A voltage measurement method and system based on Newton iteration

Abstract

The present invention relates to a voltage measurement method and system based on Newton iteration, and relates to the field of voltage measurement. The method comprises: establishing an equivalent circuit model according to an electric field distribution model; the electric field distribution model comprises a single-phase power line and a sensor probe, the sensor probe is coaxially arranged with the single-phase power line, the single-phase power line is placed inside the sensor probe, and the sensor probe is used to measure an induced voltage signal of the single-phase power line; the induced voltage signals of three time periods measured by the sensor probe are distributed as a first induced voltage signal at a first moment, a second induced voltage signal at a second moment, and a third induced voltage signal at a third moment; a voltage measurement model considering frequency offset is established according to the first induced voltage signal, the second induced voltage signal, and the third induced voltage signal; solving the phase angle deviation in the voltage measurement model based on Newton iteration; and determining the voltage of the single-phase power line according to the phase angle deviation. The present invention improves the accuracy of voltage measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage measurement, and in particular to a voltage measurement method and system based on Newton iteration. Background Art

[0002] With the large-scale development of Internet projects in various regions and the large-scale grid connection of various distributed power sources, China has formed one of the world's largest and most complex power grids, requiring more power systems to monitor electrical data to ensure the safe operation and dispatch of the power grid. At the same time, the rapid development of 5G communication technology and artificial intelligence has laid the foundation for efficient data transmission and processing. In order to achieve the construction of a smart grid with highly transparent power data, the key is to deploy a large number of electrical data monitoring devices in the system. However, traditional electromagnetic voltage transformers are difficult to be widely deployed in power systems due to their large size, high cost and inconvenient installation. Therefore, the development of micro voltage sensors and their high adaptability to the on-site environment is very urgent.

[0003] The non-contact voltage measurement method based on topological transformation achieves the elimination of environmental stray capacitance parameters at the cost of a simple equivalent circuit topological transformation, thereby achieving a higher degree of adaptability of the measuring device to the environment. This method measures the response voltage in sequence, but the waveforms of the two measurements have no time scale, resulting in a phase angle deviation between the two measured phasors due to the lack of a reference phasor. The voltage estimation requires the phasor values ​​measured successively to be substituted into the voltage estimation formula. Because the reference phasors before and after are not unified, the voltage estimation eventually deviates from the true value in a large range, and the accuracy of the voltage measurement is low. Summary of the invention

[0004] The purpose of the present invention is to provide a voltage measurement method and system based on Newton iteration, so as to improve the accuracy of voltage measurement.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] A voltage measurement method based on Newton iteration, comprising:

[0007] An equivalent circuit model is established according to the electric field distribution model; the electric field distribution model includes a single-phase power line and a sensor probe, the sensor probe is coaxially arranged with the single-phase power line, the single-phase power line is placed inside the sensor probe, and the sensor probe is used to measure the induced voltage signal of the single-phase power line;

[0008] The induced voltage signals of three time periods measured by the sensor probe are distributed as a first induced voltage signal at a first moment, a second induced voltage signal at a second moment, and a third induced voltage signal at a third moment;

[0009] Establishing a voltage measurement model taking frequency offset into consideration according to the first induced voltage signal, the second induced voltage signal and the third induced voltage signal;

[0010] Solving the phase angle deviation in the voltage measurement model based on Newton iteration;

[0011] The voltage of the single-phase power line is determined based on the phase angle deviation.

[0012] Optionally, the sensor probe includes an inner copper layer, an insulating layer, an outer copper layer and a jacket layer which are sequentially covered from the inside to the outside, and the sensor probe also includes bakelite, which is used to clamp the single-phase power line inside the inner copper layer.

[0013] Optionally, the equivalent circuit model includes a first voltage terminal, a second voltage terminal, a third voltage terminal, a first capacitor, a second capacitor, a third capacitor, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first operational amplifier, a second operational amplifier, a first switch tube and a second switch tube; the first voltage terminal is used to represent the voltage of the single-phase power line, the second voltage terminal represents the voltage of the inner copper sheet, and the third voltage terminal represents the voltage of the outer copper sheet;

