Power grid nuclear phase method and system

Abstract

The invention discloses a power grid nuclear phase method and system, and belongs to the technical field of power grid nuclear phase, and the method comprises the steps: converting a first input signal and a second input signal into non-sine wave signals, calculating a cross-correlation function to obtain the time delay corresponding to the peak point of the cross-correlation function, calculating the phase difference of the two signals according to the time delay, and calculating the phase difference of the two signals according to the phase difference. And judging whether the two phases of the two paths of signals are in the same phase according to the phase difference. According to the invention, the interference of noise signals can be suppressed to a certain extent after waveform conversion is carried out on the input signals, the nuclear phase precision is improved through waveform conversion, and the signals obtained after waveform conversion are relatively simple functions in each period. Therefore, the number of sampling points required during signal sampling after waveform conversion is less than that of sine wave signals in a power grid, so that the phasing precision can be ensured, and meanwhile, the fewer sampling points are utilized to collect signals and improve the phasing speed, that is, the phasing speed is improved through waveform conversion.

Description

Technical Field

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

[0002] In order to ensure the safe operation of the power grid, each power grid must perform phase checking before being connected to the grid. In a three-phase power system, when two systems need to be connected to the grid or two transformers need to be operated in parallel, the voltage and phase of different power grids must be measured first. Only the same two phases can be connected to ensure the normal operation of the power grid. The commonly used method for phase checking is to use a phase checker to determine the phase of the line to be tested, and the phase checking method is the key link in whether the phase checker can accurately and quickly identify the phase of the line to be tested.

[0003] At present, the commonly used nuclear phase 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 point of the same-frequency AC signal and converts the time difference into a phase difference. The waveform transformation method mainly transforms two same-frequency AC signals into rectangular signals through waveforms, and then obtains the pulse width of the two after XOR. The pulse width is the corresponding phase difference between the two. The discrete Fourier method performs discrete Fourier expansion on two same-frequency AC signals, and then takes the fundamental component and calculates the phase difference through the formula.

[0004] However, the zero-crossing detection method is easily interfered by noise when measuring the zero-crossing point, resulting in measurement errors. In addition, the current wireless phase analyzer is usually grounded through capacitive induction, not directly, which increases the noise impact during zero-crossing point acquisition, further increasing the measurement error of the zero-crossing detection method. Although the waveform change method can suppress the influence of noise to a certain extent, its suppression ability is limited and will also produce certain measurement errors. According to the standard DLT 971-2017 "Portable Phase Analyzer for Live Working", the measurement error of the phase analyzer during phase checking usually needs to be within ±10°, but in actual applications, the requirements for measurement error are more stringent, and even need to be 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 accordingly, making it difficult to meet real-time requirements. In addition, since the current model monitoring of the phase analyzer adopts a wireless capacitive induction grounding method, the input side voltage is affected by the grounding method, ambient temperature and humidity, etc., which will produce a large interference signal, increase the error of the phase analyzer during measurement, and thus reduce the accuracy of the phase analysis of the phase analyzer. Summary of the invention

[0005] The object of the present invention is to provide a power grid phase checking method and system, so as to simultaneously achieve high phase checking accuracy and fast phase checking speed in the power grid phase checking process.

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

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

[0008] 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;

[0009] 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;

[0010] calculating a 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 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.

[0014] Furthermore, the calculation of 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 pass through 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.

[0015] Further, when the second conversion signal of the first conversion signal and the second conversion signal undergoes 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:

[0016] ;

[0017] 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.

[0018] Further, 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:

[0019] ;

[0020] ;

[0021] 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.

[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] Furthermore, the waveform of the first conversion signal is a piecewise function waveform, and 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 triangle wave.

[0024] Furthermore, 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 core phase system, including a signal acquisition module, a resistor group, an operational amplifier module and a signal processing module;

[0026] 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.

[0027] 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 having a waveform other than a sine wave, and converting the second input signal into a second conversion signal having a waveform other than a sine wave;

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

[0029] calculating a 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 when the cross-correlation function reaches the peak point;

[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 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.

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

[0034] 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.

