Novel current transformer secondary current amplification circuit

Abstract

The invention provides a novel secondary current amplifying circuit of a current transformer, which comprises a sampling circuit, an equivalent circuit of the transformer, a zero-load transformer amplifying circuit, a secondary current signal amplifying circuit of the transformer, a secondary current signal equivalent circuit of the transformer and an equivalent circuit in a single operational amplifier form, the sampling circuit is composed of a current transformer and a sampling resistor, the output end of the current transformer is fixedly connected with a sampling group in parallel, the transformer equivalent circuit is composed of a transformer, an ideal transformer, a sampling resistor and a secondary coil, the ideal transformer is fixedly connected with the output end of the transformer in parallel, and the secondary coil is fixedly connected with the output end of the ideal transformer in series. The secondary current amplification circuit of the current transformer achieves the purpose of improving the measurement precision when the current transformer is used, and solves the problems that when the current transformer is used, the measurement precision is low, the cost of the current transformer is high, the measurement precision of the current transformer is limited, and the frequency range is limited when the current transformer is used at low frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of electronics, and in particular to a novel secondary current amplification circuit for a current transformer. Background Art

[0002] Current transformers are commonly used to measure alternating current, converting the primary current into a corresponding voltage signal for output to match measuring instruments or related circuits to achieve current measurement.

[0003] However, existing current transformers have problems such as low measurement accuracy during use, high cost of the transformers, and limited frequency range during low-frequency use. Summary of the Invention

[0004] The problems to be solved by the present invention are the low measurement accuracy during the use of current transformers, the high cost of the transformers, the limited measurement accuracy of the transformers, and the limited frequency range during low-frequency use.

[0005] To solve the above technical problems, the present invention provides a novel secondary current amplification circuit for a current transformer, including a sampling circuit, an equivalent circuit of the transformer, a zero-load transformer amplification circuit, a secondary current signal amplification circuit of the transformer, an equivalent circuit of the secondary current signal of the transformer, and an equivalent circuit in the form of a single operational amplifier. The sampling circuit is composed of a current transformer and a sampling resistor. A sampling resistor is fixedly connected in parallel at the output end of the current transformer. The transformer equivalent circuit is composed of a transformer, an ideal transformer, a sampling resistor, and a secondary coil. An ideal transformer is fixedly connected in parallel at the output end of the transformer. A secondary coil is fixedly connected in series at the output end of the ideal transformer. A sampling resistor is connected in parallel at the output end of the secondary coil.

[0006] Preferably, in the transformer equivalent circuit, the excitation reactance of the transformer is L', the internal resistance of the secondary coil is R', T' is an ideal transformer, and L' is made of a larger magnetic core cross-sectional area or a material with high magnetic permeability or thicker wire.

[0007] Preferably, the transformer equivalent circuit uses the virtual short principle to reduce the output load Rs of the transformer to nearly 0, and at the same time, a sampling resistor Rs is connected in parallel to form a zero-load circuit.

[0008] Preferably, the secondary current signal amplification circuit of the transformer includes Op1, Op2, and feedback resistors, and the output Vo is the same as that of the zero-load transformer amplification circuit, Vo = -Is * Rs, where Rs is the sampling resistor and Is is the secondary output current of the transformer, which is proportional to the primary input current of the transformer.

[0009] Preferably, the equivalent circuit of the secondary current signal of the current transformer is formed by replacing T in the secondary current signal amplification circuit of the current transformer with an equivalent circuit composed of an ideal transformer T' and L, R'.

[0010] Preferably, the equivalent circuit in the single-output form forms the equivalent circuit of the single operational amplifier circuit by bringing the equivalent circuit of the current transformer into the single operational amplifier circuit. At this time, the ideal transformer T' and the ideal inductor L' are disconnected from the circuit, making the equivalent circuit in the single-output form become an amplifier circuit, where point a is the input and point b is the output. If Rg / Rs' = R' / Rs, the gain of the circuit is 1, that is, the potential at point a is equal to the potential at point b. After substituting the ideal transformer T' and the ideal inductor L', since the voltage across a - b is always 0.

[0011] Compared with the prior art, the present invention provides a novel current transformer secondary current amplification circuit, which has the following beneficial effects: 1. By using an operational amplifier circuit, the present invention generates a voltage opposite to the voltage of the internal resistance of the secondary of the current transformer, compensating for the load resistance of the secondary coil of the transformer and effectively solving the measurement accuracy problem when using the current transformer.

[0012] 2. By connecting the current transformer in series and parallel with the voltage of the secondary internal resistance, the present invention effectively reduces the cost of the transformer, greatly improves the measurement accuracy of the transformer, and expands the low-frequency frequency range when using the current transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a schematic diagram of the output amplifier circuit of the present invention; Figure 2 is a schematic diagram of the equivalent circuit of the transformer of the present invention; Figure 3 is a schematic diagram of the zero-load transformer amplification circuit of the present invention; Figure 4 is a schematic diagram of the operational amplifier compensated current transformer secondary current signal amplification circuit of the present invention; Figure 5 is a schematic diagram of the operational amplifier compensated current transformer secondary current signal amplification circuit (equivalent circuit) of the present invention; Figure 6 is a schematic diagram of the equivalent circuit in the single operational amplifier form of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The present invention relates to a novel current transformer secondary current amplification circuit, as Figures 1-4As shown, it includes a sampling circuit, an equivalent circuit of a mutual inductor, a zero-load mutual inductor amplification circuit, a secondary current signal amplification circuit of the mutual inductor, an equivalent circuit of the secondary current signal of the mutual inductor, and an equivalent circuit in the form of a single operational amplifier. The sampling circuit is composed of a current mutual inductor and a sampling resistor. A sampling resistor is fixedly connected in parallel at the output end of the current mutual inductor. The equivalent circuit of the mutual inductor is composed of a mutual inductor, an ideal transformer, a sampling resistor, and a secondary coil. An ideal transformer is fixedly connected in parallel at the output end of the mutual inductor. A secondary coil is fixedly connected in series at the output end of the ideal transformer. A sampling resistor is connected in parallel at the output end of the secondary coil.

