On-line monitoring traceable calibration device and method for multi-channel voltage transformer

Abstract

The application relates to a traceable calibration device and method for online monitoring of a multi-channel voltage transformer. The device part mainly comprises a control unit, a plurality of independent voltage output channels and a measurement unit. The control unit comprises a microcontroller and a field programmable gate array which work cooperatively. Each voltage output channel comprises a direct digital synthesis waveform generator controlled by the field programmable gate array and a linear power amplifier connected with the output end of the direct digital synthesis waveform generator. The input end of the measurement unit is connected with the output end of each voltage output channel. The microcontroller receives the measurement value of the measurement unit, compares the measurement value with a set value to form a closed-loop voltage control. The application can realize independent precise adjustment of the voltage amplitude and phase of each channel, and the closed-loop feedback control of the measurement unit can guarantee the high precision and high stability of the output voltage, so that efficient and high-precision traceable calibration of online monitoring of the voltage transformer is realized.

Description

Technical Field

[0001] This application relates to the field of online monitoring technology for voltage transformers, and in particular to a traceability calibration device and calibration method for online monitoring of multi-channel voltage transformers. Background Technology

[0002] Voltage transformers are a crucial component of electricity metering systems, and their accuracy directly impacts the fairness and impartiality of electricity trade settlement. With the continuous expansion of the power grid, the number of voltage transformers requiring calibration is enormous. Traditional periodic power outage calibration methods not only severely affect power supply reliability but also result in significant waste of human and material resources. To address the numerous problems associated with traditional power outage calibration, online monitoring technology for voltage transformers has rapidly developed. Online monitoring devices acquire analog voltage signals and synchronous clock signals output from the metering windings of voltage transformers in parallel, enabling online calculation of the metering errors of operating voltage transformers.

[0003] However, as a metering instrument, the accuracy of online voltage transformer monitoring devices requires periodic traceability calibration. Currently, there is a lack of standardized traceability calibration equipment specifically for multi-channel online voltage transformer monitoring devices. Existing voltage calibration devices typically only have single or dual-channel outputs, requiring calibration of each online monitoring device individually, resulting in low calibration efficiency. Even for devices with multi-channel outputs, the voltage amplitude and phase of each channel cannot be independently adjusted, failing to simulate the real-world operating conditions where amplitude and phase differences exist between phases. Furthermore, it cannot meet the need for simultaneous calibration of online monitoring devices with different ranges and transformation ratios. In addition, existing calibration devices generally lack high-precision closed-loop control methods for the output voltage, making it difficult to guarantee the stability and accuracy of the output voltage.

[0004] Based on the above situation, for existing online monitoring devices for multi-channel voltage transformers, how to provide a traceability calibration scheme that can achieve independent and precise adjustable output of multi-channel voltage and ensure high accuracy and stability of output voltage is a problem to be solved in this technical field. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this application provides a traceability calibration device and method for online monitoring of multi-channel voltage transformers. It achieves independent and precise adjustment of the voltage amplitude and phase of each channel through a multi-channel independent direct digital synthesized waveform generator, and combines this with closed-loop feedback control of the measurement unit to ensure high accuracy and stability of the output voltage, thereby realizing efficient and high-precision traceability calibration for online monitoring of voltage transformers.

[0006] The embodiments of this application adopt the following technical solutions: In the first aspect, this application provides a traceability calibration device for online monitoring of multi-channel voltage transformers, including a control unit, multiple independent voltage output channels, and a measurement unit; The control unit includes a microcontroller and a field-programmable gate array that work together; Each of the voltage output channels includes a direct digital synthesized waveform generator controlled by the field-programmable gate array and a linear power amplifier connected to the output of the direct digital synthesized waveform generator. The voltage amplitude and phase of each voltage output channel are independently adjustable. The input terminal of the measurement unit is connected to the output terminal of each voltage output channel, and is used to synchronously acquire the actual output voltage value of each voltage output channel; The microcontroller receives the measured values ​​from the measurement unit, compares the measured values ​​with the set values, and adjusts the outputs of each of the direct digital synthesized waveform generators through the field programmable gate array according to the comparison results to form closed-loop voltage control.

[0007] The above technical solution employs a control unit that coordinates a microcontroller and a field-programmable gate array to control multiple independent direct digital synthesized waveform generators to generate voltage waveforms. These waveforms are then amplified by a linear power amplifier and output. The measurement unit synchronously collects the actual output voltage values ​​of each channel and feeds them back to the microcontroller to form a closed-loop voltage control. This achieves independent and precise output of voltage amplitude and phase for multiple channels. Each channel can be independently set with different voltage parameters, enabling high-precision traceability calibration of multiple online monitoring devices for voltage transformers simultaneously. This solves the technical problem of the lack of multi-channel, independently adjustable, high-precision, and highly stable traceability calibration equipment for online monitoring devices of voltage transformers in the existing technology.

[0008] In some implementations, the field-programmable gate array provides a unified reference clock signal and a synchronization trigger signal to the direct digital synthesized waveform generators of each voltage output channel, and achieves phase synchronization and independent phase adjustment between the output voltages of each voltage output channel by writing independent phase offset values ​​to the phase registers of each direct digital synthesized waveform generator.

[0009] The above technical solution utilizes a field-programmable gate array (FPGA) to provide a unified reference clock signal and a synchronization trigger signal to each direct digital synthesized waveform generator (DDS), ensuring strict phase synchronization of the output voltages of each channel. Simultaneously, by writing independent phase offset values ​​to the phase registers of each DDS, independent phase adjustment of each channel is achieved, resolving the contradiction between phase synchronization and independent adjustment in multi-channel output. This enables the traceability calibration device to accurately simulate the actual operating conditions where phase differences exist between phase voltages in each phase.

[0010] In some implementations, in the closed-loop voltage control, the microcontroller calculates a compensation amount using a PID control algorithm based on the deviation between the measured value and the set value of the measurement unit, and sends the compensation amount to the field-programmable gate array (FPGA). The FPGA adjusts the amplitude control word and / or phase offset value of the corresponding direct digital synthesized waveform generator according to the compensation amount until the deviation between the measured value and the set value of the measurement unit is less than a preset threshold.

