A detection circuit and evaluation method for the output voltage quality of a variable-frequency power supply used in high-voltage tests

Abstract

The present invention belongs to the technical field of power supply and power detection, and specifically relates to a detection circuit and an evaluation method for the output voltage quality of a variable-frequency power supply for high-voltage tests. The technical solution adopted is as follows: After adjusting the output frequency of the variable-frequency power supply to be tested to a maximum of 300 Hz, adjust the output voltage to reach a maximum of 350 V in steps of 5 V. Adjust the internal impedance of the variable load device to make the output of the variable-frequency power supply reach a maximum current of 1142 A, and calculate the total harmonic distortion THD of the output voltage waveform of the variable-frequency power supply to be tested by a waveform analyzer. While maintaining the maximum output voltage and maximum output current of the variable-frequency power supply to be tested, adjust the power interference generator to make the input voltage of the variable-frequency power supply fluctuate within ±5%, and calculate the output voltage instability ΔU% of the variable-frequency power supply at this time by a waveform analyzer. After the entire test is completed, reduce the output voltage through the variable-frequency power supply control box and disconnect the input of the variable-frequency power supply. The method of the present invention is simple, practical and efficient, and the results are reliable.

Description

Technical Field

[0001] The present invention belongs to the technical field of power supply and power detection, and particularly relates to a detection circuit and an evaluation method for the output voltage quality of a variable-frequency power supply for high-voltage tests. Background Art

[0002] A variable-frequency power supply is an important component of an on-site high-voltage test system, which can convert the commonly used three-phase 380V AC power supply on site into a single-phase AC power supply with adjustable voltage and frequency.

[0003] There are various types of traditional variable-frequency power supplies, with uneven prices and qualities, and the product technology is not very mature. During on-site tests, there are often situations where the on-site test cannot be carried out due to the too poor output voltage quality of the variable-frequency power supply. At present, relevant user units do not have an evaluation method and device for the output voltage quality of variable-frequency power supplies. Therefore, it is very necessary to evaluate and test the output voltage quality of variable-frequency power supplies. Summary of the Invention

[0004] The present invention overcomes the deficiencies of the prior art and provides a detection circuit and an evaluation method for the output voltage quality of a variable-frequency power supply for high-voltage tests. By adjusting the parameters of the circuit elements in the variable load device in the test circuit, the operation modes of the variable-frequency power supply under different working conditions are simulated, and the output voltage quality under several most representative working conditions is tested. The output voltage quality mainly includes the output voltage instability and the waveform distortion rate. By separately evaluating and testing these two main indicators, the overall verification of its output voltage quality is realized.

[0005] These two performance indicators are measured in the same test circuit. Except for the variable-frequency power supply to be tested, other equipment used in the test circuit, including power analyzers, variable load devices, high-voltage test lines, etc., all use high-quality and high-performance special test equipment for inspection. Each test can obtain the data of the two voltage indicators under one working condition, and different values are assigned to them according to their influence degree on the output voltage quality of the variable-frequency power supply and the set standard values. Finally, the scores of these two voltage indicators are weighted and calculated to comprehensively judge the output power quality of the variable-frequency power supply, effectively ensuring the development of on-site high-voltage test work.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a detection circuit for the output voltage quality of a variable-frequency power supply for high-voltage tests, including a power supply filtering device, a variable-frequency power supply to be tested, and a voltage transformer;

[0007] The input end of the power supply filtering device is connected to a 380V power supply system, the output end of the power supply filtering device is connected to a power supply interference generator and then connected to the input end of the variable-frequency power supply to be tested, and the output end of the variable-frequency power supply to be tested is connected to a variable load device through a low-voltage output cable to form an output loop;

[0008] The primary side of the voltage transformer is connected in parallel to the output loop and is connected to the output terminal of the frequency conversion power supply under test. The secondary side of the voltage transformer is connected to the voltage terminal of the waveform analyzer;

[0009] The frequency conversion power supply under test is connected to a frequency conversion power supply control box.

[0010] The 380V power supply system, the power filter device, the power interference generator and the frequency conversion power supply under test are connected by a low-voltage input cable.

[0011] The frequency conversion power supply control box and the frequency conversion power supply under test are connected by a control optical fiber.

[0012] The secondary side of the voltage transformer is connected to the input terminal of the waveform analyzer through a secondary test line.

