High-voltage-class resistance-capacitance type direct-current voltage divider with high measurement precision under harmonic condition and digital direct-current measurement system

Abstract

The invention discloses a high-voltage-class resistance-capacitance type direct current voltage divider with high measurement precision under a harmonic wave condition and a digital direct current measurement system, the voltage divider comprises a high-voltage arm, a low-voltage arm, a resistance-capacitance compensation unit, a secondary voltage dividing plate and an analog-to-digital conversion sampling circuit, and the resistance-capacitance compensation unit comprises a compensation resistor and a compensation capacitor which are connected in parallel; the secondary voltage dividing plate is arranged between the resistance-capacitance compensation unit and the analog-to-digital conversion sampling circuit and is provided with a channel for transmitting an analog low-voltage harmonic signal; the analog-to-digital conversion sampling circuit is provided with a differential input isolator, an anti-aliasing filter, an adjustable gain amplifier, a voltage follower, an analog-to-digital converter and an optical fiber transmission module which are connected in sequence, the differential input isolator is connected with a signal channel of the secondary voltage dividing plate, and the optical fiber transmission module is configured to be connected with the input end of the control protection system. According to the invention, the measurement precision of the extra-high-voltage direct-current voltage divider under the harmonic condition can be improved.

Description

Technical Field

[0001] This invention relates to the field of high-voltage electrical equipment, and in particular to a high-voltage-level resistive-capacitive DC voltage divider and a digital DC measurement system with high measurement accuracy under harmonic conditions. Background Technology

[0002] With the introduction of the national "dual-carbon" strategic goal, new energy power generation and DC transmission converter technology have been rapidly developed and applied. On the one hand, new energy generator units and DC converter stations will generate harmonic superposition and oscillation problems, and how to effectively manage harmonics has become a new challenge. On the other hand, the RC DC voltage divider is the main voltage measurement equipment on the DC side of the converter station, and its DC measurement accuracy directly affects the realization of real-time monitoring, power control, equipment protection and other functions of the DC transmission system, and has an important impact on the safe and stable operation of the power system.

[0003] During the measurement process of UHVDC voltage dividers, harmonic superposition can severely interfere with the accuracy of DC measurements and the stable operation of the DC system. The reasons are as follows:

[0004] 1. DC voltage dividers use a parallel resistor-capacitor configuration for voltage division. In actual operation, the voltage divider will generate stray capacitance. Under high-frequency conditions, the changes in stray capacitance are more complex, leading to nonlinear changes in the voltage division ratio of the DC voltage divider under high-frequency harmonic conditions, which cannot accurately reflect the first harmonic voltage.

[0005] Second, while harmonics cannot be accurately measured, the superposition of multiple harmonics may cause aliasing of measurement results, directly interfering with DC voltage measurement results and further affecting the accuracy of primary voltage measurement.

[0006] Third, for the long-term stable operation of DC transmission systems, harmonics will generate additional eddy current losses to increase the heat generation of the measurement system, accelerate the aging of the measurement equipment, and cause irreversible drift and deterioration of the voltage divider resistance and electronic circuit parameters of the measurement equipment, thus introducing system errors into the measurement results.

[0007] IV. Setting the protection settings and optimizing the operation mode of the DC system: Based on the measurement values ​​of the DC voltage divider, the harmonic aliasing problem in the measurement results may lead to protection judgment errors, causing the protection system to malfunction or fail to operate. At the same time, it is impossible to effectively manage harmonics of specific frequencies, forming a vicious cycle.

[0008] The application of power electronics technology in converter stations makes harmonics unavoidable in DC systems. Therefore, improving the measurement accuracy of UHVDC voltage dividers under harmonic conditions is of great significance for ensuring the long-term safe and stable operation of the power system.

[0009] The disclosure of the above background technical content is only for the purpose of assisting in understanding the concept and technical solution of this application, and does not necessarily provide technical instruction. Summary of the Invention

[0010] The purpose of this invention is to provide a method for improving the measurement accuracy of traditional DC voltage dividers for ultra-high voltage applications, especially under harmonic conditions.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A high-voltage-level RC DC voltage divider with high measurement accuracy under harmonic conditions includes a high-voltage arm, a low-voltage arm, an RC compensation unit, a secondary voltage divider board, and an analog-to-digital conversion sampling circuit. The high-voltage arm and the low-voltage arm are connected in series and configured to be connected in series between the high-voltage line and ground. The RC compensation unit is located at the electrical boundary between the high-voltage arm and the low-voltage arm. The low-voltage arm is configured to generate a low-voltage signal proportional to the high voltage of the high-voltage line.

[0013] The RC compensation unit includes a compensation resistor and a compensation capacitor connected in parallel, which are configured to correct the frequency response.

[0014] The secondary voltage divider is disposed between the resistor-capacitor compensation unit and the analog-to-digital conversion sampling circuit. It is configured with multiple signal channels, one of which is configured to output an analog low voltage signal from the low-voltage arm to the analog-to-digital conversion sampling circuit.

[0015] The secondary voltage divider is configured to generate independent harmonic signals and output them to the analog-to-digital conversion sampling circuit through another signal channel.

[0016] The analog-to-digital conversion sampling circuit is configured with a differential input isolation, an anti-aliasing filter, an adjustable gain amplifier, a voltage follower, an analog-to-digital converter, and an optical fiber transmission module connected in sequence. The differential input isolation receives the analog low-voltage harmonic signal output independently from the secondary voltage divider, and the optical fiber transmission module is configured to be connected to the input terminal of the control and protection system.

