High-precision current transformer based on active compensation

Abstract

The invention discloses a high-precision current transformer based on active compensation. Comprising an iron core coil, the other side of the iron core coil comprises a secondary current output, an output current gear switch and a differential amplifier, the secondary current output is electrically connected with a load, the load is electrically connected with a sampling voltage output, the load is electrically connected with an integral amplifier, and the integral amplifier is electrically connected with a sampling voltage output. The output current gear switching comprises a plurality of switchers, the differential amplifier is electrically connected with a voltage amplifier, and the voltage amplifier is electrically connected with a power amplifier; according to the invention, the problems of small current submission and small current verification of the standard electric energy meter are solved; the anti-interference capability is greatly improved, and the output stability is improved; active compensation is matched with automatic grading of a standard electric energy meter, so that the precision is very high; and an operational amplifier of the electronic compensation circuit adopts a reference power supply and integral feedback circuit, so that beat frequency interference of a power frequency power supply is effectively eliminated.

Description

Technical Field

[0001] The present invention belongs to the technical field of current transformers, and particularly relates to a high-precision current transformer based on active compensation. Background Art

[0002] A current transformer is an instrument that measures a large current on the primary side by converting it into a small current on the secondary side based on the principle of electromagnetic induction. A current transformer consists of a closed iron core and windings. Its primary winding has very few turns and is connected in series in the circuit where the current to be measured passes through. Therefore, it often has the full current of the circuit flowing through it. The secondary winding has more turns and is connected in series in the measuring instrument and the protection circuit. When the current transformer is working, its secondary circuit is always closed. Therefore, the impedance of the series-connected coil in the measuring instrument and the protection circuit is very small, and the working state of the current transformer is close to a short circuit. A current transformer converts a large current on the primary side into a small current on the secondary side for measurement, and the secondary side cannot be open-circuited. The existing scheme of a dual-core active compensation current transformer can make the transformer reach a very high accuracy and stability. However, there are still various problems with various current transformers on the market.

[0003] For example, a cascaded secondary small-current high-precision current transformer disclosed in the authorized publication number CN117116637A, although it realizes winding an active signal compensation winding outside the main iron core, winding an active electromotive force compensation winding outside the auxiliary iron core, and jointly winding the secondary winding on the main iron core and the auxiliary iron core; the output wire led out from the upper-level secondary winding passes through the lower-level current transformer to be used as the primary winding of the lower level, so that the upper and lower current transformers are cascaded, and the active signal compensation winding and the active electromotive force compensation winding are respectively connected to the active compensation module, and two sources are used to perform dynamic feedback zero-flux compensation on the two-level current transformers respectively, so that the error of the cascaded current ratio standard is less than 5×10 -6 , but it does not solve the problem that the existing current transformer needs to shift gears on the primary side (when there are different input currents), so it cannot meet the requirements of on-line detection by the power department. There are also problems such as the difficulty in calibration due to the heavy load in the small-current range when the standard watt-hour meter is sent for inspection, and the additional error brought to the device under test when calibrating the small current as a standard watt-hour meter. For this reason, we propose a high-precision current transformer based on active compensation. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-precision current transformer based on active compensation to solve the problems raised in the above background art.

[0005] To achieve the above object, the present invention provides the following technical solution: A high-precision current transformer based on active compensation, including an iron core coil, with a primary current input wound around one side of the iron core coil, and a number of side coils wound around the other side of the iron core coil, including a secondary current output, an output current gear shift, and a differential amplifier. A load is electrically connected to the secondary current output, a sampled voltage output is electrically connected to the load, and an integrating amplifier is electrically connected to the load. The output current gear shift includes a number of switches. A voltage amplifier is electrically connected to the differential amplifier, a power amplifier is electrically connected to the voltage amplifier, the power amplifier is electrically connected to the output current gear shift, the integrating amplifier is electrically connected to the voltage amplifier. The output current gear shift is used to achieve automatic gear shifting and realize on-line monitoring of the current in the power system. Under the action of the secondary current output and the load, the iron core coil makes the secondary of the transformer switch to a small number of turns in the case of small current, and at this time the load of the transformer is very light, using the small current of the standard watt-hour meter for inspection and calibrating the small current. A precision reference power supply is electrically connected to the differential amplifier, the voltage amplifier, and the power amplifier. The precision reference power supply, differential amplifier, voltage amplifier, and power amplifier form an electronic compensation circuit. The integrating amplifier, differential amplifier, voltage amplifier, and power amplifier form an integral feedback circuit. The operational amplifier of the electronic compensation circuit uses the reference power supply and the integral feedback circuit to eliminate the beat frequency interference of the power frequency power supply. And through the cooperation of the output current gear shift and the standard watt-hour meter for automatic grading, the zero-flux signal detected by the double-core differential is amplified by current and voltage, and the output current is given to the secondary of the current transformer. The secondary current of the current transformer is completely provided by an external power supply, and the secondary load of the transformer is approximately zero, making the transformer have high precision.

