CN115792478B - Method and system for realizing composite frequency test by using broadband volt-ampere characteristic instrument - Google Patents
Method and system for realizing composite frequency test by using broadband volt-ampere characteristic instrument Download PDFInfo
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Abstract
The invention relates to a method and a system for realizing composite frequency test by using a broadband volt-ampere characteristic instrument, which belongs to the field of volt-ampere characteristic test, and aims at solving the problem that a plurality of volt-ampere characteristic curves cannot be obtained by one-time test in the prior art, and adopts the following scheme: a method for implementing a composite frequency test using a broadband voltammetry, comprising: inputting a composite voltage signal to a tested transformer according to the requirement; gradually increasing the input voltage of the transformer to obtain volt-ampere characteristic curves of all signals and inflection points of all curves until one of the curves reaches the inflection point, and removing the signals; continuously increasing the output voltage, eliminating signals reaching inflection points one by one until the last voltage signal is reached, and continuously increasing the output voltage by a switching algorithm until the maximum output voltage or the maximum output current is reached, so as to obtain the last volt-ampere characteristic curve; the voltammetric characteristic curve after the culled signal inflection point is complemented. The system adopted by the method is convenient and quick to operate, saves a great deal of labor cost and improves efficiency.
Description
Technical Field
The invention belongs to the field of volt-ampere characteristic test, and particularly relates to a method and a system for realizing compound frequency test by using a broadband volt-ampere characteristic instrument.
Background
The current transformer reduces the large current in the primary loop of the power grid alternating current system to a value directly measured by an available instrument in proportion, so that the measurement and the electric energy calculation of the primary loop current are realized, and meanwhile, relay protection and an automatic device are matched to perform electric protection and automatic control on various faults of the power grid. The current transformer is an important foundation for realizing selectivity, rapidity, sensitivity and reliability of relay protection, thereby providing effective guarantee for safe and stable operation of the power system. The current transformer performance must therefore be tested and evaluated, with volt-ampere characteristics (also known as excitation characteristics) being one of the most important cross-connect tests of the current transformer for detecting the magnetic properties of the current transformer core. 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 testers on obtaining the volt-ampere characteristic of the low-frequency transformer at a 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 are required to be compared, multiple tests are required to be carried out, the results of the multiple frequencies are respectively compared, the curve graph and the inflection point are respectively independent, the data comparison is not visual enough, and the advanced requirement of the scientific designer on the comparison of the volt-ampere characteristics under the multiple frequencies can not be met by testing the low-frequency transformer once.
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 utilizing 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 transformer so as to meet the working demands of different personnel.
The invention adopts the following technical scheme: a method for implementing a composite frequency test using a broadband voltammetry, comprising:
and 4, complementing the volt-ampere characteristic curve after the inflection point of the removed signal according to the waveform data obtained in the step 3 so as to obtain the volt-ampere characteristic curves corresponding to the voltage signals with different frequencies in the composite voltage signal at the same time.
Further, the specific process of the step 1 is as follows:
step 1.1, setting the number of points per cycle of DAC frequency asNAt a point, the output amplitude is ac, and the voltage signal to be mixed isnAnd establishing in the memorynA table for storing the data values calculated by sine wave of each signal in the composite voltage signal, the frequency values corresponding to each signalA 1 ，A 2..... A n Each frequency correspondence table forms a set of [ respectively ]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:i takes the value1 to 1n，jTake the value of 1 toN；A ij Representing the data values calculated in terms of sine waves,Ma bit count value representing the DAC;
step 1.2, after obtaining the memory table, mixing proportionallynThe signals are fed into the output buffer table of the DAC,nthe signal duty ratios are respectivelyK 1 ，K 2 ......K n Then
WhereinH ij The method is characterized in that a voltage signal to be mixed is output from an output buffer table, and the mixed waveform is obtained after the voltage signal to be mixed is processed by a power amplification source and a step-up/step-down 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 points of each curve from the curve data obtained in step 1V imin ,V imax ]，[I imin ,I imax ]The method comprises the steps of carrying out a first treatment on the surface of the Setting the measured voltage toV is The actual measured current isI is Analog voltageV ic Analog currentI ic And current multipleIbsOrder-makingV ic =V is 1.1, calculationI ic =[(V ic -V imin )/(V imax -V imin )]*(I imax -I imin )+I imin ，Ibs=I is /I ic ；
Step 2.2, whenIbsAt > 1.5, the real point is considered to be the inflection point.
