A self-calibration device and online self-calibration method for an open current sensor

Abstract

The present invention discloses a self-calibration device and an online self-calibration method for an open-circuit current sensor. The device comprises: an open-circuit current transformer and a self-calibration system. The open-circuit current transformer comprises: a first injection winding and a second injection winding located on one side, and a detection winding located on the other side; the self-calibration system comprises: a first digital control signal generating unit, a second digital control signal generating unit, a first power amplifying unit, a second power amplifying unit, a first signal sampling unit, a second signal sampling unit, a third signal sampling unit and a self-calibration processing unit; the first digital control signal generating unit, the first power amplifying unit, the first signal sampling unit and the first injection winding constitute a cancellation circuit; the second digital control signal generating unit, the second power amplifying unit, the second signal sampling unit and the second injection winding constitute a calibration circuit; and the third signal sampling unit and the detection winding constitute a measurement circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of self-calibration of open-type current transformers, and more particularly to a self-calibration device and an online self-calibration method for an open-type current transformer. Background Art

[0002] The sensing portion of an open-core current transformer (OCT) is a current transformer with an open coil and an air gap. In the 1970s, the Soviet Union proposed the design of an open-core current transformer to address the magnetic saturation problem of closed-core current transformers. The basic principle of an open-core current transformer is to create an open core, that is, to insert an air gap magnetic resistance into the original magnetic circuit. Because the magnetic permeability of air is much lower than that of the iron core, even a small air gap can produce a large magnetic resistance, thereby reducing the magnetic flux and ensuring that the current transformer operates in the linear portion of the magnetization curve. Overseas, Canada and the United States have conducted relatively more research on open-core current transformers. The open-core current transformer designed by Eddy So, David Bennett, and others in Canada uses a multi-core structure and incorporates a shielding device. It also uses a high-amplification operational amplifier to form an active compensation circuit to achieve a zero-flux current transformer with magnetomotive force compensation. At currents of 1-200A and frequencies of 50-5000 Hz, it can achieve a 50×10 -6 The measurement accuracy is good. As a laboratory device, the power consumption of active compensation can be ignored. However, if it is used for online monitoring or live calibration of power systems, related issues must be considered.

[0003] Open-type high-precision current transformers not only have high requirements for machining processes but also have their own limitations in application. Therefore, this single-stage open-type transformer can only improve the accuracy performance of open-type current transformers to a certain extent. Traditional open-type current transformers mainly include air-core coils and iron-core coils. Iron-core coil-based open-type current transformers have magnetic saturation characteristics, ferromagnetic resonance, a small dynamic range, and a narrow frequency response. They are highly accurate and less susceptible to the position of the measured current. However, in practical applications, the influence of the test environment and the aging of the current clamp itself can increase measurement errors, making actual measurement accuracy unreliable. Open-type current transformers based on air-core coils have relatively poor ratio error measurement accuracy and are susceptible to the position of the measured current. However, they have advantages such as strong anti-interference ability, good linearity, high measurement bandwidth, high integration, and light weight. As the power electronics feature of power systems becomes increasingly prominent, power system loads exhibit wide dynamic range, fast time-varying, and highly random characteristics, requiring high-accuracy, high-bandwidth, and well-integrated standard transformers to support online monitoring, live calibration, and other services.

[0004] Therefore, there is a need for an open current sensor that can be distinguished from offline self-calibration and has an online self-calibration function during use to ensure the accuracy of the open current sensor during use. Summary of the Invention

[0005] The present invention provides a self-calibration device and an online self-calibration method for an open-type current sensor, so as to solve the problem of how to perform online self-calibration on an open-type current transformer.

[0006] In order to solve the above problems, according to one aspect of the present invention, a self-calibration device for an open current sensor is provided, the device comprising: an open current transformer and a self-calibration system, the open current transformer comprising: a first injection winding and a second injection winding located on one side, and a detection winding located on the other side; the self-calibration system comprising: a first digital control signal generating unit, a second digital control signal generating unit, a first power amplifying unit, a second power amplifying unit, a first signal sampling unit, a second signal sampling unit, a third signal sampling unit and a self-calibration processing unit; the first digital control signal generating unit, the first power amplifying unit, the first signal sampling unit and the first injection winding constitute a cancellation circuit; the second digital control signal generating unit, the second power amplifying unit, the second signal sampling unit and the second injection winding constitute a calibration circuit; the third signal sampling unit and the detection winding constitute a measurement circuit; wherein,

[0007] The first injection winding is used for coupling and offsetting the background current of the primary side;

[0008] The second injection winding is used to couple a self-calibration current for self-calibration;

[0009] The detection winding is used to couple the current injected by the circuit to be tested, the first injection winding and the second injection winding;

[0010] The first digital control signal generating unit is connected to the self-calibration processing unit and the first power amplifying unit respectively, and is used to generate a first voltage signal corresponding to the offset current based on the first control command;

[0011] The first power amplifying unit is connected to the first injection winding and the first signal sampling unit respectively, and is used to generate a compensation current required for compensation based on the first voltage signal;

[0012] The second digital control signal generating unit is connected to the self-calibration processing unit and the second power amplifying unit respectively, and is used to generate a second voltage signal corresponding to the self-calibration current based on the second control command;

[0013] The second power amplifying unit is connected to the second injection winding and the second signal sampling unit respectively, and is used to generate a self-calibration current required for self-calibration based on the second voltage signal;

[0014] The first signal sampling unit is connected to the self-calibration processing unit and is used to sample the current of the offset circuit to obtain the offset current;

[0015] The second signal sampling unit is connected to the self-calibration processing unit and is used to sample the current of the calibration circuit to obtain the self-calibration current;

[0016] The third signal sampling unit is connected to the detection winding and the self-calibration processing unit respectively, and is used to sample the measurement circuit to obtain the measurement current;

[0017] The self-calibration processing unit is used to send the first control command and the second control command; to perform feedback control on the first digital control signal generating unit and the second digital control signal generating unit based on the offset current and the self-calibration current; to perform primary current offset of the open current transformer based on the measured current and the offset current; and to perform self-calibration of the open current transformer based on the measured current and the self-calibration current.