[0017] Furthermore, based on any one or a combination of the aforementioned technical solutions, the design parameters of the resistive-capacitive DC voltage divider are determined in the following manner:

[0018] Based on the structure of the RC DC voltage divider, the transfer function of the voltage divider is derived as the relationship between the signal frequency and the resistance and capacitance of the voltage divider: Where H(jω) is the voltage divider transfer function, j is the imaginary unit, ω is the angular frequency, and R... H C is the equivalent resistance of the high-voltage arm. H R is the equivalent capacitance of the high-voltage arm. LFor the equivalent resistance of the low-voltage arm, C L The equivalent capacitance of the low-voltage arm;

[0019] Based on the requirements of the control and protection system for amplitude-frequency fluctuations and / or phase shifts, the high-voltage arm RC parameters and low-voltage arm RC parameters that meet these requirements are calculated in reverse.

[0020] Based on the frequency characteristics of the analog-to-digital conversion sampling circuit, the circuit structure parameters of the analog-to-digital conversion sampling circuit are calculated to match the signal of the secondary voltage divider, and to ensure that the measurement accuracy requirements are met within the target bandwidth.

[0021] After determining the parameters, the harmonic measurement error of the RC DC voltage divider is checked. If the check fails, the parameters are recalculated until the check passes.

[0022] Furthermore, based on any or a combination of the aforementioned technical solutions, the compensation resistor of the RC compensation unit is connected in parallel with the resistor of the low-voltage arm, and the compensation capacitor is connected in parallel with the capacitor of the low-voltage arm.

[0023] The resistance and capacitance parameters of the resistance-capacitance compensation unit are optimized in the following ways:

[0024] The transfer function from the high-voltage input to the output of the RC compensation unit is derived as follows: Among them, Z H Z is the equivalent impedance of the high-voltage arm. comp Z' is the impedance of the RC compensation unit. L This is the equivalent input impedance of the low-voltage arm and the secondary voltage divider plate;

[0025] Based on the requirements of the control and protection system for amplitude-frequency fluctuations and / or phase shifts, the impedance Z of the RC compensation unit that meets these requirements can be calculated. comp ;

[0026] According to the formula Z = R / (1 + jωRC), calculate the impedance Z that satisfies the above conditions. comp The compensation resistor and compensation capacitor.

[0027] Furthermore, following any or a combination of the aforementioned technical solutions, the high-voltage arm and the low-voltage arm are housed within an insulating sleeve, the resistance-capacitance compensation unit is housed within a local acquisition unit box, and the resistance-capacitance compensation unit is connected in parallel with the low-voltage arm via a shielded cable.

[0028] Furthermore, based on any or a combination of the aforementioned technical solutions, and considering the frequency characteristics of the analog-to-digital conversion sampling circuit, the circuit structure parameters of the analog-to-digital conversion sampling circuit are calculated to match the signal of the secondary voltage divider, ensuring that the measurement accuracy requirements are met within the target bandwidth, including:

[0029] Obtain the output impedance of the secondary voltage divider, denoted as Z. out-board To obtain the target bandwidth required by the control and protection system, and to determine the target frequency boundary, denoted as f. max ;

[0030] For differential input isolation, select an input impedance greater than the output impedance Z of the secondary voltage divider. out-board The operational amplifier is selected such that its gain-bandwidth product is higher than the target frequency boundary f. max ;

[0031] For anti-aliasing filters, a cutoff frequency greater than the target frequency boundary f is selected. max The resistance and capacitance values ​​of the filter are calculated based on the normalization coefficients corresponding to the selected cutoff frequency and filter type.

[0032] For an adjustable gain amplifier, the gain range of the gain amplifier is determined based on the minimum and maximum amplitudes of the input signal, and the effective bandwidth of the gain amplifier operating at the upper limit of the gain range is greater than the cutoff frequency of the anti-aliasing filter.

[0033] Furthermore, any one or a combination of the aforementioned technical solutions shall be verified in the following manner:

[0034] Using the established parameters, a complete mathematical model of the voltage divider is constructed. A standard harmonic signal is input, and the output value is compared with the theoretical value. The amplitude and phase errors are calculated. If the error exceeds the preset accuracy threshold, the verification fails; if the error is less than the preset accuracy threshold, the verification passes.

[0035] Furthermore, based on any one or a combination of the aforementioned technical solutions, a complete mathematical model of the voltage divider is constructed in the following manner:

[0036] Based on the determined high-voltage arm resistance and capacitance parameters and low-voltage arm resistance and capacitance parameters, construct the main voltage divider model;

[0037] The circuit structure parameters of the analog-to-digital conversion sampling circuit are calculated, including the common-mode rejection ratio and isolation voltage level of the differential input isolation, the cutoff frequency of the anti-aliasing filter, and the gain-bandwidth product of the adjustable gain amplifier. The differential input isolation, anti-aliasing filter, and adjustable gain amplifier of the analog front end in the RC supplement unit and the analog-to-digital conversion sampling circuit are modeled as an overall analog link.

[0038] The main voltage divider model is cascaded with the overall simulation link to obtain the complete mathematical model of the voltage divider.

[0039] Furthermore, based on any or a combination of the aforementioned technical solutions, the secondary voltage divider is configured with multiple signal channels, each of which is configured to output an independent analog low-voltage harmonic signal to the differential input.

[0040] The secondary voltage divider includes several branches connected in parallel across the two ends of the resistor-capacitor compensation unit. Each branch has at least two secondary voltage divider resistors connected in series and a secondary voltage divider capacitor connected in parallel across the two ends of the secondary voltage divider resistors.

