CN110244105B - An all-digital vector demodulation method for a magnetic modulator - Google Patents

Abstract

The invention discloses an all-digital vector demodulation method for a magnetic modulator, which comprises the steps of feeding a first current of known magnitude to the magnetic modulator; converting analog signals generated on excitation windings and detection windings of the magnetic modulator into digital signals signal to obtain an excitation signal and a detection signal; construct a second harmonic reference signal, remove the DC component of the detection signal to obtain a signal to be measured, and perform a correlation operation between the second harmonic reference signal and the signal to be measured to obtain the signal output amplitude; The current to be measured is fed into the magnetic modulator, and the above steps are repeated to obtain the signal output amplitude of the current to be measured; The invention improves the measurement resolution by using the second harmonic amplitude and phase of the detection winding signal at the same time, uses the all-digital method to weaken the noise interference caused by demodulation, and weakens the measurement sensitivity caused by the frequency change of the excitation power supply through the proportional coefficient self-calibration method Errors introduced by changes.

Description

An all-digital vector demodulation method for a magnetic modulator

technical field

The invention belongs to the field of electrical technology, and more particularly, relates to an all-digital vector demodulation method of a magnetic modulator.

Background technique

Magnetic modulator is a high-precision current sensor based on the principle of magnetic modulation, which is mainly composed of four parts: iron core, excitation winding, detection winding and demodulation loop. The working principle of the magnetic modulator is that the iron core is deeply saturated by exciting the winding. When there is no current flowing, that is, when there is no bias magnetic field inside the iron core, the magnetic flux inside the iron core only contains odd harmonic components; When passing through, that is, when a bias magnetic field appears inside the iron core, an even harmonic component proportional to the DC current to be measured appears in the magnetic flux inside the iron core.

The detection winding can sense the harmonics in the iron core, and the DC current to be measured can be measured by measuring the characteristic value of the even-order harmonic components on the detection winding through the demodulation loop. The traditional demodulation methods mainly include peak demodulation and phase-sensitive demodulation. The common point is that they all use analog circuits to implement demodulation algorithms and only measure a certain eigenvalue of even harmonics.

The measurement resolution of existing magnetic modulators is generally only milliampere. In terms of demodulation, the main reasons for limiting its resolution are as follows: only a single eigenvalue such as the amplitude in the even harmonics is measured, which is easily interfered by co-frequency noise of different phases, which reduces the resolution of demodulation; the use of analog circuits, Due to factors such as the temperature drift of the analog components, the measurement signal will be deviated, and measurement noise will be introduced, which will also reduce the resolution of the demodulation; the excitation source frequency is difficult to be constant, and since the measurement sensitivity changes linearly with the excitation source frequency, measurement errors will be introduced, resulting in Sensitivity is reduced. Therefore, a new magnetic modulator demodulation method is needed to improve the measurement resolution of the magnetic modulator.

SUMMARY OF THE INVENTION

In view of the defects of the prior art, the purpose of the present invention is to provide an all-digital vector demodulation method for a magnetic modulator, which aims to solve the problem that the demodulation method of the existing magnetic modulator will introduce errors and reduce the measurement resolution.

To achieve the above object, the present invention provides a full digital vector demodulation method for a magnetic modulator, comprising the following steps:

(1) Passing a first current of known magnitude in milliamps to the magnetic modulator;

(2) Convert the analog signal generated on the excitation winding and the detection winding of the magnetic modulator into a digital signal to obtain the excitation signal and the detection signal;

(3) constructing a second harmonic reference signal according to the frequency of the excitation signal, removing the DC component of the detection signal to obtain the signal to be measured, and performing a correlation operation between the second harmonic reference signal and the signal to be measured to obtain the signal output amplitude;

(4) feeding the current to be measured into the magnetic modulator, and repeating steps (2) to (3) to obtain the signal output amplitude of the current to be measured;

(5) According to the magnitude of the output amplitude of the two signals and the frequency of the two excitation signals, the magnitude of the current to be measured is obtained.

Preferably, a digital acquisition card is used to convert the analog signals on the excitation and detection windings of the magnetic modulator into digital signals.

Preferably, the expression of the second harmonic reference signal is:

为检测信号与激励信号之间的相位差，激励信号的相位设为0°。Among them, f is the excitation signal frequency, t is the current time point,

In order to detect the phase difference between the signal and the excitation signal, the phase of the excitation signal is set to 0°.

