Modulator half-wave voltage tracking method based on optical current transformer closed-loop algorithm

Abstract

The present invention discloses a modulator half-wave voltage tracking method based on an optical current transformer closed-loop algorithm, which adopts a specific modulation signal to perform closed-loop modulation and demodulation and half-wave voltage tracking on the optical current transformer; discretized sampling processing is performed on the output signal of the detector, and each segment sampling value of the detector output signal is subjected to segmented accumulation processing; a demodulation operation is performed on the result of the accumulation processing to obtain the modulation phase carrying current information, and then the current to be measured and the phase feedback value are obtained; the working half-wave voltage of the modulator is tracked in real time, and feedback adjustment is performed to ensure that the working half-wave voltage of the modulator always remains consistent with the real half-wave voltage of the modulator.

Description

Technical Field

[0001] The invention relates to a modulator half-wave voltage tracking method based on an optical current transformer closed-loop algorithm, and belongs to the technical field of current sensing. Background Art

[0002] Optical current transformer is referred to as OCT. Current transformer is an important device for monitoring the operation status of power system. Measurement, monitoring and protection control in substation rely on it to obtain the current information required for measurement, metering and protection. Traditional current transformer is electromagnetic transformer. Due to its bulky size, complex insulation structure, easy magnetic saturation, easy ferromagnetic resonance, small dynamic measurement range and narrow response frequency band, electromagnetic transformer is increasingly unable to meet the needs of the development of power system automation and digital network. Optical current transformer has the advantages of simple insulation structure, small size, light weight and good linearity, no magnetic saturation and ferromagnetic resonance problems, etc. It can replace the traditional electromagnetic transformer and has broad application prospects.

[0003] OCT uses an all-fiber structure and detects current based on the principle of Faraday magneto-optical effect: the sensing fiber ring of OCT is set in the magnetic field of the conductor, and the Faraday magneto-optical effect occurs under the influence of the current to be measured. The phase difference generated in the optical fiber is proportional to the spatial magnetic field intensity, and the magnetic field intensity is proportional to the current intensity. Therefore, the measured current can be obtained by detecting the phase difference. Because the interference light signal detected by OCT is a cosine function of the phase difference, it has defects such as low response sensitivity near zero phase difference, limited measurement range, and the interference result cannot reflect the directionality of the input current. In order to solve the problems of cosine sensitivity and directionality, a phase modulator is added to the system optical path, square wave modulation is implemented on the optical signal, and a non-reciprocal 90° phase bias is introduced in the optical fiber coil. Converting the cosine response to a sine response can effectively improve the sensitivity of optical CT.

[0004] The demodulation algorithm of OCT determines the accuracy of the device measurement to a large extent. At present, the demodulation schemes of all-fiber current transformers have two directions: open-loop demodulation and closed-loop demodulation. The open-loop scheme has problems such as limited current measurement range and poor linearity; while the closed-loop demodulation scheme can effectively solve the current measurement range and linearity problems, so it is the current mainstream demodulation direction. Therefore, the phase modulator is an important component in the OCT system, and there is an error between the standard half-wave voltage of the modulator and the actual half-wave voltage, and as the operating environment conditions change or the operating time increases, the actual half-wave voltage of the modulator may also change, which will cause errors in the phase difference obtained by demodulation and inaccurate current measurements. At present, conventional closed-loop demodulation schemes cannot track the half-wave voltage of the modulator in real time. Finding a closed-loop demodulation algorithm that can track the half-wave voltage of the modulator in real time has become an important idea to improve measurement accuracy.

[0005] Based on the above analysis, the present invention is devoted to studying a modulator half-wave voltage tracking method based on an optical current transformer closed-loop algorithm, and this case is thus generated. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a modulator half-wave voltage tracking method based on an optical current transformer closed-loop algorithm.

[0007] To achieve the above-mentioned purpose, the present invention provides a modulator half-wave voltage tracking method based on an optical current transformer closed-loop algorithm, which uses a specific modulation signal to perform closed-loop modulation and demodulation and half-wave voltage tracking on the optical current transformer; discretizes the output signal of the detector and performs segmented accumulation processing on the sampling values ​​of each segment of the detector output signal; demodulates the result of the accumulation processing to obtain the modulation phase carrying current information, and then obtains the measured current and phase feedback value; tracks the working half-wave voltage of the modulator in real time, and performs feedback adjustment to ensure that the working half-wave voltage of the modulator always remains consistent with the real half-wave voltage of the modulator.