[0041] Furthermore, following any or a combination of the aforementioned technical solutions, the secondary voltage divider and the analog-to-digital conversion sampling circuit are housed in the same local acquisition unit box, which has a shielded housing.

[0042] According to another aspect of the present invention, a high-precision digital DC measurement system is provided, including a high-voltage-level RC DC voltage divider as described above. The system further includes a merging unit, an I / O interface device, and a control and protection system. The merging unit is configured to aggregate raw sampled value messages from the analog-to-digital conversion sampling circuits of multiple DC voltage dividers, and to synchronously align and reassemble the aggregated data for distribution.

[0043] The IO interface device is configured as a bidirectional data interface for transmission between the merging unit and the control and protection system.

[0044] The beneficial effects of the technical solution provided by this invention are as follows:

[0045] a. Optimize the overall structure of the DC voltage divider, considering stray parameters of the voltage divider body and the matching degree of the input reactance of the sampling circuit, to improve the overall accuracy of the RC voltage divider DC voltage signal measurement system: Based on the design structure of the secondary voltage divider board and the load of the analog-to-digital sampling circuit, a selection principle for the isolation operational amplifier at the input port of the sampling circuit is proposed to achieve matching between the input reactance of the sampling circuit and the RC unit of the secondary voltage divider board. At the same time, the RC unit matching method is adopted to reduce the influence of stray parameters on the transmission characteristics of the voltage divider body, meet the low-power signal transmission fidelity requirements of the control and protection system, prevent bandwidth distortion caused by input reactance mismatch of the sampling circuit, and improve the measurement accuracy of the DC voltage divider.

[0046] b. While ensuring the stable linearity of the DC voltage divider's division ratio, a second-order active filter is used to implement anti-aliasing design, effectively improving the harmonic anti-aliasing performance of the sampling circuit and enhancing measurement accuracy from the sampling circuit perspective. The use of a combination of active and passive filtering circuits effectively improves the harmonic measurement anti-aliasing performance, further optimizing harmonic measurement accuracy. Compared to traditional DC voltage dividers that directly transmit analog signals via cable or through analog-to-digital conversion followed by fiber optic transmission, the use of functional filtering circuits and fiber optic transmission effectively avoids the problem of high-frequency noise aliasing affecting measurement results. It also improves the anti-interference performance of the signal transmission line, enhancing the measurement accuracy of the DC voltage divider. Furthermore, it simplifies the signal spectrum composition, improves equipment maintenance efficiency, reduces the impact of eddy current losses, enhances the operational stability of the DC voltage divider, and constructs a green and environmentally friendly power equipment solution.

[0047] c. Combining isolation and adjustable amplification gain to meet the multi-signal resolution requirements of digital control and protection systems: Digital relay protection systems have power and level signal requirements for DC voltage dividers. Traditional DC voltage dividers directly transmit the secondary voltage divider output signal via analog cable or directly perform analog-to-digital conversion and then transmit it via optical fiber. The gain cannot be adjusted, making it difficult to meet the load output requirements of future digital upgrades. In this regard, the present invention proposes a method to improve the measurement accuracy of UHV DC voltage dividers under harmonic conditions, which can fully meet the requirements of digital load output and promote the digital transformation of DC voltage dividers.

[0048] d. Adopting a digital fiber optic transmission scheme effectively improves electromagnetic interference resistance: Traditional DC voltage divider secondary voltage divider output signals are directly transmitted via analog cables, making them highly susceptible to electromagnetic interference. Long-distance transmission of low-power signals can cause voltage drop issues. At the same time, high voltage connected to the control room via cables poses safety hazards. To address these issues, this patent employs a combination of analog-to-digital conversion and fiber optic transmission, along with a multi-isolated sampling circuit transmission scheme. This effectively improves measurement accuracy and equipment operational stability, and provides theoretical support for the large-scale application of analog-to-digital conversion combined with fiber optic transmission in high-voltage measurement equipment. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 A schematic diagram of a high-voltage-level RC DC voltage divider with high measurement accuracy under harmonic conditions is provided as an exemplary embodiment of the present invention.

[0051] Figure 2 A schematic diagram of the module structure of an analog-to-digital conversion sampling circuit provided as an exemplary embodiment of the present invention;

[0052] Figure 3 A flowchart illustrating the determination of design parameters for the resistive-capacitive DC voltage divider is provided as an exemplary embodiment of the present invention. Detailed Implementation

[0053] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0054] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, apparatus, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0055] On the one hand, accurate measurement of DC voltage and harmonics can improve system status awareness and fault diagnosis capabilities, locate harmonic sources for precise management, and fully record voltage transients and harmonic component changes throughout the fault process, enabling predictive maintenance. On the other hand, accurate measurement results provide a basis for the power controller of the DC transmission system, ensuring the stability of the control system and reducing oscillation risks. Furthermore, supporting the coordinated operation of hybrid power grids, high-precision harmonic measurement of DC lines facilitates coordinated switching of AC filters and optimization of converter operation, achieving coordinated harmonic suppression of AC and DC systems, meeting the requirements of power quality supervision and standardization, and ensuring the safe operation of the power system. Based on the above, this invention aims to provide a method for improving the measurement accuracy of UHVDC voltage dividers under harmonic conditions. Addressing the shortcomings of UHVDC voltage dividers, such as the susceptibility of primary voltage division to stray capacitance, distortion of sampling signals from local acquisition devices, and interference in signal transmission, the invention optimizes the voltage divider as a whole: achieving linear changes in the voltage divider's transmission characteristics through parameter matching, while simultaneously improving the hardware performance of the sampling circuit. By optimizing the circuit structure design and specifically improving the filtering anti-aliasing performance, the DC voltage divider as a whole can achieve good wideband characteristics under harmonic conditions, and reduce the distortion rate of the signal from the primary high-voltage bus to the control and protection system.

