CN107422166B - Modulation and demodulation method for suppressing light power fluctuation for optical fiber current transformer - Google Patents
Modulation and demodulation method for suppressing light power fluctuation for optical fiber current transformer Download PDFInfo
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Abstract
The invention discloses a modulation and demodulation method for inhibiting light power fluctuation for an optical fiber current transformer, which comprises the following steps: electrifying the optical fiber current transformer, and generating a modulation waveform by the data demodulation module, wherein the modulation waveform is a four-state waveform; applying an offset with a fixed amplitude on each modulation sequence in the modulation waveforms, wherein the waveform corresponding to each four-state modulation period is a four-state waveform unit, and the signs of the offsets applied on the modulation sequences of adjacent four-state waveform units are opposite; and carrying out data demodulation on every two adjacent four-state waveform units to obtain an optical power value and a current value. The invention can effectively reduce the influence of light power fluctuation on the test accuracy, stabilize the output, not only is beneficial to improving the small current measurement precision of the optical fiber current transformer, but also has very important effect on improving the high and low temperature stability of the optical fiber current transformer.
Description
Technical Field
The invention belongs to the field of optical fiber current transformers, and particularly relates to a modulation and demodulation method for suppressing optical power fluctuation for an optical fiber current transformer.
Background
The optical fiber current transformer serving as novel current measuring equipment has the advantages of being simple in insulation, small in size, safe, reliable, digital, intelligent, integrated in metering, measuring and protecting and the like, and is key equipment for intelligent substation construction. The development of the optical fiber current transformer is started earlier abroad, and the network hanging operation is carried out at the earliest time. The development and the start of the optical fiber current transformer in China are late, but the development is rapid, the technical level is advanced greatly, in recent years, particularly under the traction of the construction requirement of an intelligent transformer substation, the market requirement of the optical fiber current transformer is continuously increased, and the optical fiber current transformer is applied to the intelligent transformer substation in small and medium batches. The optical fiber current transformer represents the development direction of the transformer industry, and the optical fiber current transformer must gradually replace the traditional electromagnetic transformer to become mainstream configuration equipment in the field of power measurement in the future.
The optical fiber current transformer is used as current sensing type current measuring equipment, and the main principle is that the magneto-optic Faraday principle is utilized, namely polarized light deflects in a magnetic field generated by current, and the deflection angle is in direct proportion to the current. The fiber current transformer converts phase change caused by a deflection angle into light intensity change by utilizing a reciprocal light path interference principle, and after a light intensity signal is converted into an electric signal by a photoelectric detector, the electric signal is demodulated by A \ D sampling. In the demodulation process, changes of loss of optical devices, extinction ratio, light source power fluctuation and the like in a reciprocal light path of the optical fiber current transformer all affect changes of optical power of the detector, and stability of demodulation current is affected. Under the condition of normal temperature, the parameter technical indexes of each optical device of the optical path are stable, but under the change of ambient temperature, the technical indexes of the optical devices can change, so that the light intensity reaching the detector changes, and the test precision and the test stability are influenced.
Interference light intensity fluctuation in the existing optical fiber current transformer can influence the stability of demodulation current. In practical application, the light intensity digital quantity cannot be directly obtained after AD sampling, and in general, the prior art means can be solved by the following methods: firstly, the stability of a light path is improved by optimizing the interference light path of the current transformer and selecting a high-performance optical device; and secondly, the light emitting stability of the light source is improved by detecting the light power and controlling the driving current in a feedback manner. In the current technical level, the optimized light path is limited by the technical level of the domestic existing optical devices, and the fluctuation of device parameters is difficult to meet the requirements; the light intensity of the light source is modulated, the technical difficulty is high, the cost is high, and the actual effect is not ideal.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method not only does not influence signal demodulation calculation, but also can demodulate the output interference optical power of a light path, and effectively removes the influence of common power fluctuation on the test of the optical fiber current transformer.
The purpose of the invention is realized by the following technical scheme: a modulation and demodulation method for suppressing optical power fluctuation for an optical fiber current transformer, the method comprising the steps of:
step 1: electrifying the optical fiber current transformer, and generating a modulation waveform by the data demodulation module, wherein the modulation waveform is a four-state waveform;
step 2: applying an offset with a fixed amplitude on each modulation sequence in the modulation waveforms, wherein the waveform corresponding to each four-state modulation period is a four-state waveform unit, and the signs of the offsets applied on the modulation sequences of adjacent four-state waveform units are opposite;
and step 3: and carrying out data demodulation on every two adjacent four-state waveform units to obtain an optical power value and a current value.
