Current measurement method based on optical fiber current sensor

Abstract

The invention discloses a current measurement method based on an optical fiber current sensor, and belongs to the field of optical fiber sensing. According to the method, the period of a basic digital square wave is set to be composed of a current signal acquisition period and a vibration signal acquisition period, and the size is related to the round-trip transit time of modulated light; a current phase shift and a vibration phase shift are respectively acquired in two acquisition periods, a first digital step wave and a second digital step wave are respectively acquired according to the two phase shifts, and the total phase of the optical fiber current sensor is kept at a sensitive point of pi / 2 in a current signal acquisition period through reset and closed-loop modulation functions. The total phase of the optical fiber current sensor is kept at a 0 non-sensitive point in a vibration signal acquisition period, a current signal and a vibration signal are obtained, the vibration generation time is determined through the vibration signal, and vibration filtering is performed on the current signal. According to the method, the measurement precision and stability can be improved, and error locking accidents are avoided.

Description

Technical Field

[0001] The present invention belongs to the field of optical fiber sensing, and more specifically, relates to a current measurement method based on an optical fiber current sensor. Background Art

[0002] Fiber-optic current sensors offer significant advantages in ultra-high voltage (UHV) power grids due to their excellent insulation, wide bandwidth, strong resistance to electromagnetic interference, large dynamic range, compact size, and light weight. They are key components of HVDC converter stations, measuring the HVDC transmission current and transmitting the results to DC control and protection equipment. The performance of fiber-optic current sensors significantly impacts the stability of converter stations and, ultimately, the DC transmission system. However, some failures have occurred in actual engineering applications, notably vibration-induced measurement failures, leading to DC lockouts or outages.

[0003] In the measurement process of fiber-optic current sensors based on the Faraday rotation effect, the presence of linear birefringence can lead to increased measurement errors. Optical fiber is an elastic material. When vibration propagates through the fiber, it causes particles within the fiber to vibrate, transferring energy to adjacent particles, causing them to also vibrate, generating a wave phenomenon. This vibration changes the linear birefringence of the sensing fiber, which in turn changes the polarization state of the light waves propagating through the sensing fiber. If the vibration signal is simply treated as a high-frequency signal and the current as a low-frequency signal, and the vibration signal is filtered out using a low-pass filter, this will inevitably filter out the meaningful high-frequency current signal (with a frequency upper limit of the modulation frequency), reducing the bandwidth of the current sensor and affecting the measurement accuracy of the fiber-optic current sensor. In current engineering applications, traditional modulation schemes that only use current closed-loop feedback cannot distinguish between vibration interference and current interference, leading to false latching. Summary of the Invention

[0004] In response to the above defects or improvement needs of the prior art, the present invention provides a current measurement method based on an optical fiber current sensor, which can simultaneously measure current and vibration signals, thereby accurately filtering out the influence of vibration and improving current measurement accuracy.

[0005] To achieve the above object, according to a first aspect of the present invention, a current measurement method based on an optical fiber current sensor is provided, the method comprising:

[0006] S1, builds the basic digital square wave V base ; Among them, V baseThe cycle length is τ, and 0~τ / 4 and τ / 2~3τ / 4 are used as the current signal acquisition period, and the corresponding square wave amplitudes are π / 2 and 0 respectively. τ / 4~τ / 2 and 3τ / 4~τ are used as the vibration signal acquisition period, and the corresponding square wave amplitudes are all 0;

[0007] S2, V base Load it into the phase modulator, pass the current to be measured into the wire, and calculate the phase difference of the signal collected by the photodetector at 0~τ / 4 and τ / 2~3τ / 4 respectively And the phase difference of the signals collected at τ / 4~τ / 2 and 3τ / 4~τ And according to Construct the first and second digital step waves V with a period of τ step_1 、V step_2 ; Among them, V step_1 Step height V step_2 Step height n1, n2 are gain coefficients;

