CN111239638B - Method for detecting periodic and random changes of output frequency of alternating current voltage source - Google Patents
Method for detecting periodic and random changes of output frequency of alternating current voltage source Download PDFInfo
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- CN111239638B CN111239638B CN202010025727.0A CN202010025727A CN111239638B CN 111239638 B CN111239638 B CN 111239638B CN 202010025727 A CN202010025727 A CN 202010025727A CN 111239638 B CN111239638 B CN 111239638B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/40—Testing power supplies
- G01R31/42—AC power supplies
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/02—Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/16—Spectrum analysis; Fourier analysis
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- Measurement Of Current Or Voltage (AREA)
- Measuring Frequencies, Analyzing Spectra (AREA)
Abstract
The invention relates to a method for detecting the periodic and random change of the output frequency of an alternating current voltage source, which comprises the following steps: measuring the full output voltage of the alternating voltage for a period of time; calculating the instantaneous frequency of the output voltage; determining a frequency modulation amplitude of the ac output voltage; summarizing all frequency modulation amplitudes after a test begins to form a time domain curve of the frequency modulation amplitudes; obtaining a frequency modulation spectrum curve of the output voltage through Fourier transform of the frequency modulation amplitude time domain curve; observing the period of the frequency change of the output voltage of the alternating voltage source and the amplitude of the frequency change of the alternating voltage source according to the curve of the frequency modulation spectrum. The invention realizes the detection function of the periodic and random changes of the output frequency around the average frequency, can visually show the periodic and random changes of the output frequency around the average frequency, and can be applied to the detection of the frequency modulation spectrum of the output voltage of all alternating voltage sources.
Description
Technical Field
The invention belongs to the technical field of alternating current voltage sources, and particularly relates to a method for detecting periodic and random changes of an output frequency of an alternating current voltage source.
Background
In modern power supply systems, generators or power electronics can be used as ac voltage sources to provide electrical energy to various electrical loads. The stability of the amplitude of the output voltage of the voltage source is of great importance to the electric load, and many existing technologies need to keep the amplitude of the output voltage stable and detect the amplitude of the output voltage. However, the stability of the frequency of the voltage source output voltage is also important for the electrical load. Although the amount of change in instantaneous frequency within 1 minute of the voltage source output voltage can be evaluated by measuring the frequency modulation amplitude, there is no clear detection method for periodic or random changes in the voltage source output voltage frequency.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a detection method for periodic and random changes of the output frequency of an alternating current voltage source, which has the advantages of reasonable design, high precision and strong intuition.
The technical problem to be solved by the invention is realized by adopting the following technical scheme:
a method for detecting the periodic and random variation of the output frequency of an alternating current voltage source comprises the following steps:
step 1, connecting a tested alternating current voltage source to a measuring circuit, and measuring the full output voltage of the alternating current voltage for a period of time;
step 2, calculating the instantaneous frequency of the output voltage;
step 3, determining the frequency modulation amplitude of the alternating current output voltage by summarizing the instantaneous voltage within a period of time;
step 4, summarizing all frequency modulation amplitudes after the test begins to form a time domain curve of the frequency modulation amplitudes;
step 5, obtaining a frequency modulation spectrum curve of the output voltage through Fourier transform of the frequency modulation amplitude time domain curve;
and 6, observing the period of the frequency change of the output voltage of the alternating current voltage source and the amplitude of the frequency change of the alternating current voltage source in the frequency change period through a curve of a frequency modulation spectrum.
The measuring circuit in the step 1 comprises a voltage transformer, a data acquisition card, a computer and a display, wherein the alternating current voltage source to be measured, the voltage transformer, the data acquisition card, the computer and the display are sequentially connected.
The sampling frequency of the voltage sensor and the data acquisition card should be at least 1.25 MHz.
The time for measuring the full output voltage of the alternating voltage in the step 1 is 5 minutes.