[0014] One end of the first capacitor is connected to the first voltage end, and the other end of the first capacitor is connected to the second voltage end; one end of the first resistor is connected to the first voltage end, and the other end of the first resistor is connected to the second voltage end; one end of the second capacitor is connected to the second voltage end, and the other end of the second capacitor is connected to the third voltage end; one end of the fourth resistor is connected to the second voltage end, and the other end of the fourth resistor is connected to the first end of the first switch tube, and the second end of the first switch tube is connected to the third voltage end; one end of the second resistor is connected to the second voltage end, and the other end of the second resistor is connected to the non-inverting input end of the first operational amplifier, and the first ends of the three resistors are connected to the first The inverting input terminal of the operational amplifier is connected to the first terminal of the fifth resistor, the second terminals of the three resistors are connected to the third voltage terminal, and the second terminal of the fifth resistor is connected to the output terminal of the first operational amplifier; the first terminal of the second switch tube is connected to the second voltage terminal, the second terminal of the second switch tube is respectively connected to the first terminal of the sixth resistor and the inverting input terminal of the second operational amplifier, the second terminal of the sixth resistor is connected to the output terminal of the second switch tube, and the non-inverting input terminal of the second switch tube is connected to the third voltage terminal; one terminal of the third capacitor is connected to the third voltage terminal, and the other terminal of the third capacitor is grounded; one terminal of the seventh resistor is connected to the third voltage terminal, and the other terminal of the seventh resistor is grounded;

[0015] The output terminal of the first operational amplifier is used to output the first induced voltage signal and the second induced voltage signal;

[0016] The output terminal of the second operational amplifier is used to output the third induced voltage signal.

[0017] Optionally, the equivalent circuit model further includes a micro-control unit, and the micro-control unit is connected to the output ends of the first switch tube and the second switch tube;

[0018] The first moment is the moment when the first switch tube and the second switch tube are both disconnected, and the first operational amplifier outputs a first induced voltage signal; the second moment is the moment when the micro-control unit detects that the first switch tube is closed, and the first operational amplifier outputs a second induced voltage signal; the third moment is the moment when the micro-control unit detects that the first switch tube and the second switch tube are both closed, and the second operational amplifier outputs a third induced voltage signal.

[0019] Optionally, the voltage measurement model is expressed as:

[0020]

[0021]

[0022] Wherein, UA represents the voltage at the first voltage terminal, U1 represents the first induced voltage signal, U2 represents the second induced voltage signal, and U3 represents the third induced voltage signal. After full-phase Fourier transformation, UA is expressed as: After full-phase Fourier transform of U3, it is expressed as parameter Rf1 represents the fifth resistor, R1 represents the third resistor, and are all phase angles, θ represents the phase angle deviation, z1 represents the impedance between the inner copper sheet and the outer copper sheet when the first switch tube and the second switch tube are both disconnected, z2 represents the impedance between the inner copper sheet and the outer copper sheet after the first switch tube is closed, z0 represents the impedance between the single-phase power line and the inner copper sheet, and zx represents the equivalent impedance between the outer copper sheet and the earth.

[0023] Optionally, solving the phase angle deviation in the voltage measurement model based on Newton iteration specifically includes:

[0024] When performing the nth Newton iteration:

[0025]

[0026] When |θ n -θn+1 |<ε, stop the iteration and set θ n+1 The output is the phase angle deviation;

[0027] Among them, θ n+1 Represents the phase angle deviation at the nth Newton iteration, θ n Indicates the phase angle deviation at the n-1th Newton iteration;

[0028] and is an intermediate parameter, Rf2 represents the sixth resistor, ε represents the set threshold, express The conjugate of represents the conjugate of z1, Indicates plural The imaginary part of .

[0029] Optionally, when performing the nth Newton iteration to obtain θ n+1 After that, judge θ n+1 Is it satisfied?

[0030] If θ n+1 Dissatisfied Then θ n+1 =2(π-α)-θ n+1 ;

[0031] in,

[0032] The present invention also discloses a voltage measurement system based on Newton iteration, comprising:

[0033] An equivalent circuit model building module is used to establish an equivalent circuit model according to an electric field distribution model; the electric field distribution model includes a single-phase power line and a sensor probe, the sensor probe is coaxially arranged with the single-phase power line, the single-phase power line is placed inside the sensor probe, and the sensor probe is used to measure the induced voltage signal of the single-phase power line;

[0034] An induced voltage signal measurement module, used to measure the induced voltage signals of three time periods through the sensor probe, which are distributed as a first induced voltage signal at a first moment, a second induced voltage signal at a second moment, and a third induced voltage signal at a third moment;

[0035] a voltage measurement model building module, configured to build a voltage measurement model taking frequency offset into consideration according to the first induced voltage signal, the second induced voltage signal and the third induced voltage signal;

[0036] A phase angle deviation solving module, used for solving the phase angle deviation in the voltage measurement model based on Newton iteration;

[0037] The single-phase power line voltage determination module is used to determine the voltage of the single-phase power line according to the phase angle deviation.

