CN107505526B - Method for detecting low-frequency common-mode interference of direct-current voltage - Google Patents

Abstract

The invention provides a method for detecting low-frequency common-mode interference of direct-current voltage, and provides a method for testing a low-frequency band conducted transmitting device below 9KHz, which aims to quickly and accurately search whether conducted disturbance exists or not and effectively evaluate and limit the conducted transmitting technology of an inverter product. The detection method is to monitor the grounding peak voltage of the low-voltage direct-current power supply end so as to judge whether the detected direct-current common mode has conducted disturbance. Particularly, the method is more suitable for detecting the common-mode disturbance voltage of the frequency band lower than 9KHz of the direct current/alternating current inversion power supply module or equipment.

Description

Detection method of low frequency common mode interference of DC voltage

technical field

The invention provides a test and investigation method for low-voltage and low-frequency direct current common mode disturbance, which is suitable for a comprehensive integrated system including an alternating voltage system and a low-voltage direct current power supply, and belongs to the field of electrical design.

Background technique

At present, the national standard GB4824 2013 "Industrial, Scientific and Medical (ISM) Radio Frequency Equipment Electromagnetic Disturbance Characteristics Limits and Measurement Methods" has no limit for the conducted emission in the frequency band below 9KHz, and usually does not test the conducted emission in the frequency band below 9KHz.

In the field of rail transit, there are no corresponding clear technical standard requirements for the ripple voltage generated by the inverter equipment at the DC power supply end. The usual way to test the ripple voltage is to test between the positive and negative lines of the DC terminal. If the ripple between the positive and negative lines is qualified, the DC positive line to ground or the negative line to the ground will not be tested. Voltage.

For DC/AC inverter products, pulsating current that is fed back to the power supply circuit is inevitably generated at the power input end, but the pulsating voltage is not easy to detect. In the design stage of the equipment level and the verification stage of the product type test, it is difficult to find the disturbance voltage problem of the DC line to the ground in advance due to the relatively ideal grounding of the DC negative line. After the device is integrated and assembled in a large system, due to the difference in the impedance of the device to the integrated system, the line pair inevitably has a large or small potential difference. In contrast, in the low frequency frequency band below 9KHz, the voltage disturbance intensity to the public ground will increase significantly, which will directly affect the normal and safe use of other equipment in the system. Produces obvious common mode disturbance problem. In addition, depending on the device or circuit design, this disturbance can also affect other relatively low frequency bands of conducted emission measurements.

The existing simple test voltage meter is a multimeter, and the test data result is generally an effective value, or an average value in a multi-cycle time, which cannot test the peak disturbance signal. If the peak duration of the disturbance signal is short but the period is long, it is impossible to test effectively with a multimeter.

In view of this, this test method is proposed and this patent is applied for.

SUMMARY OF THE INVENTION

The method for detecting low-frequency common-mode interference of DC voltage according to the present invention aims to solve the above-mentioned defects in the prior art and propose an integrated system for AC voltage system and low-voltage DC power supply, especially the test of conduction emission equipment in low-frequency frequency bands below 9KHz In order to quickly and accurately find out the existence of conducted disturbance, it can be used to effectively evaluate and limit the conducted emission technology of inverter products.

Another purpose of the invention is to quickly find out the low-frequency disturbance source by comparing the common-mode disturbance voltage, so as to find a solution to the input feedback disturbance of the DC/AC inverter product.

In order to achieve the above purpose of the invention, the method for detecting the low-frequency common mode interference of the DC voltage is to monitor the grounding peak voltage of the low-voltage DC power supply terminal to determine whether the tested DC common mode has conducted disturbance.

In particular, the method is more suitable for detecting the common mode disturbance voltage in the frequency band lower than 9KHz of the DC/AC inverter power supply module or equipment.

In order to improve the detection accuracy and efficiency. A more effective improvement measure is to use a time-domain signal test device. When the voltage probe is grounded, the probe is connected to the positive and negative lines of the low-voltage DC power supply terminal to monitor the voltage waveform during the test period. The time-domain signal testing device is preferably an oscilloscope, a power quality analyzer or other data acquisition systems.

When a common mode disturbance voltage signal is collected at multiple measuring points in the same system, the disturbance voltage intensity of different test points can be compared. The stronger the intensity, the closer the measuring point is to the disturbance source, and the disturbance source can be quickly checked .

If the same device has only the positive line or the negative line to the ground, there is disturbance voltage, then the device at the measuring point is judged to be crosstalk.

