An online early warning device for high-frequency common-mode interference

Abstract

The present invention belongs to the field of cable monitoring technology, and specifically relates to an online early warning device for high-frequency common-mode interference, comprising: a magnetic filter ring, a magnetic induction ring, a coil winding, and a noise alarm device, wherein the magnetic filter ring is non-contactly sleeved on the live wire and the neutral wire of the LED lamp driver, and is used to improve the uneven magnetic field distribution caused by the asymmetric position of the measured common-mode current; the magnetic induction ring is non-contactly sleeved on the outside of the magnetic filter ring, and is installed together with the magnetic filter ring on the outside of the LED lamp to form a double-ring structure; the coil winding is wound on the magnetic induction ring, and the output voltage is proportional to the rate of change of the measured common-mode current; the noise alarm device alarms based on the signal output by the coil winding. Compared with the prior art, the present invention has the advantages of being able to reduce the interference of high-frequency stray signals on the high-frequency common-mode current of LED lamps and having strong sensitivity.

Description

Technical Field

[0001] The invention relates to the technical field of cable monitoring, and in particular to an online early warning device for high-frequency common-mode interference. Background Art

[0002] With the advancement of urban cabling, more and more urban cables are transferred underground. LED lamps are driven by power electronic devices, which have the advantages of high efficiency and energy saving and are widely used in underground cable tunnel lighting. The frequent switching of power electronic devices will generate high-frequency common-mode interference current, which will seriously interfere with the normal operation of the cable partial discharge monitoring device when it is conducted in the grounding system of the cable tunnel. Therefore, it is necessary to monitor and warn the intensity of the high-frequency common-mode interference current of LED lamps online, and issue a timely alarm when the intensity of the interference current exceeds a certain threshold. However, the high-frequency interference current generated by the normal operation of the LED driver is divided into high-frequency common-mode current and high-frequency differential-mode current according to the flow path. The high-frequency common-mode current flows between the equipment and the ground, interfering with the operation of other equipment in the grounding system; while the high-frequency differential-mode current flows between the live wire and the neutral wire, and the high-frequency magnetic field generated by its larger amplitude will cause greater interference to the common-mode current monitoring. In order to achieve accurate early warning of high-frequency common-mode interference signals, it is necessary to design an online early warning device for high-frequency common-mode interference of cable tunnel LED lamps that is not affected by high-frequency differential mode.

[0003] Patent No. (CN201210159878.0) invented the "wireless current sensor", which uses a current transformer to sense the current in the line and extracts energy from it to send the collected signal to the receiving end through a wireless data transceiver. The invention is novel in using wireless data transmission, but the signal bandwidth that the current transformer can collect is very limited, and it is impossible to filter the aliased high-frequency current to meet the needs of high-frequency common-mode current signal monitoring.

[0004] Patent No. (CN202010258599.4) invented "an isolated current sensor", which converts the current signal into a voltage signal by collecting the voltage drop on the sampling resistor, and outputs it through isolation amplification, and collects the high-frequency current signal in the circuit through the Rogowski coil and outputs it after filtering. The invention has a simple structure and a small size, but the voltage collection on the actual sampling resistor is still in contact with the primary circuit, and the sampling resistor has limited accuracy and is easily affected by the position and temperature of the measured wire. Summary of the invention

[0005] The purpose of the present invention is to provide an online early warning device for high-frequency common-mode interference, which adopts a double-ring structure to improve the signal-to-noise ratio of high-frequency common-mode signals and reduce the interference of differential-mode current magnetic fields. The inner ring filters out high-frequency differential-mode currents according to the magnetic shielding principle, and the outer ring is a high-frequency common-mode current sensor with a magnetic core, so as to accurately extract the high-frequency common-mode interference current of the cable tunnel LED driver, and warn through an alarm device when the detected high-frequency common-mode interference signal exceeds the threshold. The early warning device designed by the present invention has the advantages of high sensitivity and non-contact, and can effectively eliminate the interference of high-frequency differential-mode magnetic fields, without affecting the normal operation of LED lamps.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A high-frequency common-mode interference online early warning device comprises: a magnetic filter ring, a magnetic induction ring, a coil winding, and a noise alarm device, wherein the magnetic filter ring is non-contactly sleeved on the live wire and the neutral wire of the LED lamp driver to improve the uneven magnetic field distribution caused by the asymmetric position of the common-mode current being measured; the magnetic induction ring is non-contactly sleeved on the outside of the magnetic filter ring and is installed together with the magnetic filter ring on the outside of the LED lamp to form a double-ring structure; the coil winding is wound on the magnetic induction ring, and the output voltage is proportional to the change rate of the common-mode current being measured; and the noise alarm device alarms based on the signal output by the coil winding.