[0006] Preferably, the differential amplifier and the voltage amplifier use MC33078DR2G operational amplifiers, and the two MC33078DR2G operational amplifiers are electrically connected to each other.

[0007] Preferably, the integrating amplifier uses an OP177 operational amplifier, and the output end of the OP177 operational amplifier is electrically connected between the two MC33078DR2G operational amplifiers.

[0008] Preferably, the output of the MC33078DR2G operational amplifier used by the voltage amplifier is electrically connected to the power amplifier. The power amplifier uses an LM675T amplifier, and the output end of the LM675T amplifier is electrically connected to the output current gear shift.

[0009] Preferably, the output current gear switching includes relays K1B, K2B, K3B, K1C, K2C, and K3C. The relays K1B, K2B, K3B, K1C, K2C, and K3C are all electrically connected to the 20T current gear, 200T current gear, and 2000T current gear.

[0010] Preferably, the relays K1B, K2B, and K3B are electrically connected to the power amplifier, and the relays K1C, K2C, and K3C are electrically connected to the integrator amplifier.

[0011] Preferably, the switching control of the 20T current gear, 200T current gear, and 2000T current gear is switches K1, K2, and K3. The switch K1 controls the 20T current gear and 200T current gear to be closed and the 2000T current gear to be opened. The switch K2 controls the 20T current gear and 2000T current gear to be closed and the 200T current gear to be opened. The switch K3 controls the 200T current gear and 2000T current gear to be closed and the 20T current gear to be opened.

[0012] Preferably, a ULN2003 composite transistor array is electrically connected to the switches K1, K2, and K3. The ULN2003 composite transistor array is used to directly process data that originally required a standard logic buffer to process, that is, to directly process the switch control of the switches K1, K2, and K3, and to control and adjust the on / off states of the relays K1B, K2B, K3B, K1C, K2C, and K3C.

[0013] Preferably, the secondary current output includes four tantalum capacitors and two triodes. A tantalum capacitor is electrically connected to the base of each of the two triodes. The four tantalum capacitors are symmetrically arranged. A capacitor R32 is electrically connected between the four tantalum capacitors, and the capacitor R32 is the load.