In the above method for modulating and demodulating optical power fluctuation suppression for the fiber current transformer, the step 3 specifically includes: sampling data of two adjacent four-state waveform units through an A/D converter to obtain sampling values of each modulation sequence of each four-state waveform unit; carrying out data demodulation on the modulation sequence through a data demodulation module to obtain the phase change and the optical power value of the light; and obtaining a current value according to a current transformer test principle formula, the optical phase change and the optical power value.
In the method for modulating and demodulating the optical power fluctuation suppression for the fiber current transformer, the sampling value of each modulation sequence of the first four-state waveform unit in the modulation sequence of each four-state waveform unit is as follows:
therein, ad
10Sample values of a first modulation sequence, ad, for a first four-state waveform element
20Sample values of the second modulation sequence, ad, for the first four-state waveform element
30Sample values of a third modulation sequence, ad, for a first four-state waveform element
40Is the sampling value of the fourth modulation sequence of the first four-state waveform unit, kappa is the photoelectric conversion coefficient of the detector, delta is the offset, I
0To be the value of the optical power,
is the phase change of the light;
the sampling value of each modulation sequence of the second four-state waveform unit in the modulation sequence of each four-state waveform unit is as follows:
wherein the content of the first and second substances,ad
11sampled values of the first modulation sequence, ad, for the second four-state waveform element
21Sampled values of a second modulation sequence, ad, for a second four-state waveform element
31Sampled value, ad, of a third modulation sequence of a second four-state waveform element
41Is the sampling value of the fourth modulation sequence of the second four-state waveform unit, kappa is the photoelectric conversion coefficient of the detector, delta is the offset, I
0To be the value of the optical power,
is the phase change of the light.
In the modulation and demodulation method for suppressing optical power fluctuation for the fiber current transformer, the phase change of light
Comprises the following steps:
optical power value I
0Comprises the following steps:
in the modulation and demodulation method for inhibiting light power fluctuation for the optical fiber current transformer, the test principle formula of the current transformer is as follows:
wherein N is the winding number of the sensitive optical fiber, V is the fiber Verdet constant, and A is the current value.
In the modulation and demodulation method for suppressing optical power fluctuation for the fiber current transformer, the current value a is:
compared with the prior art, the invention has the following beneficial effects:
(1) the invention can effectively reduce the influence of the power fluctuation of the light source on the test accuracy and improve the test stability;
(2) the invention can reduce the influence of loss transformation of each optical device of the light path on current measurement at ambient temperature and improve the high and low temperature stability of the optical fiber current transformer;
(3) the invention can demodulate the light power of the whole light path as a light path fault parameter, carry out fault alarm and improve the intelligent level of products.
Drawings
FIG. 1 is a schematic diagram of a fiber optic current transformer of the present invention;
FIG. 2 is a diagram of a four-state wave pattern after the addition of a bias in accordance with the present invention.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
fig. 1 is a schematic diagram of a fiber optic current transformer of the present invention. As shown in figure 1, under the action of a driving refrigeration circuit, light emitted by a light source enters an integrated optical device through a coupler A, the light is subjected to phase modulation through a Y waveguide integrated optical device, two beams of linearly polarized light are output, one beam of light is modulated, the two beams of linearly polarized light pass through a coupler B, enter a delay line along a fast axis and a slow axis of a polarization maintaining optical fiber respectively, are converted into two beams of circularly polarized light through a lambda/4 wave plate, one beam of the circularly polarized light is left-handed, the other beam of the circularly polarized light enters a sensitive optical fiber of an optical fiber ring for transmission, and the two beams of the elliptically polarized light generate phase difference under the combined action of the Faraday magneto-optical effect and measured current
Two beams of elliptically polarized light are transmitted to the reflector to be reflected and then enter the sensitive optical fiber again, the original left-handed light is changed into right-handed light, the original right-handed light is changed into left-handed light, and phase difference is generated under the combined action of Faraday magneto-optical effect and measured current
At this time, the total phase difference becomes
Two beams of elliptically polarized light carrying current information are converted into linearly polarized light again through a lambda/4 wave plate, meanwhile, the linearly polarized light originally transmitted along a slow axis is converted into linearly polarized light which is transmitted along a fast axis, the linearly polarized light originally transmitted along the slow axis is converted into linearly polarized light which is transmitted along the slow axis, and finally, the linearly polarized light returns to a Y waveguide integrated optical device to interfere, the interference light is output to a photoelectric detector through the integrated optical device and a coupler A, the detector converts an optical signal into an electric signal, the electric signal is sampled through an A/D, a detected signal is output after demodulation and demodulation are carried out on a digital signal according to an applied modulation signal, meanwhile, the modulation signal and a step wave are generated and fed back, and finally, the modulation signal and the step wave are applied to.