[0008] S3, V step_1 、V step_2 Superimposed on V base Get the modulated signal and load it into the phase modulator, so that the phase modulator generates The first feedback phase and the second feedback phase are mutually opposite, so that the modulation phase of the optical fiber current sensor in the current signal acquisition period and the vibration signal acquisition period always remains at π / 2 and 0 respectively within the current cycle τ, so that the optical fiber current sensor operates at the most sensitive point and the least sensitive point of current measurement in the current signal acquisition period and the vibration signal acquisition period respectively; save ΔV1 and ΔV2 corresponding to the current cycle τ, set τ=τ+1, and return to S2;

[0009] S4, performing modal decomposition on ΔV1 and ΔV2 corresponding to each period τ to obtain a target signal and a vibration signal; obtaining the vibration occurrence time according to the vibration signal, performing vibration filtering on the target signal according to the vibration occurrence time to obtain a current signal, thereby obtaining a measurement value of the current to be measured.

[0010] According to a second aspect of the present invention, there is provided an electronic device comprising: a computer-readable storage medium and a processor;

[0011] The computer-readable storage medium is used to store executable instructions;

[0012] The processor is configured to read the executable instructions stored in the computer-readable storage medium and execute the method according to the first aspect.

[0013] According to a third aspect of the present invention, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to execute the method according to the first aspect.

[0014] According to a fourth aspect of the present invention, there is provided a computer program product comprising a computer program or instructions, which implement the method according to the first aspect when executed by a processor.

[0015] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0016] The method provided by the present invention sets the period of the basic digital square wave to consist of a current signal acquisition period and a vibration signal acquisition period, the size of which is related to the round-trip transit time of the modulated light. The current phase shift and the vibration phase shift are respectively acquired in the two acquisition periods. A first digital step wave and a second digital step wave are obtained based on the two phase shifts. The reset and closed-loop modulation functions are used to achieve that the total phase of the optical fiber current sensor is maintained at a sensitive point of π / 2 during the current signal acquisition period, and the total phase of the optical fiber current sensor is maintained at an insensitive point of 0 during the vibration signal acquisition period, thereby obtaining a current signal and a vibration signal. The time of vibration occurrence is determined by the vibration signal, and the current signal is subjected to vibration filtering to obtain a current signal after vibration filtering, so as to obtain the measured value of the current to be measured. The method provided by the present invention can achieve simultaneous measurement of current and vibration, and accurately filter the vibration, thereby improving the accuracy and stability of the measurement. When vibration interference occurs, the vibration signal can be accurately distinguished to avoid the occurrence of false locking accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic flow chart of a current measurement method based on an optical fiber current sensor provided by an embodiment of the present invention;

[0018] Figure 2 It is a structural diagram of a reflective optical fiber current transformer;

[0019] Figure 3 This is a schematic diagram of the output of the optical fiber current sensor provided by an embodiment of the present invention when current is loaded;

[0020] Figure 4 is a schematic diagram of modulation phase change provided by an embodiment of the present invention;

[0021] Figure 5 Schematic diagram of step wave reset provided by an embodiment of the present invention;

[0022] Figure 6 is a digital signal waveform diagram of current and vibration provided by an embodiment of the present invention;

[0023] Figure 7 is a waveform diagram of a current modal decomposition data group and a vibration modal decomposition data group provided by an embodiment of the present invention;

[0024] Figure 8 1 is a waveform diagram of a digital current signal before and after vibration filtering according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is 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 intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0026] The embodiment of the present invention provides a current measurement method based on an optical fiber current sensor, such as Figure 1 As shown, the method includes:

[0027] S1, builds the basic digital square wave V base ; Among them, V base The cycle length is τ, and 0~τ / 4 and τ / 2~3τ / 4 are used as the current signal acquisition periods, and the corresponding square wave amplitudes are π / 2 and 0 respectively. τ / 4~τ / 2 and 3τ / 4~τ are used as the vibration signal acquisition periods, and the corresponding square wave amplitudes are all 0.

