A device and method for calibrating angle difference of wide-band resistor voltage divider

Abstract

A calibration device and method for a wide-band resistor voltage divider angle difference, comprising: a wide-band power acquisition and analysis system, comprising: a main control computer, a PXI controller and a digitizer; the PXI controller is respectively connected to the main control computer and the digitizer; the wide-band power acquisition and analysis system is used to perform high-speed synchronous sampling of the analog small signal passing through the voltage divider, and then transmit the data to the main control computer, and the signal is analyzed and processed by the compiled upper computer program; an electric power standard source is respectively connected to the main control computer, the voltage divider and the digitizer; the electric power standard source uses high-order harmonics to simulate the wide-band signal output to apply a working voltage to the voltage divider; the voltage divider is respectively connected to the electric power standard source and the digitizer as a device to be tested. The present invention adopts high-order harmonic simulation technology to generate a wide-band signal input to achieve accurate calibration of the voltage divider angle difference at different frequencies.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic measurement, and specifically refers to a calibration device and method for a wide-band resistor voltage divider angle difference. Background Art

[0002] With the rapid development of smart grid and new energy technology, higher requirements are put forward for the accuracy of power metering and the ability to measure broadband power. Whether it is the drive motor test of new energy vehicles, the efficiency evaluation of variable frequency motors, the real-time monitoring of photovoltaic power generation systems, the precise control of wind turbine converters, or the performance evaluation of DC-DC converters, these fields are facing the technical demand for accurate measurement of broadband electricity or broadband power. The broadband power measurement system is mainly composed of a broadband voltage divider, a broadband current sensor, and a broadband electricity data acquisition system. The broadband voltage and current to be measured are converted into two voltage signals adapted to the data acquisition system through a broadband voltage divider and a broadband current sensor, respectively, and the attenuated voltage and current are sampled at high speed and high accuracy, and then the discrete data obtained by sampling is analyzed and calculated to achieve the purpose of broadband power measurement. At present, the voltage channel of the main component used for broadband power measurement mainly adopts a broadband resistor voltage divider, and the highest frequency can reach MHz; the current channel can adopt a broadband shunt (frequency can reach 100kHz) or a broadband current sensor (frequency can reach MHz). In this measurement system framework, the angle difference of the voltage divider is a crucial influencing parameter. The phase difference between the low-voltage side output signal and the high-voltage side input signal of the voltage divider is the "angle difference" of the voltage divider. Due to the combined effect of various factors such as the different time constants of the resistor devices themselves, the connection method between the devices, and the structural design of the voltage divider during the design and development of the resistor divider, the voltage divider as a whole presents different impedance characteristics under the AC state. Therefore, the voltage divider will have different phase shift characteristics at different frequencies. In addition to the proportional error during the attenuation process of the voltage signal, the angle difference will also have a significant impact on the power measurement, especially in the high frequency band and low power factor. Therefore, accurate measurement, control and correction of the angle difference of the voltage divider is a prerequisite for accurate measurement of broadband power.

[0003] At present, there are several methods for calibrating the voltage divider angle difference:

[0004] (1) Stair climbing method:

[0005] The step climbing method is a method that uses dual-channel synchronous sampling technology to measure the phase angle deviation of the voltage divider. This method first uses two synchronous sampling channels, with one channel (such as CH1) as the reference channel and the other channel (such as CH2) as the comparison channel. First, a natural "0°" signal is synchronously input into the reference channel and the comparison channel to obtain the phase delay between the two synchronous sampling channels, and the obtained phase delay between the channels is corrected to 0°; secondly, a natural "0°" signal is directly input into the reference channel and the comparison channel after passing through the voltage divider to be calibrated (such as voltage divider No. 1), and the angle difference of voltage divider No. 1 can be obtained, so that the angle difference of voltage divider No. 1 becomes known; then, voltage divider No. 1 is connected to the reference channel as the reference, and voltage divider No. 2 is connected to the comparison channel, and the angle difference of voltage divider No. 2 is obtained by the above method; in this way, the angle difference calibration of voltage dividers with different ranges and different voltage divider ratios is realized by step-by-step transmission.

[0006] The step-climbing method is a method of gradually transferring from a low range to a high range, thus ignoring the voltage coefficient of the angle difference of the voltage divider being measured. In addition, for a voltage divider suitable for high voltage measurement, its phase angle deviation measurement needs to be transferred through multiple steps, and the transfer process will cause the accumulation of uncertainty.