The specific implementation method of the step 2 comprises the following steps: and calculating the reciprocal of the time interval by measuring the time interval of the adjacent positive zero-crossing point voltage to obtain the instantaneous frequency of the output voltage.
The specific implementation method of the step 3 is as follows: and taking the maximum value and the minimum value of all instantaneous frequencies measured within 1 minute, and taking the difference between the maximum value and the minimum value as the frequency modulation amplitude of the alternating current output voltage.
The specific implementation method of the step 4 comprises the following steps: summarizing all frequency modulation amplitudes 1 minute after the test starts, and forming a time domain curve of the frequency modulation amplitudes.
The invention has the advantages and positive effects that:
1. the invention realizes the detection function of the periodic and random changes of the output frequency around the average frequency by measuring the frequency modulation spectrum of the output voltage of the alternating voltage source, charts the abstract frequency concept, can intuitively show the periodic and random changes of the output frequency around the average frequency, and is suitable for the detection of the frequency modulation spectrum of the output voltage of all the alternating voltage sources.
2. In order to test the output voltage frequency of the alternating voltage source, the sampling frequency of the alternating voltage acquisition card is at least 1.25MHz, so that the accuracy of a detection result is ensured.
Drawings
FIG. 1 is a diagram of a measurement circuit used in the present invention;
FIG. 2 is a graph of frequency modulation amplitude of the output voltage of the variable frequency power supply over 1 minute;
fig. 3 is a frequency modulation spectrum obtained by frequency domain transformation of the time domain curve of fig. 2.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The design idea of the invention is as follows:
since the frequency is time dependent and the actual test procedure is a detection of the voltage source output frequency over a period of time, whereas the frequency modulation amplitude is the difference between the instantaneous frequency maximum and minimum over a 1 minute time interval, the frequency modulation amplitude excludes first of all the influence of the average frequency on the periodic and random variations. The frequency modulation amplitude can only represent the instantaneous frequency transformation quantity, but cannot represent the periodicity and the randomness of the output frequency. In this case, it is required to express the frequency modulation spectrum. The invention evaluates the periodic or random change of the frequency of the voltage source output voltage by measuring the frequency modulation spectrum. .
How to detect the frequency modulation spectrum is the core content of the present invention. First understood as a continuous spectral line with frequency modulation amplitude in the frequency domain. As shown in fig. 3, the abscissa of the spectral line is the period of frequency variation, i.e. the repetition rate, and the ordinate is the corresponding frequency modulation amplitude, so that the output voltage characteristic of the variable frequency power supply is relatively good.
Thus, in terms of detection, time domain spectral lines of frequency modulation amplitude can be obtained through detection of time domain parameters, and frequency domain spectral lines of the frequency modulation amplitude can be obtained through Fourier transformation. The method realizes the measurement of the frequency modulation spectrum, and can intuitively reflect the output voltage frequency of the voltage source, the period of conversion around the average frequency and the variation of the corresponding variation period.
Based on the design idea, the invention provides a method for detecting the periodic and random changes of the output frequency of an alternating current voltage source, which comprises the following steps:
step 1, measuring the full output voltage of the alternating voltage for 5 minutes by a voltage sensor and a data acquisition card.
In this step, the measured voltage source is measured for 5 minutes by using the measurement circuit diagram shown in fig. 1, so as to complete the detection of the electrical quantity in the time domain, and obtain the curve of the output voltage amplitude value versus the time. The voltage sensor collects the alternating voltage of the power supply to be detected and inputs the alternating voltage into the data acquisition card, and the alternating voltage obtained by measurement is output to the display for displaying after being processed by the computer. In the circuit, the sampling frequency of instruments such as a voltage sensor, a data acquisition card and the like is at least 1.25 MHz.
And 2, calculating the instantaneous frequency of the output voltage through each zero-crossing point voltage.
