CN112799001A - Mutual inductor excitation characteristic testing method and system based on minimum variance algorithm - Google Patents
Mutual inductor excitation characteristic testing method and system based on minimum variance algorithm Download PDFInfo
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Abstract
The invention discloses a mutual inductor excitation characteristic testing method and system based on a minimum variance algorithm, and relates to a testing technology of elements of a power system. The scheme is provided aiming at the problem that the testing is difficult due to overhigh power frequency voltage in the prior art. Firstly, a power loss mathematical model is established, then, an optimal parameter is searched to form an accurate loss mathematical model, and finally, the accurate loss mathematical model is utilized to restore excitation characteristic data and parameters of the mutual inductor under power frequency. The low-frequency test voltage has the advantage that the excitation characteristic test of almost all types of electromagnetic transformers can be completed by the low-frequency test voltage. The low-frequency test data and the power-frequency test data are kept completely consistent. After the frequency of the test voltage is greatly reduced, the test system can achieve very small volume and very light weight, power frequency is avoided during the test transformation ratio, and the test can be completed at higher test voltage to obtain a more accurate and stable test result. The resolution of the test result is far greater than that of a mechanical pressure regulating mode, and the test method is richer and more accurate.
Description
Technical Field
The invention relates to a method and a system for testing a mutual inductor, in particular to a method and a system for testing the excitation characteristic of the mutual inductor based on a minimum variance algorithm.
Background
Electromagnetic mutual inductors and voltage transformers are collectively called mutual inductors and are one of the most important measuring and protecting devices in an electric power system. The transformer for protection is a first ring in a relay protection system and is used for providing accurate and reliable fault signals for the protection system. In order to ensure that the relay protection system can work normally, the signal transmission capability and reliability of the mutual inductor in a fault state are the most important items for testing and detecting. The main index related to the transformer is to check whether the excitation characteristic inflection point voltage and each transformer parameter corresponding to the excitation characteristic curve can meet the design requirement.
When an excitation characteristic test is performed on the electromagnetic transformer, a test voltage and a test capacity required by equipment are determined by a saturation characteristic of the transformer. However, in the practical application process, the voltage of the knee point of the transformer for protecting the system with higher voltage level can reach thousands of volts or even dozens of kilovolts. This makes extensive field verification of such transformers almost impossible for test equipment, thus greatly limiting the detection capabilities of the transformers.
And for the mutual inductor with the saturation voltage not more than 2000V, the excitation characteristic can be detected in a power frequency mode, but the corresponding equipment is very heavy. And because such devices are typically based on a mechanical regulator approach, the resolution of the output voltage is determined by the number of regulator coil turns, and therefore the resolution of the excitation characteristics is typically very low. The mutual inductor tests of high saturation voltage and low saturation voltage cannot be compatible with each other, and the application range is narrow.
In the application of the transformer excitation characteristic with very high protection voltage, a low-frequency test mode is adopted in some schemes, test voltage is applied under lower frequency to enable the transformer to enter magnetic saturation, but the obtained excitation curve is based on data obtained under the low-frequency test condition and power frequency test data required by the actual application environment, so that great difference exists, and therefore sufficient persuasion is lacked for the actual test detection and judgment basis.
Disclosure of Invention
The invention aims to provide a transformer excitation characteristic testing method and system based on a minimum variance algorithm, so as to solve the problems in the prior art.
The invention relates to a mutual inductor excitation characteristic testing method based on a minimum variance algorithm, which comprises the following steps: establishing a power loss mathematical model; searching the optimal parameters of the power loss mathematical model to form an accurate loss mathematical model; restoring the excitation characteristic data and parameters of the mutual inductor under power frequency by using an accurate loss mathematical model;
the power loss mathematical model is as follows: pw (k 1 f Fm) mhn+k2*f2*Fm2+k3*(f*Fm)1.5(ii) a Wherein Pw is the total active loss of the transformer, f is the test voltage frequency, k1, k2, k3 and hn are respectively undetermined parameters, and Fm is the maximum magnetic flux in a cycle.
