CN114325030B - Double-square-wave modulation open-loop demodulation method based on optical current transformer - Google Patents
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Abstract
The invention relates to a double-square wave modulation open-loop demodulation method based on an optical current transformer, which utilizes the capability of accurately demodulating the current value and the stronger capability of inhibiting cross interference of double-square wave modulation, applies the double-square wave modulation to the optical current transformer, realizes the arrangement of four modulator signals by accurately modeling the output signals of a photoelectric detector in the optical current transformer, accurately demodulates the current in a current bus to be detected by combining with the accurate modeling of the total phase shift of the output optical signals of the optical current transformer, realizes the 2 pi voltage tracking of a phase modulator in the optical current transformer, and solves the problems of insufficient modulating signals, low 2 pi reset frequency of the phase modulator, insufficient capability of inhibiting cross interference of the four-state modulation and the like of the current square wave modulation.
Description
Technical Field
The invention relates to a double-wave modulation open-loop demodulation method based on an optical current transformer, belonging to the technical field of signal modulation and demodulation algorithms.
Background
As a current detection device, the Optical Current Transformer (OCT) has the advantages of strong anti-interference performance, strong insulativity, no magnetic saturation, ferromagnetic resonance problem, large dynamic range and the like. The foreign research on the Optical Current Transformer (OCT) is early, and the application of the OCT in the army and civil fields is promoted. Although domestic research starts late, with the development of optical fiber sensing technology, optical Current Transformers (OCT) based on the optical fiber sensing technology rapidly become research hotspots in the power industry, have wide application prospects in the fields of measurement in power systems and the like, and gradually become a mainstream power measurement scheme.
Meanwhile, in a measurement system of an Optical Current Transformer (OCT), current signal demodulation is an important component of the entire measurement system. At present, two modulation and demodulation schemes of square wave modulation and four-state modulation are mainly adopted, and can be used for demodulating current and calculating a result, but the two modulation schemes respectively have some problems.
Firstly, square wave modulation has only two modulation states, so that only two different phases are used for modulating signals, modulation signals generated by a modulator are fewer, and then the error of a current value demodulated by the method is not small, meanwhile, the square wave modulation is reset at a2 pi reset time, so that the reset frequency of the square wave modulation is low, the efficiency is not high, the measurement tracking and the stability of the 2 pi voltage cannot be ensured, and the detected signals are influenced by interference signals with the same frequency and the same phase of demodulation frequency introduced by the square wave modulation, namely cross interference.
Secondly, the four-state modulation is to modulate signals by four different phases, and is similar to the square wave modulation principle, except that the four-state modulation method can finish one-time error detection within a half period without waiting for 2 pi reset time, the method improves efficiency and stability on the basis of square wave modulation, solves the problem that 2 pi voltage measurement tracking is inaccurate and stable, greatly enhances instantaneity, and has the influence of bad effect of inhibiting cross interference in the four-state modulation.
Disclosure of Invention
The invention aims to solve the technical problem of providing a double-square-wave modulation open-loop demodulation method based on an optical current transformer, which adopts a brand new design method to realize the acquisition of a current value in a current bus to be measured, so that the error of the measured current value can be reduced, the 2 pi voltage of a modulator can be stably tracked and measured, and meanwhile, cross interference can be transplanted to a certain extent.