[0013] The evaluation method of the detection circuit for the output voltage quality of the frequency conversion power supply for high-voltage tests is as follows:

[0014] First step: Ensure that the ambient temperature and humidity are constant, the power supply capacity is constant, and the output voltage is stable. Carry out the following steps under the condition that the environmental and power quality data of previous tests remain unchanged;

[0015] Second step: Connect the 380V power supply system to the power filter device using a low-voltage input cable, and connect the output terminal of the power filter device to the input terminal of the power interference generator;

[0016] Third step: Connect the output terminal of the power interference generator to the input terminal of the frequency conversion power supply under test using a low-voltage input cable. The output terminal of the frequency conversion power supply under test is connected to the variable load device through a low-voltage output cable. The frequency conversion power supply under test can convert the three-phase power supply into a single-phase power supply with adjustable voltage and frequency;

[0017] Fourth step: The primary winding of the voltage transformer is connected in parallel to the output loop of the frequency conversion power supply under test, and the input terminal of the waveform analyzer is connected to the secondary winding of the voltage transformer through a secondary test line;

[0018] Fifth step: The frequency conversion power supply under test is connected to the frequency conversion power supply control box through a control optical fiber, achieving complete isolation between low voltage and high voltage while remotely controlling the output voltage and frequency;

[0019] Sixth step: Adjust the internal impedance value of the variable load device to the maximum value of 10Ω and make its power factor angle 0°;

[0020] Seventh step: Start the test loop and adjust the power filter device so that the output power supply voltage is a standard 380V voltage waveform without any harmonics;

[0021] Step 8: After adjusting the output frequency of the power supply under test to the maximum of 300 Hz, adjust the output voltage to reach the maximum of 350 V in steps of 5 V.

[0022] Step 9: By adjusting the internal impedance of the variable load device, make the output of the power supply reach the maximum current of 1142 A, and calculate the output voltage waveform distortion rate THD1 of the power supply under test by the waveform analyzer.

[0023]

[0024] Step 10: Keep the maximum output voltage and maximum output current of the power supply under test, adjust the power supply interference generator to make the input voltage of the power supply fluctuate within ±5%, and calculate the output voltage instability ΔU1% of the power supply at this time by the waveform analyzer.

[0025] Step 11: After the entire test is completed, reduce the output voltage through the power supply control box and disconnect the input of the power supply.

[0026] Step 12: Adjust the nature and magnitude of the load in the variable load device so that the power factor angles are 45°, 90°, -45°, and -90° respectively.

[0027] Step 13: Repeat the operations from Step 7 to Step 11 to obtain the output voltage instability and waveform distortion rate under each working condition, and define them as [THD2, ΔU2%], [THD3, ΔU3%], [THD4, ΔU4%], [THD5, ΔU5%] respectively.

[0028] Step 14: Take THD = max[THD1, THD2, THD3, THD4, THD5] and ΔU% = max[ΔU1%, ΔU2%, ΔU3%, ΔU4%, ΔU5%] respectively as the final assessment index quantities of the power supply under test.

[0029] Step 15: Define the characteristic values of each assessment index:

[0030] If THD ≤ 2%, λ1 = 2; if 2% < THD ≤ 4%, λ1 = 1; if 4% < THD, λ1 = 0.

[0031] If ΔU% ≤ 0.5%, λ2 = 2; if 0.5% < ΔU% ≤ 1%, λ2 = 1; if 1% < ΔU%, λ2 = 0.

[0032] Step 16: Define the qualified conditions of the power supply under test:

[0033] If min[λ1, λ2] = 0, it is determined that the power supply under test is unqualified, and the comprehensive performance quality inspection ends.

[0034] If min[λ1, λ2] ≠ 0, determine that the variable-frequency power supply under test is qualified and proceed to the next step;

[0035] Step 17: If min[λ1, λ2] ≠ 0, define the comprehensive performance index of the variable-frequency power supply under test:

[0036] λ = λ1 + λ2;

[0037] Step 18: Rate the qualified variable-frequency power supply under test:

[0038] If λ = 2, define the qualified level of the variable-frequency power supply under test,

[0039] If λ = 3, define the good level of the variable-frequency power supply under test,

[0040] If λ = 4, define the excellent level of the variable-frequency power supply under test.

[0041] The beneficial effects of the present invention compared with the prior art are:

[0042] 1. The method of the present invention is simple, practical and efficient, and the result is reliable. By adjusting the ratio of circuit elements in the variable load device, various operating conditions of the variable-frequency power supply under test are simulated.

[0043] 2. The present invention realizes the inspection of the output voltage quality of the variable-frequency power supply by detecting and evaluating two main indicators of the output voltage of the variable-frequency power supply under test.