The searching process of the optimal parameters comprises the following steps: inputting power frequency test voltage to the mutual inductor, and performing parameter scanning; respectively calculating theoretical power loss Pwlfc for each group of parameters k1, k2 and k3, testing voltage and current of the transformer under the current power frequency test voltage to obtain actual measurement power loss Pwlf, and calculating variance Q: q ═ sigma (Pwlfc-Pwlf)2(ii) a Extracting parameters hn, k1, k2 and k3 corresponding to the minimum Q value as optimal parameters;
the substep A is as follows: let the parameter hn be an extreme value in the value range, and determine a group of parameters k1, k2 and k3 by using a linear regression minimum variance method under the current power frequency test voltage; stepping hn to another extreme value in the value range of hn, and determining another group of parameters k1, k2 and k3 by using the linear regression minimum variance method; until the parameters k1, k2 and k3 with the parameter hn in the value range are scanned according to groups.
The power frequency test voltage range is 0-160V.
The value range of the parameter hn is 1-3.
The parameter hn change step size is 0.01.
The step of utilizing the accurate loss mathematical model to restore the excitation characteristic data and parameters of the mutual inductor under the power frequency is completed under the frequency lower than the power frequency test voltage; and defining the test voltage with the frequency lower than the power frequency test voltage as the low-frequency test voltage.
Under the low-frequency test voltage, the electromotive force V is integrated to obtain a magnetic flux F value, active loss Pwl and reactive loss Pq corresponding to all maximum magnetic fluxes Fm are gradually recorded, and an accurate loss mathematical model is obtained through calculation; converting the total active loss Pw to obtain corresponding power frequency loss under the same maximum magnetic flux Fm; and then, synthesizing the Pw and the Pq under the power frequency to obtain the total excitation current Ie corresponding to Fm, thereby obtaining an accurate power frequency excitation characteristic curve.
Starting boosting from 0, recording a voltage value corresponding to each sampling point and a magnetic flux curve F (t) obtained by integrating the voltage instantaneous value, and recording the maximum magnetic flux Fm corresponding to each cycle magnetic flux curve to obtain a hysteresis loop F (t) -I.
A mutual inductor excitation characteristic test system based on a minimum variance algorithm comprises an industrial personal computer, an SDP mainboard, a sampling control panel, a change-over switch, a voltage type power amplifier and a current type power amplifier;
the industrial personal computer is electrically connected with the sampling control panel through the DSP mainboard; the sampling control panel collects the voltage of the mutual inductor by a four-wire method and also collects the current at the low-voltage side of the power output end, and respectively controls the voltage type power amplifier and the current type power amplifier to output power to the mutual inductor through the power output end; the switch is used for switching the power output end between a voltage type power amplifier and a current type power amplifier;
the industrial personal computer tests the mutual inductor by controlling the DSP mainboard and the sampling control panel and utilizing the mutual inductor excitation characteristic test method.
The acquisition control panel is internally provided with a plurality of voltage acquisition grades and a plurality of current acquisition grades, and the corresponding relay arrays are used for realizing gear switching respectively.
The method and the system for testing the excitation characteristic of the mutual inductor based on the minimum variance algorithm have the advantages that the mutual inductor is saturated at low frequency, and then required power frequency test data are converted according to an accurate model. The low-frequency test voltage can complete excitation characteristic tests of almost all types of electromagnetic transformers. An accurate loss mathematical model of the excitation loss of the mutual inductor is obtained through calculation based on a minimum variance algorithm and then converted to power frequency, so that low-frequency test data and power frequency test data can be kept completely consistent. After the frequency of the test voltage is greatly reduced, the test system can achieve very small volume and very light weight, power frequency is avoided during the test transformation ratio, the test can be completed at higher test voltage, and a more accurate and stable test result can be obtained after a power frequency signal is filtered. The excitation characteristic test is carried out by generating the test voltage with variable frequency, the output voltage is controlled by 16-bit DA, and the resolution of the test result is far greater than that of a mechanical voltage regulation mode, so that the test result is richer and more accurate.
Drawings
Fig. 1 is a schematic diagram of a transformer excitation characteristic testing system according to the invention.
Fig. 2 is a schematic diagram of the DSP board.
Fig. 3 is a schematic structural diagram of an optocoupler output control unit in the sampling control board;
FIG. 4 is a schematic structural diagram of a voltage and current acquisition array in the sampling control board;
fig. 5 is a schematic structural diagram of a voltage-current power amplifier control unit in the sampling control board.
