A method for measuring the slip rate of a three-phase asynchronous motor

Abstract

The present invention relates to the field of motor detection technology, and in particular to a method for measuring the slip rate of a three-phase asynchronous motor. The present invention performs Fourier expansion on line current sampling data to obtain an expansion signal, starting from the input signal of the line current of the three-phase asynchronous motor, based on the expansion signal along the high frequency direction of the frequency, the frequency at the preset first number of comb filter effect characteristic spectral lines is used as the initial frequency; starting from the initial frequency, based on the expansion signal along the high frequency direction of the frequency, the frequency at the preset second number of filter effect characteristic spectral lines is used as the target frequency; according to the initial frequency and the target frequency, the actual speed of the three-phase asynchronous motor is determined; the actual speed is converted into the standard speed of the three-phase asynchronous motor; according to the reference frequency of the line current, the reference speed is determined; in combination with the standard speed and the reference speed, the slip rate of the three-phase asynchronous motor is determined, thereby improving the practicality of the slip rate of the three-phase asynchronous motor.

Description

Technical Field

[0001] The invention relates to the technical field of motor detection, and in particular to a method for measuring the slip rate of a three-phase asynchronous motor. Background Art

[0002] The three-phase asynchronous motor is a kind of motor equipment widely used in various fields. Its high efficiency and durability make it one of the basic equipment required by various industries. The three-phase asynchronous motor is one of the important equipment in industrial production. In the industrial manufacturing process, many machines and equipment need to be driven by three-phase asynchronous motors. For example, compressors, fans, pumps, etc. all need to use three-phase asynchronous motors to provide the required driving force to different industries, such as the automotive industry, chemical industry, mining, etc. Its high speed and high power characteristics enable it to adapt to the needs of various occasions, and its manufacturing cost is relatively low, so it is favored by enterprises and consumers. Three-phase asynchronous motors are also widely used in buildings and homes. For example, the compressors used in household air conditioners and refrigerators need to be driven by three-phase asynchronous motors. These household appliances can work faster and more stably, and have a long life, making them one of the necessary electrical equipment in the home environment. Three-phase asynchronous motors also have important applications in other markets. For example, in the aviation industry, turbine engines and steering gears need to use three-phase asynchronous motors. In the aviation field, not only efficient and reliable equipment is required, but also high temperature resistance and overload characteristics are required, which are all perfectly adapted to the three-phase asynchronous motor. In addition, three-phase asynchronous motors are also widely used in large-scale mechanical equipment such as rail transportation, ships, and military fields.

[0003] The slip rate of a three-phase asynchronous motor has an important influence on the motor's load capacity and efficiency. The size of the slip rate directly affects the motor's efficiency and load capacity. When the slip rate is small, the motor efficiency is high, but the load capacity is small; when the slip rate is large, the motor's load capacity is enhanced, but the efficiency decreases. Therefore, reasonable calculation and control are required during the selection and use of the motor. Mastering the calculation method and related knowledge of the three-phase asynchronous motor slip formula will help improve the motor's operating efficiency and service life.

[0004] At present, the common method of obtaining the slip rate of a three-phase asynchronous motor is to obtain the speed of the asynchronous motor through the magnetoelectric method, and calculate the slip rate of the motor based on the speed and synchronous speed of the asynchronous motor using the slip rate calculation formula. However, the operating environment of the three-phase asynchronous motor determines that it is difficult to install magnets or sensors on the motor. The method of obtaining the speed of the motor through the magnetoelectric method and then obtaining the motor slip rate is less practical. Summary of the invention

[0005] In order to solve the technical problem that the method of obtaining the motor speed and then obtaining the motor slip rate by the magnetoelectric method has low practicality, the purpose of the present invention is to provide a method for measuring the slip rate of a three-phase asynchronous motor. The technical scheme adopted is as follows:

[0006] The basic frequency of the line current of the three-phase asynchronous motor is obtained; the line current sampling data is Fourier expanded to obtain an expanded signal, starting from the input signal of the line current of the three-phase asynchronous motor, based on the expanded signal along the high-frequency direction of the frequency, the frequency at the preset first number of comb filter effect characteristic spectral lines is used as the initial frequency; starting from the initial frequency, based on the expanded signal along the high-frequency direction of the frequency, the frequency at the preset second number of filter effect characteristic spectral lines is used as the target frequency;

[0007] According to the initial frequency and the target frequency, the actual speed of the three-phase asynchronous motor is determined; the actual speed is converted into the standard speed of the three-phase asynchronous motor; according to the reference frequency of the line current, the reference speed is determined; and the slip rate of the three-phase asynchronous motor is determined by combining the standard speed and the reference speed.