[0014] Preferably, the precision reference power supply includes an LM431AIM3X (N1E) reference, two TL072C operational amplifiers, and two PMBT3906 (W2A) transistors. The LM431AIM3X (N1E) reference is electrically connected to the two TL072C operational amplifiers in sequence, and the two PMBT3906 (W2A) transistors are respectively electrically connected to the back ends of the two TL072C operational amplifiers.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: Due to the method of one-time through-core with one turn and multiple secondary windings and automatic gear shifting in the present invention, the on-line monitoring of the current in the power system can be realized. When the current is small, the secondary switching of the current transformer is in the gear with a small number of turns, and the load of the current transformer is very light, solving the problems existing in the inspection of small currents of standard watt-hour meters and the verification of small currents; by using double-core differential detection of zero-flux signals and adding shielding cores around the four circumferences of these two cores, the anti-interference ability of the current transformer is greatly improved, and the output stability is enhanced; by using active compensation and automatically dividing gears inside in cooperation with the standard watt-hour meter, after the zero-flux signals detected by double-core differential detection are amplified by current and voltage, the output current is supplied to the secondary of the current transformer, and the secondary current of the current transformer is completely provided by an external power supply, and the secondary load of the current transformer is approximately zero, making the current transformer have high precision; the operational amplifier of the electronic compensation circuit adopts reference power supply and integral feedback circuit, effectively eliminating the beat interference of the power frequency power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the system structure of the present invention; Figure 2 It is a schematic diagram of the circuit of the present invention; Figure 3 It is a schematic diagram of the control switching of the present invention; Figure 4 It is a schematic diagram of the control switching signal processing of the present invention; Figure 5 It is a schematic diagram of the precision reference power supply of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0018] Please refer to Figures 1-5, the present invention provides a technical solution: a high-precision current transformer based on active compensation, including an iron core coil. On one side of the iron core coil, a primary current input is wound. On the other side of the iron core coil, several side coils are wound, including a secondary current output, an output current gear shift, and a differential amplifier. A load is electrically connected to the secondary current output. A sampling voltage output is electrically connected to the load. An integrating amplifier is electrically connected to the load; The output current gear shift includes several switches. A voltage amplifier is electrically connected to the differential amplifier. A power amplifier is electrically connected to the voltage amplifier. The power amplifier is electrically connected to the output current gear shift. The integrating amplifier is electrically connected to the voltage amplifier. The output current gear shift is used to achieve automatic gear shifting and realize on-line current monitoring of the power system. Under the action of the secondary current output and the load of the iron core coil, when the current in the iron core coil is small, the secondary of the transformer is switched to the gear with fewer turns. At this time, the load of the transformer is very light, and the small current of the standard watt-hour meter is used for inspection and verification of small current; A precision reference power supply is electrically connected to the differential amplifier, the voltage amplifier, and the power amplifier. The precision reference power supply, the differential amplifier, the voltage amplifier, and the power amplifier form an electronic compensation circuit. The integrating amplifier, the differential amplifier, the voltage amplifier, and the power amplifier form an integral feedback circuit. The operational amplifier of the electronic compensation circuit adopts reference power supply and integral feedback circuit to eliminate the beat frequency interference of the power frequency power supply. And through the cooperation of the output current gear shift and the standard watt-hour meter for automatic grading, after the zero-flux signal of the double-core differential detection is amplified by current and voltage, the output current is supplied to the secondary of the current transformer. The secondary current of the current transformer is completely provided by an external power supply, and the secondary load of the transformer is approximately zero, making the transformer have high precision; Primary input current: 0.001A - 120A; Secondary output current: 100A / 0.1A, 10A / 0.1A, 1A / 0.1A; Secondary output load: 20 ohms / 200 ohms; Precision: less than 0.01% when the primary current is 0.01A - 120A, less than 0.02% when 0.001A - 0.01A; Usage: Sampling current transformer for standard watt-hour meters and power monitoring systems.

[0019] It can meet the requirements of on-line high-precision current detection in the power system; the stability of the output current is less than 0.005%; the detection current range is extremely wide. When the input current is between 1mA - 120A, the secondary can provide a highly stable and high-precision output current.

[0020] In order to perform differential amplification processing on the circuit, and to amplify the voltage for facilitating active compensation processing, in this embodiment, preferably, the differential amplifier and the voltage amplifier adopt the MC33078DR2G operational amplifier, and the two MC33078DR2G operational amplifiers are electrically connected.

[0021] In order to perform integral amplification processing on the current for facilitating the formation of an integral feedback circuit, in this embodiment, preferably, the integral amplifier adopts the OP177 operational amplifier, and the output terminal of the OP177 operational amplifier is electrically connected between the two MC33078DR2G operational amplifiers.

[0022] In order to perform amplification processing on the power for facilitating active compensation control and to achieve switching control of the current gear, in this embodiment, preferably, the output of the MC33078DR2G operational amplifier used by the voltage amplifier is electrically connected to the power amplifier, the power amplifier adopts the LM675T amplifier, and the output terminal of the LM675T amplifier is electrically connected to the output current gear switching.

[0023] In order to achieve switching control of the current gear through the integral feedback circuit, in this embodiment, preferably, the output current gear switching includes relays K1B, K2B, K3B, K1C, K2C, and K3C. The relays K1B, K2B, K3B, K1C, K2C, and K3C are all electrically connected to the 20T current gear, 200T current gear, and 2000T current gear. The relays K1B, K2B, and K3B are electrically connected to the power amplifier, and the relays K1C, K2C, and K3C are electrically connected to the integral amplifier.

