CN115792478A - Method and system for realizing composite frequency test by using broadband volt-ampere characteristic meter - Google Patents
Method and system for realizing composite frequency test by using broadband volt-ampere characteristic meter Download PDFInfo
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Abstract
The invention discloses a method and a system for realizing composite frequency test by using a broadband volt-ampere characteristic meter, belonging to the field of volt-ampere characteristic test and aiming at the problem that a plurality of volt-ampere characteristic curves cannot be obtained by one-time test in the prior art, the method adopts the following scheme: a method for realizing composite frequency test by using a broadband volt-ampere characteristic meter comprises the following steps: inputting a composite voltage signal to a tested transformer according to the requirement; gradually increasing the input voltage of the measuring transformer to obtain volt-ampere characteristic curves of all signals and inflection points of all the curves until one curve reaches the inflection point, and removing the signal; continuously improving the output voltage, eliminating the signals reaching the inflection point one by one until the last voltage signal, and continuously improving the output voltage by a switching algorithm until the maximum output voltage or the maximum output current is reached to obtain the last volt-ampere characteristic curve; and completing the volt-ampere characteristic curve after the rejected signal inflection point. The system adopted by the method is convenient and quick to operate, a large amount of labor cost is saved, and the efficiency is improved.
Description
Technical Field
The invention belongs to the field of volt-ampere characteristic testing, and particularly relates to a method and a system for realizing composite frequency testing by using a broadband volt-ampere characteristic meter.
Background
The current transformer proportionally reduces the large current in the primary loop of the power grid alternating current system to a value which can be directly measured by an instrument, so that the measurement of the current of the primary loop and the calculation of electric energy are realized, and simultaneously, the current transformer is matched with a relay protection and an automatic device to carry out electric protection and automatic control on various faults of the power grid. The current transformer is an important basis for realizing selectivity, quick action, sensitivity and reliability of relay protection, thereby providing effective guarantee for safe and stable operation of a power system. Therefore, the performance of the current transformer must be tested and evaluated, wherein the volt-ampere characteristic (also called the excitation characteristic) is one of the most important handover tests of the current transformer, and is used for detecting the magnetic performance of the iron core of the current transformer. The technical problems of the existing equipment are as follows:
1) The power output waveform of the traditional power frequency volt-ampere characteristic tester comes from a power frequency power grid, only a power frequency signal can be output for testing, and the basic requirement of a tester on obtaining the volt-ampere characteristic of a low-frequency transformer under the low frequency of 20Hz cannot be met.
2) The existing volt-ampere characteristic tester basically tests single frequency once, if the volt-ampere characteristics under different frequencies need to be compared, multiple tests need to be carried out, the results of multiple frequencies are obtained and then are compared respectively, a curve graph and an inflection point are independent respectively, data comparison is not visual enough, and the advanced requirement that scientific research designers obtain the comparison of the volt-ampere characteristics under multiple frequencies by testing a low-frequency transformer once cannot be met.
Disclosure of Invention
Aiming at the problem that a plurality of volt-ampere characteristic curves cannot be obtained through one-time test in the prior art, the invention provides a method and a system for realizing composite frequency test by using a broadband volt-ampere characteristic meter, which can stably output broadband volt-ampere characteristic curves of any single-frequency signal and any composite-frequency signal aiming at a low-frequency mutual inductor so as to meet the working requirements of different personnel.
The technical scheme adopted by the invention is as follows: a method for realizing composite frequency test by using a broadband volt-ampere characteristic meter comprises the following steps:
and 4, complementing the volt-ampere characteristic curve after the eliminated signal inflection point according to the waveform data obtained in the step 3 so as to simultaneously obtain the volt-ampere characteristic curves corresponding to the voltage signals with different frequencies in the composite voltage signal.
