Rogowski coil integrator and current sensor

Abstract

The invention relates to the technical field of current measurement, and discloses a Rogowski coil integrator and a current sensor, and the Rogowski coil integrator comprises an in-phase integrating circuit and a low-pass amplifying circuit. The in-phase integrating circuit comprises a first operational amplifier, the in-phase input end of the first operational amplifier is connected with the Rogowski coil, and a low-pass amplifying circuit is connected between the anti-phase input end of the first operational amplifier and the output end of the first operational amplifier; and the low-pass amplification circuit is used for feeding back the direct current output of the in-phase integral circuit to the inverted input end of the first operational amplifier and carrying out low-pass filtering on the low-frequency signal. According to the Rogowski coil integrator, the dynamic range of the Rogowski coil integrator can be expanded, and the expansion of the low-frequency bandwidth of the integrator is also realized.

Description

Technical Field

[0001] This invention relates to the field of current measurement technology, specifically to a Rogowski coil integrator and a current sensor. Background Technology

[0002] A Rogowski coil is a current measuring device based on the principle of electromagnetic induction. The output signal of the Rogowski coil is proportional to the derivative of the measured current. Therefore, integration is necessary to reconstruct the original current signal. The implementation of this integration process directly determines the accuracy, stability, and dynamic performance of the entire measurement system. Traditional integration schemes mainly include two types: analog integration and digital integration.

[0003] Traditional integration schemes mainly include two types: analog integrators and digital integrators. Analog integrators are typically built based on operational amplifiers and RC networks, offering advantages such as high real-time performance and low latency. However, they are susceptible to factors such as DC drift, temperature drift, and component aging, leading to saturation or error accumulation in the integration results. Digital integrators, on the other hand, rely on high-speed ADCs and digital signal processors. They can correct some errors through algorithms and offer flexible programmability. However, in high-frequency measurements, they are easily limited by sampling rate and quantization errors, and their system complexity and cost are also higher.

[0004] Currently, Rogowski coil integrator circuits mainly include inverting integrator circuits and non-inverting integrator circuits. Both inverting and non-inverting integrator circuits generate a significant DC bias at the output of the operational amplifier, thus limiting the output dynamic range and restricting the low-frequency bandwidth of the integrator. Summary of the Invention

[0005] This invention provides a Rogowski coil integrator and a current sensor to solve the technical problems of limited output dynamic range and restricted low-frequency bandwidth of the Rogowski coil integrator.

[0006] In a first aspect, the present invention provides a Rogowski coil integrator, comprising an in-phase integrator circuit and a low-pass amplifier circuit; The non-inverting integrator circuit includes a first operational amplifier, the non-inverting input of the first operational amplifier is connected to a Rogowski coil, and a low-pass amplifier circuit is connected between the inverting input of the first operational amplifier and the output of the first operational amplifier. The low-pass amplifier circuit is used to feed back the DC output of the inverting integrator circuit to the inverting input of the first operational amplifier and to perform low-pass filtering on the low-frequency signal.

[0007] In some alternative implementations, the low-pass amplifier circuit includes a second operational amplifier, a third resistor, a first low-pass filter circuit, and a feedback channel circuit. The non-inverting input of the second operational amplifier is connected to the output of the first operational amplifier through the first low-pass filter circuit. A feedback channel circuit is connected between the inverting input of the second operational amplifier and the output of the second operational amplifier. The output of the second operational amplifier is connected to the inverting input of the first operational amplifier through the third resistor.

[0008] In some alternative embodiments, the first low-pass filter circuit includes a fifth resistor and a fourth capacitor. The first end of the fifth resistor is connected to the output terminal of the first operational amplifier, the second end of the fifth resistor is connected to the first end of the fourth capacitor and the non-inverting input terminal of the second operational amplifier, and the second end of the fourth capacitor is grounded.