[0008] The relative magnetic permeability of the magnetic core of the magnetic filter ring is greater than 3000.

[0009] The relative magnetic permeability of the magnetic induction ring is less than 1 / 2 of the relative magnetic permeability of the magnetic filter ring, and the height of the magnetic induction ring is not higher than the height of the magnetic filter ring.

[0010] The wire diameter of the coil winding is determined based on the diameter of the measured wire to ensure that it does not affect the gap range between the magnetic filter ring and the magnetic induction ring.

[0011] The device also includes an integration circuit, a high-pass filter, and an interference intensity detection circuit. The input end of the integration circuit is connected to the output of the coil winding, and the output end of the integration circuit is connected to the high-pass filter, the interference intensity detection circuit, and the noise alarm device in sequence; the integration circuit is used to integrate the voltage signal output by the coil winding; the high-pass filter is used to filter out noise interference of other frequency components in the high-frequency common-mode current signal; and the interference intensity detection circuit is used to output a signal representing the interference intensity.

[0012] The number of turns of the coil winding is determined according to the frequency range of the high-frequency signal to be collected, the sensitivity and the parameters of the subsequent integration circuit, and the sensitivity and the lower limit frequency are inversely proportional to the number of turns.

[0013] The output signal of the integration circuit is in linear proportion to the common mode current being measured, and the sensitivity and lower limit frequency of the output signal of the integration circuit are proportional to the equivalent resistance value of the integration circuit.

[0014] The bandwidth of the high-pass filter output signal is greater than 500 kHz.

[0015] The cut-off frequency of the high-pass filter is greater than the switching frequency of the LED driver when it is working normally, and is greater than 100 kHz.

[0016] The output signal of the interference intensity detection circuit is a level signal, an analog signal or a PWM pulse signal:

[0017] When the output is a level signal, the interference intensity detection circuit uses a voltage comparator to compare the high-pass filter output signal with a threshold voltage, and outputs a high level if it exceeds the threshold, otherwise it outputs a low level;

[0018] When the output signal is an analog signal, the interference intensity detection circuit uses an envelope detection circuit to process the high-pass filter output signal and output an envelope analog signal;

[0019] When the output signal is a PWM pulse signal, the interference intensity detection circuit uses a voltage comparator to compare the high-pass filter output signal with a reference voltage, and connects a Schmitt trigger to output a PWM pulse signal representing the interference intensity.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) Strong anti-interference ability:

[0022] The device of the present invention uses a high-permeability magnetic ring as a magnetic filter ring, which can effectively avoid the uneven distribution of the magnetic field caused by the uneven distribution of the LED light wires, and effectively improve the accuracy of the magnetic induction ring in measuring high-frequency common-mode current. At the same time, the current sensor made of the magnetic induction ring can effectively concentrate the magnetic field, thereby reducing the interference of external signals and can still work stably in a complex electromagnetic environment.

[0023] (2) Online warning of high-frequency common-mode interference intensity:

[0024] The present invention can adapt to different scene requirements by adjusting the reference voltage, and the output mode of the interference intensity detection circuit is flexible, and can output level signals, analog signals and pulse signals, and can indicate the size of high-frequency common-mode interference noise in real time and effectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of the device of the present invention;

[0026] Figure 2is a reference voltage U in one embodiment th Schematic diagram of four-channel output waveform when it is low;

[0027] Figure 3 is a reference voltage U in one embodiment th Schematic diagram of the four-channel output waveform when the voltage is higher. DETAILED DESCRIPTION

[0028] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0029] Example 1

[0030] The present embodiment provides an online early warning device for high-frequency common-mode interference of LED lamps in cable tunnels, which solves the problem that the online monitoring of the high-frequency common-mode current of LED lamps is easily interfered by the high-frequency differential-mode current magnetic field, and improves the signal-to-noise ratio of the high-frequency common-mode interference signal. The device can not only reduce the interference of other high-frequency stray signals, but also effectively realize non-contact online monitoring of the intensity of the high-frequency common-mode interference signal of the LED lamp, and has the characteristics of safety, anti-interference and strong sensitivity.