[0038] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0039] The present invention discloses a voltage measurement method based on Newton iteration. Induction voltage signals of three time periods measured by a sensor probe are distributed as a first induced voltage signal at a first moment, a second induced voltage signal at a second moment, and a third induced voltage signal at a third moment. A voltage measurement model is constructed under the frequency offset condition of a power system where a single-phase power line is located. The Newton iteration method is used to correct the phase angle deviation θ, thereby obtaining a more accurate voltage measurement value. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 This is a schematic flow chart of a voltage measurement method based on Newton iteration according to the present invention;

[0042] Figure 2 This is a schematic diagram of the structure of a sensor probe installed on a single-phase power line of the present invention;

[0043] Figure 3 It is a schematic cross-sectional view of the sensor probe of the present invention;

[0044] Figure 4 is the first equivalent circuit model of the present invention;

[0045] Figure 5 A schematic diagram of the waveforms of single-phase voltage, sampling signal and reference signal of the present invention;

[0046] Figure 6 The phasor diagram of the voltage measurement value when there is a phase angle deviation in the present invention;

[0047] Figure 7 is the second equivalent circuit model of the present invention;

[0048] Figure 8 It is the zero point distribution diagram of the function of the present invention;

[0049] Fig. 9 The present invention is a schematic diagram of the structure of a voltage measurement system based on Newton iteration. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] The purpose of the present invention is to provide a voltage measurement method and system based on Newton iteration, so as to improve the accuracy of voltage measurement.

[0052] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] Figure 1 FIG. 1 is a flow chart of a voltage measurement method based on Newton iteration according to the present invention. Figure 1 As shown, a voltage measurement method based on Newton iteration includes:

[0054] Step 101: Establish an equivalent circuit model according to an electric field distribution model; the electric field distribution model includes a single-phase power line and a sensor probe, the sensor probe is coaxially arranged with the single-phase power line, the single-phase power line is placed inside the sensor probe, and the sensor probe is used to measure the induced voltage signal of the single-phase power line.

[0055] The single-phase power line is the A-phase power line, ie, the live line, and the electric field distribution model also includes the industrial frequency power supply.

[0056] The electric field distribution model is an electric field distribution model for a single-phase 10kV application scenario.

[0057] Industrial frequency power supplies are used to provide power to single-phase power lines.

[0058] Among them, the equivalent circuit model in step 101 is Figure 7 The second equivalent circuit model.

[0059] Step 102: The induced voltage signals of three time periods measured by the sensor probe are distributed as a first induced voltage signal at a first moment, a second induced voltage signal at a second moment, and a third induced voltage signal at a third moment.

[0060] Step 103: establishing a voltage measurement model taking frequency offset into consideration according to the first induced voltage signal, the second induced voltage signal and the third induced voltage signal.

[0061] Step 104: Solve the phase angle deviation in the voltage measurement model based on Newton iteration.

[0062] Step 105: Determine the voltage of the single-phase power line according to the phase angle deviation.

[0063] like Figure 3 As shown, the sensor probe includes an inner copper skin S4, an insulating layer S3, an outer copper skin S2 and a jacket layer S5 which are sequentially covered from the inside to the outside. The sensor probe also includes a bakelite S1 which is arranged at one end of the cylindrical sensor probe. The bakelite is used to clamp the single-phase power line S6 inside the inner copper skin. The insulating layer is polyimide (PI) with a thickness of 0.05 mm. The thickness of the inner copper skin and the thickness of the outer copper skin are both 0.05 mm. The jacket layer is a PVC (polyvinyl chloride) jacket layer.

[0064] like Figure 7 The equivalent circuit model includes a first voltage terminal (UA), a second voltage terminal, a third voltage terminal, a first capacitor C0, a second capacitor C1, a third capacitor Cx, a first resistor R0, a second resistor R, a third resistor R1, a fourth resistor R2, a fifth resistor Rf1, a sixth resistor Rf2, a seventh resistor Rx, a first operational amplifier A1, a second operational amplifier A2, a first switch tube M1 and a second switch tube M2; the first voltage terminal is used to represent the voltage of the single-phase power line, the second voltage terminal represents the voltage of the inner copper sheet, and the third voltage terminal represents the voltage of the outer copper sheet.