The invention adopts the following technical scheme for solving the technical problems: the invention designs a double-wave modulation open-loop demodulation method based on an optical current transformer, which is based on the winding of a sensing optical fiber in the optical current transformer on a current bus to be tested, and comprises the following steps A to D, so as to obtain a current value in the current bus to be tested;
Step A, obtaining modulation signal amplitude phi m (t) of the phase modulator output under the condition of respectively corresponding to four signal durations through regulating the amplitude of the square wave signal applied to the phase modulator in the optical current transformer, and then entering the step B; wherein t represents the signal duration, phi m (t) represents the amplitude of the modulated signal under the condition that the phase modulator outputs the corresponding signal duration t;
B, realizing discretization processing of continuous signals corresponding to a mathematical model of a photoelectric detector output signal in the optical current transformer based on the fact that T is equal to the product of an integer n and a preset signal sampling period T, combining a phase modulator to output modulation signal amplitude phi m (T) corresponding to four square wave signal duration respectively, obtaining an expression V PD (T) of the photoelectric detector, obtaining an output voltage signal expression V PD1(t)、VPD2(t)、 VPD3(t)、VPD4 (T) corresponding to four signal duration through assignment of the four modulation signals, and then entering the step C;
and C, carrying out equation combination aiming at output voltage signal expressions V PD1(t)、 VPD2(t)、VPD3(t)、VPD4 (t) of the photoelectric detector under the condition that the photoelectric detector corresponds to four signal durations respectively, and obtaining simultaneous equation expressions as follows:
Then enter step D; wherein P 0 represents the light intensity output by the light source in the optical current transformer, and phi s represents the total phase shift of the optical signal output by the optical current transformer;
Step D, according to the simultaneous equation expression and the total phase shift model phi s =4NVI of the optical signal output by the optical current transformer, solving and obtaining the current I in the current bus to be measured; n represents an integer number of turns of the sensing optical fiber in the optical current transformer, which is wound on the current bus to be measured, and V represents the Fisher constant of the sensing optical fiber.
As a preferred technical scheme of the invention: in the step a, by adjusting the amplitude of the square wave signal applied to the phase modulator in the optical current transformer, the amplitude phi m (t) of the modulated signal under the condition that the output of the phase modulator corresponds to four signal durations is obtained as follows:
Where τ represents half a period of the square wave signal.
As a preferred technical scheme of the invention: in the step B, based on the value that T equals to the product of the integer n and the preset signal sampling period T, discretization processing of continuous signals corresponding to the mathematical model of the output signal of the photoelectric detector in the optical current transformer is realized, the phase modulator is combined to output modulation signal amplitude phi m (T) corresponding to four square wave signal durations respectively, the expression V PD (T) of the photoelectric detector is obtained, and the four modulation signal assignments are used to obtain the expression of the output voltage signal corresponding to the four signal durations respectively as follows:
when t is more than or equal to 0 and less than or equal to tau,
When tau is less than t and less than or equal to 2 tau,
When 2τ is less than t and less than or equal to 3τ,
When 3τ is less than t and less than or equal to 4τ,
Wherein V PD1(t)、VPD2(t)、VPD3(t)、VPD4 (t) sequentially represents output voltage signal expressions of the photoelectric detector under the conditions that t is more than or equal to 0 and less than or equal to tau, tau is more than or equal to 2 tau, 2 tau is more than or equal to 3 tau, and 3 tau is more than or equal to 4 tau, and then the step C is carried out.
As a preferred technical scheme of the invention: in the step B, the mathematical model of the output signal of the photoelectric detector in the optical current transformer is as follows:
v PD (t) represents an output voltage signal expression of the photodetector corresponding to the signal duration t.