[0028] The method provided in an embodiment of the present invention is applicable to a reflective or transmissive fiber optic current sensor, wherein, if the fiber optic current sensor is a reflective fiber optic current sensor, τ=2t`; if the fiber optic current sensor is a transmissive fiber optic current sensor, τ=t`, where t` is the round-trip transit time of the modulated light.

[0029] The following description will be made using reflective fiber optic current sensing as an example.

[0030] The structure of the reflective fiber optic current sensor is as follows: Figure 2 The round-trip transit time t' of the modulated light is the time required to travel from the phase modulator to the reflector and then back to the phase modulator, measured based on the optical path length of the fiber optic current sensor. The duration of one cycle of the basic digital square wave is τ = 2t'.

[0031] Basic digital square wave V base The duration of one cycle is τ, and the duration of the current signal acquisition cycle is 0~τ / 4 and τ / 2~3τ / 4. Figure 3 The duration of the vibration collection cycle is τ / 4~τ / 2 and 3τ / 4~τ. Figure 3 Indicated by a circle;

[0032] Set the V at 0 to τ / 4 in the current signal acquisition cycle base The amplitude is the half-wave voltage of the phase modulator (the corresponding modulation phase is π / 2), and the V base The amplitude is 0; set V at τ / 4 to τ / 2 in the vibration signal acquisition period base The amplitude is 0, and V at 3τ / 4~τ in the vibration signal acquisition period base The amplitude is 0; the phase change during round-trip modulation and the total modulation phase are as follows Figure 4 As shown. It can be understood that when the circularly polarized light is reflected by the reflector, the left-handed circularly polarized light is converted into right-handed polarized light, and at the same time, the right-handed circularly polarized light is converted into left-handed polarized light. After passing through the quarter-wave plate, the polarization plane of the linearly polarized light undergoes x-axis and y-axis swapping, resulting in a phase difference between the two beams before and after passing through the phase modulator, which is

[0033] S2, V base Load it into the phase modulator, pass the current to be measured into the wire, and calculate the phase difference of the signal collected by the photodetector at 0~τ / 4 and τ / 2~3τ / 4 respectively And the phase difference of the signals collected at τ / 4~τ / 2 and 3τ / 4~τ And according to Construct the first and second digital step waves V with a period of τ step_1 、V step_2 ; Among them, V step_1 Step height V step_2 Step height n1, n2 are gain coefficients;

[0034] Specifically, and Also called first phase shift and second phase shift.

[0035] In step S2, V base After loading it into the phase modulator and passing the current to be measured into the wire, first, the difference between the signal of 0 to τ / 4 in the current signal acquisition period obtained by the photodetector signal and the signal of τ / 2 to 3τ / 4 in the current signal acquisition period obtained by the photodetector signal is calculated as the first phase shift The difference between the signal of τ / 4 to τ / 2 in the vibration signal acquisition period obtained by the photodetector signal and the signal of 3τ / 4 to τ in the vibration signal acquisition period obtained by the photodetector signal is the second phase shift

[0036] like Figure 3As shown in the figure, when the circularly polarized light in the sensing ring of the fiber optic current sensor is affected by birefringence, including the circular birefringence generated when the current flows through the conductor and the linear birefringence generated by the knocking vibration, both will cause the left-handed circularly polarized light and the right-handed circularly polarized light to generate a phase difference.

[0037] Since the total modulation phase of the fiber optic current sensor during the current signal acquisition period is π / 2, the fiber optic current sensor operates at the most sensitive point and can measure the circular birefringence generated when current flows through the conductor and the linear birefringence generated by the knocking vibration;

[0038] Since the total modulation phase of the fiber optic current sensor during the vibration signal acquisition period is 0, the fiber optic current sensor operates at the least sensitive point and can only measure the linear birefringence and loss changes caused by the knocking vibration, but is not affected by the circular birefringence generated when the current flows through the conductor, thereby realizing the measurement of the vibration signal.