Fig. 6 is a schematic flow chart of a method for testing the excitation characteristics of the transformer according to the invention.
Detailed Description
As shown in FIG. 1, the system for testing the excitation characteristics of the mutual inductor based on the minimum variance algorithm mainly comprises an industrial personal computer, a DSP (digital signal processor) main board, a sampling control board, a change-over switch, a voltage type power amplifier and a current type power amplifier. The sampling control panel mainly comprises an optocoupler output control unit, a voltage and current acquisition array and a voltage and current power amplifier control unit.
The built-in embedded XPE system of industrial computer, communicate through USB2.0 interface and DSP mainboard connection, embedded XPE system application program rank is adjusted at real-time level so that the collection that can be quick comes from the voltage of DSP mainboard, current signal.
As shown in fig. 2, a core controller of the DSP motherboard is TMS320F 2812. The DSP mainboard is integrated with a USB2.0 communication chip CY7C68013A, an AD acquisition chip AD7656 and a DA output control chip AD 669. The DSP controller completes communication and data exchange with the industrial personal computer through the USB chip. In the test process, the DSP controller adopts an internal timer to control the generation of an interrupt every 50us, and when the interrupt arrives, the data of the 16-bit DA converter AD669 is read and written in real time through the IO port. The amplitude of the output voltage is varied in accordance with a variable frequency sinusoidal signal, with no less than 400 data points per cycle update so that the distortion level of the sinusoidal signal is as low as possible. And when each interrupt arrives, the data of the AD converter AD7656 is read in through the IO port, and the AD value corresponding to the voltage and the current in the coil is obtained in real time. The collected data are transmitted to an industrial personal computer through a USB interface for storage and processing. The DSP mainboard changes the output state of the optical coupler through the optical coupler array from the high and low levels changed by the output port parameter 0/1 of the relay control unit of the DSP controller to the sampling control panel, thereby controlling the change of the switching of the relay.
As shown in fig. 3, the IO signal of the optocoupler output control unit from the DSP motherboard is connected to the negative terminal of the optocoupler input loop, and the positive terminal of the optocoupler control is connected to the 3.3V power supply through a current limiting resistor. When the IO pin of the DSP mainboard is pulled to a high level or is in a high resistance state, the output of the optical coupler is cut off, and the relay is in a closed state. When the IO pin of the DSP mainboard is pulled to a low level, the relay control is enabled, and the relay acts. When the system is reset, the IO pin of the DSP mainboard is in a high-resistance state, and all relays can not act, so that the relays can be controlled in any state.
As shown in fig. 4, all voltage sampling signals of the voltage and current acquisition array are subjected to voltage division by resistors and then enter a differential operational amplifier AD8221 for adjustment, so that the amplitude of the voltage signal input to the AD converter is ensured to be within a range of-10V to 10V. Before entering the AD8221, a double-end voltage stabilizing circuit is arranged to clamp the input voltage entering the AD8221 not to be too high so as to damage an operational amplifier circuit. The voltage acquisition of different ranges is switched by an internal relay, so that the aim of accurately measuring each voltage range is fulfilled.
The current sampling resistor is connected in series at the low-voltage end of the power output loop, and when current measurement with different measuring ranges is carried out, the measuring range is changed by the testing system through switching the resistance value of the current sampling resistor. The voltage at the two ends of the sampling resistor enters an AD8221 operational amplifier for processing after voltage stabilization clamping protection, and the signal is adjusted to be within-10V and enters an AD converter for collection.
As shown in fig. 5, the voltage-current power amplifier control unit receives a DA control signal from the DSP motherboard, and directly outputs the DA control signal to the voltage-type power amplifier for controlling voltage output after being followed by the OP07 operational amplifier, and because the control voltage amplitudes of the voltage-type power amplifier and the current-type power amplifier are different from each other, the control signal of the current-type power amplifier is derived from the divided DA signal, and is output after being followed by another OP07 operational amplifier.