As a preferred technical scheme of the invention: the step D comprises the following operations:
First define Then for/>Simplified acquisition/>
Then solving sin phi s according to the unitary quadratic equation solving mode to obtainThereby obtaining/>
Finally, the total phase shift model phi s =4NVI of the optical current transformer output optical signals is combined, and the current in the current bus to be measured is obtained through solvingWherein/>
As a preferred technical scheme of the invention: the step D comprises the following operations:
First define And defining where cos phi s ≡1, then get/>
Finally, willCombining an optical current transformer output optical signal total phase shift model phi s =4NVI, and solving to obtain current/>, in a current bus to be measuredWherein the method comprises the steps of
As a preferred technical scheme of the invention: the method also comprises the following steps I to IV, and realizes 2 pi voltage tracking of a phase modulator in the optical current transformer;
Step I, obtaining error parameters epsilon between V 2′π and V 2π according to the relation V '2π＝(1+ε)V2π between the 2 pi voltage V' 2π of the phase modulator and the standard 2 pi voltage V 2π when an optical current transformer serving as the 2 pi voltage tracking mathematical model of the phase modulator works, and then entering the step II;
Step II, based on the fact that T is equal to an integer n and the product of a preset signal sampling period T is taken, discretization processing is carried out on continuous signals corresponding to a mathematical model of output signals of the photoelectric detectors in the optical current transformer, modulation signal amplitude phi m (T) corresponding to four square wave signal duration respectively is combined with the output of the phase modulator, an output voltage signal expression V 'PD1(t)、V′PD2(t)、V′PD3(t)、V′PD4 (T) corresponding to four signal duration respectively is obtained under the condition that the photoelectric detectors are combined with error parameters epsilon between V' 2π and V 2π, and then step III is carried out;
Step III, carrying out equation simultaneous on output voltage signal expressions V 'PD1(t)、V′PD2(t)、V′PD3(t)、V′PD4 (t) of the photoelectric detector under the combination of error parameters epsilon between V' 2π and V 2π and under the condition of respectively corresponding to four signal durations to obtain simultaneous equation expressions as follows, and then entering step IV;
And IV, when DeltaV 'PD =0, V' 2π＝(1+ε)V2π＝V2π is obtained under the condition of epsilon=0, so that the tracking of the 2 pi voltage of the phase modulator in the optical current transformer is realized.
As a preferred technical scheme of the invention: in the step II, based on the product of the integer n and the preset signal sampling period T, the discretization processing of the continuous signal corresponding to the mathematical model of the output signal of the photoelectric detector in the optical current transformer is obtained, and the output voltage signal expressions of the photoelectric detector under the combination of the error parameter epsilon between V' 2π and V 2π and the four signal durations are obtained by combining the modulated signal amplitude phi m (T) of the output of the phase modulator under the four square wave signal durations respectively, wherein the output voltage signal expressions are as follows:
when t is more than or equal to 0 and less than or equal to tau,
When tau is less than t and less than or equal to 2 tau,
When 2τ is less than t and less than or equal to 3τ,
When 3τ is less than t and less than or equal to 4τ,
V 'PD1(t)、V′PD2(t)、V′PD3(t)、V′PD4 (t) sequentially represents output voltage signal expressions of the photoelectric detector under the condition that the error parameter epsilon between V' 2π and V 2π is equal to or more than 0 and less than or equal to tau, tau is equal to or less than 2 tau, 2 tau is equal to or less than 3 tau, and 3 tau is equal to or less than 4 tau, and then the step III is carried out.
As a preferred technical scheme of the invention: the optical current transformer comprises a light source, a coupler, a polarizer, a phase modulator, a lambda/4 wave plate, a photoelectric detector, a signal processing module, a digital-to-analog conversion module, an optical fiber reflector, a sensing optical fiber and a current bus to be tested; the output end of the light source is sequentially connected with the coupler, the polarizer, the phase modulator and the lambda/4 wave plate in series, and is abutted and wound on one end of a sensing optical fiber on a current bus to be tested through the lambda/4 wave plate, and the other end of the sensing optical fiber is abutted against the optical fiber reflector; meanwhile, the input end of the photoelectric detector is connected with the coupler in a butt joint manner and is used for receiving the optical signal returned by the coupler, the output end of the photoelectric detector is connected with the input end of the signal processing module in a butt joint manner, one output end of the signal processing module is connected with the phase modulator in a butt joint manner through the digital-to-analog conversion module and is used for applying square wave signals to the phase modulator, and the other output end of the signal processing module is used for outputting the current value in the current bus to be tested.
