A voltage sampling circuit and a voltage mutual inductance device

Abstract

The present invention relates to the technical field of power system equipment, and discloses a voltage sampling circuit and a voltage transformer device, wherein the voltage sampling circuit includes a voltage divider circuit, a voltage follower and an isolation amplifier. The input end of the voltage divider circuit is connected to the secondary winding of the voltage transformer, and is composed of a plurality of low-temperature drift voltage divider resistors. The input end of the voltage follower is connected to the output end of the voltage divider circuit, and the input end of the isolation amplifier is connected to the output end of the voltage follower. The voltage sampling circuit of the embodiment of the present invention divides the voltage input by the secondary winding of the voltage transformer by using a voltage divider circuit composed of low-temperature drift resistors, so as to increase the sampling range of the voltage transformer and reduce the temperature drift of the voltage sampling value. At the same time, the circuit can also isolate the high voltage generated when the secondary side of the voltage transformer is short-circuited through the isolation amplifier, so as to avoid the short circuit of the secondary side of the voltage transformer endangering the safety of people and equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of power system equipment, and in particular to a voltage sampling circuit and a voltage mutual inductance device. Background Art

[0002] In the power system, voltage transformers play a vital role. Voltage transformers can convert high voltage signals into corresponding low voltage signals, so that power meters or protection devices can accurately collect voltage, which is essential for the normal operation and dispatch of power systems. Voltage transformers can help measure voltage fluctuations and other anomalies, thereby predicting potential problems and avoiding damage to the normal operation of power systems. At present, traditional voltage transformers have disadvantages such as poor linearity, narrow output signal range, and susceptibility to temperature. To this end, it is necessary to design a high-precision voltage sampling circuit for voltage transformers to improve the above defects. Summary of the invention

[0003] In order to overcome the deficiencies of the prior art, the purpose of the present invention is to provide a voltage sampling circuit that can reduce the temperature drift of the voltage collected by the voltage transformer, increase the sampling range of the voltage transformer, and prevent the secondary side of the voltage transformer from short-circuiting and endangering the safety of people and equipment.

[0004] To solve the above problems, the technical solution adopted by the present invention is as follows: a voltage sampling circuit, comprising: a voltage divider circuit, whose input end is connected to the secondary winding of a voltage transformer and is composed of a plurality of low-temperature drift voltage divider resistors; a voltage follower, whose input end is connected to the output end of the voltage divider circuit; an isolation amplifier, whose input end is connected to the output end of the voltage follower; wherein a varistor RV1 is connected in parallel to the input end of the voltage divider circuit, and the voltage divider circuit comprises voltage divider resistors R1, R2 and R3, a first end of the voltage divider resistor R1 is connected to the first end of the secondary winding of the voltage transformer, a second end of the voltage divider resistor R1 is grounded through the voltage divider resistor R3, a connection node between the voltage divider resistor R1 and the voltage divider resistor R3 is connected to the input end of the voltage follower as the output end of the voltage divider circuit, a first end of the voltage divider resistor R2 is connected to the second end of the secondary winding of the voltage transformer, and a second end of the voltage divider resistor R2 is grounded.

[0005] Compared with the prior art, the beneficial effect of the present invention is that: the voltage of the secondary winding of the voltage transformer is sampled by a voltage-dividing circuit composed of a low-temperature voltage-dividing resistor, so as to improve the sampling range of the voltage transformer and avoid the collected voltage being affected by temperature changes. At the same time, by using an isolation amplifier to amplify the collected voltage, the high voltage generated when the secondary side of the voltage transformer is short-circuited can be isolated, so as to avoid the short-circuit of the secondary side of the voltage transformer endangering the safety of people and equipment, and the surge current generated by lightning strike is absorbed by the varistor RV1, so as to avoid the surge current generated by lightning strike damaging the sampling circuit.

