A method for measuring self-healing discharge frequency of a direct current support capacitor

Abstract

This invention relates to a method for measuring the self-healing discharge frequency of a DC-supported capacitor, comprising the following steps: placing the DC-supported capacitor to be tested in an oven set to a preset temperature and heating for a preset time; connecting the heated DC-supported capacitor to be tested to a test system; monitoring the self-healing signal of the DC-supported capacitor to be tested within a predetermined time through the test system to obtain the number of self-healing discharges and the self-healing discharge frequency; this setup enables accurate measurement of the number of self-healing discharges of the DC-supported capacitor, thereby supporting the conduct of self-healing tests on the DC-supported capacitor and improving the self-healing performance of the DC-supported capacitor.

Description

Technical Field

[0001] This invention relates to the field of power detection technology, and in particular to a method for measuring the self-healing discharge frequency of a DC-supported capacitor. Background Technology

[0002] Currently, DC-supported capacitors are used in flexible DC transmission, primarily to absorb high-amplitude pulsating currents drawn from the inverter to the DC-Link (DC bus), preventing the generation of high-amplitude pulsating voltages across the DC-Link impedance, thus keeping the power supply voltage fluctuations at the inverter end within acceptable limits. They also prevent voltage overshoot and transient overvoltages from the DC-Link from affecting the inverter. In recent years, high-voltage self-healing capacitors using metallized thin films have been widely used in DC-Link applications due to their superior electrical performance.

[0003] The main difference between high-voltage self-healing capacitors and conventional all-film capacitors lies in their thin electrodes. These thin, metallized electrodes give them self-healing properties. High-voltage self-healing capacitors use organic thin films as the energy storage medium. Due to unavoidable defects or impurities in the film during production, the dielectric strength of these areas is lower than that of the surrounding area; these areas are called electrical weak points. As the applied voltage increases, the film at the electrical weak point will break down first, forming a short circuit. Energy stored in other intact components connected in parallel with the faulty component, as well as the energy stored in the faulty component itself, will discharge through the breakdown point, forming a discharge path. Because the electrodes of high-voltage self-healing capacitors are very thin, the localized high temperature caused by the short-circuit breakdown current causes the thin metal layer at the breakdown point to evaporate rapidly, diffuse outwards, and restore insulation. Therefore, localized breakdown does not affect the entire capacitor; this process is called "self-healing." Figure 1 As shown, the capacitor can continue to operate reliably after successful self-healing. The self-healing characteristic of high-voltage self-healing capacitors largely prevents capacitor failure caused by a single weak point breakdown, greatly extending the capacitor's service life.

[0004] The main performance testing methods for DC-supported capacitors include self-healing tests and durability tests. The self-healing test requires the capacitor to possess self-healing properties, with the capacitance change after five self-healing cycles being less than ±0.5%, and the increase in the loss tangent not exceeding 20%. However, current methods for measuring the self-healing discharge of DC-supported capacitors primarily rely on sound or ultrasonic signals, which cannot accurately determine the number of self-healing cycles, making it difficult to effectively determine the number of self-healing cycles for DC-supported capacitors. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for measuring the self-healing discharge frequency of a DC-supported capacitor. Its advantage is that it can accurately measure the number of self-healing discharges of a DC-supported capacitor, thereby supporting the conduct of self-healing tests on DC-supported capacitors and improving the self-healing performance of DC-supported capacitors.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution: a method for measuring the self-healing discharge frequency of a DC-supported capacitor, comprising the following steps: Place the DC support capacitor to be tested in an oven set to a preset temperature and heat for a preset time; The heated DC support capacitor to be tested is connected to the test system; The self-healing signal of the DC support capacitor under test is monitored by the test system within a predetermined time to obtain the number of self-healing discharges and the self-healing discharge frequency.

[0007] Preferably, the method for measuring the self-healing discharge frequency of a DC-supported capacitor provided by the present invention includes a test system comprising a programmable DC power supply, a selection switch, an ultrasonic probe, a discharge resistor, an ultrasonic partial discharge analyzer, and an oscilloscope; the programmable DC power supply is connected to the DC-supported capacitor under test via the selection switch; the ultrasonic probe is attached to the middle position of the outer shell of the DC-supported capacitor under test; the oscilloscope and the ultrasonic partial discharge analyzer are both connected to the output terminal of the ultrasonic probe; the discharge resistor is connected in parallel with the DC-supported capacitor under test; the selection switch is used to switch between charging and discharging circuits; the programmable DC power supply is used to charge the DC-supported capacitor under test; and the ultrasonic probe is used to monitor the self-healing signal of the DC-supported capacitor under test.