[0008] Preferably, the period of the specific modulation signal is τ, where τ is equal to the transmission time of the optical signal in the optical current transformer;

[0009] The half-wave voltage monitoring period of the optical current transformer is T, and T=M×τ, where M is a positive integer representing the number of τ, and the modulator is subjected to a half-wave voltage detection every M-1 times τ.

[0010] Preferably, in the first M-1 τ, the output signal amplitude of the detector in each τ is divided into a signal segment U1 and a signal segment U2, where the signal segment U1 is the positive half cycle of modulation and the signal segment U2 is the negative half cycle of modulation, and the expressions are respectively:

[0011]

[0012]

[0013] Where P0 is the optical power, φ s is the phase difference caused by the measured current, ±π / 2 is the square wave modulation signal applied by the modulator, φ f is the current closed-loop feedback signal applied to the modulator.

[0014] Preferably, in the Mth τ, the output signal amplitude of the detector is divided into four signal segments U3, U4, U5 and U6, and the expressions are as follows:

[0015]

[0016]

[0017]

[0018]

[0019] Among them, the length of the U3 signal segment is equal to the length of the U5 signal segment, and the length of the U4 signal segment is equal to the length of the U6 signal segment.

[0020] Preferably, each segment of the sampling value of the detector output signal is subjected to segmented accumulation processing, including:

[0021] The detector output signal within each τ is sampled 4N times uniformly, where N is an integer greater than 0. The sampled values ​​of each segment from U1 to U6 are accumulated to obtain the accumulated value of each segment:

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028] In the above formula, U 1,2N , U 2,2N , U 3,N , U 4,N , U 5,N and U 6,N They are the accumulated values ​​corresponding to the signal segments U1, U2, U3, U4, U5 and U6 respectively; U1(n), U2(n), U3(n), U4(n), U5(n) and U6(n) are the values ​​of the nth sampling points in U1, U2, U3, U4, U5 and U6 respectively, and N is a positive integer.

[0029] Preferably, the modulation phase carrying the current information is obtained, including:

[0030] The modulation phase φ is solved according to the following formula s :

[0031] The first M-1 modulation phases:

[0032] The Mth modulation phase:

[0033] According to the phase difference produced by the measured current, a phase feedback value with equal amplitude and opposite direction is generated.

[0034] Preferably, the working half-wave voltage of the modulator is tracked in real time and feedback is adjusted to ensure that the working half-wave voltage of the modulator always remains consistent with the real half-wave voltage of the modulator, including:

[0035] There is a deviation between the working half-wave voltage of the modulator and the standard half-wave voltage of the modulator, which causes the actual amplitudes of the detector outputs U1, U2, U3 and U5 to deviate from the ideal value. The actual amplitudes of U1, U2, U3 and U5 are as follows:

[0036]

[0037]

[0038]

[0039]

[0040] In the above formula, U 1,2N’ , U 2,2N’ , U 3,N’ and U 5,N’ are the actual amplitudes of the U1, U2, U3 and U5 signal segments, respectively, Δ It is the deviation between the modulator working half-wave voltage and the standard half-wave voltage.

[0041] Preferably, the half-wave voltage deviation φ is calculated according to the following formula Δ :

[0042]

[0043] And in the subsequent modulation cycle, the half-wave voltage of the modulator is adjusted to:

[0044] V π ′=V π +φ Δ ,

[0045] Among them, V π is the half-wave voltage of the modulator before the modulation cycle, V π ' is the half-wave voltage of the modulator after the modulation period,

[0046] The positive and negative half-cycle feedback voltage actually applied to the modulator is

[0047]

[0048] Ensure that the working half-wave voltage of the modulator is always consistent with the real half-wave voltage of the modulator, and no error will be caused in the transformer due to the change of the half-wave voltage.

[0049] Preferably, the ratio of U3 to U4 signal segment lengths is 1:1.

[0050] The beneficial effects achieved by the present invention are:

[0051] The present invention adopts a specific closed-loop square wave signal, which can not only demodulate and measure the current size, but also track the modulator half-wave voltage in real time, and adjust the half-wave voltage size through feedback, thereby reducing the error caused by the modulator half-wave voltage drift and improving the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is the structural diagram of the closed-loop demodulation all-fiber current transformer;

[0053] Figure 2 is the signal waveform diagram when the half-wave voltage deviation is not considered;

[0054] Figure 3 This is the signal waveform diagram when the half-wave voltage deviation has been taken into account.

