CN117269577A - Rogowski coil measuring method and system with composite differential active integration circuit - Google Patents

Abstract

The invention belongs to the field of lightning current measurement for transmission lines, and specifically relates to a Rogowski coil measurement method and system with a composite differential active integrating circuit. The method includes the Rogowski coil inducing the measured lightning current in the transmission line and outputting a voltage signal at both ends of the sampling resistor. The sampling resistor is connected to the high-pass RC filter circuit, and the output signal is used as the input signal of the composite differential active integrating circuit. The measured lightning current contains a frequency component within the measurement bandwidth of the Rogowski coil. The sampling resistor output signal restores the frequency component by proportional output. The composite differential active integrating circuit plays a proportional amplification effect on this component. For components where the measured lightning current is less than the lower limit measurement frequency of the Rogowski coil, the output signal of the sampling resistor is the differential of the measured lightning current, and the composite differential active integrating circuit acts as an external integrating circuit to correct and output it. This method reduces the lower limit measurement frequency of the Rogowski coil, broadens the measurement frequency band, and solves the problem that traditional Rogowski coils easily produce low-frequency distortion when measuring lightning current.

Description

Rogowski coil measurement method and system with composite differential active integrating circuit

Technical field

The invention belongs to the technical field of lightning current measurement for transmission lines, and in particular relates to a Rogowski coil measurement method and system with a composite differential active integrating circuit.

Background technique

Transmission lines are widely distributed and located in complex terrain and climate conditions, making them very susceptible to lightning strikes. In recent years, lightning strikes have become a major factor in power system operation failures. Obtaining accurate lightning current parameters is not only a prerequisite for studying lightning characteristics, analyzing lightning faults, and locating lightning faults, but it is also the basis for various lightning protection designs in power systems. Therefore, it is of great practical significance to accurately measure lightning current to obtain accurate lightning current data.

Since Rogowski coil (Rogowski coil for short) does not have magnetic saturation, has no direct electrical connection with the line under test, and has the characteristics of wide measurement frequency and strong anti-interference, it is currently often used to measure lightning current parameters on transmission lines. The energy of the lightning current itself is mainly distributed in the frequency domain of 100Hz~500kHz and decreases as the frequency increases. When using a Rogowski coil to measure lightning current, the Rogowski coil measurement bandwidth needs to be able to take into account both the low-frequency and high-frequency components of the lightning current. Rogowski coil distributed capacitance is often in the order of nF. When the sampling resistor is smaller, the upper limit of the measurement frequency is It is easy to meet the upper limit frequency required for measuring lightning current. And for the lower limit measurement frequency/> , Traditional Rogowski coil sensors used for lightning current measurement often reduce the lower limit measurement frequency by increasing the Rogowski coil self-inductance or reducing the internal resistance and sampling resistance. However, increasing the self-inductance means that the number of turns of the coil increases, resulting in an increase in internal resistance. Reducing the sampling resistor value will lead to a reduction in the sensitivity of the sensor. Coupled with the constraints of coil material and structural design, //> It is difficult to meet the ideal lower limit measurement frequency required for lightning current measurement. At the same time, due to the wide frequency domain of lightning current and distortion during the transmission process, the frequency of the lightning current signal will be smaller than the lower limit measurement frequency of the Rogowski coil sensor/> The components further increase, which leads to distortion in the tail part of the measured lightning current waveform.

Contents of the invention

The invention provides a Rogowski coil measurement method and system with a composite differential active integrating circuit to solve the low-frequency distortion problem that occurs when the Rogowski coil is used to measure lightning current in the prior art.

The invention provides a Rogowski coil measurement system with a composite differential active integrating circuit, which includes: connecting the Rogowski coil H ₀ to a first-order high-pass RC filter circuit H ₁ , an RCR passive integrating circuit H ₂ and a differential active integrating circuit H in sequence _3. Three links are used to measure and restore lightning current. The filter circuit, passive integrating circuit and differential active integrating circuit form a composite differential active integrating circuit. The differential active integrating circuit includes two in-phase components with exactly the same parameters. Active integrating circuits A1, A2 and a subtractor A3, in which A1 and A2 form a differential structure.

