Error correction method and error correction circuit of alternating current transformer

Abstract

The invention relates to an error correction method and an error correction circuit of an alternating current transformer, and belongs to the technical field of power electronics. According to the error correction method and circuit for the alternating current transformer, a current integrator S is used for integrating secondary side output current i2 of the alternating current transformer to obtain integral current is, and exciting current i0 of the current transformer is obtained through a first proportional amplifier K1 and a second proportional amplifier K2; and the secondary side output current i2 and the exciting current i0 are superposed through an adder sigma to obtain an equivalent value of the primary side input current i1, so that accurate measurement of the primary side input current of the current transformer is realized. By utilizing the method and the circuit, even if a conventional protection-level current transformer is adopted, the precision requirement of a measurement-level and even metering-level transformer can be met, so that the same current transformer with lower cost can be adopted to meet dynamic measurement under large current and accurate measurement under conventional current.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, in particular to the field of power system signal acquisition technology, and specifically refers to an error correction method and circuit for an alternating current transformer. Background Art

[0002] In AC power systems, whether it is the basic needs of control, protection, and metering, or the more advanced needs of power quality analysis, electrical safety analysis, and status assessment of power grids and electrical equipment, it is inseparable from the collection of basic quantities such as current and voltage. Traditional current transformers are divided into different types according to different applications, such as current transformers for metering and monitoring (commonly known as metering-grade and measurement-grade current transformers), and current transformers for relay protection and electrical safety (commonly known as protection-grade current transformers). The former focuses on static high-precision measurement under conventional load current and small current, but the measurement range is small, while the latter focuses more on transient large-range measurement under fault or abnormal conditions of power grids or equipment, but the measurement accuracy is often insufficient. Therefore, in many occasions, it is often necessary to install multiple groups of different types of transformers to cater to different applications. If you want to use the same current transformer to simultaneously achieve high-precision measurement under conventional current and transient measurement under a large range, you need to invest a higher cost to customize it.

[0003] like Figure 1 As shown in the figure, it is known from electrical engineering theory that the primary input current i1 of the current transformer is decomposed into two parts according to its function: one part is called the excitation current i0, which is used to establish the magnetic field in the transformer core; the other part is called the secondary current i2, which is converted into the secondary output through the turns ratio for the final current measurement. The aforementioned measurement and metering grade transformers generally use a closed magnetic core with extremely high magnetic permeability, so that the current transformer only needs a very small excitation current i0 to establish the magnetic field in the core, so that the remaining secondary output current i2 is highly similar to the primary input current i1. Protection-grade current transformers need to use magnetic cores with low magnetic permeability, or to open air gaps in magnetic cores with high magnetic permeability, to achieve the purpose of non-saturation of the magnetic core under large currents. However, this requires the use of a larger excitation current i0 to establish a magnetic field of the same intensity in the magnetic core, which causes a certain degree of distortion in the secondary output current i2 remaining for measurement compared to the primary input current i1. This results in a significant decrease in the accuracy of the indirect measurement method of the primary current i1 obtained only by measuring i2 and converting the transformation ratio.

[0004] Therefore, how to use a single conventional transformer to achieve higher accuracy and wider range of current measurement has become a problem to be solved urgently in this field. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide an error correction method and an error correction circuit for an AC current transformer, so that the accuracy requirements of a measurement-level or even a metering-level current transformer can be achieved by using a conventional protection-level current transformer, so that the same current transformer with a lower cost can meet both dynamic measurement under large currents and accurate measurement under conventional currents.

[0006] In order to achieve the above-mentioned purpose, the error correction method of the AC current transformer of the present invention comprises the following steps:

[0007] (A) Apply input current i1 to the primary side of the current transformer and measure the output current i2 on the secondary side;

[0008] (B) integrating the secondary output current i2 using a current integrator S to obtain an integrated current is, and then adjusting the integrated current is by a first proportional amplifier K1 so that its fundamental effective value is equal to the fundamental effective value of the secondary output current i2;

[0009] (C) the integral current is is passed through a second proportional amplifier K2 to obtain the excitation current i0 of the current transformer;

[0010] (D) The secondary output current i2 and the excitation current i0 are superimposed by an adder ∑ to obtain an equivalent value of the primary input current i1.

[0011] In the error correction method of the AC current transformer, the current integrator S is a hardware analog integrator or a software digital integrator; when the current integrator S is a software digital integrator, the ratio of the first proportional amplifier K1 is 2*tg(π / N), where N is the number of sampling points per cycle of the power frequency.

