A lossless power frequency interference suppression system and method

Abstract

The present invention relates to a lossless power frequency interference suppression system and method. The system comprises: a signal extraction module, a phase-locking module, and an interference suppression module. The signal extraction module is configured to extract the power frequency signal and harmonic components from a sensor signal; the phase-locking module is configured to perform coherent phase-locking processing on the power frequency signal and harmonic components to obtain a corresponding interference signal; and the interference suppression module is configured to subtract the corresponding interference signal from the sensor signal. This invention overcomes the problem of existing analog and digital notch filters being unable to suppress and distort signals around the interference frequency, providing an important guarantee for achieving precise measurement of surface electric and magnetic field signals.

Description

Technical Field

[0001] The present invention relates to the field of geophysical exploration, and in particular to a lossless power frequency interference suppression system and method. Background Art

[0002] Electromagnetic exploration uses the amplitude / phase characteristics (frequency domain) and attenuation characteristics (time domain) of ground electromagnetic signals to extract information on parameters such as resistivity, dispersion, polarizability, magnetic susceptibility, and dipole. This allows for intuitive geoelectrical signatures and, combined with forward and inversion techniques, allows for the detection of stratum structure. Therefore, observing the amplitude / phase and attenuation characteristics of electromagnetic signals is a key task for electromagnetic exploration instruments.

[0003] With the development of my country's industry, electricity consumption has increased annually, and the amount of energy leaked during transmission has also increased. A large portion of this energy is coupled into the earth, generating high power-frequency signals on the surface. The amplitude of these power-frequency interference signals is far greater than the desired signal to be measured, resulting in an extremely low signal-to-noise ratio (SNR). This degrades the quality of electromagnetic data and seriously affects the depth and accuracy of electromagnetic exploration.

[0004] like Figure 1 The following diagram shows the spectrum of the surface electric and magnetic field signals measured at a measurement point in the Hongtoushan Copper Mine and Old Mine areas. It can be seen that the power frequency and harmonic components of the surface electric and magnetic fields are very rich, with amplitudes several orders of magnitude higher than the background signal, reaching over 1mV. Due to spectrum leakage and data truncation windowing in the FFT, the measurement of frequencies near the interfering signal is severely affected. While conventional analog and digital filters suppress the power frequency interference to some extent, they also weaken signals near the interfering frequency, distorting both the amplitude and phase of the measured signals.

[0005] The traditional power frequency interference suppression circuit uses a double T trap circuit such as Figure 2 Its transmission characteristics are shown as Figure 3 As shown in the figure, the traditional power frequency suppression twin-T notch circuit exhibits severe amplitude and frequency distortion near the notch frequency. An ideal notch filter should only suppress the interference frequency, while maintaining a stable amplitude and phase for signals around the interference frequency. Summary of the Invention

[0006] The purpose of the present invention is to propose a lossless power frequency interference suppression system and method to overcome the problem that existing analog notch filters and digital notch filters cannot overcome the distortion of signals around the interference frequency, providing an important guarantee for the precise measurement of surface electric field signals and magnetic field signals.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A lossless power frequency interference suppression system, comprising: a signal extraction module, a phase locking module, and an interference suppression module;

[0009] The signal extraction module is used to extract the power frequency signal and harmonic components in the sensor signal;

[0010] The phase-locking module is used to perform coherent phase-locking processing on the power frequency signal and the harmonic components to obtain the corresponding interference signal;

[0011] The interference suppression module is configured to subtract the corresponding interference signal from the sensor signal.

[0012] Optionally, the signal extraction module includes: a bandpass filter and an amplifier connected to each other, and the amplifier is also connected to the phase-locked module.

[0013] Optionally, the phase-locked module includes: a coherent phase-locked multiplier, a low-pass filter, a PI controller, a voltage-controlled oscillator, and a differentiator connected in sequence; and the outputs of the voltage-controlled oscillator and the differentiator are respectively connected to the input of the coherent phase-locked multiplier.

[0014] A lossless power frequency interference suppression method, the method comprising:

[0015] Extract the power frequency signal and harmonic components from the sensor signal;

[0016] Performing coherent phase-locked processing on the power frequency signal and the harmonic components to obtain a corresponding interference signal;

[0017] The corresponding interference signal is subtracted from the sensor signal.

[0018] Optionally, extracting the power frequency signal and harmonic components from the sensor signal includes:

[0019] Use bandpass filter to extract power frequency signal and harmonic components from sensor signal;

[0020] The amplifier is used to amplify the extracted power frequency signal and harmonic components.