[0065] One end of the first capacitor C0 is connected to the first voltage end, and the other end of the first capacitor C0 is connected to the second voltage end; one end of the first resistor R0 is connected to the first voltage end, and the other end of the first resistor R0 is connected to the second voltage end; one end of the second capacitor C1 is connected to the second voltage end, and the other end of the second capacitor C1 is connected to the third voltage end; one end of the fourth resistor R2 is connected to the second voltage end, and the other end of the fourth resistor R2 is connected to the first end of the first switch tube M1, and the second end of the first switch tube M1 is connected to the third voltage end; one end of the second resistor R is connected to the second voltage end, and the other end of the second resistor R is connected to the non-inverting input end of the first operational amplifier A1, and the first ends of the three resistors are connected to the first operational amplifier A1 respectively. The inverting input terminal of A1 is connected to the first terminal of the fifth resistor Rf1, the second terminals of the three resistors are connected to the third voltage terminal, and the second terminal of the fifth resistor Rf1 is connected to the output terminal of the first operational amplifier A1; the first terminal of the second switch tube M2 is connected to the second voltage terminal, the second terminal of the second switch tube M2 is respectively connected to the first terminal of the sixth resistor Rf2 and the inverting input terminal of the second operational amplifier A2, the second terminal of the sixth resistor Rf2 is connected to the output terminal of the second switch tube M2, and the non-inverting input terminal of the second switch tube M2 is connected to the third voltage terminal; one terminal of the third capacitor Cx is connected to the third voltage terminal, and the other terminal of the third capacitor Cx is grounded; one terminal of the seventh resistor Rx is connected to the third voltage terminal, and the other terminal of the seventh resistor Rx is grounded.

[0066] The output terminal of the first operational amplifier A1 is used to output the first induced voltage signal and the second induced voltage signal.

[0067] The output terminal of the second operational amplifier A2 is used to output the third induced voltage signal.

[0068] The equivalent circuit model further includes a micro-control unit, which is connected to the output ends of the first switch tube M1 and the second switch tube M2.

[0069] The first moment is the moment when the first switch tube M1 and the second switch tube M2 are both disconnected, and the first operational amplifier A1 outputs the first induced voltage signal; the second moment is the moment when the micro-control unit detects that the first switch tube M1 is closed, and the first operational amplifier A1 outputs the second induced voltage signal; the third moment is the moment when the micro-control unit detects that the first switch tube M1 and the second switch tube M2 are both closed, and the second operational amplifier A2 outputs the third induced voltage signal.

[0070] The voltage measurement model is expressed as:

[0071]

[0072]

[0073] Wherein, UA represents the voltage at the first voltage terminal, U1 represents the first induced voltage signal, U2 represents the second induced voltage signal, and U3 represents the third induced voltage signal. After full-phase Fourier transformation, UA is expressed as: After full-phase Fourier transform of U3, it is expressed as parameter Rf1 represents the fifth resistor, R1 represents the third resistor, and All are phase angles, θ represents the phase angle deviation, z1 represents the impedance between the inner copper sheet and the outer copper sheet when the first switch tube M1 and the second switch tube M2 are both disconnected, z2 represents the impedance between the inner copper sheet and the outer copper sheet when the first switch tube M1 is closed and the second switch tube M2 is disconnected, z0 represents the impedance between the single-phase power line (first voltage end) and the inner copper sheet, and zx represents the equivalent impedance between the outer copper sheet and the earth. z1 and z2 are measurable.

[0074] The method of solving the phase angle deviation in the voltage measurement model based on Newton iteration specifically includes:

[0075] When performing the nth Newton iteration:

[0076]

[0077] When |θ n -θ n+1 |<ε, stop the iteration and set θ n+1 The output is the phase angle deviation;

[0078] Among them, θ n+1 Indicates the phase angle deviation at the nth Newton iteration, θ n It represents the phase angle deviation at the n-1th Newton iteration, ε represents the set threshold, and ε is the minimum value;

[0079] and is an intermediate parameter, Rf2 represents the sixth resistor, express The conjugate of represents the conjugate of z1, Indicates plural The imaginary part of .

[0080] When the nth Newton iteration is performed to obtain θ n+1 After that, judge θ n+1 Is it satisfied?

[0081] If θ n+1 Dissatisfied Then θ n+1 =2(π-α)-θ n+1 .

[0082] in,

[0083] The technical idea of ​​a voltage measurement method based on Newton iteration of the present invention includes the following steps:

[0084] Step 1: Establish an electric field distribution model for a single-phase 10kV application scenario, including a single-phase line (phase A), a sensor probe, and an industrial frequency power supply, and establish an equivalent circuit model based on the electric field distribution.

[0085] The single sensor probe of the single-phase 10kV voltage measurement method of the present invention is set up as follows: Figure 2 The cross section of the sensor probe is shown in Figure 3 shown.

[0086] The sensor probe of the present invention is a double-layer copper sheet measurement. Compared with the single-layer copper sheet measurement, the advantages of the present invention are: first, when using a single-layer copper sheet solution, it is necessary to measure the voltage division of the copper sheet and the phase line, and the measuring device is at risk of direct lightning strikes, and the heat generated by the power line will also enter the measuring circuit through the conductor in the form of heat conduction, accelerating the aging of the measuring circuit equipment, while the use of a double-layer copper sheet avoids these problems. Second, when measuring voltage with a single-layer copper sheet, it is necessary to use the power line as one input end and the other input end as copper sheet. The noise signal in the power system enters the measuring system through a direct electrical connection. The two input ends of the double-layer copper sheet measuring device are both copper sheets, which prevents the power system noise from being directly input into the measuring system.