[0012] In the error correction method of the AC current transformer, the step (A) also includes obtaining the angle Φ at which the secondary output current i2 leads the input current i1; in the step (C), the amplification factor of the second proportional amplifier K2 is tg(Φ).

[0013] In the error correction method of the AC current transformer, the step (D) also includes: the equivalent value of the primary input current i1 obtained by the adder ∑ is then passed through the third proportional amplifier K3 to obtain the current i1p, that is, i1p=K3*(i2+i0); the amplification factor of the third proportional amplifier K3 is used to fine-tune the output amplitude of the current i1p, so that the fundamental effective value of the current i1p output is exactly equal to the fundamental effective value of the primary input current i1 of the current transformer.

[0014] The present invention also provides an error correction circuit for an AC current transformer, comprising:

[0015] A current integrator S is connected to the secondary side of the AC current transformer to obtain the secondary side output current i2, and is used to integrate the secondary side output current i2 to obtain the integrated current is;

[0016] A first proportional amplifier K1 is used to adjust the ratio of the integrated current is so that its fundamental effective value is equal to the fundamental effective value of the secondary output current i2;

[0017] A second proportional amplifier K2, used for obtaining the excitation current i0 of the current transformer according to the integrated current is; and

[0018] The adder Σ is used to superimpose the secondary output current i2 and the excitation current i0 to obtain an equivalent value of the primary input current i1 of the AC current transformer.

[0019] In the error correction circuit of the AC current transformer, the current integrator S is a hardware analog integrator or a software digital integrator; when the current integrator S is a software digital integrator, the ratio of the first proportional amplifier K1 is 2*tg(π / N), where N is the number of sampling points per cycle of the power frequency.

[0020] In the error correction circuit of the AC current transformer, the current integrator S further obtains the angle Φ at which the secondary output current i2 leads the input current i1; and the amplification factor of the second proportional amplifier K2 is tg(Φ).

[0021] The error correction circuit of the AC current transformer also includes: a third proportional amplifier K3, the equivalent value of the primary input current i1 obtained by the adder ∑ is then passed through the third proportional amplifier K3 to obtain the current i1p, that is, i1p=K3*(i2+i0); the amplification factor of the third proportional amplifier K3 is used to fine-tune the output amplitude of the current i1p, so that the fundamental effective value of the current i1p output is exactly equal to the fundamental effective value of the primary input current i1 of the current transformer.

[0022] The error correction method and error correction circuit of the AC current transformer of the invention are adopted, and the secondary output current i2 of the AC current transformer is integrated by the current integrator S to obtain the integrated current is, and then the excitation current i0 of the current transformer is obtained by the first proportional amplifier K1 and the second proportional amplifier K2; and then the secondary output current i2 and the excitation current i0 are superimposed by the adder ∑ to obtain the equivalent value of the primary input current i1, thereby realizing the accurate measurement of the primary input current of the current transformer. Using the method and circuit of the present invention, even if a conventional protection-grade current transformer is used, the accuracy requirements of the measurement-grade or even metering-grade transformer can be achieved, so that the same current transformer with a lower cost can meet both the dynamic measurement under large current and the accurate measurement under conventional current. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is the equivalent circuit of the current transformer and the corresponding current vector diagram and mathematical expression.

[0024] Figure 2 A schematic flow chart of an error correction method for a current transformer provided by the present invention;

[0025] Figure 3 The figure is a working principle diagram of an error correction circuit of a current transformer provided according to the present invention. DETAILED DESCRIPTION

[0026] In order to more clearly understand the technical content of the present invention, the following embodiments are given in detail.

[0027] See also Figure 2 As shown, it is a flow chart of an error correction method for a current transformer provided by the present invention.

[0028] In one embodiment, the error correction method of the AC current transformer comprises the following steps:

[0029] (A) Apply input current i1 to the primary side of the current transformer and measure the output current i2 on the secondary side;

[0030] (B) integrating the secondary output current i2 using a current integrator S to obtain an integrated current is, and then adjusting the integrated current is by a first proportional amplifier K1 so that its fundamental effective value is equal to the fundamental effective value of the secondary output current i2;

[0031] (C) the integral current is is passed through a second proportional amplifier K2 to obtain the excitation current i0 of the current transformer;

[0032] (D) The secondary output current i2 and the excitation current i0 are superimposed by an adder ∑ to obtain an equivalent value of the primary input current i1.