To sum up, the method for detecting low-frequency common-mode interference of DC voltage according to the present invention is simple and easy to implement, and can quickly and accurately detect the common-mode disturbance voltage in the frequency band lower than 9KHz, which is helpful for the disturbance voltage problem of DC line to ground. The solution effectively protects electronic components with high voltage sensitivity. At the same time, the low-frequency disturbance source can be quickly checked, and the interference of the device crosstalk phenomenon on the detection result can be eliminated.

Description of drawings

Figure 1 is a schematic diagram of testing using an oscilloscope;

Figure 2 is a test circuit diagram using the positive line to the ground;

Figure 3 is the test circuit diagram using the negative line to ground;

FIG. 4 is a waveform example diagram of a disturbance voltage signal to the ground.

As shown in Figure 1 to Figure 4, the low-voltage DC power supply bus 1, 110VDC-negative line 2, 110VDC+ positive line 3, the low-voltage DC device under test 4, the protection ground 5, the alligator clip is connected to the protection ground 6, and the probe is connected to the positive line 7 , probe 10, alligator clip (ie probe ground wire) 20.

Detailed ways

Embodiment 1, the present invention is further described in detail below with reference to the accompanying drawings.

Detect the common-mode disturbance voltage of the DC/AC inverter power supply module or equipment below 9KHz frequency band, and monitor the grounding peak voltage of the low-voltage DC power supply terminal to determine whether the tested DC common-mode has conducted disturbance.

Using an oscilloscope, when the voltage probe is grounded, connect the probe to the positive and negative wires of the low-voltage DC power supply terminal to monitor the voltage waveform during the test cycle. specifically,

As shown in Figure 1, use the "probe 10" of the voltage probe to connect the positive and negative lines of the low-voltage DC respectively, and use the alligator clip 20 of the ground wire of the probe to connect the protective ground of the device or the protective ground of the nearby device (the protective ground and the Ground common ground for large integrated systems).

As shown in Figure 2 and Figure 3, adjust the test period of the time domain signal reasonably and check the voltage waveform.

If the voltage is normal, the measured positive line to ground, such as 110VDC positive line to ground, should be displayed as a 110VDC flat voltage waveform without spikes; the measured negative line to ground should be displayed as 0VDC flat without spikes voltage waveform.

If the voltage is abnormal, the measured waveform is either not flat or has pulse voltage spikes. As shown in Figure 4, there is an example of abnormal voltage waveform between the DC negative line and the ground.

In order to ensure the safe and accurate testing of the disturbance voltage, the following measures should be taken in addition:

The oscilloscope or the equivalent time-domain test signal device selected for the test should meet at least 100M bandwidth to facilitate the capture of abnormal low-frequency voltage signals.

Test the insulation voltage probe of the oscilloscope or the equivalent time-domain test signal device, and the detection range of the selected probe to the ground should be at least greater than the voltage to be measured.

For the DC low-voltage system with the negative wire grounded, since the potential difference between the negative wire and the ground is theoretically zero, there is no risk of grounding the alligator clip.

For a DC low voltage system with a floating negative line, since the theoretical potential difference between the negative line and the ground is not completely zero, you should check the technical specifications of the probe before grounding, and the grounding alligator clip should follow the peak/rms value of the grounding point defined in the specification. the allowable voltage requirements. For a DC system with a floating negative line, or an IT DC system where the negative line is grounded through a resistor, because the impedance between the negative line and the ground is relatively large, the waveform tested by this test method is generally a flat time-domain envelope. If the waveform is not straight or has a high peak amplitude, this method can be used as a basis for judging poor insulation of the negative line to the ground.

For large-scale integrated systems, the disturbance voltage intensity of different measuring points can be compared and tested. Generally, if the intensity is strong, the measuring point is closer to the disturbance source.

If the measured signal only has pulse voltage spikes from the positive line to the ground, or only the negative line to the ground has pulse voltage spikes, generally, the equipment at the measuring point is more likely to have crosstalk.

As described above, similar technical solutions can be derived in conjunction with the content of the solutions given in the drawings and the embodiments. However, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solutions of the present invention still fall within the scope of the technical solutions of the present invention.

Claims (1)

1. a detection method of DC voltage low frequency common mode interference, it is characterized in that: the common mode disturbance voltage lower than the 9KHz frequency band of the DC/AC inverter power supply module or equipment is detected, and the grounding peak voltage of the low-voltage DC power supply terminal is detected. Monitoring to determine whether the tested DC common mode has conducted disturbance; Using the time domain signal test device, when the voltage probe is grounded, the probe is connected to the positive and negative lines of the low-voltage DC power supply terminal, and the voltage waveform in the test cycle is monitored; Compare the disturbance voltage intensity of different test points. The stronger the intensity, the closer the measurement point is to the disturbance source; if only the positive line or the negative line has disturbance voltage to the ground, it is judged that the equipment at the measuring point is crosstalk.

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