Compared with the prior art, the double-wave modulation open-loop demodulation method based on the optical current transformer has the following technical effects:
The invention designs a double-square wave modulation open-loop demodulation method based on an optical current transformer, which utilizes the capability of accurately demodulating the current value and the capability of strongly suppressing cross interference of double-square wave modulation, applies the double-square wave modulation to the optical current transformer, realizes the arrangement of four modulator signals by accurately modeling the output signals of a photoelectric detector in the optical current transformer, accurately demodulates the current in a current bus to be detected by combining with the accurate modeling of the total phase shift of the output optical signals of the optical current transformer, simultaneously realizes the 2 pi voltage tracking of the phase modulator in the optical current transformer by accurately modeling the relation between the 2 pi voltage of the phase modulator and the standard 2 pi voltage of the optical current transformer during the working of the optical current transformer, and all the modulation signal periods in the design method are used for signal demodulation, so that the independent modulation signal period does not need to be designed in the process of realizing the 2 pi voltage tracking of the phase modulator; the whole design overcomes the problems of insufficient modulating signals of the current square wave modulation, low 2 pi reset frequency of the phase modulator, insufficient capability of inhibiting cross interference of four-state modulation and the like.
Drawings
FIG. 1 is a flow chart of current value acquisition in a current bus to be tested in the design method of the present invention;
FIG. 2 is a flow chart of the 2 pi voltage tracking of the phase modulator in the design method of the present invention;
FIG. 3 is a schematic diagram of the generation of a desired modulation signal according to an embodiment of the present invention.
Detailed Description
The following describes the embodiments of the present invention in further detail with reference to the drawings.
The invention designs a double-wave modulation open-loop demodulation method based on an optical current transformer, which is applied to winding of a current bus to be tested based on a sensing optical fiber in the optical current transformer, wherein the optical current transformer specifically comprises a light source, a coupler, a polarizer, a phase modulator, a lambda/4 wave plate, a photoelectric detector, a signal processing module, a digital-to-analog conversion module, an optical fiber reflector, a sensing optical fiber and the current bus to be tested; the output end of the light source is sequentially connected with the coupler, the polarizer, the phase modulator and the lambda/4 wave plate in series, and is abutted and wound on one end of a sensing optical fiber on a current bus to be tested through the lambda/4 wave plate, and the other end of the sensing optical fiber is abutted against the optical fiber reflector; meanwhile, the input end of the photoelectric detector is connected with the coupler in a butt joint manner and is used for receiving the optical signal returned by the coupler, the output end of the photoelectric detector is connected with the input end of the signal processing module in a butt joint manner, one output end of the signal processing module is connected with the phase modulator in a butt joint manner through the digital-to-analog conversion module and is used for applying square wave signals to the phase modulator, and the other output end of the signal processing module is used for outputting the current value in the current bus to be tested.
Based on the structure of the optical current transformer, in practical application, as shown in fig. 1, the following steps a to D are specifically executed to achieve the acquisition of the current value in the current bus to be tested.
Step A, obtaining modulation signal amplitude phi m (t) of the phase modulator output under the condition of respectively corresponding to four signal durations through regulating the amplitude of the square wave signal applied to the phase modulator in the optical current transformer, and then entering the step B; where t represents the signal duration and phi m (t) represents the modulated signal amplitude at the corresponding signal duration t of the phase modulator output.
In practical application, in the step a, by adjusting the amplitude of the square wave signal applied to the phase modulator in the optical current transformer, the amplitude phi m (t) of the modulated signal under the condition that the output of the phase modulator corresponds to four signal durations is obtained as follows:
Where τ represents half a period of the square wave signal.
In a specific practical implementation, since the double square wave modulation needs to make the phase modulator generate four corresponding amplitude signals, two square waves with the same amplitude (not including zero) need to be introduced, and the two square waves are offset by half a period and subtracted to form a difference, so that four amplitude signals can be obtained. The phase modulator will be specifically described as generating a desired modulation signal: if the square wave voltage signal applied by the digital-to-analog converter (DAC) to the phase modulator is the solid line in fig. 3 (voltage amplitude is respectivelyAnd/>) The dashed lines in fig. 3 are waveforms (voltage amplitudes are/>, respectively) introduced offset from the solid lines by half a periodAnd/>) So the total phase difference introduced by the modulator is exactly the difference/>, which is subtracted after the dotted line waveform is shifted from the solid line waveform by half a periodI.e./>, is generatedAnd/>Is a non-reciprocal phase difference of (a). Therefore, the dotted waveform in fig. 3 is the modulation signal generated by the modulator, and four corresponding amplitude signals are generated.