[0011] The above technical solution employs a PID control algorithm to calculate the compensation amount in real time based on the deviation between the measured value and the set value. Adaptive closed-loop regulation is achieved by adjusting the amplitude control word and / or phase offset value of the direct digital synthesized waveform generator. A convergence threshold criterion is set to ensure that the output voltage can quickly converge to the set value and maintain high stability under different operating conditions, thereby further improving the voltage output accuracy and stability of the traceability calibration device.

[0012] In some embodiments, a clock reference unit is also included, which includes a GPS receiver and a BeiDou receiver, for receiving GPS satellite signals and BeiDou satellite signals and outputting a standard second pulse signal and an IRIG-B time code signal to the control unit. The control unit uses the standard second pulse signal as the time reference of the traceability calibration device.

[0013] Through the above technical solution, the integration of GPS receiver and Beidou receiver realizes dual-mode satellite signal reception and timing. When one satellite signal is blocked or interfered with, it can switch to the other, which improves the reliability and availability of the time reference. The output standard second pulse signal and IRIG-B time code signal provide a high-precision time reference for the traceability calibration device and provide a standard time reference for the synchronous clock performance verification of the voltage transformer online monitoring device.

[0014] In some embodiments, the clock reference unit is also used to receive the IRIG-B code signal output by the online monitoring device of the voltage transformer under test, convert the IRIG-B code signal into an electrical signal second pulse, and measure the time delay error between the electrical signal second pulse and the standard second pulse signal.

[0015] By using the above technical solution, the IRIG-B code signal output by the online monitoring device of the voltage transformer under test is converted into an electrical signal second pulse, and the time delay is compared with the standard second pulse signal output by the clock reference unit. This enables accurate measurement of the synchronous clock delay of the device under test, ensuring the consistency of the time reference for synchronous measurement of the online monitoring device, thereby improving the accuracy of error measurement of the online monitoring device.

[0016] Secondly, this application provides a calibration method for online monitoring of a multi-channel voltage transformer, applied to the traceability calibration device for online monitoring of the multi-channel voltage transformer described in the first aspect. The method includes the following steps: Connect each voltage output channel of the traceability calibration device to the voltage input terminal of the online monitoring device for the voltage transformer under test; Set the output voltage amplitude and phase parameters for each of the voltage output channels; When the voltage output is started, each of the direct digital synthesized waveform generators generates a voltage waveform signal according to the set parameters, which is then amplified by the corresponding linear power amplifier and output as a standard test voltage. The measurement unit synchronously acquires the actual output voltage value of each voltage output channel. The microcontroller adjusts the output of each direct digital synthesized waveform generator through the field programmable gate array according to the deviation between the actual output voltage value and the set value, so that the actual output voltage value of each voltage output channel converges to the set value. The measurement data of the online monitoring device for the voltage transformer under test is obtained, and the measurement data is compared with the measurement value of the measurement unit to calculate the ratio error and angle error of the online monitoring device for the voltage transformer under test.

[0017] The above technical solution integrates voltage output, closed-loop control, data acquisition, and error calculation into a coherent calibration process. Closed-loop voltage control ensures the accuracy and stability of the standard test voltage, and the error is automatically calculated by comparing the measurement data of the device under test with the standard measurement value, thus achieving high-precision calibration of the ratio difference and angle difference of the online monitoring device of the voltage transformer.

[0018] In some implementations, an automatic switching step between multiple calibration points is also included: Multiple calibration points are preset, each corresponding to a different voltage amplitude and / or phase parameter; After completing the calculation of the ratio difference and angle difference error at the current calibration point, the microcontroller automatically switches to the voltage amplitude and phase parameters corresponding to the next calibration point, and repeats the steps of voltage output, closed-loop voltage control and error calculation until the calibration of all preset calibration points is completed.

[0019] By using the above technical solution, multiple calibration points are preset and the system automatically switches to the next calibration point after completing the current calibration point. This achieves automated calibration of multiple calibration points across the entire range, eliminating the need for manual parameter setting and operation at each point. This greatly improves calibration efficiency and reduces the workload of manual operation and the errors introduced by manual operation.

[0020] In some implementations, when setting the parameters of each voltage output channel, the first voltage output channel is set as a reference channel with a rated voltage value, and the remaining voltage output channels are respectively set with ratio difference and angle difference values ​​relative to the first voltage output channel, so as to establish a known amplitude deviation and phase deviation relationship between each voltage output channel.

[0021] By using the above technical solution, and by setting the first voltage output channel as the reference channel and the other channels with ratio and angle differences relative to the reference channel, a known amplitude and phase deviation relationship is established between the channels. This can simulate the working condition where the voltage of each phase differs in actual operation, and also meet the need to simultaneously calibrate online monitoring devices for voltage transformers with different ranges and ratios, thereby enhancing the applicability and flexibility of the device.

[0022] In some embodiments, the step of acquiring the measurement data of the online monitoring device for the voltage transformer under test includes: establishing a communication connection with the online monitoring device for the voltage transformer under test through a communication interface, automatically reading the voltage amplitude, phase, and error data of the online monitoring device for the voltage transformer under test; the microcontroller comparing the automatically read measurement data with the measurement values ​​of the measurement unit, automatically calculating the ratio difference and phase difference errors, and storing the calibration results.

[0023] The above technical solution automatically reads the measurement data of the online monitoring device of the voltage transformer under test through the communication interface and automatically calculates the ratio difference and angle difference error, avoiding the manual operation of reading data and calculating errors. This saves labor costs, eliminates human interpretation errors, and improves the accuracy and reliability of calibration results.

[0024] In some implementations, a second pulse delay calibration step is also included: The IRIG-B code signal output by the online monitoring device of the voltage transformer under test is input to the clock reference unit of the traceability calibration device; The clock reference unit converts the received IRIG-B code signal into an electrical signal second pulse; The time delay error between the electrical signal second pulse and the standard second pulse signal output by the clock reference unit is measured to determine the synchronous clock performance of the online monitoring device for the voltage transformer under test.

[0025] By using the above technical solution, the IRIG-B code signal of the device under test is converted into an electrical signal second pulse and compared with the time delay of a standard second pulse. This achieves quantitative calibration of the synchronous clock delay of the online monitoring device for voltage transformers, ensuring the consistency of the time reference of the online monitoring device with the national standard time, thereby improving the accuracy of error calculation based on the synchronous clock by the online monitoring device.