[0033] For ease of description, in each implementation, the primary-to-secondary turns ratio of the current transformer is set to 1: 1. When the actual turns ratio must be considered, the actual primary input current of the current transformer can be divided by the turns ratio of the transformer to obtain the primary input current i1 used in the implementation.

[0034] In a more preferred embodiment, the current integrator S is a hardware analog integrator or a software digital integrator; when the current integrator S is a software digital integrator, the ratio of the first proportional amplifier K1 is 2*tg(π / N), where N is the number of sampling points per cycle of the power frequency.

[0035] In a further preferred embodiment, the step (A) further includes obtaining an angle Φ at which the secondary output current i2 leads the input current i1; and the amplification factor of the second proportional amplifier K2 in the step (C) is tg(Φ).

[0036] In a more preferred embodiment, the step (D) further includes: the equivalent value of the primary input current i1 obtained by the adder ∑ is then passed through the third proportional amplifier K3 to obtain the current i1p, that is, i1p=K3*(i2+i0); the amplification factor of the third proportional amplifier K3 is used to fine-tune the output amplitude of the current i1p, so that the fundamental effective value of the current i1p output is exactly equal to the fundamental effective value of the primary input current i1 of the current transformer.

[0037] The present invention also provides an error correction circuit for an AC current transformer, such as Figure 3 As shown, the error correction circuit includes: a current integrator S, a first proportional amplifier K1, a second proportional amplifier K2 and an adder Σ.

[0038] The current integrator S is connected to the secondary side of the AC current transformer to obtain the secondary side output current i2, and is used to integrate the secondary side output current i2 to obtain the integrated current is;

[0039] The first proportional amplifier K1 is used to adjust the multiplication factor of the integrated current is so that its fundamental effective value is equal to the fundamental effective value of the secondary side output current i2;

[0040] The second proportional amplifier K2 is used to obtain the excitation current i0 of the current transformer according to the integrated current is; and

[0041] The adder Σ is used to superimpose the secondary output current i2 and the excitation current i0 to obtain an equivalent value of the primary input current i1 of the AC current transformer.

[0042] In a more preferred embodiment, the current integrator S is a hardware analog integrator or a software digital integrator; when the current integrator S is a software digital integrator, the ratio of the first proportional amplifier K1 is 2*tg(π / N), where N is the number of sampling points per cycle of the power frequency.

[0043] In a further preferred embodiment, the current integrator S further obtains an angle Φ at which the secondary output current i2 leads the input current i1; and the gain of the second proportional amplifier K2 is tg(Φ).

[0044] In a more preferred embodiment, the error correction circuit of the AC current transformer further includes a third proportional amplifier K3, such as Figure 3 As shown, the equivalent value of the primary input current i1 obtained by the adder ∑ is then passed through the third proportional amplifier K3 to obtain the current i1p, that is, i1p=K3*(i2+i0); the amplification factor of the third proportional amplifier K3 is used to fine-tune the output amplitude of the current i1p, so that the fundamental effective value of the current i1p output is exactly equal to the fundamental effective value of the primary input current i1 of the current transformer.

[0045] In practical applications, such as Figure 3 As shown, an error correction circuit corresponding to an error correction method for an AC current transformer provided by the present invention includes a current integrator S, a proportional amplifier K1, a proportional amplifier K2, an adder Σ and a proportional amplifier K3.

[0046] The current integrator S can be a hardware analog integrator constructed by a series of resistors, capacitors and integrated circuits, or a software digital integrator implemented by a software algorithm.

[0047] The proportional amplifier K1 is used to adjust the amplitude of the output value is so that the fundamental effective values ​​of is and i2 at the same time are exactly the same. When the current integrator S is a software digital integrator, the ratio of the proportional amplifier K1 has a preferred value of 2*tg(π / N), where N is the number of sampling points per cycle of the power frequency.

[0048] The ratio of the proportional amplification link K2 also has a preferred value, which is the tangent value tg(Φ) of the fundamental wave angle Φ of i2 leading i1.

[0049] The adder Σ is used to add the instantaneous values ​​of i2 and i0, so as to synthesize the secondary output current i2 of the current transformer and the equivalent excitation current i0 of the current transformer obtained through a series of processing.

[0050] The proportional amplification link K3 is an optional fine-tuning link, which is used to make the fundamental effective value of the primary side input current equivalent value i1p obtained by the above method exactly equal to the fundamental effective value of the primary side input current i1 of the current transformer at the same time.

