Submicrosecond punctuality method suitable for overhead line fault monitoring terminal

Abstract

The invention discloses a sub-microsecond timekeeping method suitable for an overhead line fault monitoring terminal, and belongs to the technical field of power system power transmission line fault monitoring, and the timekeeping method comprises the following specific steps: I, receiving and smoothing a 1PPS signal output by a satellite, and updating an average count value in real time; iI, comparing the count value per second output by the temperature compensation crystal oscillator with the average count value in real time, and dynamically adjusting the output frequency of the temperature compensation crystal oscillator according to a comparison result; iII, automatically switching a working mode in real time according to the quality of the 1PPS signal output by the satellite; according to the invention, low cost, low power consumption and submicrosecond-level high-precision time keeping are realized, and the method is suitable for applications with limited energy taking, such as an overhead line distributed fault distance measurement terminal and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of power system transmission line fault monitoring, and in particular to a sub-microsecond timekeeping method applicable to an overhead line fault monitoring terminal. Background Art

[0002] When a transmission line fails, the fault point will generate a traveling current wave that propagates at nearly the speed of light to both ends of the line. Distributed fault monitoring terminals installed on the line can collect the traveling wave currents one after another after the fault occurs. Based on the time difference in arrival of the traveling waves collected by the terminals on both sides of the fault point, combined with the installation distance between the two terminals and the traveling wave propagation speed, the distance between the fault point and the collection terminal can be calculated, thereby accurately locating the fault point. The time synchronization accuracy of the monitoring terminal has a great impact on the accuracy of fault location. At a wave speed of 3×10 8 Taking m / s as an example, a time synchronization error of 1μs means a positioning error of about 300 meters. Therefore, the design of a high-precision timekeeping solution for the monitoring terminal is crucial.

[0003] Existing timing solutions based on FPGAs or CPLDs plus Beidou / GPS modules use programmable logic devices to implement hardware timing control for sampling and storage, achieving sub-microsecond timing accuracy. However, this solution has the following problems when applied to overhead lines:

[0004] (1) Excessive power consumption: FPGA chips often consume more than 1W of power, requiring a large-capacity CT power supply device, which makes it difficult to provide stable power when the load current fluctuates;

[0005] (2) Poor environmental adaptability: The traditional temperature-compensated crystal oscillator frequency compensation algorithm is prone to lose lock when the temperature suddenly changes, resulting in the accumulation of timing errors;

[0006] (3) Insufficient anti-jitter capability: The pulse-per-second (1PPS) signal is easily affected by electromagnetic interference and produces ±100ns jitter, which directly affects the measurement accuracy of the arrival time difference of the fault traveling wave. Summary of the Invention

[0007] The purpose of the present invention is to solve the defects in the prior art and to propose a sub-microsecond timekeeping method suitable for overhead line fault monitoring terminals.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A sub-microsecond timekeeping method applicable to an overhead line fault monitoring terminal, the specific steps of the timekeeping method are as follows:

[0010] Ⅰ. Receive and smooth the 1PPS signal output by the satellite, and update the average count value in real time;

[0011] II. Compare the counts per second output by the temperature-compensated crystal oscillator with the average counts in real time, and dynamically adjust the output frequency of the temperature-compensated crystal oscillator based on the comparison results;

[0012] Ⅲ. Automatically switch working mode according to the quality of 1PPS signal output by satellite in real time.

[0013] As a further solution of the present invention, the specific steps of receiving and smoothing the 1PPS signal output by the satellite in step I are as follows:

[0014] S1.1: Every time a 1PPS signal is received, the low-power MCU counter records the count value at each signal reception moment, and then establishes a sliding window of length N. According to the established sliding window, the count values of N consecutive second pulses are saved and recorded as T1, T2, ..., T N ;

[0015] S1.2: Perform sliding average on the N second pulse count values stored in the sliding window to obtain the average count value T within N seconds AVG , then set the filter threshold ΔT TH , calculate the count value T1 to be entered into the window and the average count value T in real time AVG The deviation between ΔT1;

[0016] S1.3: If ΔT1 is greater than ΔT TH , then discard the count value T1 to be entered into the window. If ΔT1 is less than ΔT TH , then add the count value T1 to be entered into the sliding window and update the average count value T AVG .

[0017] As a further solution of the present invention, the specific calculation formula of the sliding average in S1.2 is as follows:

[0018]

[0019] Where, T AVG represents the average count value; T N Represents the Nth second pulse count value in the sliding window; N represents the total number of second pulse count values in the sliding window.