[0021] Optionally, performing coherent phase-locked processing on the power frequency signal and the harmonic components includes:

[0022] Multiply the input signal with power frequency interference with the local output signal of the voltage-controlled oscillator to obtain power frequency phase information;

[0023] Multiplying the interference signal with the local output signal of the voltage-controlled oscillator to obtain phase information;

[0024] The power frequency phase information is picked up by a low-pass filter phase to obtain a first output signal;

[0025] Adjusting the signal amplitude of the first output signal through PI control; wherein the phase of the adjusted signal is zero;

[0026] oscillating the regulated signal using a voltage-controlled oscillator to obtain an output signal of the voltage-controlled oscillator;

[0027] Using a differentiator to phase-shift the output signal of the voltage-controlled oscillator;

[0028] After multiplying the output of the differentiator by the interference signal, performing phase picking on the multiplied signal through a low-pass filter to obtain the amplitude of the interference signal;

[0029] The amplitude of the interference signal is multiplied by the interference signal to obtain a composite signal, ie, the interference signal.

[0030] Optionally, the local output signal of the voltage-controlled oscillator is:

[0031]

[0032] in, is the local output signal of the voltage controlled oscillator, f1 is the output frequency of the voltage controlled oscillator, is the voltage controlled oscillator output signal amplitude, is the time variable, is the initial phase of the voltage controlled oscillator;

[0033] The interference signal is:

[0034]

[0035] in, is the interference signal, f2 is the interference signal frequency, is the interference signal amplitude;

[0036] The phase information is:

[0037]

[0038] in, is the phase information;

[0039] The first output signal is:

[0040]

[0041] in, is the first output signal;

[0042] The output signal of the voltage controlled oscillator is:

[0043]

[0044] in, Output signal for voltage controlled oscillator;

[0045] The output signal of the differentiator is:

[0046]

[0047] in, is the output signal of the differentiator, R is the differentiator resistance, C is the differentiator capacitance, and the negative sign indicates a 180-degree phase reversal;

[0048] The synthetic signal is:

[0049]

[0050] in, is a synthetic signal.

[0051] The beneficial effects of the present invention are:

[0052] The present invention utilizes a signal extraction module to extract the power frequency signal and harmonic components from the sensor signal; a phase-locking module performs coherent phase-locking processing on the power frequency signal and harmonic components to obtain the corresponding interference signal; and an interference suppression module subtracts the corresponding interference signal from the sensor signal. This invention overcomes the problem of existing analog and digital notch filters that suppress and distort signals around the interference frequency, providing a crucial guarantee for the precise measurement of surface electric and magnetic field signals.

[0053] This invention utilizes coherent phase locking to suppress power-frequency interference, avoiding the problems of conventional notch filters that suppress signals near the notch frequency and cause phase distortion. The interference signal can be suppressed to a level of 36.5dB, and higher levels are expected to be achieved through parameter adjustment, significantly improving the dynamic range of weak signal detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0055] Figure 1 This is a schematic diagram of the surface electric and magnetic field measurement signals;

[0056] Figure 2 This is a schematic diagram of a traditional power frequency suppression double-T trap circuit;

[0057] Figure 3Schematic diagram of transmission characteristics of a conventional power frequency suppression double-T trap circuit according to an embodiment of the present invention;

[0058] Figure 4 This is a block diagram of a lossless power frequency interference suppression circuit according to an embodiment of the present invention;

[0059] Figure 5 Schematic diagram of the power frequency interference suppression principle of the lossless power frequency interference suppression circuit according to an embodiment of the present invention;

[0060] Figure 6 Schematic diagram of a differential circuit according to an embodiment of the present invention achieving a 90° phase shift;

[0061] Figure 7 Schematic diagram of the effect of lossless power frequency suppression according to an embodiment of the present invention;

[0062] Figure 8 Schematic diagram of a simulation model of a lossless power frequency signal tracking circuit according to an embodiment of the present invention;

[0063] Figure 9 Schematic diagram of the phase-locking process of the power frequency signal according to an embodiment of the present invention;

[0064] Figure 10 FIG. 4 is a schematic diagram of a tracking error signal according to an embodiment of the present invention. DETAILED DESCRIPTION

[0065] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0066] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0067] This embodiment proposes a lossless power frequency interference suppression system, including: a signal extraction module, a phase locking module, and an interference suppression module;

[0068] The signal extraction module is used to extract the power frequency signal and harmonic components in the sensor signal;

[0069] The phase-locking module is used to perform coherent phase-locking processing on the power frequency signal and the harmonic components to obtain the corresponding interference signal;

[0070] The interference suppression module is configured to subtract the corresponding interference signal from the sensor signal.