[0009] In some alternative implementations, the feedback channel circuit includes a sixth resistor, a seventh resistor, and a fifth capacitor. The first terminal of the sixth resistor is grounded, the second terminal of the sixth resistor is connected to the first terminal of the seventh resistor and the inverting input terminal of the second operational amplifier, the second terminal of the seventh resistor is connected to the output terminal of the second operational amplifier, and the fifth capacitor and the seventh resistor are connected in parallel.

[0010] In some alternative implementations, the Rogowski coil integrator further includes a high-pass output circuit, the input of which is connected to the output of the first operational amplifier, and the output of which is connected to the signal output of the integrator.

[0011] In some alternative implementations, the Qualcomm output circuit includes a third capacitor and a fourth resistor. The first terminal of the third capacitor is connected to the output terminal of the first operational amplifier, the second terminal of the third capacitor is connected to the first terminal of the fourth resistor and the signal output terminal of the integrator, and the second terminal of the fourth resistor is grounded.

[0012] In some optional embodiments, the in-phase integrator circuit further includes a first resistor, a second resistor, a first capacitor, and a second capacitor. The first end of the first resistor is connected to a Rogowski coil, the second end of the first resistor is connected to the first end of the first capacitor and the non-inverting input of the first operational amplifier, the second end of the first capacitor is grounded, the first end of the second resistor is grounded, the second end of the second resistor is connected to the first end of the second capacitor and the inverting input of the first operational amplifier, and the second end of the second capacitor is connected to the output of the first operational amplifier.

[0013] In a second aspect, the present invention provides a current sensor comprising a Rogowski coil and a Rogowski coil integrator as described in any of the first aspects of the present invention, wherein the output terminal of the Rogowski coil is connected to the Rogowski coil integrator.

[0014] The present invention has at least the following beneficial effects: The Rogowski coil integrator of this invention adds a low-pass amplifier circuit to the negative feedback channel of the in-phase integrator circuit, feeding back the DC output of the in-phase integrator circuit to the inverting input of the first operational amplifier, thereby canceling the input offset voltage of the first operational amplifier. This achieves automatic offset calibration of the integrating operational amplifier, reducing the DC bias caused by the input offset voltage of the operational amplifier to a negligible range, greatly improving the dynamic range of the Rogowski coil integrator, and also expanding the low-frequency bandwidth of the integrator, thus improving the overall bandwidth performance of the Rogowski coil integrator. Attached Figure Description

[0015] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of an inverting integrator circuit in related technologies; Figure 2 This is a schematic diagram of the non-inverting integrator circuit in related technologies. Figure 3 This is a schematic diagram of the Rogowski coil integrator in an embodiment of the present invention; Figure 4 The Bode plot of the Rogowski coil in-phase integrator in related technologies; Figure 5 This is a Bode plot of the Rogowski coil integrator in an embodiment of the present invention.

[0017] Explanation of reference numerals in the attached figures: 101. Inverting integrator circuit; 102. High-pass output circuit; 103. Low-pass amplifier circuit; 1031. First low-pass filter circuit; 1032. Feedback channel circuit; U1. First operational amplifier; U2. Second operational amplifier; R1. First resistor; R2. Second resistor; R3. Third resistor; R4. Fourth resistor; R5. Fifth resistor; R6. Sixth resistor; R7. Seventh resistor; C1. First capacitor; C2. Second capacitor; C3. Third capacitor; C4. Fourth capacitor; C5. Fifth capacitor. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Currently, Rogowski coil integrator circuits mainly include inverting integrator circuits and non-inverting integrator circuits. An inverting integrator circuit is as follows: Figure 1 As shown, the non-inverting input of operational amplifier U1 is grounded, and the signal output from the Rogowski coil is input from the inverting input. The signal is integrated through resistor R1 and capacitor C1. To reduce the DC drift of the integrating capacitor, resistor R2 is connected in parallel with capacitor C1. Typically, R2 is much larger than R1, resulting in a very high amplification factor for DC signals by operational amplifier U1. Since operational amplifier U1 itself has an input offset voltage, this amplified signal forms a significant DC bias voltage at the output of operational amplifier U1. To eliminate the DC bias, capacitor C2 is added for DC isolation, and resistor R3 is used for matching. The low-frequency bandwidth of the inverting integrator is limited by R2 × C1, and its dynamic range is also limited by resistor R2. Furthermore, the input noise of the inverting integrator is easily transmitted directly to the output through resistor R1 and capacitor C1, resulting in poor noise immunity. Therefore, inverting integrators have gradually been abandoned. They have been replaced by non-inverting integrators, such as... Figure 2 As shown, in the non-inverting integrator, the signal is input from the non-inverting input of operational amplifier U1, making it difficult for high-frequency noise to be directly transmitted to the output. At low frequencies, integration is primarily achieved using resistor R2 and capacitor C2, while at high frequencies, integration is achieved using resistor R1 and capacitor C1. The two input parameters of the operational amplifier are symmetrical, resulting in better performance compared to the inverting integrator. However, it also suffers from integration drift, requiring the addition of resistor R3 for suppression; typically, resistor R3 is much larger than resistor R2. Similar to the inverting integrator, the introduction of resistor R3 limits the low-frequency bandwidth of the non-inverting integrator to R3 × C2. The input offset voltage of operational amplifier U1 will generate a significant DC bias at the output of the operational amplifier, thus limiting the output dynamic range.