The embodiment provides a modulation and demodulation method for suppressing optical power fluctuation for an optical fiber current transformer, which comprises the following steps:
(1) electrifying the optical fiber current transformer, and generating a modulation waveform by the data demodulation module, wherein the modulation waveform is a four-state waveform;
(2) applying an offset with a fixed amplitude on each modulation sequence in the modulation waveforms, wherein the waveform corresponding to each four-state modulation period is a four-state waveform unit, and the signs of the offsets applied on the modulation sequences of adjacent four-state waveform units are opposite;
(3) and carrying out data demodulation on every two adjacent four-state waveform units to obtain an optical power value and a current value.
Further, the step (3) specifically comprises:
sampling data of two adjacent four-state waveform units through an A/D converter to obtain sampling values of each modulation sequence of each four-state waveform unit;
carrying out data demodulation on the modulation sequence through a data demodulation module to obtain the phase change and the optical power value of the light;
and obtaining a current value according to a current transformer test principle formula, the optical phase change and the optical power value.
Specifically, in order to demodulate the light intensity, a fixed offset δ needs to be superimposed on the modulation waveform, and the offset modulation is added, so that the light intensity signal can be demodulated, the demodulation of the detected signal is not affected, and the fixed offset δ needs to be inverted once every complete modulation period. The four-state modulation waveform after the offset δ is added is shown in fig. 2, and the demodulation data is fed back once every two four-state waveform units.
After the offset signal delta and the four-state waveform unit are modulated and applied according to the interference output function of the optical fiber current transformer, the sampling value of the A/D converter in the corresponding modulation period is as follows:
therein, ad
10Sample values of a first modulation sequence, ad, for a first four-state waveform element
20Sample values of the second modulation sequence, ad, for the first four-state waveform element
30Sample values of a third modulation sequence, ad, for a first four-state waveform element
40Is the sampling value of the fourth modulation sequence of the first four-state waveform unit, kappa is the photoelectric conversion coefficient of the detector, delta is the offset, I
0To be the value of the optical power,
is the phase change of the light.
After 1 modulation period, namely the adjacent second four-state waveform unit, the bias is reversed, and then:
therein, ad
11Sampled values of the first modulation sequence, ad, for the second four-state waveform element
21Sampled values of a second modulation sequence, ad, for a second four-state waveform element
31Sampled value, ad, of a third modulation sequence of a second four-state waveform element
41Is the sampling value of the fourth modulation sequence of the second four-state waveform unit, kappa is the photoelectric conversion coefficient of the detector, delta is the offset, I
0To be the value of the optical power,
is the phase change of the light.
After simplification and approximation, the sampling data of the AD in the first four-state waveform unit is:
therein, ad
10Sample values of a first modulation sequence, ad, for a first four-state waveform element
20Sample values of the second modulation sequence, ad, for the first four-state waveform element
30Is firstSample value, ad, of a third modulation sequence of a four-state waveform element
40Is the sampling value of the fourth modulation sequence of the first four-state waveform unit, kappa is the photoelectric conversion coefficient of the detector, delta is the offset, I
0To be the value of the optical power,
is the phase change of the light.
The AD samples data in the second four-state waveform unit as:
therein, ad
11Sampled values of the first modulation sequence, ad, for the second four-state waveform element
21Sampled values of a second modulation sequence, ad, for a second four-state waveform element
31Sampled value, ad, of a third modulation sequence of a second four-state waveform element
41Is the sampling value of the fourth modulation sequence of the second four-state waveform unit, kappa is the photoelectric conversion coefficient of the detector, delta is the offset, I
0To be the value of the optical power,
is the phase change of the light.
The two four-state modulation sampling data are processed by (-, +, +, +, -) calculation to obtain the phase change of the light
Comprises the following steps:
the two four-state modulation sampling data are processed by (-, +, +, +, -, +) calculation to obtain the light-emitting power value I
0Comprises the following steps:
I
0the total optical power in the optical path can reflect the optical power fluctuation of the optical path and the fault condition of optical path devices, and under the normal condition, the optical power of the optical path fluctuates along with the changes of temperature and stress; in the event of a fault, the light power level is severely degraded, so I
0The demodulation of the data size can not only inhibit power fluctuation, but also serve as a light path fault parameter to carry out fault alarm. Optical path alarm implementation to demodulate I
0Data is a reference value, and when the size of the data is reduced to a certain value, i.e. a threshold value (usually 60% of the original value), I
0And sending out an optical power alarm signal after the optical power is smaller than the set threshold.
In addition, according to the current transformer test principle:
the current value a is then:
n is the winding number of the sensitive optical fiber, V is the fiber Vield constant, and delta is the known given offset, the obtained current value is irrelevant to the optical power and is not influenced by the optical power output by the light source and the loss change of the optical path device.