[0007] (2) Method for tracing the phase angle deviation of the resistor divider based on the power thermoelectric comparator:

[0008] The phase angle deviation calibration system is composed of three core parts: zero power factor standard source, resistor voltage divider and power thermoelectric comparator. The zero power factor standard source is composed of a dual-channel signal generator, an AC voltage source, a positive and negative amplifier and an AC effective value voltmeter. The dual-channel signal generator generates two 1V orthogonal voltage signals UREF and UVAR. UVAR is used as a phase-locked signal to control the AC voltage source to output a high-voltage signal U that is orthogonal to UREF and supplies it to the resistor voltage divider. The output of the voltage divider and UREF are input to the power thermoelectric comparator through a follower. When UREF and UVAR are 90 degrees, the output signal of the power thermoelectric comparator is a constant value, and its potential is affected by the phase angle deviation of the voltage divider and the error of the comparator itself. By correcting the comparator's own phase angle deviation, the measurement of the voltage divider phase angle deviation is achieved.

[0009] This method has high requirements on the signal source and needs to output two unequal orthogonal signals at high frequency. At the same time, the verification system is relatively complex and has many uncertainty components, resulting in a large uncertainty in the final verification result.

[0010] (3) Phase angle deviation tracing method of MN type resistor divider based on series-parallel structure:

[0011] This method quantitatively analyzes the relationship between the phase angle deviation of the MN type resistor divider and each parasitic parameter, and converts the problem that the phase angle deviation of the voltage divider is difficult to directly verify into the problem of measuring the difference of the phase angle deviation, so as to realize the value traceability of the phase angle deviation of the MN type resistor divider. The precision AC voltage source is a resistor divider of 100Ω and 1kΩ, respectively, through the required AC voltage signal, and the output end of the voltage divider is connected to the two channels of the high-precision sampling system through two precision voltage followers B1 and B2. In order to ensure the accuracy of the measurement, two identical coaxial lines are used to connect the output end of the follower to the sampling channel to ensure that the parasitic capacitance introduced by the coaxial line is consistent in size, so as to reduce the influence of the inconsistency of the external load errors of the two branches. Finally, the measurement of the difference of the phase angle deviation of the two voltage dividers is realized through dual-channel sampling. The entire measurement system is connected through a coaxial line with a shielding layer to reduce the interference of the external environment in the line, and is connected to the host computer through the IEEE-488 bus to realize automatic control of the system.

[0012] This method is not suitable for conventional voltage divider angle difference calibration. In addition, the development of MN type resistor voltage dividers with series-parallel structures of different voltage division ratios and different ranges requires the use of a large number of imported high-precision resistors of the same batch and the same specifications, which is costly.

[0013] (4) Phase angle deviation calibration method based on cascade structure inductive voltage divider

[0014] Taking the self-checking binary inductive voltage divider BIVDstd as the reference benchmark, the phase angle deviation of the voltage dividers BIVD1, BIVD2 and BIVD3 can be verified. After measuring the cascade errors between BIVD1 and BIVD2, and BIVD2 and BIVD3 respectively by the incremental method, the phase angle deviation of the 8:1 inductive voltage divider composed of the three-stage cascade of BIVD1, BIVD2 and BIVD3 can be determined; the three-stage cascade structure of the 8:1 inductive voltage divider can be used as a reference benchmark to verify the phase angle deviation of the single-stage 8:1 inductive voltage divider, and then after determining the phase angle deviation of the binary inductive voltage divider BIVD itself and the cascade error between it and the single-stage 8:1 inductive voltage divider, the phase angle deviation of the cascade structure 16:1 inductive voltage divider can be determined. By analogy, the phase angle deviation of the cascade structure inductive voltage divider with a voltage division ratio of 2n:1 can be verified.

[0015] This method requires the use of a large number of cascaded binary inductive voltage dividers when the voltage division ratio is high, which is costly and has a complicated verification process. Summary of the invention

[0016] The technical problem to be solved by the present invention is to provide a calibration device and method for the angular difference of a broadband resistor divider, so as to realize rapid and accurate calibration of the angular difference of the broadband resistor divider at different frequencies.

[0017] The present invention is achieved in that:

[0018] A calibration device for a wide-band resistor voltage divider angle difference, comprising:

[0019] A broadband power acquisition and analysis system comprises: a main control computer, a PXI controller and a digitizer; the PXI controller is connected to the main control computer and the digitizer respectively; the broadband power acquisition and analysis system is used to perform high-speed synchronous sampling on the analog small signal passing through the voltage divider, and then transmit the data to the main control computer, and the signal is analyzed and processed by the compiled upper computer program;

[0020] The electric power standard source is connected to the main control computer, the voltage divider and the digitizer respectively; the electric power standard source is a multifunctional signal source capable of editing high-order harmonics, and uses high-order harmonics to simulate broadband signal output to apply working voltage to the voltage divider; the signal source also has a sampling reference signal and a system phase reference signal for synchronizing the internal clock, wherein the sampling reference signal serves as an external trigger signal of the digitizer, and the system phase reference signal serves as a calculation reference for phase comparison;

[0021] The voltage divider is a wide-band resistor voltage divider, and is connected to the electric power standard source and the digitizer as a device under test.