The voltage-mode power amplifier and the current-mode power amplifier of the test system are integrated power amplification units, and the output voltage range of the power amplification units is AC0-160V, and the output current range of the power amplification units is AC 0-1A. The output of the voltage-mode power amplifier is scaled by the control signal with an amplification factor of about 22, i.e., the control DA control signals AC 0-7V can generate test voltages of AC0-160V with the same frequency and phase at the output of the voltage-mode power amplifier. The current mode power amplifier functions similarly to a voltage mode power amplifier, and its output current is substantially at the same frequency and in phase with the control signal. The voltage-mode power amplifier and the current-mode power amplifier can also generate constant direct-current voltage and direct current for testing through the direct-current control signal. When the system carries out direct current resistance test, the current type power amplifier is in a working state, the control signal at the moment is direct current, and the amplitude of the output current is about 0.5A direct current. And the power output of the mutual inductor is switched by the power amplifier type through the change-over switch.
The method for testing the excitation characteristic of the transformer can be carried out by using the testing system, and the testing process is shown in fig. 6. Firstly, inputting and configuring test parameters on an industrial personal computer software interface; the industrial personal computer transmits the configured test parameters to the DSP mainboard; and after the parameter configuration is finished, the DSP mainboard finishes the self-checking of the DA converter, the AD converter and the external wiring. And during self-checking, the DSP controller outputs a voltage signal with a small amplitude, and performs reasoning according to the currently selected test template and the corresponding test logic to check whether the output signal and the feedback signal accord with the current wiring logic. If the wiring logic is correct, the test continues, otherwise a report of a test wiring error is given.
After the test connection line is judged, the DSP controller further configures the current measurement voltage, the current measurement current and the voltage-current power amplifier working mode according to the test template. And starting power amplifier output, acquiring voltage and current signals in real time in the process, continuously detecting whether the test voltage and current and the test parameters reach the condition of completing the test, and transmitting all the acquired voltage signals and current signals to the industrial personal computer for storage in the process. And when the test is finished, the industrial personal computer performs data processing and calculation according to all the voltage and current signals acquired in the test process.
Before a transformer excitation characteristic test is carried out, a mathematical model of transformer power consumption is determined through scanning by a minimum variance algorithm. The test system measures the coil exciting voltage, exciting current and power loss at different frequencies within the range of 0.1Hz to 60Hz and adjusts the parameters of the search model. The method comprises the steps of applying power frequency test voltage and low frequency test voltage to two ends of a transformer coil respectively, measuring parameters such as exciting current, active power loss, reactive power loss and maximum magnetic flux under different voltages in the process of boosting, and forming an excitation characteristic test data table under two frequencies respectively. And searching out an optimal model parameter value, so that the quadratic variance sum of the actual loss value and the theoretical calculation loss value is minimum under different frequencies obtained by the theoretical calculation of the model and the same magnetic field intensity, and taking a corresponding parameter when the quadratic variance sum is minimum as an accurate parameter of the model.
The power loss mathematical model of the mutual inductor is as follows:
Pw＝k1*f*Fmhn+k2*f2*Fm2+k3*(f*Fm)1.5
pw corresponds to the total active loss of the transformer, f is the test voltage frequency, and B is the magnetic field strength in the coil. k1, k2, k3 are constants relating to the transformer material and the core size, respectively, and the corresponding losses are the hysteresis loss, the eddy current loss, and the residual loss of the core, respectively. Fm is the maximum magnetic flux in a cycle, hn is a parameter related to an iron core material and the like, and the value range of the parameter is about 1-3.
Firstly, under a power frequency test voltage, taking test data within AC0-160V as reference, and respectively calculating the maximum magnetic flux, the excitation voltage, the excitation current, the active loss and the reactive loss corresponding to each excitation data point. In the data table obtained by testing at the power frequency voltage, the unknown parameters of the model are k1, k2, k3 and hn. Since hn is a value in the range of 1 to 3, it can be assumed that hn is 1, and values of k1, k2 and k3 are calculated by sampling linear regression minimum variance method from excitation voltage current and magnetic flux data obtained by a test in the range of AC0 to 160V. On the basis, the theoretical power loss Pwlfc at the position Fm corresponding to each excitation current in the low-frequency excitation test data is calculated through the model, and the variance of theoretical values and measured values under hn is constructed through the theoretical power loss Pwlfc and the measured power loss Pwlf:
Q＝∑(Pwlfc-Pwlf)2
and then, the hn is increased progressively according to the step length of 0.01, corresponding Q values are respectively calculated, and the hn value corresponding to the minimum Q value is taken as an accurate model parameter. Thereby obtaining an accurate mathematical model of the losses and corresponding values of k1, k2, k3 and hn.