Further, the T-RMS method is adopted for calculation: the sampling frequency is set as the frequency output frequency, and the sampling point number is set as each periodNA plurality of points;
the T-RMS calculation method is to calculate the square average root value of the sampling point and collectNThe sampling points form a sampling setA i1 ,A i2 ,A i3 ,…A iN ]At the time of calculation
Wherein G (i) is a full wave effective value.
Further, the FFT method is adopted to calculate the mode to be related to the frequency, 3 variables are firstly established and are respectively the real part R (j) and the 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 withjThe value changes, and the calculated frequency changes accordingly, so that the effective value under different frequencies can be obtained.
Further, the specific process of the step 4 is as follows: setting the frequency of the last voltage signal toA n Dividing the frequencies of the other signals with the frequencies removed respectively 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 to complement the curve waveform after the inflection points of the voltage signals at the other frequencies. In order to prevent the tested transformer from being saturated in advance, the voltage signals reaching the inflection points are eliminated one by one, the curve obtained by the last voltage signal is complete, the eliminated voltage signals are missing after the inflection points, and the curve is complemented according to the frequency proportion, so that a large amount of labor cost can be saved, and the testing efficiency is improved.
A system for realizing composite frequency test by using a broadband volt-ampere characteristic instrument comprises an arbitrary wave generation module, a calculation and analysis module, a sampling module and a display module, wherein:
the arbitrary wave generation module is used for inputting composite voltage signals mixed with voltage signals with different frequencies to the tested transformer;
the sampling module is used for collecting the output voltage and the output current of the tested transformer;
the calculation analysis module is used for obtaining volt-ampere characteristic curve data of each voltage signal by utilizing 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 utilizing a T-RMS algorithm, and scaling the volt-ampere characteristic curve data of the last voltage signal according to a frequency ratio to complement curve waveforms after the inflection points of the eliminated signals;
the display module is used for displaying volt-ampere characteristic curves of 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 generation 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 step-up/step-down transformer is used for improving the output voltage of the power amplification source so as to realize that multiple gears all have good output resolution.
Further, the first partial 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, and 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 sent 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.
Further, the second part of the circuit comprises an H bridge circuit, an output filter and a load which are sequentially connected, the H bridge circuit is powered by a high-power voltage-stabilizing power supply, the pulse width modulation signal generated by the first part drives the IGBT to carry out high-frequency switching at the H bridge circuit, the filter filters high-frequency components and then obtains a high-power output waveform which is the same as the input composite voltage signal at the load, and the output power depends on the withstand voltage of the IGBT device and the allowed current value.
Depending on a low-frequency power transmission demonstration project, in order to meet the performance test requirement of a low-frequency transformer used in the project, 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 is also realized, in addition, the scientific research requirement of the early stage and the follow-up tracking of the demonstration project is considered, the compound frequency test function of the design can realize that the volt-ampere characteristic curve and the inflection point under various frequencies can be obtained by one test, and is convenient for researching the structural design and the technical parameters of the transformer under different frequencies.
The invention has the beneficial effects that:
1. compared with the prior art, the invention can output voltage signals mixed with different frequencies at one time, and meets the basic requirement of testers on obtaining the volt-ampere characteristic of the low-frequency transformer at 20Hz low frequency; meanwhile, the function of using the power frequency power grid signal as a reference signal to be output to a power amplification source to measure the traditional transformer is reserved.
2. Compared with the prior art, the invention can designate a plurality of frequency signals, can realize volt-ampere characteristic test under different frequencies without repeated operation, has convenient and quick test, reduces a great deal of repeated labor, saves a great deal of labor cost and improves the test efficiency.