[0087] The edge effect of the induction probe can be reduced by increasing the length of the sensor probe and reducing its diameter. Therefore, the present invention believes that the coupling effect between the induction probe with two layers of copper and the single-phase power line can be described by a distributed capacitance network formed by a coaxial cylindrical conductor. Since the electric field lines of the coaxial cylindrical conductor are perpendicular to the inner copper skin and terminate at the inner copper skin, the conductor (single-phase power line) does not form a coupling capacitance with the outer copper skin. In actual working conditions, the air medium contains fine dust, and free charges are often attached to the fine dust. Under the condition of an external electric field, the fine dust can move in a directed manner with the free charges to form a transport current. Therefore, the equivalent electrical connection between the inner copper skin and the conductor and between the outer copper skin and the ground is a parallel connection of an equivalent capacitance and an equivalent admittance. Its equivalent measurement circuit (first equivalent circuit model) is as follows: Figure 4 shown.

[0088] Step 2: By selecting the measurement path of the subsequent measurement circuit through MOSFET, the response signals of the two time periods before and after are obtained, a voltage measurement model considering the frequency offset of the power system is established, and the mechanism of measurement error caused by the frequency offset of the power system is analyzed.

[0089] The measurement is divided into two time periods by the on and off of the mosfet switch tube. During the time period 0-T1, the mosfet is disconnected, and the measuring device collects the voltage waveform between the two layers of copper skin during this period. After T1, the voltage waveform between the two layers of copper skin is measured again.

[0090] Step 2.1: Considering the power system has no frequency offset, analyze the principle of voltage measurement:

[0091] like Figure 5 As shown, in the time period t1 (the time period from 0 to T1), the full phase Fourier transform of UA, E1, and U1 is performed, and the results are:

[0092]

[0093] The signal is generated by a crystal oscillator inside the measuring device with a frequency of 50 Hz. The E1 signal is a unit sinusoidal signal with an amplitude of 1, which acts as a reference phasor. The sensor probe is part of the measuring device, which also includes circuits for collecting and transmitting signals. is the phase angle. Using KVL (Kirchhoff's voltage law) for the measurement circuit, we have:

[0094]

[0095] At time T1, the mosfet (first switch) is turned on, and the fourth resistor R2 enters the measurement loop. Due to the presence of energy storage elements, the device needs to go through a transient process. In order to avoid transient signals, U2 needs a period of time t2 to enter a steady state. At the same time, since the MCU needs time to detect the state of the mosfet (first switch), this time is also classified as transient time, so the t2 time is often unknown.

[0096] After that, the full phase Fourier transform is performed on UA, E1, and U2 in the time period t3, and we have

[0097]

[0098] Where Δt=t1+t2, this period of time has an effect on the measurement circuit using KVL

[0099]

[0100] The amplitude of UA can be obtained as

[0101]

[0102] in

[0103]

[0104] It can be obtained that, since the grid frequency is 50 Hz, even if the transient interval t2 is unknown, when there is a 50 Hz reference signal E1, after dividing the phasor of the measured signal by the phasor of the reference signal, the phase angle difference in formula (5) is a constant, and there will be no phase angle deviation due to avoiding the transient time.

[0105] Step 2.2: Analyze the error mechanism of voltage measurement when considering the power system frequency offset:

[0106] When the grid frequency is f 1 =f 0 +Δf, if the 50Hz reference signal is still used, a phase shift related to the transient time t2 will be generated, resulting in measurement errors, f 0 is the grid set frequency, Δf is the frequency deviation. For example, when the grid frequency deviates, in the t3 time period, the phasor value of U2 with E1 as the reference phasor is 2π·Δf·Δt is a phase angle deviation, Δt is the difference between the start times of the two calculation zones. Since the transient time t2 is unknown, Δt is obviously unknown. However, the estimation of the phase voltage value requires accurate U1 and U2 phasor calculations, otherwise there will be errors in the voltage measurement, and even the voltage estimation value will deviate too much from the actual voltage value.

[0107] When the grid frequency is offset, the fixed frequency 50Hz E1 crystal signal can no longer achieve the fixed phase difference between two measurement signals. Therefore, when the system frequency is offset, the E1 signal cannot be selected as a reference signal, so the E1 signal is directly omitted.