[0020] As current measurement scenarios become increasingly diverse and demanding in terms of performance, such as short-circuit fault protection, current monitoring of high-frequency power electronic devices, and high-precision energy metering, the system requires the integrator circuit to have high bandwidth and low phase distortion, while also ensuring good DC characteristics and anti-interference capabilities. Therefore, designing a Rogowski coil integrator that can effectively suppress drift, has a wide dynamic range, and is easy to implement has become a key challenge in improving the performance of current sensing systems.

[0021] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] According to an embodiment of the present invention, a Rogowski coil integrator is provided. For example... Figure 3 As shown, the Rogowski coil integrator includes an in-phase integrator circuit 101 and a low-pass amplifier circuit 103. The non-inverting integrator circuit 101 includes a first operational amplifier U1, the non-inverting input terminal of the first operational amplifier U1 is connected to a Rogowski coil, and a low-pass amplifier circuit 103 is connected between the inverting input terminal and the output terminal of the first operational amplifier U1. The low-pass amplifier circuit 103 is used to feed back the DC output of the in-phase integrator circuit 101 to the inverting input of the first operational amplifier U1 and to perform low-pass filtering on the low-frequency signal.

[0023] Specifically, the in-phase integrator circuit 101 has the characteristics of high input impedance and low attenuation of input signal, and can perform voltage signal integration.

[0024] The voltage signal generated by the Rogowski coil, i.e., the input signal VIN, is input to the non-inverting integrator circuit 101 from the non-inverting input terminal of the first operational amplifier U1. The positive and negative power supply pins of the first operational amplifier U1 are connected to the positive power supply VDD and the negative power supply VEE, respectively. Generally, the voltage of VDD is +15V and the voltage of VEE is -15V.

[0025] The low-pass amplifier circuit 103 is a circuit that combines low-pass filtering and signal amplification functions, allowing low-frequency signals to pass through while suppressing high-frequency interference.

[0026] Specifically, since the first operational amplifier U1 has an input offset voltage, it will generate a DC output at the output terminal of the first operational amplifier U1. The low-pass amplifier circuit 103 feeds back the DC output of the non-inverting integrator circuit 101 to the inverting input terminal of the first operational amplifier U1, thereby canceling the input offset voltage of the first operational amplifier U1. This significantly reduces the DC bias of the output of the non-inverting integrator circuit 101. The larger the amplification factor A of the low-pass amplifier circuit 103, the lower the DC bias of the output of the non-inverting integrator circuit 101. By designing an appropriate amplification factor, the DC bias can be reduced to a negligible range, thereby significantly improving the dynamic range of the integrator and eliminating the DC bias in the output signal of the integrator.

[0027] Furthermore, the low-pass amplifier circuit 103 also has a low-pass filtering function. Its low-pass cutoff frequency is much lower than the target low-frequency cutoff frequency of the integrator. Therefore, in the low-frequency range of the integrator, the output of the low-pass amplifier circuit 103 is close to 0V, thereby greatly improving the low-frequency characteristics of the integrator.