When the mutual inductor excitation characteristic test is carried out, the excitation characteristic of the mutual inductor coil is further measured by using lower frequency and is saturated, and the low-frequency voltage, the current and the excitation loss in the process are recorded. And restoring excitation characteristic data and parameters of the mutual inductor at the power frequency according to the voltage, current and excitation loss measured and calculated at the low frequency and the accurate mathematical model of the mutual inductor measured and calculated before.
The method comprises the steps of dividing the exciting current of a mutual inductor under the same exciting voltage into active loss current and reactive loss current, wherein the active loss current corresponds to active loss Pw, and the value of the active loss Pw changes along with the change of the testing voltage frequency of the mutual inductor. The reactive loss current corresponds to the reactive power, and the value thereof does not change when the maximum magnetic flux Fm is fixed, so that the reactive current value Iq is the same for the same maximum magnetic flux Fm. The system can obtain the value of the magnetic flux F of the iron core by integrating the electromotive force V under low-frequency test voltage, and the magnetic flux F of the iron core can be saturated by reducing the test frequency and enabling the lower test voltage. And converting the Pw by using the accurate loss mathematical model obtained by calculation to obtain the corresponding power frequency loss Pw under the same Fm. And then, synthesizing the Pw and the Pq under the power frequency to obtain the total excitation current Ie corresponding to Fm, thereby obtaining an accurate power frequency excitation characteristic curve.
And starting boosting from 0, recording a voltage value corresponding to each sampling point and a magnetic flux curve F (t) obtained after integrating the voltage instantaneous value, and recording the maximum magnetic flux Fm corresponding to each cycle magnetic flux curve to accurately obtain a hysteresis line F (t) -I of the magnetic flux passing through the iron core of the transformer to the excitation current.
The test system can change the amplitude and frequency of the output voltage and current in real time by adjusting the value of the DA output, and can accurately measure the starting point and the end point of the cycle of each output voltage waveform. The testing system collects voltage signals and current signal waveforms of the transformer coil in real time, and calculates a phase angle corresponding to voltage and current as well as active loss and reactive loss loaded on the transformer coil.
The voltage type power amplifier and the current type power amplifier are controlled by a sine signal generated after the DA signal output by the DSP mainboard is subjected to amplitude adjustment through the signal acquisition board, and the power output selection is controlled and switched by the DSP mainboard. The method of measuring the coil resistance by adopting a four-wire method is adopted, and a voltage signal on a transformer coil is introduced into a voltage measuring channel of a system through a special measuring wire. The allowable input voltage range is AC0-160V, and in order to accurately measure the voltage amplitude, the voltage amplitude is set by steps in the system, namely 0-1V, 0-10V, 0-80V and 0-160V, so as to ensure that the voltage of all signal segments can be accurately measured. The current measuring channel is built in the power output loop, and the measurement of four gears of 10A, 2A, 0.2A and 0.02A is built in, so as to realize the accurate measurement of the current in the range of 0.1mA to 10A.
And measuring the direct current resistance value of the transformer iron core through direct current output, recording the voltage amplitudes at two ends of the transformer at high speed in the process, and roughly calculating to obtain the maximum peak magnetic flux Fm of the transformer iron core through the integral of the voltage amplitudes. The maximum saturation voltage of the transformer at the power frequency and the test frequency required to be used when the low-frequency test is carried out can be estimated according to the maximum magnetic flux.
When the maximum saturation voltage of the mutual inductor does not exceed the maximum power frequency voltage output by the system, the system adopts a power frequency test mode to directly measure the excitation characteristic of the mutual inductor. And when the maximum saturation voltage exceeds the maximum output power frequency voltage, reducing the test frequency, wherein the lowest test frequency can be reduced to 0.1Hz, and the test frequency selected by the test system meets (Vo) 50.0/f) > Vknee, wherein Vo is the maximum output voltage of the system, and Vknee corresponds to the saturation voltage of the transformer.