3. According to the invention, the test voltage and the test current are acquired with high precision, the volt-ampere characteristic curve under each frequency is obtained, the inflection point calculation is carried out, and the volt-ampere characteristic curve is fed back to the main control unit in real time to adjust the output amplitude of a lower frequency signal, so that the influence of the early saturation of the transformer on the subsequent measurement of a higher frequency component is avoided, the volt-ampere characteristic curve and the inflection point under different frequencies can be simultaneously and completely presented, the data is more visual, and the comparison and the analysis are more convenient.
Drawings
FIG. 1 is a test flow chart;
FIG. 2 is a schematic diagram of a mixed waveform;
FIG. 3 is a graph of measured volt-ampere characteristics prior to completion;
FIG. 4 is a graph of the volt-ampere characteristics plotted after completion;
FIG. 5 is a schematic diagram of a test system;
FIG. 6 is a schematic diagram of a power amplification source structure;
FIG. 7 is a schematic diagram of a pulse width modulated 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; 15-H bridge circuit; a 16-output filter; 17-load; 18-a high-power regulated power supply; 2-calculating and analyzing module; 3-sampling module.
Detailed Description
The technical solutions of the embodiments of the present invention will be 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 the embodiments. Based on the examples in the implementation manner, other examples obtained by a person skilled in the art without making creative efforts fall within the protection scope of the present invention.
Example 1
The method for implementing the composite frequency test by using the broadband voltammetry in the embodiment, as shown in fig. 1, includes:
step 1.1, setting the trigger frequency of the timer to the lowest frequency of 10Hz, and setting the number of points per cycle of the DAC frequency asNAnd (3) setting up 3 tables in the memory if the output amplitude is ac and the number of voltage signals to be mixed is 3, and 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 forms a set of [A 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 value is 1 to 3,jtake the value of 1 toN；A j1 、A j2 、A j3 Representing the data value calculated in sine wave, 4096 represents the number of bits of the DACA count value;
step 1.2, after obtaining the memory table, mixing proportionallynThe signals are fed into the output buffer table of the DAC,nthe signal duty ratios are 33%, 33% and 33%, respectively, then
WhereinH j1 、H j2 AndH j3 and the output buffer tables are respectively corresponding to 10Hz, 20Hz and 40Hz, the voltage signals to be mixed are output from the output buffer tables, and the mixed waveforms are obtained after being processed by a power amplification source and a step-up/step-down transformer, as shown in fig. 2.
step 2.1, estimating the range of inflection points of each curve from the curve data obtained in step 1V imin ,V imax ]，[I imin ,I imax ]The method comprises the steps of carrying out a first treatment on the surface of the Setting the measured voltage toV is The actual measured current isI is Analog voltageV c Analog currentI c And current multipleIbsOrder-makingV 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, whenIbsAt > 1.5, the real point is considered to be the inflection point.
Taking the measured voltage value of 1.35V as an example, it is judged 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 1.179-1.276;
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, it can be considered to be the inflection point or to have been in the vicinity of the inflection point.
Taking the measured voltage value of 2.71V as an example, judging whether the measured voltage value is an inflection point of a 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。Ibsexceeding 1.5 reaches 2, which can be considered to be the inflection point or to have been in the vicinity of the inflection point.
Taking the measured voltage value of 5.4V as an example to judge whether the measured voltage value is the inflection point of a 40Hz curve:
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。Ibsexceeding 1.5 reaches 2, which can be considered to be the inflection point or to have been in the vicinity of the inflection point.
the sampling point number is 100 points per cycle, the T-RMS calculation mode is to calculate the square root value of the sampling points, for example, 100 sampling points are collected, and the obtained sampling set is [ [A i1 ,A i2 …A i100 ]At the time of calculation
Wherein G (i) is a full wave effective value.
In this example, the 10Hz and 20Hz curves stopped with only the inflection point, and only the 40Hz curve was measured in its entirety. As shown in fig. 3, the data after 20Hz to 2.71V were none, nor the data after 10Hz to 1.352V. The missing data of the two are required to be complemented by the actually measured 40Hz signal, and the voltage of the transformer is reduced in the same proportion as the voltage of the transformer at each frequency, and the current is basically different, so that the missing data points of 20Hz and 10Hz are the same as the current of 40Hz, and the voltage is one half and one fourth of the voltage point of 40Hz respectively. For example, a point of 5.7V, 2.85V after 20Hz conversion, 1.425V after 10Hz conversion, and so on. The measured values and the complement values of the curves at 10Hz and 20Hz are shown in Table 1, and the curves formed by the data in Table 1 are shown in FIG. 4, thereby obtaining complete graphs corresponding to the three frequencies.