First-order high-pass RC filter circuit H ₁ is the first capacitor with the first resistor/> RC filter circuit composed of; passive integrating circuit H ₂ is the second resistor/> , the second capacitor/> and the third resistor/> The RCR passive integrating circuit is composed of; the first in-phase active integrating circuit A1 includes a fourth resistor/> , the third capacitor/> , the first operational amplifier U ₃ and the fifth resistor/> ;The second non-phase active integrating circuit A2 includes a second operational amplifier U _os and a sixth resistor/> , the fourth capacitor/> and seventh resistor/> ;Subtractor A3 includes an eighth resistor/> , the ninth resistance/> , the third operational amplifier U ₄ , the tenth resistor/> and the eleventh resistor/> .

The invention also provides a Rogowski coil measurement system method with a composite differential active integrating circuit, including the Rogowski coil H ₀ inductive transmission line to measure the lightning current And output a voltage signal at both ends of the sampling resistor/> . Both ends of the sampling resistor are connected to the first-order high-pass RC filter circuit H ₁ to output the signal/> As the input signal of the composite differential active integrating circuit. For the measured lightning current/> Measurement bandwidth included in Rogowski coils/> The frequency component within the sampling resistor output signal/> The proportional output is restored, and the composite differential active integrating circuit only plays a proportional amplification role for this component. For the measured lightning current/> Less than the lower limit measurement frequency of Rogowski coil/> The composition of the sampling resistor output signal/> is the measured lightning current/> The differential, composite differential active integrating circuit acts as an external integrating circuit to correct it and output it. In the differential active integrating circuit _H3 , the output _U2 of the RCR passive integrating circuit _H2 is used as the input signal of the non-inverting active integrating circuit A1, and the ground signal is used as the input signal of the non-inverting active integrating circuit A2. The outputs of both The signal is used as the input signal of subtractor A3.

According to the method of Rogowski coil measurement system with composite differential active integrating circuit provided by the present invention, the method specifically includes the following steps:

Find the expression of the transfer function H ₀ ( s ) of the Rogowski coil H ₀ link;

Simplified Rogowski coil H ₀ link transfer function H ₀ ( s );

Put the Rogowski coil H ₀ output signal As the input signal of the composite differential active integrating circuit;

Eliminate the input offset voltage present _in the non-ideal operational amplifier through the RCR passive integrating circuit H2 and _the differential active integrating circuit H3 and bias current/> The resulting ramp error output/> ;

Based on the transfer functions of the first-order high-pass RC filter circuit H ₁ , the passive integrating circuit H ₂ and the differential active integrating circuit H ₃ , the transfer function H ( s ) of the measurement system is obtained;

Select various parameters of the composite differential active integrating circuit;

Determine the high-speed operational amplifier model;

make To eliminate the error of subtractor A3, where V _os and I _os are the offset voltage and offset current of the determined operational amplifier respectively.

Compared with the prior art, the beneficial effects of the present invention are:

The present invention proposes a lightning current measurement method and system using a Rogowski coil with a composite differential active integrating circuit in view of the low-frequency distortion that is easily produced by the traditional Rogowski coil when measuring lightning current. The proposed measurement method and system are based on the perspective of the frequency domain and re-analyze the The transfer function, working principle and amplitude-frequency characteristics of Rogowski coil when measuring lightning current are composed of four links: Rogowski coil H ₀ , first-order high-pass RC filter circuit H ₁ , RCR passive integrating circuit H ₂ and differential active integrating circuit H ₃ The cascade was carried out from the perspective of the working frequency domain. By designing the parameters of the composite differential active integration circuit, the lower limit measurement frequency of the Rogowski coil was reduced, the measurement frequency band was broadened, and the problem of low-frequency distortion easily produced by the traditional Rogowski coil when measuring lightning current was solved. .

In addition, the design of the composite cascade of the three links of the first-order high-pass RC filter circuit H ₁ , RCR passive integrating circuit H ₂ and differential active integrating circuit H ₃ as an external integrating circuit in the present invention can reduce the lower limit measurement frequency of the entire measurement system. And while maintaining a more appropriate measurement sensitivity, it does not bring greater low-frequency gain to reduce the error caused by low-frequency signals. Finally, by using a differential structure for the active integrating circuit, the drift error caused by the non-ideal operational amplifier is eliminated. , improve the system measurement accuracy and better restore the lightning current waveform.

Description of the drawings

In order to more clearly illustrate the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are the drawings of the present invention. For some embodiments, those of ordinary skill in the art can also obtain other drawings based on these drawings without exerting creative efforts.