[0044] 3. The present invention realizes the detection of the output voltage quality of the variable-frequency power supply for the first time, improves the reliability level of the equipment, and ensures the smooth progress of on-site test work. Description of the Drawings

[0045] The present invention will be further described below with reference to the accompanying drawings.

[0046] Figure 1 It is the detection circuit diagram of the output voltage quality of the variable-frequency power supply of the present invention.

[0047] In the figure: 1 is the power supply filtering device, 2 is the variable-frequency power supply under test, 3 is the voltage transformer, 4 is the 380V power supply system, 5 is the power supply interference generator, 6 is the low-voltage output cable, 7 is the variable load device, 8 is the waveform analyzer, 9 is the variable-frequency power supply control box, 10 is the low-voltage input cable, 11 is the control optical fiber, and 12 is the secondary test line. Detailed Embodiments

[0048] As shown in the figure, a detection circuit for the output voltage quality of a variable-frequency power supply for high-voltage tests includes a power supply filtering device 1, a variable-frequency power supply 2 under test, and a voltage transformer 3;

[0049] The input end of the power supply filtering device 1 is connected to the 380V power supply system 4. The output end of the power supply filtering device 1 is connected to the power interference generator 5 and then to the input end of the frequency conversion power supply under test 2. The output end of the frequency conversion power supply under test 2 is connected to the variable load device 7 through the low-voltage output cable 6 to form an output loop.

[0050] The primary side of the voltage transformer 3 is connected in parallel to the output loop and is connected to the output end of the frequency conversion power supply under test 2. The secondary side of the voltage transformer 3 is connected to the voltage terminal of the waveform analyzer 8.

[0051] A frequency conversion power supply control box 9 is connected to the frequency conversion power supply under test 2.

[0052] Preferably, the 380V power supply system 4, the power supply filtering device 1, the power interference generator 5 and the frequency conversion power supply under test 2 are connected through the low-voltage input cable 10.

[0053] Preferably, the frequency conversion power supply control box 9 and the frequency conversion power supply under test 2 are connected through the control optical fiber 11.

[0054] Preferably, the secondary side of the voltage transformer 3 and the input end of the waveform analyzer 8 are connected through the secondary test line 12.

[0055] The evaluation method of the detection circuit for the output voltage quality of the frequency conversion power supply for high-voltage test is as follows:

[0056] First step: The detection requires constant ambient temperature and humidity, constant power supply capacity, stable output voltage, and the following steps are carried out under the condition that the ambient and power supply quality data of previous detections remain unchanged.

[0057] Second step: Connect the 380V power supply system 4 to the power supply filtering device 1 through the low-voltage input cable 10, and connect the output end of the power supply filtering device 1 to the input end of the power interference generator 5.

[0058] Third step: Connect the output end of the power interference generator 5 to the input end of the frequency conversion power supply under test 2 through the low-voltage input cable 10. The output end of the frequency conversion power supply under test 2 is connected to the variable load device 7 through the low-voltage output cable 6. The frequency conversion power supply under test 2 can convert the three-phase power supply into a single-phase power supply with adjustable voltage and frequency.

[0059] Fourth step: The primary winding of the voltage transformer 3 is connected in parallel to the output loop of the frequency conversion power supply under test 2, and the input end of the waveform analyzer 8 is connected to the secondary winding of the voltage transformer 3 through the secondary test line 12.

[0060] Fifth step: The frequency conversion power supply under test 2 is connected to the frequency conversion power supply control box 9 through the control optical fiber 11, achieving complete isolation between low voltage and high voltage while remotely controlling the output voltage and frequency.

[0061] Step 6: Adjust the internal impedance value of the variable load device 7 to the maximum value of 10 Ω and make its power factor angle 0°;

[0062] Step 7: Start the test circuit and adjust the power supply filtering device 1 so that the output power supply voltage is a standard 380V voltage waveform without any harmonics;

[0063] Step 8: After adjusting the output frequency of the tested variable-frequency power supply 2 to the maximum of 300 Hz, adjust the output voltage to the maximum of 350 V in steps of 5 V;

[0064] Step 9: Adjust the internal impedance of the variable load device 7 to make the output of the variable-frequency power supply reach the maximum current of 1142 A, and calculate the output voltage waveform distortion rate THD1 of the tested variable-frequency power supply 2 by the waveform analyzer 8,

[0065]

[0066] Step 10: Keep the maximum output voltage and maximum output current of the tested variable-frequency power supply 2, adjust the power supply interference generator 5 to make the input voltage of the variable-frequency power supply fluctuate within ±5%, and calculate the output voltage instability ΔU1% of the variable-frequency power supply at this time by the waveform analyzer 8,