[0028] The Rogowski coil integrator of this invention adds a low-pass amplifier circuit 103 to the negative feedback channel of the in-phase integrator circuit 101, feeding back the DC output of the in-phase integrator circuit 101 to the inverting input of the first operational amplifier U1, thereby canceling the input offset voltage of the first operational amplifier U1. This achieves automatic offset calibration of the integrating operational amplifier, reducing the DC bias caused by the input offset voltage of the operational amplifier to a negligible range, greatly improving the dynamic range of the Rogowski coil integrator, and also expanding the low-frequency bandwidth of the integrator, thus greatly improving the overall bandwidth performance of the Rogowski coil integrator.

[0029] In some embodiments, the non-inverting integrator circuit 101 further includes a first resistor R1, a second resistor R2, a first capacitor C1, and a second capacitor C2. The first end of the first resistor R1 is connected to a Rogowski coil, the second end of the first resistor R1 is connected to the first end of the first capacitor C1 and the non-inverting input terminal of the first operational amplifier U1, the second end of the first capacitor C1 is grounded, the first end of the second resistor R2 is grounded, the second end of the second resistor R2 is connected to the first end of the second capacitor C2 and the inverting input terminal of the first operational amplifier U1, and the second end of the second capacitor C2 is connected to the output terminal of the first operational amplifier U1.

[0030] Specifically, the first resistor R1 and the first capacitor C1 form an input RC filter network, connected to the Rogowski coil and the non-inverting input of the first operational amplifier U1, which can filter out high-frequency interference in the Rogowski coil output signal. At low frequencies, the non-inverting integrator 101 mainly relies on the second resistor R2 and the second capacitor C2 for integration, while at high frequencies it relies on the first resistor R1 and the first capacitor C1 for integration. The resistance value of the first resistor R1... The resistance value of the second resistor R2 The capacitance value of the first capacitor C1 The capacitance value of the second capacitor C2 The following relationship must be satisfied: Among them, the circuit integration time constant of the in-phase integrator 101 is... for:

[0031] By using an in-phase integrator circuit 101 to integrate the input signal VIN, it has stronger anti-interference capabilities and better performance compared to an inverting integrator.

[0032] In some embodiments, the Rogowski coil integrator further includes a high-pass output circuit 102, the input terminal of which is connected to the output terminal of the first operational amplifier U1, and the output terminal of the high-pass output circuit 102 is connected to the signal output terminal of the integrator.

[0033] Specifically, the Qualcomm output circuit 102 includes a third capacitor C3 and a fourth resistor R4. The first end of the third capacitor C3 is connected to the output terminal of the first operational amplifier U1, the second end of the third capacitor C3 is connected to the first end of the fourth resistor R4 and the signal output terminal VOUT of the integrator, and the second end of the fourth resistor R4 is grounded.

[0034] The passive RC high-pass structure, consisting of the third capacitor C3 and the fourth resistor R4, uses the third capacitor C3 connected in series in the signal path to block the DC component, while the fourth resistor R4 is grounded to provide a DC discharge path. Together, these components allow for precise setting of the high-pass cutoff frequency, meeting the needs of current detection in different frequency bands. It should be understood that the cutoff frequency design value is much lower than the integrator's target low-frequency cutoff frequency.

[0035] The Qualcomm output circuit 102 can filter out the DC component and ultra-low frequency interference in the integrated output signal, retaining only the effective AC signal related to the measured current, thereby improving the signal-to-noise ratio of the final output signal.

[0036] In some embodiments, the low-pass amplifier circuit 103 includes a second operational amplifier U2, a third resistor R3, a first low-pass filter circuit 1031, and a feedback channel circuit 1032. The non-inverting input terminal of the second operational amplifier U2 is connected to the output terminal of the first operational amplifier U1 through the first low-pass filter circuit 1031. The feedback channel circuit 1032 is connected between the inverting input terminal of the second operational amplifier U2 and the output terminal of the second operational amplifier U2. The output terminal of the second operational amplifier U2 is connected to the inverting input terminal of the first operational amplifier U1 through the third resistor R3.