[0108] When the grid frequency is f 1 =f 0 +Δf, if the 50Hz reference signal is still used, a phase offset related to the transient time t2 will be generated, resulting in measurement errors. For example, when the grid frequency is offset, in the t3 time period, the phasor value of U2 with E1 as the reference phasor is 2π·Δf·Δt is a phase angle deviation, Δt is the difference between the start times of the two calculation zones. Since the transient time t2 is unknown, Δt is obviously unknown. However, the estimation of the phase voltage value requires accurate U1 and U2 phasor calculations, otherwise there will be errors in the voltage measurement, and even the voltage estimation value will deviate too much from the actual voltage value.

[0109] When the grid frequency is offset, the fixed frequency 50Hz E1 crystal signal can no longer achieve the fixed phase difference between two measurement signals. Therefore, when the system frequency is offset, the E1 signal cannot be selected as a reference signal, so the E1 signal is directly omitted.

[0110] The KVL without reference signal is written as follows:

[0111]

[0112]

[0113] Combining the above two equations, it can be seen that when there is a phase angle deviation, the phase voltage estimation equation (5) will be rewritten as follows:

[0114]

[0115] Where θ = 2π·f·Δt. Since θ is unknown, when there is a phase angle deviation θ, there will be an error in the voltage estimation.

[0116] Step 3: Based on the voltage measurement model considering the power system frequency offset constructed in Step 2, further analyze the characteristics of the phase angle deviation of the phasor measured twice in succession.

[0117] According to the voltage measurement model considering the power system frequency offset constructed in Step 2, the characteristics of the phase angle deviation of the two consecutive measurements are further analyzed:

[0118] make

[0119] When the phase angle deviation θ is accurately estimated:

[0120]

[0121] Since zx+z0 is close to capacitive and |z1|>|z2|, it is obvious that Since |z1|,|z0| are larger than |zx|, and Therefore

[0122]

[0123] If θ is considered as a variable, The trajectory of will be a circle, such as Figure 6 As shown, and The phase angles are different, but the amplitudes are the same. The voltage value calculated according to equation (8) is a periodic function of θ, and the function has a maximum and a minimum value.

[0124] Step 4: According to the characteristics of the voltage measurement model established in Step 2 and Step 3 and the phase angle deviation of two consecutive phasors, a method of correcting the parameter θ using the Newton iteration method is proposed. This method corrects the phase angle deviation θ through the added response equation, and determines the iterative correction scheme and shutdown criterion according to the characteristics of the phase angle deviation of two consecutive measurements of the phasor, so as to achieve accurate estimation of the phase angle deviation θ, thereby achieving the purpose of accurate voltage estimation.

[0125] Step 4.1: Summarize the characteristics of the current problem, add a response equation, and use Newton's method to correct the phase angle deviation θ:

[0126] The problem can currently be characterized as follows:

[0127] 1) Due to the unknown phase angle deviation θ, the unknowns in the equation are UA, z0+zx, θ.

[0128] 2) When the phase angle deviation θ is accurately estimated, the characteristics of equation (10) are satisfied.

[0129] 3) The function about θ defined in equation (8) is a real function.

[0130] 4) If the period before and after the closure of the MOSFET (the first switch) is considered as one cycle, two equations can be written in one cycle. Therefore, in one cycle time period, the system of equations is underdetermined.

[0131] Since the equation is underdetermined, the phase angle deviation θ cannot be uniquely determined by only two equations of one cycle. Therefore, a measurement link is added to each measurement cycle. The purpose of correcting the parameter θ is achieved by relying on the added measurement link. The schematic diagram (the second equivalent circuit model) is shown as follows: Figure 7 As shown:

[0132] When the MOSFET (second switch) is closed, since the open-loop gain of the op amp is very high, the potentials of the two input terminals of the op amp are approximately the same, and the two layers of copper are equivalent to being directly short-circuited, and there are:

[0133]

[0134] The solution of the present invention is: using iterative solution, assuming that the value of the nth iteration of the phase angle deviation θ is θ n , using equations (6) and (7) to solve |z0+zx| n , with |UA| n , and substitute it into equation (11) to correct the phase angle deviation θ using Newton iteration. The specific process is as follows:

[0135] According to formula (9), at the nth iteration:

[0136]

[0137]

[0138]

[0139] set up

[0140] When θ n When iterating to the true value θ*, f(θ*) = 0. Since f(θ) is a real function, the true value can be obtained using Newton iteration.

[0141]

[0142] The correction equation for the phase angle deviation θ is as follows:

[0143]

[0144] Step 4.2: Determine the iterative correction scheme and shutdown criteria based on the characteristics of the phase angle deviation of the phasor measured twice in succession to achieve accurate estimation of the phase angle deviation θ, thereby achieving the purpose of accurate voltage estimation.