[0026] In some implementations, the closed-loop voltage control employs a feedforward prediction and adaptive variable integral PID composite control method, specifically including: when the setpoint changes abruptly due to a switching calibration point, the microcontroller first calculates the feedforward amplitude control word based on the target setpoint and the pre-stored voltage output channel transfer function, and outputs it to the direct digital synthesized waveform generator to control the output voltage to approach the target setpoint in an open loop; subsequently, the microcontroller switches to PID closed-loop feedback control, calculates the deviation rate between the actual output voltage value and the setpoint in real time, and dynamically adjusts the integral coefficient of the PID control according to the deviation rate: when the deviation rate is greater than a first threshold, the integral coefficient is set to zero; when the deviation rate is between the first threshold and a second threshold, the integral coefficient is linearly increased as the deviation rate decreases; when the deviation rate is less than the second threshold, the integral coefficient is set to a maximum preset value until the deviation rate is less than a preset convergence threshold.

[0027] The above technical solution, by introducing a composite control scheme of feedforward prediction and adaptive variable integral PID, solves the technical challenge of a standard source struggling to balance rapid dynamic response (no overshoot) and extremely high steady-state accuracy (no oscillation) when facing unknown, complex, and variable loads (different models of online monitoring devices) and performing high-frequency calibration point switching. Feedforward control eliminates delay and overshoot during abrupt changes in one step; the variable integral algorithm based on deviation rate segmentation acts as an intelligent braking and fine-tuning mechanism, cutting off integral anti-oscillation for large deviations and maximizing integral to eliminate residual errors for small deviations. This composite control strategy for a specific scenario is a deeply optimized solution for automated traceability calibration processes, reducing convergence time to within 0.2 seconds and ensuring 0.02% accuracy while protecting the tested equipment.

[0028] In summary, this application includes at least the following beneficial technical effects: 1. By using multiple independent direct digital synthesized waveform generators in conjunction with the closed-loop voltage control of the measurement unit, independent and precise adjustment of the voltage amplitude and phase of multiple channels is achieved. This enables high-precision traceability calibration of multiple online monitoring devices for voltage transformers simultaneously. The calibration efficiency is 2 to 4 times higher than that of single-channel or dual-channel devices, solving the technical problem of the lack of multi-channel independently adjustable high-precision traceability calibration devices in the existing technology.

[0029] 2. It integrates GPS and Beidou dual-mode synchronous clock references and has the function of measuring the time delay of the second pulse of the IRIG-B code-to-electrical signal. The time delay measurement accuracy is better than 0.5 microseconds, which realizes the accurate verification of the synchronous clock performance of the voltage transformer online monitoring device and ensures the consistency of the time reference for online monitoring error measurement.

[0030] 3. The device automatically reads the measurement data of the device under test through the communication interface and automatically calculates the calibration error. With the automatic switching function of multiple calibration points, the calibration process is highly automated, avoiding human interpretation errors and improving calibration efficiency and accuracy. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is an overall architecture diagram of the traceability calibration device for online monitoring of multi-channel voltage transformers provided in the embodiments of this application; Figure 2 This is a schematic diagram of the multi-channel voltage output and closed-loop control provided in the embodiments of this application; Figure 3 A schematic diagram of multi-channel phase synchronization control for a direct digital synthesized waveform generator provided in this application embodiment; Figure 4 This application provides a schematic diagram of the clock reference and second pulse delay measurement principle. Figure 5 A flowchart illustrating the calibration method for online monitoring of multi-channel voltage transformers provided in this application embodiment. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Furthermore, the technical features involved in the various embodiments described below can be combined with each other as long as they do not conflict with each other. The application will now be described in detail with reference to the accompanying drawings and embodiments. Example 1

[0034] This embodiment describes the overall architecture of a traceability calibration device for online monitoring of multi-channel voltage transformers.

[0035] It should be noted that voltage transformer online monitoring devices, as measuring instruments, require periodic traceability calibration. However, the existing calibration equipment has insufficient channels, and each channel cannot independently adjust the voltage amplitude and phase, which cannot meet the requirement of calibrating multiple online monitoring devices simultaneously.

[0036] To solve the above problems, refer to Figure 1This embodiment provides a traceability calibration device for online monitoring of multi-channel voltage transformers. The traceability calibration device mainly consists of a control unit, a clock reference unit, a measurement unit, a voltage output channel, a communication unit, an input display unit, and a power supply unit. The units interact with each other through an internal bus to collaboratively complete the traceability calibration function of the online monitoring device for voltage transformers.

[0037] The control unit employs a system architecture that combines a microcontroller and a field-programmable gate array (FPGA), serving as the core control and data processing unit of the entire system. The microcontroller is responsible for system management, human-machine interaction, communication protocol processing, and error calculation; the FPGA is responsible for high-speed signal generation, timing control, parallel data acquisition, and digital signal processing. Working together, they enable functions such as measurement data processing and error calculation, signal generation and control for voltage output channels, alarm handling, key input processing, and communication data processing.

[0038] In this embodiment, the traceability calibration device includes four independent voltage output channels. (Reference) Figure 2 Each voltage output channel includes a direct digital synthesized waveform generator (DDS-PGR) and a linear power amplifier. The DDS-PGR is controlled by a field-programmable gate array (FPGA) to generate high-precision analog voltage waveform signals. The linear power amplifier is connected to the output of the DDS-PGR to amplify the voltage waveform signals, enabling them to drive the online monitoring device for the voltage transformer under test. The linear power amplifier features low distortion and high stability. The output voltage amplitude and phase of each voltage output channel can be independently set, thus achieving multi-channel independently adjustable voltage output.

[0039] The measurement unit serves as the working standard for calibration accuracy. It is designed with a high-precision, multi-channel voltage standard meter and uses a 16-bit analog-to-digital converter chip in conjunction with a precision signal conditioning circuit. The input terminal of the measurement unit is connected to the output terminals of the four voltage output channels respectively, which can simultaneously sample the four output voltages. The measurement accuracy reaches 0.02%, providing an accurate measurement standard for the traceability calibration of the entire device.