Further, the specific process of step 1 is as follows:
step 1.1, set the number of points per cycle of DAC frequency toNPoint, output amplitude ac, voltage signal to be mixed isnIf it is, it is established in the memorynA table for storing data values calculated by sine wave for each signal in the composite voltage signal, frequency values corresponding to the data valuesA 1 ，A 2..... A n The set formed by each frequency correspondence table is respectively [ 2 ]A 11 ,A 12 ,A 13 ,…A N1 ]，[A 21 ,A 22 ,A 23 ,…A N2 ]、[A 31 ,A 32 ,A 33 ,…A N3 ]......[A n1 ,A n2 ,A n3 ,…A nN ]，
Wherein:value of i1 ton，jValue of 1 toN；A ij Representing data values calculated as a sine wave,Ma bit count value representing a DAC;
step 1.2, after obtaining the memory table, mixing the memory table and the memory table according to the proportionnThe signal is fed into the output buffer table of the DAC,neach signal ratio is respectivelyK 1 ，K 2 ......K n Then, then
In whichH ij The voltage signal to be mixed is output by taking a value from the output buffer table, and the mixed waveform is obtained after the processing of the power amplification source and the rising/falling transformer.
Further, in step 2, the specific process of calculating the inflection point of each signal volt-ampere characteristic curve in the composite voltage signal is as follows:
step 2.1, estimating the range of inflection point of each curve from the curve data obtained in step 1V imin ,V imax ]，[I imin ,I imax ](ii) a Setting the measured voltage toV is The measured current isI is Analog voltageV ic Analog currentI ic And multiple of currentIbsLet us orderV ic =V is 1.1, calculatingI ic =[(V ic -V imin )/(V imax -V imin )]*(I imax -I imin )+I imin ，Ibs=I is /I ic ；
Step 2.2, whenIbsIf > 1.5, the actual point is considered as an inflection point.
Further, a T-RMS method is adopted for calculation: the sampling frequency is set as the frequency output frequency, and the number of sampling points is per periodNPoint;
the T-RMS calculation mode is to calculate the root mean square value of the sampling point and collectNEach sampling point constitutes a sampling setA i1 ,A i2 ,A i3 ,…A iN ]When calculating
Wherein G (i) is a full-wave effective value.
Furthermore, an FFT method is adopted to calculate the relation with the frequency, 3 variables are established firstly, wherein the variables are respectively a real part R (j), an imaginary part Ig (j), and a frequency effective value is
The sampled analog-to-digital conversion value CD (j) is calculated as follows:
then
。
With followingjThe value changes, and the calculated frequency changes accordingly, so that effective values under different frequencies can be obtained.
Further, the specific process of step 4 is as follows: setting the frequency of the last voltage signal toA n Dividing the frequencies of the signals which are removed by the frequencies to obtain the scaling coefficients corresponding to the frequencies in turnA n /A 1 ，A n /A 2 ……A n /A n-1 And scaling the curve data of the last voltage signal according to the coefficient so as to complement the curve waveform after the inflection point of the voltage signals under other frequencies. In order to prevent the transformer to be detected from being saturated in advance, the voltage signals reaching the inflection point are removed one by one, except that the curve obtained by the last voltage signal is complete, and the removed voltage signalsThe numbers are lost after the inflection point, a large amount of labor cost can be saved according to the frequency proportion completion curve, and the testing efficiency is improved.
The utility model provides a system for utilize wide band volt-ampere characteristic appearance to realize compound frequency test, includes arbitrary ripples generation module, computational analysis module, sampling module and display module, wherein:
the arbitrary wave generation module is used for inputting a composite voltage signal mixed with voltage signals with different frequencies to a tested transformer;
the sampling module is used for collecting the output voltage and the output current of the tested mutual inductor;
the calculation analysis module is used for obtaining volt-ampere characteristic curve data of each voltage signal by using an FFT algorithm, calculating inflection points of each voltage signal, eliminating the voltage signals reaching the inflection points until the last voltage signal is remained, obtaining a volt-ampere characteristic curve of the last voltage signal by using a T-RMS algorithm, and scaling the volt-ampere characteristic curve data of the last voltage signal according to a frequency ratio to complete a curve waveform after the eliminated signal inflection points;
the display module is used for displaying the volt-ampere characteristic curves of the voltage signals with different frequencies in the composite voltage signal.
