A fiber-optic current transformer with controllable delay time

Abstract

This invention discloses a fiber optic current transformer with controllable delay time. It adds a photoelectric conversion unit, an error accumulation unit, a delay control unit, and a variable delay unit to a traditional fiber optic interferometer. By adjusting the intrinsic period of the fiber optic interferometer in real time, it is always made to be exactly equal to half the period of the modulated square wave, thereby eliminating the additional pulse signal introduced by the period mismatch, and thus eliminating the zero bias current error of the fiber optic current transformer. This enables the intrinsic period of the fiber optic interferometer to be dynamically adjustable and matched with the period of the modulated square wave in real time.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and more specifically to a fiber optic current transformer with controllable delay time. Background Technology

[0002] Existing closed-loop detection type fiber optic current transformers employ a reflective fiber optic interferometer and achieve closed-loop current tracking detection by applying a square wave + stepped wave signal to an electro-optic phase modulator. Ideally, the intrinsic period of the fiber optic interferometer is half of the modulated square wave. However, the square wave is usually generated by an FPGA or other digital circuits, and its period is determined by the crystal oscillator frequency, making continuous adjustment difficult and causing period inaccuracies. In practice, the square wave period can only be approximately adjusted to the required size through software settings, but minor inaccuracies cannot be completely eliminated. Square wave period inaccuracies cause positive pulse signals in the interference light intensity at the beginning or end of the square wave half-cycle, which adds a zero-bias current error to the fiber optic current transformer output signal, affecting measurement accuracy.

[0003] Existing solutions involve subtracting this zero-bias error from the software. However, due to factors such as thermal expansion and contraction, this zero-bias error changes with temperature, rendering the error subtraction method ineffective. Another approach is to use a voltage-controlled crystal oscillator (VCO) instead of a fixed-frequency crystal oscillator, adjusting the crystal frequency by voltage to eliminate period inaccuracy. However, VCOs typically have a limited frequency range that can be adjusted, and the frequency cannot be continuously adjusted, inevitably resulting in residual inaccuracy, thus failing to fundamentally solve the problem. Summary of the Invention

[0004] Therefore, in order to overcome the problem of misalignment between the eigencycle and the half-cycle of the modulated square wave in existing interferometers, this invention provides a fiber optic current transformer with controllable delay time, so as to realize the dynamic adjustment of the eigencycle of the fiber optic interferometer and its real-time matching with the modulated square wave period.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] The present invention provides a fiber optic current transformer with controllable delay time, comprising: a photoelectric conversion unit, an error accumulation unit, a delay control unit, a variable delay unit, and a fiber optic interferometer, wherein the fiber optic interferometer comprises: a light source, a photodetector, a coupler, a polarizer, an electro-optic phase modulator, a fixed delay fiber, and a fiber optic measurement coil.

[0007] The photoelectric conversion unit is used to convert the light intensity signal received by the photodetector into a voltage signal of equal proportion.

[0008] The error accumulation unit is used to analyze the characteristics of the output voltage signal of the photoelectric conversion unit to obtain the periodic misalignment error signal;

[0009] The delay control unit controls the variable delay unit according to the periodic misalignment error signal. The variable delay unit changes the optical wave delay time through voltage control, wherein the magnitude of the optical wave delay time is positively correlated with the amplitude of the control voltage.

[0010] The fixed-delay fiber is located between the electro-optic phase modulator and the fiber measurement coil, and the variable-delay unit is located between the electro-optic phase modulator and the fixed-delay fiber, or between the fixed-delay fiber and the fiber measurement coil.

[0011] In one embodiment, the duty cycle of the modulated square wave signal applied to the electro-optic phase modulator is 50%.

[0012] In one embodiment, the error accumulation unit includes a phase detection multiplication circuit, an integrator circuit, and an adder circuit. The phase detection multiplication circuit uses two different phase detection square waves. When the intrinsic period of the fiber optic interferometer is less than half the period of the modulation square wave, a positive pulse exists at the beginning of the half-period of the square wave. This positive pulse is phase-detected by the phase detection multiplication circuit and then integrated and accumulated by the integrator circuit to obtain a positive error signal. When the intrinsic period of the fiber optic interferometer is greater than half the period of the modulation square wave, a positive pulse exists at the end of the half-period of the square wave. This positive pulse is phase-detected by the phase detection multiplication circuit and then integrated and accumulated by the integrator circuit to obtain a negative error signal. The adder circuit accumulates all positive and negative error signals to obtain the output signal of the error accumulation unit.

[0013] In one embodiment, the delay control unit first inverts the output signal of the error accumulation unit, then performs PID processing before outputting it to the variable delay unit; or it first performs PID processing on the output signal of the error accumulation unit and then inverts it before outputting it to the variable delay unit.

[0014] In one embodiment, the variable delay unit is an electrically controlled optical delay line.

[0015] In one embodiment, the variable delay unit is a cylindrical piezoelectric ceramic tightly wound with an optical fiber.