[0006] In the above-mentioned voltage sampling circuit, the voltage follower includes an operational amplifier U1A, a plurality of resistors and a TVS diode TVS1. The non-inverting input terminal of the operational amplifier U1A is connected to the output terminal of the voltage divider circuit through a resistor R2, the inverting input terminal of the operational amplifier U1A is connected to its output terminal through a resistor R4, the end of the resistor R2 facing away from the operational amplifier U1A is grounded through the TVS diode TVS1, and the output terminal of the operational amplifier U1A is connected to the positive input terminal of the isolation amplifier.

[0007] The above-mentioned voltage sampling circuit further includes a filter circuit, and the output end of the isolation amplifier is connected to the input end of the filter circuit.

[0008] In the above-mentioned voltage sampling circuit, the filtering circuit is a second-order RC low-pass filtering circuit.

[0009] In the above-mentioned voltage sampling circuit, the isolation amplifier adopts a fully differential isolation amplifier of model CA-IS1300.

[0010] The above-mentioned voltage sampling circuit also includes a constant voltage source and a compensation circuit. The output end of the constant voltage source is connected to the input end of the voltage divider circuit through a controllable switch S3. The output end of the constant voltage source is also connected to the input end of the compensation circuit through a controllable switch S4. The output end of the compensation circuit is connected to the output end of the isolation amplifier. The compensation circuit, controllable switch S3 and controllable switch S4 are all controlled by a controller. The compensation circuit generates a compensation voltage under the control of the controller. The input end of the voltage divider circuit is connected to the secondary winding of the voltage transformer through a controllable switch S1.

[0011] The above-mentioned voltage sampling circuit, the compensation circuit includes an operational amplifier U1 B, a resistor R8 and a digital potentiometer R9, the non-inverting input terminal of the operational amplifier U1 B is connected to the controllable switch S4 through the resistor R8, the inverting input terminal of the operational amplifier U1 B is connected to the output terminal of the operational amplifier U1 B through the digital potentiometer R9, the output terminal of the operational amplifier U1 B is connected to the output terminal of the isolation amplifier through the controllable switch S5, and the control terminal of the digital potentiometer R9 is connected to the controller.

[0012] The above-mentioned voltage sampling circuit further includes a standard voltage transformer, and the secondary winding of the standard voltage transformer is connected to the input end of the voltage divider circuit through a controllable switch S2, and the controllable switch S2 is controlled by a controller.

[0013] A voltage transformer device comprises a voltage transformer and the above-mentioned voltage sampling circuit, wherein an input end of the voltage sampling circuit is connected to a secondary winding of the voltage transformer.

[0014] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a circuit schematic diagram of a voltage sampling circuit according to a first embodiment of the present invention;

[0016] Figure 2 FIG. 4 is a circuit schematic diagram of a voltage sampling circuit according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0017] The embodiments of the present invention are described in detail below. Figure 1 The embodiment of the present invention provides a voltage sampling circuit, including a voltage divider circuit, a voltage follower circuit and an isolation amplifier. The input end of the voltage divider circuit is connected to the secondary winding of the voltage transformer and is composed of a plurality of low temperature drift voltage divider resistors. The input end of the voltage follower is connected to the output end of the voltage divider circuit, the input end of the isolation amplifier is connected to the output end of the voltage follower, and the output end of the isolation amplifier is connected to the AD chip or AD input channel of the controller.

[0018] The voltage sampling circuit of the embodiment of the present invention performs voltage sampling on the voltage output by the secondary winding of the voltage transformer through a voltage divider circuit composed of low-temperature drift resistors, so as to improve the sampling range of the voltage transformer while avoiding the collected voltage from being affected by temperature changes and reducing the temperature drift of the collected voltage. At the same time, by using an isolation amplifier to amplify the collected voltage, the high voltage generated when a secondary side short circuit occurs in the voltage follower can be isolated to prevent the high voltage generated at this time from being input into the low voltage circuit connected to the secondary side, thereby preventing the secondary side short circuit of the voltage transformer from endangering the safety of people and equipment. The voltage follower is used to buffer and isolate the voltage input through the voltage divider circuit to improve the load capacity of the circuit.