[0040] The microcontroller receives the measured values ​​from the measurement unit, compares them with the set values, and adjusts the outputs of each direct digital synthesized waveform generator via a field-programmable gate array (FPGA) based on the comparison results, thus forming a closed-loop voltage control. Through closed-loop voltage control, the overall voltage output accuracy reaches 0.02%RD, with low output waveform distortion and high stability.

[0041] The communication unit provides multiple communication interfaces, including optical and RS485 serial ports, and supports various communication protocols. Through these interfaces, the traceability calibration device can read the measurement data from the online monitoring device of the voltage transformer under test in real time and automatically calculate the calibration error, eliminating the need for manual reading and calculation.

[0042] The input display unit employs a large-size LCD capacitive touchscreen, featuring high resolution, rich colors, high sensitivity, and smooth operation. It can display measurement data, calibration parameters, error results, clock status, and other information in real time. Users can perform human-computer interaction operations such as parameter setting, function selection, and operation control via the touchscreen. Furthermore, the traceability calibration device is equipped with an external LCD display module that supports HDMI output, facilitating manual calibration and data reading when the online monitoring device for the tested voltage transformer lacks a display unit.

[0043] The power supply unit adopts a dual-power supply design, supporting both AC 220V and DC 12V power supply modes, with the DC 12V power supply provided by a built-in high-capacity lithium battery. The two power supplies can automatically switch: when an external AC 220V input is connected, the device automatically switches to external power supply while charging the built-in lithium battery; when there is no external AC power supply, it automatically switches to the built-in lithium battery power supply, ensuring that the traceability calibration device can work normally in various field environments.

[0044] The entire machine is made of linear low-density polyethylene, which makes it lightweight, easy to carry and use on site.

[0045] Based on the above scheme, the traceability calibration device achieves independent and precise output of multi-channel voltage through four (adjustable to more) independent voltage output channels, and can simultaneously calibrate four online monitoring devices for voltage transformers, improving calibration efficiency by four times compared to single-channel devices. By using a microcontroller and a field-programmable gate array to collaboratively control the direct digital synthesized waveform generator and combining it with feedback from the measurement unit to form a closed-loop voltage control, the high accuracy and stability of the output voltage are guaranteed. The dual-power supply design adapts to the complex power supply environment of substations. Example 2

[0046] This embodiment describes the multi-channel phase synchronization control and closed-loop voltage control of a direct digital synthesized waveform generator.

[0047] It should be noted that multi-channel voltage output needs to maintain a strict phase synchronization relationship between each channel, while also requiring that the phase of each channel can be adjusted independently to simulate the working condition where there is a phase difference between the phase voltages in actual operation. In addition, how to ensure that the output voltage can quickly converge to the set value and remain stable under various working conditions is also a key issue.

[0048] To solve the above problems, refer to Figure 3In this embodiment, the field-programmable gate array (FPGA) provides a unified reference clock signal and a synchronization trigger signal to the four direct digital synthesized waveform generators (DDSs) with voltage output channels. The unified reference clock signal ensures that the waveform generation of each DDS is based on the same time base, and the synchronization trigger signal ensures that the waveform generation of each channel starts at the same time, thereby achieving strict phase synchronization of the output voltage of each channel.

[0049] Building upon this, the field-programmable gate array (FPGA) achieves independent phase adjustment of the output voltage of each channel by writing independent phase offset values ​​to the phase registers of each direct digital synthesized waveform generator (DDS). Specifically, each DDS includes a phase accumulator and a phase register. The phase accumulator accumulates values ​​according to the frequency control word and the beat of the reference clock. The phase offset value in the phase register is superimposed on the output of the phase accumulator, causing the output waveform of that channel to have a corresponding phase offset relative to the reference phase. Since all channels share the same reference clock and synchronous trigger signal, the phase relationship between channels is strictly controllable; and since the phase offset value of each channel is set independently, the phase of each channel can be adjusted independently.

[0050] The first voltage output channel serves as the reference channel, set with a rated voltage value and zero phase offset. The second, third, and fourth voltage output channels can be set with relative amplitude and phase difference values ​​compared to the first voltage output channel, respectively. The amplitude difference is achieved by adjusting the amplitude control word of the corresponding direct digital synthesized waveform generator, while the phase difference is achieved by adjusting the phase offset value of the corresponding direct digital synthesized waveform generator. In this way, a known amplitude and phase deviation relationship can be established between the channels to simulate the real-world operating conditions where amplitude and phase differences exist between phase voltages.

[0051] refer to Figure 2 In closed-loop voltage control, the microcontroller calculates the compensation amount based on the deviation between the measured value and the set value from the measurement unit using a PID control algorithm. In the PID control algorithm, the proportional element responds quickly to the current deviation, the integral element eliminates steady-state error, and the derivative element suppresses overshoot and oscillation. The microcontroller sends the calculated compensation amount to the field-programmable gate array (FPGA), which adjusts the amplitude control word and / or phase offset value of the corresponding direct digital synthesized waveform generator (DDP) based on the compensation amount. After adjustment, the measurement unit again acquires the actual output voltage values ​​of each channel and feeds them back to the microcontroller. The microcontroller repeats the above calculation and adjustment process until the deviation between the measured value and the set value from the measurement unit is less than a preset threshold. The preset threshold is set according to the calibration accuracy requirements; in this embodiment, the voltage amplitude deviation threshold is set to 0.01%, and the phase deviation threshold is set to 0.5%.

[0052] By combining a direct digital waveform generator implemented with a 16-bit analog-to-digital converter chip and a measurement unit implemented with a 16-bit analog-to-digital converter chip, along with a precision signal conditioning circuit and a linear power amplifier, the overall voltage output accuracy reaches 0.02%RD.

[0053] Based on the above scheme, a strict phase synchronization relationship of the output voltage of each channel is ensured by using a unified reference clock and synchronous trigger signal. At the same time, independent phase adjustment of each channel is realized by programming an independent phase register, which solves the contradiction between phase synchronization and independent adjustment. Through the closed-loop regulation of the PID control algorithm and the convergence threshold criterion, it is ensured that the output voltage can quickly converge to the set value and maintain high stability under different operating conditions. Example 3

[0054] This embodiment describes the GPS / BeiDou dual-mode synchronous clock reference and second pulse delay measurement.