[0039] Then, in step S2, a first digital step wave that can be automatically reset and has a step height corresponding to a first feedback phase is generated within the current signal acquisition period based on the first phase shift; a second digital step wave that can be automatically reset and has a step height corresponding to a second feedback phase is generated within the vibration signal acquisition time based on the second phase shift; the first digital step wave and the second digital step wave are superimposed on the basic digital square wave to obtain a digital modulated signal.

[0040] Specifically, let the digital step wave be V step , the modulation voltage after the digital step wave is superimposed on the basic digital square wave is V modulation , the full-wave voltage of the phase modulator is V π , the positive overflow modulation voltage is V over_p , the negative overflow modulation voltage is V over_n ;

[0041] In the digital logic circuit, set the first digital step wave V step_1 , the step height is The second digital step wave V step_2 , the step height Among them, n1 and n2 are gain coefficients, which can be set by yourself;

[0042] Determine the modulation voltage V modulation =V base +V step_1 +V step_2 In the overflow situation, when V modulation >V π , the positive overflow modulation voltage is V over_p =V modulation -V π , when Vmodulation <-V π , the negative overflow modulation voltage is V over_n =V modulation +V π ; Among them, it can be understood that since the fiber optic current sensor can measure currents of different polarities, there is also and Accordingly, when the modulation voltage V modulation <-V π There will be a negative overflow situation;

[0043] When positive overflow occurs, V modulation =V over_p , when negative overflow occurs, the V modulation =V over_n , in order to achieve automatic reset;

[0044] The calculation method of the first digital step wave and the second digital step wave of automatic reset is the same, such as Figure 5 shown.

[0045] S3, V step_1 、V step_2 Superimposed on V base Get the modulated signal and load it into the phase modulator, so that the phase modulator generates The first feedback phase and the second feedback phase are opposite to each other, so that the modulation phase of the optical fiber current sensor in the current signal acquisition period and the vibration signal acquisition period is always maintained at π / 2 and 0 respectively within the current period τ, so that the optical fiber current sensor works at the most sensitive point and the least sensitive point of current measurement in the current signal acquisition period and the vibration signal acquisition period respectively; save ΔV1 and ΔV2 corresponding to the current period τ, set τ=τ+1, and return to S2.

[0046] Specifically, within a current signal acquisition cycle, the total modulation phase of the fiber optic current sensor is controlled by a first feedback phase and a first phase shift. To keep the fiber optic current sensor operating at its most sensitive point to measure the current signal, the first feedback phase is adjusted within each current signal acquisition cycle. The first feedback phase and the first phase shift are equal in magnitude and opposite in sign, thereby maintaining the total modulation phase of the fiber optic current sensor at π / 2, thereby achieving closed-loop modulation of the fiber optic current sensor.

[0047] During the vibration signal acquisition cycle, the total modulation phase of the fiber optic current sensor is controlled by the second feedback phase and the second phase shift. In order to keep the fiber optic current sensor operating at the least sensitive point to measure the vibration signal while avoiding the influence of the current signal, the second feedback phase is adjusted during each vibration signal acquisition cycle. The second feedback phase is equal to the second phase shift in magnitude but opposite in sign, thereby keeping the total modulation phase of the fiber optic current sensor at 0, thereby realizing closed-loop modulation of the fiber optic current sensor.

[0048] At the same time, the first feedback phase is stored in the current signal acquisition period to obtain a digital signal of current; and the second feedback phase is stored in the vibration signal acquisition period to obtain a digital signal of vibration.