[0008] Preferably, the method for determining the actual speed of the three-phase asynchronous motor according to the initial frequency and the target frequency is:

[0009] R=Freq in *(1-(Freq in -(Freq end -Freq start ) / (Sn start -Sn end )) / Freq in )

[0010] Among them, Freq in is the fundamental frequency of the input line current; Freq start is the initial frequency; Freq end is the target frequency; Sn start and Sn end is the serial number of the characteristic spectral line corresponding to the corresponding initial frequency and target frequency, and R is the actual rotation speed.

[0011] Preferably, the calculation formula of the slip rate is:

[0012] s=(N–RPM engine ) / N

[0013] Among them, s is the slip rate of the three-phase asynchronous motor; N is the reference speed of the three-phase asynchronous motor; RPM engine It is the standard speed of three-phase asynchronous motor.

[0014] Preferably, the tooth width of the comb filter is obtained by estimating the approximate range of the slip rate based on the known motor parameters and the collected motor line current information, estimating the error interval of the tooth width based on the normal distribution curve, and recording the error interval of the tooth width as the tooth width basic range; when the width of the moiré pattern is K tooth widths, the moiré pattern width and the tooth width of the comb filter satisfy the following equation;

[0015] Freqm=K*Freq1=1 / (Freq real -Freq1)

[0016] Among them, Freqm is the moiré pattern width; Freq1 is the tooth width of the comb filter; Freq real is the frequency of the current line.

[0017] The embodiments of the present invention have at least the following beneficial effects:

[0018] The present invention relates to the technical field of motor detection. First, the line current sampling data is Fourier expanded to obtain an expanded signal, starting from the input signal of the line current of the three-phase asynchronous motor, based on the expanded signal along the high frequency direction of the frequency, the frequency at the preset first number of comb filter effect characteristic spectrum lines is used as the initial frequency; starting from the initial frequency, based on the expanded signal along the high frequency direction of the frequency, the frequency at the preset second number of filter effect characteristic spectrum lines is used as the target frequency; according to the initial frequency and the target frequency, the actual speed of the three-phase asynchronous motor is determined; the actual speed is converted into the standard speed of the three-phase asynchronous motor; according to the reference frequency of the line current, the reference speed is determined; the slip rate of the three-phase asynchronous motor is determined in combination with the standard speed and the reference speed, thereby avoiding the problem of low practicality caused by installing a sensor or electromagnetic on the motor, and by analyzing the line current of the three-phase asynchronous motor, the actual speed of the three-phase asynchronous motor is determined according to the difference in the frequency at the comb filter effect characteristic spectrum line, and then the slip rate of the three-phase asynchronous motor is determined, thereby improving the practicality of the slip rate of the three-phase asynchronous motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A method flow chart of a method for measuring the slip rate of a three-phase asynchronous motor provided by an embodiment of the present invention;

[0021] Figure 2A schematic diagram of a simplified circuit for stator-rotor comb filtering of a three-phase motor provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of a method for measuring the slip rate of a three-phase asynchronous motor proposed by the present invention, its specific implementation method, structure, features and effects, in conjunction with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0023] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0024] The embodiment of the present invention provides a specific implementation method of a method for measuring the slip rate of a three-phase asynchronous motor, and the method is applicable to the measurement scenario of the slip rate of a three-phase asynchronous motor. In this scenario, in order to solve the problem of low practicality of the method for obtaining the rotation speed of the motor by the magnetoelectric method and then obtaining the motor slip rate. The present invention analyzes the line current of the three-phase asynchronous motor, determines the actual rotation speed of the three-phase asynchronous motor according to the difference in the frequency at the characteristic spectrum line of the comb filter effect, and then determines the slip rate of the three-phase asynchronous motor, thereby improving the practicality of the slip rate of the three-phase asynchronous motor.