Further, the arbitrary wave generation module includes an arbitrary wave generation circuit, a power amplification source, and a step-up/step-down transformer, wherein:
the arbitrary wave generating circuit is used for generating a composite voltage signal;
the power amplification source adopts a single-phase DC-AC rectification inversion structure and comprises two parts of circuits, wherein the first part of circuits is used for obtaining a high-frequency pulse width modulation signal to drive the second part of circuits;
the up/down transformer is used for improving the output voltage of the power amplification source so as to realize that multiple gears have good output resolution.
Furthermore, the first part of circuit comprises a voltage amplifier, a triangular wave generator, a comparator and a pulse shaping circuit, wherein the input end of the voltage amplifier is connected with the output end of the arbitrary wave generation module, the output end of the voltage amplifier and the output end of the triangular wave generator are both connected with the input end of the comparator, so that an input composite voltage signal is compared with a high-frequency triangular wave emitted by the triangular wave generator through the comparator, and the output end of the comparator is connected with the input end of the pulse shaping circuit, so that a pulse width modulation signal is obtained after the signal processed by the comparator is processed by the pulse shaping circuit.
Furthermore, the second part of circuit comprises an H-bridge circuit, an output filter and a load which are connected in sequence, the H-bridge circuit is powered by a high-power stabilized voltage supply, the IGBT is driven by the pulse width modulation signal generated by the first part at the H-bridge circuit to carry out high-frequency switching, a high-power output waveform which is the same as the input composite voltage signal is obtained at the load after the high-frequency component is filtered by the filter, and the output power depends on the withstand voltage of the IGBT device and the allowed current value.
Depending on low-frequency power transmission demonstration engineering, in order to meet the performance test requirements of a low-frequency transformer used in the engineering, aiming at the condition that an original power frequency volt-ampere characteristic tester cannot be used, the existing tester is improved, the volt-ampere characteristic test of the low-frequency transformer under 20Hz is realized, the volt-ampere characteristic test of the transformer under the original power frequency can also be performed, and the scientific research requirements of early and subsequent tracking of the demonstration engineering are considered, the composite frequency test function can realize one-time test to obtain volt-ampere characteristic curves and inflection points under various frequencies, and the structural design and the technical parameters of the transformer under different frequencies can be conveniently researched.
The invention has the following beneficial effects:
1. compared with the prior art, the low-frequency transformer can output and mix voltage signals with different frequencies at one time, and meets the basic requirement of testers on obtaining the volt-ampere characteristic of the low-frequency transformer under the low frequency of 20 Hz; meanwhile, the function of using the power frequency power grid signal as a reference signal to be output to a power amplification source for measurement of the traditional mutual inductor is reserved.
2. Compared with the prior art, the invention can specify a plurality of frequency signals, can realize the volt-ampere characteristic test under different frequencies without a plurality of operations, has convenient and rapid test, reduces a large amount of repeated labor, saves a large amount of labor cost and improves the test efficiency.
3. According to the invention, the volt-ampere characteristic curves under various frequencies are obtained by collecting the test voltage and the test current with high precision, inflection point calculation is carried out, and the volt-ampere characteristic curves and the inflection points are fed back to the main control unit in real time to adjust the output amplitude of a signal with lower frequency, so that the mutual inductor is prevented from influencing the subsequent measurement of a component with higher frequency due to early saturation, the volt-ampere characteristic curves and the inflection points under different frequencies are presented simultaneously and completely, the data is more visual, and the comparison and analysis are more convenient.
Drawings
FIG. 1 is a test flow diagram;
FIG. 2 is a schematic diagram of a mixed waveform;
FIG. 3 is a graph of measured current-voltage characteristics before completion;
FIG. 4 is a plot of current-voltage characteristics plotted after completion;
FIG. 5 is a schematic diagram of a test system;
FIG. 6 is a schematic diagram of a power amplifier source;
FIG. 7 is a schematic diagram of a pulse width modulation waveform;
wherein: 1-an arbitrary wave generation module; 11-a voltage amplifier; 12-a triangular wave generator; 13-a comparator; 14-a pulse shaping circuit; a 15-H bridge circuit; 16-an output filter; 17-load; 18-high power regulated power supply; 2-a computational analysis module; and 3, a sampling module.