Figure 1 is an equivalent circuit diagram of a Rogowski coil according to an embodiment of the present invention;

Figure 2 is a Rogowski coil with composite differential active integrating circuit diagram according to an embodiment of the present invention;

Figure 3 is a diagram of the amplitude-frequency characteristics of each link and the overall measurement system according to the embodiment of the present invention;

Figure 4 is a comparison diagram between the corrected output waveform and the 8/20us lightning current test waveform according to the embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention more clear, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention. , not all examples. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Rogowski coils are often used as the core device for measuring lightning current parameters. However, when using traditional Rogowski coils to measure lightning current, it is difficult to obtain an ideal lower limit measurement frequency. , components in the lightning current that are less than the lower limit measurement frequency will cause distortion and affect the measurement results. The Rogowski coil measurement method and system with a composite differential active integrating circuit in this embodiment solves the problems of the prior art.

This embodiment is implemented through the following technical solution. The Rogowski coil measurement method with a composite differential active integrating circuit includes the following steps:

Step 1. The measurement method is based on the equivalent circuit of the Rogowski coil when measuring lightning current. The equivalent circuit diagram is shown in Figure 1, where M is the mutual inductance coefficient between the measured conductor passing through the Rogowski coil and the coil, L is the Rogowski coil self-inductance, C is the Rogowski coil distributed capacitance, and R ₀ is the external sampling resistor. Lightning current measured on Rogowski coil induction transmission line And output a voltage signal at both ends of the sampling resistor R ₀ /> . Rogowski coil link transfer function ,/> ,/> .

Step 2. The transfer function H ₀ ( s ) of the Rogowski coil link can be equivalent to the proportional link , differential link/> And two inertia links/> ,/> of series connection. The value of Rogowski coil distributed capacitance C is generally a number/> , when the value of R ₀ is small, perform spectrum analysis on the transfer function H ₀ ( s ) of the Rogowski coil link, and the upper limit of the measurement frequency/> It is far satisfied with the upper limit required to measure lightning current, so it can be ignored/> The subsequent amplitude-frequency characteristics, that is, the inertia link can be ignored The influence on the amplitude-frequency characteristics of the Rogowski coil is obtained, and the simplified transfer function of the Rogowski coil link is obtained. ,/> .

Step 3. The Rogowski coil with composite differential active integrating circuit is shown in Figure 2. The two ends of the sampling resistor R ₀ are connected in sequence to the first-order high-pass RC filter circuit H ₁ , the RCR passive integrating circuit H ₂ and the differential active integrating circuit H ₃ Three links, including filter circuit, passive integrating circuit and differential active integrating circuit form a composite differential active integrating circuit. output signal As the input signal of the composite differential active integrating circuit.

Step 4. The differential active integrating circuit _H3 includes two in-phase active integrating circuits A1 and A2 with identical parameters and a subtractor A3, where A1 and A2 form a differential structure. The output signal U ₂ of the RCR passive integrating circuit H ₂ is used as the input signal of the non-inverting active integrating circuit A1, the ground signal is used as the input signal of the non-inverting active integrating circuit A2, and the output signals of A1 and A2 are used as the subtractor A3 input signal. Can eliminate the input offset voltage present in non-ideal op amps and bias current/> The slope error output caused by the accumulation of non-ideal factors/> .

Step 5. Deduced through traditional circuit principles, the transfer functions of the three links of the first-order high-pass RC filter circuit H ₁ , RCR passive integrating circuit H ₂ and differential active integrating circuit H ₃ are respectively ,/> , ,/> ,/> ,/> ,/> ,/> .

Combined with Rogowski coil link transfer function , and pass the parameter design command/> , the transfer function H ( s ) of the entire measurement system can be obtained:

The overall amplitude-frequency characteristics of each link and the measurement system are shown in Figure 3. For the measured lightning current Measurement bandwidth included in Rogowski coils/> Frequency components within, such as in area III, the Rogowski coil H ₀ works in a self-integrating state, and the sampling resistor outputs a signal/> The proportional output is restored, and the composite differential active integrating circuit only plays a proportional amplification role for this component. For the measured lightning current/> Less than the lower limit measurement frequency of Rogowski coil/> components, such as area I and area II, the sampling resistor output signal/> is the measured lightning current/> The differential active integral link H ₃ and the passive integral link H ₂ function as external integral circuits respectively to correct the differential signal output by the sampling resistor. In addition, the combination of first-order high-pass RC filter circuit H ₁ , RCR passive integrating circuit H2 and differential active integrating circuit H3 can enable the measurement system to reduce the lower limit measurement frequency without bringing about greater low-frequency gain.