[0008] Preferably, in the method for measuring the self-healing discharge frequency of a DC-supported capacitor provided by the present invention, the ultrasonic probe is bonded to the middle position of the outer shell of the DC-supported capacitor to be tested via a coupling agent.

[0009] Preferably, the method for measuring the self-healing discharge frequency of a DC-supported capacitor provided by the present invention, wherein the self-healing signal of the DC-supported capacitor under test is monitored by the test system within a predetermined time to obtain the number of self-healing discharges and the self-healing discharge frequency, includes: When the selection switch is set to position a, the programmable DC power supply applies a preset DC voltage to the DC support capacitor under test for a predetermined time. The ultrasonic probe collects the self-healing signal within a predetermined time and transmits it synchronously to the ultrasonic partial discharge instrument and the oscilloscope. When the ultrasonic partial discharge instrument detects the self-healing electrical signal, the oscilloscope triggers and records the waveform of the self-healing discharge signal. The number of self-healing discharges within a predetermined time period is obtained based on the number of times the oscilloscope is triggered, and the self-healing discharge frequency is calculated based on the period of the waveform of the self-healing discharge signal.

[0010] Preferably, the method for measuring the self-healing discharge frequency of a DC-supported capacitor provided by the present invention, after monitoring the self-healing signal of the DC-supported capacitor under test within a predetermined time through the test system to obtain the number of self-healing discharges and the self-healing discharge frequency, further includes: After the predetermined time for maintaining the preset DC voltage has elapsed, the selection switch is set to position b, and the DC support capacitor under test is discharged through the discharge resistor, causing the voltage of the DC support capacitor under test to drop to 0.

[0011] Preferably, the method for measuring the self-healing discharge frequency of a DC-supported capacitor provided by the present invention, after connecting the heated DC-supported capacitor to the test system and before monitoring the self-healing signal of the DC-supported capacitor to the test within a predetermined time through the test system to obtain the number of self-healing discharges and the self-healing discharge frequency, further includes: The ultrasonic partial discharge instrument was calibrated using a calibrator, and a preset threshold was set. Adjust the trigger voltage value of the oscilloscope so that the oscilloscope is not triggered when no DC voltage is applied to the DC support capacitor under test.

[0012] Preferably, in the method for measuring the self-healing discharge frequency of the DC support capacitor provided by the present invention, the preset duration t is in the range of t≥20h.

[0013] Preferably, the method for measuring the self-healing discharge frequency of a DC-supported capacitor provided by the present invention... When the selector switch is set to position a, the programmable DC power supply applies a preset DC voltage to the DC support capacitor under test for a predetermined time, including: When the selector switch is set to position a, the programmable DC power supply applies 1.1 times the rated voltage to the DC support capacitor under test for 30 seconds; or, when the selector switch is set to position a, the programmable DC power supply applies 1.25 times the rated voltage to the DC support capacitor under test for 10 seconds.

[0014] Preferably, in the method for measuring the self-healing discharge frequency of the DC-supported capacitor provided by the present invention, the preset DC voltage range is: the preset temperature range is 68℃-72℃.

[0015] Preferably, in the method for measuring the self-healing discharge frequency of the DC support capacitor provided by the present invention, the trigger voltage value ranges from 0.5V to 0.6V.

[0016] In summary, the beneficial technical effects of the present invention are as follows: The method for measuring the self-healing discharge frequency of a DC-supported capacitor provided in this application includes the following steps: placing the DC-supported capacitor to be tested in an oven set to a preset temperature and heating it for a preset time; connecting the heated DC-supported capacitor to be tested to a test system; monitoring the self-healing signal of the DC-supported capacitor to be tested within a predetermined time through the test system to obtain the number of self-healing discharges and the self-healing discharge frequency; with this setup, the number of self-healing discharges of the DC-supported capacitor can be accurately measured to support the conduct of self-healing tests of the DC-supported capacitor and improve the self-healing performance of the DC-supported capacitor. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the self-healing mechanism of a high-voltage self-healing capacitor.