[0020] As a further solution of the present invention, the specific steps of dynamically adjusting the output frequency of the temperature-compensated crystal oscillator in step II are as follows:

[0021] S2.1: The average count value T after smoothing through the sliding window AVG As a reference value, collect the counts per second output of the temperature-compensated crystal oscillator in real time, and calculate the counts per second output of the temperature-compensated crystal oscillator and the corresponding T AVG The difference between ΔT raw ;

[0022] S2.2: The difference ΔT obtained by real-time comparison raw In the input controller, the controller obtains the control quantity through the incremental PID control algorithm, and converts the control quantity through the DAC to generate the corresponding compensation voltage;

[0023] S2.3: The compensation voltage is transmitted to the voltage control terminal of the temperature-compensated crystal oscillator. The temperature-compensated crystal oscillator then adjusts the output frequency under the action of the compensation voltage to reduce the deviation from the 1PPS signal.

[0024] As a further solution of the present invention, the specific calculation formula of the incremental PID control algorithm described in S2.2 is as follows:

[0025] ΔT raw (k) = T k -T AVG

[0026]

[0027] Δu(k)=K p ·[e(k)-e(k-1)]+K i ·e(k)+K d [e(k)-2e(k-1)+e(k-2)]

[0028] u(k)=u(k-1)+Δu(k)

[0029] Where, e(k) represents the ratio of the count value difference to the frequency deviation; f TCXO Represents the nominal frequency of the temperature-compensated crystal oscillator; K p , K i and K d Represent the proportional, integral and differential coefficients respectively; Δu(k) represents the control quantity increment; u(k) represents the cumulative control quantity.

[0030] As a further solution of the present invention, the specific steps of automatically switching the working mode according to the quality of the 1PPS signal output by the satellite in real time in step III are as follows:

[0031] S3.1: When the satellite signal is good, keep the monitoring terminal in taming mode and obtain second pulses normally to measure the time error. Then, use the PID control algorithm to calculate the control variable and adjust the frequency output of the temperature-compensated crystal oscillator.

[0032] S3.2: When the satellite signal is unstable or disappears, the monitoring terminal is switched to the self-timekeeping mode, and the second pulse count value stored in the taming mode is used as the reference value for time error measurement. The PID integral term is frozen during measurement, and only the proportional and differential terms are retained.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] This sub-microsecond timing method is suitable for overhead line fault monitoring terminals. When the satellite signal is normal, the system is in taming mode. Each time a 1PPS signal is received, the MCU counter records the pulse-per-second count value and saves N consecutive values through a sliding window. The average count value is calculated, a filtering threshold is set, and the deviation between the new count value and the average count value is compared in real time. If the new count value exceeds the threshold, the new count value is discarded. If it meets the threshold, it is included in the window and the average count value is updated. Using the average count value as a reference, the output count value of the temperature-compensated crystal oscillator is collected in real time, and the difference between the new count value and the average count value is calculated. The difference is input into an incremental PID controller, and the output control variable is converted into a compensation voltage by a DAC and applied to the voltage control terminal of the temperature-compensated crystal oscillator. The output frequency is dynamically adjusted to reduce the deviation from the 1PPS. When the signal is abnormal or interrupted, the system switches to self-timekeeping mode, using the historical count value as a reference and freezing the PID integral term. Only the proportional and differential control terms are retained to ensure frequency stability. This method achieves low-cost, low-power, and sub-microsecond high-precision timing. It is suitable for applications with limited energy access, such as distributed fault location terminals for overhead lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0036] Figure 1 This is a flowchart of a sub-microsecond timekeeping method applicable to an overhead line fault monitoring terminal proposed by the present invention;

[0037] Figure 2 Schematic diagram of a method for compensating frequency offset of a temperature-compensated crystal oscillator for a sub-microsecond timekeeping method applicable to an overhead line fault monitoring terminal proposed by the present invention;

[0038] Figure 3 This is a timing flow chart of a distributed fault ranging terminal for a sub-microsecond timing method applicable to an overhead line fault monitoring terminal proposed by the present invention. DETAILED DESCRIPTION

[0039] Reference Figure 1-3 A sub-microsecond timekeeping method for an overhead line fault monitoring terminal is provided. The specific steps of the timekeeping method are as follows:

[0040] Receive and smooth the 1PPS signal output by the satellite, and update the average count value in real time.