[0016] In one embodiment, the delay control unit is an analog PID circuit.

[0017] In one embodiment, the delay control unit includes an analog-to-digital converter circuit, a digital PID circuit, and a digital-to-analog converter circuit.

[0018] The technical solution of this invention has the following advantages:

[0019] 1. The fiber optic current transformer with controllable delay time proposed in this invention adjusts the intrinsic period of the fiber optic interferometer in real time so that it is always accurately equal to the half period of the modulated square wave, thereby eliminating the additional pulse signal introduced by the period mismatch and thus eliminating the zero bias current error of the fiber optic current transformer.

[0020] 2. The fiber optic current transformer with controllable delay time proposed in this invention includes an error accumulation unit, a phase detection multiplication circuit, an addition circuit, and an integration circuit. The phase relationship between the phase detection square wave and the modulation square wave is clear, simple, and easy to generate. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 The equivalent optical path diagram is an example of an optical fiber current transformer with controllable delay time provided in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram showing the timing relationship between the intrinsic period of the fiber optic interferometer and the half-period of the modulated square wave under misalignment conditions, and a schematic diagram showing the matching of the intrinsic period of the fiber optic interferometer with the modulated square wave period after dynamic adjustment.

[0024] Figure 3 This is a schematic diagram of two phase detection square waves used in the error accumulation unit provided in the embodiments of the present invention.

[0025] Figure 4 This is a schematic diagram of the circuit principle of one embodiment of the error accumulation unit provided in this invention.

[0026] Figure label:

[0027] 1-Light source; 2-Photodetector; 3-Coupler; 4-Polarizer; 5-Electro-optic phase modulator; 6-Fiber optic with fixed delay; 7-Fiber optic measurement coil; 8-Current-carrying conductor. Detailed Implementation

[0028] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] Example

[0031] The present invention provides a fiber optic current transformer with controllable delay time, which adds a photoelectric conversion unit, an error accumulation unit, a delay control unit, and a variable delay unit to a traditional fiber optic interferometer. The fiber optic interferometer includes: a light source, a photodetector, a coupler, a polarizer, an electro-optic phase modulator, a fixed delay fiber, and a fiber optic measurement coil. Figure 1 The optical connections between the light source 1, photodetector 2, coupler 3, polarizer 4, electro-optic phase modulator 5, variable delay unit, fixed delay fiber 6, fiber optic measurement coil 7, and current-carrying conductor 8 (it should be noted that the current-carrying conductor is not part of the fiber optic interferometer, but is only marked to illustrate the use of the fiber optic current transformer) are shown, as well as the circuit connections between the photodetector 2 and the photoelectric conversion unit, error accumulation unit, delay control unit, and variable delay unit.

[0032] It should be noted that, in Figure 1 In one embodiment, the variable delay unit is located between the electro-optic phase modulator 5 and the fixed delay fiber 6. In other embodiments, the variable delay unit may also be located between the fixed delay fiber 6 and the fiber measurement coil 7.

[0033] In this embodiment of the invention, a photoelectric conversion unit is used to convert the light intensity signal received by the photodetector into a proportional voltage signal; an error accumulation unit is used to perform characteristic analysis on the voltage signal output by the photoelectric conversion unit to obtain a periodic misalignment error signal; a delay control unit controls a variable delay unit according to the periodic misalignment error signal, wherein the variable delay unit changes the light wave delay time by voltage control, wherein the magnitude of the light wave delay time is positively correlated with the amplitude of the control voltage, and the variable delay unit is a cylindrical piezoelectric ceramic or an electrically controlled optical delay line tightly wound with optical fiber.

[0034] In this embodiment of the invention, Figure 2 As shown, the duty cycle of the modulated square wave signal applied to the electro-optic phase modulation is 50%. By adjusting the intrinsic period of the fiber optic interferometer, the intrinsic period of the fiber optic interferometer is made to be exactly equal to half of the modulated square wave period. The output voltage of the photoelectric conversion unit is a straight line, thereby eliminating the additional pulse signal introduced by the period mismatch, and thus eliminating the zero bias current error of the fiber optic current transformer.

[0035] The error accumulation unit in this embodiment of the invention includes: a phase-detection multiplication circuit, an addition circuit, and an integration circuit, such as... Figure 4As shown, the phase detection multiplication circuit can be a multiplier, and the addition circuit can be an adder. The specific implementation process of the error accumulation unit is as follows:

[0036] (1) When the intrinsic period of the fiber optic interferometer is less than half the period of the modulated square wave, a positive pulse exists at the beginning of the half-period of the square wave (e.g., Figure 2 As shown, this positive pulse is phase-detected by a multiplier and then integrated and accumulated by an integrator circuit to obtain a positive error signal.

[0037] (2) Figure 2 As shown, when the intrinsic period of the fiber optic interferometer is greater than half the period of the modulated square wave, a positive pulse exists at the tail of the half-period of the square wave (e.g., Figure 2 As shown, by integrating and accumulating this positive pulse through an integrator circuit after it has been fed into a phase detector, a negative error signal is obtained.