[0018] Preferably, the first signal sampling unit, the second signal sampling unit and the third signal sampling unit each comprise: an I / V conversion circuit, a signal conditioning circuit and an A / D sampling circuit connected in sequence; wherein,

[0019] The I / V conversion circuit is used to convert the input current into voltage and output a voltage signal;

[0020] The signal conditioning circuit is used to perform signal conditioning on the input voltage signal;

[0021] The A / D sampling circuit is used to convert the conditioned voltage signal from an analog signal to a digital signal.

[0022] Preferably, the open-circuit current transformer to be measured is a clamp-on current transformer.

[0023] Preferably, the self-calibration processing unit performs primary current offset of the open current transformer based on the measured current and the offset current, including:

[0024] According to the measured current i2 of the measuring circuit after the open current transformer is clamped on the measured line, the initial value of the offset current i3 is generated to offset the line current i1;

[0025] By adjusting i3 so that the value of i2 decreases until it reaches 0 or is less than a preset current threshold, it is determined that the primary current compensation is completed.

[0026] Preferably, the self-calibration unit performs self-calibration of the open-circuit current transformer based on the measured current and the self-calibration current, comprising:

[0027] When the magnetic field generated by the line current i1 on the measured line in the iron core is zero or the amplitude is offset to zero, an equal ampere-turn current is injected through the second injection winding of the calibration circuit; wherein the magnitude of the equal ampere-turn current is a first preset percentage of the rated current;

[0028] Measure the measurement current i2 of the measurement circuit at this time, calculate the ratio difference correction factor and the phase difference correction factor of the open current transformer at this time, and determine whether the current ratio difference correction factor and the phase difference correction factor meet the amplitude range and the phase range;

[0029] When the amplitude range and phase range are met, the ratio difference correction factor and phase difference correction factor of the open current transformer are calculated when injecting the equal ampere-turn current of other preset percentages of the rated current, and the amplitude range and phase range are judged;

[0030] If all amplitudes and phases meet the amplitude range and phase range, it is determined that the open-type current transformer meets the accuracy requirement; otherwise, if there is an amplitude that does not meet the amplitude range or the phase does not meet the phase range, it is determined that the open-type current transformer does not meet the accuracy requirement.

[0031] Preferably, the self-calibration unit obtains the ratio difference correction factor and the phase difference correction factor and determines the amplitude range and the phase range in the following manner:

[0032] ,

[0033] ,

[0034] Among them, A 0i and are the amplitude and phase of the primary current i1 of the measured circuit when the equal ampere-turn current is injected for the i-th time; A 2i and are the amplitude and phase of the current i2 in the measuring circuit when the equal ampere-turn current is injected for the i-th time; f bi and δ bi are the ratio difference and phase difference of the open-circuit current transformer when the equal ampere-turn current is injected for the i-th time; and are the transformer ratio difference limit and ratio difference correction factor under the corresponding accuracy level respectively; and are the transformer phase difference limit and phase difference correction factor under the corresponding accuracy level; n2 is the number of turns of the detection winding.

[0035] Preferably, the self-calibration unit is further used for:

[0036] Fitting is performed based on all ratio difference correction factors and phase difference correction factors to obtain an amplitude compensation curve and a phase compensation curve.

[0037] According to another aspect of the present invention, there is provided an online self-calibration method based on the self-calibration device of the open current sensor as described above, the method comprising:

[0038] The signal sampling unit samples the measurement circuit to obtain the measurement current;

[0039] The cancellation circuit is connected to the self-calibration device, and the self-calibration processing unit sends a first control command to the first digital control signal generating unit;

[0040] A first digital control signal generating unit generates a first voltage signal corresponding to the offset current based on the first control command;

[0041] The first power amplifying unit generates a compensation current required for compensation based on the first voltage signal;

[0042] The first signal sampling unit samples the offset circuit to obtain the offset current;

[0043] The self-calibration processing unit performs primary current cancellation of the open current transformer based on the cancellation current and the measured current, and disconnects the cancellation circuit after the cancellation is completed;

[0044] The calibration circuit is connected to the self-calibration device, and the self-calibration processing unit sends a second control command to the second digital control signal generating unit;

[0045] A second digital control signal generating unit generates a second voltage signal corresponding to the self-calibration current based on the second control command;

[0046] The second power amplifying unit generates a self-calibration current required for self-calibration based on the second voltage signal;

[0047] The self-calibration processing unit performs self-calibration of the open-circuit current transformer based on the measured current and the self-calibration current.

[0048] Preferably, the first signal sampling unit, the second signal sampling unit and the third signal sampling unit each comprise: an I / V conversion circuit, a signal conditioning circuit and an A / D sampling circuit connected in sequence; wherein,

[0049] The input current is converted into voltage using an I / V conversion circuit, and a voltage signal is output;

[0050] Performing signal conditioning on the input voltage signal using a signal conditioning circuit;

[0051] The conditioned voltage signal is converted from an analog signal to a digital signal using an A / D sampling circuit.

[0052] Preferably, the open-circuit current transformer to be measured is a clamp-on current transformer.

[0053] Preferably, the self-calibration processing unit performs primary current offset of the open current transformer based on the offset current and the measured current, comprising:

[0054] According to the measured current i2 of the measuring circuit after the open current transformer is clamped on the measured line, the initial value of the offset current i3 is generated to offset the line current i1;

[0055] By adjusting i3 so that the value of i2 decreases until it reaches 0 or is less than a preset current threshold, it is determined that the primary current compensation is completed.