[0051] The error correction method and error correction circuit of the AC current transformer of the invention are adopted, and the secondary output current i2 of the AC current transformer is integrated by the current integrator S to obtain the integrated current is, and then the excitation current i0 of the current transformer is obtained by the first proportional amplifier K1 and the second proportional amplifier K2; and then the secondary output current i2 and the excitation current i0 are superimposed by the adder ∑ to obtain the equivalent value of the primary input current i1, thereby realizing the accurate measurement of the primary input current of the current transformer. Using the method and circuit of the present invention, even if a conventional protection-grade current transformer is used, the accuracy requirements of the measurement-grade or even metering-grade transformer can be achieved, so that the same current transformer with a lower cost can meet the dynamic measurement under large current and the accurate measurement under conventional current.

[0052] In this specification, the present invention has been described with reference to specific embodiments thereof. However, it is apparent that various modifications and variations may be made without departing from the spirit and scope of the present invention. Therefore, the specification and drawings should be regarded as illustrative rather than restrictive.

Claims

1. An error correction method for an AC current transformer, characterized in that: The steps include: (A) Apply input current i1 to the primary side of the current transformer and measure the output current i2 on the secondary side; (B) integrating the secondary output current i2 using a current integrator S to obtain an integrated current is, and then adjusting the integrated current is by a first proportional amplifier K1 so that its fundamental effective value is equal to the fundamental effective value of the secondary output current i2; (C) the integral current is is passed through a second proportional amplifier K2 to obtain the excitation current i0 of the current transformer; (D) The secondary output current i2 and the excitation current i0 are superimposed by an adder ∑ to obtain an equivalent value of the primary input current i1.

2. The error correction method of AC current transformer according to claim 1, characterized in that: The current integrator S is a hardware analog integrator or a software digital integrator. When the current integrator S is a software digital integrator, the magnification of the first proportional amplifier K1 is 2*tg(π / N), where N is the number of sampling points per cycle of the power frequency.

3. The error correction method of AC current transformer according to claim 1, characterized in that: The step (A) further includes obtaining an angle Φ at which the secondary output current i2 leads the input current i1; and in the step (C), the amplification factor of the second proportional amplifier K2 is tg(Φ).

4. The error correction method of AC current transformer according to claim 3, characterized in that: The step (D) further includes: the equivalent value of the primary input current i1 obtained by the adder ∑ is then passed through the third proportional amplifier K3 to obtain the current i1p, that is, i1p=K3*(i2+i0); the amplification factor of the third proportional amplifier K3 is used to fine-tune the output amplitude of the current i1p, so that the fundamental effective value of the current i1p output is exactly equal to the fundamental effective value of the primary input current i1 of the current transformer.

5. An error correction circuit for an AC current transformer, characterized in that: include: A current integrator S is connected to the secondary side of the AC current transformer to obtain the secondary side output current i2, and is used to integrate the secondary side output current i2 to obtain the integrated current is; A first proportional amplifier K1 is used to adjust the ratio of the integrated current is so that its fundamental effective value is equal to the fundamental effective value of the secondary output current i2; A second proportional amplifier K2, used for obtaining the excitation current i0 of the current transformer according to the integrated current is; as well as The adder Σ is used to superimpose the secondary output current i2 and the excitation current i0 to obtain an equivalent value of the primary input current i1 of the AC current transformer.

6. The error correction circuit of the AC current transformer according to claim 5, characterized in that: The current integrator S is a hardware analog integrator or a software digital integrator. When the current integrator S is a software digital integrator, the magnification of the first proportional amplifier K1 is 2*tg(π / N), where N is the number of sampling points per cycle of the power frequency.

7. The error correction circuit of the AC current transformer according to claim 5, characterized in that: The current integrator S also obtains the angle Φ at which the secondary output current i2 leads the input current i1; the gain of the second proportional amplifier K2 is tg(Φ).

8. The error correction circuit of the AC current transformer according to claim 7, characterized in that: Also includes: The third proportional amplifier K3, the equivalent value of the primary input current i1 obtained by the adder ∑ is then passed through the third proportional amplifier K3 to obtain the current i1p, that is, i1p=K3*(i2+i0); the amplification factor of the third proportional amplifier K3 is used to fine-tune the output amplitude of the current i1p, so that the fundamental effective value of the current i1p output is exactly equal to the fundamental effective value of the primary input current i1 of the current transformer.

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