Background
The current transformer is one of the most critical power transmission and transformation equipment in the power system, and is widely applied to relay protection, current measurement and power system analysis. Traditional electromagnetic induction type current transformer along with electric power system's rapid development has constantly exposed a series of shortcomings: the method has the advantages of poor insulation performance, low electromagnetic interference resistance, small dynamic range, narrow frequency band, incapability of measuring direct current and the like, and is difficult to meet the development requirements of on-line detection, high-precision fault diagnosis, power grid digitization and the like of a new generation of power system.
Therefore, the development of new electrical measurement methods and devices is urgently needed. The all-fiber optical current transformer is a new generation electronic transformer which is outstanding. The all-fiber current transformer combines the optical principles of fiber-optic gyroscope and Faraday magneto-optical effect, is an optical precision instrument established on the basis of polarized light interference, mainly comprises optical elements such as an SLD light source, a phase controller (namely a phase modulator), a photoelectric detector and the like, and transmits digital signals by adopting the optical measurement principle, thereby realizing the source digitization of electric quantity information transmission. Compared with the traditional electromagnetic current transformer, the all-fiber current transformer has the advantages of large dynamic range, high measurement precision, good linearity, no magnetic saturation, small volume, light weight, complete primary and secondary isolation, no open-circuit danger at the low-voltage side and the like.
However, in the actual operation process of the all-fiber current transformer, the system error is increased or the function is disabled due to the external environment change or the performance degradation of the internal optical device, which is mainly caused by the fact that the half-wave voltage of the phase modulator in the all-fiber current transformer is easily affected by the external environment change or the performance of the internal optical device to generate deviation. The phase difference of Faraday magneto-optical effect polarized light caused by input current can be adjusted by applying half-wave voltage to the phase modulator, and the phase modulator is a key link influencing sampling precision, so that the real-time tracking and dynamic adjustment of the half-wave voltage value are very important to the improvement of the reliability and stability of the whole system.
In the prior art, named as ' optical fiber current transformer key state online detection technology research ', the author is Liu Boyang, in a professional Master's academic paper with the date of 2017 and 6 months, the half-wave voltage is controlled and tracked by a proportional integral algorithm through detecting the light intensity difference between the first period after overflow and the last period before overflow. Tracking is achieved by adjusting proper integration time and coefficient, however, in the operation process of the optical fiber current transformer, sometimes the temperature change is extremely small, the light intensity change is a very slow process, and the selection accuracy of the integration time and the coefficient is extremely low, so that accurate control and correction of the half-wave voltage cannot be performed.
Disclosure of Invention
The application aims to provide a half-wave voltage correction method of an all-fiber current transformer, which is used for solving the problem of low accuracy of the existing method; simultaneously, the all-fiber current transformer is used for solving the problem that the system error of the existing all-fiber current transformer is large.
In order to achieve the above object, the present invention provides a half-wave voltage correction method for an all-fiber current transformer, which comprises the following steps:
when the device runs, acquiring emergent light in real time, and calculating a light intensity value and an extra light intensity difference of the emergent light; the additional light intensity difference is: the difference between the light intensity value of the first transition period after the 2 pi overflow and the light intensity value of the last transition period before the 2 pi overflow;
correcting the half-wave voltage through the half-wave voltage correction quantity by taking the extra light intensity difference as a target, wherein the extra light intensity difference is zero; the half-wave voltage correction at least comprises two gradients, and each gradient corresponds to the range of the absolute value of the extra light intensity difference;
when the extra light intensity difference is larger than 0, according to the range of the absolute value of the extra light intensity difference, gradually increasing the corresponding half-wave voltage correction amount each time to enable the extra light intensity difference to be 0;
when the extra light intensity difference is less than 0, the extra light intensity difference is made to be 0 by gradually reducing the corresponding half-wave voltage correction amount each time according to the range of the absolute value of the extra light intensity difference.
The beneficial effects are that: the absolute value of the extra light intensity difference is divided into different ranges, and corresponding half-wave voltage correction quantity is gradually increased or decreased in the different ranges, so that the extra light intensity difference is 0, real-time tracking and accurate correction of half-wave voltage are realized, the system error of the all-fiber current transformer is reduced, and the detection precision of the all-fiber current transformer is further improved.