TABLE 1
The FFT method is adopted to calculate the mode to be related to the frequency, 3 variables are firstly established and are respectively the real part R (j), the 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 then the effective value under different frequencies can be obtained.
The calculation mode is the same as the calculation mode of the mixed signals with different frequencies output by the DAC, and the trigonometric function is processed to obtain values with different frequencies.
In order to prevent the tested transformer from being saturated in advance, the signals with the volt-ampere characteristic curves reaching the inflection points are eliminated one by one, the curve obtained by the last voltage signal is complete, the eliminated voltage signals are missing after the inflection points, and the curve is complemented according to the frequency proportion, so that a large amount of labor cost can be saved, and the testing efficiency is improved.
Example 2
The embodiment is a system for implementing a composite frequency test by using a broadband volt-ampere characteristic meter, as shown in fig. 5, 6 and 7, including an arbitrary wave generating module 1, a calculation and 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 transformer to be tested; 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 generation 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 step-up/step-down transformer is used for improving the output voltage of the power amplification source so as to realize that multiple gears all have good output resolution;
the sampling module 3 is used for collecting the output voltage and the output current of the tested transformer;
the calculation and analysis module 2 is used for obtaining volt-ampere characteristic curve data of each voltage signal by utilizing 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 utilizing a T-RMS algorithm, and scaling the volt-ampere characteristic curve data of the last voltage signal according to a frequency ratio to complement curve waveforms after the inflection points of the eliminated signals;
the display module is used for displaying volt-ampere characteristic curves of 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, wherein an input end of the voltage amplifier 11 is connected with an output end of the arbitrary wave generating module 1, and an output end of the voltage amplifier 11 and an output end of the triangular wave generator 12 are both connected with 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, and an output end of the comparator 13 is connected with 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 partial circuit includes an H-bridge circuit 15, an output filter 16 and a load 17, which are sequentially connected, the H-bridge circuit 15 is powered by a high-power regulated power supply 18, the pulse width modulation signal generated by the first partial circuit drives the IGBT to perform high-frequency switching at the H-bridge circuit 15, the filter filters out the high-frequency component, and then the load 17 obtains a high-power output waveform as the same as the input composite voltage signal, and the output power depends on the withstand voltage and the allowed current value of the IGBT device.
In this embodiment, the arbitrary wave generating module 1 uses a 12-bit DAC in the main control, and since the main control is powered by 3.3V, the output voltage is between 0 and 3.3V, the output sine wave does not have a negative half cycle, and an offset is required to be performed on the waveform output by the main control, and the offset is 1.65V (i.e., half of 3.3V); thus, the main control can only output sine waveforms with the peak value of 0-3.3V, and the effective value is approximately 1.167V; the external operational amplifier circuit deducts the offset of 1.65V by hardware and amplifies the waveform to about 7V, fixes the trigger frequency of the timer of the DAC, and changes the data table in the chip memory, thus the DAC can output various waveforms with different frequencies and different amplitudes.
The random wave generating circuit is used for generating voltage signals with random waveforms, the random wave generating circuit is realized by a DAC (digital-to-analog converter) in the main control MCU, the direct current power supply is used for supplying power, the main control adjusting software codes can be used for generating signal quantities of direct current, alternating current and other random 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 by matching with the functions of the DMA (direct memory access) and the TIM (timer) inside the chip, without any intervention of the CPU. The triggering of DMA (direct memory access) is triggered by timing overflow of an internal TIM (timer), and after triggering, the array data stored in the internal memory is automatically sent to a register of a DAC (digital-to-analog converter) and is output by the DAC (digital-to-analog converter). Therefore, the output frequency can be changed only by changing the count overflow value of the timer; changing the array data in the memory can change the output waveform. Any integer single frequency test between 10Hz and 1kHz is supported, the voltage is 0-240V, and the maximum power is 3.5kW.