[0022] Furthermore, the voltage divider is also connected to a voltage follower.

[0023] A method for calibrating a wide-band resistor divider angle difference is provided, wherein the calibration is performed using the above-mentioned calibration device for calibrating a wide-band resistor divider angle difference. The calibration method comprises the following steps:

[0024] Step S1: using the 0° and 180° natural phase standards, correcting the delay between the two channels of the broadband power acquisition and analysis system, and establishing a "phase-frequency" relationship model to provide a reference channel for subsequent calibration of the analog output of the signal source through a phase reference signal;

[0025] Step S2: using a multifunctional signal source to provide a voltage signal, using each harmonic to simulate a sine wave of different frequencies, so that each harmonic signal is used as an input signal of a voltage divider at different frequencies, that is, providing a test signal for calibrating the angle difference of the voltage divider;

[0026] Step S3: Set the signal source to output the fundamental wave and the superimposed first harmonic, the amplitude of the fundamental wave is the same as the amplitude of the superimposed harmonic, the frequency of the harmonic is set to the frequency to be calibrated by the voltage divider, the initial phase of the fundamental wave is set to 0°, and the initial phase of each calibrated harmonic is set to the same value; the output signal of the signal source is connected to the comparison channel CH2 of the wide-band power acquisition and analysis system, and the phase reference signal is connected to the reference channel CH1 of the wide-band power acquisition and analysis system. Through this experiment, the phase shift of the fundamental wave and the superimposed harmonic relative to the phase reference signal of the wide-band power acquisition and analysis system is obtained when the signal source outputs an analog signal directly connected to the wide-band power acquisition and analysis system;

[0027] Step S4: Set the signal source, output the fundamental wave and the superimposed first harmonic, the amplitude of the fundamental wave is the same as the amplitude of the superimposed harmonic, the frequency of the harmonic is set to the frequency to be calibrated by the voltage divider, the initial phase of the fundamental wave is set to 0°, and the initial phase of each calibrated harmonic is set to the same value; the output signal of the signal source is connected to the comparison channel CH2 of the wide-band power acquisition and analysis system after passing through the voltage divider, and the phase reference signal is connected to the reference channel CH1 of the wide-band power acquisition and analysis system. Through this experiment, the additional phase shift of the fundamental wave and the superimposed harmonic relative to the phase reference signal of the wide-band power acquisition and analysis system is obtained when the output analog signal of the signal source is connected to the wide-band power acquisition and analysis system through the voltage divider;

[0028] Step S5: using the result of step S3 to correct step S4, the angle difference of the wideband voltage divider at the set harmonic frequency can be obtained;

[0029] Step S6: Change the order of the superimposed harmonics, repeat steps S3 to S5, and complete the angle difference calibration of the calibrated voltage divider at other frequencies.

[0030] Furthermore, in step S1, the phase delay correction of the acquisition channel is carried out through the following steps:

[0031] (1) Using 0° and 180° standard signals as test signals, measure the phase difference between comparison channel CH2 and reference channel CH1 respectively;

[0032] (2) Interchange channels CH1 and CH2 to eliminate other system errors except the inherent phase delay between acquisition channels;

[0033] (3) Change the frequency of the input signal, establish a relationship model between phase delay and input signal frequency, and correct the phase delay of the acquisition channel based on the model.

[0034] The advantages of the present invention are:

[0035] 1. The present invention adopts high-order harmonic simulation technology to generate broadband signal input, realizes accurate calibration of voltage divider angle difference at different frequencies, significantly expands the calibration frequency range, reduces the requirements for broadband signal source, and thus effectively reduces calibration cost.

[0036] 2. The present invention is based on digital sampling technology and can obtain the characteristics of amplitude and phase information based on the Fourier analysis method, and converts the angular difference calibration of the voltage divider into amplitude measurement. There is no need to obtain the phase difference through two-way comparison. Therefore, there is no need to use a standard voltage divider with a known angular difference, which realizes self-calibration and simplifies the calibration process, making calibration more economical and easy to operate.

[0037] 3. The present invention has the ability to simulate high-voltage side signal input over a full range. This feature effectively avoids the potential influence of the voltage coefficient of the voltage divider on the phase angle deviation of the voltage divider, ensures the accuracy of the calibration process, and improves the reliability of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0039] Figure 1 It is a hardware block diagram of the voltage divider angle difference calibration device of the present invention.

[0040] Figure 2 This is a test signal diagram for high-order harmonic simulation angle difference calibration of the present invention.