[0037] The first low-pass filter circuit 1031 is connected to the output of the first operational amplifier U1 and the in-phase input of the second operational amplifier U2. It first performs preliminary low-frequency filtering on the integral output signal to filter out some interference in advance and reduce the processing pressure of subsequent circuits.

[0038] The feedback channel circuit 1032 connects the inverting input and output terminals of the second operational amplifier U2, allowing for flexible adjustment of the amplification factor and filtering characteristics of the second operational amplifier U2. This adapts to Rogowski coil signals of different frequency ranges, enhancing the versatility of the circuit.

[0039] Specifically, the first low-pass filter circuit 1031 includes a fifth resistor R5 and a fourth capacitor C4. The first end of the fifth resistor R5 is connected to the output terminal of the first operational amplifier U1, the second end of the fifth resistor R5 is connected to the first end of the fourth capacitor C4 and the non-inverting input terminal of the second operational amplifier U2, and the second end of the fourth capacitor C4 is grounded.

[0040] Among them, the first low-pass filter circuit 1031, composed of five resistors and the fourth capacitor C4, plays the role of first-order low-pass filtering, and its cutoff frequency design value is much lower than the target low-frequency cutoff frequency of the integrator.

[0041] Furthermore, the feedback channel circuit 1032 includes a sixth resistor R6, a seventh resistor R7, and a fifth capacitor C5. The first end of the sixth resistor R6 is grounded, the second end of the sixth resistor R6 is connected to the first end of the seventh resistor R7 and the inverting input of the second operational amplifier U2, the second end of the seventh resistor R7 is connected to the output of the second operational amplifier U2, and the fifth capacitor C5 and the seventh resistor R7 are connected in parallel.

[0042] One end of the sixth resistor R6 is connected to ground (GND), and the other end is connected to the inverting input of the second operational amplifier U2, the seventh resistor R7, and the fifth capacitor C5. The seventh resistor R7 and the fifth capacitor C5 are connected in parallel. The sixth resistor R6 and the seventh resistor R7 form the feedback path of the amplifier, and the amplification factor A is:

[0043] In the formula, and These are the resistance values ​​of the sixth resistor R6 and the seventh resistor R7, respectively.

[0044] The sixth resistor R6 and the fifth capacitor C5 form a first-order low-pass filter, which together with the first low-pass filter circuit 1031 formed by the fifth resistor R5 and the fourth capacitor C4 forms a second-order low-pass filter, making the cutoff frequency of the low-pass amplifier circuit 103 much lower than the target low-frequency cutoff frequency of the integrator.

[0045] The working principle of the Rogowski coil integrator according to an embodiment of the present invention will be described in detail below.

[0046] In the in-phase integrator circuit 101, due to the input offset voltage of the first operational amplifier U1, a DC output is generated at the output terminal of the operational amplifier. The low-pass amplifier circuit 103 feeds back the DC output of the in-phase integrator circuit 101 to the inverting input terminal of the first operational amplifier U1, thereby canceling the input offset voltage of the first operational amplifier U1. This significantly reduces the DC bias of the output of the in-phase integrator circuit 101. The larger the amplification factor A, the lower the DC bias of the output of the in-phase integrator circuit 101. By designing an appropriate amplification factor A, the DC bias can be reduced to a negligible range, thereby significantly improving the dynamic range of the integrator. Then, through the high-pass filtering of the high-pass output circuit 102, the DC bias of the output signal of the integrator is completely eliminated.