[0055] Explanation of the numbers in the figure: 1: light source; 2: coupler; 3: polarizer; 4: modulator; 5: polarization-maintaining fiber / cable; 6: 1 / 4 wave plate; 7: reflector; 8: sensing fiber; 9: detector; 10: A / D converter; 11: signal processing unit; 12: D / A converter; 13: measured current output; 14: square wave modulation signal φ m (t) Output; 15: Step wave compensation signal φ f (t) output; 16: current carrying conductor. DETAILED DESCRIPTION

[0056] The following examples are only used to more clearly illustrate the technical solution of the present invention, and are not intended to limit the scope of protection of the present invention. Figure 1 As shown, the all-fiber current transformer includes a light source 1, a coupler 2, a polarizer 3, a phase modulator 4, a polarization-maintaining fiber / cable 5, a quarter wave plate 6, a sensing fiber 7, a reflector 8, and a detector 9. The closed-loop demodulation device of the all-fiber current transformer includes an A / D converter 10, a signal processing unit 11, and a D / A converter 12. Figure 1 13 is the measured current signal output by the signal processing unit, and 14 and 15 are square wave signals used to superimpose a specific closed-loop modulation signal.

[0057] In the all-fiber current transformer, the light emitted by the light source 1 passes through the coupler 2 and the polarizer 3 to form linear polarized light. After the linear polarized light is injected into the phase modulator 4 at 45°, it is divided into two orthogonal linear polarized light beams that are transmitted along the fast and slow axes of the polarization-maintaining optical fiber 5 respectively. After the two linear polarized light beams pass through the 1 / 4 wave plate 6, they become left-handed and right-handed circularly polarized light respectively, and enter the sensing optical fiber 7 surrounding the measured current. As a Faraday material, the sensing optical fiber 7 is wound around the current-carrying conductor 16 to induce the magnetic field generated by the measured current. The Faraday magneto-optical effect causes the two circularly polarized light beams to produce a phase difference proportional to the magnitude of the measured current. After the two circularly polarized light beams are reflected by the reflector 8, the polarization modes are interchanged and they pass through the sensing optical fiber 7 again, doubling the non-reciprocal phase shift generated. After the two circularly polarized light beams pass through the 1 / 4 wave plate 6 again, they are restored to linear polarized light, interfere at the polarizer 3, and finally output light carrying phase information through the coupler 2. The light carrying the phase information enters the detector 9 and the A / D converter 10, is converted into an electrical signal, and then sent to the signal processing unit 11 to demodulate the phase difference; the demodulated phase difference is added to the feedback step wave signal to generate the measured current signal 12 for output.

[0058] The signal processing unit 11 sends a square wave modulation signal 13 to the modulator, and generates a closed-loop feedback step wave signal 14 according to the measured current signal 12, which is used to compensate for the phase difference generated by the measured current. The square wave signal 13 and the step wave signal 14 are superimposed and output to the phase modulator 4 through the D / A converter 15.

[0059] (1) Closed-loop modulation signal input

[0060] Ideally, the output signal of the closed-loop OCT detector PD is:

[0061]

[0062] In the above formula, P0 is the input light intensity; φ s is the Faraday phase difference generated on the sensing fiber 7, and φ s =4KVI, K is the number of turns of the sensing optical fiber 7, V is the Voldet constant of the sensing optical fiber 7, and I is the measured current; φ m is the applied square wave modulation signal 13; φ f is the applied step wave feedback signal 14.

[0063] like Figure 2 As shown in (a) and (b), the signal processing unit 11 sends two modulation signals, one of which is a square wave modulation signal 13φ m (t), the other is the step wave feedback signal 14φ f (t), the two modulated signals are superimposed and output to the modulator 4 to achieve phase modulation of the optical signal.

[0064] Figure 2 is the signal waveform diagram when the half-wave voltage deviation is not considered, where (a) is the square wave modulation signal φ m (t) waveform, (b) is the step wave compensation signal φ f (t) is the waveform diagram, and (c) is the detector output waveform diagram.

[0065] like Figure 2 As shown in (a), the standard square wave signal 13φ m (t), without considering the amplitude error, in the first M-1 modulation cycles, the square wave modulation signal is divided into positive and negative half cycles according to time, and the amplitudes are U m_1 , U m_2 ; In the Mth cycle, the modulated signal is divided into 4 signal segments, with amplitudes of U m_3 ~U m_6 , where U m_3 with U m_5 The signal segment length is equal, U m_4 with U m_6 The signal segment length is equal, U m_3 with U m_4 The signal segment length ratio can be adjusted according to needs, and the default is 1:1. m_1 ~U m_6 The expression is as follows:

[0066]

[0067]

[0068]

[0069] U m_4 =0,

[0070]

[0071] U m_6 =0,

[0072] like Figure 2 As shown in (b), the step wave feedback signal 14φ f (t) is used to compensate for the phase difference of the measured current, so that the optical CT system always works near the zero point of the sin function, thereby maintaining the best sensitivity and linearity. That is, the Rth cycle of φ f Can be expressed as

[0073] φ f_R =-φ s_R-1 .