[0041] Figure 3 It is a working mechanism diagram of the internal clock signal of the signal source of the present invention.

[0042] Figure 4 It is a diagram of the phase reference signal and analog output fundamental wave signal of the present invention.

[0043] Figure 5 It is a diagram of the phase reference signal and the in-phase 50th harmonic signal (waveform expansion) of the present invention.

[0044] Figure 6 1 is an additional phase shift diagram of the voltage divider of the present invention.

[0045] Figure 7 Software synchronization flow chart in the present invention.

[0046] Figure 8 It is a flow chart of the voltage divider angle difference calibration steps of the present invention.

[0047] Figure 9~Figure 13 It is a waveform diagram of the test result without a voltage divider in the present invention.

[0048] Figure 14~Figure 18 It is a waveform diagram of the test result with a voltage divider in the present invention. DETAILED DESCRIPTION

[0049] A calibration device for the angle difference of a wide-band resistor divider, the system block diagram of which is shown in FIG. Figure 1 As shown, including:

[0050] A broadband power acquisition and analysis system comprises: a main control computer, a PXI controller and a digitizer; the PXI controller is connected to the main control computer and the digitizer respectively; the broadband power acquisition and analysis system is used to perform high-speed synchronous sampling on the analog small signal passing through the voltage divider, and then transmit the data to the main control computer, and the signal is analyzed and processed by the compiled upper computer program;

[0051] The electric power standard source is connected to the main control computer, the voltage divider and the digitizer respectively; the electric power standard source is a multifunctional signal source capable of editing high-order harmonics, and uses high-order harmonics to simulate broadband signal output to apply working voltage to the voltage divider; the signal source also has a sampling reference signal and a system phase reference signal for synchronizing the internal clock; wherein the sampling reference signal is used as an external trigger signal of the digitizer, and the system phase reference signal is used as a calculation reference for phase comparison;

[0052] The voltage divider is a wide-band resistor voltage divider, and is connected to the electric power standard source and the digitizer as a device under test.

[0053] Among them, the digitizer is the PXI-5922 variable resolution digitizer, which is a high-performance data acquisition device with a maximum sampling rate of 15MS / s and a maximum resolution of 24bit. In order to enable it to perform at its best, the sampling function should be scientifically and reasonably configured according to the characteristics of the measured signal. The PXI-5922 variable resolution digitizer uses an internal 6-bit 120MS / sADC, which integrates a noise shaping circuit that can move the quantization noise output by the ADC from a lower frequency to a higher frequency, and then correct the data from the ADC to 24-bit accuracy in real time in the digital linearization block, thereby correcting the static and dynamic errors in the ADC. The linearization block is configured during self-calibration, and the data generated by the linearization module is applied with a digital low-pass filter to remove all noise except a small part of the original quantization noise, and then the signal is resampled to a lower sampling frequency and higher resolution.

[0054] Among them, the host computer program controls the signal source to generate the test signal for calibration and controls the digitizer to synchronously sample the test signal according to the predetermined sampling beat. The specific process is as follows:

[0055] The measurement control program activates the sampling reference signal of the signal source. The sampling reference is used to synchronize the sampling measurement with the internal sampling clock of the signal source. It is a +5V to CMOS logic signal with a valid falling edge. The sampling reference output can be activated from the system menu or through GPIB (OUTPut:ROSCillator ON / OFF). When the sampling reference output is activated, the output signal remains high until the next positive zero crossing of the fundamental wave of the analog output signal, and then the signal will remain high until it is disabled. The phase reference output signal is a +5 V CMOS logic drive that provides a rising edge, synchronized to the fundamental wave of the analog output signal, and the signal duty cycle is 50%. The sampling reference pulse does not appear immediately after the sampling reference turn-on command. The first falling edge and the rising edge of the phase reference occur simultaneously at the positive zero crossing of the fundamental wave of the analog output signal. The digitizer samples the analog signal at every falling edge of the "trigger" signal, thereby locking the sampling with the analog output and realizing synchronous sampling in hardware.

[0056] Angular difference measurement principle:

[0057] After the analog signal is digitized, Fourier analysis can be performed to obtain the amplitude and phase information of the analog signal, so the phase of the signal to be measured can be indirectly obtained by measuring the signal amplitude. If the starting point of the fundamental wave cycle is taken as time 0, the information of the harmonic phase obtained has a built-in timestamp feature, and the measurement of phase shift can be completed in one measurement channel, so there is no need to compare the two signals to obtain the relative phase (i.e. phase shift) of one of the signals. Because there is no dedicated measuring instrument, it is difficult to obtain the phase shift between the input signal and the output signal of a voltage divider with a high voltage divider ratio (such as 1000:1) through a single direct measurement, and it is also necessary to consider that the voltage divider actually works at different frequencies, so the angle difference measurement of a wide-band voltage divider at different frequencies is an extremely complicated process. If the voltage divider is calibrated at a low frequency point (such as 50Hz / 100Hz) to obtain an angle difference, this frequency point is used as the fundamental frequency, and the input signal of the voltage divider at another frequency to be calibrated is simulated by superimposing a harmonic on the fundamental frequency. Then, the angle difference of the voltage divider at the harmonic frequency can be obtained by analyzing the phase shift of the superimposed harmonic relative to the fundamental frequency. Figure 2 As shown, assuming that the fundamental wave is 50Hz and the 10th-order harmonic is superimposed, the harmonic frequency is 500Hz. When the harmonic passes through the voltage divider, it is equivalent to a sine wave of 500Hz. Therefore, analog calibration signals at different frequencies of the voltage divider can be generated by superimposing harmonics of different orders. Assume that the voltage divider has the following input signal, which consists of the fundamental wave and the nth harmonic, and its analytical expression is shown in equation (1).

[0058]

[0059] Where:

[0060] ——fundamental wave amplitude on the input side, V;

[0061] ——the amplitude of the nth harmonic on the input side, V;

[0062] ——fundamental frequency, Hz;

[0063] ——Initial phase of fundamental wave at input side, °;

[0064] ——Initial phase of the nth harmonic at the input side, °.

[0065] After the above signal passes through the voltage divider, both the fundamental wave and the harmonic wave signals produce phase shift. At this time, the output signal of the voltage divider can be expressed by formula (2).

[0066]

[0067] Where:

[0068] ——Fundamental wave amplitude on the output side, V;

[0069] ——The amplitude of the nth harmonic on the output side, V;

[0070] ——fundamental frequency, Hz;

[0071] ——Initial phase of fundamental wave at output side, °;

[0072] ——The initial phase of the nth harmonic at the output side, °.

[0073] Therefore, the phase shifts of the fundamental and harmonic outputs on the low-voltage side of the voltage divider are and The calculation formulas are as follows (3) and (4). The above process considers the fundamental wave and harmonic wave independently. In addition, It is relative to the fundamental wave, so the phase shift of the nth harmonic is actually for and The sum of the angular difference of the voltage divider at n times the fundamental frequency.

[0074]

[0075]

[0076] Figure 3The internal signal trigger mechanism of the selected electric power standard source (signal source) is shown. The sampling reference signal of the signal source, the system phase reference and the starting point of the analog output signal cycle (here refers to the positive zero crossing point) have a fixed phase relationship. Based on this feature, the voltage and current channels can be compared independently with the system phase reference, so that the phase relationship of the output analog signal is fixed to the phase reference.

[0077] 1) Fundamental wave phase-locking performance

[0078] In order to obtain an accurate calibration signal, it is necessary to verify the phase-locking performance of the fundamental wave of the analog output signal and the phase reference signal. The frequency of the system phase reference signal is the same as the fundamental wave frequency of the analog output signal, and theoretically they should be in phase. The measured signal waveform is shown in the figure below. The two signals are collected by a digital oscilloscope with a high sampling rate and high storage depth. The actual waveform is as follows Figure 4 As shown, by measuring the difference between the rising edge of the phase reference signal and the positive zero crossing of the analog output signal, the time delay between the two (usually 0) can be obtained.

[0079] 2) Harmonic phase-locking performance (harmonic inherent phase shift)

[0080] The initial phase of the superimposed harmonics (which can be set arbitrarily) should have a fixed relationship with the phase shift of the fundamental wave. An initial error is allowed, but the error should remain stable and be corrected in subsequent applications through accurate measurement. The system phase reference signal has the same fundamental frequency as the analog output signal, which is 100Hz. Set an appropriate fundamental amplitude. For ease of calculation, the initial phase of the fundamental wave is set to 0°. Set a single higher-order harmonic, set the harmonic amplitude to the same as the fundamental wave, and set the harmonic initial phase to 0° (or other). After superimposing higher-order harmonics, there is a phase shift between the analog output signal and the phase reference signal. In subsequent experiments, this phase shift needs to be corrected. Higher-order harmonics represent sine waves of different frequencies. The waveforms of the expanded harmonics and phase reference signals are as follows: Figure 5 shown.

[0081] 3) Voltage divider additional phase shift verification

[0082] After passing through the voltage divider, the high-order harmonics will produce additional phase shift. In order to clarify this feature, a comparative test is needed. On the basis of the above test, the analog output signal of the signal source is passed through the voltage divider and then collected by an oscilloscope. The setting method of the fundamental wave and harmonics is the same as above. Figure 6 The results shown show that the analog output signal has an additional phase shift after passing through the voltage divider. The 50th harmonic signal (equivalent to a frequency of 5kHz) has a time delay of 0.7μs relative to the phase reference signal, which is equivalent to an additional phase shift of 0.025°.

