An anti-saturation device for electromagnetic current transformers

Abstract

The application relates to an anti-saturation device for an electromagnetic current transformer, comprising a negative resistance circuit and a negative inductance circuit connected in series; the negative resistance circuit comprises a first resistor, a second resistor, a third resistor and a first operational amplifier, the first resistor is connected to the inverting input end of the first operational amplifier, the first resistor is also connected to the output end of the first operational amplifier, the second resistor is connected to the non-inverting input end of the first operational amplifier, the second resistor is also connected to the output end of the first operational amplifier, and the third resistor is connected to the non-inverting input end of the first operational amplifier; the negative inductance circuit comprises an inductor, a fourth resistor, a fifth resistor and a second operational amplifier, the inductor is connected to the inverting input end of the second operational amplifier, the inductor is also connected to the output end of the second operational amplifier, the fourth resistor is connected to the non-inverting input end of the second operational amplifier, the fourth resistor is also connected to the output end of the second operational amplifier, and the fifth resistor is connected to the non-inverting input end of the second operational amplifier.

Description

Technical Field

[0001] The present application relates to the technical field of current transformers, and in particular to an anti-saturation device for electromagnetic current transformers. Background Art

[0002] Traditional current measurement methods are mostly based on electromagnetic current transformers, which linearly convert the large primary current to be measured into a smaller secondary current before measurement. However, with the increasing proportion of renewable energy generation in recent years, the integration of renewable energy sources such as wind and solar power into power systems has made it difficult for traditional electromagnetic current transformers, designed for industrial frequency sinusoidal signals, to accurately measure multi-characteristic, wide-range current signals containing harmonics and DC components. The measured current can easily cause the current transformer core to saturate, preventing the current transformer from performing linear transmission. This distorts the secondary current and prevents it from linearly reflecting the primary current. Summary of the Invention

[0003] The purpose of this application is to provide an anti-saturation device for an electromagnetic current transformer to prevent the iron core of the electromagnetic current transformer from entering a saturation state.

[0004] To achieve the above-mentioned object, an embodiment of the present application provides an anti-saturation device for an electromagnetic current transformer, wherein the anti-saturation device is connected in series to the secondary side circuit of the electromagnetic current transformer and includes a negative resistance circuit and a negative inductance circuit connected in series;

[0005] The negative resistance circuit includes a first resistor, a second resistor, a third resistor and a first operational amplifier, wherein a first end of the first resistor is connected to an inverting input terminal of the first operational amplifier, a second end of the first resistor is connected to an output terminal of the first operational amplifier, a first end of the second resistor is connected to a non-inverting input terminal of the first operational amplifier, a second end of the second resistor is connected to the output terminal of the first operational amplifier, and a first end of the third resistor is connected to the non-inverting input terminal of the first operational amplifier;

[0006] The negative inductance circuit includes an inductor, a fourth resistor, a fifth resistor, and a second operational amplifier, wherein a first end of the inductor is connected to an inverting input terminal of the second operational amplifier, a second end of the inductor is connected to an output terminal of the second operational amplifier, a first end of the fourth resistor is connected to a non-inverting input terminal of the second operational amplifier, a second end of the fourth resistor is connected to the output terminal of the second operational amplifier, and a first end of the fifth resistor is connected to the non-inverting input terminal of the second operational amplifier;

[0007] The second end of the third resistor is connected to the inverting input end of the second operational amplifier;

[0008] The first end of the first resistor is the positive electrode of the anti-saturation device, and the second end of the fifth resistor is the negative electrode of the anti-saturation device.

[0009] Furthermore, the resistance values ​​of the second resistor, the third resistor, the fourth resistor and the fifth resistor are equal.

[0010] Furthermore, the first resistor has a resistance value equal to that of an equivalent resistance of a secondary side circuit of the electromagnetic current transformer.

[0011] Furthermore, the inductance value of the inductor is equal to the equivalent inductance of the secondary side loop of the electromagnetic current transformer.