[0071] Among them, the power frequency signal is Figure 4 The fundamental wave in the signal is a 50Hz power frequency signal. Due to the nonlinearity of high-power equipment, a large number of harmonics are generated. The fundamental wave and harmonics together act as interference sources in the detection device.

[0072] Furthermore, the signal extraction module includes: a bandpass filter and an amplifier connected to each other, and the amplifier is also connected to the phase-locked module.

[0073] Furthermore, the phase-locked module includes: a coherent phase-locked multiplier, a low-pass filter, a PI controller, a voltage-controlled oscillator, and a differentiator connected in sequence; and the outputs of the voltage-controlled oscillator and the differentiator are respectively connected to the input of the coherent phase-locked multiplier.

[0074] Specifically, the technical solution of this embodiment is as follows: Figure 4 As shown, the sensor signal is filtered through a bandpass filter to extract the power frequency signal. This signal is then amplified G times (typically to above 100mV) before entering the coherent phase-locked multiplier input X. The multiplier output is low-pass filtered, compared with a reference zero, and fed into a PI controller. The PI controller output serves as the input to the voltage-controlled oscillator (VCO), which oscillates and outputs a square wave. The VCO's output waveform is controllable within a frequency range of 49.5-50.5Hz. The VCO output waveform is divided by 315 and then converted to a corresponding sinusoidal waveform using a square-wave to sine-wave converter. This serves as the coherent phase-locked multiplier input Y. The VCO output is divided by 315 to obtain the fundamental phase-locked signal; by 105 to obtain the third harmonic phase-locked signal; by 93 to obtain the fifth harmonic phase-locked signal; by 45 to obtain the seventh harmonic phase-locked signal; and by 35 to obtain the ninth harmonic signal. The fundamental wave and the 3rd, 5th, 7th and 9th harmonics are coherently filtered on the input signal to obtain the amplitude information of the corresponding fundamental wave and harmonics. Finally, the amplitude is multiplied by the unit amplitude (Vpp=1V) of the fundamental wave and the corresponding harmonics to obtain the waveform of the corresponding fundamental wave and its harmonics of the interference signal, and all the corresponding interference waveforms are subtracted from the input signal to achieve the goal of its suppression.

[0075] This embodiment also proposes a lossless power frequency interference suppression method, including:

[0076] Extract the power frequency signal and harmonic components from the sensor signal;

[0077] Performing coherent phase-locked processing on the power frequency signal and the harmonic components to obtain a corresponding interference signal;

[0078] The corresponding interference signal is subtracted from the sensor signal.

[0079] Furthermore, extracting the power frequency signal and harmonic components from the sensor signal includes:

[0080] Use bandpass filter to extract power frequency signal and harmonic components from sensor signal;

[0081] The amplifier is used to amplify the extracted power frequency signal and harmonic components.

[0082] Furthermore, performing coherent phase-locking processing on the power frequency signal and the harmonic components includes:

[0083] Multiply the input signal with power frequency interference with the local output signal of the voltage-controlled oscillator to obtain power frequency phase information;

[0084] The power frequency phase information is picked up by a low-pass filter phase to obtain a first output signal;

[0085] Adjusting the signal amplitude of the first output signal through PI control; wherein the phase of the adjusted signal is zero;

[0086] oscillating the regulated signal using a voltage-controlled oscillator to obtain an output signal of the voltage-controlled oscillator;

[0087] Using a differentiator to phase-shift the output signal of the voltage-controlled oscillator;

[0088] After multiplying the output of the differentiator by the interference signal, performing phase picking on the multiplied signal through a low-pass filter to obtain the amplitude of the interference signal;

[0089] The amplitude of the interference signal is multiplied by the interference signal to obtain a composite signal, ie, the interference signal.

