Test Circuit and Method for Voltage-sharing Capacitors of HVDC Converter Valve Assemblies

Abstract

The present invention provides a voltage-sharing capacitor test circuit and method for a high-voltage DC transmission converter valve assembly. The converter valve assembly includes a plurality of serially-connected thyristor stages, and the assembly voltage-sharing capacitor is connected in parallel across the two ends of the series branch of the plurality of serially-connected thyristor stages. The test voltage source is connected in series with a sampling resistor and then connected in parallel across the two ends of the assembly voltage-sharing capacitor. The follower includes an operational amplifier. The test voltage source is connected to the positive input terminal of the operational amplifier through the sampling resistor. The negative input terminal of the operational amplifier is connected to the output terminal and then connected to any position between the plurality of serially-connected thyristor stages. The output terminal of the follower is in a high-impedance state. By collecting the voltage across the sampling resistor, the current value flowing through the assembly voltage-sharing capacitor can be accurately calculated, and based on the voltage and current values of the assembly voltage-sharing capacitor, the capacitance value of the assembly voltage-sharing capacitor can be obtained. The present invention simplifies the test process of the assembly voltage-sharing capacitor and improves the accuracy and working efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage direct current (HVDC) converter valve, and particularly to a test circuit and method for the grading capacitors of an HVDC converter valve assembly. Background Art

[0002] Converter valves are important components in HVDC transmission projects and are of great significance to the safe operation of DC transmission. To meet the requirements of high voltage for converter valves, a single converter valve is composed of multiple thyristors connected in series. Generally, a valve assembly is composed of 6 - 15 thyristor levels connected in series, and then multiple valve assemblies form a valve tower, and each valve hall is equipped with multiple valve towers. The stray capacitance distribution in the valve tower is very complex, and these stray capacitances may cause uneven voltage distribution under the condition of steep-front wave voltage, especially the uneven voltage between valve assemblies. Therefore, grading capacitors filled with SF6 gas and with a capacitance of several nanofarads are designed in the valve assembly.

[0003] According to the requirements of the converter valve maintenance standard "DLT 273 - 2012 ±800kV UHVDC Equipment Preventive Test Regulations", it is necessary to regularly detect the parameter values of the grading capacitors of the valve assembly. However, since there are hundreds of valve assemblies in a single converter station, the workload of measuring the parameter of the grading capacitor of the valve assembly during maintenance is huge. The traditional method for testing the grading capacitor of the valve assembly is mainly to directly test it using a multimeter, a bridge, etc. This method requires removing the original circuit and measuring one by one, which can ensure the test accuracy, but it is easy to cause problems such as excessive contact resistance at the joints when reconnecting the circuit, and there are potential safety hazards. Moreover, the test steps are cumbersome and the efficiency is very low.

[0004] Therefore, how to provide a test circuit and method that can accurately and quickly test the parameter of the grading capacitor of the valve assembly is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a test circuit and method for the grading capacitors of an HVDC converter valve assembly, which can simplify the test process of the grading capacitor of the assembly and improve the work efficiency and accuracy by adding a voltage source and designing a follower and a sampling resistor for the test circuit of the grading capacitor of the assembly.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] On one hand, the present invention provides a test circuit for the grading capacitors of an HVDC converter valve assembly. The converter valve assembly includes multiple thyristor levels connected in series, and the grading capacitor of the assembly is connected in parallel at both ends of the series branch of the multiple thyristor levels connected in series. The test circuit includes a test voltage source, a follower, and a sampling resistor; wherein,

[0008] The test voltage source is connected in series with the sampling resistor and then connected in parallel across both ends of the component equalizing capacitor;

[0009] The follower includes an operational amplifier. The test voltage source is connected to the positive input terminal of the operational amplifier through the sampling resistor. The negative input terminal of the operational amplifier is connected to the output terminal and then connected to any position between the multiple series-connected thyristor levels; the output terminal of the follower is in a high-impedance state.

[0010] Preferably, the test voltage source outputs a sinusoidal AC voltage with adjustable frequency.

[0011] Preferably, the test voltage source includes: a sine wave generator outputs an AC voltage signal, and through a signal regulator and a power amplifier, a sinusoidal AC voltage is output.