In this embodiment, a fixed offset δ is added on the basis of the four-state wave modulation, and the demodulation data is fed back once every two four-state modulation waves. The offset is reversed every 2 eigenperiods 2 tau, the four-state modulation amplitude becomes pi/2 + delta, 3 pi/2 + delta, -3 pi/2 + delta, offsetAfter the displacement is reversed, the four-state modulation amplitude becomes pi/2-delta, 3 pi/2-delta, -3 pi/2-delta. When AD sampling data is demodulated, the data is operated according to the corresponding four-state modulation sequence, and phase shift caused by Faraday effect can still be calculated
Is not influenced by the applied offset; calculating the light output power I according to the known bias delta
0And the influence of the optical power fluctuation on the test is effectively removed.
The invention can effectively reduce the influence of light power fluctuation on the test accuracy, stabilize the output, not only is beneficial to improving the small current measurement precision of the optical fiber current transformer, but also has very important function on improving the high and low temperature stability of the optical fiber current transformer, and simultaneously can realize the light path fault alarm and improve the equipment intelligence level. The invention can reduce the influence of loss transformation of each optical device of the light path on current measurement at ambient temperature and improve the high and low temperature stability of the optical fiber current transformer.
The above-described embodiments are merely preferred embodiments of the present invention, and general changes and substitutions by those skilled in the art within the technical scope of the present invention are included in the protection scope of the present invention.
Claims (4)
1. A modulation and demodulation method for suppressing optical power fluctuation for an optical fiber current transformer is characterized by comprising the following steps:
step 1: electrifying the optical fiber current transformer, and generating a modulation waveform by the data demodulation module, wherein the modulation waveform is a four-state waveform;
step 2: applying an offset with a fixed amplitude on each modulation sequence in the modulation waveforms, wherein the waveform corresponding to each four-state modulation period is a four-state waveform unit, and the signs of the offsets applied on the modulation sequences of adjacent four-state waveform units are opposite;
and step 3: carrying out data demodulation on every two adjacent four-state waveform units to obtain an optical power value and a current value; wherein the content of the first and second substances,
the step 3 specifically includes:
sampling data of two adjacent four-state waveform units through an A/D converter to obtain sampling values of each modulation sequence of each four-state waveform unit;
carrying out data demodulation on the modulation sequence through a data demodulation module to obtain the phase change and the optical power value of the light;
obtaining a current value according to a current transformer test principle formula, optical phase change and an optical power value;
the sampling value of each modulation sequence of the first four-state waveform unit in the modulation sequence of each four-state waveform unit is as follows:
therein, ad
10Sample values of a first modulation sequence, ad, for a first four-state waveform element
20Sample values of the second modulation sequence, ad, for the first four-state waveform element
30Sample values of a third modulation sequence, ad, for a first four-state waveform element
40Is the sampling value of the fourth modulation sequence of the first four-state waveform unit, kappa is the photoelectric conversion coefficient of the detector, delta is the offset, I
0To be the value of the optical power,
is the phase change of the light;
the sampling value of each modulation sequence of the second four-state waveform unit in the modulation sequence of each four-state waveform unit is as follows:
therein, ad
11Sampled values of the first modulation sequence, ad, for the second four-state waveform element
21Sampled values of a second modulation sequence, ad, for a second four-state waveform element
31Sampled value, ad, of a third modulation sequence of a second four-state waveform element
41Is the sampling value of the fourth modulation sequence of the second four-state waveform unit, kappa is the photoelectric conversion coefficient of the detector, delta is the offset, I
0To be the value of the optical power,
is the phase change of the light.
2. The modulation and demodulation method for suppressing optical power fluctuation for the fiber current transformer according to claim 1, characterized in that: phase change of light
Comprises the following steps:
optical power value I
0Comprises the following steps:
3. the method for modulating and demodulating the optical power fluctuation suppression for the fiber current transformer according to claim 2, wherein: the test principle formula of the current transformer is as follows:
wherein N is the winding number of the sensitive optical fiber, V is the fiber Verdet constant, and A is the current value.
4. The modulation and demodulation method for suppressing optical power fluctuation for the fiber current transformer according to claim 3, characterized in that: the current value A is:
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| CN109375138B (en) * | 2018-11-06 | 2021-04-09 | 国网内蒙古东部电力有限公司电力科学研究院 | Light path fault self-diagnosis alarm device and method for optical fiber current transformer |
| CN110988432B (en) * | 2019-12-13 | 2021-09-28 | 东南大学 | All-fiber current transformer open-loop demodulation and half-wave voltage tracking method |
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