[0019] Reference Figure 1 In some embodiments, the voltage divider circuit is composed of voltage divider resistors R1, R3 and R5. The first end of the voltage divider resistor R1 is connected to the first end of the secondary winding of the voltage transformer, the second end of the voltage divider resistor R1 is grounded through the voltage divider resistor R3, the connection node of the voltage divider resistor R1 and the voltage divider resistor R3 is connected to the input end of the voltage follower as the output end of the voltage divider circuit, the first end of the voltage divider resistor R2 is connected to the second end of the secondary winding of the voltage transformer, and the second end of the voltage divider resistor R2 is grounded. It can be understood that the voltage divider resistors R1, R3 and R5 should preferably use resistors with a temperature coefficient in the range of 10-25ppm. In this embodiment, a resistor with a temperature coefficient of 25ppm is selected. The resistance value of the voltage divider resistor should be determined according to the maximum voltage value of the secondary side of the voltage transformer, and it is necessary to ensure that the voltage value at both ends of the voltage divider resistor R3 after voltage division is within 250mV.

[0020] Reference Figure 1 In some embodiments, in order to prevent surge current generated by lightning from damaging the voltage sampling circuit, a varistor RV1 is provided between the voltage-dividing resistors R1 and R5 and one end connected to the voltage transformer.

[0021] Reference Figure 1 In some embodiments, the voltage follower includes an operational amplifier U1A, a plurality of resistors and a TVS diode TVS1. The non-inverting input terminal of the operational amplifier U1A is connected to the output terminal of the voltage divider circuit through a resistor R2, and the inverting input terminal of the operational amplifier U1A is connected to its input terminal through a resistor R4. The end of the resistor R2 away from the operational amplifier U1A is grounded through the TVS diode TVS1, and the output terminal of the operational amplifier U1A is connected to the positive input terminal of the isolation amplifier.

[0022] Reference Figure 1 In some embodiments, the isolation amplifier uses a fully differential isolation amplifier U2 of model CA-IS1300, which has the advantages of low temperature drift, high precision, wide input range and high isolation. Pin 2 of the fully differential isolation amplifier U2 is its positive input terminal, connected to the output terminal of the operational amplifier U1A, pin 1 is connected to the driving voltage 5V1 on the input side, pin 3 is the negative input terminal of the fully differential isolation amplifier U2, and pin 4 is connected to the ground on the input side. Pin 1 of the fully differential isolation amplifier U2 is also connected to the ground on the input side through the filter capacitor C2, pin 8 is connected to the driving voltage VDD5V on the output side, pin 5 is connected to the ground on the output side, pin 8 is also connected to the ground on the output side through the filter capacitor C1, and pins 6 and 7 are respectively the positive output terminal and negative output terminal of the fully differential isolation amplifier U2.

[0023] Reference Figure 1 In some embodiments, in order to improve the sampling accuracy of the voltage sampling circuit, the output end of the fully differential isolation amplifier U2 is connected to a filter circuit. In this embodiment, the filter circuit is a second-order RC low-pass filter circuit to suppress high-frequency interference, including resistors R6, R7 and capacitor C3. The first end of the resistor R6 is connected to the 7-pin of the fully differential isolation amplifier U2, and the first end serves as the positive output end of the voltage sampling circuit. The first end of the resistor R7 is connected to the 6-pin of the fully differential isolation amplifier U2, and the second end serves as the negative output end of the voltage sampling circuit. Capacitor C3 is arranged between the resistor R6 and one end of the resistor R7 facing away from the differential isolation amplifier U2.

[0024] Reference Figure 2In some embodiments, in order to realize online calibration of the transformation ratio of the voltage sampling circuit, the voltage sampling circuit also includes a constant voltage source and a compensation circuit. The output end of the constant voltage source is connected to the input end of the voltage divider circuit through a controllable switch S3. The output end of the constant voltage source is also connected to the input end of the compensation circuit through a controllable switch S4. The output end of the compensation circuit is connected to the output end of the isolation amplifier. The compensation circuit, the controllable switch S3 and the controllable switch S4 are all controlled by a controller. The compensation circuit generates a compensation voltage under the control of the controller. The input end of the voltage divider circuit is connected to the secondary winding of the voltage transformer through the controllable switch S1.