[0049] That is, in step S3, the digital modulation signal is applied to the phase modulator after passing through the digital-to-analog converter to generate a first feedback phase and a second feedback phase; wherein the first feedback phase is equal to the first phase shift in magnitude and opposite in sign, so that the total modulation phase of the optical fiber current sensor during the current signal acquisition period is π / 2; the second feedback phase is equal to the second phase shift in magnitude and opposite in sign, so that the total modulation phase of the optical fiber current sensor during the vibration signal acquisition period is 0; thereby realizing the normal reset and closed-loop modulation of the optical fiber current sensor.

[0050] After the current cycle τ ends, the next cycle is entered, that is, τ=τ+1, and the process returns to step S2 until all cycles are traversed.

[0051] S4, performing modal decomposition on ΔV1 and ΔV2 corresponding to each period τ to obtain a target signal and a vibration signal; obtaining the vibration occurrence time according to the vibration signal, performing vibration filtering on the target signal according to the vibration occurrence time to obtain a current signal, thereby obtaining a measurement value of the current to be measured.

[0052] Specifically, the modulation amount ΔV1 for generating the first feedback phase is stored in the current signal acquisition cycle. It is a dimensionless number. Since the first feedback phase Δw1 is different from the first phase shift Related, And the first phase shift Including the phase shift caused by the current to be measured and the phase shift caused by vibration, according to The magnitude of the current to be measured can be calculated; similarly, the modulation amount ΔV2 for generating the second feedback phase is stored during the vibration signal acquisition period. Accordingly, Includes phase shifts caused by vibrations.

[0053] In order to more clearly show the effect of the vibration generated by tapping the sensor ring on the current signal and the vibration signal, Figure 6It can be found that the signal ΔV1 collected during the current signal acquisition period includes the current signal and the vibration signal, but the time when the vibration occurred cannot be intuitively distinguished from the time domain. At the same time, the signal ΔV2 collected during the vibration signal acquisition period also cannot be intuitively distinguished from the time domain when the vibration occurred. Therefore, modal decomposition processing is required:

[0054] Performing modal decomposition processing on the signal ΔV1 collected during the current signal acquisition period to obtain a current modal decomposition data group, wherein the current modal decomposition data group includes current and vibration signals, that is, the target signal obtained by performing modal decomposition processing on ΔV1 includes current signals and vibration signals; performing modal decomposition processing on the signal ΔV2 collected during the vibration signal acquisition period to obtain a vibration modal decomposition data group, wherein the vibration modal decomposition data group only includes vibration signals; comparing the current modal decomposition group with the vibration modal decomposition group to determine the time when the vibration occurs, performing vibration filtering on the current signal at the corresponding time point, and separating the current signal, which represents the phase shift caused by the current. According to the formula Calculate the magnitude of the current to be measured, where N is the number of turns of the sensing fiber, V is the Wedel constant, which is related to the material properties; and I is the magnitude of the current to be measured, that is, the measured value.

[0055] In order to more clearly demonstrate the ability to identify the time of vibration after knock mode decomposition, combined with Figure 7 It can be found that the vibration is at the same position in the current modal decomposition data group and the vibration modal decomposition data group. The vibration occurrence time is successfully analyzed, and the vibration interference in the current signal can be accurately filtered out. The current signal comparison before and after vibration filtering is as follows: Figure 8 In the optical fiber current sensor system of this embodiment, the measured current signal acquisition period and the vibration signal acquisition period are both 3.976 μs, and the sampling rate is 251.5 kSa / s.

[0056] The modal decomposition method used is one of EMD, EEMD, CEEMDAN and VMD.

[0057] In summary, the method provided by the embodiment of the present invention decomposes the period τ of a basic digital square wave of an existing optical fiber current sensor into two parts, and performs closed-loop feedback modulation according to the corresponding phase shift. Due to the difference in the total modulation phase of the two parts, dual-sensitivity measurement is achieved; the total phase of the optical fiber current sensor during the current signal acquisition period is maintained at a sensitive point of π / 2, with maximum sensitivity to current, and the total phase of the optical fiber current sensor during the vibration signal acquisition period is maintained at an insensitive point of 0, with minimum sensitivity to current. When vibration occurs, the data of the current signal acquisition period includes the current signal and the vibration signal, but the data of the vibration signal acquisition period only includes the vibration signal; the time when the vibration occurs is determined based on the vibration signal, so as to achieve purposeful vibration filtering of the current digital signal.