[0056] In one embodiment of the present invention, a high-voltage-level resistive-capacitive DC voltage divider with high measurement accuracy under harmonic conditions is provided, such as... Figure 1 As shown, the voltage divider includes a high-voltage arm, a low-voltage arm, a resistance-capacitance compensation unit, a secondary voltage divider plate, and an analog-to-digital conversion sampling circuit. The voltage divider typically has an insulating sleeve, with the high-voltage arm located inside the insulating sleeve and the low-voltage arm located inside the voltage divider base within the insulating sleeve.

[0057] The high-voltage arm and the low-voltage arm are connected in series and configured to be connected in series between the high-voltage line and ground. The low-voltage arm is configured to generate a low-voltage signal proportional to the high voltage of the high-voltage line.

[0058] The RC compensation unit is located at the electrical boundary between the high-voltage arm and the low-voltage arm; for example Figure 1 As shown, the RC compensation unit includes a compensation resistor and a compensation capacitor connected in parallel, which is configured to correct the frequency response. The RC compensation unit is located outside the insulating sleeve and outside the base, preferably inside the local acquisition unit box. The RC compensation unit is connected in parallel with the low-voltage arm through a shielded cable. In this way, the measurement accuracy of the DC voltage divider can be improved without changing the original structure of the high-voltage arm and the low-voltage arm in the original DC voltage divider.

[0059] See also Figure 1A secondary voltage divider board is positioned between the RC compensation unit and the analog-to-digital conversion sampling circuit. The secondary voltage divider board includes several branches connected in parallel across the RC compensation unit. Each branch has at least two secondary voltage divider resistors connected in series and a secondary voltage divider capacitor connected in parallel across the secondary voltage divider resistors. The secondary voltage divider board and the analog-to-digital conversion sampling circuit are housed in the same local acquisition unit box, which has a shielded enclosure. The secondary voltage divider board is configured with multiple signal channels to generate independent harmonic signals and output analog low-voltage harmonic signals to the analog-to-digital conversion sampling circuit through one or more signal channels. After receiving the harmonic signals from multiple signal channels, the final control and protection system can process them, such as performing data alignment and verification, to filter out harmonic signals that are significantly different from those of other channels, thereby ensuring optimized system control. Under actual operating conditions, the compensation capacitor is calculated based on the measured stray parameters and the transfer function calculation formula. A resistor-capacitor (RC) compensation unit is connected in parallel between the secondary voltage divider plate and the main voltage divider. By adjusting the compensation resistor and capacitor, the voltage division ratio of the DC voltage divider can be kept stable, reducing the nonlinear influence of stray capacitance and harmonics on the broadband transfer characteristics of the voltage divider circuit. The voltage division ratio of traditional UHVDC voltage dividers in converter stations is highly susceptible to environmental stray parameters. Under high-frequency harmonic conditions, the signal output by the voltage divider cannot accurately reproduce the actual waveform of the DC bus voltage, especially since high-frequency components are attenuated or phase-shifted, leading to deviations in the measured effective voltage value, harmonic content, and other parameters. This invention compensates for the influence of actual stray parameters through an RC compensation unit, effectively reducing the impact of stray parameters on the voltage division ratio of the voltage divider and improving the measurement accuracy of the equipment.

[0060] A major improvement in this invention is the adoption of a modular analog-to-digital (ADC) sampling circuit scheme to replace the traditional resistor-divided analog signal transmission cable scheme. By adjusting the parameters of the RC compensation unit, reconstructing the ADC sampling circuit structure, and using fiber optic transmission methods, this effectively replaces the traditional analog voltage transmission scheme while ensuring insulation strength and thermal stability requirements are met. This optimizes the frequency characteristics of the measuring device and improves its anti-interference performance, providing theoretical support for the large-scale application of analog-to-digital conversion combined with fiber optic transmission schemes in high-voltage measuring equipment. Specifically, as follows... Figure 2 As shown, the analog-to-digital conversion sampling circuit is configured with a differential input isolation, an anti-aliasing filter, an adjustable gain amplifier, a voltage follower, an analog-to-digital converter, and an optical fiber transmission module connected in sequence. The differential input isolation receives the analog low-voltage harmonic signal output by the independent secondary voltage divider, and the optical fiber transmission module is configured to be connected to the input of the control and protection system.

[0061] The following is a brief introduction to the innovative design of the analog-to-digital conversion sampling circuit:

[0062] Firstly, a differential input structure is designed to suppress common-mode interference, and selection principles for the input operational amplifier are proposed. A differential input operational amplifier is used at the input of the analog-to-digital sampling circuit to effectively suppress common-mode interference from ground loops, power supply fluctuations, and external electromagnetic fields, improving the system's common-mode rejection ratio (CMRR) to over 90dB. The selection of the input operational amplifier mainly focuses on performance indicators such as input reactance, bandwidth, CMRR, and slew rate. Bandwidth performance is selected based on harmonic measurement requirements, and a differential input operational amplifier chip with a high CMRR is chosen for further selection. Simultaneously, the required operational amplifier chip is obtained according to the principle of matching the operational amplifier's input reactance with the voltage divider's RC unit. When an operational amplifier with mismatched input reactance is connected to the voltage divider circuit, circuit coupling may cause complex nonlinear effects on the voltage divider's transmission characteristics. This embodiment adopts the operational amplifier selection principle of matching the input reactance of the operational amplifier with the resistor-capacitor unit, which solves the problem of resistor-capacitor unit mismatch and avoids the output signal attenuation caused by it. At the same time, the degree of attenuation is related to the input signal frequency, which causes irregular distortion of the bandwidth and directly affects the measurement accuracy of the equipment. This also avoids the adverse consequences. It reveals a high-precision acquisition design method for analog-to-digital sampling circuits.