The test system can split the whole test process into several independent sub-steps: 1. completing a direct current resistance test of the transformer coil; 2. carrying out demagnetization processing of the mutual inductor; 3. measuring the turns ratio of a transformer coil; 4. measuring the specific difference and the angular difference of the mutual inductor; 5. and measuring the excitation characteristic of the transformer.
In the direct current resistance test of the mutual inductor, a test system controls a current power amplifier to output DC 0.5A test current so that a coil of the mutual inductor reaches magnetic saturation, and then the ratio of the voltage and the current after the magnetic saturation is recorded and is used as the direct current resistance of the coil of the mutual inductor. During the charging process, the voltage at the end of the 2 nd end of the transformer coil can be collected at a high speed in real time, and integration is carried out, so that a change curve of the internal magnetic flux of the transformer coil is obtained.
The transformer demagnetization test means that after the direct current resistance test of the transformer is completed, a coil of the transformer has a large amount of remanence, and at the moment, the purpose of demagnetizing the coil of the transformer is achieved by slowly boosting an alternating current voltage signal and then reducing the voltage.
The transformer turn ratio measurement means that a test system outputs a test voltage with frequency higher than high frequency to the 2 ends of the transformer coils, measures induced voltage at the 2 ends of the other coils of the transformer, controls the exciting current of the coils to be at a very low amplitude, and can calculate the ratio of the accurate electromotive force of the 2 coils, namely the turn ratio of the transformer, by combining the exciting current measured at the moment.
The transformer specific difference angular difference measurement means that power frequency test voltage is applied to the end 2 of the transformer coil, all other coils are kept open-circuited, and the data of the transformer coil excitation voltage and excitation current are recorded in the process from 0 to the maximum power frequency test voltage which can be output, and the data can be used for subsequent excitation characteristic test modeling of the transformer. Usually, the applied excitation voltage under the power frequency is only a part of the whole process of the excitation characteristic of the transformer, even a very small part, but the test system can obtain a large number of excitation voltage-to-excitation current data points by improving the resolution of the applied voltage, and parameters such as active loss, reactive loss and the like in the process.
The measurement of the excitation characteristic of the mutual inductor means that a test system selects required low-frequency test frequency according to the approximate saturation voltage of the mutual inductor obtained by the direct-current resistance, and then the low-frequency test voltage is boosted from 0 and applied to the coil 2 side of the mutual inductor until the mutual inductor reaches magnetic saturation. At the moment, the test system continuously detects parameters such as coil voltage, coil current, magnetic flux of a coil iron core, active loss, reactive loss and the like, and stores all test data in the process. And after the test current reaches the set target stop current, the mutual inductor enters a deep saturation test to be ended. The test system selects excitation data under power frequency test voltage and a part of low-frequency excitation test data approximately consistent with the test voltage range of the power frequency voltage according to all test data stored in the industrial personal computer, and models to obtain an accurate transformer coil active loss mathematical model by adopting a minimum quadratic variance mode. All actually measured power frequency excitation characteristic data active loss and all low-frequency excitation characteristic test data active loss participating in calculation in the low-voltage section under the mathematical model are completely matched with the calculated value of the model. And then correcting subsequent higher excitation voltage test point data of the excitation characteristic by using the mathematical model, changing the excitation current corresponding to the active power, and then carrying out secondary synthesis with the reactive current to obtain accurate excitation current Ie, wherein Ie at the moment is the corresponding excitation characteristic loss current under the power frequency test condition, and the magnetic flux corresponding to the test voltage point at the moment can be converted into the corresponding excitation voltage under the power frequency. And the low-frequency excitation characteristic test curve is completely restored to a power frequency voltage test curve after model conversion.
It will be apparent to those skilled in the art that various other changes and modifications may be made in the above-described embodiments and concepts and all such changes and modifications are intended to be within the scope of the appended claims.
Claims (10)
1. A mutual inductor excitation characteristic test method based on a minimum variance algorithm is characterized by comprising the following steps: establishing a power loss mathematical model; searching the optimal parameters of the power loss mathematical model to form an accurate loss mathematical model; restoring the excitation characteristic data and parameters of the mutual inductor under power frequency by using an accurate loss mathematical model;
the power loss mathematical model is as follows: pw (k 1 f Fm) mhn+k2*f2*Fm2+k3*(f*Fm)1.5(ii) a Wherein Pw is the total active loss of the transformer, f is the test voltage frequency, k1, k2, k3 and hn are respectively undetermined parameters, and Fm is the maximum magnetic flux in a cycle.