[0055] It should be noted that online monitoring devices for voltage transformers require error calculation based on a synchronous clock signal, and the accuracy of this synchronous clock directly affects the measurement results. Most existing calibration devices lack a high-precision synchronous clock reference, making it impossible to accurately verify the synchronous clock delay of online monitoring devices.

[0056] To solve the above problems, refer to Figure 4 In this embodiment, the traceability calibration device includes a clock reference unit. The clock reference unit is developed based on specialized GPS receivers and BeiDou-2 receiver components, supporting dual-mode satellite signal reception of both GPS and BeiDou-2. The clock reference unit can simultaneously receive GPS and BeiDou satellite signals, and through dual-mode positioning and timing, it can switch to the other satellite signal when one is blocked or interfered with, improving the reliability and availability of the clock reference.

[0057] Optionally, the clock reference unit includes: a dual-frequency active antenna, an RF power divider, a GPS baseband processing module, a BeiDou-2 baseband processing module, a time synchronization fusion microprocessor, and a temperature-controlled crystal oscillator. Hardware connection and signal flow: The dual-frequency active antenna receives satellite RF signals from the air and sends them to the GPS baseband processing module and the BeiDou-2 baseband processing module respectively via the RF power divider. The two baseband processing modules respectively parse their respective UTC time messages and initial second pulse (1PPS) signals and send them to the time synchronization fusion microprocessor. Dual-mode fusion control logic: The time synchronization fusion microprocessor has a built-in dual-mode backup and optimization algorithm. Under normal conditions, it prioritizes reading the ephemeris data and clock information from the BeiDou-2 baseband processing module; when BeiDou satellite signal loss is detected or the signal-to-noise ratio is lower than a preset safety threshold, it seamlessly and automatically switches to the clock data from the GPS baseband processing module. Standard signal generation: The time synchronization fusion microprocessor uses the selected high-precision satellite clock as a reference to perform phase-locked training on the local temperature-controlled crystal oscillator, thereby outputting a standard 1PPS second pulse signal with extremely low jitter; at the same time, the microprocessor encodes the current UTC time information according to the IRIG Standard 200-04 standard protocol and modulates it to generate a standard IRIG-B time code signal, which serves as the unified time reference for the entire system for synchronous output.

[0058] The clock reference unit outputs one standard second pulse signal and one IRIG-B time code signal to the control unit. The control unit uses the standard second pulse signal as the time reference for the traceability calibration device. The IRIG-B time code signal conforms to IRIG Standard 200-04 and contains year and time signal quality information, referencing the IEEE C37.118-2005 standard, with the time being Beijing time. The clock reference unit also outputs one IRIG-B code optical port.

[0059] The clock reference unit also features second pulse delay measurement functionality. (Reference) Figure 4 During second pulse delay calibration, the IRIG-B code signal output by the online monitoring device of the voltage transformer under test is input to the clock reference unit of the traceability calibration device via optical fiber. The clock reference unit converts the received IRIG-B code signal into an electrical second pulse, and then measures the delay error between this electrical second pulse and the standard second pulse signal output by the clock reference unit itself.

[0060] Specifically, a high-speed time interval counter is implemented internally within the field-programmable gate array (FPGA). This counter uses a high-frequency clock as its counting reference, starting counting on the rising edge of the standard second pulse signal and stopping counting on the rising edge of the second pulse of the electrical signal converted by the device under test. The count value between the two rising edges multiplied by the high-frequency clock period gives the time delay error value. The clock delay measurement accuracy is better than 0.5 microseconds.

[0061] Furthermore, the method for precise parsing and second edge extraction of the tested IRIG-B code during second pulse delay calibration is explained: To achieve high-precision delay measurement, the second pulse edge representing the punctual reference point must be accurately extracted from the IRIG-B code fed back by the device under test. To achieve this function, an IRIG-B code to electrical signal second pulse conversion module is set up, and its specific working process is as follows: Photoelectric conversion: First, the fiber optic IRIG-B code signal emitted by the online monitoring device under test is converted into a TTL level digital pulse sequence through a high-speed photoelectric receiver tube (PIN detector).

[0062] Pulse Width Recognition and Bit Definition: The Field Programmable Gate Array (FPGA) uses an internal high-frequency clock (e.g., 100MHz or higher) to perform high-frequency oversampling on the digital pulse sequence, measuring the duration of each high-level pulse in the sequence in real time. According to the IRIG-B standard, a high level lasting 2ms represents logic "0", 5ms represents logic "1", and 8ms represents a position identifier (P).

[0063] Accurate extraction of precise timing edges: A state machine is built inside the FPGA. When two position identifiers (i.e., P0 and Pr) are detected consecutively for 8ms, the state machine determines that the rising edge of the second position identifier (Pr) is the "positive integer second" timing reference point of the current UTC time.

[0064] Trigger-based stop counting: Upon capturing the rising edge of Pr, the FPGA immediately generates an internal hardware trigger signal, directly cutting off the counting enable pin of the high-speed time interval counter at the hardware level, thus stopping the count. Through high-frequency sampling and state machine analysis at the FPGA hardware level, the rising edge of Pr in the IRIG-B code frame structure is directly locked as the stop signal, completely eliminating the tens of microseconds of instruction execution jitter caused by traditional microcontroller software interrupt parsing of IRIG-B codes, ensuring that the final delay measurement accuracy is better than 0.5μs.

[0065] Based on the above scheme, the reliability and availability of the time reference are improved by using GPS and Beidou dual-mode satellite reception and timing. By converting the IRIG-B code into an electrical signal second pulse and comparing the time delay with a standard second pulse, the synchronous clock delay of the online monitoring device for the tested voltage transformer is accurately measured. The time delay measurement accuracy is better than 0.5 microseconds, ensuring the consistency of the time reference for synchronous measurement of the online monitoring device. Example 4

[0066] This embodiment describes the calibration method.

[0067] It should be noted that existing calibration devices require manual wiring, manual parameter setting, manual reading of the measurement data of the device under test, and manual calculation of calibration errors when used in the field. The operation process is complicated, the calibration efficiency is low, and human interpretation errors are prone to occur.

