A power grid phase checking method and system

Abstract

The present invention discloses a power grid phase verification method and system, belonging to the technical field of power grid phase verification. The method includes: first converting a first input signal and a second input signal into non-sinusoidal signals, then calculating the cross-correlation function to obtain the time delay corresponding to the peak point of the cross-correlation function, calculating the phase difference between the two signals according to the time delay, and judging whether the two phases providing the two signals are in the same phase according to the phase difference. The present invention can, to a certain extent, suppress the interference of noise signals after converting the input signals through waveform conversion, improve the phase verification accuracy through waveform conversion, and the signals obtained after waveform conversion are relatively simple functions within each period. Therefore, the number of sampling points required for signal sampling after waveform conversion is less than that of sinusoidal signals in the power grid. Furthermore, while ensuring the phase verification accuracy, fewer sampling points can be used to collect signals, improving the phase verification speed, that is, improving the phase verification speed through waveform conversion.

Description

Technical Field

[0001] The present invention relates to a power grid phase verification method and system, belonging to the technical field of power grid phase verification. Background Art

[0002] In order to ensure the safe operation of the power grid, phase verification operations must be carried out before grid connection of each power grid. In a three-phase power system, when two systems need to be grid-connected or two transformers need to operate in parallel, it is first necessary to measure the voltage and phase of different power grids. Only the same two phases can be connected to ensure the normal operation of the power grid. The commonly used method for phase verification is to use a phase verification instrument to judge the phase of the line to be measured, and the phase verification method is the key link for whether the phase verification instrument can accurately and quickly identify the phase of the line to be measured.

[0003] Currently, the commonly used phase verification methods mainly include zero-crossing detection method, waveform transformation method, discrete Fourier method and correlation analysis method. The zero-crossing detection method mainly compares the time difference of the zero-crossing points of the same-frequency alternating current signals and converts this time difference into a phase difference. The waveform transformation method mainly transforms two same-frequency alternating current signals into rectangular signals through waveform transformation, and then obtains the pulse width of the two after XOR operation. This pulse width is the corresponding phase difference between the two. The discrete Fourier method expands two same-frequency alternating current signals by discrete Fourier transform, and then calculates the phase difference through a formula after taking the fundamental wave component.

[0004] However, the zero-crossing detection method is easily affected by noise when measuring the zero-crossing point, resulting in measurement errors. And currently, wireless phase verification instruments usually ground through capacitive induction, not directly grounded, which increases the noise influence during zero-crossing point acquisition, and further increases the measurement errors of the zero-crossing detection method. Although the waveform transformation method can suppress the influence of noise to a certain extent, its suppression ability is limited and it will also generate certain measurement errors. According to the description in the standard DLT 971-2017 "Portable Phase Verification Instrument for Live Working", the measurement error during phase verification by the phase verification instrument usually needs to be within ±10°, but in actual applications, the requirements for measurement errors are more stringent, even within ±1°. The measurement accuracy of the discrete Fourier method and the correlation analysis method is positively correlated with the number of sampling points, that is, as the number of sampling points increases, the measurement accuracy of these two methods will increase accordingly, but the algorithm complexity will also increase, making it difficult to meet the real-time requirements. In addition, due to the current wireless capacitive induction grounding method for model monitoring of phase verification instruments, the input-side voltage is affected by grounding methods, environmental temperature and humidity, etc., and large interference signals will be generated, increasing the errors during phase verification by the phase verification instrument, and thus reducing the accuracy of phase verification by the phase verification instrument. Summary of the Invention

[0005] The purpose of the present invention is to provide a power grid phase verification method and system to simultaneously achieve high phase verification accuracy and fast phase verification speed during the power grid phase verification process.

[0006] To achieve the above object, the present invention is implemented by the following technical solutions:

[0007] In a first aspect, the present invention provides a power grid phase verification method, including:

[0008] Obtain a first input signal and a second input signal from two different power grids. Both the first input signal and the second input signal are current signals and their waveforms are both sine waves;

[0009] Convert the first input signal into a first conversion signal with a waveform other than a sine wave, and convert the second input signal into a second conversion signal with a waveform other than a sine wave;

[0010] Calculate the cross-correlation function of the first conversion signal and the second conversion signal;

[0011] Find the peak point from the cross-correlation function, so as to obtain the time delay corresponding to when the cross-correlation function reaches the peak point;

[0012] Calculate the phase difference between the first input signal and the second input signal according to the time delay;

[0013] If the phase difference is less than a preset value, the phase of the first input signal in the power grid sending the first input signal is the same as the phase of the second input signal in the power grid sending the second input signal, otherwise they are different.