[0024] In order to achieve switching control of the current gear and perform precise control adjustment, in this embodiment, preferably, the switching control of the 20T current gear, 200T current gear, and 2000T current gear is switches K1, K2, and K3. The switch K1 controls the 20T current gear and 200T current gear to be closed, and the 2000T current gear to be opened. The switch K2 controls the 20T current gear and 2000T current gear to be closed, and the 200T current gear to be opened. The switch K3 controls the 200T current gear and 2000T current gear to be closed, and the 20T current gear to be opened.

[0025] In order to calculate and process the control values of the current gear positions to facilitate precise control and adjustment, in this embodiment, preferably, the switches K1, K2, and K3 are electrically connected to a ULN2003 composite transistor array. The ULN2003 composite transistor array is used to directly process the data that originally required a standard logic buffer to process, that is, to directly process the switch controls of the switches K1, K2, and K3, and to control and adjust the on / off states of the relays K1B, K2B, K3B, K1C, K2C, and K3C.

[0026] In order to achieve the control of the secondary current output and enable the load to consume electricity, and to facilitate the detection of the current, in this embodiment, preferably, the secondary current output includes four tantalum capacitors and two triodes. One tantalum capacitor is electrically connected to the base of each of the two triodes, and the four tantalum capacitors are symmetrically arranged. A capacitor R32 is electrically connected between the four tantalum capacitors, and the capacitor R32 is the load.

[0027] In order to provide a reference voltage and implement a line electronic compensation circuit using a reference power supply and an integral feedback circuit, effectively eliminating the beat interference of the power frequency power supply, in this embodiment, preferably, the precision reference power supply includes an LM431AIM3X (N1E) voltage reference. The precision reference power supply also includes two TL072C operational amplifiers and two PMBT3906 (W2A) transistors. The LM431AIM3X (N1E) voltage reference is sequentially electrically connected to the two TL072C operational amplifiers, and the two PMBT3906 (W2A) transistors are respectively electrically connected to the back ends of the two TL072C operational amplifiers.

[0028] Working principle and usage process of the present invention: When in use, it is powered by sequentially inputting current on one side of the iron core coil, facilitating the realization of induced current in the side coil on the other side, facilitating the output of secondary current to supply power to the load, facilitating the adoption of voltage output, facilitating the small-current inspection and verification of small current in a standard watt-hour meter. There is a precision reference power supply electrically connected to the differential amplifier, voltage amplifier, and power amplifier. Internal power supply is achieved through the precision reference power supply, and the precision reference power supply, differential amplifier, voltage amplifier, and power amplifier form an electronic compensation circuit. The integrator amplifier, differential amplifier, voltage amplifier, and power amplifier form an integral feedback circuit. The operational amplifier of the electronic compensation circuit adopts reference power supply and integral feedback circuit to eliminate the beat frequency interference of the power frequency power supply. And through the output current gear switching and automatic grading with the standard watt-hour meter, the zero-flux signal detected by the double-iron-core differential is amplified by current and voltage and then the output current is sent to the secondary of the current transformer. The secondary current of the current transformer is completely provided by the external power supply, and the secondary load of the transformer is approximately zero, making the transformer have high precision. When the iron core coil is at a small current, the secondary of the transformer switches to a gear with a small number of turns, and at this time the load of the transformer is very light, enabling the small-current inspection and verification of small current using a standard watt-hour meter. Furthermore, it can achieve a primary input current of 0.001 A - 120 A on one side of the iron core coil; a secondary output current of 100 A / 0.1 A, 10 A / 0.1 A, 1 A / 0.1 A can be obtained on the other side of the iron core coil; secondary output load: 20 Ω / 200 Ω; accuracy: less than 0.01% when the primary current is 0.01 A - 120 A, less than 0.02% when 0.001 A - 0.01 A; usage: used as a sampling current transformer for a standard watt-hour meter and a power monitoring system.