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

[0036] The present invention provides a power grid phase core method and system. After the input signal is subjected to waveform conversion, the interference of noise signals can be suppressed to a certain extent. The phase core accuracy is improved through waveform conversion. The signal obtained after the waveform conversion is a relatively simple function in each cycle. Therefore, the number of sampling points required for signal sampling after the waveform conversion is less than that of the sine wave signal in the power grid. Therefore, while ensuring the phase core accuracy, fewer sampling points can be used to collect signals, thereby improving the phase core speed, that is, improving the phase core speed through waveform conversion;

[0037] Under the premise of using the same number of sampling points as the existing phase-checking method, the phase-checking accuracy of the present invention can reach ±0.1°, which can meet the measurement error in practical applications. When the number of sampling points is reduced to one tenth of the original number, the phase-checking accuracy is basically unchanged, while the phase-checking speed is increased by nearly one-fold. The present invention can not only use fewer sampling points to increase the phase-checking speed, but also significantly suppress the influence of noise and improve the phase-checking accuracy, which is helpful for fast and accurate phase-checking when the power grid is connected to the grid, improves the phase-checking efficiency, and reduces the waste of human resources. In addition, the present invention can be used for phase-checking between high-voltage cables and between low-voltage lines and between low-voltage lines, and can also be used for phase-checking between high-voltage cables and low-voltage lines, expanding the scope of application of the phase-checking method. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a flow chart of a power grid phase core method corresponding to Embodiment 1 of the present invention;

[0039] Figure 2 is a flow chart of a power grid phase core method corresponding to Embodiment 2 of the present invention;

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

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

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

[0043] Figure 6 1 is a waveform diagram of a signal u1(t) in the A1 phase of L1 and a signal u2(t) in the A2 phase of L2 provided in Embodiment 5 of the present invention;

[0044] Figure 7 u1 is the secondary side live test hole provided in Example 5 of the present invention (t) and u2 (t) waveform diagram;

[0045] Figure 8 u1 is a square wave after waveform conversion provided by Embodiment 5 of the present invention. (t) and u2 (t) waveform diagram;

[0046] Fig. 9 is u1 provided in Example 5 of the present invention (t) and u2 (t) is the waveform diagram of the cross-correlation function;

[0047] Fig.10is u1 provided in Example 5 of the present invention (t) and u2 (t) is the waveform diagram of the cross-correlation function;

[0048] Fig.11 It is a waveform diagram of the cross-correlation function of the square wave signal after waveform conversion when the number of sampling points provided by Example 5 of the present invention is 10,000. DETAILED DESCRIPTION

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

[0050] Example 1

[0051] like Figure 1 As shown, this embodiment provides a power grid phase core method, including:

[0052] 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;

[0053] 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;

[0054] calculating a 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 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.

[0058] The present invention can suppress the interference of noise signals to a certain extent after waveform conversion of the input signal, and improve the phase-core accuracy through waveform conversion. 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 sinusoidal wave signal in the power grid. Therefore, while ensuring the phase-core accuracy, fewer sampling points can be used to collect signals, thereby improving the phase-core speed, that is, improving the phase-core speed through waveform conversion.

[0059] Example 2

[0060] Due to the influence of factors such as equipment, environment, and grounding method, when performing grid phase core analysis, the two input AC signals will be mixed with random noise signals. From the perspective of correlation, the correlation between the noise signal and the input periodic AC signal is very small, and it will be greatly suppressed when the correlation principle is used to detect the phase difference. The accuracy of detecting the phase difference using the correlation principle is positively correlated with the number of sampling points. If the two input sinusoidal wave signals are sampled directly, more sampling points will be required to ensure accuracy.

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

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

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

[0064] 3) Use the following formula (1) to calculate the cross-correlation function of the two signals after waveform conversion, where the second converted signal is delayed by the delay time Then perform the above calculations;

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

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

[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 sinusoidal wave signals are in phase; if the phase difference is greater than or equal to 30°, it indicates that they are out of phase.

[0068] The present invention provides a power grid phase core method, the specific process is as follows:

[0069] Firstly, the waveforms of the first input signal and the second input signal from two different power grids are respectively transformed by hardware or software, and the first input signal and the second input signal are converted into other waveform signals (i.e., 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, the first input signal and the second input signal are both current signals and both are sinusoidal wave signals (in a power grid, the current signal is generally a sinusoidal wave signal, and this embodiment is for a 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-correction accuracy can be improved. On the other hand, the signal obtained after conversion is a relatively simple function in each cycle. For example, the signal after conversion to a square wave has two fixed values ​​in each cycle; the signal after conversion to a triangle wave is a simple piecewise function in each cycle, and it 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, and thus the signal can be collected with fewer sampling points while ensuring the phase-correction accuracy, thereby improving the phase-correction speed. Among them, the hardware can be implemented through Schmitt triggers, comparators, 555 timers, etc., and the software can obtain signals of other waveforms through digital signal processing (DSP) technology by sampling, quantizing, filtering, and other steps of the sine wave signal.

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

[0073] Afterwards, in order to further improve the phase accuracy, the cross-correlation function of the two signals after waveform conversion is calculated using formula (1), where the second converted signal is delayed by the delay time Then perform the above calculations. The process of calculating the cross-correlation function can be Figure 3 reflect.