Detailed Description
The technical solutions of the embodiments of the present invention are explained and illustrated below with reference to the drawings of the present invention, but the following embodiments are only preferred embodiments of the present invention, and not all embodiments. Based on the embodiments in the implementation, other embodiments obtained by those skilled in the art without any creative effort belong to the protection scope of the present invention.
Example 1
The method for implementing complex frequency test by using a broadband voltammeter of the present embodiment, as shown in fig. 1, includes:
step 1.1, setting the trigger frequency of the timer with the lowest frequency of 10Hz, and setting the points of the DAC frequency per period asNAnd (3) establishing 3 tables in a memory if the output amplitude is ac and the number of the voltage signals to be mixed is 3, respectively storing data values calculated by sine waves of each frequency in the composite voltage signal, wherein the frequency values respectively correspond to 10Hz, 20Hz and 40Hz.
Each frequency correspondence table is formed as a set ofA 11 ,A 12 ,A 13 ,…A N1 ]，[A 21 ,A 22 ,A 23 ,…A N2 ]、[A 31 ,A 32 ,A 33 ,…A N3 ]，
Wherein:ithe value of the sum is 1 to 3,jvalue of 1 toN；A j1 、A j2 、A j3 Denotes a data value calculated as a sine wave, 4096 denotes a bit count value of the DAC;
step 1.2, after obtaining the memory table, mixing the memory table and the memory table according to the proportionnThe signal is fed into the output buffer table of the DAC,nthe signal ratio is 33%, 33% and 33%, respectively
In whichH j1 、H j2 AndH j3 are respectively 10Hz,In the output buffer tables corresponding to 20Hz and 40Hz, the voltage signals to be mixed are sampled from the output buffer tables and output, and the mixed waveforms are obtained after the processing of the power amplification source and the up/down transformer, as shown in fig. 2.
step 2.1, estimating the range of inflection point of each curve from the curve data obtained in step 1V imin ,V imax ]，[I imin ,I imax ](ii) a Setting the measured voltage toV is Measured current ofI is Analog voltageV c Analog currentI c And multiple of currentIbsLet us orderV c =V is 1.1, calculationI c =[(V c -V imin )/(V imax -V imin )]*(I imax -I imin )+I imin ，Ibs=I is /I c ；
Step 2.2, whenIbsIf > 1.5, the actual point is considered as an inflection point.
Taking the measured voltage value of 1.35V as an example, judge whether it is the inflection point of the 10Hz curve (the following measured data can be obtained in table 1):
V c =1.352*0.909=1.229V；V c between 1.179 and 1.276;
I c =((1.229-1.179)/(1.276-1.179))*(0.0054-0.0042)+0.0042=0.0056；Ibs=0.0092/0.0056=1.643。Ibsbeyond 1.5, the point may be considered to be an inflection point or may be considered to be already near an inflection point.
Taking the measured voltage value of 2.71V as an example to judge whether the measured voltage value is the inflection point of the 20Hz curve:
V c =2.71*0.909=2.463V；V c between 2.346-2.551;
I c =((2.463-2.346)/(2.551-2.346))*(0.0051-0.0047)+0.0047=0.0049A；Ibs=0.0098/0.0049=2。Ibsbeyond 1.5 to 2, the point may be considered an inflection point or may be considered to be already near the inflection point.
Taking the actually measured voltage value of 5.4V as an example, whether the actually measured voltage value is the inflection point of the 40Hz curve is judged:
V c =5.4*0.909=4.9V；V c between 4.7 and 5.1V;
I c =((4.9-4.7)/(5.1-4.7))*(0.0049-0.0039)+0.0039=0.0044A；Ibs=0.0088/0.0044=2。Ibsbeyond 1.5 to 2, the point may be considered as an inflection point or may be considered as being already near an inflection point.
the number of sampling points is 100 points per cycle, and the T-RMS calculation mode is to calculate the square root of the sampling points, for example, 100 sampling points are collected to obtain a sampling setA i1 ,A i2 …A i100 ]When calculating
Wherein G (i) is a full-wave effective value.