[0012] The embodiment of the present application uses an operational amplifier to form a negative resistance circuit and a negative inductance circuit, and connects the compensation device in series in the secondary circuit of the current transformer to compensate for the potential generated by the secondary impedance of the electromagnetic current transformer, thereby making the iron core of the electromagnetic current transformer operate in a constant magnetic flux state, preventing the iron core of the electromagnetic current transformer from entering a saturation state, effectively widening the measuring range of the electromagnetic current transformer, and improving the measurement accuracy of the current transformer.

[0013] More features and advantages of the embodiments of the present application are reflected below. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] Figure 1 This is a schematic diagram of the overall structure of an anti-saturation device for an electromagnetic current transformer in an embodiment of the present application.

[0016] Figure 2 Schematic diagram of the structure of the negative resistance circuit in the embodiment of the present application.

[0017] Figure 3 Schematic diagram of the structure of the negative inductance circuit in the embodiment of the present application.

[0018] Figure 4 Schematic diagram of the simulation model in the embodiment of the present application.

[0019] Figure 5 Schematic diagram of simulation parameter settings for the current transformer in an embodiment of the present application.

[0020] Figure 6 I1=100%~200%I in the simulation of the embodiment of this applicationN The current transformer transducing effect.

[0021] Figure 7 The contrast schematic diagram before and after compensation of the anti-saturation device in the simulation in the embodiment of the present application. DETAILED DESCRIPTION

[0022] As Figure 1 shown, the anti-saturation device for the electromagnetic current transformer provided by the embodiment of the present application is connected in series in the secondary side loop of the electromagnetic current transformer, and includes a negative resistance circuit and a negative inductance circuit connected in series.

[0023] As Figure 2 shown, the negative resistance circuit includes a first resistor R, a second resistor R1, a third resistor R2 and a first operational amplifier, the first end of the first resistor R is connected to the inverting input terminal of the first operational amplifier, the second end of the first resistor R is connected to the output terminal of the first operational amplifier, the first end of the second resistor R1 is connected to the non-inverting input terminal of the first operational amplifier, the second end of the second resistor R1 is connected to the output terminal of the first operational amplifier, and the first end of the third resistor R2 is connected to the non-inverting input terminal of the first operational amplifier.

[0024] As Figure 3 shown, the negative inductance circuit includes an inductor L, a fourth resistor R1, a fifth resistor R2 and a second operational amplifier, the first end of the inductor L is connected to the inverting input terminal of the second operational amplifier, the second end of the inductor L is connected to the output terminal of the second operational amplifier, the first end of the fourth resistor R1 is connected to the non-inverting input terminal of the second operational amplifier, the second end of the fourth resistor R1 is connected to the output terminal of the second operational amplifier, and the first end of the fifth resistor R2 is connected to the non-inverting input terminal of the second operational amplifier; because the resistance values of the second resistor and the fourth resistor are the same, they are represented as R1 in the formula (1) and the formula (2) respectively, and because the resistance values of the third resistor and the fifth resistor are the same, they are represented as R2 in the formula (1) and the formula (2) respectively. Figure 2 and 3 Figure 2 and 3

[0025] The second end of the third resistor is connected to the inverting input terminal of the second operational amplifier.

[0026] The first end of the first resistor is the positive electrode of the anti-saturation device, the second end of the fifth resistor is the negative electrode of the anti-saturation device, and the anti-saturation device is connected in series in the secondary side loop of the electromagnetic current transformer, as Figure 1 shown.

[0027] Further, the resistance values of the second resistor, the third resistor, the fourth resistor and the fifth resistor are equal.​​

[0028] Furthermore, the first resistor has a resistance value equal to that of an equivalent resistance of a secondary side circuit of the electromagnetic current transformer.

[0029] Furthermore, the inductance value of the inductor is equal to the equivalent inductance of the secondary side loop of the electromagnetic current transformer.