[0025] The specific scheme of the method for measuring the slip rate of a three-phase asynchronous motor provided by the present invention is described in detail below with reference to the accompanying drawings.

[0026] See also Figure 1 , which shows a flow chart of a method for measuring the slip rate of a three-phase asynchronous motor provided by an embodiment of the present invention, the method comprising the following steps:

[0027] Step S100, obtaining the basic frequency of the line current of the three-phase asynchronous motor; performing Fourier expansion on the line current sampling data to obtain an expanded signal, starting from the input signal of the line current of the three-phase asynchronous motor, based on the expanded signal along the high-frequency direction of the frequency, taking the frequency at the preset first number of comb filter effect characteristic spectral lines as the initial frequency; starting from the initial frequency, based on the expanded signal along the high-frequency direction of the frequency, taking the frequency at the preset second number of filter effect characteristic spectral lines as the target frequency.

[0028] When using a three-phase asynchronous motor, there is an important parameter that needs to be measured, called slip, which describes the speed difference between the rotor and stator of the motor. The rotor of a three-phase motor has no magnetic field itself. It needs to be excited by the rotating magnetic field of the stator, and then an induced current is generated before there is a magnetic field. The two magnetic fields interact to generate torque. If the stator magnetic field and the rotor magnetic field are relatively stationary, the rotor induced current will disappear. Therefore, in actual use, there will be a relative rotation speed difference in any situation, and the concept of slip is also there.

[0029] Slip s=(motor synchronous speed n1-rotor speed n) / motor synchronous speed n1.

[0030] The traditional slip measurement is to install a speed sensor to measure the actual speed of the motor, and then calculate the slip according to the slip calculation formula. Here, the present invention uses the fast Fourier transform (FFT) of the current waveform signal to obtain the main frequency by analyzing the current spectrum, and this main frequency is the motor speed.

[0031] For example, for a specific stator coil, when the magnetic field generated by it cuts the rotor magnetic lines of force at a frequency of 10Hz, because the speeds of the stator and rotor are not synchronized, the rotor also cuts the magnetic lines of force at a speed difference relative to the stator. The difference between the two frequencies, for example, the stator magnetic field rotation speed is 10Hz, and the rotor speed is 9.935Hz, then the difference between the stator and rotor frequencies = 0.065Hz, close to 0Hz. This action of cutting the magnetic lines of force can also excite the induced current on the stator coil.

[0032] The phase of the induced current on the rotor will lag about π / 2 degrees relative to the original input line current, based on the original input frequency. Then the rotor induced current with a phase lag of π / 2 will cut the stator coil, and the phase lags π / 2 again, forming the primary feedback induced current on the stator coil again.

[0033] The principle is that when a three-phase asynchronous motor is in use, it can be found that in its line current waveform, the base frequency signal is mixed with some high-frequency jitter. A brief comparative analysis will show that this ripple does not change with the signal frequency or load changes. It is caused by some step-like step signals generated by the inverter itself when it converts DC to AC and outputs a sinusoidal waveform using the table lookup method. If you zoom in on the center of the corresponding spectrum line in the spectrum, you will find another waveform feature.

[0034] The spectrum is cut evenly and equally around this frequency band, resulting in a comb filtering effect. Figure 2 , Figure 2The schematic diagram of the simplified circuit of the three-phase motor stator-rotor comb filter. The phase-shifted signal is superimposed on the original signal to produce a comb filter effect. The comb filter is produced because the angle between the stator phase current and the induced current on the rotor should be 90 degrees, that is, the rotor induced current will lag 90 degrees, and this induced current will be returned to the coil where the stator phase current is located through magnetic coupling again, and will lag 90 degrees again, just showing a reverse effect. Therefore, for the comb filter, the first anti-phase suppression point is just near the reference frequency of the power input signal. It is easy to imagine that if the current signal frequency is 2×Freq, 3×Freq, or 4×Freq times the current input voltage frequency, the anti-phase suppression state will still be maintained. Therefore, for the comb filter, its tooth width is almost equal to the line current input frequency. This ruler will extend infinitely to higher frequency bands, that is, this comb filter effect will continue to spread from the input signal frequency point to the high frequency direction in the spectrum.