In this embodiment, the curves of 10Hz and 20Hz are stopped only by measuring the inflection point, and only the curve of 40Hz is completely measured. As shown in FIG. 3, the data after 20Hz data to 2.71V is none, and the data after 10Hz to 1.352V is none. The missing data of the two data points need to be completed by a 40Hz signal which is actually measured, and because the curve of the mutual inductor is almost under each frequency, the voltage reduced by the frequency can be reduced by the same proportion, and the current basically has little difference, so the missing data points of 20Hz and 10Hz have the same current and 40Hz, and the voltage is one half and one quarter of the voltage point of 40Hz respectively. For example, a point of 5.7V is converted to 2.85V at 20Hz, 1.425V at 10Hz, and so on. The measured values and the complementary values of the curves at 10Hz and 20Hz are shown in Table 1, and the data in Table 1 are plotted in FIG. 4, thereby obtaining a complete graph corresponding to the three frequencies.
TABLE 1
The FFT method is adopted to calculate the relation with the frequency, 3 variables are established firstly, wherein the variables are respectively a real part R (j) and an imaginary part Ig (j), and the effective value of the frequency is
The sampled analog-to-digital conversion value CD (j) is calculated as follows:
then
。
Along with the change of the j value, the calculated frequency is changed, and effective values under different frequencies can be obtained.
In fact, the calculation method here is the same as the calculation method of the DAC outputting the mixed signals with different frequencies, and all the calculation methods are to process the trigonometric functions to obtain values with different frequencies.
In order to prevent the tested mutual inductor from being saturated in advance, signals of a volt-ampere characteristic curve reaching an inflection point are removed one by one, the curve obtained except the last voltage signal is complete, the removed voltage signals are all absent after the inflection point, the curve is completed according to the frequency proportion, a large amount of labor cost can be saved, and the testing efficiency is improved.
Example 2
The present embodiment is a system for implementing a complex frequency test by using a wideband voltammeter, as shown in fig. 5, fig. 6, and fig. 7, the system includes an arbitrary wave generation module 1, a calculation analysis module 2, a sampling module 3, and a display module, wherein:
the arbitrary wave generation module 1 is used for inputting a composite voltage signal mixed with voltage signals with different frequencies to a tested transformer; the arbitrary wave generation module 1 includes an arbitrary wave generation circuit, a power amplification source, and a step-up/step-down transformer, wherein:
the arbitrary wave generating circuit is used for generating a composite voltage signal;
the power amplification source adopts a single-phase DC-AC rectification inversion structure and comprises two partial circuits, wherein the first partial circuit is used for obtaining a high-frequency pulse width modulation signal to drive the second partial circuit;
the up/down transformer is used for improving the output voltage of the power amplification source so as to realize that multiple gears have good output resolution;
the sampling module 3 is used for collecting the output voltage and the output current of the tested mutual inductor;
the calculation analysis module 2 is used for obtaining volt-ampere characteristic curve data of each voltage signal by using an FFT algorithm, calculating inflection points of each voltage signal, eliminating the voltage signals reaching the inflection points until the last voltage signal remains, obtaining a volt-ampere characteristic curve of the last voltage signal by using a T-RMS algorithm, and scaling the volt-ampere characteristic curve data of the last voltage signal according to a frequency ratio to complement a curve waveform after the eliminated signal inflection points;
the display module is used for displaying the volt-ampere characteristic curves of the voltage signals with different frequencies in the composite voltage signal.
As shown in fig. 6, the first partial circuit includes a voltage amplifier 11, a triangular wave generator 12, a comparator 13 and a pulse shaping circuit 14, an input end of the voltage amplifier 11 is connected to an output end of the arbitrary wave generating module 1, an output end of the voltage amplifier 11 and an output end of the triangular wave generator 12 are both connected to an input end of the comparator 13, so that an input composite voltage signal is compared with a high-frequency triangular wave emitted by the triangular wave generator 12 through the comparator 13, an output end of the comparator 13 is connected to an input end of the pulse shaping circuit 14, so that a signal processed by the comparator 13 is processed by the pulse shaping circuit 14 to obtain a pulse width modulation signal.