[0041] Specifically, refer to Figure 1 、 Figure 3It can be seen that each time a 1PPS signal is received, the low-power MCU counter records the count value at each signal reception moment, and then establishes a sliding window of length N. According to the established sliding window, the count values of consecutive N second pulses are saved and recorded as T1, T2, ..., T N , perform sliding average on the N second pulse count values stored in the sliding window to obtain the average count value T within N seconds AVG , then set the filter threshold ΔT TH , calculate the count value T1 to be entered into the window and the average count value T in real time AVG The deviation ΔT1 between them, if ΔT1 is greater than ΔT TH , then discard the count value T1 to be entered into the window. If ΔT1 is less than ΔT TH , then add the count value T1 to be entered into the sliding window and update the average count value T AVG .

[0042] It should be further explained that the specific calculation formula of the sliding average is as follows:

[0043]

[0044] Where, T AVG represents the average count value; T N Represents the Nth second pulse count value in the sliding window; N represents the total number of second pulse count values in the sliding window.

[0045] Compare the counts per second output by the temperature-compensated crystal oscillator with the average counts in real time, and dynamically adjust the output frequency of the temperature-compensated crystal oscillator based on the comparison results.

[0046] Specifically, refer to Figure 1-3 It can be seen that the average count value T after smoothing through the sliding window AVG As a reference value, collect the counts per second output of the temperature-compensated crystal oscillator in real time, and calculate the counts per second output of the temperature-compensated crystal oscillator and the corresponding T AVG The difference between ΔT raw , the difference ΔT obtained by real-time comparison raw In the input controller, the controller obtains the control quantity through the incremental PID control algorithm, and generates the corresponding compensation voltage after converting the control quantity through the DAC. The compensation voltage is transmitted to the voltage control end of the temperature-compensated crystal oscillator. Then, the temperature-compensated crystal oscillator adjusts the output frequency under the action of the compensation voltage to reduce the deviation from the 1PPS signal.

[0047] It should be noted that the specific calculation formula of the incremental PID control algorithm is as follows:

[0048] ΔT raw (k) = T k -T AVG

[0049]

[0050] Δu(k)=K p ·[e(k)-e(k-1)]+K i ·e(k)+K d [e(k)-2e(k-1)+e(k-2)]

[0051] u(k)=u(k-1)+Δu(k)

[0052] Where, e(k) represents the ratio of the count value difference to the frequency deviation; f TCXO Represents the nominal frequency of the temperature-compensated crystal oscillator; K p , K i and K d Represent the proportional, integral and differential coefficients respectively; Δu(k) represents the control quantity increment; u(k) represents the cumulative control quantity.

[0053] In addition, it should be further explained that the compensation voltage needs to be limited to meet the voltage tolerance range of the temperature-compensated crystal oscillator voltage control terminal. The limiting formula is as follows:

[0054]

[0055] Among them, V low Represents the minimum voltage that the temperature-compensated crystal oscillator voltage control terminal can withstand; V high Represents the maximum voltage that the temperature compensated crystal oscillator voltage control terminal can withstand.

[0056] The working mode is automatically switched in real time according to the quality of the 1PPS signal output by the satellite.

[0057] Specifically, when the satellite signal is good, the monitoring terminal is kept working in the taming mode, and the second pulse is normally obtained to measure the time error. The frequency output of the temperature-compensated crystal oscillator is adjusted by calculating the control quantity through the PID control algorithm. When the satellite signal is unstable or the signal disappears, the monitoring terminal is switched to the self-keeping mode, and the second pulse count value stored in the taming mode is used as the reference value for time error measurement. The PID integral term is frozen during measurement, and only the proportional and differential terms are retained.

[0058] It should be noted that the taming process is as follows: the first step is to perform smoothing window filtering on the input second pulse to suppress the second pulse jitter; the second step is to use the average count value T of the second pulse after smoothing window filtering AVG and the local second pulse count value to calculate the time error; the third step is to use the incremental PID control algorithm to calculate the control quantity; the fourth step is to perform DAC conversion on the control quantity; the fifth step is to adjust the output frequency of the temperature compensated crystal oscillator according to the input compensation voltage.

[0059] In addition, the low-power and high-timekeeping precision distributed fault monitoring terminal used in the present invention has an STM32L5 series low-power MCU (power consumption in operating mode ≤ 50mW) as the main control unit, and an integrated hardware capture and comparison unit (for 1PPS signal processing); the Beidou module uses NEO-M8T, whose 1PPS precision output accuracy is ≤ 20ns; the temperature-compensated crystal oscillator uses SiT5357, whose frequency stability is ≤ ±0.1ppm and the operating temperature range is -40℃ to 85℃.