And B, realizing discretization processing of continuous signals corresponding to a mathematical model of the output signals of the photoelectric detectors in the optical current transformer based on the fact that T is equal to the product of an integer n and a preset signal sampling period T, combining a phase modulator to output modulation signal amplitude phi m (T) corresponding to four square wave signal durations respectively, obtaining an expression V PD (T) of the photoelectric detectors, obtaining an output voltage signal expression V PD1(t)、VPD2(t)、 VPD3(t)、VPD4 (T) corresponding to the four signal durations through assignment of the four modulation signals, and then entering the step C.
In the specific application, in the step B, based on the value of the product of the T equal to the integer n and the preset signal sampling period T, the mathematical model of the output signal of the photoelectric detector in the optical current transformer is realizedDiscretization of the corresponding continuous signal, wherein V PD (t) represents an output voltage signal expression of the photoelectric detector under the corresponding signal duration t.
Then, combining the phase modulator to output modulation signal amplitude phi m (t) corresponding to four square wave signal duration respectively, obtaining an expression V PD (t) of the photoelectric detector, and obtaining an output voltage signal expression corresponding to four signal duration respectively through four modulation signal assignment as follows:
when t is more than or equal to 0 and less than or equal to tau,
When tau is less than t and less than or equal to 2 tau,
When 2τ is less than t and less than or equal to 3τ,
When 3τ is less than t and less than or equal to 4τ,
Wherein V PD1(t)、VPD2(t)、VPD3(t)、VPD4 (t) sequentially represents output voltage signal expressions of the photoelectric detector under the conditions that t is more than or equal to 0 and less than or equal to tau, tau is more than or equal to 2 tau, 2 tau is more than or equal to 3 tau, and 3 tau is more than or equal to 4 tau, and then the step C is carried out.
And C, carrying out equation combination aiming at output voltage signal expressions V PD1(t)、 VPD2(t)、VPD3(t)、VPD4 (t) of the photoelectric detector under the condition that the photoelectric detector corresponds to four signal durations respectively, and obtaining simultaneous equation expressions as follows:
Then enter step D; where P 0 represents the light intensity output by the light source in the optical current transformer, and φ s represents the total phase shift of the optical current transformer output optical signal.
Step D, according to the simultaneous equation expression and the total phase shift model phi s =4NVI of the optical signal output by the optical current transformer, solving and obtaining the current I in the current bus to be measured; n represents an integer number of turns of the sensing optical fiber in the optical current transformer, which is wound on the current bus to be measured, and V represents the Fisher constant of the sensing optical fiber.
For the solution of the current I in the current bus to be measured in the step D, two embodiments may be specifically applied in practical applications, where one of the above steps D specifically performs the following operations:
First define Then for/>Simplified acquisition/>
Then solving sin phi s according to the unitary quadratic equation solving mode to obtainThereby obtaining/>
Finally, the total phase shift model phi s =4NVI of the optical current transformer output optical signals is combined, and the current in the current bus to be measured is obtained through solvingWherein/>
Secondly, the following operations are specifically executed in the step D:
First define And defining where cos phi s ≡1, then get/>
Finally, willCombining an optical current transformer output optical signal total phase shift model phi s =4NVI, and solving to obtain current/>, in a current bus to be measuredWherein/>
The steps a to D are further designed to track the pi voltage of the phase modulator 2 in the optical current transformer while obtaining the current value in the current bus to be tested, as shown in fig. 2, and the following steps I to IV are specifically executed.
And I, obtaining an error parameter epsilon between V ' 2π and V 2π according to a relation V ' 2π＝(1+ε)V2π between the 2 pi voltage V ' 2π of the phase modulator and the standard 2 pi voltage V 2π when the optical current transformer serving as the 2 pi voltage tracking mathematical model of the phase modulator works, and then entering the step II.