As shown in fig. 6, the second part of circuit includes an H-bridge circuit 15, an output filter 16 and a load 17 connected in sequence, the H-bridge circuit 15 is powered by a high-power regulated power supply 18, the pulse width modulation signal generated by the first part drives an IGBT to perform high-frequency switching at the H-bridge circuit 15, and after a high-frequency component is filtered by the filter, a high-power output waveform identical to an input composite voltage signal is obtained at the load 17, and the output power depends on the withstand voltage of the IGBT device and the allowed current value.
In this embodiment, the arbitrary wave generation module 1 uses a main control internal self-contained 12-bit DAC, and since the main control is powered by 3.3V, the output voltage is between 0 and 3.3V, the output sine wave has no negative half cycle, and an offset needs to be performed on the waveform output by the main control, where the offset is 1.65V (i.e., half of 3.3V); therefore, the main control can only output a sine waveform with a peak value of 0-3.3V, and the effective value is about 1.167V; the external operational amplifier circuit deducts the offset of 1.65V by hardware, amplifies the waveform to about 7V, fixes the trigger frequency of the DAC timer, and changes the data table in the chip memory, so that the DAC can output various waveforms with different frequencies and different amplitudes.
The arbitrary wave generating circuit is used for generating voltage signals with arbitrary waveforms, the arbitrary wave generating circuit is realized by using a DAC (digital-to-analog converter) arranged in the main control MCU, the direct current power supply supplies power, the main control adjusting software code can be used for generating direct current, alternating current and other signal quantities with arbitrary components, and various component signals and frequencies can be set for signal output. In this embodiment, the DAC (digital-to-analog converter) has 12-bit resolution and dual channels, and can fully automatically trigger digital-to-analog conversion without any intervention of the CPU by matching with the functions of the DMA (direct memory access) and the TIM (timer) inside the chip. The triggering of DMA (direct memory access) is triggered by timing overflow of an internal TIM (timer), and after triggering, the data stored in the internal memory is automatically sent to a register of a DAC (digital-to-analog converter), and the DAC (digital-to-analog converter) is enabled to output. Therefore, the output frequency can be changed only by changing the counting overflow value of the timer; the output waveform can be changed by changing the array data in the memory. The test method supports single frequency test of any integer between 10Hz to 1kHz, the voltage is 0 to 240V, and the maximum power is 3.5kW.
Alternating current signals and frequency of the power frequency power grid are changed at any moment, so that the risk of interference by the power grid is caused, and the test repeatability is low. The waveform signal generated by the waveform generating circuit has very stable size, component and frequency. Under the conditions of 50Hz and 6.3V effective value output, the output amplitude variation is lower than 0.1 percent, the frequency variation is lower than 0.01 percent, and the same test condition is ensured in each test. However, the module generates a voltage signal without any driving capability, and needs to be used together with signal amplification by a power amplification source.
The upper limit of the output voltage of the power amplification source is 140V, the upper limit of the output current is 25A-3.5 kW, and the upper limit is within 120V, 20A-2.4 kW recommended for normal work.
The reason for setting up the step-up/step-down transformer is: the power amplification source and a signal finally output to a tested transformer need to be isolated, and the tested product does not need such high voltage or the voltage is not enough, so that a high-power step-up/step-down device needs to be matched to convert the output of 0 to 120V of the power amplification source into multi-gear output voltage of 0 to 240V, and each gear has good output resolution.
The sampling measurement module uses ADC (analog-to-digital converter) which is produced by ADI company, the model is AD7606, the sampling measurement module is a 16-bit and 8-channel synchronous sampling AD chip, and the parallel sampling rate is as high as 200ksps. AD7606 is currently one of the most commonly used ADC sampling chips in power systems. The AD7606 chip integrates analog input clamping protection, a second-order anti-aliasing filter, a tracking and holding amplifier, a 16-bit charge redistribution successive approximation type ADC inner core, a digital filter, a 2.5V reference voltage source and a buffer, and a high-speed serial and parallel interface. AD7606 adopts a 5V single power supply for power supply, positive and negative double power supplies are not needed any more, and bipolar signal input of +/-10V or +/-5V is supported. All channels can be sampled at a rate of up to 200ksps, while the input clamp protection circuit can withstand voltages up to ± 16.5V. At present, AD7606 is widely applied to power line detection and protection systems, multi-motor control, instruments and control systems, and multi-axis positioning system nuclear Data Acquisition Systems (DAS).