2. The method for testing the excitation characteristic of the mutual inductor based on the minimum variance algorithm as claimed in claim 1, wherein the search process of the optimal parameters is as follows: inputting power frequency test voltage to the mutual inductor, and performing parameter scanning; respectively calculating theoretical power loss Pwlfc for each group of parameters k1, k2 and k3, testing voltage and current of the transformer under the current power frequency test voltage to obtain actual measurement power loss Pwlf, and calculating variance Q: q ═ sigma (Pwlfc-Pwlf)2(ii) a Extracting parameters hn, k1, k2 and k3 corresponding to the minimum Q value as optimal parameters;
the substep A is as follows: let the parameter hn be an extreme value in the value range, and determine a group of parameters k1, k2 and k3 by using a linear regression minimum variance method under the current power frequency test voltage; stepping hn to another extreme value in the value range of hn, and determining another group of parameters k1, k2 and k3 by using the linear regression minimum variance method; until the parameters k1, k2 and k3 with the parameter hn in the value range are scanned according to groups.
3. The method for testing the excitation characteristic of the mutual inductor based on the minimum variance algorithm as claimed in claim 2, wherein the power frequency test voltage is in a range of 0-160V.
4. The method for testing the excitation characteristic of the mutual inductor based on the minimum variance algorithm as claimed in claim 2, wherein the parameter hn ranges from 1 to 3.
5. The method for testing the excitation characteristic of the mutual inductor based on the minimum variance algorithm, according to claim 4, wherein the parameter hn change step size is 0.01.
6. The method for testing the excitation characteristics of the mutual inductor based on the minimum variance algorithm as claimed in claim 1, wherein the step of restoring the excitation characteristic data and parameters of the mutual inductor at power frequency by using the accurate loss mathematical model is performed at a frequency lower than the power frequency test voltage; and defining the test voltage with the frequency lower than the power frequency test voltage as the low-frequency test voltage.
7. The method for testing the excitation characteristics of the mutual inductor based on the minimum variance algorithm according to claim 6,
under the low-frequency test voltage, the electromotive force V is integrated to obtain a magnetic flux F value, active loss Pwl and reactive loss Pq corresponding to all maximum magnetic fluxes Fm are gradually recorded, and an accurate loss mathematical model is obtained through calculation; converting the total active loss Pw to obtain corresponding power frequency loss under the same maximum magnetic flux Fm; and then, synthesizing the Pw and the Pq under the power frequency to obtain the total excitation current Ie corresponding to Fm, thereby obtaining an accurate power frequency excitation characteristic curve.
8. The method for testing the excitation characteristics of the mutual inductor based on the minimum variance algorithm as claimed in claim 1, wherein the voltage is increased from 0, the voltage value corresponding to each sampling point and the magnetic flux curve f (t) obtained by integrating the instantaneous voltage value are recorded, and the hysteresis loop f (t) -I is obtained by recording the maximum magnetic flux Fm corresponding to each cycle magnetic flux curve.
9. A mutual inductor excitation characteristic test system based on a minimum variance algorithm is characterized by comprising an industrial personal computer, an SDP mainboard, a sampling control panel, a selector switch, a voltage type power amplifier and a current type power amplifier;
the industrial personal computer is electrically connected with the sampling control panel through the DSP mainboard; the sampling control panel collects the voltage of the mutual inductor by a four-wire method and also collects the current at the low-voltage side of the power output end, and respectively controls the voltage type power amplifier and the current type power amplifier to output power to the mutual inductor through the power output end; the switch is used for switching the power output end between a voltage type power amplifier and a current type power amplifier;
the industrial personal computer tests the mutual inductor by controlling the DSP mainboard and the sampling control panel and by using the mutual inductor excitation characteristic test method as claimed in any one of claims 1 to 9.
10. The system for testing the excitation characteristics of the mutual inductor based on the minimum variance algorithm as claimed in claim 9, wherein a plurality of voltage acquisition grades and a plurality of current acquisition grades are arranged in the acquisition control board, and the corresponding relay arrays are respectively used for realizing gear switching.
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