[0056] Preferably, the self-calibration unit performs self-calibration of the open current transformer based on the measured current and the self-calibration current, comprising:

[0057] When the magnetic field generated by the line current i1 on the measured line in the iron core is 0 or the amplitude is offset to 0, an equal ampere-turn current of a second preset percentage of the rated current is injected through the second injection winding of the calibration circuit;

[0058] Measure the measurement current i2 of the measurement circuit at this time, calculate the ratio difference correction factor and the phase difference correction factor of the open current transformer at this time, and determine whether the current ratio difference correction factor and the phase difference correction factor meet the amplitude range and the phase range;

[0059] When the amplitude range and phase range are met, the ratio difference correction factor and phase difference correction factor of the open current transformer are calculated when injecting the equal ampere-turn current of other preset percentages of the rated current, and the amplitude range and phase range are judged;

[0060] If all amplitudes and phases meet the amplitude range and phase range, it is determined that the open-type current transformer meets the accuracy requirement; otherwise, if there is an amplitude that does not meet the amplitude range or the phase does not meet the phase range, it is determined that the open-type current transformer does not meet the accuracy requirement.

[0061] Preferably, the method uses the following method to obtain the ratio difference correction factor and the phase difference correction factor, and to determine the amplitude range and the phase range, including:

[0062] ,

[0063] ,

[0064] Among them, A 0i and are the amplitude and phase of the primary current i1 of the measured circuit when the equal ampere-turn current is injected for the i-th time; A2i and are the amplitude and phase of the current i2 in the measuring circuit when the equal ampere-turn current is injected for the i-th time; f bi and δ bi are the ratio difference and phase difference of the open-circuit current transformer when the equal ampere-turn current is injected for the i-th time; and are the transformer ratio difference limit and ratio difference correction factor under the corresponding accuracy level respectively; and are the transformer phase difference limit and phase difference correction factor under the corresponding accuracy level; n2 is the number of turns of the detection winding.

[0065] Preferably, the method further comprises:

[0066] The self-calibration unit performs fitting according to all ratio difference correction factors and phase difference correction factors to obtain an amplitude compensation curve and a phase compensation curve.

[0067] The present invention provides a self-calibration device and an online self-calibration method for an open current sensor, wherein the device comprises: a first injection winding for coupling and offsetting the background current on the primary side; a second injection winding for coupling the self-calibration current for self-calibration; a detection winding for coupling the current injected by the circuit to be tested, the first injection winding and the second injection winding; a first digital control signal generating unit for generating a first voltage signal corresponding to the offset current based on the first control command; a first power amplifying unit for generating the offset current required for offset based on the first voltage signal; a second digital control signal generating unit for generating a second voltage signal corresponding to the self-calibration current based on the second control command; a second power amplifying unit for generating a second voltage signal corresponding to the self-calibration current based on the first control command; and a second digital control signal generating unit for generating a second voltage signal corresponding to the self-calibration current based on the second control command. The self-calibration current required for the self-calibration of the two voltage signals; a first signal sampling unit for sampling the current of the offset circuit to obtain the offset current; a second signal sampling unit for sampling the current of the calibration circuit to obtain the self-calibration current; a third signal sampling unit for sampling the measurement circuit to obtain the measurement current; a self-calibration processing unit for sending the first control command and the second control command; for performing feedback control on the first digital control signal generating unit and the second digital control signal generating unit based on the offset current and the self-calibration current; for performing primary current offset of the open-circuit current transformer based on the measurement current and the offset current; for performing self-calibration of the open-circuit current transformer based on the measurement current and the self-calibration current. The present invention can efficiently realize high-accuracy and low-cost on-site online calibration of open-circuit current transformers, can promote the transformation of current transformers from periodic calibration to status evaluation and inaccurate replacement, and can actively contribute to innovations in online monitoring and live calibration of current transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0069] Figure 1 Schematic diagram of the structure of a self-calibration device 100 for an open current sensor according to an embodiment of the present invention;

[0070] Figure 2 2. A structural diagram of a self-calibration device for an open-circuit current sensor according to an embodiment of the present invention;

[0071] Figure 3 is a flow chart of a calibration process according to an embodiment of the present invention;

[0072] Figure 4 FIG. 4 is a flow chart of a self-calibration method 400 for an open circuit current sensor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0073] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a thorough and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments shown in the accompanying drawings is not intended to limit the present invention. In the accompanying drawings, identical elements are denoted by the same reference numerals.

[0074] Unless otherwise specified, the terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have meanings consistent with the context of their relevant fields and should not be interpreted as idealized or overly formal.

[0075] The present invention designs a high-accuracy open-circuit current sensor self-calibration device. The basic working principle is: clamp an open-circuit current transformer to the circuit to be measured and perform a current offset to be measured; then perform a self-calibration of the open-circuit current transformer, calculate the ratio difference correction factor and phase difference correction factor at the current point of 1%-120%, and fit the amplitude compensation curve and phase compensation curve.