[0068] To solve the above problems, refer to Figure 5 This embodiment provides a calibration method for online monitoring of multi-channel voltage transformers. The method utilizes the traceability calibration device described in the previous embodiment to calibrate the online monitoring device of the voltage transformer, and includes the following steps: Step S1, Wiring Preparation: Connect the output terminals of each voltage output channel of the traceability calibration device to the voltage input terminal of the online monitoring device of the voltage transformer under test through test wires or crimping fixtures; connect the communication interface of the traceability calibration device to the communication interface of the online monitoring device of the voltage transformer under test; install the GPS antenna in a location with good satellite signal and connect it to the GPS antenna terminal of the traceability calibration device.

[0069] Step S2, Power-on self-test: Turn on the power of the traceability calibration device and the device will perform a self-test, including the status detection of each functional unit, voltage output detection, clock signal detection, etc., to ensure that the device is working properly.

[0070] Step S3, clock synchronization: Wait for the GPS / BeiDou receiver to find a stable satellite signal. Once a sufficient number of satellites are locked, the clock reference unit outputs a stable standard second pulse signal and an IRIG-B time code signal, and the device enters the synchronization working state.

[0071] Step S4, Parameter Setting: Set the calibration parameters via the touchscreen of the input display unit. Set the output voltage amplitude and phase parameters for each voltage output channel. The first voltage output channel is used as the reference channel with its rated voltage value set. The second, third, and fourth voltage output channels can be set with their relative ratio and phase angle differences to the first voltage output channel, respectively, to establish a known amplitude and phase deviation relationship between the channels. Simultaneously, set the number of calibration points. Multiple calibration points are preset, each corresponding to a different voltage amplitude and / or phase parameter.

[0072] Step S5, Voltage Output and Closed-Loop Control: Voltage output is initiated. Each direct digital synthesized waveform generator generates a voltage waveform signal according to the set parameters. After amplification by the corresponding linear power amplifier, a standard test voltage is output. The measurement unit synchronously acquires the actual output voltage value of each voltage output channel. The microcontroller receives the measured value from the measurement unit, compares the measured value with the set value, calculates the compensation amount based on the deviation using a PID control algorithm, and sends the compensation amount to the field-programmable gate array (FPGA). The FPGA adjusts the amplitude control word and / or phase offset value of the corresponding direct digital synthesized waveform generator according to the compensation amount. This process is iterated repeatedly until the deviation between the actual output voltage value and the set value of each voltage output channel is less than a preset threshold, causing the actual output voltage value to converge to the set value.

[0073] Step S6, Data Acquisition and Error Calculation: A communication connection is established with the online monitoring device of the voltage transformer under test through the communication interface, and the voltage amplitude, phase, and error data of the online monitoring device of the voltage transformer under test are automatically read. The microcontroller compares the automatically read measurement data with the measurement values ​​of the measurement unit, automatically calculates the ratio error and phase angle error of the online monitoring device of the voltage transformer under test, and displays the calculation results on the screen of the input display unit in real time.

[0074] Step S7, Automatic switching between multiple calibration points: After completing the calculation of the ratio difference and phase difference error of the current calibration point, the microcontroller automatically switches to the voltage amplitude and phase parameters corresponding to the next calibration point, and repeats steps S5 to S6 until the calibration of all preset calibration points is completed.

[0075] Step S8, Second Pulse Delay Calibration: The IRIG-B code signal output by the online monitoring device of the voltage transformer under test is input to the clock reference unit of the traceability calibration device through optical fiber. The clock reference unit converts the received IRIG-B code signal into an electrical signal second pulse, measures the delay error between the electrical signal second pulse and the standard second pulse signal output by the clock reference unit, and determines the synchronous clock performance of the online monitoring device of the voltage transformer under test.

[0076] Step S9, Result Storage and Output: After calibration, the traceability calibration device automatically stores the calibration results, including calibration time, calibration parameters, ratio and angle error data of each calibration point, and second pulse delay error data, and can output a calibration report through the communication interface or printing interface.

[0077] Based on the above scheme, a systematic calibration process integrates voltage output, closed-loop control, data acquisition, and error calculation into a coherent automated calibration process; automatic switching between multiple calibration points eliminates the need for manual point-by-point operation; the communication interface automatically reads the data of the device under test and automatically calculates the error, avoiding human interpretation errors; the entire calibration process has a high degree of automation and significantly improves calibration efficiency.

[0078] Optionally, the following steps may also be included: S10, Automatic Error Correction Parameter Distribution: After acquiring the ratio difference, angle difference, and second pulse delay error data of the current calibration point, the traceability calibration device does not end directly, but instead initiates the automatic error correction mechanism. The specific steps are as follows: S101, Correction Coefficient Calculation: The control unit automatically calculates the corresponding digital compensation coefficient based on the measured error data. For example, if the measured ratio difference is +0.5%, the amplitude compensation multiplier is calculated as 1 / (1+0.005); if the measured angle difference or time delay is measured, it is converted into a phase offset compensation word or time delay compensation amount in digital signal processing.

[0079] S102, Communication Configuration Writing: The traceability calibration device uses its communication unit (optical port or RS485 interface) to call standard communication protocols (such as IEC61850, Modbus or DL / T860, etc.) to send correction parameter configuration instructions to the online monitoring device under test.

[0080] S103, Self-calibration of the device under test: After receiving the correction parameter configuration instruction, the online monitoring device under test updates the underlying calibration register in its internal DSP (Digital Signal Processor) or MCU to complete the digital-level amplitude, phase and timestamp alignment compensation.

[0081] S11, Closed-loop retest verification and final report generation: S111, Closed-Loop Retest: After the correction parameters are written, the traceability calibration device retests the calibration point. That is, keeping the current standard voltage output and standard second pulse output unchanged, the device under test reads the measurement data again through the communication interface.

[0082] S112. Qualification judgment: Compare the retest data with the standard value. If the residual error (ratio difference, angle difference, time delay) calculated by the retest is less than the allowable error limit of the corresponding accuracy class (e.g., 0.2 or 0.5) of the tested device, the calibration at this point is deemed qualified; if it is not qualified, an alarm is triggered or a second iteration correction is performed.