[0030] Figure 1 In the equation, i1(t) and i2(t) are the primary and secondary currents of the current transformer respectively; u ct (t) is the voltage across the current transformer core; R b 、L b are the equivalent resistance and inductance of the secondary circuit of the current transformer, including the secondary circuit line impedance and load impedance; u b (t) is the equivalent potential of the secondary circuit of the current transformer, that is, R b and L b The voltage at both ends; the anti-saturation device is connected in series in the secondary circuit of the current transformer, u c (t) is the potential generated by the anti-saturation device.

[0031] According to Kirchhoff's voltage law of the secondary circuit of the current transformer, the voltage u across the current transformer core is ct (t) can be expressed as:

[0032] u ct (t) = u b (t)+u c (t) (3-1)

[0033] Therefore, according to Faraday's law of electromagnetic induction, the magnetic flux Φ(t) of the iron core at any time can be calculated by the following formula:

[0034]

[0035] Wherein, Φ(t0) is the magnetic flux of the current transformer core at time t0.

[0036] At this time, if the potential u generated by the anti-saturation device is c (t) and the equivalent potential u of the secondary circuit of the current transformer b If the sum of (t) is 0, then:

[0037]

[0038] Φ(t)=Φ(t0) (3-4)

[0039] Equation (3-4) shows that under this condition, the magnetic flux Φ(t) of the current transformer will not change with time and will always maintain a constant value Φ(t0), so that the current transformer will not saturate.

[0040] Based on Figure 1 The equivalent circuit of the current transformer is shown in the figure. According to Ohm's law, the equivalent potential u of the secondary circuit of the current transformer is b (t) can be expressed by the secondary current i2(t) as:

[0041]

[0042] Therefore, if the magnetic flux of the current transformer is to be kept constant, the potential u generated by the anti-saturation device needs to be controlled to satisfy the following equation: c (t) = 0 (3-6)

[0043] u c (t) + u b (t) = 0 (3-6)

[0044]

[0045] In the negative resistance circuit, according to the virtual short and virtual open properties of the operational amplifier, the VCR relationship at the a and b terminals is obtained by applying the external power supply method, and thus the input resistance, i.e., the equivalent resistance at the a and b terminals, is:

[0046]

[0047] By replacing the resistance R in the negative resistance circuit with an inductance L, a negative inductance circuit is obtained. Similarly, the equivalent inductance at the a and b terminals of the negative inductance circuit is:

[0048]

[0049] The negative resistance circuit and the negative inductance circuit are connected in series to form an anti-saturation device. By reasonably setting the parameters of the negative resistance circuit and the negative inductance circuit, i.e., R1 = R2, R = R b , L = L b , the equivalent resistance R eq of the negative resistance circuit and the equivalent inductance L eq of the negative inductance circuit can be made equal to the negative equivalent resistance -R b and the inductance -L b of the secondary circuit of the current transformer, respectively. At this time, the potential generated by the anti-saturation device is:

[0050]

[0051] i.e., it satisfies equation (3-7). Therefore, the anti-saturation device composed of the negative resistance circuit and the negative inductance circuit in series can keep the magnetic flux of the current transformer constant at all times, thereby suppressing the saturation of the current transformer.

[0052] By building a simulation model of the anti-saturation device proposed in this invention in the MATLAB / Simulink platform, the effectiveness of the anti-saturation device in suppressing the saturation of the current transformer is verified. Figure 4 As shown, the parameter settings of the current transformer are as follows Figure 5 As shown. R1 is the current limiting resistor of the primary circuit, fixed at 1Ω; R b 、L b are the equivalent resistance and inductance of the current transformer secondary circuit, which are 20Ω and 1e-6H, respectively. The simulation model outputs the effective values ​​of the primary and secondary currents of the current transformer through the RMS module, and outputs the ideal waveform of the secondary current through the amplifier for comparison with the actual waveform of the secondary current.

[0053] When the primary current I1 is 100% to 200% of the rated current I N range, every 20%I N The operating state of the current transformer is simulated once, and the actual secondary current I2 and the ideal secondary current I calculated by linear transformation according to the transformation ratio k are obtained respectively. 2k , draw the waveforms of the actual secondary current and the ideal secondary current on the same graph for comparison. The comparison results are as follows Figure 6 shown.