Step 6. Take the value of the sampling resistor R ₀ as 1Ω, and according to the structural parameters of the Rogowski coil (mutual inductance coefficient M , self-inductance L , distributed capacitance C ), follow the steps in step 5. The design principle is used to determine the values of the resistors and capacitors R ₁ , C ₁ , R ₂ , C ₂ , R 3 , R ₄ , C _{3 ,} R ₅ , R ₆ , and R ₇ included in the composite differential active integrating circuit . design. At the same time, in order to meet the requirements for measuring the low-frequency components of lightning current, the fourth resistor in the _H3 link of the differential active integrating circuit/> , the third capacitor/> Select appropriate parameters to extend the system's lower limit measurement frequency to 60Hz. At the same time, it should be noted that while ensuring that the entire measurement system H ( s ) has a high sensitivity, the amplitude of the input and output signals of the measured lightning current signal in the active integration link must not exceed the ±15V supply voltage of the selected op amp. restriction requirements.

Step 7. In order to ensure the normal operation of the operational amplifier in the composite differential active integrating circuit, according to the structural parameters of the Rogowski coil in step 6 (mutual inductance coefficient M , self-inductance L , distributed capacitance C ), sampling resistor R ₀ and first resistor R ₁ , the second resistor R ₂ , the third resistor R ₃ , the fourth resistor R ₄ , the fifth resistor R ₅ , the sixth resistor R ₆ , the seventh resistor R ₇ , the first capacitor C ₁ , the second capacitor C ₂ , the For the values of the three capacitors C ₃ , calculate that the gain bandwidth product (GBW) of the operational amplifier in the composite differential active integrating circuit should be greater than 1MHz, and the slew rate (SR) should be greater than 156V/µs, and select a suitable type of high-speed operational amplifier. .

Step 8. For subtractor A3, let ( V _os and I _os are the offset voltage and offset current of the selected operational amplifier) Eliminate the error caused by the offset voltage and offset current to the subtraction circuit.

The following is a simulation verification of the Rogowski coil measurement method with a composite differential active integrating circuit in this embodiment. The 8/20us impulse current waveform is used as the lightning current test waveform to verify the measurement method. The comparison between the corrected output waveform of channel B and the 8/20us lightning current test waveform of channel A is shown in Figure 4. It can be seen that the corrected output waveform fits well with the 8/20us lightning current test waveform, indicating that the lightning current measurement method with a composite differential active integrating circuit in this embodiment can accurately restore the lightning current generated on the transmission line. According to the parameters in step 6, the corrected system 3dB lower limit measurement frequency is extended to 60Hz, and the system measurement sensitivity is 0.247V/kA.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be used Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent substitutions are made to some of the technical features; however, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (9)