And II, based on the fact that T is equal to an integer n and the product of a preset signal sampling period T, discretizing the continuous signal corresponding to a mathematical model of the output signal of the photoelectric detector in the optical current transformer, combining the output of the phase modulator with the amplitude phi m (T) of the modulation signal corresponding to the time length of the four square wave signals respectively, obtaining an output voltage signal expression V 'PD1(t)、V′PD2(t)、V′PD3(t)、V′PD4 (T) of the photoelectric detector corresponding to the time length of the four signals respectively under the combination of error parameters epsilon between V' 2π and V 2π, and then entering the step III.
In the specific practical application, in the step II, based on the product of T being equal to the integer n and the preset signal sampling period T, the discretization processing of the continuous signal corresponding to the mathematical model of the output signal of the photoelectric detector in the optical current transformer is obtained, and the output voltage signal expression of the photoelectric detector under the combination of the error parameter epsilon between V' 2π and V 2π and the respective corresponding four signal durations is obtained by combining the modulation signal amplitude phi m (T) of the output of the phase modulator under the respective corresponding four square wave signal durations as follows:
when t is more than or equal to 0 and less than or equal to tau,
When tau is less than t and less than or equal to 2 tau,
When 2τ is less than t and less than or equal to 3τ,
When 3τ is less than t and less than or equal to 4τ,
V 'PD1(t)、V′PD2(t)、V′PD3(t)、V′PD4 (t) sequentially represents output voltage signal expressions of the photoelectric detector under the condition that the error parameter epsilon between V' 2π and V 2π is equal to or more than 0 and less than or equal to tau, tau is equal to or less than 2 tau, 2 tau is equal to or less than 3 tau, and 3 tau is equal to or less than 4 tau, and then the step III is carried out.
Step III, carrying out equation simultaneous on output voltage signal expressions V 'PD1(t)、V′PD2(t)、V′PD3(t)、V′PD4 (t) of the photoelectric detector under the combination of error parameters epsilon between V' 2π and V 2π and under the condition of respectively corresponding to four signal durations to obtain simultaneous equation expressions as follows, and then entering step IV;
And IV, when DeltaV 'PD =0, V' 2π＝(1+ε)V2π＝V2π is obtained under the condition of epsilon=0, so that the tracking of the 2 pi voltage of the phase modulator in the optical current transformer is realized.
The double-square wave modulation open-loop demodulation method based on the optical current transformer is designed by the technical scheme, the double-square wave modulation is applied to the optical current transformer by utilizing the capacity of accurately demodulating the current value and the stronger capacity of inhibiting cross interference, the setting of four modulator signals is realized by accurately modeling the output signals of the photoelectric detectors in the optical current transformer, the current in a current bus to be measured is accurately demodulated by combining with the accurate modeling of the total phase shift of the output optical signals of the optical current transformer, meanwhile, the tracking of the 2 pi voltage of the phase modulator in the optical current transformer is realized by accurately modeling the relation between the 2 pi voltage of the phase modulator and the standard 2 pi voltage of the optical current transformer during the working, and all the modulation signal periods in the design method are used for signal demodulation, so that the independent modulation signal period does not need to be designed in the process of realizing the 2 pi voltage tracking of the phase modulator; the whole design overcomes the problems of insufficient modulating signals of the current square wave modulation, low 2 pi reset frequency of the phase modulator, insufficient capability of inhibiting cross interference of four-state modulation and the like.
While the embodiments of the present invention have been described in detail with reference to the drawings, the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present invention.