[0014] Further, the calculating the cross-correlation function of the first conversion signal and the second conversion signal includes: making any one of the first conversion signal and the second conversion signal pass through a preset delay time, and then calculating the cross-correlation function of the first conversion signal and the second conversion signal after passing through the preset delay time.

[0015] Further, when it is the second conversion signal among the first conversion signal and the second conversion signal that passes through the preset delay time, the calculating the cross-correlation function of the first conversion signal and the second conversion signal after passing through the preset delay time is carried out by the following formula:

[0016] ;

[0017] Wherein, is the cross-correlation function of the first conversion signal and the second conversion signal after passing through the preset delay time, T is the period of the first conversion signal and the second conversion signal, is the first conversion signal, is the second conversion signal after passing through the preset delay time, is the preset delay time, and t represents the time independent variable.

[0018] Further, calculate the phase difference between the first input signal and the second input signal according to the time delay, using any one of the following two formulas:

[0019] ;

[0020] ;

[0021] wherein, is the phase difference between the first input signal and the second input signal in radians, f is the frequency of the first input signal and the second input signal, is the time delay corresponding to the peak point of the cross-correlation function, is the phase difference between the first input signal and the second input signal in degrees.

[0022] Further, when the phase difference is the phase difference between the first input signal and the second input signal in degrees, the preset value is 30°.

[0023] Further, the waveform of the first conversion signal is a piecewise function waveform, the waveform of the second conversion signal is a piecewise function waveform, and the piecewise function waveform includes a square wave, a trapezoidal wave, and a triangular wave.

[0024] Further, the conversion is implemented by hardware or software. The hardware includes a Schmitt trigger, a comparator, and a 555 timer, and the software includes digital signal processing technology.

[0025] In a second aspect, the present invention further provides a power grid phase checking system, including a signal acquisition module, a resistor bank, an operational amplifier module, and a signal processing module;

[0026] The signal acquisition module is configured to acquire the first input signal and the second input signal and transmit them to the operational amplifier module through the resistor bank. Both the first input signal and the second input signal are current signals and their waveforms are sine waves;

[0027] The operational amplifier module is configured to amplify and convert the first input signal and the second input signal and transmit them to the signal processing module. The conversion includes: converting the first input signal into a first conversion signal with a waveform other than a sine wave, and converting the second input signal into a second conversion signal with a waveform other than a sine wave;

[0028] The signal processing module is configured to perform the following operations:

[0029] Calculate the cross-correlation function of the first conversion signal and the second conversion signal;

[0030] Find the peak point from the cross-correlation function, so as to obtain the time delay corresponding to the peak point of the cross-correlation function;

[0031] Calculate the phase difference between the first input signal and the second input signal according to the time delay;

[0032] If the phase difference is less than a preset value, the phases of the first input signal in the power grid that sends the first input signal and the same phase of the second input signal in the power grid that sends the second input signal are the same; otherwise, they are different.

[0033] Further, the signal processing module is MCU1, the operational amplifier module includes operational amplifiers U1 and U2, the resistor group includes resistors R1, R2, R3, and R4, and the signal acquisition module includes a first signal input terminal IN1 and a second signal input terminal IN2;

[0034] One end of resistor R1 is connected to the first signal input terminal IN1 for receiving the first input signal. The other end of resistor R1 is connected to one end of resistor R2 and then connected to the inverting input terminal IN1- of operational amplifier U1. The other end of resistor R2 is grounded. The non-inverting input terminal IN1+ of operational amplifier U1 is grounded. The signal output terminal OUT1 of operational amplifier U1 is connected to the first signal input terminal IN_A of MCU1. One end of resistor R3 is connected to the second signal input terminal IN2 for receiving the second input signal. The other end of resistor R3 is connected to one end of resistor R4 and then connected to the inverting input terminal IN2- of operational amplifier U2. The other end of resistor R4 is grounded. The non-inverting input terminal IN2+ of operational amplifier U2 is grounded. The signal output terminal OUT2 of operational amplifier U2 is connected to the second signal input terminal IN_B of MCU1.