[0025] When the transformation ratio of the voltage sampling circuit needs to be calibrated, the controller first controls the controllable switch S1 and the controllable switch S4 to be disconnected, and controls the controllable switch S4 to be closed. At this time, the voltage sampling circuit samples the voltage output by the constant voltage source, and outputs the sampling result to the controller. Since the output voltage of the constant voltage source is known, the controller can calculate the transformation ratio of the entire voltage sampling circuit according to the output voltage of the constant voltage source and the voltage output by the voltage sampling circuit, and compare the calculated transformation ratio with the preset standard transformation ratio to obtain the error of the voltage sampling circuit. If it is detected that there is a sampling error in the voltage sampling circuit, then the controllable switches S1 and S4 are controlled to be closed, and the controllable switch S3 is controlled to be disconnected. The controller adjusts the transformation ratio of the compensation circuit according to the sampling error, so that the compensation circuit scales the voltage output by the constant voltage source, generates a compensation voltage and loads the compensation voltage on the output end of the voltage sampling circuit to achieve compensation for the sampling error; if it is detected that there is no error in the voltage sampling circuit, the controllable switch S1 is controlled to be closed, and the controllable switches S3 and S4 are controlled to be disconnected.

[0026] It is understandable that the compensation circuit can be a voltage regulating circuit such as an operational amplifier circuit with adjustable amplification factor, Figure 2 In this embodiment, the compensation circuit includes an operational amplifier U1B, a resistor R8 and a digital positioner R9. The in-phase input terminal of the operational amplifier U1B is connected to the controllable switch S4 through the resistor R8, and the inverting input terminal is connected to the output terminal of the operational amplifier U1B through the digital potentiometer R9. The output terminal of the operational amplifier U1B is connected to the output terminal of the isolation amplifier through the controllable switch S5. The control terminal of the digital potentiometer R9 is electrically connected to the controller. The controller adjusts the amplification factor of the compensation circuit by adjusting the resistance value of the digital potentiometer R9 to scale the voltage output by the constant voltage source and generate the required compensation voltage. When the voltage sampling circuit needs to be compensated, the controller controls the controllable switch S5 to close.

[0027] In some embodiments, in order to realize online detection and compensation of the ratio of the voltage transformer, the voltage sampling circuit also includes a standard voltage transformer, and the secondary winding of the standard voltage transformer is connected to the input end of the voltage divider circuit through a controllable switch S2, and the controllable switch S2 is controlled by a controller. When it is necessary to perform online detection and compensation on the ratio of the voltage transformer, the controller controls the controllable switch S2 to close, and controls the controllable switch S1 to open, and the bus voltage is sampled to the voltage sampling circuit through the standard voltage transformer. Since the sampling accuracy of the standard voltage transformer is higher, the controller can obtain the sampling error of the voltage transformer by comparing the voltage sampled by the standard voltage transformer and the voltage transformer. If the voltage transformer has a sampling error relative to a voltage transformer with higher accuracy, the controller controls the controllable switches S1, S4 and S5 to close, and controls the controllable switch S2 to open, calculates the voltage value to be compensated according to the obtained sampling error of the voltage transformer, and controls the compensation circuit to scale the voltage output by the constant voltage source, generates the required compensation voltage, and applies it to the output end of the voltage sampling circuit to compensate for the sampling error, so as to further improve the sampling accuracy.

[0028] An embodiment of the present invention further provides a voltage transformer device, comprising the above-mentioned voltage sampling circuit, wherein an input end of the voltage sampling circuit is connected to a secondary winding of a voltage transformer.

[0029] It should be noted that in the description of the present invention, if there are any orientation descriptions, such as up, down, front, back, left, right, etc., the orientations or positional relationships indicated are all based on the orientations or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed or operated in a specific orientation, and cannot be understood as a limitation on the present invention.