Claims (9)
1. A double-square-wave modulation open-loop demodulation method based on an optical current transformer is characterized in that: the method comprises the following steps of A to D, obtaining a current value in a current bus to be tested;
step A, obtaining modulation signal amplitude phi m (t) of the phase modulator output under the condition of respectively corresponding to four signal durations through regulating the amplitude of the square wave signal applied to the phase modulator in the optical current transformer, and then entering the step B; wherein t represents the signal duration, phi m (t) represents the amplitude of the modulated signal under the condition that the phase modulator outputs the corresponding signal duration t;
b, realizing discretization processing of continuous signals corresponding to a mathematical model of a photoelectric detector output signal in the optical current transformer based on the fact that T is equal to the product of an integer n and a preset signal sampling period T, combining a phase modulator to output modulation signal amplitude phi m (T) corresponding to four square wave signal duration respectively, obtaining an expression V PD (T) of the photoelectric detector, obtaining an output voltage signal expression V PD1(t)、VPD2(t)、VPD3(t)、VPD4 (T) corresponding to four signal duration through assignment of the four modulation signals, and then entering the step C;
and C, carrying out equation combination aiming at output voltage signal expressions V PD1(t)、VPD2(t)、VPD3(t)、VPD4 (t) of the photoelectric detector under the condition that the photoelectric detector corresponds to four signal durations respectively, and obtaining simultaneous equation expressions as follows:
Then enter step D; wherein P 0 represents the light intensity output by the light source in the optical current transformer, and phi s represents the total phase shift of the optical signal output by the optical current transformer;
Step D, according to the simultaneous equation expression and the total phase shift model phi s =4NVI of the optical signal output by the optical current transformer, solving and obtaining the current I in the current bus to be measured; n represents an integer number of turns of the sensing optical fiber in the optical current transformer, which is wound on the current bus to be measured, and V represents the Fisher constant of the sensing optical fiber.
2. The double-square-wave modulation open-loop demodulation method based on the optical current transformer according to claim 1, wherein the method comprises the following steps: in the step a, by adjusting the amplitude of the square wave signal applied to the phase modulator in the optical current transformer, the amplitude phi m (t) of the modulated signal under the condition that the output of the phase modulator corresponds to four signal durations is obtained as follows:
Where τ represents half a period of the square wave signal.
3. The double-square-wave modulation open-loop demodulation method based on the optical current transformer according to claim 2, wherein the method comprises the following steps: in the step B, based on the value that T equals to the product of the integer n and the preset signal sampling period T, discretization processing of continuous signals corresponding to the mathematical model of the output signal of the photoelectric detector in the optical current transformer is realized, the phase modulator is combined to output modulation signal amplitude phi m (T) corresponding to four square wave signal durations respectively, the expression V PD (T) of the photoelectric detector is obtained, and the four modulation signal assignments are used to obtain the expression of the output voltage signal corresponding to the four signal durations respectively as follows:
when t is more than or equal to 0 and less than or equal to tau,
When tau is less than t and less than or equal to 2 tau,
When 2τ is less than t and less than or equal to 3τ,
When 3τ is less than t and less than or equal to 4τ,
Wherein V PD1(t)、VPD2(t)、VPD3(t)、VPD4 (t) sequentially represents output voltage signal expressions of the photoelectric detector under the conditions that t is more than or equal to 0 and less than or equal to tau, tau is more than or equal to 2 tau, 2 tau is more than or equal to 3 tau, and 3 tau is more than or equal to 4 tau, and then the step C is carried out.
4. The double-square-wave modulation open-loop demodulation method based on the optical current transformer according to claim 1, wherein the method comprises the following steps: in the step B, the mathematical model of the output signal of the photoelectric detector in the optical current transformer is as follows:
v PD (t) represents an output voltage signal expression of the photodetector corresponding to the signal duration t.