[0035] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0036] A power grid phase verification method and system provided by the present invention can, to a certain extent, suppress the interference of noise signals after converting the input signals through waveform conversion, improve the phase verification accuracy through waveform conversion. The signals obtained after waveform conversion are relatively simple functions in each cycle. Therefore, the number of sampling points required for signal sampling after waveform conversion is less than that of the sine wave signals in the power grid. Furthermore, while ensuring the phase verification accuracy, fewer sampling points can be used to collect signals, thereby improving the phase verification speed, that is, improving the phase verification speed through waveform conversion;

[0037] On the premise of using the same number of sampling points as the existing phase discrimination method, the phase discrimination accuracy of the present invention can reach ±0.1°, which can meet the measurement error in practical applications. Moreover, when the number of sampling points is reduced to one-tenth of the original, the phase discrimination accuracy basically remains unchanged, while the phase discrimination speed is increased by nearly one-fold. The present invention can not only use fewer sampling points to improve the phase discrimination speed, but also significantly suppress the influence of noise and improve the phase discrimination accuracy, which helps to quickly and accurately discriminate the phases during the grid connection, improve the phase discrimination efficiency, and reduce the waste of human resources. In addition, the present invention can be used for phase discrimination between high-voltage cables and high-voltage cables, between low-voltage lines and low-voltage lines, and also between high-voltage cables and low-voltage lines, expanding the applicable range of the phase discrimination method. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a flowchart of a power grid phase discrimination method corresponding to Embodiment 1 of the present invention;

[0039] Figure 2 is a flowchart of a power grid phase discrimination method corresponding to Embodiment 2 of the present invention;

[0040] Figure 3 is a flowchart of calculating the cross-correlation function provided by the present invention;

[0041] Figure 4 is a phase discrimination schematic diagram provided by an embodiment of the present invention;

[0042] Figure 5 is a circuit schematic diagram of a power grid phase discrimination system provided by an embodiment of the present invention;

[0043] Figure 6 is the signal u 1 in the A phase of L1 1 (t) and the signal u 2 in the A phase of L2 2 (t);

[0044] Figure 7 is the u 1 (t) of the secondary side live test hole and u 2 (t) provided by Embodiment 5 of the present invention;

[0045] Figure 8 is the u 1 (t) and u 2 (t) which are converted into square waves after waveform conversion provided by Embodiment 5 of the present invention;

[0046] Figure 9 is the u provided by Embodiment 5 of the present invention1 (t) and u 2 Waveform diagram of the cross-correlation function of (t);

[0047] Figure 10 is u provided in Embodiment 5 of the present invention 1 (t) and u 2 Waveform diagram of the cross-correlation function of (t);

[0048] Figure 11 is the waveform diagram of the cross-correlation function of the square wave signal after waveform conversion when the number of sampling points is 10,000 provided in Embodiment 5 of the present invention. Detailed implementation manners

[0049] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0050] Embodiment 1

[0051] As Figure 1 shown, this embodiment provides a method for grid phase comparison, including:

[0052] Obtain a first input signal and a second input signal from two different power grids. The first input signal and the second input signal are both current signals and the waveforms are both sine waves;

[0053] Convert the first input signal into a first conversion signal with a waveform other than a sine wave, and convert the second input signal into a second conversion signal with a waveform other than a sine wave;

[0054] Calculate the cross-correlation function of the first conversion signal and the second conversion signal;

[0055] Find the peak point from the cross-correlation function, so as to obtain the time delay corresponding to when the cross-correlation function reaches the peak point;

[0056] Calculate the phase difference between the first input signal and the second input signal according to the time delay;

[0057] If the phase difference is less than a preset value, the phases of the first input signal in the power grid sending the first input signal and the second input signal in the power grid sending the second input signal are the same phase, otherwise they are different phases.

[0058] The present invention can suppress the interference of noise signals to a certain extent after converting the input signal through waveform conversion, improve the phase discrimination accuracy through waveform conversion, and the signal obtained after waveform conversion is a relatively simple function in each cycle. Therefore, the number of sampling points required for signal sampling after waveform conversion is less than that of the sine wave signal in the power grid. Furthermore, while ensuring the phase discrimination accuracy, fewer sampling points can be used to collect signals, improving the phase discrimination speed, that is, improving the phase discrimination speed through waveform conversion.

[0059] Embodiment 2

[0060] Due to the influence of factors such as equipment, environment, grounding method, etc., when performing power grid phase discrimination, the two input alternating current signals will be doped with random noise signals. Considering from the perspective of correlation, the correlation between the noise signal and the input periodic alternating current signal is very small and will be greatly suppressed when using the correlation principle to detect the phase difference. The accuracy of using the correlation principle to detect the phase difference is positively correlated with the number of sampling points. If the two input sine wave signals are directly sampled, more sampling points will be required to ensure the accuracy.