[0076] Figure 1 FIG. 1 is a schematic structural diagram of a self-calibration device 100 for an open current sensor according to an embodiment of the present invention. Figure 1As shown, the self-calibration device for an open-circuit current sensor provided in an embodiment of the present invention can efficiently achieve high-accuracy, low-cost on-site online calibration of an open-circuit current transformer, promote the transformation of current transformers from periodic calibration to status evaluation and inaccuracy replacement, and actively contribute to innovations in online monitoring and live calibration of current transformers. The self-calibration device 100 for an open-circuit current sensor provided in an embodiment of the present invention includes: an open-circuit current transformer 101 and a self-calibration system 102. The open-circuit current transformer 101 includes: a first injection winding 1011 and a second injection winding 1012 located on one side, and a detection winding 1013 located on the other side; the self-calibration system 102 includes: a first digital control signal generating unit 1021, a second digital control signal generating unit 1022, a first power amplifying unit 1023, a second power amplifying unit 1024, a first signal sampling unit 1025, a second signal sampling unit 1026, a third signal sampling unit 1027, and a self-calibration processing unit 1028. The first digital control signal generating unit 1021, the first power amplifying unit 1023, the first signal sampling unit 1025 and the first injection winding 1011 constitute a cancellation circuit; the second digital control signal generating unit 1022, the second power amplifying unit 1024, the second signal sampling unit 1026 and the second injection winding 1012 constitute a calibration circuit; the third signal sampling unit 1027 and the detection winding 1013 constitute a measurement circuit.

[0077] Preferably, the first injection winding 1011 is used for coupling and offsetting the background current on the primary side.

[0078] Preferably, the second injection winding 1012 is used to couple a self-calibration current for self-calibration.

[0079] Preferably, the detection winding 1013 is used to couple the currents injected by the circuit to be tested, the first injection winding and the second injection winding.

[0080] Preferably, the first digital control signal generating unit 1021 is connected to the self-calibration processing unit and the first power amplifying unit respectively, and is used to generate a first voltage signal corresponding to the offset current based on the first control command.

[0081] Preferably, the first power amplifying unit 1023 is connected to the first injection winding and the first signal sampling unit respectively, and is used to generate the offset current required for offset based on the first voltage signal.

[0082] Preferably, the second digital control signal generating unit 1022 is connected to the self-calibration processing unit and the second power amplification unit respectively, and is used to generate a second voltage signal corresponding to the self-calibration current based on the second control command.

[0083] Preferably, the second power amplifying unit 1024 is connected to the second injection winding and the second signal sampling unit respectively, and is used to generate a self-calibration current required for self-calibration based on the second voltage signal.

[0084] Preferably, the first signal sampling unit 1025 is connected to the self-calibration processing unit, and is used to sample the current of the offset circuit to obtain the offset current.

[0085] Preferably, the second signal sampling unit 1026 is connected to the self-calibration processing unit, and is used to sample the current of the calibration circuit to obtain the self-calibration current.

[0086] Preferably, the third signal sampling unit 1027 is connected to the detection winding and the self-calibration processing unit respectively, and is used to sample the measurement circuit to obtain the measurement current.

[0087] Preferably, the first signal sampling unit 1025, the second signal sampling unit 1026 and the third signal sampling unit 1027 each include: an I / V conversion circuit, a signal conditioning circuit and an A / D sampling circuit connected in sequence; wherein,

[0088] The I / V conversion circuit is used to convert the input current into voltage and output a voltage signal;

[0089] The signal conditioning circuit is used to perform signal conditioning on the input voltage signal;

[0090] The A / D sampling circuit is used to convert the conditioned voltage signal from an analog signal to a digital signal.

[0091] Preferably, the open-circuit current transformer to be measured is a clamp-on current transformer.

[0092] Preferably, the self-calibration processing unit 1028 is used to send the first control command and the second control command; to perform feedback control on the first digital control signal generating unit and the second digital control signal generating unit based on the offset current and the self-calibration current; to perform primary current offset of the open current transformer based on the measured current and the offset current; and to perform self-calibration of the open current transformer based on the measured current and the self-calibration current.

[0093] Combine Figure 2 As shown, in the present invention, the entire device consists of a clamp-on transformer and a self-calibration circuit system.

[0094] The clamp-on transformer consists of a housing, an iron core within the housing, two injection windings (first injection winding n3 and second injection winding n4) on the left half of the core, a detection winding on the right half of the core, and an "X"-shaped handle that controls the separation of the clamps. The injection windings have the same number of turns as the detection winding, and their placement can be flexibly adjusted to the same side of the core. The first and second injection windings are used for cancellation and self-calibration, respectively, coupling the primary current used for cancellation and the operating current used for self-calibration. The detection winding is used to couple the current injected by the measured circuit or the injection winding.

[0095] exist Figure 2 In the figure, i1, i2, i3, and i4 are the primary current to be measured, the secondary induced current, the offset current used for cancellation, and the self-calibration current used for self-calibration, respectively. n2, n3, and n4 are the number of turns of the winding used for measurement, the number of turns of the injection winding used for cancellation, and the number of turns of the injection winding used for self-calibration, respectively. S1 and S2 are the programmable switches for the injection circuit used for cancellation and the injection circuit used for self-calibration, respectively.

[0096] Combine Figure 2 As shown, the self-calibration circuit system consists of a digital control signal generating unit 1 (i.e., the first digital control signal generating unit), a digital control signal generating unit 2 (i.e., the second digital control signal generating unit), a power amplifier unit 1 (i.e., the first power amplifier unit), a power amplifier unit 2 (i.e., the second power amplifier unit), a signal sampling unit 1 (i.e., the first signal sampling unit), a signal sampling unit 2 (i.e., the second signal sampling unit), a signal sampling unit 3 (i.e., the third signal sampling unit), and a self-calibration processing unit. Power amplifier unit 1 outputs the offset current required for offset. Power amplifier unit 2 outputs the self-calibration current required for self-calibration. Digital control signal generating units 1 and 2 are controlled by the self-calibration processing unit to generate voltage signals corresponding to the offset current and the self-calibration current, which are output to the power amplifier unit. The signal sampling unit consists of an I / V conversion circuit, a signal conditioning circuit, and an A / D sampling circuit. The I / V conversion circuit performs I / V conversion on the currents in the injection and detection circuits, outputting voltage signals. The signal conditioning circuit amplifies, filters, and voltage-boosts the input signal, outputting a voltage signal that meets AD sampling requirements. The A / D sampling circuit converts the input voltage signal from analog to digital. Signal sampling unit 1 samples the injection circuit used for cancellation, signal sampling unit 2 samples the injection circuit used for self-calibration, and signal sampling unit 3 samples the measurement circuit used for detection. The self-calibration processing unit controls the entire cancellation and self-calibration process.