Claims

1. A sub-microsecond timekeeping method for an overhead line fault monitoring terminal, characterized in that: The specific steps of this timekeeping method are as follows: Ⅰ. Receive and smooth the 1PPS signal output by the satellite, and update the average count value in real time; II. Compare the counts per second output by the temperature-compensated crystal oscillator with the average counts in real time, and dynamically adjust the output frequency of the temperature-compensated crystal oscillator based on the comparison results; Ⅲ. Automatically switch working mode according to the quality of 1PPS signal output by satellite in real time.

2. A sub-microsecond timekeeping method for an overhead line fault monitoring terminal according to claim 1, characterized in that: The specific steps for receiving and smoothing the 1PPS signal output by the satellite described in step I are as follows: S1.1: Every time a 1PPS signal is received, the low-power MCU counter records the count value at each signal reception moment, and then establishes a sliding window of length N. According to the established sliding window, the count values of N consecutive second pulses are saved and recorded as T1, T2, ..., T N ; S1.2: Perform sliding average on the N second pulse count values stored in the sliding window to obtain the average count value T within N seconds AVG , then set the filter threshold ΔT TH , calculate the count value T1 to be entered into the window and the average count value T in real time AVG The deviation between ΔT1; S1.3: If ΔT1 is greater than ΔT TH , then discard the count value T1 to be entered into the window. If ΔT1 is less than ΔT TH , then add the count value T1 to be entered into the sliding window and update the average count value T AVG .

3. The sub-microsecond timekeeping method for an overhead line fault monitoring terminal according to claim 2, characterized in that: The specific calculation formula for the sliding average described in S1.2 is as follows: Where, T AVG represents the average count value; T N Represents the Nth second pulse count value in the sliding window; N represents the total number of pulse-per-second counts in the sliding window.

4. The sub-microsecond timekeeping method for an overhead line fault monitoring terminal according to claim 2, characterized in that: The specific steps for dynamically adjusting the output frequency of the temperature-compensated crystal oscillator described in step II are as follows: S2.1: The average count value T after smoothing through the sliding window AVG As a reference value, collect the counts per second output of the temperature-compensated crystal oscillator in real time, and calculate the counts per second output of the temperature-compensated crystal oscillator and the corresponding T AVG The difference between ΔT raw ; S2.2: The difference ΔT obtained by real-time comparison raw In the input controller, the controller obtains the control quantity through the incremental PID control algorithm, and converts the control quantity through the DAC to generate the corresponding compensation voltage; S2.3: The compensation voltage is transmitted to the voltage control terminal of the temperature-compensated crystal oscillator. The temperature-compensated crystal oscillator then adjusts the output frequency under the action of the compensation voltage to reduce the deviation from the 1PPS signal.

5. The sub-microsecond timekeeping method for an overhead line fault monitoring terminal according to claim 4, characterized in that: The specific calculation formula of the incremental PID control algorithm described in S2.2 is as follows: ΔT raw (k)=T k -T AVG Δu(k)=K p [e(k)-e(k-1)]+K i ·e(k)+K d [e(k)-2e(k-1)+e(k-2)] u(k)=u(k-1)+Δu(k) Where, e(k) represents the ratio of the count value difference to the frequency deviation; f TCXO Represents the nominal frequency of the temperature-compensated crystal oscillator; K p , K i and K d Represent the proportional, integral and differential coefficients respectively; Δu(k) represents the control quantity increment; u(k) represents the cumulative control amount.

6. The sub-microsecond timekeeping method for an overhead line fault monitoring terminal according to claim 4, characterized in that: The specific steps for automatically switching the working mode according to the 1PPS signal quality output by the satellite in real time in step III are as follows: S3.1: When the satellite signal is good, keep the monitoring terminal in taming mode and obtain second pulses normally to measure the time error. Then, use the PID control algorithm to calculate the control variable and adjust the frequency output of the temperature-compensated crystal oscillator. S3.2: When the satellite signal is unstable or disappears, the monitoring terminal is switched to the self-timekeeping mode, and the second pulse count value stored in the taming mode is used as the reference value for time error measurement. The PID integral term is frozen during measurement, and only the proportional and differential terms are retained.

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