[0018] Figure 2 This is a flowchart of a method for measuring the self-healing discharge frequency of a DC-supported capacitor provided in an embodiment of the present invention.

[0019] Figure 3 This is a circuit diagram of the test system in the method for measuring the self-healing discharge frequency of a DC-supported capacitor provided in an embodiment of the present invention.

[0020] In the diagram, 10 is the test system; 1 is the programmable DC power supply; 2 is the selector switch; 3 is the DC support capacitor under test; 4 is the ultrasonic probe; 5 is the oscilloscope; 6 is the discharge resistor; 7 is the grounding terminal; and 8 is the ultrasonic partial discharge instrument. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the accompanying drawings.

[0022] Reference Figure 2 The present invention discloses a self-healing discharge frequency for a DC-supported capacitor, comprising the following steps: S101. Place the DC support capacitor 3 to be tested in an oven set to a preset temperature and heat for a preset time. S102. Connect the heated DC support capacitor 3 to the test system 10. S103. The self-healing signal of the DC support capacitor 3 under test is monitored by the test system 10 within a predetermined time to obtain the number of self-healing discharges and the self-healing discharge frequency. With this setting, the number of self-healing discharges of the DC support capacitor can be accurately measured to support the conduct of the self-healing test of the DC support capacitor and improve the self-healing performance of the DC support capacitor.

[0023] Continue to refer to Figure 3In this embodiment, the test system 10 includes a programmable DC power supply 1, a selection switch 2, an ultrasonic probe 4, a discharge resistor 6, an ultrasonic partial discharge analyzer 8, and an oscilloscope 5. The programmable DC power supply 1 is connected to the DC support capacitor 3 under test via the selection switch 2. The ultrasonic probe 4 is attached to the middle of the outer shell of the DC support capacitor 3 under test. The oscilloscope 5 and the ultrasonic partial discharge analyzer 8 are both connected to the output terminal of the ultrasonic probe 4. The discharge resistor 6 is connected in parallel with the DC support capacitor 3 under test. The selection switch 2 is used to switch between charging and discharging circuits. The programmable DC power supply 1 is used to charge the DC support capacitor 3 under test. The ultrasonic probe 4 is used to monitor the self-healing signal of the DC support capacitor 3 under test.

[0024] Specifically, the test system 10 is also equipped with a grounding terminal 7 to ground the test system 10.

[0025] The selector switch 2 includes position a (charging position) and position b (discharging position). When the selector switch 2 is in position a, the programmable DC power supply 1 applies a preset DC voltage to the terminals of the DC support capacitor 3 under test to charge it. When the selector switch 2 is in position b, the discharge resistor 6 discharges the terminals of the DC support capacitor 3 under test, causing the voltage between the terminals of the DC support capacitor 3 under test to drop to 0.

[0026] The ultrasonic probe 4 is bonded to the middle of the shell of the DC support capacitor 3 to be tested using a coupling agent. This setting ensures that the ultrasonic probe 4 will not shake, and the precise fit ensures that the discharge ultrasonic signal will not be significantly attenuated.

[0027] Specifically, the preset temperature range is 68℃-72℃; the preset duration t range is t≥20h; in this embodiment, the preset temperature is 70℃, that is, the DC support capacitor 3 to be tested is placed in an oven with a set temperature of 70℃ and heated for at least 20h so that the DC support capacitor 3 to be tested reaches the upper limit temperature that may be reached under actual operating conditions.

[0028] Furthermore, in this embodiment, after connecting the heated DC support capacitor 3 to the test system 10 in S102, and before monitoring the self-healing signal of the DC support capacitor 3 to be tested within a predetermined time through the test system 10 in S103 to obtain the number of self-healing discharges and the self-healing discharge frequency, the method further includes: calibrating the ultrasonic partial discharge instrument 8 using a calibrator and setting a preset threshold; adjusting the trigger voltage value of the oscilloscope 5 so that the oscilloscope 5 is not triggered when no DC voltage is applied to the DC support capacitor 3 to be tested.

[0029] Specifically, the calibrator model includes, but is not limited to, TWUS-8182. In this embodiment, the calibrator model TWUS-8182 is used to calibrate the ultrasonic partial discharge instrument 8 as an example. The calibration process is as follows: the ultrasonic probe 4 is attached to the output end of the calibrator; then the calibrator is turned on, and the output is adjusted to 80KHZ and 10PC (PC is the unit of partial discharge charge); calibration is started on the ultrasonic partial discharge instrument 8, the signal is set to 10PC, and the calibration is saved after completion; after the calibration is completed, a preset threshold is set for the ultrasonic partial discharge instrument 8 to ensure that the self-healing signal can be accurately detected.