[0031] like Figure 1 As shown, the device includes: a magnetic filter ring 1, a magnetic induction ring 2, a coil winding 3, an integration circuit 4, a high-pass filter 5, an interference intensity detection circuit 6 and a noise alarm device 7.

[0032] (1) Magnetic filter ring 1

[0033] The magnetic filter ring 1 is non-contactly sleeved on the live wire and the neutral wire of the LED lamp driver, and forms a double ring structure with the magnetic induction ring 2. The materials used for the magnetic core of the magnetic filter ring 1 include but are not limited to manganese-zinc ferrite and permalloy materials, and the relative magnetic permeability should be greater than 3000. The magnetic filter ring 1 is used to improve the uneven magnetic field distribution caused by the asymmetric position of the measured current, so that the magnetic field outside the magnetic ring is evenly distributed, and the LED high-frequency common-mode interference current is accurately extracted.

[0034] (2) Magnetic induction ring 2

[0035] The magnetic induction ring 2 is non-contactly sleeved on the outside of the magnetic filter ring 1, and is installed together with the magnetic filter ring 1 on the outside of the LED lamp to form a double-ring structure. The magnetic induction ring 2 is wrapped with insulating material, and its skeleton material includes but is not limited to silicon steel sheets and ferrites for magnetic conductivity. The magnetic induction ring 2 and the externally wound coil winding 3 together form a Rogowski coil current sensor with a magnetic core. The relative magnetic permeability of the magnetic induction ring 2 should be less than 1 / 2 of the relative magnetic permeability of the magnetic filter ring, and the height of the magnetic induction ring should not be higher than the height of the magnetic filter ring.

[0036] The present invention uses a magnetic filter ring to offset and filter high-frequency differential mode signals, thereby improving the accuracy of common-mode current extraction, and uses a magnetic induction ring to collect high-frequency common-mode interference current due to electromagnetic induction, so as to perform non-contact cable tunnel high-frequency common-mode interference monitoring and early warning.

[0037] (3) Coil winding 3

[0038] The coil winding 3 is a multi-turn winding, wound evenly or unevenly on the magnetic induction ring 2, and the output is connected to the integration circuit 4. The output voltage u of the coil winding 3 is cm Proportional to the rate of change of the measured common mode current. Coil materials include but are not limited to enameled wire and sheathed wire. The number of coil turns is determined by the frequency range of the high-frequency signal to be collected, the sensitivity, and the parameters of the post-stage integration circuit 4, and the sensitivity and the lower limit frequency are inversely proportional to the number of turns. The wire diameter needs to take into account the diameter of the measured wire, and it must not affect the gap range between the magnetic filter ring and the magnetic induction ring.

[0039] (4) Integrator circuit 4

[0040] The input end of the integration circuit 4 is connected to the output of the coil winding 3, and the output end of the integration circuit 4 is connected to the high-pass filter 5, the interference intensity detection circuit 6, and the noise alarm device 7 in sequence. The integration circuit 4 can be in the form of a self-integration circuit composed of terminal resistors and an external integration circuit composed of an operational amplifier. The function of the integration circuit is to integrate the voltage signal output by the coil winding that is proportional to the differential of the common-mode current being measured, and its output signal i cm It is linearly proportional to the measured common mode current. The sensitivity and lower limit frequency of the output signal of the integration circuit are proportional to the equivalent resistance value of the integration circuit.

[0041] (5) High pass filter 5

[0042] The high-pass filter 5 is used to filter out the noise interference of other frequency components in the high-frequency common-mode current signal, such as the noise interference of the PWM ripple and the rectifier double frequency component. The output signal i of the high-pass filter 5 is cmhf The bandwidth is greater than 500kHz. The high-pass filter 5 may be in the form of, but not limited to, digital and analog high-pass filters, whose cut-off frequency is greater than the switching frequency of the LED driver when it is working normally, and greater than 100kHz. Digital filters include, but are not limited to, digital filtering algorithms using DSP, single-chip microcomputers, and computer platforms, and analog filters include, but are not limited to, first-order RC high-pass filters.