[0058] An embodiment of the present invention provides an electronic device, comprising: a computer-readable storage medium and a processor;

[0059] The computer-readable storage medium is used to store executable instructions;

[0060] The processor is configured to read the executable instructions stored in the computer-readable storage medium and execute the method described in the above embodiment.

[0061] An embodiment of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to execute the method described in the above embodiment.

[0062] An embodiment of the present invention provides a computer program product, including a computer program or instructions, wherein when the computer program or instructions are executed by a processor, the method described in the above embodiment is implemented.

[0063] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A current measurement method based on an optical fiber current sensor, characterized in that: The method comprises: S1, build the basic digital square wave V base ; Among them, V base The cycle length is τ, 0~τ / 4 and τ / 2~3τ / 4 are used as the current signal acquisition cycle, and the corresponding square wave amplitudes are π / 2 and 0 respectively, and τ / 4~τ / 2 and 3τ / 4~τ are used as the vibration signal acquisition cycle, and the corresponding square wave amplitudes are all 0; S2, V base Load it into the phase modulator, pass the current to be measured into the wire, and calculate the phase difference of the signal collected by the photodetector at 0~τ / 4 and τ / 2~3τ / 4 respectively And the phase difference of the signals collected at τ / 4~τ / 2 and 3τ / 4~τ And according to Construct the first and second digital step waves V with a period length of τ step_1 、V step_2 ; Among them, V step_1 Step height V step_2 Step height n1, n2 are gain coefficients; S3, V step_1 、V step_2 Superimposed to V base The modulated signal is obtained and loaded into the phase modulator, so that the phase modulator generates The first feedback phase and the second feedback phase are mutually opposite, so that the modulation phase of the optical fiber current sensor in the current signal acquisition cycle and the vibration signal acquisition cycle is always maintained at π / 2 and 0 respectively in the current cycle τ, so that the optical fiber current sensor works at the most sensitive point and the least sensitive point of current measurement in the current signal acquisition cycle and the vibration signal acquisition cycle respectively; save ΔV1 and ΔV2 corresponding to the current cycle τ, set τ=τ+1, and return to S2; S4, respectively performing modal decomposition on ΔV1 and ΔV2 corresponding to each period τ to obtain a target signal and a vibration signal; obtaining the vibration occurrence time according to the vibration signal, and performing vibration filtering on the target signal according to the vibration occurrence time to obtain a current signal, thereby obtaining a measurement value of the current to be measured.

2. The method according to claim 1, characterized in that Before step S4, the process also includes: determining the modulation voltage V of the current cycle τ modulation Is it greater than V π or less than -V π , if V modulation >V π , then let V modulation =V over_p , if V modulation <-V π , then let V modulation =V over_n ; Among them, V over_p =V modulation -V π , V over_n =V modulation +V π , V π is the full-wave voltage of the phase modulator.

3. The method according to claim 1 or 2, characterized in that If the optical fiber current sensor is a reflection optical fiber current sensor, then τ=2t`; if the optical fiber current sensor is a transmission optical fiber current sensor, then τ=t`, where t` is the round-trip transit time of the modulated light.

4. The method according to claim 3, characterized in that In step S4, according to the formula Calculate the measured value I of the current to be measured; where, is the current signal, N is the number of windings of the sensing optical fiber, and V is the Weddell constant.

5. An electronic device, characterized in that: include: A computer readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the method according to any one of claims 1 to 4.

6. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to execute the method according to any one of claims 1 to 4.

7. A computer program product comprising a computer program or instructions, characterized in that When the computer program or instruction is executed by a processor, the method according to any one of claims 1 to 4 is implemented.

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