[0074] like Figure 3 As shown, the first input signal A(t) is converted into a first conversion signal A'(t) through waveform conversion, and the second input signal B(t) is converted into a second conversion signal B'(t) through waveform conversion. The second conversion signal B'(t) is input into the delay device and is delayed for a time. Then it is multiplied with the first conversion signal A'(t) in the multiplier, and the second conversion signal B'(t) is delayed by a time delay. Then expressed as B'(t+ ), the multiplication result is input into the integrator ∫, and the cross-correlation function of the two signals after waveform conversion is obtained. :

[0075] (1);

[0076] 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, because it is the core phase in the power grid, the signal period in the power grid is generally fixed to 0.02s, that is, the frequency is 50Hz, 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.

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

[0078] (2);

[0079] (3);

[0080] 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 (the frequencies of the two input signals are the same, for the reason described above for the signal period), 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.

[0081] 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°.

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

[0083] Example 3

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

[0085] The signal acquisition module is used for acquiring a first input signal and a second input signal and transmitting the signals to the operational amplifier module through the resistor group, wherein the first input signal and the second input signal are both current signals and both have sinusoidal waveforms;

[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, and 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] calculating a 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 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.

[0092] Example 4

[0093] like Figure 5 As shown, this embodiment provides a power grid core phase system. On the basis of Example 3, the signal processing module is MCU1, the operational amplifier module includes an operational amplifier U1 and an 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 terminal IN1 and a second signal input terminal IN2.

[0094] 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.

[0095] Example 5

[0096] like Figure 5As shown, this embodiment provides a method for performing power grid phase core using the power grid phase core system described in Example 4.

[0097] In this embodiment, the sine wave signal (the first input signal and the second input signal) is converted into a square wave signal (the first conversion signal and the second conversion signal) as an example. Figure 4 As shown, it is assumed that it is necessary to measure whether the A1 phase of the first power grid L1 (the phase for sending the first input signal) and the A2 phase of the second power grid L2 (the phase for sending the second input signal) are in phase. In this embodiment, the expression of the first input signal in the A1 phase of the first power grid L1 is u1(t)=10000sin(100 t), the expression of the second input signal in the A2 phase of the second power grid L2 is u2(t)=10000sin(100 t+120°). Since the voltage on the primary side of the nuclear phase cabinet is too high, direct measurement is too dangerous and prone to safety accidents. Therefore, in this embodiment, the measurement is performed on the secondary side. The transformation 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 embodiment, phase A1 is connected to phase A in the ring main unit, phase B1 is connected to phase B in the ring main unit, phase C1 is connected to phase C in the ring main unit, phase A2 is connected to phase A in the ring main unit through a switch, phase B2 is connected to phase B in the ring main unit through a switch, and phase C2 is connected to phase C in the ring main unit through a switch.

[0098] In addition, in this embodiment, Figure 5 The circuit schematic diagram shown is further described.

[0099] like Figure 5 As shown, 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 reverse input terminal IN1- of the operational amplifier U1, and the other end of the resistor R2 is grounded (i.e. Figure 5GND in the figure), the in-phase input terminal IN1+ of the operational amplifier U1 is grounded, the negative power supply electrode V1- of the operational amplifier U1 is connected to the -12V power supply, the positive power supply electrode V1+ of the operational amplifier U1 is connected to the -12V power supply, 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, the negative power supply electrode V2- of the operational amplifier U2 is connected to the -12V power supply, the positive power supply electrode V2+ of the operational amplifier U2 is connected to the -12V power supply, and the signal output terminal OUT2 of the operational amplifier U2 is connected to the second signal input terminal IN_B of the MCU1.

[0100] In this embodiment, the operational amplifier U1 and the operational amplifier U2 are both LM321 (a general-purpose single-channel operational amplifier).

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

[0102] Step 1: From the A1 phase of the first power grid L1 and the secondary side corresponding to A2 of the second power grid L2, the live test hole (such as Figure 4 Two wires are led out of the circuit (as shown), and the two wires are respectively connected to the first signal input terminal IN1 for receiving the first input signal and the second signal input terminal IN2 for receiving the second input signal. Then, the comparator composed of the operational amplifier U1 and the operational amplifier U2 converts the first input signal into a first conversion signal in the form of a square wave, and the comparator composed of the operational amplifier U1 and the operational amplifier U2 converts the second input signal into a second conversion signal in the form of a square wave. Specifically, when the input sinusoidal wave signal (the first input signal and the second input signal) is positive, since the in-phase input terminal IN1+ of the operational amplifier U1 and the in-phase input terminal IN2+ of the operational amplifier U2 are directly grounded, the signal output terminal OUT1 of the operational amplifier U1 and the signal output terminal OUT2 of the operational amplifier U2 will output a high level; when the input sinusoidal wave signal (the first input signal and the second input signal) is negative, the output terminal of the operational amplifier will output a low level (i.e., the signal output terminal OUT1 of the operational amplifier U1 and the signal output terminal OUT2 of the operational amplifier U2). In addition, resistors R1 and R2 form a voltage divider circuit to prevent the voltage of the input signal from being too large and damaging the port of the operational amplifier. The same applies to resistors R3 and R4.