[0054] according to Figure 6 It can be seen that when the primary side current of the current transformer is near the rated current, the waveform curves of the actual secondary current and the ideal secondary current almost coincide with each other. At this time, the current transformer has a good transmission characteristic, which is close to linear transmission. However, as the primary current increases, I1 exceeds the measuring range of the current transformer. At this time, the iron core enters the saturation region, and the current transformer cannot transmit linearly, causing the curves of the actual secondary current and the ideal secondary current to gradually no longer coincide.

[0055] The anti-saturation device of the embodiment of the present application is connected in series in the secondary circuit of the current transformer, and the current transformer is simulated under the working state of the primary current being 200% of the rated current, and the comparison before and after the compensation of the anti-saturation device is obtained, as shown in FIG. Figure 7 As shown in the figure, before compensation, the calculated current transformer ratio error was -33.68%, and the angle difference was 1638'. After compensation, the ratio error was 0.17%, and the angle difference was 5.4'. Therefore, this compensation device effectively improves the measurement accuracy of the current transformer and widens its measuring range.

[0056] The embodiments of the present application have the following advantages:

[0057] The negative resistance circuit and negative inductance circuit composed of operational amplifiers can directly provide a compensation potential related to the secondary current of the current transformer. Therefore, the compensation range is large, the real-time performance is good, the compensation device structure is simple, and no complex control algorithm is involved.

[0058] By directly connecting the anti-saturation device in series in the secondary circuit of the current transformer, the secondary current of the current transformer can be directly converted into a compensation potential without the need for additional monitoring devices.

[0059] By means of compensation, the voltage at both ends of the core is always zero, the saturation of the current transformer core is suppressed, and the saturation of the current transformer is solved from the root.

[0060] While various embodiments of the present application have been described above, the above descriptions are illustrative, non-exhaustive, and not intended to be limiting of the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or technological improvements in the marketplace, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. An anti-saturation device for an electromagnetic current transformer, characterized in that: The anti-saturation device is connected in series to the secondary side circuit of the electromagnetic current transformer, and includes a negative resistance circuit and a negative inductance circuit connected in series; The negative resistance circuit includes a first resistor, a second resistor, a third resistor and a first operational amplifier, wherein a first end of the first resistor is connected to an inverting input terminal of the first operational amplifier, a second end of the first resistor is connected to an output terminal of the first operational amplifier, a first end of the second resistor is connected to a non-inverting input terminal of the first operational amplifier, a second end of the second resistor is connected to the output terminal of the first operational amplifier, and a first end of the third resistor is connected to the non-inverting input terminal of the first operational amplifier; The negative inductance circuit includes an inductor, a fourth resistor, a fifth resistor, and a second operational amplifier, wherein a first end of the inductor is connected to an inverting input terminal of the second operational amplifier, a second end of the inductor is connected to an output terminal of the second operational amplifier, a first end of the fourth resistor is connected to a non-inverting input terminal of the second operational amplifier, a second end of the fourth resistor is connected to the output terminal of the second operational amplifier, and a first end of the fifth resistor is connected to the non-inverting input terminal of the second operational amplifier; The second end of the third resistor is connected to the inverting input end of the second operational amplifier; The first end of the first resistor is the positive electrode of the anti-saturation device, and the second end of the fifth resistor is the negative electrode of the anti-saturation device.

2. The anti-saturation device for electromagnetic current transformer according to claim 1, characterized in that: The resistance values ​​of the second resistor, the third resistor, the fourth resistor, and the fifth resistor are equal.

3. The anti-saturation device for electromagnetic current transformer according to claim 2, characterized in that: The first resistor has a resistance value equal to that of an equivalent resistance of a secondary side circuit of the electromagnetic current transformer.

4. The anti-saturation device for electromagnetic current transformer according to claim 3, characterized in that: The inductance value of the inductor is equal to the equivalent inductance of the secondary side loop of the electromagnetic current transformer.

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