[0090] Specifically, in this embodiment, fundamental wave suppression is taken as an example for explanation, and its detailed block diagram is as follows: Figure 5 As shown:

[0091] The phase-locked link process is as follows: the front-end circuit signal is multiplied by the output signal of the local voltage-controlled oscillator (adjustable frequency range 49.5-50.5Hz) to form a phase detector to obtain phase information. Assuming the output frequency of the voltage-controlled oscillator is f1, its signal is:

[0092] (1)

[0093] The interference signal frequency is f2, and its signal is:

[0094] (2)

[0095] The signal after multiplication is:

[0096] (3)

[0097] Here, S2 refers to the superposition of the interference signal and the measured signal, obtained directly from the front-end sensor. Because the interference signal and the measured signal have different frequencies, and the voltage-controlled oscillator frequency is fine-tuned to the power frequency (49.5-50.5), it is easy to separate the power frequency signal from the measured signal by multiplying it with the voltage-controlled oscillator. For ease of analysis, the input signal will be treated directly as the interference signal. Figure 4 The channel input signal in is S2.

[0098] After phase picking through low-pass filtering, the output signal is:

[0099] (4)

[0100] Through the PI controller, the amplitude of the S4 signal is adjusted to 0. At this time, the phase of the S4 signal is zero, satisfying:

[0101] (5)

[0102] At this time, the interference signal and the local voltage-controlled oscillator signal have the same frequency and phase, completing the phase-locking function. Assume that the voltage-controlled oscillator output is V1:

[0103] (6)

[0104] Set the phase-locked signal amplitude to 1, that is, A1=1, then:

[0105] (7)

[0106] The phase shift of 90 degrees is completed by the differential circuit. Figure 6 shown.

[0107] The input S1 of the local oscillator is used as the input of the differentiator. According to the differential circuit, we can get:

[0108] (6)

[0109] Substituting formula (5) into formula (6) yields:

[0110] (7)

[0111] By selecting parameters, make A1RC=1, then:

[0112] (8)

[0113] Multiply S5 by the interference signal S2, and after picking up the amplitude through low-pass filtering, we get the interference signal amplitude S6=A2. Finally, multiply the interference signal amplitude S6 by the interference phase-locked signal S5 to obtain:

[0114] (9)

[0115] At this point, the composite signal is equal to the interference signal and is subtracted from the input signal, achieving lossless suppression of the interference signal.

[0116] In addition to the power frequency signal, the measured signal also contains a large number of harmonic components, such as Figure 1 As shown in the figure, in addition to the 50 Hz fundamental wave, it also includes the 3rd, 5th, 7th, and 9th harmonics. The amplitude of higher harmonic components has dropped to close to the background noise and can be ignored. Figure 1 It was also found that the data contained 2nd, 4th, 6th, 8th, and 10th harmonics, which was caused by the fact that the acquisition frequency of the collector was not synchronized with the interference signal.

[0117] When the local oscillator is phase-locked with the external interference, its phase is 0 relative to the local oscillator signal, which is an odd function. Then the harmonic components of the device only contain odd harmonic components. Therefore, it is necessary to process the local oscillator signal by 3, 5, 7, and 9 times, and then extract the amplitude of each harmonic according to the coherence principle introduced above, and remove them from the input signal. The overall functional block diagram is shown as follows: Figure 4 shown.

[0118] Figure 4 It is a process of suppressing the total interference of power frequency and its harmonics at the same time; because the basic principle of harmonic suppression is the same as that of fundamental wave suppression, Figure 5 The process of suppressing the power frequency component alone is described. Figure 4 The division by 315 indicates that the voltage controlled oscillator output is 315 times the power frequency signal, which is used for subsequent frequency reduction processing to obtain the fundamental wave and its harmonic phase-locked signal. The reason for this treatment is that if the voltage controlled oscillator directly outputs the power frequency, it is difficult to obtain a symmetrical sine wave with the frequency-multiplied signal. Figure 4 It is easy to obtain the ideal fundamental wave and its harmonics by first doubling the frequency and then reducing the frequency.

[0119] Assuming that the interference signals include 50Hz amplitude 30mV, 150Hz amplitude 10mV, 250Hz amplitude 6mV, 350Hz amplitude 4.3mV, mixed with the measurement signal 49Hz amplitude 1mV, the proposed technical solution can achieve the effect of lossless power frequency suppression. Figure 7 shown.

[0120] Since the measurement signal is very low, the output signal is basically equal to the interference signal (including 50Hz and its harmonics) at the beginning. Figure 7 As shown in the lower left corner; as the suppression system starts to work, the output signal gradually suppresses the interference signal until the output is a measurement signal that basically does not contain interference, as shown in Figure 7 Shown below right.

