before performing frequency calculation according to the positive sequence frequency measurement method, determining whether the current vector meets the set current condition, and if the current vector meets the set current condition, performing the subsequent step of calculating the time of the measurement before the time of the first set time interval, the vector value corresponding to the time of the second set time interval before the time of the measurement, or performing frequency calculation according to the positive sequence frequency measurement method; thus, when the CT no-flow condition is met, the subsequent calculation steps can be saved; or in other embodiments, the frequency value of the corresponding variable frequency motor may be obtained by performing frequency calculation according to a positive sequence frequency measurement method, then judging whether the current vector meets the set current condition, if so, taking the frequency value of the corresponding variable frequency motor obtained by the positive sequence frequency measurement method as an intermediate value, and obtaining the actual frequency of the variable frequency motor corresponding to the current measurement according to the intermediate value; otherwise, directly taking the actual frequency of the variable frequency motor corresponding to the last measurement as the actual frequency of the variable frequency motor corresponding to the current measurement. This method is also applicable to the case where the rated frequency corresponding to the current measurement described below is in the long-window measurement frequency range.
At the same time, to ensure the real-time characteristic of the calculated frequency, the vector value of the three-phase current at the present moment is calculated by adopting Fourier transformationMoment vector value k resampling points before three-phase current +.>And a moment vector value before 2k resampling points of the three-phase current +.>And the adopted frequency is the actual frequency of the variable frequency motor corresponding to the last measurement, so as to ensure real-time tracking when the frequency is changed.
Through testing, the frequency measurement error of the calculation mode is smaller than 0.01Hz when the frequency is 25-70 Hz, and the requirement of protecting the frequency measurement precision can be met.
If the rated frequency corresponding to the current measurement is judged to be in the long-window frequency measurement frequency range, calculating the vector value of the current moment (namely the current test moment) of the CT three-phase current of the motor end of the variable-frequency motor through Fourier transformation according to the rated frequency corresponding to the measurement Vector value of three-phase current at a time 3k resampling points before (i.e. the time of the first set time interval is advanced by the time of the current measurement)>And a vector value of the three-phase current 6k times before the resampling point (i.e. the time of the second set time interval is advanced)>
Then according to the vector values of the 3 moments, correspondingly calculating R of positive sequence components of the current vector value corresponding to the current test moment ml And imaginary part I ml The current measurement time advances by a first set time interval to the real part R of the positive sequence component of the current flow value m-3k And imaginary part I m-3k And advancing the real part R of the positive sequence component of the current magnitude corresponding to the moment of the second set time interval at the moment of the current measurement m-6k And imaginary part I m-6k The three groups of real part and imaginary part data are applied to a positive sequence frequency measurement method to obtain the frequency value of a corresponding variable frequency motor as an intermediate value; obtaining the actual frequency of the variable frequency motor corresponding to the measurement according to the intermediate value; under the condition that the rated frequency is in the long-window frequency measuring frequency range, the frequency calculation mode according to the positive sequence frequency measuring method is as follows:
wherein f l In order to obtain the frequency value of the corresponding variable frequency motor by a positive sequence frequency measurement method, T s Resampling fixed interval, 3 kxT s The first set time interval corresponding to the rated frequency in the short window frequency measuring frequency range is obtained.
In this embodiment, through creative analysis, it is found that the frequency mutation condition existing in the working process of the variable frequency motor will cause the actual frequency value of the variable frequency motor calculated through the first and second set time intervals corresponding to the frequency range where the rated frequency is located to exceed the frequency range where the rated frequency is located, that is, the condition that the first and second set time intervals corresponding to the frequency range where the rated frequency is located are not suitable for the actual frequency value of the motor after mutation actually occurs, and the accuracy of the calculated actual frequency value of the variable frequency motor is affected, so the manner of obtaining the actual frequency of the variable frequency motor corresponding to the measurement according to the intermediate value includes:
if the obtained intermediate value is larger than the upper threshold value of the frequency range of the rated frequency corresponding to measurement, determining new values of the first and second set time intervals according to the frequency range of the intermediate value, and updating the intermediate value according to the current vector corresponding to the current measurement time, the first set time interval of the current measurement time and the second set time interval of the current measurement time. Therefore, the values of the first and second set time intervals can be timely adjusted, and the accuracy of the actual frequency value of the variable frequency motor calculated by the new first and second set time intervals which are more in line with the actual frequency value of the motor is ensured.
Meanwhile, in order to avoid abnormal jitter caused by frequency mutation or sampling abnormality, setting a mutation threshold value delta t, and when the absolute value of the difference between the intermediate value and the actual frequency of the variable frequency motor corresponding to the last measurement is smaller than delta t, immediately updating the measurement frequency, and immediately according to the actual frequency of the variable frequency motor; otherwise, the time delay is set for a time length (the set time length of the embodiment is 2/n cycle time), and then the actual frequency of the variable frequency motor is obtained according to the intermediate value.