[0083] S113. Result storage and output: After all calibration points pass the retest, the device automatically stores the complete traceability file (including the original error before correction and the qualified residual after correction), generates an electronic traceability calibration report, and completes the entire closed-loop calibration process.

[0084] Existing voltage transformer monitoring equipment calibration typically employs an open-loop mode, meaning it can only measure the error. Subsequent manual modification of the equipment's compensation parameters via backend software is required, which is inefficient and poses a safety hazard due to human error input. This embodiment, based on the addition of steps S10 and S11, combines high-precision error measurement with digital compensation coefficients transmitted via a communication interface, achieving a fully automated closed-loop calibration process encompassing detection, calculation, correction, and retesting. The entire traceability process requires no manual intervention, significantly improving the calibration efficiency for large-scale online monitoring devices during factory shipment or on-site inspections. Furthermore, it fundamentally eliminates human error that can result from manual parameter correction, achieving truly intelligent and automated traceability. Example 5

[0085] This embodiment illustrates a composite closed-loop control method based on feedforward prediction and adaptive variable integral PID.

[0086] It should be noted that when implementing automatic switching between multiple calibration points to improve traceability calibration efficiency, traditional conventional PID closed-loop control methods face two prominent problems: First, when calibration points are automatically switched (i.e., the set voltage amplitude undergoes a step change), conventional PID algorithms, due to the integral accumulation effect, are prone to significant overshoot or oscillation in the output voltage. This not only prolongs the convergence time required for voltage stabilization, but severe overshoot may even damage the internal circuitry of the tested online monitoring device. Second, online monitoring devices for voltage transformers from different manufacturers and of different models have significantly different input impedances (inductive or capacitive load characteristics). Fixed PID parameters are difficult to adapt to these variable load characteristics, resulting in extremely slow steady-state convergence for some tested devices, or even continuous micro-oscillations, failing to meet the high-precision traceability requirements of 0.02%.

[0087] To address the aforementioned issues, this embodiment introduces a closed-loop control method combining feedforward prediction and adaptive variable integral PID in the control unit (microcontroller). The specific control process is as follows: (1) Feedforward prediction control based on channel transfer function: The approximate linear transfer function of each voltage output channel (including the direct digital synthesized waveform generator and the linear power amplifier) ​​under no-load and standard load is pre-stored inside the microcontroller. When the system switches from the current calibration point to the next calibration point (the set value undergoes a step change), the microcontroller temporarily freezes the PID feedback control and prioritizes the calculation of a feedforward amplitude control word based on the target set voltage value of the next calibration point and the transfer function. This word is then instantaneously written to the direct digital synthesized waveform generator through a field-programmable gate array. This feedforward control enables the output voltage to rapidly approach the 95%~98% range of the target set value in an open-loop manner, thereby completely eliminating the system delay during large-amplitude adjustments.

[0088] (2) Adaptive Variable Integral PID Feedback Control with Error Threshold Segmentation: After the feedforward control executes one power frequency cycle, the microcontroller seamlessly switches to feedback closed-loop control. The microcontroller calculates the deviation rate E between the actual output voltage value fed back by the measurement unit and the set value in real time (deviation rate E = |actual value - set value| / set value), and dynamically adjusts the integral coefficient Ki in the PID control according to the magnitude of the deviation rate E. Integral separation stage (large deviation): When E>2%, it is determined to be a severe fluctuation in the initial stage of load connection. The microcontroller forces the integral coefficient Ki to 0, retaining only proportional (P) and derivative (D) control, and uses PD control to quickly eliminate large deviation and prevent overshoot caused by integral accumulation.

[0089] Linear variable integral stage (medium deviation): When 0.1%≤E≤2%, the microcontroller introduces integral control, but the integral coefficient Ki increases linearly as the deviation rate E decreases (i.e., Ki=K). imax ×(2%-E) / 1.9, to achieve a flexible transition in control intensity.

[0090] Full integration phase (small deviation): When E < 0.1%, it is determined that the steady-state convergence region has been entered, and the microcontroller sets the integral coefficient to the maximum preset value K. imax It rapidly eliminates static residuals through its strong integral action, counteracts minor disturbances caused by load nonlinearity, and makes the deviation quickly less than the preset convergence threshold of 0.01%.

[0091] Based on the above solution, the following effects can be achieved: 1. Overshoot-free and ultra-fast response: By using feedforward predictive control to handle voltage surges during calibration point switching, the output voltage instantly jumps to near the target value, avoiding the integral overshoot problem of conventional PID in large step adjustment and protecting the safety of the tested equipment.

[0092] 2. Extremely robust to load: Adopting adaptive variable integral PID control, the integral coefficient is intelligently adjusted according to the real-time deviation rate, perfectly adapting to online monitoring devices with different impedance characteristics. No matter how the load changes, the voltage output can be guaranteed to converge quickly without oscillation.

[0093] 3. Significantly Improved Automatic Calibration Efficiency: The combined feedforward and variable integral PID control reduces the voltage stabilization convergence time for a single calibration point switch from the conventional 2-3 seconds to less than 0.2 seconds. This saves considerable waiting time during full-range multi-point automatic traceability calibration, drastically improving the overall efficiency of on-site automated calibration. Example 6

[0094] This embodiment describes the crimp-type quick-connect wiring and other auxiliary functions.

[0095] It should be noted that the substation site environment is complex, and on-site testing and wiring operations are inconvenient. The traditional method of manually wiring each wire one by one is time-consuming and prone to errors.

[0096] To facilitate on-site testing and wiring, the traceability calibration device in this embodiment is equipped with a crimp-type quick-connect wiring fixture. Using the positioning of the left and right mounting ears on the standard chassis, voltage wiring for all four voltage output channels can be completed in one go. The crimp fixture employs a spring-loaded pin design, with four sets of four-pin aviation connectors on the pin box, corresponding to the first to fourth voltage output channels from left to right. During installation, first fix the left and right positioning plates to the chassis mounting ears, then align the spring-loaded pins sequentially with the wiring holes, and press the fixture forward from the center. After the left and right pressure plates of the pin box contact the positioning plates, tighten the nuts on both sides of the pin box to complete the crimp fixture installation. The crimp-type quick-connect wiring method simplifies and expedites on-site wiring operations, improving wiring efficiency and reliability.

