Integrator direct-current error elimination and low-frequency noise reduction circuit based on Rogowski coil

Abstract

An integrator direct current error elimination and low frequency noise reduction circuit based on Rogowski coils solves the technical problem of how to eliminate direct current errors in an integrator circuit composed of Rogowski coils, and adopts the technical scheme that the circuit comprises an integrating circuit composed of a first amplifier and an integrating capacitor, the in-phase end of the first amplifier is used as the current input end a of the Rogowski coil, and the key point is that a T-type network filter circuit is connected between the feedback output end b of the integrating circuit and the inverted input end of the first amplifier. The utility model has the advantages that due to the existence of the T-type network filter circuit, oscillation is avoided, feedback is taken from the tail end of the integral circuit, the direct current offset of the whole forward channel can be eliminated, the three-order high-pass filter function is realized, the maximum low-frequency noise is low, and the signal-to-noise ratio is improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of integrator processing circuits, and relates to a circuit capable of eliminating direct current errors and reducing low-frequency noise, and is particularly suitable for an integrator of a Rogowski coil. Background Art

[0002] The simplest traditional integrator circuit consists of a resistor and a capacitor. The capacitor serves as a DC-blocking coupling capacitor between the output stage circuits to achieve the integration function. However, when using a Rogowski coil, the presence of the DC-blocking coupling capacitor reduces amplitude and angle measurement accuracy and narrows the measurement frequency bandwidth. Therefore, a zero-drift op amp must be used, rather than an ultra-low-noise op amp.

[0003] Several existing approaches address this issue. Chinese Utility Model Patent No. CN210572699U provides a Rogowski coil integrator DC error elimination circuit. This circuit, by adding two unit circuits, an integrator and a low-pass filter, creates a closed-loop control system to eliminate the DC component of the Rogowski coil signal and the DC offset of the operational amplifier, thereby improving the measurement accuracy and stability of a novel electronic transformer. However, since the feedback is taken before the first integrator, it cannot eliminate the DC offset of the first integrator, and thus the system DC offset. It can only eliminate the DC offset caused by the preamplifier, which consists of an inverting amplifier and a non-inverting amplifier. The preamplifier has a low DC gain, so its DC offset is small. The DC gain of the first integrator is equal to the open-loop gain of its operational amplifier, which can be as high as 100dB. Multiplied by the DC offset of the operational amplifier, the gain is very large. Therefore, the DC offset caused by the first integrator is the main component of the system offset. Therefore, this patent does not address the actual problem. If the patent takes feedback from the first integrator, the 180-degree phase shift caused by the first and second integrators, combined with the phase shift caused by the low-pass stage, exceeds 180 degrees. Adding the 180-degree feedback, the total phase shift exceeds 360 degrees, causing oscillation and causing the system to malfunction. Furthermore, the patent uses an inverting input with low input impedance, drawing more current from the Rogowski coil. This causes the coil to self-integrate, resulting in angle and amplitude errors.

[0004] In summary, further improvements based on the patented solution cannot eliminate the DC error, so a feasible circuit must be re-studied. Utility Model Content

[0005] In order to solve the technical problem of how to eliminate DC errors in an integrator circuit composed of Rogowski coils, the utility model designs a circuit for eliminating DC errors and reducing low-frequency noise in an integrator based on Rogowski coils. A second-order low-pass filter circuit is added to the feedback output end of the integrator circuit, and a third-order high-pass filter circuit is formed by T-type network resistors, thereby fundamentally eliminating the DC offset of the forward channel of the integrator circuit.

[0006] The technical solution adopted by the utility model is an integrator DC error elimination and low-frequency noise reduction circuit based on a Rogowski coil, including an integrating circuit composed of a first amplifier and an integrating capacitor, wherein the non-inverting terminal of the first amplifier serves as the input terminal a of the induced electromotive force of the Rogowski coil, and the key point is that a T-type network filter circuit is connected between the feedback output terminal b of the integrating circuit and the inverting input terminal of the first amplifier.

[0007] The T-type network filter circuit includes a series voltage-dividing resistor connected in parallel at both ends of an integrating capacitor, a T-type network capacitor is connected to the voltage-dividing end of the series voltage-dividing resistor, the other end of the T-type network capacitor is grounded, a first low-pass filter circuit consisting of a second amplifier and a first low-pass filter capacitor, and a second low-pass filter circuit consisting of a third amplifier and a second low-pass filter capacitor are sequentially connected to the feedback output end b of the integrating circuit, the output end of the second amplifier is connected to the inverting input end of the third amplifier, the output end of the third amplifier is connected to the inverting input end of the first amplifier, and the non-inverting input ends of the second amplifier and the third amplifier are respectively grounded.

[0008] A matching resistor is also provided in the circuit structure of the T-type network filter circuit.

[0009] The circuit structure of this utility model is based on the principle that the electromotive force induced by the Rogowski coil is fed back through the output of the first amplifier in the integration circuit to the first low-pass filter circuit. After first-order filtering and amplification, it is fed to the second low-pass filter circuit. After second-order filtering and amplification, it is connected to the inverting terminal of the first amplifier in the integration circuit through a resistor. Due to the negative feedback effect, the first and second low-pass filter circuits are transformed into a high-pass filter circuit in the overall forward channel. This circuit uses a T-type feedback network and a second-order low-pass feedback network to form a third-order high-pass filter network, which greatly reduces low-frequency noise, achieves a high signal-to-noise ratio, and significantly improves the amplitude and angle measurement accuracy of the Rogowski coil.