5. The double-square-wave modulation open-loop demodulation method based on the optical current transformer according to claim 1, wherein the method comprises the following steps: the step D comprises the following operations:
First define Then for/>Simplified acquisition/>
Then solving sin phi s according to the unitary quadratic equation solving mode to obtainThereby obtaining/>
Finally, the total phase shift model phi s =4NVI of the optical current transformer output optical signals is combined, and the current in the current bus to be measured is obtained through solvingWherein/>
6. The double-square-wave modulation open-loop demodulation method based on the optical current transformer according to claim 1, wherein the method comprises the following steps: the step D comprises the following operations:
First define And defining where cos phi s ≡1, then get/>
Finally, willCombining an optical current transformer output optical signal total phase shift model phi s =4NVI, and solving to obtain current/>, in a current bus to be measuredWherein the method comprises the steps of
7. The double-square-wave modulation open-loop demodulation method based on the optical current transformer according to claim 1, wherein the method comprises the following steps: the method also comprises the following steps I to IV, and realizes 2 pi voltage tracking of a phase modulator in the optical current transformer;
Step I, obtaining an error parameter epsilon between V ' 2π and V 2π according to a relation V ' 2π＝(1+ε)V2π between the 2 pi voltage V ' 2π of the phase modulator and the standard 2 pi voltage V 2π when an optical current transformer serving as the 2 pi voltage tracking mathematical model of the phase modulator works, and then entering the step II;
Step II, based on the fact that T is equal to an integer n and the product of a preset signal sampling period T is taken, discretization processing is carried out on continuous signals corresponding to a mathematical model of output signals of the photoelectric detectors in the optical current transformer, modulation signal amplitude phi m (T) corresponding to four square wave signal duration respectively is combined with the output of the phase modulator, an output voltage signal expression V 'PD1(t)、V′PD2(t)、V′PD3(t)、V′PD4 (T) corresponding to four signal duration respectively is obtained under the condition that the photoelectric detectors are combined with error parameters epsilon between V' 2π and V 2π, and then step III is carried out;
Step III, carrying out equation simultaneous on output voltage signal expressions V 'PD1(t)、V′PD2(t)、V′PD3(t)、V′PD4 (t) of the photoelectric detector under the combination of error parameters epsilon between V' 2π and V 2π and under the condition of respectively corresponding to four signal durations to obtain simultaneous equation expressions as follows, and then entering step IV;
And IV, when DeltaV 'PD =0, V' 2π＝(1+ε)V2π＝V2π is obtained under the condition of epsilon=0, so that the tracking of the 2 pi voltage of the phase modulator in the optical current transformer is realized.
8. The double-square-wave modulation open-loop demodulation method based on the optical current transformer as claimed in claim 7, wherein the method comprises the following steps: in the step II, based on the product of the integer n and the preset signal sampling period T, the discretization processing of the continuous signal corresponding to the mathematical model of the output signal of the photoelectric detector in the optical current transformer is obtained, and the output voltage signal expressions of the photoelectric detector under the combination of the error parameter epsilon between V' 2π and V 2π and the four signal durations are obtained by combining the modulated signal amplitude phi m (T) of the output of the phase modulator under the four square wave signal durations respectively, wherein the output voltage signal expressions are as follows:
when t is more than or equal to 0 and less than or equal to tau,
When tau is less than t and less than or equal to 2 tau,
When 2τ is less than t and less than or equal to 3τ,
When 3τ is less than t and less than or equal to 4τ,
V 'PD1(t)、V′PD2(t)、V′PD3(t)、V′PD4 (t) sequentially represents output voltage signal expressions of the photoelectric detector under the condition that the error parameter epsilon between V' 2π and V 2π is equal to or more than 0 and less than or equal to tau, tau is equal to or less than 2 tau, 2 tau is equal to or less than 3 tau, and 3 tau is equal to or less than 4 tau, and then the step III is carried out.
9. The method for demodulating double-wave modulation open loop based on optical current transformer according to any one of claims 1 to 8, wherein: the optical current transformer comprises a light source, a coupler, a polarizer, a phase modulator, a lambda/4 wave plate, a photoelectric detector, a signal processing module, a digital-to-analog conversion module, an optical fiber reflector, a sensing optical fiber and a current bus to be tested; the output end of the light source is sequentially connected with the coupler, the polarizer, the phase modulator and the lambda/4 wave plate in series, and is abutted and wound on one end of a sensing optical fiber on a current bus to be tested through the lambda/4 wave plate, and the other end of the sensing optical fiber is abutted against the optical fiber reflector; meanwhile, the input end of the photoelectric detector is connected with the coupler in a butt joint manner and is used for receiving the optical signal returned by the coupler, the output end of the photoelectric detector is connected with the input end of the signal processing module in a butt joint manner, one output end of the signal processing module is connected with the phase modulator in a butt joint manner through the digital-to-analog conversion module and is used for applying square wave signals to the phase modulator, and the other output end of the signal processing module is used for outputting the current value in the current bus to be tested.
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