[0030] The trigger voltage range is 0.5V-0.6V. In this embodiment, the trigger voltage is 0.5V. That is, the trigger value of oscilloscope 5 is adjusted to set the trigger voltage to 0.5V, the trigger mode is rising edge triggering, and the trigger voltage value is higher than the maximum signal value measured by oscilloscope 5 when no voltage is applied, so that oscilloscope 5 does not trigger when no voltage is applied, avoiding false triggering that may affect the measurement results.

[0031] Further, in this embodiment, S103, monitoring the self-healing signal of the DC support capacitor 3 under test within a predetermined time using the test system 10 to obtain the number of self-healing discharges and the self-healing discharge frequency includes: S1031. Set the selector switch 2 to position a, and the programmable DC power supply 1 applies a preset DC voltage to the DC support capacitor 3 under test for a predetermined time.

[0032] S1031, when the selector switch 2 is in position a, the programmable DC power supply 1 applies a preset DC voltage to the DC support capacitor 3 under test and continues for a predetermined time, includes: when the selector switch 2 is in position a, the programmable DC power supply 1 applies 1.1 times the rated voltage to the DC support capacitor 3 under test and continues for 30s, or when the selector switch 2 is in position a, the programmable DC power supply 1 applies 1.25 times the rated voltage to the DC support capacitor 3 under test and continues for 10s.

[0033] S1032, the ultrasonic probe 4 collects the self-healing signal within a predetermined time and transmits it synchronously to the ultrasonic partial discharge instrument 8 and the oscilloscope 5. When the ultrasonic partial discharge instrument 8 detects the self-healing electrical signal, the oscilloscope 5 triggers and records the waveform of the self-healing discharge signal.

[0034] Specifically, the ultrasonic probe 4 continuously monitors the self-healing signal of the DC support capacitor 3 to be tested within a predetermined time. When the ultrasonic partial discharge instrument 8 detects a signal exceeding a preset threshold, it is determined to be a self-healing signal. At this time, the oscilloscope 5 is synchronously triggered and records the waveform of the self-healing discharge ultrasonic signal. The waveform of the oscilloscope 5 that appears synchronously with the self-healing signal detected by the ultrasonic partial discharge instrument 8 is the self-healing discharge ultrasonic signal waveform. One self-healing corresponds to one self-healing discharge waveform.

[0035] S1033. Obtain the number of self-healing discharges within a predetermined time based on the number of times the oscilloscope is triggered, and calculate the self-healing discharge frequency based on the period of the waveform of the self-healing discharge signal.

[0036] Specifically, based on the self-healing discharge signal waveform recorded by oscilloscope 5, the period of the waveform is read, and the self-healing discharge frequency of the DC support capacitor 3 under test is calculated according to the inverse relationship between period and frequency (i.e., frequency = 1 / period).

[0037] Furthermore, in this embodiment, after monitoring the self-healing signal of the DC support capacitor 3 under test within a predetermined time through the test system 10 to obtain the number of self-healing discharges and the self-healing discharge frequency, the method further includes: after the predetermined time of maintaining the preset DC voltage ends, selecting the switch 2 to position b, and discharging the DC support capacitor 3 under test through the discharge resistor 6, so that the voltage of the DC support capacitor 3 under test drops to 0.

[0038] The method for measuring the self-healing discharge frequency of a DC-supported capacitor provided in this application includes the following steps: placing the DC-supported capacitor 3 to be tested in an oven set to a preset temperature and heating it for a preset time; connecting the heated DC-supported capacitor 3 to be tested to a test system 10; monitoring the self-healing signal of the DC-supported capacitor 3 to be tested within a predetermined time through the test system 10 to obtain the number of self-healing discharges and the self-healing discharge frequency; with this setup, the number of self-healing discharges of the DC-supported capacitor can be accurately measured to support the conduct of self-healing tests of the DC-supported capacitor and improve the self-healing performance of the DC-supported capacitor.

[0039] It should be noted that, in this document, relational terms such as "first" and "second" are used merely 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 limitation, 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.