While the invention has been described with reference to specific embodiments, the scope of the invention is not limited thereto, and those skilled in the art will appreciate that the invention includes, but is not limited to, the accompanying drawings and the description of the embodiments above. Any modification which does not depart from the functional and structural principles of the present invention is intended to be included within the scope of the claims.
Claims (10)
1. A method for realizing composite frequency test by using a broadband volt-ampere characteristic meter is characterized by comprising the following steps:
step 1, inputting and mixing composite voltage signals with voltage signals of different frequencies to a tested mutual inductor according to requirements;
step 2, gradually increasing the input voltage of the tested transformer, detecting the output voltage and current of the transformer in real time, obtaining volt-ampere characteristic curve data of each signal in the composite voltage signal by adopting an FFT algorithm, simultaneously calculating inflection points corresponding to each volt-ampere characteristic curve until the volt-ampere characteristic curve of one signal reaches the inflection point, enabling the transformer to reach or approach saturation, and then removing the signal; wherein, the inflection point means a point where a voltage is increased by 10% and a current is increased by 50%;
step 3, continuing to improve the input voltage, eliminating the signals of the volt-ampere characteristic curve reaching the inflection point one by one until the last voltage signal is left, switching the calculation mode from the FFT algorithm to the T-RMS algorithm, continuing to improve the input voltage of the tested transformer until the tested transformer reaches the maximum output voltage or the maximum output current, and obtaining the volt-ampere characteristic curve of the last signal;
and 4, completing the volt-ampere characteristic curve after the eliminated signal inflection point according to the waveform data obtained in the step 3 so as to simultaneously obtain the volt-ampere characteristic curves corresponding to the voltage signals with different frequencies in the composite voltage signal.
2. The method for realizing composite frequency testing by using the broadband voltammeter according to claim 1, wherein the specific process of step 1 is as follows:
step 1.1, set the number of points per cycle of DAC frequency toNIf the output amplitude is ac and the number of the voltage signals to be mixed is n, n tables are established in the memory, the data values calculated by sine waves of all the signals in the composite voltage signal are respectively stored, and the frequency values respectively correspond to the frequency valuesA 1 ，A 2 .....A n The set formed by each frequency correspondence table is respectively [ 2 ]A 11 ,A 12 ,A 13 ,…A N1 ]，[A 21 ,A 22 ,A 23 ,…A N2 ]、[A 31 ,A 32 ,A 33 ,…A N3 ]......[A n1 ,A n2 ,A n3 ,…A nN ]，
Wherein:itake a value of 1 ton，jValue of 1 toN；A ij Representing data values calculated as a sine wave,Ma bit count value representing a DAC;
step 1.2, after obtaining the memory table, mixing the memory table and the memory table according to the proportionnThe signals are fed into the output buffer table of the DAC,neach signal ratio is respectivelyK 1 ，K 2 ......K n Then, then
In which H ij The voltage signal to be mixed is output by taking a value from the output buffer table, and the mixed waveform is obtained after the processing of the power amplification source and the rising/falling transformer.
3. The method for realizing composite frequency testing by using the broadband volt-ampere characteristic meter according to claim 1, wherein in the step 2, the specific process of calculating the inflection point of each volt-ampere characteristic curve of the signal in the composite voltage signal comprises the following steps:
step 2.1, estimating the range of inflection point of each curve from the curve data obtained in step 1V imin ,V imax ]，[I imin ,I imax ](ii) a Setting the measured voltage toV is The measured current isI is Analog voltageV ic Analog currentI ic And multiple of currentIbsLet us orderV ic =V is 1.1, calculatingI ic =[(V ic -V imin )/(V imax -V imin )]*(I imax -I imin )+I imin ，Ibs=I is /I ic ；
Step 2.2, whenIbsIf > 1.5, the actual point is considered as an inflection point.