[0063] Secondly, to address the aliasing problem in harmonic measurements, an anti-interference enhancement and anti-aliasing filter was designed. To address the aliasing issue in harmonic measurements, an active and passive filter circuit was used in conjunction with the design. A second-order active low-pass filter with an adjustable cutoff frequency was designed. Its core parameters are set according to the Nyquist sampling theorem and the system's highest-priority harmonic frequency to determine the filter's cutoff frequency, thus retaining all effective harmonic components while sharply suppressing high-frequency noise and preventing aliasing distortion. Simultaneously, an RC filter network was set between the output of the analog-to-digital converter (ADC) driver operational amplifier and the ADC input pin. This serves as a supplement to the anti-aliasing filter and also limits the current surge generated during ADC sampling, protecting the front-end operational amplifier and optimizing its setup performance. To address the vulnerability of traditional UHVDC voltage divider local acquisition devices and lines to interference, the introduced high-frequency noise can cause harmonic aliasing, severely interfering with both DC and harmonic measurement results. The anti-aliasing filter design effectively isolates high-frequency noise outside the bandwidth while providing good protection for the ADC, effectively improving the equipment's anti-interference capability. This invention discloses an overall design structure for an ultra-high voltage DC voltage divider, which effectively improves the metering performance of the DC voltage divider and promotes the digital development of the DC voltage divider.

[0064] Thirdly, focusing on the performance of the analog-to-digital converter (ADC), high-performance ADC conversion and sampling parameter optimization are performed. A successive approximation ADC is selected, whose key performance parameters must meet the requirements for resolution, throughput, DC accuracy, dynamic characteristics, signal-to-noise ratio, and total harmonic distortion (THD). A voltage follower is installed before the ADC to provide good protection for the ADC while fully restoring the transmitted signal. The sampling rate setting is optimized. Based on the characteristic harmonics of the UHVDC transmission system, mainly the 4th, 8th, 12th, and 24th harmonics, the sampling rate needs to be set according to the highest target measurement frequency to ensure high-fidelity reconstruction of the harmonic waveform. Then, the ADC output signal is transmitted into the control and protection system via optical fiber to ensure that the signal accurately reflects the bus voltage waveform.

[0065] In summary, the embodiments of the present invention have made an innovative structural design for the sampling circuit of the DC voltage divider, so as to realize that the DC voltage divider has good wideband characteristics under harmonic conditions, reduce the distortion rate of the signal in the process of output to the control and protection system, improve the measurement accuracy of the equipment, and solve the defects of UHV DC voltage dividers under harmonic conditions, such as insufficient measurement accuracy, anti-aliasing filtering performance, anti-interference ability, and susceptibility to stray parameters.

[0066] based on Figure 1 and Figure 2 The structure of the resistive-capacitive DC voltage divider shown is achieved through, as... Figure 3 The design parameters of the RC DC voltage divider are determined as shown in the following manner:

[0067] S100: Derive the transfer function of the voltage divider as the relationship between the signal frequency and the resistance and capacitance of the high-voltage and low-voltage arms of the voltage divider: Where H(jω) is the voltage divider transfer function, j is the imaginary unit, ω is the angular frequency, and R... H C is the equivalent resistance of the high-voltage arm. H R is the equivalent capacitance of the high-voltage arm. L For the equivalent resistance of the low-voltage arm, C L The equivalent capacitance of the low-voltage arm;

[0068] The high-pressure arm and low-pressure arm of the voltage divider constitute the primary voltage divider, and the high-pressure arm and low-pressure arm in the secondary voltage divider plate constitute the secondary voltage divider. In this embodiment, the transfer function corresponding to the secondary voltage divider is the same as above.

[0069] S200: Based on the requirements of the control and protection system for amplitude-frequency fluctuations and / or phase shifts, calculate the high-voltage arm RC parameters and low-voltage arm RC parameters that meet these requirements, i.e., satisfy the relationship in step S100; the calculated high-voltage arm RC parameters R... H C H Low-voltage arm resistance-capacitance parameters R L C L It is not the only solution.

[0070] Similarly, the resistance and capacitance parameters of the secondary pressure divider plate are calculated.

[0071] S300: Based on the frequency characteristics of the analog-to-digital conversion sampling circuit, calculate the circuit structure parameters of the analog-to-digital conversion sampling circuit to match the signal of the secondary voltage divider, and ensure that the measurement accuracy requirements are met within the target bandwidth; specifically as follows:

[0072] Assume the rated output voltage range of the secondary voltage divider is ±5V, and denoted as Z for its output impedance. out-board This determines the magnitude of the load effect exerted on it by subsequent circuits. The target bandwidth is determined by the requirements of the control and protection system. For example, if it is necessary to accurately measure the 40th harmonic and the power frequency is 50Hz, then the maximum frequency is 2000Hz. This is the appropriate frequency boundary, denoted as f. max This frequency boundary ensures that the measurement accuracy requirements are met within the target bandwidth.