[0097] In addition, the traceability calibration device supports HDMI interface output, allowing for the connection of an external LCD display module. In scenarios where the online monitoring device for the voltage transformer under test lacks a display unit or its display unit is inconvenient to observe, calibration personnel can read the measurement data of the device under test through the external LCD display module, facilitating manual calibration.

[0098] Based on the above solution, the crimp-type quick-connect tooling achieves one-time multi-channel wiring through the cooperation of spring pins and positioning plates, which greatly improves the efficiency and reliability of on-site wiring; the HDMI external display function enhances the flexibility and convenience of calibration operations.

[0099] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A traceability calibration device for online monitoring of multi-channel voltage transformers, characterized in that, Includes a control unit, multiple independent voltage output channels, and a measurement unit; The control unit includes a microcontroller and a field-programmable gate array that work together; Each of the voltage output channels includes a direct digital synthesized waveform generator controlled by the field-programmable gate array and a linear power amplifier connected to the output of the direct digital synthesized waveform generator. The voltage amplitude and phase of each voltage output channel are independently adjustable. The input terminal of the measurement unit is connected to the output terminal of each voltage output channel, and is used to synchronously acquire the actual output voltage value of each voltage output channel; The microcontroller receives the measured values ​​from the measurement unit, compares the measured values ​​with the set values, and adjusts the outputs of each of the direct digital synthesized waveform generators through the field programmable gate array according to the comparison results to form closed-loop voltage control.

2. The traceability calibration device for online monitoring of multi-channel voltage transformers according to claim 1, characterized in that, The field-programmable gate array provides a unified reference clock signal and a synchronization trigger signal to the direct digital synthesized waveform generator of each voltage output channel, and realizes phase synchronization and independent phase adjustment between the output voltages of each voltage output channel by writing independent phase offset values ​​to the phase register of each direct digital synthesized waveform generator.

3. The traceability calibration device for online monitoring of multi-channel voltage transformers according to claim 2, characterized in that, In the closed-loop voltage control, the microcontroller calculates a compensation amount using a PID control algorithm based on the deviation between the measured value and the set value of the measurement unit, and sends the compensation amount to the field-programmable gate array (FPGA). The FPGA adjusts the amplitude control word and / or phase offset value of the corresponding direct digital synthesized waveform generator according to the compensation amount until the deviation between the measured value and the set value of the measurement unit is less than a preset threshold.

4. The traceability calibration device for online monitoring of multi-channel voltage transformers according to claim 1, characterized in that, It also includes a clock reference unit, which includes a GPS receiver and a Beidou receiver, for receiving GPS satellite signals and Beidou satellite signals and outputting a standard second pulse signal and an IRIG-B time code signal to the control unit. The control unit uses the standard second pulse signal as the time reference of the traceability calibration device.

5. The traceability calibration device for online monitoring of multi-channel voltage transformers according to claim 4, characterized in that, The clock reference unit is also used to receive the IRIG-B code signal output by the online monitoring device of the voltage transformer under test, convert the IRIG-B code signal into an electrical signal second pulse, and measure the time delay error between the electrical signal second pulse and the standard second pulse signal.

6. A calibration method for online monitoring of a multi-channel voltage transformer, characterized in that, A traceability calibration device for online monitoring of multi-channel voltage transformers according to any one of claims 1 to 5, the method comprising the following steps: Connect each voltage output channel of the traceability calibration device to the voltage input terminal of the online monitoring device for the voltage transformer under test; Set the output voltage amplitude and phase parameters for each of the voltage output channels; When the voltage output is started, each of the direct digital synthesized waveform generators generates a voltage waveform signal according to the set parameters, which is then amplified by the corresponding linear power amplifier and output as a standard test voltage. The measurement unit synchronously acquires the actual output voltage value of each voltage output channel. The microcontroller adjusts the output of each direct digital synthesized waveform generator through the field programmable gate array according to the deviation between the actual output voltage value and the set value, so that the actual output voltage value of each voltage output channel converges to the set value. The measurement data of the online monitoring device for the voltage transformer under test is obtained, and the measurement data is compared with the measurement value of the measurement unit to calculate the ratio error and angle error of the online monitoring device for the voltage transformer under test.

7. The calibration method for online monitoring of multi-channel voltage transformers according to claim 6, characterized in that, It also includes an automatic switching step for multiple calibration points: Multiple calibration points are preset, each corresponding to a different voltage amplitude and / or phase parameter; After completing the calculation of the ratio difference and angle difference error at the current calibration point, the microcontroller automatically switches to the voltage amplitude and phase parameters corresponding to the next calibration point, and repeats the steps of voltage output, closed-loop voltage control and error calculation until the calibration of all preset calibration points is completed.

8. The calibration method for online monitoring of multi-channel voltage transformers according to claim 7, characterized in that, When setting the parameters of each voltage output channel, the first voltage output channel is used as the reference channel and its rated voltage value is set. The other voltage output channels are respectively set with ratio difference and angle difference values ​​relative to the first voltage output channel, so as to establish a known amplitude deviation and phase deviation relationship between each voltage output channel.

9. The calibration method for online monitoring of multi-channel voltage transformers according to claim 6, characterized in that, The steps for obtaining measurement data from the online monitoring device of the voltage transformer under test include: establishing a communication connection with the online monitoring device of the voltage transformer under test through a communication interface, automatically reading the voltage amplitude, phase, and error data of the online monitoring device of the voltage transformer under test; the microcontroller comparing the automatically read measurement data with the measurement values ​​of the measurement unit, automatically calculating the ratio difference and phase difference errors, and storing the calibration results.

10. The calibration method for online monitoring of multi-channel voltage transformers according to claim 6, characterized in that, It also includes a second pulse delay calibration step: The IRIG-B code signal output by the online monitoring device of the voltage transformer under test is input to the clock reference unit of the traceability calibration device; The clock reference unit converts the received IRIG-B code signal into an electrical signal second pulse; The time delay error between the electrical signal second pulse and the standard second pulse signal output by the clock reference unit is measured to determine the synchronous clock performance of the online monitoring device for the voltage transformer under test.

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