[0012] Preferably, a data acquisition circuit is further included, and the data acquisition circuit acquires the sampling voltage across both ends of the sampling resistor.

[0013] Preferably, the data acquisition circuit includes: a filter amplification circuit, a true RMS conversion circuit, and an analog / digital conversion circuit connected in sequence;

[0014] The sampling voltage is connected to the filter amplification circuit for high-frequency interference filtering and signal amplification; the DC signal output by the true RMS conversion circuit is input to the analog / digital conversion circuit. The analog / digital conversion circuit is controlled by a single-chip microcomputer to perform synchronous sampling of the AD of the voltage and current channels, and converts each analog signal into a digital signal.

[0015] Preferably, an industrial-grade embedded main board is further included, which receives the sampling voltage across both ends of the sampling resistor and communicates with the single-chip microcomputer through a serial port to complete the calculation, storage, and display of the component equalizing capacitor value.

[0016] On the other hand, the present invention also provides a test method for the high-voltage DC transmission converter valve component equalizing capacitor test circuit according to the first aspect. The capacitance value is calculated based on the voltage and current of the component equalizing capacitor:

[0017]

[0018] In the formula, U is the voltage across the component equalizing capacitor, I is the current flowing through the component equalizing capacitor, and ω is the frequency of the applied test voltage source. I is the current across the sampling resistor and is obtained by dividing the sampling voltage across the sampling resistor by the resistance value of the sampling resistor.

[0019] It can be seen from the above technical solutions that compared with the prior art, the beneficial effects of the present invention include:

[0020] Through circuit design, the output terminal of the voltage follower of the present invention is in a high-impedance state. The test voltage source only forms a measurement loop with the component equalizing capacitor. The actual value of the component equalizing capacitor can be calculated according to the voltage and current collected by the sampling resistor. It is possible to achieve fast and accurate measurement without removing the lead wires of the equalizing capacitor, reduce the outage time of the valve component, and improve work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings;

[0022] Figure 1 FIG. is a schematic diagram of the circuit connection structure of the converter valve component provided by the embodiment of the present invention;

[0023] Figure 2 is a test circuit diagram of the equalizing capacitor of the high-voltage DC transmission converter valve component provided by the embodiment of the present invention;

[0024] Figure 3 is a block diagram of the test platform for the equalizing capacitor of the converter valve component provided by the embodiment of the present invention;

[0025] Figure 4 is a schematic diagram of the working principle of the test voltage source provided by the embodiment of the present invention;

[0026] Figure 5 is a schematic diagram of the working principle of the voltage follower provided by the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0028] The valve component is the basic electrical unit of the converter valve. From a mechanical structure, each single valve is composed of a certain number of valve components. The structure of the valve component is as Figure 1 shown. Each valve component is composed of several thyristor levels. Each thyristor level is composed of a damping capacitor, a damping resistor, a thyristor, and an equalizing capacitor. Several thyristor levels and a series-connected saturated valve reactor form a valve component. The valve component also includes a component equalizing capacitor.

[0029] Due to the high voltage level of the HVDC transmission project, the number of series-connected thyristors is very large, and the size of the converter valve body is relatively large. For this reason, the non-uniformity of the dynamic voltage distribution on the converter valve modules and components caused by the dispersion of the stray capacitance distribution is increased. Under the action of the steep-front impulse voltage, due to the very high dv / dt, the effect of the dispersion of the stray capacitance distribution will be further enhanced, and this non-uniform distribution of the dynamic voltage will become more obvious. The component grading capacitors can play a good voltage equalizing role when the valve is subjected to high-frequency impulse voltage.

[0030] Since the component grading capacitors are connected in parallel at both ends of the thyristor stage, and a group of thyristor stages consists of multiple thyristors, the capacitance value of the component grading capacitors is generally several nanofarads. The capacitance of the thyristor stage damping circuit is in the microfarad range, which is much larger than the capacitance value of the component grading capacitors. Therefore, it is difficult to directly measure the capacitance value of the component grading capacitors with a capacitance meter. To accurately measure the capacitance value of the component grading capacitors, this patent adopts an indirect measurement method.