[0010] The beneficial effects of the present utility model are:

[0011] 1. The T-network filter circuit avoids oscillation. Feedback is taken from the end of the integration circuit, which can eliminate the DC offset of the entire forward channel.

[0012] 2. It has a third-order high-pass filter, which greatly reduces low-frequency noise and improves the signal-to-noise ratio.

[0013] 3. The DC blocking capacitor is eliminated, and an ultra-low noise operational amplifier can be used, which is beneficial to improve the amplitude and angle measurement accuracy, and the signal frequency bandwidth can be greatly expanded.

[0014] 4. The signal is input from the in-phase terminal, the input impedance is extremely large, and almost no current is absorbed from the Rogowski coil, avoiding self-integration and improving the voltage amplitude and phase angle accuracy of the Rogowski coil output. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a circuit principle diagram of the utility model.

[0016] In the accompanying drawings, C1 is an integrating capacitor, C2 is a T-type network capacitor, C3 is a first low-pass filter capacitor, C4 is a second low-pass filter capacitor, U1 is a first amplifier, U2 is a second amplifier, U3 is a third amplifier, and R1-R6 are resistors. DETAILED DESCRIPTION

[0017] The present invention will be further described below through specific embodiments.

[0018] See Figure 1 The integrator DC error elimination and low-frequency noise reduction circuit based on the Rogowski coil includes an integration circuit composed of a first amplifier U1 and an integration capacitor C1. The non-inverting end of the first amplifier U1 serves as the input end a of the induced electromotive force of the Rogowski coil, and a T-type network filter circuit is connected between the feedback output end b of the integration circuit and the inverting input end of the first amplifier U1. Due to the presence of the T-type network filter circuit, the utility model avoids oscillation. The feedback is taken from the very end of the integration circuit, which can eliminate the DC offset of the entire forward channel. At the same time, because the DC blocking capacitor is eliminated, an ultra-low noise operational amplifier can be used, which is beneficial to improving the amplitude and angle measurement accuracy, and the signal frequency bandwidth can be greatly expanded.

[0019] The T-type network filter circuit includes a series voltage-dividing resistor connected in parallel at both ends of the integrating capacitor C1, a T-type network capacitor C2 is connected to the voltage-dividing end of the series voltage-dividing resistor, the other end of the T-type network capacitor C2 is grounded, and a first low-pass filter circuit composed of a second amplifier U2 and a first low-pass filter capacitor C3, and a second low-pass filter circuit composed of a third amplifier U3 and a second low-pass filter capacitor C4 are connected in sequence to the feedback output end b of the integrating circuit, the output end of the second amplifier U2 is connected to the inverting input end of the third amplifier U3, the output end of the third amplifier U3 is connected to the inverting input end of the first amplifier U1, and the non-inverting input ends of the second amplifier U2 and the third amplifier U3 are grounded respectively.

[0020] The integrator processing circuit input a of the present invention receives the electromotive force induced by the Rogowski coil, and after calculation by the integration circuit composed of the first amplifier U1 and the integration capacitor C1, the feedback output terminal outputs the voltage. In this process, the feedback current passes through the second-order low-pass filter circuit composed of the first low-pass filter capacitor C3, the second amplifier U2, the third network capacitor C4, and the third amplifier U3, and undergoes two low-pass filtering processes, which greatly reduces low-frequency noise, improves the signal-to-noise ratio, and improves the voltage amplitude and phase angle accuracy of the Rogowski coil output. At the same time, this circuit uses a T-type network capacitor C2, a first low-pass filter capacitor C3, and a second low-pass filter capacitor C4 to form a third-order high-pass filter network, which greatly reduces low-frequency noise, obtains a high signal-to-noise ratio, and greatly improves the amplitude measurement accuracy and angle measurement accuracy of the Rogowski coil. In addition, the present invention uses negative feedback to eliminate DC offset, can use an ultra-low-noise operational amplifier, and the signal frequency bandwidth can be greatly expanded.

Claims

1. A circuit for eliminating DC errors and reducing low-frequency noise in an integrator based on a Rogowski coil, comprising an integrating circuit consisting of a first amplifier (U1) and an integrating capacitor (C1), wherein the non-inverting terminal of the first amplifier (U1) serves as an input terminal a of the induced electromotive force of the Rogowski coil, and is characterized in that: A T-type network filter circuit is connected between the feedback output terminal b of the integration circuit and the inverting input terminal of the first amplifier (U1). The T-type network filter circuit comprises a series voltage-dividing resistor connected in parallel at both ends of an integrating capacitor (C1); a T-type network capacitor (C2) is connected to the voltage-dividing end of the series voltage-dividing resistor; the other end of the T-type network capacitor (C2) is grounded; a first low-pass filter circuit consisting of a second amplifier (U2) and a first low-pass filter capacitor (C3) and a second low-pass filter circuit consisting of a third amplifier (U3) and a second low-pass filter capacitor (C4) are sequentially connected to the feedback output end b of the integrating circuit; the output end of the second amplifier (U2) is connected to the inverting input end of the third amplifier (U3); the output end of the third amplifier (U3) is connected to the inverting input end of the first amplifier (U1); and the non-inverting input ends of the second amplifier (U2) and the third amplifier (U3) are grounded respectively.

2. The integrator DC error elimination and low-frequency noise reduction circuit based on a Rogowski coil according to claim 1, characterized in that: A matching resistor is also provided in the circuit structure of the T-type network filter circuit.

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