[0040] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method of measuring the self-healing discharge frequency of a DC support capacitor, characterized by: Includes the following steps: Place the DC support capacitor to be tested in an oven set to a preset temperature and heat for a preset time; The heated DC support capacitor to be tested is connected to the test system; The self-healing signal of the DC support capacitor under test is monitored by the test system within a predetermined time to obtain the number of self-healing discharges and the self-healing discharge frequency.

2. The method of claim 1, wherein: The testing system includes a programmable DC power supply, a selection switch, an ultrasonic probe, a discharge resistor, an ultrasonic partial discharge instrument, and an oscilloscope. The programmable DC power supply is connected to the DC support capacitor under test via the selection switch. The ultrasonic probe is attached to the middle of the outer shell of the DC support capacitor under test. The oscilloscope and the ultrasonic partial discharge instrument are both connected to the output terminal of the ultrasonic probe. The discharge resistor is connected in parallel with the DC support capacitor under test. The selector switch is used to switch between charging and discharging circuits; The programmable DC power supply is used to charge the DC support capacitor under test. The ultrasonic probe is used to monitor the self-healing signal of the DC-supported capacitor under test.

3. The method of claim 2, wherein the frequency of the self-healing discharge of the DC support capacitor is measured by: The ultrasonic probe is bonded to the middle of the housing of the DC-supported capacitor under test using a coupling agent.

4. The method of measuring the self-healing discharge frequency of a DC support capacitor according to any one of claims 2-3, characterized in that: The step of monitoring the self-healing signal of the DC support capacitor under test within a predetermined time using the test system to obtain the number of self-healing discharges and the self-healing discharge frequency includes: When the selection switch is set to position a, the programmable DC power supply applies a preset DC voltage to the DC support capacitor under test for a predetermined time. The ultrasonic probe collects the self-healing signal within a predetermined time and transmits it synchronously to the ultrasonic partial discharge instrument and the oscilloscope. When the ultrasonic partial discharge instrument detects the self-healing electrical signal, the oscilloscope triggers and records the waveform of the self-healing discharge signal. The number of self-healing discharges within a predetermined time period is obtained based on the number of times the oscilloscope is triggered, and the self-healing discharge frequency is calculated based on the period of the waveform of the self-healing discharge signal.

5. The method of claim 4, wherein the frequency of the self-healing discharge of the DC support capacitor is measured by: After monitoring the self-healing signal of the DC support capacitor under test within a predetermined time using the test system to obtain the number of self-healing discharges and the self-healing discharge frequency, the method further includes: After the predetermined time for maintaining the preset DC voltage has elapsed, the selection switch is set to position b, and the DC support capacitor under test is discharged through the discharge resistor, causing the voltage of the DC support capacitor under test to drop to 0.

6. The method for measuring the self-healing discharge frequency of a DC-supported capacitor according to claim 2, characterized in that: After connecting the heated DC-supported capacitor under test to the test system, and before monitoring the self-healing signal of the DC-supported capacitor under test within a predetermined time through the test system to obtain the number of self-healing discharges and the self-healing discharge frequency, the process further includes: The ultrasonic partial discharge instrument was calibrated using a calibrator, and a preset threshold was set. Adjust the trigger voltage value of the oscilloscope so that the oscilloscope is not triggered when no DC voltage is applied to the DC support capacitor under test.

7. The method for measuring the self-healing discharge frequency of a DC-supported capacitor according to claim 1, characterized in that: The preset duration t is in the range of t≥20h.

8. The method for measuring the self-healing discharge frequency of a DC-supported capacitor according to claim 4, characterized in that: When the selector switch is set to position a, the programmable DC power supply applies a preset DC voltage to the DC support capacitor under test for a predetermined time, including: When the selector switch is set to position a, the programmable DC power supply applies 1.1 times the rated voltage to the DC support capacitor under test for 30 seconds; or, when the selector switch is set to position a, the programmable DC power supply applies 1.25 times the rated voltage to the DC support capacitor under test for 10 seconds.

9. The method for measuring the self-healing discharge frequency of a DC-supported capacitor according to claim 1, characterized in that: The preset temperature range is 68℃-72℃.

10. The method for measuring the self-healing discharge frequency of a DC-supported capacitor according to claim 6, characterized in that: The trigger voltage value ranges from 0.5V to 0.6V.

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