[0097] Preferably, the self-calibration processing unit 1028 performs primary current offset of the open current transformer based on the measured current and the offset current, including:

[0098] According to the measured current i2 of the measuring circuit after the open current transformer is clamped on the measured line, the initial value of the offset current i3 is generated to offset the line current i1;

[0099] By adjusting i3 so that the value of i2 decreases until it reaches 0 or is less than a preset current threshold, it is determined that the primary current compensation is completed.

[0100] In the present invention, the primary current offset method of the open current transformer is:

[0101] Step 1: After the open-circuit current transformer is clamped around the line under test, measure i2.

[0102] Step 2: The self-calibration processing unit generates an initial value of the offset injection current i3 based on i2 to offset the background current i1, which can be expressed as follows. Among them, there is a relationship between the currents: , where ε2 is the magnetomotive force to be offset.

[0103] Step 3: The self-calibration processing unit controls the injection current i3, and by adjusting i3, the value of i2 is reduced until it is 0 or less than the threshold i A When the current is offset once, the system enters the self-calibration mode.

[0104] Preferably, the self-calibration unit 1028 performs self-calibration of the open current transformer based on the measured current and the self-calibration current, including:

[0105] When the magnetic field generated by the line current i1 on the measured line in the iron core is zero or the amplitude is offset to zero, an equal ampere-turn current is injected through the second injection winding of the calibration circuit; wherein the magnitude of the equal ampere-turn current is a first preset percentage of the rated current;

[0106] Measure the measurement current i2 of the measurement circuit at this time, calculate the ratio difference correction factor and the phase difference correction factor of the open current transformer at this time, and determine whether the current ratio difference correction factor and the phase difference correction factor meet the amplitude range and the phase range;

[0107] When the amplitude range and phase range are met, the ratio difference correction factor and phase difference correction factor of the open current transformer are calculated when injecting the equal ampere-turn current of other preset percentages of the rated current, and the amplitude range and phase range are judged;

[0108] If all amplitudes and phases meet the amplitude range and phase range, it is determined that the open-type current transformer meets the accuracy requirement; otherwise, if there is an amplitude that does not meet the amplitude range or the phase does not meet the phase range, it is determined that the open-type current transformer does not meet the accuracy requirement.

[0109] Preferably, the self-calibration unit 1028 obtains the ratio difference correction factor and the phase difference correction factor and determines the amplitude range and the phase range in the following manner:

[0110] ,

[0111] ,

[0112] Among them, A 0i and are the amplitude and phase of the primary current i1 of the measured circuit when the equal ampere-turn current is injected for the i-th time; A 2i and are the amplitude and phase of the current i2 in the measuring circuit when the equal ampere-turn current is injected for the i-th time; f bi and δ bi are the ratio difference and phase difference of the open-circuit current transformer when the equal ampere-turn current is injected for the i-th time; and are the transformer ratio difference limit and ratio difference correction factor under the corresponding accuracy level respectively; and are the transformer phase difference limit and phase difference correction factor under the corresponding accuracy level; n2 is the number of turns of the detection winding.

[0113] In the present invention, the self-calibration method of the open current transformer is:

[0114] Step 1: When the magnetic field generated by the measured circuit i1 in the iron core is zero or the amplitude is offset to zero, i4 injects a current equal to 1% of the rated current and measures the corresponding current i2.

[0115] Step 2: Calculate the ratio difference correction factor and phase difference correction factor of the open current transformer at this time, and determine whether the current ratio difference correction factor and phase difference correction factor meet the amplitude range and phase range. Assuming that during measurement, the amplitude of i1 is A0 and the phase is φ0, and the amplitude of i2 is A2 and the phase is φ2, the ratio difference correction factor and phase difference correction factor can be obtained and the amplitude range and phase range can be determined using the following method:

[0116] ,

[0117] ,

[0118] Among them, A 0i and are the amplitude and phase of the primary current i1 of the measured circuit when the equal ampere-turn current is injected for the i-th time; A 2i and are the amplitude and phase of the current i2 in the measuring circuit when the equal ampere-turn current is injected for the i-th time; f bi and δ bi are the ratio difference and phase difference of the open-circuit current transformer when the equal ampere-turn current is injected for the i-th time; and are the transformer ratio difference limit and ratio difference correction factor under the corresponding accuracy level respectively; and are the transformer phase difference limit and phase difference correction factor under the corresponding accuracy level; n2 is the number of turns of the detection winding.

[0119] Step 3: If the ratio difference correction factor and phase difference correction factor satisfy the amplitude range and phase range when injecting an equal ampere-turn current of 1% of the rated current, then measure and calculate the ratio difference correction factor and phase difference correction factor at 5%, 20%, 100%, and 120% according to the above steps, and determine the amplitude range and phase range respectively. In the present invention, when injecting equal ampere-turn currents of different percentages of the rated current, the corresponding amplitude range and phase range are different.

[0120] Step 4: If all amplitudes and phases meet the amplitude range and phase range, it is determined that the open-type current transformer meets the accuracy requirement; otherwise, if there is an amplitude that does not meet the amplitude range or the phase does not meet the phase range, it is determined that the open-type current transformer does not meet the accuracy requirement.

[0121] Preferably, the self-calibration unit 1028 is further configured to:

[0122] Fitting is performed based on all ratio difference correction factors and phase difference correction factors to obtain an amplitude compensation curve and a phase compensation curve.