[0145] It is observed that f(θ) has two zeros θ1 and θ2 on [0,2π], as Figure 8 As shown:

[0146] Obviously there are:

[0147] θ1+θ2=2(π-α) (17)

[0148] in When using the Newton iteration method to correct θ, in order to make the zero point converge to the correct root, the present invention sets the following iterative calibration method.

[0149] From the analysis of step 3, we can see that when the Newton algorithm iteration stops, the correct phase angle deviation θ n Because of satisfaction Otherwise, the current phase angle deviation θ n Make the following adjustments

[0150] θ n =2(π-α)-θ n (18)

[0151] The current and subsequent phase angle deviations meet

[0152] |θ n -θ n+1 |<ε (19)

[0153] Exit the loop, thereby obtaining the accurate phase angle deviation, and thus estimating the accurate voltage value according to (13).

[0154] The beneficial effects of the present invention are:

[0155] In view of the fact that the current non-contact voltage measurement method based on topological transformation measures waveforms twice in succession without a time stamp, resulting in a phase angle deviation in the two measured phasors due to the absence of a reference phasor, which ultimately causes the voltage estimation to deviate from the true value in a large range, the present invention first analyzes the problem that when there is a frequency offset in the power system, the measuring device cannot avoid the phase angle deviation in the two measured phasors through a 50Hz reference signal. Then, by converting the problem of correcting the phase angle deviation into a zero point problem for solving an additional response equation, the present invention provides a method for accurately estimating the phase angle deviation when the measuring device has no reference signal. The method uses Newton's method to correct the phase angle deviation, thereby improving the accuracy of voltage measurement.

[0156] Fig. 9 FIG. 1 is a schematic diagram of a voltage measurement system based on Newton iteration according to the present invention. Fig. 9 As shown, a voltage measurement system based on Newton iteration includes:

[0157] The equivalent circuit model building module 201 is used to establish an equivalent circuit model according to the electric field distribution model; the electric field distribution model includes a single-phase power line and a sensor probe, the sensor probe is coaxially arranged with the single-phase power line, the single-phase power line is placed inside the sensor probe, and the sensor probe is used to measure the induced voltage signal of the single-phase power line.

[0158] The induced voltage signal measuring module 202 is used to measure the induced voltage signals of three time periods through the sensor probe, which are distributed as a first induced voltage signal at a first moment, a second induced voltage signal at a second moment, and a third induced voltage signal at a third moment.

[0159] The voltage measurement model building module 203 is used to build a voltage measurement model taking frequency offset into consideration according to the first induced voltage signal, the second induced voltage signal and the third induced voltage signal.

[0160] The phase angle deviation solving module 204 is used to solve the phase angle deviation in the voltage measurement model based on Newton iteration.

[0161] The single-phase power line voltage determination module 205 is used to determine the voltage of the single-phase power line according to the phase angle deviation.