[0074] like Figure 2As shown in (c), the optical signal is affected by the measured current, resulting in a phase difference φ s (t), and at the same time, after feedback modulation, it is affected by the modulation signal. In the first M-1 modulation cycles, the modulation signals received by the detector 9 can be expressed as U1 and U2. In the Mth modulation cycle, the modulation signals received by the detector 9 can be expressed as U3 to U6:

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081] (2) Discrete signal sampling

[0082] Discrete sampling is performed on the output signal of detector 9. The default ratio of the length of the U3 and U4 signal segments is 1:1. Then, the output signal is uniformly sampled 4N times in each modulation period τ, and the sampling values ​​of each segment of U1 to U6 are accumulated to obtain the accumulated value of each segment:

[0083]

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] In the above formula, U 1,2N , U 2,2N , U 3,N , U 4,N , U 5,N and U 6,N , are the accumulated values ​​corresponding to the signal segments U1 to U6, U1(n) to U6(n) are the values ​​of the nth sampling points in U1 to U6, and N is a positive integer.

[0090] (3) Demodulation to obtain the modulation phase φ s

[0091] According to the accumulated results of the sampling values ​​in different time periods, the demodulation operation is performed to obtain the modulation phase φ carrying the current magnitude information. s The demodulation algorithm is as follows:

[0092] In the first M-1 modulation cycles, ((2) - (1)) / ((2) + (1)), taking into account the phase difference φ caused by the measured current s Much smaller than 2π, the measured current phase difference is:

[0093]

[0094] In the Mth cycle, according to (Equation (5) - Equation (3)) / (Equation (5) + Equation (13)), the measured current phase difference is:

[0095] According to the phase difference produced by the measured current, a phase feedback value with equal amplitude and opposite direction is generated.

[0096] (4) Tracking modulator half-wave voltage

[0097] Figure 3 is the signal waveform diagram when the half-wave voltage deviation is considered, where (a) is the square wave modulation signal φ m (t) Waveform diagram; (b) is the step wave compensation signal φ f (t) Waveform diagram; (c) is the detector output waveform diagram.

[0098] like Figure 3 As shown, in actual operation, the working half-wave voltage of the modulator 4 may drift. The standard half-wave voltage V is applied to the modulator 4. π When the phase difference is π / 2, it may be π / 2+φ. Δ .

[0099] The deviation of the half-wave voltage causes the amplitudes of the signal segments U1, U2, U3 and U5 output by the detector 9 to deviate from the ideal situation. The actual amplitudes are:

[0100]

[0101]

[0102]

[0103]

[0104] In the Mth modulation cycle, there are

[0105]

[0106] Due to feedback phase shift φf Used to compensate the phase difference φ generated by the measured current in the previous modulation cycle s , so in the Mth modulation cycle, there is

[0107] φ f_M =-φ s_M-1 ,

[0108] For steady-state current, the amplitude of the current value changes very little, so it can be considered that

[0109] cos(φ s_M +φ f_M )=cos(φ s_M -φ s_M-1 )≈1,

[0110] According to formula (11), the difference between the actual output phase difference of modulator 4 and the standard phase difference after applying the standard half-wave voltage can be calculated: Δ :

[0111]

[0112] Then the actual half-wave voltage of the modulator can be adjusted as:

[0113] V π ′=V π +φ Δ (13)

[0114] Among them, V π is the half-wave voltage of the modulator before the modulation cycle, V π ' is the half-wave voltage of the modulator after the modulation cycle. In the subsequent modulation cycle, the signal processing unit 11 adjusts the output positive and negative half-cycle feedback modulation voltage 14 according to formula (12):

[0115] Dynamic feedback regulation can ensure that the working half-wave voltage Vπ' of the modulator 4 is always kept near the actual working half-wave voltage Vπ of the modulator, thereby ensuring that the optical CT system has the best sensitivity and linearity and does not cause errors in the transformer due to changes in the half-wave voltage.