[0083] Since the hardware synchronous sampling method cannot eliminate the sampling asynchrony, the sampling data also needs to be synchronized. The most commonly used method is software synchronization. A reference signal is selected, which is synchronized with the measured signal. The reference signal includes the start time, sampling interval and instantaneous sampling value. According to the information of the measured signal, the frequency range of the fundamental wave is specified, including the upper and lower limits of the fundamental wave frequency. In order to measure the frequency of the fundamental wave, it is also necessary to redesign the low-pass filter coefficients, including parameters such as the passband edge frequency, passband ripple, stopband edge frequency and stopband attenuation. By processing the reference signal, a more accurate zero-crossing time and average fundamental frequency can be obtained. The process of software synchronization is as follows: Figure 7 As shown, the specific steps are as follows:

[0084] ① Check whether the sampling rate and passband edge frequency of the reference signal satisfy the Nyquist sampling theorem. They should satisfy the relationship of formula (5);

[0085] Where:

[0086] —sampling rate, Hz;

[0087] —Signal frequency lower limit, Hz;

[0088] — signal frequency upper limit, Hz;

[0089] — Upper limit of passband edge frequency, Hz;

[0090] —Upper limit of stopband edge frequency, Hz.

[0091] ② Calculate the downsampling factor Kdf and the downsampling frequency fds. According to the sampling rate, upper frequency limit and stopband edge frequency of the reference signal, set the appropriate frequency range as needed to obtain Kdf and fds.

[0092] ③ The low-pass filter coefficient is obtained by adding a Kaiser window filter to the down-sampling extraction frequency fds, the signal maximum frequency fmax, the frequency measurement range, the set passband ripple and other parameters.

[0093] ④ The passband edge frequency, passband ripple, stopband edge frequency and stopband attenuation parameters set by the filter design specifications are added with a Kaiser window filter to obtain the bandpass filter coefficients.

[0094] ⑤ Based on the obtained low-pass and band-pass filter coefficients, the reference signal is first subjected to low-pass FIR windowing filtering, the signal after low-pass filtering is downsampled according to the downsampling factor, and then subjected to band-pass FIR windowing filtering.

[0095] ⑥ The signal after the FIR window filtering above calculates the zero crossing point and the average fundamental frequency. The calculation result of the zero crossing point includes the time of zero crossing and the number of crossings in one cycle.

[0096] ⑦ The zero-crossing time information obtained after zero-crossing detection is used as a new sampling trigger signal to perform full-cycle sampling on the original signal, thus achieving synchronous sampling of the signal to be measured.

[0097] The voltage divider is a wide-band resistor divider. The secondary output impedance of the wide-band resistor divider is generally high, ranging from several hundred ohms to several thousand ohms. The input impedance of the selected digitizer is "50Ω or 1MΩ" optional, and it is configured to 1MΩ specification when used. Impedance adaptation will cause a large load error. In order to isolate the front and rear stage measurement circuits, when measuring AC electrical parameters, it is generally necessary to add a voltage follower between the voltage divider and the digitizer to reduce the secondary impedance of the voltage divider. The wide-band resistor divider itself has a phase shift feature, and the connected voltage follower also has a phase shift, and the two are not linearly superimposed with frequency, so the two need to be calibrated as a whole for angle difference.

[0098] The following describes a method for calibrating the angle difference of a wide-band resistor divider. Figure 8 The steps shown include:

[0099] Step S1: using the 0° and 180° natural phase standards, correcting the delay between the two channels of the broadband power acquisition and analysis system, and establishing a "phase-frequency" relationship model to provide a reference channel for subsequent calibration of the analog output of the signal source through a phase reference signal;

[0100] In order to ensure the accuracy of the sampled data analysis, the synchronization of the hardware needs to be ensured. Therefore, the broadband power acquisition and analysis system should reasonably configure the sampling parameters. The configuration is as follows: (1) The input terminal is configured to unbalanced differential mode (pseudo differential), DC coupling; (2) The input impedance is set to "1MΩ"; (3) The "sampling rate" and "storage depth" are set adaptively according to the test frequency; (4) The trigger source is set to an external trigger source, the trigger type is "falling edge", and the trigger coupling is DC mode;

[0101] Due to slight differences in the time base jitter of the sampling synchronization clock, the device consistency of the ADC converter, and the analog bandwidth between the two synchronous channels of the broadband power acquisition and analysis system, there will be time delays between the channels when processing analog input signals. When two synchronous sampling channels are used as phase measurement standards, the phase delay of the two acquisition channels should be corrected, and the relationship between the phase delay and the input signal frequency should be clarified. To this end, the phase delay correction of the acquisition channel is carried out through the following steps:

[0102] (1) Using 0° and 180° standard signals as test signals, measure the phase difference between comparison channel CH2 and reference channel CH1 respectively;

[0103] (2) Interchange channels CH1 and CH2 to eliminate other system errors except the inherent phase delay between acquisition channels;

[0104] (3) Change the frequency of the input signal, establish a relationship model between phase delay and input signal frequency, and correct the phase delay of the acquisition channel based on the model;

[0105] Step S2: using a multifunctional signal source to provide a voltage signal, using each harmonic to simulate a sine wave of different frequencies, so that each harmonic signal is used as an input signal of a voltage divider at different frequencies, that is, providing a test signal for calibrating the angle difference of the voltage divider;

[0106] Step S3: Set the signal source to output the fundamental wave and the superimposed first harmonic, the amplitude of the fundamental wave is the same as the amplitude of the superimposed harmonic, the frequency of the harmonic is set to the frequency to be calibrated by the voltage divider, the initial phase of the fundamental wave is set to 0°, and the initial phase of each calibrated harmonic is set to the same value; the output signal of the signal source is connected to the comparison channel CH2 of the wide-band power acquisition and analysis system, and the phase reference signal is connected to the reference channel CH1 of the wide-band power acquisition and analysis system. Through this experiment, the phase shift of the fundamental wave and the superimposed harmonic relative to the phase reference signal of the wide-band power acquisition and analysis system is obtained when the signal source outputs an analog signal directly connected to the wide-band power acquisition and analysis system;

[0107] When there is no voltage divider, set the fundamental amplitude, frequency and initial phase. Under the premise of determining the fundamental frequency, set the frequency point of the voltage divider to be calibrated to an integer multiple of the fundamental frequency. Therefore, the voltage divider test frequency signal can be simulated by setting the nth harmonic. The set parameters are the amplitude and initial phase of the nth harmonic, and the set signal model is as shown in formula (1); the parameter settings are shown in Table 1;

[0108] Table 1 Signal source settings (without voltage divider)

[0109]

[0110] Without a voltage divider, on the one hand, the phase-locked relationship between the fundamental wave, harmonics and phase reference can be verified; on the other hand, the initial phase shift error of the voltage divider calibration system can be obtained, which can also be understood as a verification of the voltage divider angle difference calibration system;

[0111] Step S4: Set the signal source, output the fundamental wave and the superimposed first harmonic, the amplitude of the fundamental wave is the same as the amplitude of the superimposed harmonic, the frequency of the harmonic is set to the frequency to be calibrated by the voltage divider, the initial phase of the fundamental wave is set to 0°, and the initial phase of each calibrated harmonic is set to the same value; the output signal of the signal source is connected to the comparison channel CH2 of the wide-band power acquisition and analysis system after passing through the voltage divider, and the phase reference signal is connected to the reference channel CH1 of the wide-band power acquisition and analysis system. Through this experiment, the additional phase shift of the fundamental wave and the superimposed harmonic relative to the phase reference signal of the wide-band power acquisition and analysis system is obtained when the output analog signal of the signal source is connected to the wide-band power acquisition and analysis system through the voltage divider;

[0112] According to the trigger mechanism of the internal signal of the signal source, after the signal source passes through the voltage divider, the relationship between the input signal of the voltage divider and the phase reference remains unchanged, and the output signal of the voltage divider will produce a phase shift as a whole, including the fundamental wave and harmonics; the parameter settings are shown in Table 2:

[0113] Table 2 Signal source settings (with voltage divider)

[0114]

[0115] Step S5: using the result of step S3 to correct step S4, the angle difference of the wideband voltage divider at the set harmonic frequency can be obtained;

[0116] Step S6: Change the order of the superimposed harmonics, repeat steps S3 to S5, and complete the angle difference calibration of the calibrated voltage divider at other frequencies.

[0117] The technical specifications of the wide-band resistor divider used in the test are shown in Table 3.

[0118] Table 3 Technical specifications of wide-band resistor divider for testing:

[0119]

[0120] 1) Test results and waveforms

[0121] ①Test data:

[0122] Table 4 Angle difference calibration test data:

[0123]

[0124] ② Real-time waveform acquisition

[0125] Figure 9~Figure 13 The waveform diagram shows the test results without a voltage divider.

[0126] Figure 14~Figure 18 The waveform diagram of the test results with a voltage divider is shown.