Further, in order to correct the half-wave voltage more accurately, the range of the absolute value of the extra light intensity difference is divided into three, the absolute value of the extra light intensity difference in the first range is greater than the absolute value of the extra light intensity difference in the second range is greater than the absolute value of the extra light intensity difference in the third range, and the first half-wave voltage correction amount corresponding to the first range is greater than the second half-wave voltage correction amount corresponding to the second range and is greater than the third half-wave voltage correction amount corresponding to the third range.
Further, in order to obtain the light intensity value of the emergent light more accurately, the light intensity value of the emergent light is calculated through an average filtering method.
Further, in order to ensure the working reliability of the all-fiber current transformer, if the corrected half-wave voltage exceeds a set threshold value of the half-wave voltage, an alarm is given.
In addition, the invention also provides an all-fiber current transformer, which comprises a light source, an optical fiber sensing ring, a phase modulator, a photoelectric detector and a controller, wherein the controller comprises a memory and a processor, and the processor is used for executing instructions stored in the memory to realize the following method:
when the device runs, acquiring emergent light in real time, and calculating a light intensity value and an extra light intensity difference of the emergent light; the additional light intensity difference is: the difference between the light intensity value of the first transition period after the 2 pi overflow and the light intensity value of the last transition period before the 2 pi overflow;
correcting the half-wave voltage through the half-wave voltage correction quantity by taking the extra light intensity difference as a target, wherein the extra light intensity difference is zero; the half-wave voltage correction at least comprises two gradients, and each gradient corresponds to the range of the absolute value of the extra light intensity difference;
when the extra light intensity difference is larger than 0, according to the range of the absolute value of the extra light intensity difference, gradually increasing the corresponding half-wave voltage correction amount each time to enable the extra light intensity difference to be 0;
when the extra light intensity difference is less than 0, the extra light intensity difference is made to be 0 by gradually reducing the corresponding half-wave voltage correction amount each time according to the range of the absolute value of the extra light intensity difference.
Has the advantages that: according to the invention, the absolute value of the extra light intensity difference is divided into different ranges, and the corresponding half-wave voltage correction amount is gradually increased or decreased in the different ranges, so that the extra light intensity difference is 0, the accurate correction of the half-wave voltage is realized, the system error of the all-fiber current transformer is reduced, and the detection precision of the all-fiber current transformer is further improved.
Further, in order to correct the half-wave voltage more accurately, the range of the absolute value of the extra light intensity difference is divided into three, the absolute value of the extra light intensity difference in the first range is greater than the absolute value of the extra light intensity difference in the second range is greater than the absolute value of the extra light intensity difference in the third range, and the first half-wave voltage correction amount corresponding to the first range is greater than the second half-wave voltage correction amount corresponding to the second range and is greater than the third half-wave voltage correction amount corresponding to the third range.
Furthermore, in order to obtain the light intensity value of the emergent light more quickly and accurately, the controller is an FPGA, and the light intensity value of the emergent light is calculated through an average filtering method.
Furthermore, in order to ensure the working reliability of the all-fiber current transformer, the all-fiber current transformer further comprises an alarm module, wherein the alarm module is connected with the controller, and if the corrected half-wave voltage exceeds a set threshold value of the half-wave voltage, an alarm is given.
Detailed Description
All-fiber current transformer embodiment:
the all-fiber current transformer provided by the embodiment comprises a light source, a fiber sensing ring (a sensing ring for short), a phase modulator, a photoelectric detector and a controller. The controller includes a memory and a processor for executing instructions stored in the memory to implement a half-wave voltage correction method for an all-fiber current transformer.
The all-fiber current transformer utilizes Faraday magneto-optical effect principle and interference measurement principle to control internal optical signals in a closed loop mode, and demodulates implicit current information. The specific structure of the all-fiber current transformer is shown in fig. 1, and comprises an electronic circuit, an optical circuit and a sensing ring; the optical loop comprises an SDL light source, a phase modulator and an optical fiber detector; the electronic loop comprises a controller, and in order to realize the correction method more accurately, the controller comprises a tracking acquisition module, a correction feedback module, and a corresponding ADC (analog-to-digital) and DAC (digital-to-analog).