[0035] The slip rate will also be coupled to the tooth spacing of this comb filter. For a three-phase motor, the speed of the rotor is always less than the rotation speed of the stator magnetic field. The above-mentioned electromagnetic coupling exists between the stator and the rotor. Once the signal is transmitted to this system, in addition to the regular -180-degree phase shift effect generated by the stator-rotor coupling circuit relative to the input signal frequency, due to the existence of the rotor speed difference, a phase shift effect will be superimposed on the original signal.

[0036] If we look for the peaks or valleys of the comb filter in the spectrum, the factors caused by the slip rate will accumulate between each tooth gap. in , since Freq in At the beginning, count 100 comb teeth in the high frequency direction of the spectrum, and count the first spectrum peak as Freq No1 , the frequency reading of the 100th comb tooth is Freq No100 That is, starting from the input signal frequency of the line current of the three-phase asynchronous motor, along the high frequency direction, the frequencies at the preset first number of comb filter effect characteristic spectral lines are used as the initial frequency; starting from the initial frequency, along the high frequency direction, the frequencies at the preset second number of filter effect characteristic spectral lines are used as the target frequency.

[0037] When the comb filter phenomenon occurs, if there are no other restrictions, it will extend infinitely in the signal spectrum. This feature can be used as the basis for further analysis to obtain the tooth width of the comb filter. Since the signal to be measured may be noisy, it is difficult to extract the characteristics of the signal through time domain analysis. And the signal to be measured may be a changing signal or an occasional signal. At this time, frequency domain analysis cannot achieve the required accuracy because the frequency resolution in the frequency domain depends on the sampling time. When the signal is sampled and calculated, it is limited by storage space and operation speed, and the number of points cannot be too high. Among them, due to the accuracy of the crystal oscillator itself, the accuracy of the sampling rate can be very high, and this feature is used for measurement. When two periodic signals with different frequencies are superimposed, moiré will appear; and the comb filter itself is a periodic signal; the period of the moiré can be obtained by reading the FFT spectrum, so this mode can be used to solve the required comb filter line width.

[0038] Assume that the basic range of the tooth width of the comb filter can be obtained from the circuit characteristics. It should be noted that the obtained comb filter tooth width Freq1 has an error. Based on the known motor parameters and the collected motor line current information, the approximate range of the slip rate can be estimated. Therefore, the error interval of the tooth width can be estimated based on the normal distribution curve, and the error interval of the tooth width is recorded as the basic range of the tooth width. In actual measurement, the sampling frequency will be continuously changed in the roughly estimated slip rate interval. When moiré appears, the result is output. When the operating frequency of the motor is known, the basic range of the tooth width can be roughly determined. Then the sampling time can be set to 1 / Freq1. At this time, after solving the FFT spectrum, the moiré pattern shown on the spectrum will generally appear as a regular maximum or minimum value. If the width of this moiré pattern is 37 tooth widths, that is, the tooth width is the same as Freq1, then the moiré pattern width and the tooth width of the comb filter satisfy the following equation:

[0039] Freqm=37*Freq1=1 / (Freq real -Freq1);

[0040] Freqm is the moiré pattern width; Freq1 is the comb filter tooth width; Freq real is the frequency of the current line. When the width of the moiré pattern is K tooth width, the moiré pattern width and the tooth width of the comb filter satisfy the following equation;

[0041] Freqm=K*Freq1=1 / (Freq real -Freq1)

[0042] Among them, Freqm is the moiré pattern width; Freq1 is the tooth width of the comb filter; Freqreal is the frequency of the current line.

[0043] The multiples of the equation satisfying the relationship between the moiré pattern width and the tooth width of the comb filter change according to the ratio of the moiré pattern to the tooth width. Freq1 is always greater than Freq real To be smaller.