1. A Rogowski coil measurement system with a composite differential active integrating circuit, which is characterized in that it includes a composite differential active integrating circuit and a Rogowski coil measurement circuit H ₀ ; the Rogowski coil measurement circuit H ₀ includes a Rogowski coil and a sampling resistor connected in parallel with it ;Composite differential active integrating circuit includes sampling resistor/> The first-order high-pass RC filter circuit H ₁ , the passive integrating circuit H ₂ and the differential active integrating circuit H ₃ are connected in sequence; the differential active integrating circuit H ₃ includes two first in-phase active integrating circuits A1 with identical parameters , a second in-phase active integrating circuit A2 and a subtractor A3, in which the first in-phase active integrating circuit A1 and the second in-phase active integrating circuit A2 form a differential structure. 2. The Rogowski coil measurement system with a composite differential active integrating circuit according to claim 1, characterized in that the first-order high-pass RC filter circuit H1 is the first _capacitor with the first resistor/> RC filter circuit composed of; passive integrating circuit H ₂ is the second resistor/> , the second capacitor/> and the third resistor/> The RCR passive integrating circuit is composed of; the first in-phase active integrating circuit A1 includes a fourth resistor/> , the third capacitor/> , the first operational amplifier U ₃ and the fifth resistor/> ;The second non-phase active integrating circuit A2 includes a second operational amplifier U _os and a sixth resistor/> , the fourth capacitor/> and seventh resistor/> ;Subtractor A3 includes an eighth resistor/> , the ninth resistance/> , the third operational amplifier U ₄ , the tenth resistor/> and the eleventh resistor/> . 3. The measurement method of the Rogowski coil measurement system with a composite differential active integrating circuit according to any one of claims 1-2, characterized in that it includes: the Rogowski coil H ₀ induces the measured lightning current of the transmission line And in the sampling resistor/> Output voltage signal at both ends/> ;The two ends of the sampling resistor R ₀ are connected to the first-order high-pass RC filter circuit H ₁ to output the signal/> As the input signal of the composite differential active integrating circuit; for the measured lightning current/> Measurement bandwidth included in Rogowski coils/> Frequency components within, sampling resistor/> Output signal/> The proportional output is restored, and the composite differential active integrating circuit proportionally amplifies the frequency component; for the measured lightning current/> Less than the lower limit measurement frequency of Rogowski coil/> The composition of the sampling resistor/> Output signal/> is the measured lightning current/> The differential, the composite differential active integrating circuit is used as an external integrating circuit to correct and output it; in the differential active integrating circuit H ₃ , the output U ₂ of the RCR passive integrating circuit H ₂ is used as the first in-phase active integrating circuit The input signal of A1 and the ground signal are used as the input signal of the second non-inverting active integrating circuit A2, and the output signals of both are used as the input signal of the subtractor A3. 4. The measurement method of the Rogowski coil measurement system with a composite differential active integrating circuit according to claim 3, characterized in that the specific steps of the method are as follows: Find the expression of the transfer function H ₀ ( s ) of the Rogowski coil H ₀ link; Simplified Rogowski coil H ₀ link transfer function H ₀ ( s ); Put the Rogowski coil H ₀ output signal As the input signal of the composite differential active integrating circuit; Eliminate the input offset voltage present _in the non-ideal operational amplifier through the RCR passive integrating circuit H2 and _the differential active integrating circuit H3 and bias current/> The resulting ramp error output/> ; Based on the transfer functions of the first-order high-pass RC filter circuit H ₁ , the passive integrating circuit H ₂ and the differential active integrating circuit H ₃ , the transfer function H ( s ) of the measurement system is obtained; Select various parameters of the composite differential active integrating circuit; Determine the high-speed operational amplifier model; make To eliminate the error of subtractor A3, where V _os and I _os are the offset voltage and offset current of the determined operational amplifier respectively. 5. The measurement method of the Rogowski coil measurement system with a composite differential active integrating circuit according to claim 3, characterized in that the Rogowski coil H ₀ link transfer function is: in, ,/> ; M is the mutual inductance coefficient between the measured conductor passing through the Rogowski coil and the coil, L is the Rogowski coil self-inductance, C is the Rogowski coil distributed capacitance,/> It is an external sampling resistor; the lightning current measured in the Rogowski coil induction transmission line/> And in the sampling resistor/> Output voltage signal at both ends/> . 6. The measurement method of the Rogowski coil measurement system with a composite differential active integrating circuit according to claim 3, characterized in that the simplified Rogowski coil H ₀ link transfer function H ₀ ( s ) includes: The Rogowski coil link transfer function H ₀ ( s ) is equivalent to a proportional link , differential link/> and two inertia links ,/> series connection; obtain the simplified Rogowski coil link transfer function/> , . 7. The measurement method of the Rogowski coil measurement system with a composite differential active integrating circuit according to claim 3, characterized in that, according to the Rogowski coil link transfer function , first-order high-pass RC filter link transfer function/> , RCR passive integral link transfer function/> and differential active integral link transfer function/> The transfer function H ( s ) of the measurement system is obtained: . 8. The measurement method of the Rogowski coil measurement system with a composite differential active integrating circuit according to claim 3, characterized in that the selection of various parameters in the composite differential active integrating circuit includes: The sampling resistor R ₀ has a value of 1Ω, and the values of the parameters of the composite differential active integrating circuit meet the following conditions: ,/> ,/> ; By selecting the fourth resistor in the H ₃ link of the differential active integrating circuit Third capacitor/> parameters, extending the lower limit measurement frequency of the measurement system to 60Hz; The amplitude of the input and output signals of the measured lightning current signal in the active integration link does not exceed the ±15V supply voltage limit of the selected operational amplifier. 9. The measurement method of the Rogowski coil measurement system with a composite differential active integrating circuit according to claim 8, wherein the composite differential active integral is calculated according to various parameters of the selected composite differential active integrating circuit. The gain bandwidth product GBW of the operational amplifier in the circuit is greater than 1MHz, and the slew rate SR is greater than 156V/µs; select the operational amplifier based on these conditions.