Preferably, a correlation operation is performed on the second harmonic reference signal and the signal to be measured, and the calculation method is as follows: multiplying the amplitude of the second harmonic reference signal at a single time point and the amplitude of the signal to be measured to obtain a single time point output Signal amplitude U _i , where i represents the sequence number of the current time point, sum the output signal amplitude U _i at each time point within the multiple integer cycle time T of the excitation signal to obtain the total output amplitude U.

Preferably, the average value of the detection signals within the multiple times the whole cycle time T of the excitation signal is calculated to obtain the DC component of the detection signal, and the DC component is subtracted from the detection signal to obtain the signal to be measured, so as to weaken the zero point error.

Preferably, the expression of the current to be measured is:

Among them, U is the signal output amplitude of the current to be measured, K ₀ is the ratio of the signal output amplitude of the first current to the magnitude of the first current, f is the frequency of the excitation signal when measuring the current to be measured, and f ₀ is the measurement of the first current The frequency of the excitation signal when the current is present.

Through the above technical solutions conceived by the present invention, compared with the prior art, the following beneficial effects can be achieved:

1. The all-digital vector demodulation method of the magnetic modulator provided by the present invention adopts the vector detection method, only measures the signal amplitude of a specific phase, avoids the noise interference of different phases, and improves the resolution of current measurement;

2. The all-digital vector demodulation method of the magnetic modulator provided by the present invention converts the input analog signal into a digital signal, and uses the all-digital method for demodulation, which avoids the introduction of some analog elements in the demodulation process of the analog signal. Inherent microampere current reduces noise interference and improves measurement resolution;

3. The all-digital vector demodulation method of the magnetic modulator provided by the present invention adopts the proportional coefficient self-calibration method, and performs real-time calibration by multiplying the measurement sensitivity by the frequency variation, so as to prevent the problem that the measurement sensitivity changes linearly with the frequency, and can weaken the excitation power supply. Frequency changes cause errors introduced by changes in measurement sensitivity.

Description of drawings

FIG. 1 is a schematic flowchart of an all-digital vector demodulation method for a magnetic modulator provided by an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The present invention provides an all-digital vector demodulation method of a magnetic modulator, aiming to improve the measurement resolution by improving the demodulation method of the magnetic modulator. More specifically, the demodulation method is mainly improved in three aspects, namely, by At the same time, the second harmonic amplitude and phase of the detection winding signal are used to improve the measurement resolution, the noise interference caused by demodulation is weakened by using the all-digital method, and the measurement sensitivity caused by the change of the excitation power frequency is reduced by the proportional coefficient self-calibration method. error.

In order to achieve the above purpose, the following steps are included:

(1) Passing a first current of known magnitude to the magnetic modulator;

(2) Convert the analog signal generated on the excitation winding and the detection winding of the magnetic modulator into a digital signal to obtain the excitation signal and the detection signal;

(3) Constructing a second harmonic reference signal according to the frequency of the excitation signal, removing the DC component of the detection signal to obtain a signal to be measured, and performing a correlation operation on the second harmonic reference signal and the signal to be measured to obtain the signal output amplitude ;

(4) feeding the current to be measured into the magnetic modulator, and repeating steps (2) to (3) to obtain the signal output amplitude of the current to be measured;

(5) According to the magnitude of the output amplitude of the two signals and the frequency of the two excitation signals, the magnitude of the current to be measured is obtained.

Specifically, a digital acquisition card is used to convert the analog signals on the excitation and detection windings of the magnetic modulator into digital signals.

Specifically, the expression of the second harmonic reference signal is:

为检测信号与激励信号之间的相位差，激励信号的相位设为0°。Among them, f is the excitation signal frequency, t is the current time point,

In order to detect the phase difference between the signal and the excitation signal, the phase of the excitation signal is set to 0°.

Specifically, a correlation operation is performed on the second harmonic reference signal and the signal to be measured, and the calculation method is as follows: multiplying the amplitude of the second harmonic reference signal at a single time point and the amplitude of the signal to be measured to obtain the output at a single time point Signal amplitude U _i , where i represents the sequence number of the current time point, sum the output signal amplitude U _i at each time point within the multiple integer cycle time T of the excitation signal to obtain the total output amplitude U.

Specifically, the average value is calculated for the detection signals within the multiple times the whole cycle time T of the excitation signal to obtain the DC component of the detection signal, and the DC component is subtracted from the detection signal to obtain the signal to be measured to weaken the zero point error.