[0123] In the present invention, the ratio difference correction factors and phase difference correction factors at calibration points such as 1%, 5%, 20%, 100%, and 120% can be fitted separately (the fitting method can use polynomial fitting, but is not limited to polynomial fitting), and an amplitude compensation curve and a phase compensation curve can be fitted and stored in the self-calibration unit for compensation of non-calibration points.

[0124] Specifically, combined Figure 3 As shown in Figure 1, the self-calibration process of the open-type current transformer includes:

[0125] Step 1: Clamp the open-circuit current transformer to the circuit to be tested and proceed to the next step;

[0126] Step 2: Measure i2. If i2 is 0, go to step 4; if i2 is not 0, go to the next step;

[0127] Step 3: Close the "control switch (S1)" to start the current offset function of the circuit under test. When the current offset function is completed, proceed to the next step;

[0128] Step 4: Close the "control switch (S2)" to start self-calibration, set the calibration current points (including 1%, 5%, 20%, 100%, and 120% of the rated current), and proceed to the next step;

[0129] Step 5: According to the set calibration current point, the self-calibration processing unit controls the digital control signal generating unit to generate a self-calibration signal and proceed to the next step;

[0130] Step 6: Collect the signals of the injection winding and the detection winding and proceed to the next step;

[0131] Step 7: The self-calibration processing unit processes the collected injection winding signal and detection signal data, calculates the ratio difference correction factor and the phase difference correction factor, and performs a range judgment; if the judgment result is that the ratio difference correction factor and the phase difference correction factor meet the amplitude range and the phase range, the next step is carried out; otherwise, it is directly determined that the open current transformer does not meet the accuracy requirements and needs to be repaired, and the self-calibration process ends;

[0132] Step 8: Determine whether all self-calibration current points have completed self-calibration. If so, proceed to the next step. If not, proceed to step 4 to set the next calibration current point.

[0133] Step 9: If all amplitudes and phases meet the amplitude range and phase range, it is determined that the open current transformer meets the accuracy requirements;

[0134] Step 10: Fit the amplitude and phase compensation curve and store it in the self-calibration processing unit.

[0135] Figure 4 FIG. 4 is a flow chart of a self-calibration method 400 for an open current sensor according to an embodiment of the present invention. Figure 4 As shown, an online self-calibration method 400 based on the self-calibration device of the open current sensor provided by an embodiment of the present invention starts from step 401. In step 401, a signal sampling unit samples a measurement circuit to obtain a measurement current.

[0136] In step 402 , the cancellation circuit is connected to a self-calibration device, and the self-calibration processing unit sends a first control command to a first digital control signal generating unit.

[0137] In step 403 , a first digital control signal generating unit generates a first voltage signal corresponding to the offset current based on the first control command.

[0138] In step 404 , the first power amplifying unit generates a cancellation current required for cancellation based on the first voltage signal.

[0139] In step 405 , the first signal sampling unit samples the cancellation circuit to obtain the cancellation current.

[0140] In step 406 , the self-calibration processing unit performs primary current cancellation of the open current transformer based on the cancellation current and the measured current, and disconnects the cancellation circuit after the cancellation is completed.

[0141] In step 407 , the calibration circuit is connected to the self-calibration device, and the self-calibration processing unit sends a second control command to the second digital control signal generating unit.

[0142] In step 408 , the second digital control signal generating unit generates a second voltage signal corresponding to the self-calibration current based on the second control command.

[0143] In step 409 , the second power amplifying unit generates a self-calibration current required for self-calibration based on the second voltage signal.

[0144] In step 410 , the self-calibration processing unit performs self-calibration of the open circuit current transformer based on the measured current and the self-calibration current.

[0145] Preferably, the first signal sampling unit, the second signal sampling unit and the third signal sampling unit each comprise: an I / V conversion circuit, a signal conditioning circuit and an A / D sampling circuit connected in sequence; wherein,

[0146] The input current is converted into voltage using an I / V conversion circuit, and a voltage signal is output;

[0147] Performing signal conditioning on the input voltage signal using a signal conditioning circuit;

[0148] The conditioned voltage signal is converted from an analog signal to a digital signal using an A / D sampling circuit.

[0149] Preferably, the open-circuit current transformer to be measured is a clamp-on current transformer.

[0150] Preferably, the self-calibration processing unit performs primary current offset of the open current transformer based on the offset current and the measured current, comprising:

[0151] According to the measured current i2 of the measuring circuit after the open current transformer is clamped on the measured line, the initial value of the offset current i3 is generated to offset the line current i1;

[0152] By adjusting i3 so that the value of i2 decreases until it reaches 0 or is less than a preset current threshold, it is determined that the primary current compensation is completed.

[0153] Preferably, the self-calibration unit performs self-calibration of the open current transformer based on the measured current and the self-calibration current, comprising:

[0154] When the magnetic field generated by the line current i1 on the measured line in the iron core is zero or the amplitude is offset to zero, an equal ampere-turn current is injected through the second injection winding of the calibration circuit; wherein the magnitude of the equal ampere-turn current is a first preset percentage of the rated current;

[0155] Measure the measurement current i2 of the measurement circuit at this time, calculate the ratio difference correction factor and the phase difference correction factor of the open current transformer at this time, and determine whether the current ratio difference correction factor and the phase difference correction factor meet the amplitude range and the phase range;

[0156] When the amplitude range and phase range are met, the ratio difference correction factor and phase difference correction factor of the open current transformer are calculated when injecting the equal ampere-turn current of other preset percentages of the rated current, and the amplitude range and phase range are judged;

[0157] If all amplitudes and phases meet the amplitude range and phase range, it is determined that the open-type current transformer meets the accuracy requirement; otherwise, if there is an amplitude that does not meet the amplitude range or the phase does not meet the phase range, it is determined that the open-type current transformer does not meet the accuracy requirement.