[0162] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0163] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A voltage measurement method based on Newton iteration, It is characterized in that include: An equivalent circuit model is established according to the electric field distribution model; the electric field distribution model includes a single-phase power line and a sensor probe, the sensor probe is coaxially arranged with the single-phase power line, the single-phase power line is placed inside the sensor probe, and the sensor probe is used to measure the induced voltage signal of the single-phase power line; The induced voltage signals of three time periods measured by the sensor probe are distributed as a first induced voltage signal at a first moment, a second induced voltage signal at a second moment, and a third induced voltage signal at a third moment; Establishing a voltage measurement model taking frequency offset into consideration according to the first induced voltage signal, the second induced voltage signal and the third induced voltage signal; Solving the phase angle deviation in the voltage measurement model based on Newton iteration; determining the voltage of the single-phase power line according to the phase angle deviation; The sensor probe comprises an inner copper layer, an insulating layer, an outer copper layer and a jacket layer which are sequentially covered from the inside to the outside, and the sensor probe further comprises bakelite, which is used to clamp the single-phase power line inside the inner copper layer; The equivalent circuit model includes a first voltage terminal, a second voltage terminal, a third voltage terminal, a first capacitor, a second capacitor, a third capacitor, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first operational amplifier, a second operational amplifier, a first switch tube and a second switch tube; the first voltage terminal is used to represent the voltage of the single-phase power line, the second voltage terminal represents the voltage of the inner copper sheet, and the third voltage terminal represents the voltage of the outer copper sheet; One end of the first capacitor is connected to the first voltage end, and the other end of the first capacitor is connected to the second voltage end; one end of the first resistor is connected to the first voltage end, and the other end of the first resistor is connected to the second voltage end; one end of the second capacitor is connected to the second voltage end, and the other end of the second capacitor is connected to the third voltage end; one end of the fourth resistor is connected to the second voltage end, and the other end of the fourth resistor is connected to the first end of the first switch tube, and the second end of the first switch tube is connected to the third voltage end; one end of the second resistor is connected to the second voltage end, and the other end of the second resistor is connected to the non-inverting input end of the first operational amplifier, and the first ends of the three resistors are connected to the first and second terminals of the first operational amplifier, respectively. An inverting input terminal of an operational amplifier is connected to a first terminal of the fifth resistor, second terminals of the three resistors are connected to the third voltage terminal, and a second terminal of the fifth resistor is connected to an output terminal of the first operational amplifier; a first terminal of the second switch tube is connected to the second voltage terminal, a second terminal of the second switch tube is respectively connected to a first terminal of the sixth resistor and an inverting input terminal of the second operational amplifier, a second terminal of the sixth resistor is connected to the output terminal of the second switch tube, and a non-inverting input terminal of the second switch tube is connected to the third voltage terminal; one terminal of the third capacitor is connected to the third voltage terminal, and the other terminal of the third capacitor is grounded; one terminal of the seventh resistor is connected to the third voltage terminal, and the other terminal of the seventh resistor is grounded; The output terminal of the first operational amplifier is used to output the first induced voltage signal and the second induced voltage signal; The output terminal of the second operational amplifier is used to output the third induced voltage signal; The voltage measurement model is expressed as: Wherein, UA represents the voltage at the first voltage terminal, U1 represents the first induced voltage signal, U2 represents the second induced voltage signal, and U3 represents the third induced voltage signal. After full-phase Fourier transformation, UA is expressed as: After full-phase Fourier transform of U3, it is expressed as parameter Rf1 represents the fifth resistor, R1 represents the third resistor, and are all phase angles, θ represents the phase angle deviation, z1 represents the impedance between the inner copper skin and the outer copper skin when the first switch tube and the second switch tube are both disconnected, z2 represents the impedance between the inner copper skin and the outer copper skin after the first switch tube is closed, z0 represents the impedance between the single-phase power line and the inner copper skin, zx represents the equivalent impedance between the outer copper skin and the earth, and Rf2 represents the sixth resistor.

2. The voltage measurement method based on Newton iteration according to claim 1, It is characterized in that The equivalent circuit model further includes a micro-control unit, and the micro-control unit is connected to the output ends of the first switch tube and the second switch tube; The first moment is the moment when the first switch tube and the second switch tube are both disconnected, and the first operational amplifier outputs a first induced voltage signal; the second moment is the moment when the micro-control unit detects that the first switch tube is closed, and the first operational amplifier outputs a second induced voltage signal; the third moment is the moment when the micro-control unit detects that the first switch tube and the second switch tube are both closed, and the second operational amplifier outputs a third induced voltage signal.

3. The voltage measurement method based on Newton iteration according to claim 1, It is characterized in that The method of solving the phase angle deviation in the voltage measurement model based on Newton iteration specifically includes: When performing the nth Newton iteration: When |θ n -θ n+1 |<ε, stop the iteration and set θ n+1 The output is the phase angle deviation; Among them, θ n+1 Represents the phase angle deviation at the nth Newton iteration, θ n Indicates the phase angle deviation at the n-1th Newton iteration; and is the intermediate parameter, ε represents the set threshold, express The conjugate of represents the conjugate of z1, Indicates plural The imaginary part of .

4. The voltage measurement method based on Newton iteration according to claim 3, It is characterized in that When the nth Newton iteration is performed to obtain θ n+1 After that, judge θ n+1 Is it satisfied? If θ n+1 Dissatisfied Then θ n+1 =2(π-α)-θ n+1 ; in, 5. A voltage measurement system based on Newton iteration, It is characterized in that The voltage measurement system based on Newton iteration is used to implement the voltage measurement method based on Newton iteration according to claim 1, and the voltage measurement system based on Newton iteration includes: An equivalent circuit model building module is used to establish an equivalent circuit model according to an electric field distribution model; the electric field distribution model includes a single-phase power line and a sensor probe, the sensor probe is coaxially arranged with the single-phase power line, the single-phase power line is placed inside the sensor probe, and the sensor probe is used to measure the induced voltage signal of the single-phase power line; An induced voltage signal measurement module, used to measure the induced voltage signals of three time periods through the sensor probe, which are distributed as a first induced voltage signal at a first moment, a second induced voltage signal at a second moment, and a third induced voltage signal at a third moment; a voltage measurement model building module, configured to build a voltage measurement model taking frequency offset into consideration according to the first induced voltage signal, the second induced voltage signal and the third induced voltage signal; A phase angle deviation solving module, used for solving the phase angle deviation in the voltage measurement model based on Newton iteration; The single-phase power line voltage determination module is used to determine the voltage of the single-phase power line according to the phase angle deviation.

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