Specifically, the expression of the current to be measured is:

Among them, U is the signal output amplitude of the current to be measured, K ₀ is the ratio of the signal output amplitude of the first current to the magnitude of the first current, f is the frequency of the excitation signal when measuring the current to be measured, and f ₀ is the measurement of the first current The frequency of the excitation signal when the current is present.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. As shown in Figure 1, the specific steps of demodulating to obtain the magnitude of the current value to be measured are as follows:

Step 1. Passing a first current I ₀ of known magnitude in milliamps to the magnetic modulator;

为初始检测信号与初始激励信号之间的相位差；Step 2. Convert the analog signal generated on the excitation winding and detection winding of the magnetic modulator into digital signals to obtain the initial excitation signal and the initial detection signal, and perform fast Fourier transform on the initial excitation signal to obtain the frequency f ₀ =165Hz , the phase of the initial excitation signal is set to 0°,

is the phase difference between the initial detection signal and the initial excitation signal;

Step 3: Construct an initial second harmonic reference signal according to the frequency f ₀ of the initial excitation signal, remove the DC component of the initial detection signal to obtain an initial signal to be measured, and perform a correlation operation on the initial second harmonic reference signal and the initial signal to be measured to obtain The signal output amplitude U ₀ of the first current is obtained, thereby obtaining the initial proportional coefficient K ₀ =U ₀ /I ₀ =0.4257;

为检测信号与激励信号之间的相位差，为-1.26rad；Step 4: Pass the current to be measured into the magnetic modulator, convert the analog signal generated on the excitation winding and detection winding of the magnetic modulator into a digital signal, obtain the excitation signal and the detection signal, and perform fast Fourier transform on the excitation signal to obtain Its frequency f=161Hz, the phase of the excitation signal is set to 0°,

is the phase difference between the detection signal and the excitation signal, which is -1.26rad;

Step 5. Construct the second harmonic reference signal according to the frequency f of the excitation signal. In this embodiment, the 1650 times the whole period of the excitation signal is selected for 10s, and the DC component DC=113.32mV of the detection signal is removed to obtain the signal to be measured, the second harmonic The reference signal and the signal to be measured are correlated, and the signal output amplitude of the current to be measured is obtained within 10s U=48.14mV;

Step 6. Obtain the magnitude of the current to be measured according to the magnitude of the output amplitude of the two signals and the frequency of the two excitation signals.

The resolution of the measurement system of the present invention reaches the microampere level, which is greatly improved compared with the milliampere level resolution of the existing non-contact current measuring device.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (6)

1. A method for fully digital vector demodulation of a magnetic modulator, comprising the steps of:

(1) passing a first current of known magnitude to the magnetic modulator;

(2) converting analog signals generated on an excitation winding and a detection winding of the magnetic modulator into digital signals to obtain an excitation signal and a detection signal;

(3) constructing a second harmonic reference signal according to the frequency of the excitation signal, removing the direct current component of the detection signal to obtain a signal to be detected, and multiplying the amplitude of the second harmonic reference signal at a single time point by the amplitude of the signal to be detected to obtain a signal output amplitude;

(4) introducing the current to be detected into the magnetic modulator, and repeating the steps (2) to (3) to obtain a signal output amplitude of the current to be detected;

(5) and obtaining the magnitude of the current to be measured according to the magnitude of the output amplitude of the two signals and the frequency of the two excitation signals.

2. The method of claim 1, wherein the conversion of the analog signal to a digital signal is performed by a digital acquisition card.

3. The method of claim 1, wherein the second harmonic reference signal is expressed by:

wherein f is the frequency of the excitation signal, t is the current time point,

to detect the phase difference between the signal and the excitation signal, the phase of the excitation signal is set to 0 °.

4. The method of claim 1, wherein the acquiring of the signal under test comprises: and calculating the average value of the detection signals in the excitation signal multiple times of the whole period to obtain the direct current component of the detection signals.

5. A method according to claim 3, wherein the signal output amplitude is the sum of the signal output amplitudes at each time point within a multiple of the full period of the excitation signal.

6. The method of claim 1, wherein the current to be measured is expressed by:

wherein U is the signal output amplitude of the current to be measured, K₀The ratio of the signal output amplitude of the first current to the magnitude of the first current, f is the frequency of the excitation signal when the current to be measured is measured, f₀To measure the frequency of the excitation signal at the first current.

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