[0158] Preferably, the method uses the following method to obtain the ratio difference correction factor and the phase difference correction factor, and to determine the amplitude range and the phase range, including:

[0159] ,

[0160] ,

[0161] Among them, A 0i and are the amplitude and phase of the primary current i1 of the measured circuit when the equal ampere-turn current is injected for the i-th time; A 2i and are the amplitude and phase of the current i2 in the measuring circuit when the equal ampere-turn current is injected for the i-th time; f bi and δ bi are the ratio difference and phase difference of the open-circuit current transformer when the equal ampere-turn current is injected for the i-th time; and are the transformer ratio difference limit and ratio difference correction factor under the corresponding accuracy level respectively; and are the transformer phase difference limit and phase difference correction factor under the corresponding accuracy level; n2 is the number of turns of the detection winding.

[0162] Preferably, the method further comprises:

[0163] The self-calibration unit performs fitting according to all ratio difference correction factors and phase difference correction factors to obtain an amplitude compensation curve and a phase compensation curve.

[0164] The self-calibration method 400 for an open-circuit current sensor according to an embodiment of the present invention corresponds to the self-calibration device 100 for an open-circuit current sensor according to another embodiment of the present invention, and will not be described in detail herein.

[0165] The present invention has been described with reference to a few embodiments. However, it is apparent to those skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the present invention.

[0166] Generally, all terms used in this disclosure are to be interpreted according to their ordinary meaning in the art, unless explicitly defined otherwise herein. All references to "a / the / the [device, component, etc.]" are to be interpreted openly as referring to at least one instance of the device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily need to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0167] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0168] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0169] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0170] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 The steps for the function specified in one or more boxes.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A self-calibration device for an open-circuit current transformer, characterized in that: The device includes: an open current transformer and a self-calibration system, wherein the open current transformer includes: a first injection winding and a second injection winding located on one side, and a detection winding located on the other side; the self-calibration system includes: a first digital control signal generating unit, a second digital control signal generating unit, a first power amplifying unit, a second power amplifying unit, a first signal sampling unit, a second signal sampling unit, a third signal sampling unit and a self-calibration processing unit; the first digital control signal generating unit, the first power amplifying unit, the first signal sampling unit and the first injection winding constitute a cancellation circuit; the second digital control signal generating unit, the second power amplifying unit, the second signal sampling unit and the second injection winding constitute a calibration circuit; the third signal sampling unit and the detection winding constitute a measurement circuit; wherein, The first injection winding is used for coupling and offsetting the background current of the primary side; The second injection winding is used to couple a self-calibration current for self-calibration; The detection winding is used to couple the current injected by the circuit to be tested, the first injection winding and the second injection winding; The first digital control signal generating unit is connected to the self-calibration processing unit and the first power amplifying unit respectively, and is used to generate a first voltage signal corresponding to the offset current based on the first control command; The first power amplifying unit is connected to the first injection winding and the first signal sampling unit respectively, and is used to generate a compensation current required for compensation based on the first voltage signal; The second digital control signal generating unit is connected to the self-calibration processing unit and the second power amplifying unit respectively, and is used to generate a second voltage signal corresponding to the self-calibration current based on the second control command; The second power amplifying unit is connected to the second injection winding and the second signal sampling unit respectively, and is used to generate a self-calibration current required for self-calibration based on the second voltage signal; The first signal sampling unit is connected to the self-calibration processing unit and is used to sample the current of the offset circuit to obtain the offset current; The second signal sampling unit is connected to the self-calibration processing unit and is used to sample the current of the calibration circuit to obtain the self-calibration current; The third signal sampling unit is connected to the detection winding and the self-calibration processing unit respectively, and is used to sample the measurement circuit to obtain the measurement current; The self-calibration processing unit is used to send the first control command and the second control command; to perform feedback control on the first digital control signal generating unit and the second digital control signal generating unit based on the offset current and the self-calibration current; to perform primary current offset of the open current transformer based on the measured current and the offset current; and to perform self-calibration of the open current transformer based on the measured current and the self-calibration current.

2. The device according to claim 1, characterized in that The first signal sampling unit, the second signal sampling unit and the third signal sampling unit each include: an I / V conversion circuit, a signal conditioning circuit and an A / D sampling circuit connected in sequence; wherein, The I / V conversion circuit is used to convert the input current into voltage and output a voltage signal; The signal conditioning circuit is used to perform signal conditioning on the input voltage signal; The A / D sampling circuit is used to convert the conditioned voltage signal from an analog signal to a digital signal.

3. The device according to claim 1, characterized in that The open-type current transformer to be measured is a clamp-on current transformer.

4. The device according to claim 1, characterized in that The self-calibration processing unit performs primary current offset of the open current transformer based on the measured current and the offset current, including: According to the measured current i2 of the measuring circuit after the open current transformer is clamped on the measured line, the initial value of the offset current i3 is generated to offset the line current i1; By adjusting i3 so that the value of i2 decreases until it reaches 0 or is less than a preset current threshold, it is determined that the primary current compensation is completed.

5. The device according to claim 1, characterized in that The self-calibration processing unit performs self-calibration of the open-circuit current transformer based on the measured current and the self-calibration current, including: When the magnetic field generated by the line current i1 on the measured line in the iron core is zero or the amplitude is offset to zero, an equal ampere-turn current is injected through the second injection winding of the calibration circuit; wherein the magnitude of the equal ampere-turn current is a first preset percentage of the rated current; Measure the measurement current i2 of the measurement circuit at this time, calculate the ratio difference correction factor and the phase difference correction factor of the open current transformer at this time, and determine whether the current ratio difference correction factor and the phase difference correction factor meet the amplitude range and the phase range; When the amplitude range and phase range are met, the ratio difference correction factor and phase difference correction factor of the open current transformer are calculated when injecting the equal ampere-turn current of other preset percentages of the rated current, and the amplitude range and phase range are judged; If all amplitudes and phases meet the amplitude range and phase range, it is determined that the open-type current transformer meets the accuracy requirement; otherwise, if there is an amplitude that does not meet the amplitude range or the phase does not meet the phase range, it is determined that the open-type current transformer does not meet the accuracy requirement.