[0073] The sampling circuit typically refers to the analog front-end before the ADC, and mainly consists of three modules, the parameters of which need to be calculated one by one:

[0074] The first step is impedance matching and buffering for differential input isolation. A precision operational amplifier with extremely high input impedance and extremely low output impedance should be selected; its input impedance should be much greater than the output impedance Z of the secondary voltage divider. out-board Its operational amplifier output impedance should be low enough to drive subsequent stages; the gain-bandwidth product of the operational amplifier needs to be much higher than the aforementioned frequency boundary f. max This ensures stable gain and small phase shift within the target bandwidth.

[0075] Secondly, the cutoff frequency of the anti-aliasing filter should be greater than the aforementioned frequency boundary f. max This can be slightly larger. The resistance and capacitance values ​​of the filter are calculated based on the normalization coefficients corresponding to the selected cutoff frequency and filter type. For example, for Butterworth filters, there are readily available design tables. The capacitance value can be fixed as a standard value (e.g., 1nF) first, and then the resistance value can be calculated.

[0076] Third, the gain range of the adjustable gain amplifier is determined based on the minimum and maximum amplitude of the input signal. The effective bandwidth of the gain amplifier operating at maximum gain must be greater than the cutoff frequency of the anti-aliasing filter, thereby ensuring the amplitude and phase accuracy of the entire signal chain within the target frequency band.

[0077] S400: Verify the harmonic measurement error of the RC DC voltage divider after the parameters are determined. If the verification fails, recalculate the parameters until the verification passes.

[0078] In step S200, the high-voltage arm resistance-capacitance parameter R is determined. H C HLow-voltage arm resistance-capacitance parameters R L C L After determining the parameters of the three modules of the analog front end of the sampling circuit in step S300, a complete mathematical model of the voltage divider is constructed, a standard harmonic signal is input, the output value is compared with the theoretical value, and the amplitude and phase errors are calculated. If the error exceeds the preset accuracy threshold, the verification fails; if the error is less than the preset accuracy threshold, the verification passes.

[0079] Specifically, the complete mathematical model of the voltage divider is constructed in the following way:

[0080] Based on the determined high-voltage arm resistance and capacitance parameters and low-voltage arm resistance and capacitance parameters, construct the main voltage divider model;

[0081] The circuit structure parameters of the analog-to-digital conversion sampling circuit are calculated, including the common-mode rejection ratio and isolation voltage level of the differential input isolation, the cutoff frequency of the anti-aliasing filter, and the gain-bandwidth product of the adjustable gain amplifier. The differential input isolation, anti-aliasing filter, and adjustable gain amplifier of the analog front end in the RC supplement unit and the analog-to-digital conversion sampling circuit are modeled as an overall analog link.

[0082] The main voltage divider model is cascaded with the overall simulation link to obtain the complete mathematical model of the voltage divider.

[0083] For the RC compensation unit, its compensation resistor is connected in parallel with the resistor of the low-voltage arm, and its compensation capacitor is connected in parallel with the capacitor of the low-voltage arm.

[0084] The resistance and capacitance parameters of the resistance-capacitance compensation unit are optimized in the following ways:

[0085] The transfer function from the high-voltage input to the output of the RC compensation unit is derived as follows: Among them, Z H Z is the equivalent impedance of the high-voltage arm. comp Z represents the impedance of the RC compensation unit. ' L This is the equivalent input impedance of the low-voltage arm and the secondary voltage divider plate;

[0086] Based on the requirements of the control and protection system for amplitude-frequency fluctuations and / or phase shifts, the impedance Z of the RC compensation unit that meets these requirements can be calculated. comp ;

[0087] According to the formula Z = R / (1 + jωRC), calculate the impedance Z that satisfies the above conditions. comp compensation resistor R comp and compensation capacitor C comp The calculation result here is not a unique solution.

[0088] In constructing a complete mathematical model of the voltage divider, it is also necessary to base it on the impedance Z.comp compensation resistor R comp and compensation capacitor C comp .

[0089] According to another aspect of the present invention, a high-precision digital DC measurement system is provided, such as... Figure 1 As shown, the measurement system includes a high-voltage-level RC DC voltage divider as described above. The system also includes a merging unit, an I / O interface device, and a control and protection system. The merging unit is configured to aggregate raw sampled value messages from the analog-to-digital conversion sampling circuits of multiple DC voltage dividers, and to synchronize, align, reassemble, and publish the aggregated data.

[0090] The IO interface device is configured as a bidirectional data interface for transmission between the merging unit and the control and protection system.

[0091] This invention aims to optimize the design of voltage divider and sampling circuits in traditional UHVDC voltage dividers based on the sampling accuracy requirements of control and protection systems, thereby improving the wideband sampling performance of the equipment. The method includes designing an RC compensation unit for the DC voltage divider according to sampling requirements, designing specific structural parameters of the modular sampling circuit based on wideband transmission characteristics, and verifying harmonic measurement errors. By simulating the wideband transmission characteristics of the voltage divider body, secondary voltage divider board, and sampling circuit as a whole, and the relationship between harmonic measurement and frequency characteristics, a modular sampling circuit design is adopted to optimize structural parameters and wideband measurement accuracy. This method successfully improves the sampling accuracy of the local acquisition device for traditional DC voltage dividers, enhances electromagnetic compatibility, improves the anti-aliasing capability of harmonic measurements and the reliability of equipment operation, and promotes the digital transformation of high-voltage measurement equipment, while ensuring electromagnetic interference resistance, thermal balance parameters, and meeting measurement error requirements. Specifically, this method focuses on the design of the secondary voltage divider plate and analog-to-digital sampling circuit within the local acquisition device of the DC voltage divider. Its circuit structure parameters are highly correlated with harmonic acquisition and analog-to-digital conversion output. By simulating and calculating its transfer function, its wideband transmission characteristics can be further obtained, facilitating the design of specific structural parameters for the DC voltage divider sampling circuit. This method can provide a theoretical basis for the structural design and error control of DC voltage dividers in high-voltage power metering devices, further optimizing the accuracy and stability of power metering.