In the optical loop, light emitted by a light source passes through a sensing ring and then enters a photoelectric detector through a phase modulator, the phase modulator is used for adjusting the phase difference of Faraday magneto-optical effect polarized light caused by input current, a half-wave voltage value is a corresponding parameter of the phase modulator for adjusting the phase difference, and the accuracy of the half-wave voltage value becomes a key factor influencing the scale factor of the current transformer. The specific operation of the optical circuit is prior art and the present invention is not described in great detail.
As shown in fig. 2, the working process of the tracking and collecting module is to obtain the emergent light from the photodetector, calculate the light intensity value of the emergent light, and apply an initial half-wave voltage to the phase modulator, where the initial half-wave voltage is a factory-calibrated half-wave voltage of the phase modulator (the half-wave voltage is a voltage input value when the phase difference information corresponds to pi), and continue to apply the corrected half-wave voltage to the phase modulator after correction.
The working process of the correction feedback module is as shown in fig. 3, after receiving the light intensity value of the emergent light calculated by the tracking acquisition module, regularly (4 transition periods can be used) superimposing a 2 pi modulation signal, when the half-wave voltage has an error (the actual half-wave voltage of the phase modulator is different from the applied half-wave voltage), an extra light intensity difference is generated when the phase modulator integrates to 2 pi overflow, and the light intensity difference is the correction quantity of the half-wave voltage, and the half-wave voltage is corrected by adopting a 2 pi overflow confirmation logic, so that the corrected half-wave voltage value is obtained.
Specifically, the half-wave voltage correction method of the all-fiber current transformer comprises the following steps:
when the device is operated (the current measurement is started), the tracking and collecting module acquires emergent light in real time and calculates the light intensity value of the emergent light;
the 2 pi overflow validation logic of the correction feedback module is: the light intensity value of the first transition period after the 2 pi overflow is differed from the light intensity value of the last transition period before the 2 pi overflow, so as to obtain the extra light intensity difference generated during the 2 pi overflow;
correcting the half-wave voltage through the half-wave voltage correction quantity by taking the extra light intensity difference as a target, wherein the extra light intensity difference is zero; the half-wave voltage correction at least comprises two gradients, and each gradient corresponds to the range of the absolute value of the extra light intensity difference;
when the extra light intensity difference is larger than 0, according to the range of the absolute value of the extra light intensity difference, gradually increasing the corresponding half-wave voltage correction amount each time to enable the extra light intensity difference to be 0;
when the extra light intensity difference is less than 0, the extra light intensity difference is made to be 0 by gradually reducing the corresponding half-wave voltage correction amount each time according to the range of the absolute value of the extra light intensity difference.
In this embodiment, in order to correct the half-wave voltage more accurately, the range of the absolute value of the extra light intensity difference is divided into three ranges, the absolute value of the extra light intensity difference in the first range > the absolute value of the extra light intensity difference in the second range > the absolute value of the extra light intensity difference in the third range, and the first half-wave voltage correction amount corresponding to the first range > the second half-wave voltage correction amount corresponding to the second range > the third half-wave voltage correction amount corresponding to the third range.
Specifically, as shown in fig. 4, since the photodetector converts the optical signal into an electrical signal (analog signal), and the ADC converts the analog signal into a digital signal, each light intensity corresponds to a digital signal, the digital signal corresponding to the absolute value of the extra light intensity difference in the first range is greater than 1000, the digital signal corresponding to the absolute value of the extra light intensity difference in the second range is 500-1000, and the digital signal corresponding to the absolute value of the extra light intensity difference in the third range is 0-500, similarly, the first range corresponds to the first half-wave voltage correction amount being 100, the second range corresponds to the second half-wave voltage correction amount being 5, and the third range corresponds to the third half-wave voltage correction amount being 1.
The correction process is as follows: the digital signal of the extra intensity difference is represented by an intensity digital quantity av,
when the delta V is more than or equal to 1000, the half-wave voltage is gradually increased by 100 each time; when the delta V is less than or equal to-1000, the half-wave voltage is gradually reduced by 100 each time, and the process is a fast adjusting process;
when the voltage is more than 1000 and delta V is more than or equal to 500, the half-wave voltage is gradually increased by 5 each time; when the delta V is more than 1000 and less than or equal to 500, the half-wave voltage is gradually reduced by 5 each time, and the process is a slow regulation process;
when 500 is more than delta V is more than 0, the half-wave voltage is gradually increased by 1 each time; when the delta V is more than 500 and less than 0, the half-wave voltage is gradually reduced by 1 each time, and the process is a fine adjustment process;
the correction is stopped until the next 2 pi overflow, where Δ V ═ 0 is not absolutely equal to 0, as long as Δ V ≈ 0.