6. The device according to claim 5, characterized in that The self-calibration processing unit obtains the ratio difference correction factor and the phase difference correction factor and determines the amplitude range and the phase range in the following manner: Among them, A 0i and are the amplitude and phase of the primary current i1 of the measured circuit when the equal ampere-turn current is injected for the i-th time; A 2i and are the amplitude and phase of the current i2 in the measuring circuit when the equal ampere-turn current is injected for the i-th time; f bi and δ bi are the ratio difference and phase difference of the open-circuit current transformer when the equal ampere-turn current is injected for the i-th time; α ci and α bi are the transformer ratio difference limit and ratio difference correction factor under the corresponding accuracy level; β ci and β bi are the transformer phase difference limit and phase difference correction factor under the corresponding accuracy level; n2 is the number of turns of the detection winding.

7. The device according to claim 5, characterized in that The self-calibration processing unit is further used for: Fitting is performed based on all ratio difference correction factors and phase difference correction factors to obtain an amplitude compensation curve and a phase compensation curve.

8. An online self-calibration method for a self-calibration device for an open-circuit current transformer according to any one of claims 1 to 7, characterized in that: The method comprises: The third signal sampling unit samples the measurement circuit to obtain a measurement current; The cancellation circuit is connected to the self-calibration device, and the self-calibration processing unit sends a first control command to the first digital control signal generating unit; A first digital control signal generating unit generates a first voltage signal corresponding to the offset current based on the first control command; The first power amplifying unit generates a compensation current required for compensation based on the first voltage signal; The first signal sampling unit samples the offset circuit to obtain the offset current; The self-calibration processing unit performs primary current cancellation of the open current transformer based on the cancellation current and the measured current, and disconnects the cancellation circuit after the cancellation is completed; The calibration circuit is connected to the self-calibration device, and the self-calibration processing unit sends a second control command to the second digital control signal generating unit; A second digital control signal generating unit generates a second voltage signal corresponding to the self-calibration current based on the second control command; The second power amplifying unit generates a self-calibration current required for self-calibration based on the second voltage signal; The self-calibration processing unit performs self-calibration of the open-circuit current transformer based on the measured current and the self-calibration current.

9. The method according to claim 8, characterized in that The first signal sampling unit, the second signal sampling unit and the third signal sampling unit each include: an I / V conversion circuit, a signal conditioning circuit and an A / D sampling circuit connected in sequence; wherein, The input current is converted into voltage using an I / V conversion circuit, and a voltage signal is output; Performing signal conditioning on the input voltage signal using a signal conditioning circuit; The conditioned voltage signal is converted from an analog signal to a digital signal using an A / D sampling circuit.

10. The method according to claim 8, characterized in that The open-type current transformer to be measured is a clamp-on current transformer.

11. The method according to claim 8, characterized in that The self-calibration processing unit performs primary current offset of the open current transformer based on the offset current and the measurement current, including: According to the measured current i2 of the measuring circuit after the open current transformer is clamped on the measured line, the initial value of the offset current i3 is generated to offset the line current i1; By adjusting i3 so that the value of i2 decreases until it reaches 0 or is less than a preset current threshold, it is determined that the primary current compensation is completed.

12. The method according to claim 8, characterized in that The self-calibration processing unit performs self-calibration of the open-circuit current transformer based on the measured current and the self-calibration current, including: When the magnetic field generated by the line current i1 on the measured line in the iron core is zero or the amplitude is offset to zero, an equal ampere-turn current is injected through the second injection winding of the calibration circuit; wherein the magnitude of the equal ampere-turn current is a first preset percentage of the rated current; Measure the measurement current i2 of the measurement circuit at this time, calculate the ratio difference correction factor and the phase difference correction factor of the open current transformer at this time, and determine whether the current ratio difference correction factor and the phase difference correction factor meet the amplitude range and the phase range; When the amplitude range and phase range are met, the ratio difference correction factor and phase difference correction factor of the open current transformer are calculated when injecting the equal ampere-turn current of other preset percentages of the rated current, and the amplitude range and phase range are judged; If all amplitudes and phases meet the amplitude range and phase range, it is determined that the open-type current transformer meets the accuracy requirement; otherwise, if there is an amplitude that does not meet the amplitude range or the phase does not meet the phase range, it is determined that the open-type current transformer does not meet the accuracy requirement.

13. The method according to claim 12, characterized in that The method uses the following method to obtain the ratio difference correction factor and the phase difference correction factor, and to determine the amplitude range and the phase range, including: Among them, A 0i and are the amplitude and phase of the primary current i1 of the measured circuit when the equal ampere-turn current is injected for the i-th time; A 2i and are the amplitude and phase of the current i2 in the measuring circuit when the equal ampere-turn current is injected for the i-th time; f bi and δ bi are the ratio difference and phase difference of the open-circuit current transformer when the equal ampere-turn current is injected for the i-th time; α ci and α bi are the transformer ratio difference limit and ratio difference correction factor under the corresponding accuracy level; β ci and β bi are the transformer phase difference limit and phase difference correction factor under the corresponding accuracy level; n2 is the number of turns of the detection winding.

14. The method according to claim 12, characterized in that The method further comprises: The self-calibration processing unit performs fitting according to all ratio difference correction factors and phase difference correction factors to obtain an amplitude compensation curve and a phase compensation curve.

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