[0038] (3) The adder circuit accumulates all positive and negative error signals to obtain the output signal of the error accumulation unit.

[0039] In this embodiment of the invention, the delay control unit can be an analog PID circuit, which first inverts the output signal of the error accumulation unit, then performs PID processing before outputting it to the variable delay unit; or it can be an analog-to-digital converter, a digital PID circuit, and a digital-to-analog converter, performing analog-to-digital conversion-digital signal processing-digital-to-analog conversion, first performing PID processing on the output signal of the error accumulation unit and then inverting it. The control objective of the delay control unit is to make the output of the error accumulation unit zero, which ensures that the eigencycle period of the fiber optic interferometer is equal to the half-cycle of the modulated square wave, and that there is no additional pulse signal in the interference light intensity.

[0040] The fiber optic current transformer with controllable delay time provided in this embodiment is implemented in the actual modulation process as follows:

[0041] (1) Obtain the error signal caused by the misalignment between the intrinsic period of the fiber optic interferometer and the half-period of the modulated square wave, and refer to... Figure 2 ;

[0042] (2) The periodic misalignment error signal is integrated and accumulated through the error accumulation unit. For the specific implementation of the error accumulation unit, please refer to [link / reference]. Figure 4 , Figure 4 The two phase-detection square waves used in the reference and their phase relationship with the modulation square wave are discussed. Figure 3 ;

[0043] (3) The output of the error accumulation unit is sent to the delay control unit. The delay control unit adopts the PID negative feedback regulation method, and its output acts on the variable delay unit.

[0044] (4) The variable delay unit is the final execution unit. It uses the output signal of the delay control unit to change the intrinsic period of the fiber interferometer so that it is exactly equal to the half period of the modulated square wave.

[0045] This embodiment adjusts the intrinsic period of the fiber optic interferometer in real time to ensure that it is always accurately equal to half the period of the modulated square wave, thereby eliminating the additional pulse signal introduced by the period mismatch and thus eliminating the zero bias current error of the fiber optic current transformer.

[0046] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A fiber optic current transformer with controllable delay time, characterized in that, include: The system includes a photoelectric conversion unit, an error accumulation unit, a delay control unit, a variable delay unit, and a fiber optic interferometer. The fiber optic interferometer comprises a light source, a photodetector, a coupler, a polarizer, an electro-optic phase modulator, a fixed delay fiber, and a fiber optic measurement coil. The photoelectric conversion unit is used to convert the light intensity signal received by the photodetector into a voltage signal of equal proportion. The error accumulation unit is used to analyze the characteristics of the output voltage signal of the photoelectric conversion unit to obtain the periodic misalignment error signal; The delay control unit controls the variable delay unit according to the periodic misalignment error signal. The variable delay unit changes the optical wave delay time through voltage control, wherein the magnitude of the optical wave delay time is positively correlated with the amplitude of the control voltage. The fixed-delay fiber is located between the electro-optic phase modulator and the fiber measurement coil, and the variable-delay unit is located between the electro-optic phase modulator and the fixed-delay fiber, or between the fixed-delay fiber and the fiber measurement coil; the duty cycle of the modulation square wave signal applied to the electro-optic phase modulator is 50%; the error accumulation unit includes: a phase detection multiplication circuit, an integrator circuit, and an adder circuit. The phase detection multiplication circuit uses two different phase detection square waves. When the intrinsic period of the fiber interferometer is less than half the modulation square wave period, a positive pulse exists at the beginning of the square wave half-period. This positive pulse is phase-detected by the phase detection multiplication circuit and then integrated and accumulated by the integrator circuit to obtain a positive error signal. When the intrinsic period of the fiber interferometer is greater than half the modulation square wave period, a positive pulse exists at the end of the square wave half-period. This positive pulse is phase-detected by the phase detection multiplication circuit and then integrated and accumulated by the integrator circuit to obtain a negative error signal. The adder circuit accumulates all positive and negative error signals to obtain the output signal of the error accumulation unit.

2. The fiber optic current transformer with controllable delay time according to claim 1, characterized in that, The delay control unit first inverts the output signal of the error accumulation unit, then performs PID processing before outputting it to the variable delay unit; or it first performs PID processing on the output signal of the error accumulation unit and then inverts it before outputting it to the variable delay unit.

3. The fiber optic current transformer with controllable delay time according to claim 1, characterized in that, The variable delay unit is an electrically controlled optical delay line.

4. The fiber optic current transformer with controllable delay time according to claim 1, characterized in that, The variable delay unit is a cylindrical piezoelectric ceramic tightly wound with an optical fiber.

5. The fiber optic current transformer with controllable delay time according to claim 1, characterized in that, The delay control unit is an analog PID circuit.

6. The fiber optic current transformer with controllable delay time according to claim 1, characterized in that, The delay control unit includes an analog-to-digital converter circuit, a digital PID circuit, and a digital-to-analog converter circuit.

Images