[0061] In order to reduce the number of sampling points, improve the phase discrimination speed and accuracy, as Figure 2 shown, this embodiment provides a power grid phase discrimination method, including:

[0062] 1) Obtain two input sine wave signals (i.e., the first input signal and the second input signal);

[0063] 2) Convert the two sine wave signals into other waveform signals through waveform conversion technology to obtain the first conversion signal and the second conversion signal;

[0064] 3) Calculate the cross-correlation function of the two signals after waveform conversion using the following formula (1), where the second conversion signal is delayed by a delay time and then the above calculation is performed;

[0065] 4) Find the peak point from the cross-correlation function and record the time delay corresponding to this peak point;

[0066] 5) According to the time delay corresponding to the recorded peak point, calculate the phase difference between the two input sine wave signals using the following formula (2) and formula (3);

[0067] 6) Determine whether the obtained phase difference is less than 30°. If the phase difference is less than 30°, it indicates that the two input sine wave signals are in phase; if the phase difference is greater than or equal to 30°, it means they are out of phase.

[0068] A power grid phase discrimination method provided by the present invention has the following specific process:

[0069] First, the first input signal and the second input signal from two different power grids are respectively subjected to waveform transformation in a hardware or software manner, and the first input signal and the second input signal are converted into other waveform signals (that is, the first input signal is converted into a first conversion signal with a waveform other than a sine wave, and the second input signal is converted into a second conversion signal with a waveform other than a sine wave).

[0070] In this embodiment, both the first input signal and the second input signal are current signals and are both sine wave signals (in a power grid, generally the current signal is a sine wave signal, and this embodiment is for the power grid environment).

[0071] On the one hand, after waveform conversion, the interference of noise signals can be suppressed to a certain extent, and the phase comparison accuracy can be improved. On the other hand, the signals obtained after conversion are relatively simple functions within each period. For example, for the signal converted into a square wave, it has two fixed values within each period; for the signal converted into a triangular wave, it is a simple piecewise function within each period and is a linear function. Therefore, the number of sampling points required for sampling the converted signal is less than that of the sine wave signal. Furthermore, while ensuring the phase comparison accuracy, fewer sampling points can be used to collect signals, thereby improving the phase comparison speed. Among them, the hardware can be implemented through a Schmitt trigger, a comparator, a 555 timer, etc., and the software can use digital signal processing (DSP) technology to obtain signals with other waveforms after sampling, quantization, filtering, etc. of the sine wave signal.

[0072] In specific implementation, the waveform of the signal after waveform conversion is a piecewise function waveform, and the piecewise function waveform includes a square wave, a trapezoidal wave, a triangular wave, etc. Such piecewise function waveforms have clear mathematical expressions and piecewise linear characteristics. Compared with the continuous and smooth waveform of the sine wave, they can effectively reduce the computational complexity of cross-correlation coefficient calculation in a signal processing system, thereby improving the calculation efficiency. At the same time, their inherent waveform mutation characteristics are conducive to improving the accuracy of feature point recognition, and further enhancing the accuracy of related operations.

[0073] After that, in order to further improve the phase comparison accuracy, the cross-correlation function of the two signals after waveform conversion is calculated using formula (1), where the second conversion signal is delayed by a delay time and then the above calculation is performed. The process of calculating the cross-correlation function can be passed through Figure 3 embodied.

[0074] As Figure 3 shown, the first input signal A(t) is subjected to waveform conversion to obtain the first conversion signal A’(t), and the second input signal B(t) is subjected to waveform conversion to obtain the second conversion signal B’(t). The second conversion signal B’(t) is input into the delay device and delayed by a delay time and then multiplied by the first conversion signal A'(t) in a multiplier. The second conversion signal B'(t) is delayed by a delay time and then expressed as B'(t + ). The result of the multiplication is input into the integrator ∫ to obtain the cross-correlation function of the two signals after waveform conversion :

[0075] (1);

[0076] where is the cross-correlation function of the first conversion signal and the second conversion signal after a preset delay time, T is the period of the first conversion signal and the second conversion signal. Since it is a phase comparison within the power grid, the signal period in the power grid is generally fixed at 0.02 s, that is, the frequency is 50 Hz, is the first conversion signal, is the second conversion signal after a preset delay time, is the preset delay time, and t represents the time independent variable.