4. The method for realizing the composite frequency test by using the broadband voltammeter as claimed in claim 1, wherein the T-RMS calculation method is adopted: the number of sampling points is per periodNThe calculation mode of point and T-RMS is to calculate the root mean square value of the sampling point and collectNThe sampling points form a sampling setA i1 ,A i2 ,A i3 ,…A iN ]When calculating
Wherein G (i) is a full-wave effective value.
5. The method as claimed in claim 1, wherein the FFT calculation method is used to determine the relationship between the frequency and the variable, and the variable is first established into 3 variables, i.e., a real part R (j), an imaginary part Ig (j), and an effective frequency value
The sampled analog-to-digital conversion value CD (j) is calculated as follows:
then
。
6. The method for realizing composite frequency testing by using the broadband voltammeter according to claim 1, wherein the specific process of step 4 is as follows: setting the frequency of the last voltage signal toA n Dividing the frequencies of the signals which are eliminated by the frequencies to obtain scaling coefficients corresponding to the frequencies in turnA n /A 1 ，A n /A 2 ……A n /A n-1 And scaling the curve data of the last voltage signal according to the coefficient so as to complement the curve waveform after the inflection point of the voltage signals under other frequencies.
7. The utility model provides a system for utilize wide band volt-ampere characteristic appearance to realize compound frequency test which characterized in that, includes arbitrary ripples and takes place module, computational analysis module, sampling module and display module, wherein:
the arbitrary wave generation module is used for inputting a composite voltage signal mixed with voltage signals with different frequencies to a tested transformer;
the sampling module is used for collecting the output voltage and the output current of the tested mutual inductor;
the calculation analysis module is used for obtaining curve data of each voltage signal by using an FFT algorithm, calculating inflection points of each voltage signal, eliminating the voltage signal reaching the inflection points until the last voltage signal is remained, obtaining a volt-ampere characteristic curve of the last voltage signal by using a T-RMS algorithm, and scaling the curve data of the last voltage signal according to a frequency ratio to complete the curve waveform after the eliminated signal inflection points;
the display module is used for displaying the volt-ampere characteristic curves of the voltage signals with different frequencies in the composite voltage signal.
8. The system of claim 7, wherein the arbitrary wave generation module comprises an arbitrary wave generation circuit, a power amplification source and a step-up/step-down transformer, and wherein:
the arbitrary wave generating circuit is used for generating a composite voltage signal;
the power amplification source adopts a single-phase DC-AC rectification inversion structure and comprises two partial circuits, wherein the first partial circuit is used for obtaining a high-frequency pulse width modulation signal to drive the second partial circuit;
the up/down transformer is used for improving the output voltage of the power amplification source so as to realize that multiple gears have good output resolution.
9. The system for realizing composite frequency testing by using a broadband volt-ampere characteristic meter according to claim 8, wherein the first part of circuits comprises a voltage amplifier, a triangular wave generator, a comparator and a pulse shaping circuit, an input end of the voltage amplifier is connected with an output end of the arbitrary wave generation module, an output end of the voltage amplifier and an output end of the triangular wave generator are both connected with an input end of the comparator, so that an input composite voltage signal is compared with a high-frequency triangular wave emitted by the triangular wave generator through the comparator, and an output end of the comparator is connected with an input end of the pulse shaping circuit, so that a pulse width modulation signal is obtained after the signal processed by the comparator is processed by the pulse shaping circuit.
10. The system for realizing composite frequency testing by using the broadband volt-ampere characteristic meter according to claim 8, wherein the second part of the circuit comprises an H-bridge circuit, an output filter and a load which are connected in sequence, the H-bridge circuit is powered by a high-power stabilized voltage supply, the pulse width modulation signal generated by the first part drives an IGBT (insulated gate bipolar transistor) to perform high-frequency switching at the H-bridge circuit, a high-power output waveform which is the same as an input composite voltage signal is obtained at the load after high-frequency components are filtered by the filter, and the output power depends on the withstand voltage of the IGBT device and the allowed current value.
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