[0047] Due to the low-pass filtering characteristics of the low-pass amplifier circuit 103, its low-pass cutoff frequency is much lower than the target low-frequency cutoff frequency of the integrator. Therefore, in the low-frequency range of the integrator, the output of the low-pass amplifier circuit 103 is close to 0V, and the end of the third resistor R3 connected to the output terminal of the second operational amplifier U2 is approximately grounded, thereby greatly improving the low-frequency characteristics of the integrator. Figure 4 The Bode plot of a traditional Rogowski coil in-phase integrator shows that its low-frequency cutoff frequency is 76.062Hz. Figure 5 The Bode plot of the Rogowski coil integrator proposed in this embodiment of the invention, which uses the same integration parameters, shows that its low-frequency cutoff frequency is broadened to 5.442Hz, while the high-frequency part is almost the same as that of the conventional integrator. Therefore, this embodiment of the invention significantly improves the overall bandwidth performance of the Rogowski coil integrator.

[0048] This invention also proposes a current sensor, including a Rogowski coil and a Rogowski coil integrator as described in any of the above embodiments of the invention, wherein the output terminal of the Rogowski coil is connected to the Rogowski coil integrator.

[0049] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A Rogowski coil integrator, characterized in that, Including in-phase integrator circuits and low-pass amplifier circuits; The in-phase integrator circuit includes a first operational amplifier, the non-inverting input of the first operational amplifier is connected to a Rogowski coil, and the low-pass amplifier circuit is connected between the inverting input of the first operational amplifier and the output of the first operational amplifier. The low-pass amplifier circuit is used to feed back the DC output of the in-phase integrator circuit to the inverting input of the first operational amplifier and to perform low-pass filtering on the low-frequency signal.

2. The Rogowski coil integrator according to claim 1, characterized in that, The low-pass amplifier circuit includes a second operational amplifier, a third resistor, a first low-pass filter circuit, and a feedback channel circuit. The non-inverting input terminal of the second operational amplifier is connected to the output terminal of the first operational amplifier through the first low-pass filter circuit. The feedback channel circuit is connected between the inverting input terminal and the output terminal of the second operational amplifier. The output terminal of the second operational amplifier is connected to the inverting input terminal of the first operational amplifier through the third resistor.

3. The Rogowski coil integrator according to claim 2, characterized in that, The first low-pass filter circuit includes a fifth resistor and a fourth capacitor. The first end of the fifth resistor is connected to the output terminal of the first operational amplifier, the second end of the fifth resistor is connected to the first end of the fourth capacitor and the non-inverting input terminal of the second operational amplifier, and the second end of the fourth capacitor is grounded.

4. The Rogowski coil integrator according to claim 3, characterized in that, The feedback channel circuit includes a sixth resistor, a seventh resistor, and a fifth capacitor. The first end of the sixth resistor is grounded, the second end of the sixth resistor is connected to the first end of the seventh resistor and the inverting input of the second operational amplifier, the second end of the seventh resistor is connected to the output of the second operational amplifier, and the fifth capacitor is connected in parallel with the seventh resistor.

5. The Rogowski coil integrator according to claim 1, characterized in that, It also includes a high-pass output circuit, the input of which is connected to the output of the first operational amplifier, and the output of which is connected to the signal output of the integrator.

6. The Rogowski coil integrator according to claim 5, characterized in that, The high-pass output circuit includes a third capacitor and a fourth resistor. The first terminal of the third capacitor is connected to the output terminal of the first operational amplifier, the second terminal of the third capacitor is connected to the first terminal of the fourth resistor and the signal output terminal of the integrator, and the second terminal of the fourth resistor is grounded.

7. The Rogowski coil integrator according to claim 1, characterized in that, The in-phase integrator circuit further includes a first resistor, a second resistor, a first capacitor, and a second capacitor. The first end of the first resistor is connected to a Rogowski coil. The second end of the first resistor is connected to the first end of the first capacitor and the non-inverting input of the first operational amplifier. The second end of the first capacitor is grounded. The first end of the second resistor is grounded. The second end of the second resistor is connected to the first end of the second capacitor and the inverting input of the first operational amplifier. The second end of the second capacitor is connected to the output of the first operational amplifier.

8. A current sensor, characterized in that, It includes a Rogowski coil and a Rogowski coil integrator as described in any one of claims 1 to 7, wherein the output terminal of the Rogowski coil is connected to the Rogowski coil integrator.

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