[0077] Record the peak point of the above cross-correlation function. Then, obtain the time delay corresponding to the peak point according to the peak point. Finally, according to the time delay corresponding to the peak point and the signal frequency, use formula (2) and formula (3) to calculate the phase difference between the two input sine wave signals, and determine whether the two phases providing the two sine wave signals in the two power grids are in phase:

[0078] (2);

[0079] (3);

[0080] where is the phase difference between the first input signal and the second input signal in radians, f is the frequency of the first input signal and the second input signal (the frequencies of the two input signals are the same, for the reason see the above description of the signal period), is the time delay corresponding to the cross-correlation function when it reaches the peak point, is the phase difference between the first input signal and the second input signal in degrees.

[0081] When the phase difference is the phase difference between the first input signal and the second input signal in degrees, the preset value is 30°.

[0082] As a signal processing technology, the cross-correlation function can calculate the similarity between two signals in the time series to measure the correlation between them. The difference in phase between two signals with the same frequency is essentially the difference in their relative positions on the time axis. Therefore, the phase difference between the two signals can be obtained by measuring the time delay when the cross-correlation function of the two signals reaches the peak point.

[0083] Embodiment 3

[0084] Based on the same inventive concept as Embodiment 1, this embodiment provides a power grid phase verification system, which includes a signal acquisition module, a resistor group, an operational amplifier module, and a signal processing module;

[0085] The signal acquisition module is used to acquire a first input signal and a second input signal and transmit them to the operational amplifier module through the resistor group. Both the first input signal and the second input signal are current signals and their waveforms are sine waves;

[0086] The operational amplifier module is used to amplify and convert the first input signal and the second input signal and transmit them to the signal processing module. The conversion includes: converting the first input signal into a first conversion signal with a waveform other than a sine wave, and converting the second input signal into a second conversion signal with a waveform other than a sine wave;

[0087] The signal processing module is used to perform the following operations:

[0088] Calculate the cross-correlation function of the first conversion signal and the second conversion signal;

[0089] Find the peak point from the cross-correlation function, so as to obtain the time delay corresponding to when the cross-correlation function reaches the peak point;

[0090] Calculate the phase difference between the first input signal and the second input signal according to the time delay;

[0091] If the phase difference is less than the preset value, the phases of the first input signal in the power grid sending the first input signal and the second input signal in the power grid sending the second input signal are the same phase, otherwise they are different phases.

[0092] Embodiment 4

[0093] As Figure 5 shown, this embodiment provides a power grid phase verification system. On the basis of Embodiment 3, the signal processing module is MCU1, the operational amplifier module includes operational amplifier U1 and operational amplifier U2, the resistor group includes resistor R1, resistor R2, resistor R3, and resistor R4, and the signal acquisition module includes a first signal input end IN1 and a second signal input end IN2.

[0094] One end of resistor R1 is connected to the first signal input terminal IN1 for receiving the first input signal. The other end of resistor R1 is connected to one end of resistor R2 and then connected to the inverting input terminal IN1- of operational amplifier U1. The other end of resistor R2 is grounded. The non-inverting input terminal IN1+ of operational amplifier U1 is grounded. The signal output terminal OUT1 of operational amplifier U1 is connected to the first signal input terminal IN_A of MCU1. One end of resistor R3 is connected to the second signal input terminal IN2 for receiving the second input signal. The other end of resistor R3 is connected to one end of resistor R4 and then connected to the inverting input terminal IN2- of operational amplifier U2. The other end of resistor R4 is grounded. The non-inverting input terminal IN2+ of operational amplifier U2 is grounded. The signal output terminal OUT2 of operational amplifier U2 is connected to the second signal input terminal IN_B of MCU1.

[0095] Embodiment 5

[0096] As Figure 5 shown, this embodiment provides a method for network phase verification using the network phase verification system described in Embodiment 4.

[0097] In this embodiment, as an example, the sine wave signals (the first input signal and the second input signal) are converted into square wave signals (the first conversion signal and the second conversion signal). As Figure 4 shown, assume that it is necessary to measure whether the A 1 phase (the phase sending the first input signal) of the first power grid L1 and the A 2 phase (the phase sending the second input signal) of the second power grid L2 are in the same phase. In this embodiment, the expression of the first input signal in the A 1 phase of the first power grid L1 is u 1 (t) = 10000sin(100 t), and the expression of the second input signal in the A 2 phase of the second power grid L2 is u 2 (t) = 10000sin(100 t + 120°). Since the voltage on the primary side of the phase verification cabinet is too high, direct measurement is too dangerous and prone to safety accidents. Therefore, in this embodiment, measurement is selected on the secondary side. Among them, the turns ratio of the primary side to the secondary side is 100 / 1, that is, when the voltage on the primary side is 10000V, the voltage on the secondary side is 10V. Figure 4 In, the A 1 phase is connected to the A phase in the ring main unit, the B 1 phase is connected to the B phase in the ring main unit, the C 1 phase is connected to the C phase in the ring main unit, the A 2 phase and the A phase in the ring main unit are connected through a switch, the B 2 phase and the B phase in the ring main unit are connected through a switch, the C 2The C phase in the phase-summing ring main unit is connected through a switch.