[0031] As Figure 2 shown, an embodiment of the present invention proposes a test circuit for the component grading capacitors of a HVDC converter valve, including a test voltage source, a follower, and a sampling resistor; the test voltage source is connected in series with the sampling resistor and then connected in parallel at both ends of the component grading capacitors; the follower includes an operational amplifier, the test voltage source is connected to the positive input terminal of the operational amplifier through the sampling resistor, the negative input terminal of the operational amplifier is connected to the output terminal, and then connected to any position between multiple series-connected thyristor stages; the output terminal of the follower is in a high-impedance state.

[0032] In this embodiment, the output terminal of the operational amplifier is connected to any position between multiple series-connected thyristor stages, including being connected between the series nodes of every two thyristor stages, and not including the two end nodes of the series branch.

[0033] In this embodiment, as Figure 5 shown, the voltage at the positive input terminal of the follower is equal to the voltage at the output terminal, and the current is zero. The output terminal of the follower is in a high-impedance state. The test voltage source only forms a measurement loop with the component grading capacitors. The output voltage of the voltage follower is basically the same as the input voltage, and it is in a high-impedance state for the front-stage circuit and in a low-impedance state for the rear-stage circuit. Therefore, it plays an "isolation" role for the front-stage and rear-stage circuits, and the output current of the test source only flows through the component grading capacitors. According to the voltage and current collected by the sampling resistor, the voltage and current at both ends of the component grading capacitors can be calculated.

[0034] In one embodiment, the test platform for the component grading capacitors of the converter valve is as Figure 3 shown, including four parts: a test voltage source, a data acquisition circuit, an industrial-grade embedded main board, and a follower.

[0035] In one embodiment, the test voltage source outputs a sinusoidal AC voltage with adjustable frequency.

[0036] In this embodiment, the working principle of the test voltage source is as shown in the appendix Figure 4 As shown, the single-chip microcomputer controls the waveform generator to output an AC voltage signal, which is output through signal regulation and power amplification. The sine wave generating circuit uses a precision high-frequency waveform generator MAX038, which can generate accurate standard sine AC signals. The output voltage frequency can be controlled separately by adjusting the current, voltage or resistance, and the amplitude of the output voltage can be adjusted to the voltage value required for testing through a signal regulator. In this embodiment, the power amplification circuit uses high-power high-voltage DMOS transistors TDA7293. To increase the output power, three power amplifier transistors are connected in parallel for the power amplification device, and they work in a master-slave mode, that is, all circuits from input to output of the master chip are working, and the front-stage parts of the other two slave chips are shielded, and only the power output part of the rear stage is working. To improve the accuracy of the test voltage, the output voltage accuracy is made more accurate by readjusting through the voltage feedback signal.

[0037] In one embodiment, the data acquisition circuit acquires the sampling voltage across the sampling resistor.

[0038] In this embodiment, the data acquisition circuit includes a filter amplification circuit, a true RMS conversion circuit, and an analog / digital conversion circuit connected in sequence. Since the equalizing capacitor of the valve assembly is only a few nanofarads and the flowing test current is small, a precision resistor is used to convert the current signal into a voltage signal. The sampling voltage is connected to the filter amplification circuit for high-frequency interference filtering and signal amplification. The DC signal output by the true RMS conversion circuit is input to the analog / digital conversion circuit. The analog / digital conversion circuit is controlled by the single-chip microcomputer to perform synchronous sampling of the AD of the voltage and current channels, convert each analog signal into a digital signal, and the single-chip microcomputer reads the digital signal.

[0039] In one embodiment, the industrial-grade embedded mainboard receives the sampling voltage across the sampling resistor and communicates with the single-chip microcomputer through a serial port to complete the calculation, storage, and display of the equalizing capacitor value of the component.

[0040] In this embodiment, the industrial-grade embedded mainboard includes a microprocessor, a chipset, an LVDS (Low-Voltage Differential Signaling) interface, a CF (Compact Flash) card interface, a USB (Universal Serial BUS) interface, and a GPIO (General Purpose Input Output) interface. The mainboard communicates with the single-chip microcomputer through a serial port to complete the calculation, storage, and display of the component capacitance value, the setting of the amplitude and frequency of the test voltage source, and realizes human-machine interface interaction through the LVDS interface.