[0030] In the description of the present invention, "several" means one or more, "more" means two or more, "greater than", "less than", "exceed" etc. are understood to exclude the number itself, and "above", "below", "within" etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used to distinguish the technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0031] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0032] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A voltage sampling circuit, characterized in that: include: The voltage divider circuit has an input end connected to the secondary winding of the voltage transformer and is composed of a number of low-temperature drift voltage divider resistors; A voltage follower, whose input end is connected to the output end of the voltage divider circuit; an isolation amplifier, an input end of which is connected to the output end of the voltage follower; Among them, a varistor RV1 is connected in parallel to the input end of the voltage divider circuit, and the voltage divider circuit includes voltage divider resistors R1, R2 and R3. The first end of the voltage divider resistor R1 is connected to the first end of the secondary winding of the voltage transformer, and the second end of the voltage divider resistor R1 is grounded through the voltage divider resistor R3. The connection node between the voltage divider resistor R1 and the voltage divider resistor R3 is connected to the input end of the voltage follower as the output end of the voltage divider circuit, the first end of the voltage divider resistor R2 is connected to the second end of the secondary winding of the voltage transformer, and the second end of the voltage divider resistor R2 is grounded.

2. The voltage sampling circuit according to claim 1, characterized in that: The voltage follower includes an operational amplifier U1A, a plurality of resistors and a TVS diode TVS1. The non-inverting input terminal of the operational amplifier U1A is connected to the output terminal of the voltage divider circuit through a resistor R2, the inverting input terminal of the operational amplifier U1A is connected to its output terminal through a resistor R4, the end of the resistor R2 facing away from the operational amplifier U1A is grounded through the TVS diode TVS1, and the output terminal of the operational amplifier U1A is connected to the positive input terminal of the isolation amplifier.

3. The voltage sampling circuit according to claim 1, characterized in that: A filter circuit is also included, and the output end of the isolation amplifier is connected to the input end of the filter circuit.

4. The voltage sampling circuit according to claim 3, characterized in that: The filter circuit is a second-order RC low-pass filter circuit.

5. The voltage sampling circuit according to claim 1, characterized in that: The isolation amplifier is a fully differential isolation amplifier of model CA-IS1300.

6. The voltage sampling circuit according to claim 1, characterized in that: It also includes a constant voltage source and a compensation circuit, wherein the output end of the constant voltage source is connected to the input end of the voltage divider circuit through a controllable switch S3, and the output end of the constant voltage source is also connected to the input end of the compensation circuit through a controllable switch S4, and the output end of the compensation circuit is connected to the output end of the isolation amplifier, and the compensation circuit, the controllable switch S3 and the controllable switch S4 are all controlled by a controller, and the compensation circuit generates a compensation voltage under the control of the controller, and the input end of the voltage divider circuit is connected to the secondary winding of the voltage transformer through a controllable switch S1.

7. The voltage sampling circuit according to claim 6, characterized in that: The compensation circuit includes an operational amplifier U1B, a resistor R8 and a digital potentiometer R9. The non-inverting input terminal of the operational amplifier U1B is connected to the controllable switch S4 through the resistor R8, the inverting input terminal of the operational amplifier U1B is connected to the output terminal of the operational amplifier U1B through the digital potentiometer R9, the output terminal of the operational amplifier U1B is connected to the output terminal of the isolation amplifier through the controllable switch S5, and the control terminal of the digital potentiometer R9 is connected to the controller.

8. The voltage sampling circuit according to claim 6, characterized in that: It also includes a standard voltage transformer, the secondary winding of which is connected to the input end of the voltage divider circuit via a controllable switch S2, and the controllable switch S2 is controlled by a controller.

9. A voltage mutual inductance device, characterized in that: It comprises a voltage transformer and a voltage sampling circuit according to any one of claims 1 to 8, wherein an input end of the voltage sampling circuit is connected to a secondary winding of the voltage transformer.

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