And the corresponding set current condition isWherein I is n T is a secondary rated value, and the value range of t is 0.005-0.02, t is multiplied by I n I.e. the set flow threshold value. Then whenWhen the current vector is judged to meet the set current condition, namely CT has current, the corresponding frequency value f of the variable frequency motor can be obtained by a positive sequence frequency measurement method l As an intermediate value, measuring the actual frequency of the corresponding variable frequency motor according to the intermediate value; otherwise, judging that the CT is not flowing, and taking the actual frequency of the variable frequency motor corresponding to the last measurement as the actual frequency of the variable frequency motor corresponding to the current measurement.
It can be seen that the actual frequency measurement method of the variable frequency motor in this embodiment is aimed at the typical wiring mode of the motor with the frequency converter, and when the motor works in the range of 10-70Hz without adding PT, the accuracy and the rapidity of frequency measurement are ensured.
Actual frequency measurement System embodiment of variable frequency Motor
The embodiment provides an actual frequency measurement system of a variable frequency motor, which comprises a processor, wherein the processor is used for executing program instructions to realize the actual frequency measurement method of the variable frequency motor in the embodiment of the actual frequency measurement method of the variable frequency motor.
Because the specific working process and principle of the measuring system have been described in detail in the above embodiment of the actual frequency measuring method of the variable frequency motor, the detailed description thereof is omitted herein.
The invention is characterized in that:
1) By dividing different frequency ranges, for working conditions with lower frequency and longer period, selecting current corresponding to forward pushing time with longer distance and larger interval for calculating the actual frequency of the variable frequency motor, thereby avoiding the situation that the calculated actual frequency value of the variable frequency motor shakes to cause larger calculated actual frequency error of the variable frequency motor as much as possible; for the working conditions of higher frequency and shorter period, selecting current corresponding to forward pushing moments with shorter distance and smaller interval for calculating the actual frequency of the variable frequency motor, so that the situation that the calculation result for calculating the frequency of the variable frequency motor is wrong because the selected points comprise other cyclic waves besides the point in a single cyclic wave can be avoided; therefore, the excessive or insufficient interval between the corresponding moments of the selected current for calculating the actual frequency can be avoided, and the accuracy of the actual frequency calculation result of the variable frequency motor is improved.
2) The method comprises the steps that when a frequency mutation condition existing in the working process of a variable frequency motor is found, a situation that a first set time interval and a second set time interval corresponding to a frequency range where a rated frequency is located are not suitable for a situation that a motor real frequency value after mutation actually occurs, accuracy of a calculated variable frequency motor real frequency value is affected, an intermediate value used for obtaining the actual frequency of the variable frequency motor corresponding to the measurement is set, when the calculated intermediate value is larger than an upper limit threshold value of the frequency range where the rated frequency corresponding to the measurement is located, a new value of the first set time interval and a new value of the second set time interval are determined again according to the frequency range where the intermediate value is located, and then the intermediate value is updated according to current vectors corresponding to the current measuring moment, the first set time interval which is pushed forward at the current measuring moment and the second set time interval which is pushed forward at the current measuring moment, and the actual frequency of the variable frequency motor corresponding to the measurement is obtained through the updated intermediate value. Therefore, the values of the first and second set time intervals can be timely adjusted, and the accuracy of the actual frequency value of the variable frequency motor calculated by the new first and second set time intervals which are more in line with the actual frequency value of the motor is ensured.
3) Setting a set current condition corresponding to the current vector, only when the current vector meets the set current condition, namely judging that the CT has current, calculating an intermediate value according to the three-phase current vector corresponding to the current measuring moment, the moment of the current measuring moment forward pushing a first set time interval, the moment of the current measuring moment forward pushing a second set time interval, and obtaining the actual frequency of the variable frequency motor corresponding to the current measuring according to the intermediate value; otherwise, judging that the CT is not flowing, and obtaining the actual frequency of the variable frequency motor corresponding to the current measurement according to the actual frequency of the variable frequency motor corresponding to the last measurement, so that the situation that the CT is not flowing in the working process of the variable frequency motor can be found out in time according to whether the current vector meets the set current condition, and the actual frequency of the variable frequency motor corresponding to the last test is adopted as the actual frequency of the variable frequency motor corresponding to the current test aiming at the situation, thereby avoiding the influence of the actual frequency of the variable frequency motor with larger error calculated according to the current on the subsequent test.
4) The corresponding current vector is obtained by pushing forward the resampling point at a set time interval, so that the method is convenient to adapt to the resampling technology commonly used in the prior art.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explanation of the principles of the present invention and are in no way limiting of the invention.