The alternating current signal and the frequency of the power frequency power grid are all changed at the moment, the risk of interference by the power grid exists, and the repeatability of the test is low. The waveform signal generated by the waveform generation circuit has very stable size, composition and frequency. Under the conditions of 50Hz and 6.3V output of effective values, the output amplitude variation is lower than 0.1%, and the frequency variation is lower than 0.01%, so that the same test condition is ensured. However, the module generates a voltage signal without any driving capability, and the power amplification source is required to amplify the signal for use.
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 normal operation is recommended to be within 120V, 20A-2.4 kW.
The reason for setting up the step-up/step-down transformer: the power amplification source and the signal finally output to the tested transformer need to be isolated, and the tested product may not need such high voltage or the voltage is insufficient, so that a high-power step-up/step-down device needs to be matched, the 0-120V output of the power amplification source is converted into a multi-gear output voltage of 0-240V, and each gear has good output resolution.
The sampling measurement module uses an ADC (analog-to-digital converter), is generated by ADI company, has the model of AD7606, is a 16-bit and 8-channel synchronous sampling AD chip, and has a parallel sampling rate of up to 200ksps. AD7606 is one of the most commonly used ADC sampling chips in current power systems. Analog input clamping protection, a second-order anti-aliasing filter, a track-and-hold amplifier, a 16-bit charge redistribution successive approximation type ADC (analog to digital converter) kernel, a digital filter, a 2.5V reference voltage source, a buffer, and high-speed serial and parallel interfaces are integrated on an AD7606 chip. AD7606 is powered by a 5V single power supply, does not need positive and negative double power supplies, and supports bipolar signal input of +/-10V or +/-5V. All channels can be sampled at rates up to 200ksps while the input clamp protection circuit can withstand voltages up to + -16.5V. Currently, AD7606 has been widely used in power line detection and protection systems, multiple motor control, instrumentation and control systems, multi-axis positioning system nuclear Data Acquisition Systems (DAS).
While the invention has been described in terms of specific embodiments, it will be appreciated by those skilled in the art that the invention is not limited thereto but includes, but is not limited to, those shown in the drawings and described in the foregoing detailed description. Any modifications which do not depart from the functional and structural principles of the present invention are intended to be included within the scope of the appended claims.
Claims (7)
1. A method for implementing a composite frequency test using a broadband voltammetry, comprising:
step 1, inputting composite voltage signals mixed with voltage signals with different frequencies to a transformer to be tested according to the requirements; the specific process is as follows:
step 1.1, setting the number of points per cycle of DAC frequency asNIf the output amplitude is ac and the number of voltage signals to be mixed is n, n tables are built in the memory, the data values calculated by sine waves of all signals in the composite voltage signals are respectively stored, and the frequency values respectively correspond toA 1 ，A 2 .....A n Each frequency correspondence table forms a set of [ respectively ]A 11 ,A 12 ,A 13 ,…A 1N ]，[A 21 ,A 22 ,A 23 ,…A 2N ]、[A 31 ,A 32 ,A 33 ,…A 3N ]......[A n1 ,A n2 ,A n3 ,…A nN ]，
Wherein:itake the value of 1 ton，jTake the value of 1 toN；A ij Representing the data values calculated in terms of sine waves,Ma bit count value representing the DAC;
step 1.2, after obtaining the memory table, mixing proportionallynThe signals are fed into the output buffer table of the DAC,nthe signal duty ratios are respectivelyK 1 ，K 2 ......K n Then
Wherein H is ij The method is characterized in that a voltage signal to be mixed is output from an output buffer table, and a mixed waveform is obtained after the voltage signal to be mixed is processed by a power amplification source and a step-up/step-down transformer;
step 2, gradually increasing the input voltage of a tested transformer, detecting the output voltage and current of the transformer in real time, adopting an FFT algorithm to obtain the volt-ampere characteristic curve data of each signal in the composite voltage signal, simultaneously calculating the inflection point 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 the voltage increases by 10% and the current increases by 50%; the specific process for calculating the inflection point of each signal volt-ampere characteristic curve in the composite voltage signal comprises the following steps:
step 2.1, estimating the range of inflection points of each curve from the curve data obtained in step 1V imin ,V imax ]，[I imin ,I imax ]The method comprises the steps of carrying out a first treatment on the surface of the Setting the measured voltage toV is The actual measured current isI is Analog voltageV ic Analog currentI ic And current multipleIbsOrder-makingV ic =V is 1.1, calculationI ic =[(V ic -V imin )/(V imax -V imin )]*(I imax -I imin )+I imin ，Ibs=I is /I ic ；
Step 2.2, whenIbsWhen the real point is more than 1.5, the real point is considered to be an inflection point;
step 3, continuously increasing the input voltage, eliminating the signals of which the volt-ampere characteristic curves reach inflection points one by one until the last voltage signal is left, switching the calculation mode from the FFT algorithm to the T-RMS algorithm, continuously increasing 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;
step (a)4, complementing the volt-ampere characteristic curve after the removed signal inflection point according to the waveform data obtained in the step 3 so as to obtain the volt-ampere characteristic curves corresponding to the voltage signals with different frequencies in the composite voltage signals at the same time; the specific process is as follows: setting the frequency of the last voltage signal toA n Dividing the frequencies of the other signals with the frequencies removed respectively 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 to complement the curve waveform after the inflection points of the voltage signals at the other frequencies.
2. The method for realizing the composite frequency test by using the broadband volt-ampere characteristic meter according to claim 1, wherein the method for calculating the composite frequency is characterized by adopting a T-RMS method: the sampling point number is per cycleNThe calculation mode of the T-RMS of each point is to calculate the square average root value of the sampling point and collectNThe sampling points form a sampling setA i1 ,A i2 ,A i3 ,…A iN ]At the time of calculation
Wherein G (i) is a full wave effective value.
3. The method for realizing composite frequency test by using broadband volt-ampere characteristic instrument according to claim 1, wherein the FFT method calculation mode is related to frequency, 3 variables are established firstly, namely a real part R (j), an imaginary part Ig (j) and a frequency effective value
The sampled analog-to-digital conversion value CD (j) is calculated as follows:
then
。
4. A system for implementing a composite frequency test using a wideband voltammetry, which is suitable for the method for implementing a composite frequency test using a wideband voltammetry according to any one of claims 1 to 3, and is characterized by comprising an arbitrary wave generation module, a calculation analysis module, a sampling module and a display module, wherein:
the arbitrary wave generation module is used for inputting composite voltage signals mixed with voltage signals with different frequencies to the tested transformer;
the sampling module is used for collecting the output voltage and the output current of the tested transformer;
the calculation analysis module is used for obtaining curve data of each voltage signal by utilizing 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 utilizing a T-RMS algorithm, and scaling the curve data of the last voltage signal according to a frequency ratio to complement curve waveforms after the inflection points of the eliminated signals;
the display module is used for displaying volt-ampere characteristic curves of voltage signals with different frequencies in the composite voltage signal.
5. The system for implementing a composite frequency test using a broadband voltammetric device according to claim 4, wherein said arbitrary wave generation module comprises an arbitrary wave generation circuit, a power amplification source, and a step-up/step-down transformer, wherein:
the arbitrary wave generation 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 step-up/step-down transformer is used for improving the output voltage of the power amplification source so as to realize that multiple gears all have good output resolution.
6. The system for realizing the composite frequency test by using the broadband volt-ampere characteristic meter according to claim 5, wherein the first partial 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 sent 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.
7. The system for realizing the composite frequency test by using the broadband volt-ampere characteristic instrument according to claim 5, wherein the second partial circuit comprises an H-bridge circuit, an output filter and a load which are sequentially connected, the H-bridge circuit is powered by a high-power voltage-stabilizing power supply, the pulse width modulation signal generated by the first part drives the IGBT to carry out high-frequency switching at the H-bridge circuit, the filter filters high-frequency components and then obtains a high-power output waveform which is the same as the input composite voltage signal at the load, and the output power depends on the withstand voltage and the allowed current value of the IGBT device.
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