[0041] The embodiments of the present invention also disclose a test method based on the above-mentioned voltage-sharing capacitor test circuit of the high-voltage DC transmission converter valve assembly. The capacitance value is calculated according to the voltage and current of the component voltage-sharing capacitor:

[0042]

[0043]

[0044] In the formula, U is the voltage across the component voltage-sharing capacitor, I is the current flowing through the component voltage-sharing capacitor, and ω is the frequency of the applied test voltage source.

[0045] Apply the test voltage across the component voltage-sharing capacitor. The current value flowing through the component voltage-sharing capacitor can be accurately calculated by collecting the voltage across the sampling resistor. According to the voltage and current values of the component voltage-sharing capacitor, the capacitance value of the component voltage-sharing capacitor can be calculated by formula (2). The test results are saved in a computer-readable storage medium and displayed on an LCD display screen. The test method is simple and easy to implement, and has high working efficiency.

[0046] Compared with the traditional test methods using multimeters, bridges, etc., this embodiment is faster and more accurate in the test process. The traditional method requires removing the capacitor leads, reconnecting after the test is completed, and then performing a low-voltage test on the converter valve to confirm good wiring. The whole process takes about 2 hours. Using the method of this embodiment only takes about 10 minutes and no converter valve-related tests are required.

[0047] The above has introduced in detail the voltage-sharing capacitor test circuit and method of the high-voltage DC transmission converter valve assembly provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

[0048] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A voltage-sharing capacitor test circuit for a high-voltage DC transmission converter valve assembly, where the converter valve assembly includes a plurality of serially-connected thyristor levels, and the assembly voltage-sharing capacitors are connected in parallel across both ends of the series branch of the plurality of serially-connected thyristor levels; characterized in that, It includes a test voltage source, a follower, and a sampling resistor; among them, the test voltage source is connected in series with the sampling resistor and then connected in parallel across both ends of the component equalizing capacitor; the follower includes an operational amplifier. The test voltage source is connected to the positive input terminal of the operational amplifier through the sampling resistor. The negative input terminal of the operational amplifier is connected to the output terminal and then connected to any position between the multiple series-connected thyristor stages; the output terminal of the follower is in a high-impedance state.

2. The voltage-sharing capacitor test circuit for a high-voltage DC transmission converter valve assembly according to claim 1, characterized in that, The test voltage source outputs a sinusoidal AC voltage with adjustable frequency.

3. The voltage-sharing capacitor test circuit for a high-voltage DC transmission converter valve assembly according to claim 2, characterized in that, The test voltage source includes: a sine wave generator outputs an AC voltage signal, and through a signal regulator and a power amplifier, outputs a sinusoidal AC voltage.

4. The voltage-sharing capacitor test circuit for a high-voltage DC transmission converter valve assembly according to claim 1, characterized in that, It also includes a data acquisition circuit, and the data acquisition circuit acquires the sampling voltage across both ends of the sampling resistor.

5. The voltage-sharing capacitor test circuit for a high-voltage DC transmission converter valve assembly according to claim 4, characterized in that, The data acquisition circuit includes: a filter amplification circuit, a true RMS conversion circuit, and an analog / digital conversion circuit connected in sequence; the sampling voltage is connected to the filter amplification circuit for high-frequency interference filtering and signal amplification; the DC signal output by the true RMS conversion circuit is input to the analog / digital conversion circuit. The analog / digital conversion circuit is controlled by a single-chip microcomputer to perform synchronous sampling of the AD of the voltage and current channels, and converts each analog signal into a digital signal.

6. The voltage-sharing capacitor test circuit for a high-voltage DC transmission converter valve assembly according to claim 4, characterized in that, It also includes an industrial-grade embedded mainboard, which receives the sampling voltage across both ends of the sampling resistor and communicates with the single-chip microcomputer through a serial port to complete the calculation, storage, and display of the component equalizing capacitor value.

7. A test method for the voltage-sharing capacitor test circuit for a high-voltage DC transmission converter valve assembly according to any one of claims 1-6, characterized in that, Calculate the capacitance value according to the voltage and current of the component equalizing capacitor: In the formula, U is the voltage across both ends of the component equalizing capacitor, I is the current flowing through the component equalizing capacitor, and ω is the frequency of the applied test voltage source.

Images