Each specific judgment range and the corresponding correction amount can be flexibly adjusted according to actual conditions, and are not limited to the above numerical values.
In this embodiment, in order to calculate the light intensity value of the emergent light more quickly, the tracking and collecting module in the controller is specifically an FPGA, and the light intensity value of the emergent light is calculated by an average filtering method. The FPGA chip realizes the whole closed-loop control logic and belongs to the category of hardware control. The FPGA is different from a CPU processing chip, has no peripheral RAM and FLASH, and has strong anti-interference capability; in addition, the FPGA has strong real-time performance for processing data, can process multi-channel data in parallel, has high control precision, can reach nanosecond level, and can communicate with ADC chips with sampling rates of more than hundred mega. The characteristics of the FPGA chip can completely meet the requirements of real-time tracking and half-wave voltage control. Of course, as another embodiment, other processing chips may be used as long as the corresponding functions can be realized.
The FPGA reads an optical signal value (the sampling frequency is not lower than 100MHz) obtained by ADC chip conversion in real time under the excitation of a high-speed clock, and stores the optical signal value into an RAM buffer area, takes transition time as a calculation period, obtains two queues to be calculated from the RAM buffer area, one high step corresponding to comb waves and one low step corresponding to comb waves, filters optical noise in an optical intensity signal by adopting a median average filtering method, respectively removes the maximum value and the minimum value in the two queues, obtains the optical intensity value of each step by taking the residual data as an average algorithm, makes a difference between the optical intensity values of the high step and the low step, and converts the corresponding optical intensity value of emergent light according to the difference between the high step and the low step. Meanwhile, the FPGA distributes the modulation voltage value of each modulation period in a stepped mode according to the correction quantity until the extra light intensity difference value is close to 0 when the next 2 pi overflows.
In this embodiment, in order to ensure the working reliability of the all-fiber current transformer, the all-fiber current transformer further includes an alarm module, where the alarm module is connected to the controller, and if the corrected half-wave voltage exceeds a set threshold of the half-wave voltage (the set threshold is a threshold set by a manufacturer when the phase modulator leaves a factory), the half-wave voltage is alarmed to prompt that the current all-fiber current transformer is unavailable or abnormal. Of course, if the half-wave voltage exceeds the set threshold value, the alarm may not be given if the half-wave voltage is displayed through other data.
The embodiment of the half-wave voltage correction method of the all-fiber current transformer comprises the following steps:
the half-wave voltage correction method for the all-fiber current transformer provided by the embodiment comprises the following steps of:
when the device runs, acquiring emergent light in real time, and calculating a light intensity value and an extra light intensity difference of the emergent light; the additional light intensity difference is: the difference between the light intensity value of the first transition period after the 2 pi overflow and the light intensity value of the last transition period before the 2 pi overflow;
correcting the half-wave voltage through the half-wave voltage correction quantity by taking the extra light intensity difference as a target, wherein the extra light intensity difference is zero; the half-wave voltage correction at least comprises two gradients, and each gradient corresponds to the range of the absolute value of the extra light intensity difference;
when the extra light intensity difference is larger than 0, according to the range of the absolute value of the extra light intensity difference, gradually increasing the corresponding half-wave voltage correction amount each time to enable the extra light intensity difference to be 0;
when the extra light intensity difference is less than 0, the extra light intensity difference is made to be 0 by gradually reducing the corresponding half-wave voltage correction amount each time according to the range of the absolute value of the extra light intensity difference.
The specific implementation process of the half-wave voltage correction method of the all-fiber current transformer is described in the above-mentioned embodiment of the all-fiber current transformer, and is not described herein again.
The present invention has been described in relation to particular embodiments thereof, but the invention is not limited to the described embodiments. In the thought given by the present invention, the technical means in the above embodiments are changed, replaced, modified in a manner that is easily imaginable to those skilled in the art, and the functions are basically the same as the corresponding technical means in the present invention, and the purpose of the invention is basically the same, so that the technical scheme formed by fine tuning the above embodiments still falls into the protection scope of the present invention.