In this embodiment, the instantaneous frequency of the output voltage is calculated using the following method: and calculating the reciprocal of the time interval by measuring the time interval of the adjacent positive zero-crossing point voltage, namely the instantaneous frequency.
And 3, summarizing the instantaneous voltage within 1 minute to determine the frequency modulation amplitude of the alternating current output voltage.
In this embodiment, the frequency modulation amplitude of the ac output voltage is determined by the following method: and taking the maximum value and the minimum value of all instantaneous frequencies measured within 1 minute, and taking the difference between the maximum value and the minimum value as the frequency modulation amplitude of the alternating current output voltage.
And 4, summarizing all frequency modulation amplitudes after the test is started for 1 minute to form a time domain curve of the frequency modulation amplitudes, as shown in fig. 2.
And 5, obtaining a frequency modulation spectrum curve of the output voltage through Fourier transform of the frequency modulation amplitude time domain curve, as shown in fig. 3.
And 6, observing the period of the frequency change of the output voltage of the alternating current voltage source and the amplitude of the frequency change of the alternating current voltage source according to the curve of the frequency modulation spectrum obtained in the step 5.
As can be seen from the two waveforms shown in fig. 2 and 3, the output voltage characteristic of the variable frequency power supply is better than that of the generator. The variable frequency power supply is a static variable power supply on the ground of the airplane, and has better output voltage characteristic for a professional power supply. The time domain curve shows that the frequency of the output voltage of the variable frequency power supply is relatively stable, the frequency modulation amplitude of the variable frequency power supply is relatively small and relatively stable, and the same frequency modulation amplitude can be maintained for a relatively long time, that is, the frequency of the output voltage does not change relatively frequently but only changes in stages. The frequency modulation amplitude of the low frequency is larger on the spectrogram, and the frequency modulation amplitude of the high frequency is smaller.
It should be emphasized that the embodiments described herein are illustrative rather than restrictive, and thus the present invention is not limited to the embodiments described in the detailed description, but other embodiments derived from the technical solutions of the present invention by those skilled in the art are also within the scope of the present invention.
Claims (5)
1. A method for detecting the periodic and random variation of the output frequency of an alternating current voltage source is characterized by comprising the following steps:
step 1, connecting a tested alternating current voltage source to a measuring circuit, and measuring the full output voltage of the alternating current voltage for a period of time;
step 2, calculating the instantaneous frequency of the output voltage;
step 3, determining the frequency modulation amplitude of the alternating current output voltage through the instantaneous voltage within 1 minute; the frequency modulation amplitude is the difference between the maximum value and the minimum value of the instantaneous frequency within 1 minute;
step 4, summarizing all frequency modulation amplitudes after the test starts for 1 minute to form a time domain curve of the frequency modulation amplitudes;
step 5, obtaining a frequency modulation spectrum curve of the output voltage through Fourier transform of the frequency modulation amplitude time domain curve;
and 6, observing the period of the frequency change of the output voltage of the alternating current voltage source and the amplitude of the frequency change of the alternating current voltage source in the frequency change period through a curve of a frequency modulation spectrum.
2. The method of claim 1, wherein the method comprises the steps of: the measuring circuit in the step 1 comprises a voltage transformer, a data acquisition card, a computer and a display, wherein the alternating current voltage source to be measured, the voltage transformer, the data acquisition card, the computer and the display are sequentially connected.
3. A method as claimed in claim 2, wherein said method comprises the steps of: the sampling frequency of the voltage sensor and the data acquisition card should be at least 1.25 MHz.
4. A method as claimed in claim 1, 2 or 3, wherein said method comprises the steps of: the time for measuring the full output voltage of the alternating voltage in the step 1 is 5 minutes.
5. A method as claimed in claim 1, 2 or 3, wherein said method comprises the steps of: the specific implementation method of the step 2 comprises the following steps: and calculating the reciprocal of the time interval by measuring the time interval of the adjacent positive zero-crossing point voltage to obtain the instantaneous frequency of the output voltage.
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