[0098] In addition, in this embodiment, Figure 5 the circuit schematic diagram shown is used for further description.

[0099] As Figure 5 shown, one end of resistor R1 is connected to the first signal input terminal IN1 for receiving the first input signal. The other end of resistor R1 is connected to one end of resistor R2 and then connected to the inverting input terminal IN1- of operational amplifier U1. The other end of resistor R2 is grounded (i.e., Figure 5 GND in

[0100] ). The non-inverting input terminal IN1+ of operational amplifier U1 is grounded. The negative power supply terminal V1- of operational amplifier U1 is connected to a -12V power supply. The positive power supply terminal V1+ of operational amplifier U1 is connected to a -12V power supply. The signal output terminal OUT1 of operational amplifier U1 is connected to the first signal input terminal IN_A of MCU1. One end of resistor R3 is connected to the second signal input terminal IN2 for receiving the second input signal. The other end of resistor R3 is connected to one end of resistor R4 and then connected to the inverting input terminal IN2- of operational amplifier U2. The other end of resistor R4 is grounded. The non-inverting input terminal IN2+ of operational amplifier U2 is grounded. The negative power supply terminal V2- of operational amplifier U2 is connected to a -12V power supply. The positive power supply terminal V2+ of operational amplifier U2 is connected to a -12V power supply. The signal output terminal OUT2 of operational amplifier U2 is connected to the second signal input terminal IN_B of MCU1.

[0101] In this embodiment, the phase-detection process of the provided power grid phase-detection system is specifically as follows:

[0102] Step 1: From the A 1 phase of the first power grid L1 and the A 2 phase of the second power grid L2, corresponding live test holes on the secondary side (such as Figure 4Two wires are led out from within (as shown), and the two wires are respectively connected to a first signal input terminal IN1 for receiving a first input signal and a second signal input terminal IN2 for receiving a second input signal. Then, a comparator composed of operational amplifiers U1 and U2 converts the first input signal into a first conversion signal in the form of a square wave, and a comparator composed of operational amplifiers U1 and U2 converts the second input signal into a second conversion signal in the form of a square wave. Specifically, when the input sine wave signals (the first input signal and the second input signal) are positive, since the non-inverting input terminals IN1+ of operational amplifier U1 and IN2+ of operational amplifier U2 are directly grounded, the signal output terminals OUT1 of operational amplifier U1 and OUT2 of operational amplifier U2 will output a high level; when the input sine wave signals (the first input signal and the second input signal) are negative, the output terminals of the operational amplifiers will output a low level (i.e., the signal output terminal OUT1 of operational amplifier U1 and the signal output terminal OUT2 of operational amplifier U2). In addition, resistors R1 and R2 form a voltage dividing circuit to prevent the voltage of the input signal from being too large and damaging the ports of the operational amplifiers, and the same applies to resistors R3 and R4.

[0103] Step 2: The converted square wave signals (the first conversion signal and the second conversion signal) are respectively output to the first signal input terminal IN_A and the second signal input terminal IN_B of MCU1. At this time, after the waveform conversion converts the sine wave into a square wave, the signal (the first conversion signal) of phase A in the first power grid L1 1 has the expression u 1 (t)=10sign(sin(100 t)), and the signal (the second conversion signal after delay) of phase A in the second power grid L2 2 has the expression u 2 (t)=10sign(sin(100 t + 120°)), where sign represents a function for judging the sign of a value, and its return value depends on the positive or negative situation of the input value, and sin represents the sine function.

[0104] Step 3: MCU1 uses formula (1) in Embodiment 2 to calculate the cross-correlation function of the two signals after waveform conversion. The specific calculation process is as follows: The second conversion signal is input into a delay device and delayed by a delay time and then multiplied by the first conversion signal in a multiplier, and the result of the multiplication is then input into an integrator ∫ to obtain the cross-correlation function of the two signals after waveform conversion. In this embodiment, the calculation process of the cross-correlation function can also be reflected by formula (4):

[0105]

[0106] (4);

[0107] wherein, is the cross-correlation function of the first conversion signal and the second conversion signal, T is the period of the first conversion signal and the second conversion signal. Since the phase comparison is performed within the power grid, the signal period in the power grid is generally fixed at 0.02 s, that is, the frequency is 50 Hz.