[0127] 2) Conclusion and analysis

[0128] Refer to the test data in Table 4. When there is no voltage divider, the initial phase of each superimposed harmonic relative to the fundamental wave is obtained by comparing the phase reference signal with the fundamental wave phase frequency. It can be regarded as the signal source generating a phase shift on each superimposed harmonic, which can be regarded as the inherent phase shift of the harmonic, that is, the background error of the angle difference calibration. When the harmonic signal passes through the voltage divider, an additional phase shift will be generated. The angle difference measured with the voltage divider minus the background error is the additional phase shift caused by the voltage divider. According to equations (3) and (4), the actual angle difference of the voltage divider is the sum of the fundamental wave phase shift with the voltage divider and the additional phase shift at each frequency.

[0129] The above embodiments and drawings do not limit the product form and style of the present invention. Any appropriate changes or modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A method for calibrating the angle difference of a broadband resistor divider, characterized in that: First, a calibration device for a wide-band resistor divider angle difference is provided for calibration, comprising: A broadband power acquisition and analysis system comprises: a main control computer, a PXI controller and a digitizer; the PXI controller is connected to the main control computer and the digitizer respectively; the broadband power acquisition and analysis system is used to perform high-speed synchronous sampling on the analog small signal passing through the voltage divider, and then transmit the data to the main control computer, and the signal is analyzed and processed by the compiled upper computer program; The electric power standard source is connected to the main control computer, the voltage divider and the digitizer respectively; the electric power standard source is a multifunctional signal source capable of editing high-order harmonics, and uses high-order harmonics to simulate broadband signal output to apply working voltage to the voltage divider; the signal source also has a sampling reference signal and a system phase reference signal for synchronizing the internal clock, wherein the sampling reference signal serves as an external trigger signal of the digitizer, and the system phase reference signal serves as a calculation reference for phase comparison; The voltage divider is a wide-band resistor voltage divider, which is connected to the electric power standard source and the digitizer as the device under test; the voltage divider is also connected to a voltage follower; The calibration method comprises the following steps: Step S1: Using the 0° and 180° natural phase standards, the delay between the two channels of the broadband power acquisition and analysis system is corrected, and a "phase-frequency" relationship model is established to provide a reference channel for the subsequent calibration of the analog output of the signal source through the phase reference signal; Step S2: using a multifunctional signal source to provide a voltage signal, using each harmonic to simulate a sine wave of different frequencies, so that each harmonic signal is used as an input signal of a voltage divider at different frequencies, that is, providing a test signal for calibrating the angle difference of the voltage divider; Step S3: Set the signal source to output the fundamental wave and the superimposed first harmonic, the amplitude of the fundamental wave is the same as the amplitude of the superimposed harmonic, the frequency of the harmonic is set to the frequency to be calibrated by the voltage divider, the initial phase of the fundamental wave is set to 0°, and the initial phase of each calibrated harmonic is set to the same value; the output signal of the signal source is connected to the comparison channel CH2 of the wide-band power acquisition and analysis system, and the phase reference signal is connected to the reference channel CH1 of the wide-band power acquisition and analysis system. Through this experiment, the phase shift of the fundamental wave and the superimposed harmonic relative to the phase reference signal of the wide-band power acquisition and analysis system is obtained when the signal source outputs an analog signal directly connected to the wide-band power acquisition and analysis system; Step S4: Set the signal source to output the fundamental wave and the superimposed first harmonic, the amplitude of the fundamental wave is the same as the amplitude of the superimposed harmonic, the frequency of the harmonic is set to the frequency to be calibrated by the voltage divider, the initial phase of the fundamental wave is set to 0°, and the initial phase of each calibrated harmonic is set to the same value; the output signal of the signal source is connected to the comparison channel CH2 of the wide-band power acquisition and analysis system after passing through the voltage divider, and the phase reference signal is connected to the reference channel CH1 of the wide-band power acquisition and analysis system. Through this experiment, the additional phase shift of the fundamental wave and the superimposed harmonic relative to the phase reference signal of the wide-band power acquisition and analysis system is obtained when the output analog signal of the signal source is connected to the wide-band power acquisition and analysis system through the voltage divider; Step S5: using the result of step S3 to correct step S4, the angle difference of the wideband voltage divider at the set harmonic frequency can be obtained; Step S6: Change the order of the superimposed harmonics, repeat steps S3 to S5, and complete the angle difference calibration of the calibrated voltage divider at other frequencies.

2. A method for calibrating a wideband resistor divider angle difference as claimed in claim 1, characterized in that In step S1, the phase delay correction of the acquisition channel is carried out through the following steps: (1) Using 0° and 180° standard signals as test signals, measure the phase difference between comparison channel CH2 and reference channel CH1 respectively; (2) Interchange channels CH1 and CH2 to eliminate other system errors except the inherent phase delay between acquisition channels; (3) Change the frequency of the input signal, establish a relationship model between phase delay and input signal frequency, and correct the phase delay of the acquisition channel based on the model.

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