[0067] Step 11: After the whole test is completed, reduce the output voltage through the variable-frequency power supply control box 9 and disconnect the input of the variable-frequency power supply;

[0068] Step 12: Adjust the nature and magnitude of the load in the variable load device 7 so that its power factor angles are 45°, 90°, -45°, -90° respectively;

[0069] Step 13: Repeat the operations from Step 7 to Step 11 to obtain the output voltage instability and waveform distortion rate under each working condition, and define them as [THD2, ΔU2%], [THD3, ΔU3%], [THD4, ΔU4%], [THD5, ΔU5%] respectively;

[0070] Step 14: Respectively take THD = max[THD1, THD2, THD3, THD4, THD5], ΔU% = max[ΔU1%, ΔU2%, ΔU3%, ΔU4%, ΔU5%] as the final assessment index quantities of the tested variable-frequency power supply 2;

[0071] Step 15: Define the characteristic values of each assessment index:

[0072] If THD ≤ 2%, λ1 = 2; if 2% < THD ≤ 4%, λ1 = 1; if 4% < THD, λ1 = 0,

[0073] If ΔU% ≤ 0.5%, λ2 = 2; if 0.5% < ΔU% ≤ 1%, λ2 = 1; if 1% < ΔU%, λ2 = 0;

[0074] Step 16: Define the qualification conditions for the tested variable-frequency power supply 2:

[0075] If min[λ1, λ2] = 0, it is determined that the tested variable-frequency power supply 2 is unqualified, and the comprehensive performance quality inspection ends;

[0076] If min[λ1, λ2] ≠ 0, it is determined that the tested variable-frequency power supply 2 is qualified, and proceed to the next step;

[0077] Step 17: If min[λ1, λ2] ≠ 0, define the comprehensive performance index of the tested variable-frequency power supply 2:

[0078] λ = λ1 + λ2;

[0079] Step 18: Rate the qualified tested variable-frequency power supply 2:

[0080] If λ = 2, define the qualified grade of the tested variable-frequency power supply 2,

[0081] If λ = 3, define the good grade of the tested variable-frequency power supply 2,

[0082] If λ = 4, define the excellent grade of the tested variable-frequency power supply 2.

[0083] The operation process of the present invention:

[0084] After starting the test circuit, by adjusting various ratio combinations of circuit elements in the variable load device, simulate the operation modes of the tested variable-frequency power supply under different working conditions, select the five most representative operation modes, so as to obtain two voltage index parameters under various operation modes, and conduct a weighted judgment on the output voltage quality of the tested variable-frequency power supply according to the judgment criteria, effectively carrying out the evaluation and detection work on the output voltage quality of the variable-frequency power supply.