[0108] Step 4: After the MCU1 calculates the cross-correlation function (i.e., after calculating the values of each point of the cross-correlation function), it will calculate the peak point of the cross-correlation function and record the time delay corresponding to when the cross-correlation function reaches the peak, denoted as .

[0109] Step 5: The MCU1 then uses the formulas (2) and (3) in Embodiment 2 to calculate the phase difference of the two signals (the first input signal and the second input signal). Among them, the sampling interval is selected as 0.02 μs, that is, the number of samples within a period of 0.02 s is 1,000,000. At this time, the time delay corresponding to when the peak is obtained is 0.006667 s. According to this time delay, using the formulas (2) and (3), the phase difference between the two phases can be calculated as 120.006°. Therefore, the MCU1 determines that phase A 1 and phase A 2 are not in the same phase.

[0110] This embodiment also performs a simulation on the implementation method corresponding to the system provided in this embodiment based on the above assumptions. Figure 6 is the waveform diagram of the signal u 1 (t) in phase A of the first power grid L1 and the signal u 1 (t) in phase A of the second power grid L2 within one period, where one period is 0.02 s. As can be seen from 2 phase A 2 (t) and the signal u Figure 6 in 1 (t) and u 2 (t) is 120°.

[0111] Figure 7 is the waveform diagram obtained from the live test hole on the secondary side after the signal u 1 (t) in phase A of the first power grid L1 and the signal u 1 (t) in phase A of the second power grid L2 pass through the coil. Since the turns ratio of the primary side to the secondary side is 100 / 1 in this embodiment, so 2 phase A 2 (t) in Figure 7 u 1 (t) and u 2 The voltage amplitudes of (t) are respectively Figure 6 in u 1 (t) and u 2 one percent of the voltage amplitudes of (t).

[0112] Figure 8 is u 1 (t) and u 2 After waveform conversion of (t), the corresponding square-wave signal u 1 (t) and u 2 (t) and the waveform diagram of u Figure 7 and Figure 8 It can be known that when u 1 (t) and u 2 (t) have positive amplitudes, the amplitude of the square-wave signal after waveform conversion is also positive, and the amplitude is fixed at 10 V; when u 1 (t) and u 2 (t) have negative amplitudes, the amplitude of the square-wave signal after waveform conversion is also negative, and the amplitude is fixed at -10 V.

[0113] Figure 9 is u obtained from the live test hole on the secondary side 1 (t) and u 2 (t) and the cross-correlation function waveform diagram. It can be known from Figure 9 that the peak point of this cross-correlation function appears when the time delay is 0.006105 s. Through formula (2) and formula (3), the phase difference between u 1 (t) and u 2 (t) can be calculated to be 109.89°. Although this phase difference (109.89°) can reflect the phase difference between the signal in phase A of the first power grid L1 1 and the signal in phase A of the second power grid L2 2 that is, it shows that the two phases are not in the same phase, but the calculation result has a large error from the actual situation.

[0114] Figure 10 is the cross-correlation function waveform diagram of u 1 (t) and u 2 (t) obtained after waveform conversion. It can be known fromFigure 10 It can be seen that the peak point of this cross-correlation function appears at a time delay of 0.006667 s, and u can be calculated through formulas (2) and (3). 1 (t) and the phase difference between u 2 (t) is 120.006°. Compared with directly calculating the cross-correlation function of u 1 (t) and u 2 (t), calculating the cross-correlation function after waveform conversion will significantly reduce the error of the phase difference. In addition, as Figure 11 shown, when the number of sampling points is reduced to 10,000, the peak point of the cross-correlation function of the square wave signal obtained after waveform conversion basically remains unchanged, which also shows that the present invention can reduce the number of sampling points on the basis of ensuring the phase discrimination accuracy, thereby improving the phase discrimination speed.