[0044] In engineering applications, the number of sampling points is limited during real-time calculations. The actual sampling frequency of the AD corresponding to the tooth width of the comb filter is actually to use one comb to match another comb, and then indirectly calculate the actual tooth width of the comb filter based on the appearance of moiré patterns, and then get the actual sampling speed of the AD motor.

[0045] For line current, the identification of the fundamental frequency is relatively simple and will not be described in detail here. Assume that the motor fundamental frequency is Freq sig Note that the sampling rate needs to be able to identify the inverter operating frequency band. Perform Fourier expansion on the line current sampling data. sig ×7 to the high frequency direction, find the peak point of the spectrum line, and erase the signal within 7 times the frequency to avoid the odd-order clutter interference caused by electromagnetic coupling. The frequency of the first peak point of the spectrum line is recorded as Freq No1 , the serial number is 1. According to the actual sampling rate, the high-frequency spectrum limit value Freq can be obtained No.x , serial number is x.

[0046] Step S200, determining the actual speed of the three-phase asynchronous motor according to the initial frequency and the target frequency; converting the actual speed into the standard speed of the three-phase asynchronous motor; determining the reference speed according to the reference frequency of the line current; and determining the slip rate of the three-phase asynchronous motor by combining the standard speed and the reference speed.

[0047] According to the initial frequency and the target frequency, the actual speed of the three-phase asynchronous motor is determined. Specifically, the difference between the initial frequency and the target frequency is used as the numerator, the difference between the preset second quantity and the preset first quantity is used as the denominator, and the ratio corresponding to the numerator and the denominator is used as the actual speed of the three-phase asynchronous motor.

[0048] Assume that the current input signal is Freq in , since Freq in At the beginning, count 100 comb teeth in the high frequency direction of the spectrum, and count the first spectrum peak as Freq No1 , the frequency reading of the 100th comb tooth is Freq No1000 , that is, the first number is preset to 1, and the second number is preset to 100, then the calculation formula for the actual speed of the corresponding three-phase asynchronous motor is:

[0049] R=Freq in*(1-(Freq in -(Freq end -Freq start ) / (Sn start -Sn end )) / Freq in );

[0050] Among them, Freq in is the fundamental frequency of the input line current; Freq start is the initial frequency; Freq end is the target frequency. Sn start and Sn end is the serial number of the characteristic spectral line corresponding to the corresponding initial frequency and target frequency, and R is the actual rotation speed.

[0051] Among them, the unit of the actual speed of the three-phase asynchronous motor is Hz.

[0052] It should be noted that the tooth width and line current frequency of the comb filter can already reflect the slip rate, but the physical formula of the slip rate is obtained from the speed, so the actual speed calculation process needs to be multiplied by some coefficients that will eventually be simplified. If the above actual speed is converted to the standard three-phase motor speed, the following changes need to be made, that is, the actual speed is converted to the standard speed of the three-phase asynchronous motor, specifically:

[0053] The calculation formula for the standard speed is:

[0054] RPM engine =60*R / n;

[0055] Where n is the number of pole pairs of the motor; R is the actual speed of the three-phase asynchronous motor; RPM engine It is the standard speed of three-phase asynchronous motor.

[0056] The factor of the number of poles can actually be eliminated in subsequent calculations. The slip rate s is ultimately just a dimensionless ratio. Therefore, whether the speed is represented by frequency or actual rotation speed, it is just multiplying the measured value by a coefficient of the same size, which does not affect the calculation result.

[0057] Furthermore, the reference speed is determined according to the reference frequency of the line current. It should be noted that the method of determining the speed according to the frequency is a well-known technology for those skilled in the art and will not be described in detail here.

[0058] Combine the obtained standard speed and reference speed to determine the slip rate of the three-phase asynchronous motor. Specifically:

[0059] The calculation formula of the slip rate is:

[0060] s=(N–RPM engine ) / N;

[0061] Among them, s is the slip rate of the three-phase asynchronous motor; N is the reference speed of the three-phase asynchronous motor; RPM engine It is the standard speed of three-phase asynchronous motor.