[0015] Furthermore, in the equivalent circuit of the mutual inductor, the exciting reactance of the mutual inductor is L’, the internal resistance of the secondary coil is R’, T’ is an ideal transformer, and L’ uses a larger magnetic core cross-sectional area or a material with high magnetic permeability or thicker wire.

[0016] Furthermore, the equivalent circuit of the mutual inductor uses the virtual short principle to reduce the output load Rs of the mutual inductor to nearly 0, and at the same time, a sampling resistor Rs is connected in parallel to form a zero-load circuit.

[0017] Furthermore, the secondary current signal amplification circuit of the mutual inductor includes Op1, Op2 and feedback resistors. The output Vo is the same as that of the zero-load mutual inductor amplification circuit, Vo = -Is * Rs, where Rs is the sampling resistor and Is is the secondary output current of the mutual inductor, which is proportional to the primary input current of the mutual inductor.

[0018] Furthermore, the equivalent circuit of the secondary current signal of the current mutual inductor is formed by replacing T in the secondary current signal amplification circuit of the current mutual inductor with an equivalent circuit composed of an ideal mutual inductor T’ and L, R’.

[0019] Furthermore, the equivalent circuit in the form of a single amplifier forms the equivalent circuit of the single operational amplifier circuit by substituting the equivalent circuit of the current mutual inductor into the single operational amplifier circuit. At this time, the ideal transformer T’ and the ideal inductor L’ are disconnected from the circuit, making the equivalent circuit in the form of a single amplifier become an amplification circuit, where point a is the input and point b is the output. If Rg / Rs’ = R’ / Rs, the gain of the circuit is 1, that is, the potential at point a is equal to the potential at point b. After substituting the ideal transformer T’ and the ideal inductor L’, since the voltage of a - b is always 0.

[0020] When in use, as shown in the form of a single operational amplifier, the single operational amplifier method is adopted, and the output signal can be taken from Vo or Vo’. At the same time, it is also necessary to satisfy Rg / Rs’ ≤ R’ / Rs to ensure the normal operation of the circuit.

[0021] The equivalent circuit in the form of a single amplifier substitutes the equivalent circuit of the current mutual inductor into the operational amplifier form, and the equivalent circuit of the operational amplifier form can be obtained. Temporarily disconnect the ideal transformer T’ and the ideal inductor L’ from the circuit. Figure 6It becomes an amplifier circuit, where point a is the input and point b is the output. If Rg / Rs’ = R’ / Rs, the gain of the circuit is 1, that is, the potential at point a is equal to the potential at point b. After substituting the ideal transformer T’ and the ideal inductor L’, since the voltage across a-b is always 0, the voltage drops of the internal resistance and the sampling resistance are compensated.

[0022] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. Additionally, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A novel current transformer secondary current amplifier circuit, including a sampling circuit, an equivalent circuit of a transformer, a zero-load transformer amplifier circuit, a transformer secondary current signal amplifier circuit, a transformer secondary current signal equivalent circuit, and an equivalent circuit in the form of a single operational amplifier, characterized in that: The sampling circuit is composed of a current transformer and a sampling resistor. The output end of the current transformer is fixedly connected in parallel with a sampling resistor. The transformer equivalent circuit is composed of a transformer, an ideal transformer, a sampling resistor, and a secondary coil. The output end of the transformer is fixedly connected in parallel with an ideal transformer, the output end of the ideal transformer is fixedly connected in series with a secondary coil, and the output end of the secondary coil is connected in parallel with a sampling resistor.

2. A novel current transformer secondary current amplification circuit according to claim 1, characterized in that: In the transformer equivalent circuit, the transformer excitation reactance is L', the secondary coil internal resistance is R', T' is an ideal transformer, and L' adopts a larger core cross-sectional area or a material with high magnetic permeability or a thicker wire.

3. A novel current transformer secondary current amplification circuit according to claim 1, characterized in that: The transformer equivalent circuit reduces the output load Rs of the transformer to nearly 0 by using the virtual short principle, and simultaneously connects the sampling resistor Rs in parallel to form a zero-load circuit.

4. A novel current transformer secondary current amplification circuit according to claim 1, characterized in that: The transformer secondary current signal amplifier circuit includes Op1, Op2 and feedback resistor, and the output Vo is the same as the zero-load transformer amplifier circuit, Vo = -Is*Rs, where Rs is the sampling resistor, Is is the secondary output current of the transformer, which is proportional to the primary input current of the transformer.

5. A novel current transformer secondary current amplification circuit according to claim 1, characterized in that: The secondary current signal equivalent circuit of the current transformer is formed by replacing T in the secondary current signal amplification circuit of the current transformer with an equivalent circuit formed by an ideal transformer T', L, R'.

6. A novel current transformer secondary current amplification circuit according to claim 1, characterized in that: The single-amp equivalent circuit is formed by bringing the equivalent circuit of the current transformer into the single op amp circuit to form the equivalent circuit of the single op amp circuit. At this time, the ideal transformer T' and the ideal inductor L' are disconnected from the circuit, so that the single-amp equivalent circuit becomes an amplifier circuit, where point a is the input and point b is the output. If Rg / Rs'=R' / Rs, the gain of the circuit is 1, that is, the potential at point a is equal to the potential at point b. After substituting the ideal transformer T' and the ideal inductor L', the voltage ab is always 0.

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