[0029] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-precision current transformer based on active compensation, comprising an iron core coil, characterized in that: A primary current input is wound on one side of the core coil, and a plurality of side coils are wound on the other side of the core coil, including a secondary current output, an output current gear switch and a differential amplifier, the secondary current output is electrically connected to a load, the load is electrically connected to a sampling voltage output, and the load is electrically connected to an integral amplifier; The output current gear switching includes a plurality of switches, the differential amplifier is electrically connected to a voltage amplifier, the voltage amplifier is electrically connected to a power amplifier, the power amplifier is electrically connected to the output current gear switching, the integral amplifier is electrically connected to the voltage amplifier, the output current gear switching is used to realize automatic gear shifting, and realize online monitoring of the current of the power system, the iron core coil is output through the secondary current and the load, so that the secondary switch of the transformer of the iron core coil is in a gear with a small number of turns when the current is small, at this time the load of the transformer is very light, and the small current of the standard electric energy meter is used for inspection and verification of the small current; The differential amplifier, the voltage amplifier and the power amplifier are electrically connected to a precision reference power supply, the precision reference power supply, the differential amplifier, the voltage amplifier and the power amplifier form an electronic compensation circuit, the integral amplifier, the differential amplifier, the voltage amplifier and the power amplifier form an integral feedback circuit, the operational amplifier of the electronic compensation circuit adopts a reference power supply and an integral feedback circuit, the beat frequency interference of the industrial frequency power supply is eliminated, and the output current gear is switched through the output current gear to automatically divide the gears in coordination with the standard electric energy meter, the zero flux signal of the double-core differential detection is amplified by the current and voltage, and the output current is given to the secondary of the current transformer, the secondary current of the current transformer is completely provided by an external power supply, the secondary load of the transformer is approximately zero, so that the transformer has high precision.

2. A high-precision current transformer based on active compensation according to claim 1, characterized in that: The differential amplifier and the voltage amplifier use MC33078DR2G operational amplifiers, and the two MC33078DR2G operational amplifiers are electrically connected.

3. A high-precision current transformer based on active compensation according to claim 2, characterized in that: The integrating amplifier is an OP177 operational amplifier, and the output end of the OP177 operational amplifier is electrically connected between the two MC33078DR2G operational amplifiers.

4. A high-precision current transformer based on active compensation according to claim 3, characterized in that: The output of the MC33078DR2G operational amplifier used by the voltage amplifier is electrically connected to the power amplifier, and the power amplifier uses an LM675T amplifier. The output end of the LM675T amplifier is electrically connected to the output current gear switch.

5. The high-precision current transformer based on active compensation according to claim 1, characterized in that: The output current gear switching includes relay K1B, relay K2B, relay K3B, relay K1C, relay K2C and relay K3C, and the relay K1B, relay K2B, relay K3B, relay K1C, relay K2C and relay K3C are all electrically connected at 20T current gear, 200T current gear and 2000T current gear.

6. A high-precision current transformer based on active compensation according to claim 5, characterized in that: The relay K1B, the relay K2B, and the relay K3B are electrically connected to the power amplifier, and the relay K1C, the relay K2C, and the relay K3C are electrically connected to the integrating amplifier.

7. A high-precision current transformer based on active compensation according to claim 6, characterized in that: The switching control of the 20T current gear, the 200T current gear and the 2000T current gear is switch K1, switch K2 and switch K3, and the switch K1 controls the 20T current gear and the 200T current gear to be closed, and the 2000T current gear to be opened, the switch K2 controls the 20T current gear and the 2000T current gear to be closed, and the 200T current gear to be opened, and the switch K3 controls the 200T current gear and the 2000T current gear to be closed, and the 20T current gear to be opened.

8. A high-precision current transformer based on active compensation according to claim 7, characterized in that: The switch K1, the switch K2 and the switch K3 are electrically connected to a ULN2003 compound transistor array, and the ULN2003 compound transistor array is used to directly process data that originally needs to be processed by a standard logic buffer, that is, to directly process the switch control of the switch K1, the switch K2 and the switch K3, and realize the control and regulation of the on and off of the relay K1B, the relay K2B, the relay K3B, the relay K1C, the relay K2C and the relay K3C.

9. The high-precision current transformer based on active compensation according to claim 1, characterized in that: The secondary current output includes four tantalum capacitors and two transistors. The bases of the two transistors are electrically connected to a tantalum capacitor, and the four tantalum capacitors are symmetrically arranged. A capacitor R32 is electrically connected between the four tantalum capacitors, and the capacitor R32 is the load.

10. The high-precision current transformer based on active compensation according to claim 1, characterized in that: The precision reference power supply includes an LM431AIM3X (N1E) reference device, and the precision reference power supply also includes two TL072C op amps and two PMBT3906 (W2A) transistors. The LM431AIM3X (N1E) reference device is electrically connected to the two TL072C op amps in sequence, and the two PMBT3906 (W2A) transistors are electrically connected to the rear ends of the two TL072C op amps respectively.

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