[0115] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A power grid phase core method, characterized in that: include: Acquire a first input signal and a second input signal from two different power grids, wherein the first input signal and the second input signal are both current signals and both have sinusoidal waveforms; Converting a first input signal into a first conversion signal of a piecewise function waveform, and converting a second input signal into a second conversion signal of a piecewise function waveform; calculating a cross-correlation function of the first conversion signal and the second conversion signal; Find the peak point from the cross-correlation function, so as to obtain the time delay corresponding to when the cross-correlation function reaches the peak point; Calculate the phase difference between the first input signal and the second input signal according to the time delay; If the phase difference is less than a preset value, the phase of the first input signal in the power grid that sends the first input signal and the second input signal in the power grid that sends the second input signal are the same phase, otherwise they are different phases.

2. The power grid phase core method according to claim 1, characterized in that: The method of calculating the cross-correlation function of the first conversion signal and the second conversion signal includes: allowing any one of the first conversion signal and the second conversion signal to undergo a preset delay time, and then calculating the cross-correlation function of the first conversion signal and the second conversion signal after the preset delay time.

3. The power grid phase core method according to claim 2, characterized in that: When the second conversion signal of the first conversion signal and the second conversion signal has passed a preset delay time, the cross-correlation function of the first conversion signal and the second conversion signal after the preset delay time is calculated by the following formula: ； in, is the cross-correlation function of the first conversion signal and the second conversion signal after a preset delay time, T is the period of the first conversion signal and the second conversion signal, is the first conversion signal, It is the second conversion signal after the preset delay time. is the preset delay time, and t represents the time independent variable.

4. The power grid phase core method according to claim 1, characterized in that: The phase difference between the first input signal and the second input signal is calculated according to the time delay, using any one of the following two formulas: ； ； in, is the phase difference between the first input signal and the second input signal in radians, f is the frequency of the first input signal and the second input signal, is the time delay corresponding to the peak point of the cross-correlation function, is the phase difference between the first input signal and the second input signal in degrees.

5. The power grid phase core method according to claim 1, characterized in that: When the phase difference is a phase difference between the first input signal and the second input signal in degrees, the preset value is 30°.

6. The power grid phase core method according to claim 1, characterized in that: The piecewise function waveform includes a square wave, a trapezoidal wave and a triangle wave.

7. The power grid phase core method according to claim 1, characterized in that: The conversion is implemented by hardware or software, wherein the hardware includes a Schmitt trigger, a comparator and a 555 timer, and the software includes a digital signal processing technique.

8. A power grid core phase system, characterized in that: It includes a signal acquisition module, a resistor group, an operational amplifier module and a signal processing module; The signal acquisition module is used to acquire a first input signal and a second input signal and transmit them to the operational amplifier module through the resistor group. The first input signal and the second input signal are both current signals and both have sinusoidal waveforms. The operational amplifier module is used to amplify and convert the first input signal and the second input signal and transmit them to the signal processing module, wherein the conversion includes: converting the first input signal into a first conversion signal of a piecewise function waveform, and converting the second input signal into a second conversion signal of a piecewise function waveform; The signal processing module is used to perform the following operations: calculating a cross-correlation function of the first conversion signal and the second conversion signal; Find the peak point from the cross-correlation function, so as to obtain the time delay corresponding to when the cross-correlation function reaches the peak point; Calculate the phase difference between the first input signal and the second input signal according to the time delay; If the phase difference is less than a preset value, the phase of the first input signal in the power grid that sends the first input signal and the second input signal in the power grid that sends the second input signal are the same phase, otherwise they are different phases.

9. The power grid core phase system according to claim 8, characterized in that: The signal processing module is MCU1, the operational amplifier module includes operational amplifiers U1 and U2, the resistor group includes resistors R1, R2, R3 and R4, and the signal acquisition module includes a first signal input terminal IN1 and a second signal input terminal IN2; One end of the resistor R1 is connected to the first signal input terminal IN1 for receiving the first input signal, the other end of the resistor R1 is connected to one end of the resistor R2 and then connected to the inverting input terminal IN1- of the operational amplifier U1, the other end of the resistor R2 is grounded, the in-phase input terminal IN1+ of the operational amplifier U1 is grounded, the signal output terminal OUT1 of the operational amplifier U1 is connected to the first signal input terminal IN_A of the MCU1, one end of the resistor R3 is connected to the second signal input terminal IN2 for receiving the second input signal, the other end of the resistor R3 is connected to one end of the resistor R4 and then connected to the inverting input terminal IN2- of the operational amplifier U2, the other end of the resistor R4 is grounded, the in-phase input terminal IN2+ of the operational amplifier U2 is grounded, and the signal output terminal OUT2 of the operational amplifier U2 is connected to the second signal input terminal IN_B of the MCU1.

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