[0121] The key to this method is the phase locking of the 50Hz power frequency signal. As long as the phase locking is successfully completed and two orthogonal signals, sine and cosine, are generated, the subsequent lossless suppression can be achieved. The following is a circuit simulation of the phase locking of the 50Hz power frequency signal. The circuit model is as follows: Figure 8 shown.

[0122] Figure 8 S1, S2, S3, S4 and S5 in Figure 5 The signals in the simulation are in one-to-one correspondence. Figure 9 shown.

[0123] It can be seen that after less than 2 seconds, the local oscillator signal is completely phase-locked to the input power frequency signal, completing the tracking error of the input power frequency interference signal. Figure 10 shown.

[0124] It can be seen that the tracking error signal reaches about 15mV when it reaches the steady state, and the interference is suppressed by 36.5dB.

[0125] The novel approach of using coherent phase locking to suppress power-frequency interference proposed in this embodiment avoids the problems of conventional notch filters suppressing signals near the notch frequency and causing phase distortion. The interference signal can be suppressed to a level of 36.5dB, and higher levels are expected to be achieved through parameter adjustment, significantly improving the dynamic range of weak signal detection.

[0126] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A lossless power frequency interference suppression method, characterized in that: include: Extract the power frequency signal and harmonic components from the sensor signal; Performing coherent phase-locked processing on the power frequency signal and the harmonic components to obtain a corresponding interference signal; The coherent phase-locking process of the power frequency signal and the harmonic components includes: Multiply the input signal with power frequency interference with the local output signal of the voltage-controlled oscillator to obtain power frequency phase information; Multiplying the interference signal with the local output signal of the voltage-controlled oscillator to obtain phase information; The power frequency phase information is picked up by a low-pass filter phase to obtain a first output signal; Adjusting the signal amplitude of the first output signal through PI control; wherein the phase of the adjusted signal is zero; oscillating the regulated signal using a voltage-controlled oscillator to obtain an output signal of the voltage-controlled oscillator; Using a differentiator to phase-shift the output signal of the voltage-controlled oscillator; After multiplying the output of the differentiator by the interference signal, performing phase picking on the multiplied signal through a low-pass filter to obtain the amplitude of the interference signal; multiplying the interference signal by the amplitude of the interference signal to obtain a composite signal, i.e., the interference signal; subtracting a corresponding interference signal from the sensor signal; The lossless power frequency interference suppression method is implemented based on a lossless power frequency interference suppression system; the system includes: Signal extraction module, phase-locked module, interference suppression module; The signal extraction module is used to extract the power frequency signal and harmonic components in the sensor signal; The phase-locking module is used to perform coherent phase-locking processing on the power frequency signal and the harmonic components to obtain the corresponding interference signal; The phase-locked module includes: a coherent phase-locked multiplier, a low-pass filter, a PI controller, a voltage-controlled oscillator, and a differentiator connected in sequence; and the outputs of the voltage-controlled oscillator and the differentiator are respectively connected to the input of the coherent phase-locked multiplier; The interference suppression module is configured to subtract the corresponding interference signal from the sensor signal.

2. The lossless power frequency interference suppression method according to claim 1, characterized in that: Extracting the power frequency signal and harmonic components from the sensor signal includes: Use bandpass filter to extract power frequency signal and harmonic components from sensor signal; An amplifier is used to amplify the extracted power frequency signal and harmonic components.

3. The lossless power frequency interference suppression method according to claim 2, characterized in that: The local output signal of the voltage controlled oscillator is: in, is the local output signal of the voltage controlled oscillator, f1 is the output frequency of the voltage controlled oscillator, is the voltage controlled oscillator output signal amplitude, is the time variable, is the initial phase of the voltage controlled oscillator; The interference signal is: in, is the interference signal, f2 is the interference signal frequency, is the interference signal amplitude; The phase information is: in, is the phase information; The first output signal is: in, is the first output signal; The output signal of the voltage controlled oscillator is: in, Output signal for voltage controlled oscillator; The output signal of the differentiator is: in, is the output signal of the differentiator, R is the differentiator resistance, C is the differentiator capacitance, and the negative sign indicates a 180-degree phase reversal; The synthetic signal is: in, is a synthetic signal.

4. The lossless power frequency interference suppression method according to claim 1, characterized in that: The signal extraction module includes: a bandpass filter and an amplifier connected to each other, and the amplifier is also connected to the phase-locked module.

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