[0062] It should be noted that if you want to measure the slip rate s more accurately, you only need to increase the sampling rate and count more comb teeth in the higher frequency band of the input signal spectrum. In actual measurement, other methods are used to collect the motor speed, and the frequency analysis results of the comb filter are compared. Substituting the frequency point data of 100 teeth, the slip rate does reach a measurement accuracy of 1%.

[0063] The comb filter effect is caused by the mutual inductance and slip rate between the stator and rotor of the three-phase motor, which is a characteristic of the motor itself. Therefore, the relevant method can be applied to both occasions with inverters and occasions without inverters and directly connected to the industrial frequency signal.

[0064] In summary, the present invention relates to motor detection, which performs Fourier expansion on line current sampling data to obtain an expanded signal, starting from the input signal of the line current of the three-phase asynchronous motor, based on the expanded signal along the high-frequency direction of the frequency, the frequency at the preset first number of comb filter effect characteristic spectral lines is used as the initial frequency; starting from the initial frequency, based on the expanded signal along the high-frequency direction of the frequency, the frequency at the preset second number of filter effect characteristic spectral lines is used as the target frequency; according to the initial frequency and the target frequency, the actual speed of the three-phase asynchronous motor is determined; the actual speed is converted into the standard speed of the three-phase asynchronous motor; according to the reference frequency of the line current, the reference speed is determined; and the slip rate of the three-phase asynchronous motor is determined in combination with the standard speed and the reference speed, thereby improving the practicality of the slip rate of the three-phase asynchronous motor.

[0065] It should be noted that the sequence of the above embodiments of the present invention is only for description and does not represent the advantages and disadvantages of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0066] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

Claims

1. A method for measuring the slip rate of a three-phase asynchronous motor, characterized in that: The method comprises the following steps: The basic frequency of the line current of the three-phase asynchronous motor is obtained; the line current sampling data is Fourier expanded to obtain an expanded signal, starting from the input signal of the line current of the three-phase asynchronous motor, based on the expanded signal along the high-frequency direction of the frequency, the frequency at the preset first number of comb filter effect characteristic spectral lines is used as the initial frequency; starting from the initial frequency, based on the expanded signal along the high-frequency direction of the frequency, the frequency at the preset second number of filter effect characteristic spectral lines is used as the target frequency; Determine the actual speed of the three-phase asynchronous motor according to the initial frequency and the target frequency; convert the actual speed into the standard speed of the three-phase asynchronous motor; determine the reference speed according to the reference frequency of the line current; determine the slip rate of the three-phase asynchronous motor by combining the standard speed and the reference speed; Among them, the method for determining the actual speed of the three-phase asynchronous motor according to the initial frequency and the target frequency is: R=Freq in *(1-(Freq in -(Freq end -Freq start ) / (Sn start -Sn end )) / Freq in ) Among them, Freq in is the fundamental frequency of the input line current; Freq start is the initial frequency; Freq end is the target frequency; Sn start and Sn end is the serial number of the characteristic spectral line corresponding to the corresponding initial frequency and target frequency, and R is the actual rotation speed.

2. The method for measuring the slip rate of a three-phase asynchronous motor according to claim 1, characterized in that: The calculation formula of the slip rate is: s=(N–RPM engine ) / N Among them, s is the slip rate of the three-phase asynchronous motor; N is the reference speed of the three-phase asynchronous motor; RPM engine It is the standard speed of three-phase asynchronous motor.

3. The method for measuring the slip rate of a three-phase asynchronous motor according to claim 1, characterized in that: The method for obtaining the tooth width of the comb filter is: Based on the known motor parameters and the collected motor line current information, the approximate range of the slip rate can be estimated, and the error interval of the tooth width can be estimated based on the normal distribution curve, and the error interval of the tooth width is recorded as the basic range of the tooth width; when the width of the moiré pattern is K tooth widths, the moiré pattern width and the tooth width of the comb filter satisfy the following equation; Freqm=K*Freq1=1 / (Freq real -Freq1) Among them, Freqm is the moiré pattern width; Freq1 is the tooth width of the comb filter; Freq real is the frequency of the current line.

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