[0085] The above embodiments are only used to exemplarily illustrate the principle and its effects of the present invention, rather than to limit the present invention. Those who are familiar with this technology can modify or improve the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A detection circuit and evaluation method for the output voltage quality of a variable-frequency power supply used in high-voltage tests, including a power supply filtering device (1), a variable-frequency power supply under test (2), and a voltage transformer (3); The input end of the power supply filtering device (1) is connected to a 380V power supply system (4), the output end of the power supply filtering device (1) is connected to a power supply interference generator (5) and then connected to the input end of the variable-frequency power supply under test (2), and the output end of the variable-frequency power supply under test (2) is connected to a variable load device (7) through a low-voltage output cable (6) to form an output loop; The primary side of the voltage transformer (3) is connected in parallel to the output loop and connected to the output end of the variable-frequency power supply under test (2), and the secondary side of the voltage transformer (3) is connected to the voltage terminal of a waveform analyzer (8); The frequency conversion power supply to be inspected (2) is connected with a frequency conversion power supply control box (9), and is characterized in that, It includes the following steps: The first step: The detection requires that the environmental temperature and humidity are constant, the power supply capacity is constant, the output voltage is stable, and the following steps are carried out under the condition that the environmental and power supply quality data of previous detections remain unchanged; The second step: Use a low-voltage input cable (10) to connect the 380V power supply system (4) to the power supply filtering device (1), and connect the output end of the power supply filtering device (1) to the input end of the power supply interference generator (5); The third step: Use a low-voltage input cable (10) to connect the output end of the power supply interference generator (5) to the input end of the variable-frequency power supply under test (2), the output end of the variable-frequency power supply under test (2) is connected to the variable load device (7) through a low-voltage output cable (6), and the variable-frequency power supply under test (2) can convert a three-phase power supply into a single-phase power supply with adjustable voltage and frequency; The fourth step: The primary winding of the voltage transformer (3) is connected in parallel to the output loop of the variable-frequency power supply under test (2), and the input end of the waveform analyzer (8) is connected to the secondary winding of the voltage transformer (3) through a secondary test line (12); The fifth step: The variable-frequency power supply under test (2) is connected to a variable-frequency power supply control box (9) through a control optical fiber (11), achieving complete isolation between low voltage and high voltage while remotely controlling the output voltage and frequency; The sixth step: Adjust the internal impedance value of the variable load device (7) to the maximum value of 10Ω and make its power factor angle 0°; The seventh step: Start the test loop and adjust the power supply filtering device (1) so that the output power supply voltage is a standard 380V voltage waveform without any harmonics; The eighth step: After adjusting the output frequency of the variable-frequency power supply under test (2) to the maximum of 300Hz, adjust the output voltage to reach the maximum of 350V in steps of 5V; Step 9: Adjust the impedance in the variable load device (7) to make the output of the variable-frequency power supply reach the maximum current of 1142 A, and calculate the total harmonic distortion THD1 of the output voltage waveform of the variable-frequency power supply under test (2) with the waveform analyzer (8). Step 10: Keep the maximum output voltage and maximum output current of the frequency conversion power supply (2) under test, adjust the power supply interference generator (5) to make the input voltage of the frequency conversion power supply fluctuate within ±5%, and calculate the output voltage instability ΔU1% of the frequency conversion power supply at this time by the waveform analyzer (8). The eleventh step: After the entire test is completed, reduce the output voltage through the variable-frequency power supply control box (9) and disconnect the input of the variable-frequency power supply; The twelfth step: Adjust the nature and magnitude of the load inside the variable load device (7) so that its power factor angles are 45°, 90°, -45°, and -90° respectively; The thirteenth step: Repeat the operations in the seventh step to the eleventh step to obtain the output voltage instability and waveform distortion rate under each working condition, and define them as [THD2, ΔU2%], [THD3, ΔU3%], [THD4, ΔU4%], [THD5, ΔU5%] respectively; Step 14: Respectively take THD = max[THD1, THD2, THD3, THD4, THD5], ΔU% = max[ΔU1%, ΔU2%, ΔU3%, ΔU4%, ΔU5%], which are the final assessment index quantities of the frequency conversion power supply (2) to be tested; Step 15: Define the characteristic values of each assessment index: If THD ≤ 2%, λ1 = 2; if 2% < THD ≤ 4%, λ1 = 1; if 4% < THD, λ1 = 0, If ΔU% ≤ 0.5%, λ2 = 2; if 0.5% < ΔU% ≤ 1%, λ2 = 1; if 1% < ΔU%, λ2 = 0; Step 16: Define the qualified conditions of the frequency conversion power supply (2) to be tested: If min[λ1, λ2] = 0, it is determined that the frequency conversion power supply (2) to be tested is unqualified, and the comprehensive performance quality inspection ends; If min[λ1, λ2] ≠ 0, it is determined that the frequency conversion power supply (2) to be tested is qualified, and proceed to the next step; Step 17: If min[λ1, λ2] ≠ 0, define the comprehensive performance index of the frequency conversion power supply (2) to be tested: λ = λ1 + λ2; Step 18: Rate the qualified frequency conversion power supply (2) to be tested: if λ = 2, define the qualified grade of the frequency conversion power supply (2) to be tested; if λ = 3, define the good grade of the frequency conversion power supply (2) to be tested; if λ = 4, define the excellent grade of the frequency conversion power supply (2) to be tested.

2. The detection circuit and evaluation method for the output voltage quality of a variable-frequency power supply used in high-voltage tests according to claim 1, characterized in that, The 380V power supply system (4), the power supply filtering device (1), the power supply interference generator (5) and the frequency conversion power supply (2) to be tested are connected through a low-voltage input cable (10).

3. The detection circuit and evaluation method for the output voltage quality of a variable-frequency power supply used in high-voltage tests according to claim 2, wherein, The frequency conversion power supply control box (9) and the frequency conversion power supply (2) to be tested are connected through a control optical fiber (11).

4. The detection circuit and evaluation method for the output voltage quality of a variable-frequency power supply used in high-voltage tests according to claim 3, characterized in that, The secondary side of the voltage transformer (3) is connected to the input end of the waveform analyzer (8) through a secondary test line (12).

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