[0103] Step 2: The converted square wave signals (first conversion signal and second conversion signal) are output to the first signal input terminal IN_A and the second signal input terminal IN_B of MCU1 respectively. At this time, after the sine wave is converted into a square wave through waveform conversion, the expression of the signal (first conversion signal) of phase A1 in the first power grid L1 is u1 (t)=10sign(sin(100 t), the expression of the signal of phase A2 in the second power grid L2 (the second conversion signal after delay) is u2 (t)=10sign(sin(100 t+120°)), sign represents a function used to determine the sign of a value, and its return value depends on the positive or negative condition of the input value, and sin represents the sine function.

[0104] Step 3: MCU1 uses formula (1) in Example 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 the delay device for a delay time Then, it is multiplied with the first conversion signal in the multiplier, and the multiplication result is then input into the 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] in, 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. Because it is the core phase in the power grid, the signal period in the power grid is generally fixed to 0.02s, that is, the frequency is 50Hz.

[0108] Step 4: After 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 the peak value of the cross-correlation function, which is recorded as .

[0109] Step 5: MCU1 uses formula (2) and formula (3) in Example 2 to calculate the phase difference between the two signals (the first input signal and the second input signal). Among them, the sampling interval is selected as 0.02μs, that is, the number of samples in a period of 0.02s is 1000000. At this time, the corresponding delay when the peak is obtained is 0.006667s. According to this delay, the phase difference between the two phases can be calculated using formula (2) and formula (3) to be 120.006°. Therefore, MCU1 determines that phase A1 and phase A2 are not in phase.

[0110] This embodiment also simulates the implementation method corresponding to the system provided by this embodiment based on the above assumptions. Figure 6 It is the waveform diagram of the signal u1(t) in the A1 phase of the first power grid L1 and the signal u2(t) in the A2 phase of the second power grid L2 in one cycle, where one cycle is 0.02s. Figure 6 It can be seen that the phase difference between u1(t) and u2(t) is 120°.

[0111] Figure 7 It is the waveform diagram of the signal u1(t) in the A1 phase of the first power grid L1 and the signal u2(t) in the A2 phase of the second power grid L2 obtained from the secondary side live test hole after passing through the coil. Since the transformation ratio of the primary side to the secondary side is 100 / 1 in this embodiment, Figure 7 Medium u1 (t) and u2 The voltage amplitudes of (t) are Figure 6 One percent of the voltage amplitudes of u1(t) and u2(t).

[0112] Figure 8 It is u1 (t) and u2 (t) After waveform conversion, the corresponding square wave signal u1 is obtained (t) and u2 (t) waveform diagram. Figure 7 and Figure 8 It can be seen that when u1 (t) and u2 When the amplitude of (t) is positive, the amplitude of the square wave signal after waveform conversion is also positive, and the amplitude is fixed at 10V; when u1 (t) and u2 When the amplitude of (t) is negative, the amplitude of the square wave signal after waveform conversion is also negative, and the amplitude is fixed at -10V.

[0113] Fig. 9 It is u1 obtained in the secondary side live test hole (t) and u2 (t) is the cross-correlation function waveform. Fig. 9It can be seen that the peak point of the cross-correlation function appears when the delay is 0.006105s. By using formula (2) and formula (3), u1 can be calculated: (t) and u2 The phase difference between (t) is 109.89°. Although the phase difference (109.89°) can reflect that there is a phase difference between the signal in the A1 phase of the first power grid L1 and the signal in the A2 phase of the second power grid L2, that is, the two phases are not in phase, the calculated result has a large error compared with the actual result.

[0114] Fig.10 is u1 obtained after waveform conversion (t) and u2 (t) is the cross-correlation function waveform. Fig.10 It can be seen that the peak point of the cross-correlation function appears when the delay is 0.006667s. By using formula (2) and formula (3), u1 can be calculated: (t) and u2 The phase difference between (t) is 120.006°. (t) and u2 Compared with the cross-correlation function of (t), the cross-correlation function is calculated after waveform conversion, which will significantly reduce the phase difference error. Fig.11 As 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 does not change substantially, which also shows that the present invention can reduce the number of sampling points while ensuring the nuclear phase accuracy, thereby improving the nuclear phase speed.

[0115] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A 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 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; 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 waveform of the first conversion signal is a piecewise function waveform, and the waveform of the second conversion signal is a piecewise function waveform, wherein 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 having a waveform other than a sine wave, and converting the second input signal into a second conversion signal having a waveform other than a sine wave; 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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