[0092] To improve the measurement accuracy of high-voltage DC dividers, and even ultra-high-voltage DC dividers, under harmonic conditions, this invention derives the transfer function of the DC divider's RC unit, designs an RC compensation unit based on the influence of stray parameters on the voltage division ratio, quantitatively analyzes the relationship between different input frequency signals and the electromagnetic unit structure design, and, based on measurement accuracy requirements, proposes a design principle for matching the input reactance of the sampling circuit operational amplifier with the voltage divider circuit while designing the RC compensation unit to match stray parameters. This reveals the design principles and methods for the DC divider's RC unit. Further matching the input reactance of the sampling circuit operational amplifier, and designing the specific structural parameters of the analog-to-digital conversion sampling circuit based on wideband transmission characteristics, and verifying harmonic measurement errors, a modular analog-to-digital sampling circuit scheme is proposed to replace the simple resistor-divided analog signal cable transmission scheme. While ensuring electromagnetic interference resistance, thermal balance parameters, and meeting measurement error requirements, this invention successfully improves the sampling accuracy of traditional DC voltage divider local acquisition devices under harmonic conditions, improves electromagnetic compatibility characteristics, enhances the anti-aliasing capability of harmonic measurements and the reliability of equipment operation, and promotes the digital transformation of high-voltage measurement equipment. An innovative analog-to-digital sampling circuit structure can replace the simple resistor-divider analog signal transmission cable scheme while meeting the requirements of anti-harmonic aliasing and electromagnetic compatibility. This effectively improves the measurement accuracy and operational stability of the equipment, and proposes a solution that combines high precision and anti-interference capability.

[0093] Compared with existing traditional ultra-high voltage DC voltage dividers, the advantages of this invention are:

[0094] 1. Promote digital transformation. The development of digital grids requires measurement equipment to evolve towards low-power mode. Through the adjustable gain design of sampling circuits, traditional DC voltage dividers can accurately meet the low-power signal transmission needs in smart grid construction. At the same time, the structured design of power electronics enhances the scalability of sampling circuits, adapts to subsequent digital upgrades, and aligns with the trend of digital transformation of power systems.

[0095] 2. Improved accuracy of the overall measurement system for RC DC voltage dividers. By designing matching RC units and matching sampling circuit input reactance in the voltage divider circuit, an innovative modular sampling circuit design is implemented. This improves the voltage division ratio performance, significantly enhances anti-aliasing filtering capability, and directly improves the accuracy of DC and harmonic measurements. This provides theoretical support for the large-scale application of modular design in the sampling circuits of measurement equipment.

[0096] 3. Based on improving the measurement accuracy of the entire DC voltage divider system under harmonic conditions, operational reliability is enhanced by employing a fiber optic transmission scheme with local digitization and anti-aliasing filtering. Compared to traditional DC voltage dividers that directly transmit analog signals via cable or through fiber optic after analog-to-digital conversion, the combination of functional filtering circuits and fiber optic transmission effectively avoids high-frequency noise aliasing, strengthens the anti-interference performance of the signal transmission line, simplifies the harmonic signal spectrum composition, improves equipment maintenance efficiency, and enhances the economic benefits and operational reliability of the DC voltage divider.

[0097] This invention provides theoretical and practical guidance for improving the measurement accuracy of ultra-high voltage DC voltage dividers under harmonic conditions, and ensures the reliability and accuracy of high voltage measurement devices.

[0098] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0099] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A high-voltage-level RC DC voltage divider with high measurement accuracy under harmonic conditions, characterized in that, It includes a high-voltage arm, a low-voltage arm, a resistance-capacitance compensation unit, a secondary voltage divider board, and an analog-to-digital conversion sampling circuit. The high-voltage arm and the low-voltage arm are connected in series and configured to be connected in series between the high-voltage line and ground. The resistance-capacitance compensation unit is located at the electrical boundary between the high-voltage arm and the low-voltage arm. The low-voltage arm is configured to generate a low-voltage signal proportional to the high voltage of the high-voltage line. The RC compensation unit includes a compensation resistor and a compensation capacitor connected in parallel, which are configured to correct the frequency response. The secondary voltage divider is disposed between the resistor-capacitor compensation unit and the analog-to-digital conversion sampling circuit, and the secondary voltage divider is configured to generate independent harmonic signals. The analog-to-digital conversion sampling circuit is configured with a differential input isolation, an anti-aliasing filter, an adjustable gain amplifier, a voltage follower, an analog-to-digital converter, and an optical fiber transmission module connected in sequence. The differential input isolation receives the analog low-voltage harmonic signal output independently from the secondary voltage divider, and the optical fiber transmission module is configured to be connected to the input terminal of the control and protection system.