[0116] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A modulator half-wave voltage tracking method based on an optical current transformer closed-loop algorithm, characterized in that: A specific modulation signal is used to perform closed-loop modulation and demodulation and half-wave voltage tracking on the optical current transformer; the output signal of the detector is sampled discretely, and each segment of the sampling value of the detector output signal is accumulated in sections; The result of the accumulation processing is demodulated to obtain the modulation phase carrying the current information, and then the measured current and phase feedback value are obtained; the working half-wave voltage of the modulator is tracked in real time, and feedback adjustment is performed to ensure that the working half-wave voltage of the modulator always remains consistent with the real half-wave voltage of the modulator; The period of the specific modulation signal is τ, where τ is equal to the transmission time of the optical signal in the optical current transformer; The half-wave voltage monitoring period of the optical current transformer is T, and T=M×τ, where M is a positive integer representing the number of τ, and the modulator is tested for half-wave voltage every M-1 times τ; In the first M-1 τ, the output signal amplitude of the detector in each τ is divided into signal segment U1 and signal segment U2. Signal segment U1 is the positive half cycle of modulation, and signal segment U2 is the negative half cycle of modulation. The expressions are: Where P0 is the optical power, φ s is the phase difference caused by the measured current, ±π / 2 is the square wave modulation signal applied by the modulator, φ f is the current closed-loop feedback signal applied to the modulator; In the Mth τ, the output signal amplitude of the detector is divided into four signal segments U3, U4, U5 and U6, and the expressions are as follows: Among them, the length of the U3 signal segment is equal to the length of the U5 signal segment, and the length of the U4 signal segment is equal to the length of the U6 signal segment.

2. The modulator half-wave voltage tracking method based on the optical current transformer closed-loop algorithm according to claim 1 is characterized in that: The sampling values ​​of each segment of the detector output signal are processed by segment accumulation, including: The detector output signal within each τ is sampled 4N times uniformly, where N is an integer greater than 0. The sampled values ​​of each segment from U1 to U6 are accumulated to obtain the accumulated value of each segment: In the above formula, U 1,2N , U 2,2N , U 3,N , U 4,N , U 5,N and U 6,N They are the accumulated values ​​corresponding to the signal segments U1, U2, U3, U4, U5 and U6 respectively; U1(n), U2(n), U3(n), U4(n), U5(n) and U6(n) are the values ​​of the nth sampling points in U1, U2, U3, U4, U5 and U6 respectively, and N is a positive integer.

3. The modulator half-wave voltage tracking method based on the optical current transformer closed-loop algorithm according to claim 2 is characterized in that: Get the modulation phase that carries the current information, including: The modulation phase φ is solved according to the following formula s : The first M-1 modulation phases: The Mth modulation phase: According to the phase difference produced by the measured current, a phase feedback value with equal amplitude and opposite direction is generated.

4. The modulator half-wave voltage tracking method based on the optical current transformer closed-loop algorithm according to claim 2 is characterized in that: Track the modulator's operating half-wave voltage in real time and perform feedback adjustment to ensure that the modulator's operating half-wave voltage always remains consistent with the modulator's true half-wave voltage, including: There is a deviation between the working half-wave voltage of the modulator and the standard half-wave voltage of the modulator, which causes the actual amplitudes of the detector outputs U1, U2, U3 and U5 to deviate from the ideal value. The actual amplitudes of U1, U2, U3 and U5 are as follows: In the above formula, U 1,2N’ , U 2,2N’ , U 3,N’ and U 5,N’ are the actual amplitudes of the U1, U2, U3 and U5 signal segments, respectively, Δ It is the deviation between the modulator working half-wave voltage and the standard half-wave voltage.

5. The modulator half-wave voltage tracking method based on optical current transformer closed-loop algorithm according to claim 4 is characterized in that: The half-wave voltage deviation φ is calculated according to the following formula: Δ : And in the subsequent modulation cycle, the half-wave voltage of the modulator is adjusted to: V π ′=V π +φ Δ , Among them, V π is the half-wave voltage of the modulator before the modulation cycle, V π ' is the half-wave voltage of the modulator after the modulation period, The positive and negative half-cycle feedback voltage actually applied to the modulator is Ensure that the working half-wave voltage of the modulator is always consistent with the real half-wave voltage of the modulator, and no error will be caused in the transformer due to the change of the half-wave voltage.

6. The modulator half-wave voltage tracking method based on optical current transformer closed-loop algorithm according to claim 1, characterized in that: The ratio of the U3 and U4 signal segment lengths is 1:1.

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