Claims (10)

1. The actual frequency measuring method of the variable frequency motor is characterized in that after the variable frequency motor starts to operate, the frequency range of the variable frequency motor is judged according to the rated frequency corresponding to measurement according to a certain measuring interval, the values of a first set time interval and a second set time interval are determined according to the frequency range of the rated frequency, and the first set time interval is smaller than the second set time interval; obtaining the actual frequency of the variable frequency motor corresponding to the current measurement at least according to the current vector corresponding to the current measurement time, the first set time interval of the forward pushing of the current measurement time and the second set time interval of the forward pushing of the current measurement time;
the frequency ranges are divided according to the frequency sizes, rated frequencies in different frequency ranges correspond to different first and second set time intervals respectively, and the smaller the upper threshold value of the frequency range where the rated frequency is located is, the larger the corresponding first and second set time intervals are.
2. The method of measuring an actual frequency of a variable frequency motor according to claim 1, wherein the second set time interval has a value twice that of the first set time interval.
3. The method for measuring the actual frequency of the variable frequency motor according to claim 1 or 2, wherein the first measurement after the operation of the variable frequency motor is started takes the initial value of the set frequency as the rated frequency corresponding to the measurement, and then each measurement determines the rated frequency corresponding to the measurement according to the actual frequency of the variable frequency motor corresponding to the last measurement.
4. The method for measuring an actual frequency of a variable frequency motor according to claim 1 or 2, wherein the current vector is a vector of three-phase current corresponding to the variable frequency motor, and the method for obtaining the actual frequency of the variable frequency motor corresponding to the current measurement based on at least the current vector corresponding to the current measurement time, the time of the current measurement time being advanced by a first set time interval, and the time of the current measurement time being advanced by a second set time interval comprises:
if the current vector meets the set current condition, respectively obtaining a real part and an imaginary part of a current positive sequence component of the three-phase current vector according to the three-phase current vector corresponding to the moment of the current measurement moment, the first set time interval of the current measurement moment and the second set time interval of the current measurement moment; obtaining a frequency value of the corresponding variable frequency motor as an intermediate value according to the real part and the imaginary part; and obtaining the actual frequency of the variable frequency motor corresponding to the current measurement according to the intermediate value.
5. The method for measuring the actual frequency of the inverter motor according to claim 4, wherein the step of obtaining the actual frequency of the inverter motor corresponding to the current measurement based on the intermediate value comprises:
if the obtained intermediate value is larger than the upper threshold value of the frequency range of the rated frequency corresponding to measurement, determining new values of the first and second set time intervals according to the frequency range of the intermediate value, and updating the intermediate value according to the current vector corresponding to the current measurement time, the first set time interval of the current measurement time and the second set time interval of the current measurement time.
6. The method for measuring an actual frequency of a variable frequency motor according to claim 5, wherein the means for obtaining the actual frequency of the variable frequency motor corresponding to the current measurement from the intermediate value further comprises:
if the absolute value of the difference between the obtained intermediate value and the actual frequency of the variable frequency motor corresponding to the last measurement is smaller than a set abrupt change threshold value, immediately obtaining the actual frequency of the variable frequency motor according to the intermediate value; otherwise, delaying for a set time length, and then obtaining the actual frequency of the variable frequency motor according to the intermediate value.
7. The method according to claim 4, wherein if a maximum value of the model values of the three-phase current vectors corresponding to the present measurement time is greater than a set current threshold value, it is determined that the current vectors satisfy a set current condition; the method for obtaining the actual frequency of the variable frequency motor corresponding to the current measurement at least according to the current vector corresponding to the current measurement time, the first set time interval of forward pushing of the current measurement time and the second set time interval of forward pushing of the current measurement time further comprises the following steps:
and if the current vector does not meet the set current condition, obtaining the actual frequency of the variable frequency motor corresponding to the current measurement according to the actual frequency of the variable frequency motor corresponding to the last measurement.
8. The method according to claim 1 or 2, wherein the current vector obtaining means corresponding to the present measurement time, the time at which the present measurement time is advanced by the first set time interval, and the time at which the present measurement time is advanced by the second set time interval includes:
determining resampling points corresponding to the current measurement time, the number of resampling points corresponding to the first set time interval and the number of resampling points corresponding to the second set time interval; taking the current vector at the resampling point corresponding to the current measurement time as the current vector corresponding to the current measurement time; and taking the resampling points corresponding to the measuring time as a reference, and taking the current vectors at the resampling points corresponding to the first set time interval and the resampling points corresponding to the second set time interval as the current vectors corresponding to the time of forward pushing the first set time interval and the second set time interval.
9. Method according to claim 1 or 2, characterized in that the upper and/or lower threshold value of the frequency range for dividing the frequency range is determined in accordance with the accuracy requirements of the actual frequency of the variable frequency motor.
10. An actual frequency measurement system of a variable frequency motor, comprising a processor for executing program instructions to implement the actual frequency measurement method of a variable frequency motor according to any of the preceding claims 1-9.
CN202311634060.4A 2023-11-30 2023-11-30 Actual frequency measurement method and system of variable frequency motor Pending CN117706195A (en)

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