2. The high-voltage-level RC DC voltage divider according to claim 1, characterized in that, The design parameters of the resistive-capacitive DC voltage divider are determined using the following method: Based on the structure of the RC DC voltage divider, the transfer function of the voltage divider is derived as the relationship between the signal frequency and the resistance and capacitance of the voltage divider: Where H(jω) is the voltage divider transfer function, j is the imaginary unit, ω is the angular frequency, and R... H C is the equivalent resistance of the high-voltage arm. H R is the equivalent capacitance of the high-voltage arm. L For the equivalent resistance of the low-voltage arm, C L The equivalent capacitance of the low-voltage arm; Based on the requirements of the control and protection system for amplitude-frequency fluctuations and / or phase shifts, the high-voltage arm RC parameters and low-voltage arm RC parameters that meet these requirements are calculated in reverse. Based on the frequency characteristics of the analog-to-digital conversion sampling circuit, the circuit structure parameters of the analog-to-digital conversion sampling circuit are calculated to match the signal of the secondary voltage divider, and to ensure that the measurement accuracy requirements are met within the target bandwidth. After determining the parameters, the harmonic measurement error of the RC DC voltage divider is checked. If the check fails, the parameters are recalculated until the check passes.

3. The high-voltage-level RC DC voltage divider according to claim 2, characterized in that, The compensation resistor of the RC compensation unit is connected in parallel with the resistor of the low-voltage arm, and the compensation capacitor is connected in parallel with the capacitor of the low-voltage arm. The resistance and capacitance parameters of the resistance-capacitance compensation unit are optimized in the following ways: The transfer function from the high-voltage input to the output of the RC compensation unit is derived as follows: Among them, Z H Z is the equivalent impedance of the high-voltage arm. comp Z' is the impedance of the RC compensation unit. L This is the equivalent input impedance of the low-voltage arm and the secondary voltage divider plate; Based on the requirements of the control and protection system for amplitude-frequency fluctuations and / or phase shifts, the impedance Z of the RC compensation unit that meets these requirements can be calculated. comp ; According to the formula Z = R / (1 + jωRC), calculate the impedance Z that satisfies the above conditions. comp The compensation resistor and compensation capacitor.

4. The high-voltage-level RC DC voltage divider according to claim 3, characterized in that, The high-voltage arm and the low-voltage arm are installed inside an insulating sleeve, and the resistance-capacitance compensation unit is installed inside a local acquisition unit box. The resistance-capacitance compensation unit is connected in parallel with the low-voltage arm through a shielded cable.

5. The high-voltage-level RC DC voltage divider according to claim 2, characterized in that, Based on the frequency characteristics of the analog-to-digital conversion sampling circuit, calculate the circuit structure parameters of the analog-to-digital conversion sampling circuit to match the signal of the secondary voltage divider, and ensure that the measurement accuracy requirements are met within the target bandwidth, including: Obtain the output impedance of the secondary voltage divider, denoted as Z. out-board To obtain the target bandwidth required by the control and protection system, and to determine the target frequency boundary, denoted as f. max ; For differential input isolation, select an input impedance greater than the output impedance Z of the secondary voltage divider. out-board The operational amplifier is selected such that its gain-bandwidth product is higher than the target frequency boundary f. max ; For anti-aliasing filters, a cutoff frequency greater than the target frequency boundary f is selected. max The resistance and capacitance values ​​of the filter are calculated based on the normalization coefficients corresponding to the selected cutoff frequency and filter type. For an adjustable gain amplifier, the gain range of the gain amplifier is determined based on the minimum and maximum amplitudes of the input signal, and the effective bandwidth of the gain amplifier operating at the upper limit of the gain range is greater than the cutoff frequency of the anti-aliasing filter.

6. The high-voltage-level resistive-capacitive DC voltage divider according to any one of claims 2 to 5, characterized in that, Verification can be performed in the following ways: Using the established parameters, a complete mathematical model of the voltage divider is constructed. A standard harmonic signal is input, and the output value is compared with the theoretical value. The amplitude and phase errors are calculated. If the error exceeds the preset accuracy threshold, the verification fails; if the error is less than the preset accuracy threshold, the verification passes.

7. The high-voltage-level RC DC voltage divider according to claim 6, characterized in that, The complete mathematical model of the voltage divider is constructed in the following way: Based on the determined high-voltage arm resistance and capacitance parameters and low-voltage arm resistance and capacitance parameters, construct the main voltage divider model; The circuit structure parameters of the analog-to-digital conversion sampling circuit are calculated, including the common-mode rejection ratio and isolation voltage level of the differential input isolation, the cutoff frequency of the anti-aliasing filter, and the gain-bandwidth product of the adjustable gain amplifier. The differential input isolation, anti-aliasing filter, and adjustable gain amplifier of the analog front end in the RC supplement unit and the analog-to-digital conversion sampling circuit are modeled as an overall analog link. The main voltage divider model is cascaded with the overall simulation link to obtain the complete mathematical model of the voltage divider.

8. The high-voltage-level RC DC voltage divider according to claim 1, characterized in that, The secondary voltage divider is configured with multiple signal channels, each of which is configured to output an independent analog low-voltage harmonic signal to the differential input. The secondary voltage divider includes several branches connected in parallel across the two ends of the resistor-capacitor compensation unit. Each branch has at least two secondary voltage divider resistors connected in series and a secondary voltage divider capacitor connected in parallel across the two ends of the secondary voltage divider resistors.

9. The high-voltage-level RC DC voltage divider according to claim 8, characterized in that, The secondary voltage divider and the analog-to-digital conversion sampling circuit are housed in the same local acquisition unit box, which has a shielded housing.

10. A high-precision digital DC measurement system, characterized in that, The system includes a high-voltage-level RC DC voltage divider as described in any one of claims 1 to 8, and further includes a merging unit, an I / O interface device, and a control and protection system, wherein the merging unit is configured to aggregate raw sampled value messages from the analog-to-digital conversion sampling circuits of multiple DC voltage dividers, and to synchronize, align, reassemble, and publish the aggregated data. The IO interface device is configured as a bidirectional data interface for transmission between the merging unit and the control and protection system.

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