[0043] (6) Interference intensity detection circuit 6

[0044] The input end of the interference intensity monitoring circuit 6 is connected to the previous stage high-pass filter 5, and the output end is connected to the next stage noise alarm device 7. The output signal of the interference intensity detection circuit 6 is a level signal, an analog signal or a PWM pulse signal.

[0045] When the output is a level signal, the interference intensity detection circuit 6 uses a voltage comparator to convert the high-pass filter 5 output signal i cmhf Compare with the threshold voltage, if it exceeds the threshold, it will output a high level, otherwise it will output a low level;

[0046] When the output signal is an analog signal, the interference intensity detection circuit 6 uses an envelope detection circuit to detect the output signal i of the high-pass filter 5. cmhf Processing is performed to output envelope analog signals;

[0047] When the output signal is a PWM pulse signal, the interference intensity detection circuit 6 uses a voltage comparator to convert the high-pass filter 5 output signal i cmhf Compared with the reference voltage, the Schmitt trigger is connected to output a PWM pulse signal representing the interference intensity.

[0048] (7) Noise alarm device 7

[0049] The noise alarm device 7 may be used in the form of, but not limited to, a buzzer and a warning light. th When the alarm device exceeds the threshold, it will alarm, and will not alarm within the threshold range.

[0050] Example 2

[0051] This embodiment verifies the feasibility and effectiveness of the high-frequency common-mode interference online warning device for cable tunnel LED lights described in Example 1 through experiments. Figure 1 As shown, it consists of an AC power supply, an actual LED lamp in a cable tunnel, an LED driver, a magnetic filter ring 1, a magnetic induction ring 2, a coil winding 3, an integration circuit 4, a high-pass filter 5, an interference intensity detection circuit 6, and a noise alarm device 7. The design parameters of the LED lamp, the magnetic induction ring and the magnetic filter ring are shown in Tables 1, 2, and 3. The present invention was applied in an experimental system to carry out a monitoring and early warning experiment.

[0052] Table 1 Actual LED lamp parameters in a cable tunnel

[0053] parameter Numeric Rated voltage 220V / 50Hz power 20W Protection level IP65 Corrosion resistance WF2 Product light source High power integrated chip

[0054] Table 2 Magnetic filter ring parameters

[0055] parameter Numeric inner diameter 23mm outer diameter 31mm high 21mm Relative magnetic permeability 5000 Core material MXO

[0056] Table 3 Parameters of magnetic induction ring device

[0057] parameter Numeric inner diameter 40mm outer diameter 60mm high 20mm Relative magnetic permeability 2000 Core material MXO Coil turns 20 turns Terminal resistance 100Ω

[0058] When the LED lamp is operating normally, different reference voltages are set to measure the output waveform of the channel of the device as follows Figure 2 , 3 As shown, by adjusting the reference voltage U th It is observed that the alarm intensity changes in accordance with expectations; the first channel outputs the response voltage signal of the current sensor integration circuit, the second channel sets the comparison voltage signal of the comparator, the third channel is the switch event signal output by the Schmitt trigger after comparison by the voltage comparator, and the fourth channel is the voltage signal at both ends of the alarm. It can be seen that the four channel signals of the present invention are all in line with expectations. When the comparison voltage of the second channel is increased from 1.79V to 2.54V, the amplitude of the switch event signal output by the third channel is significantly weakened, and the number of pulse voltages received by both ends of the alarm light output by the fourth channel is significantly reduced. At this time, the brightness of the alarm light becomes significantly dimmer, that is, the alarm is lifted. The above examples show that the device can effectively reflect the size of the high-frequency common-mode noise generated by the tunnel LED lights and provide real-time warnings.

[0059] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning, or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A high-frequency common-mode interference online early warning device, characterized in that: include: A magnetic filter ring (1), a magnetic induction ring (2), a coil winding (3), an integration circuit (4), and a noise alarm device (7), wherein the magnetic filter ring (1) is non-contactly sleeved on the live wire and the neutral wire of an LED lamp driver, and is used to improve the uneven magnetic field distribution caused by the asymmetric position of the common mode current to be measured, and the relative magnetic permeability of the magnetic core of the magnetic filter ring (1) is greater than 3000; the magnetic induction ring (2) is non-contactly sleeved on the outside of the magnetic filter ring (1), and is installed together with the magnetic filter ring (1) on the outside of the LED lamp to form a double ring structure; the coil winding (3) is wound on the magnetic induction ring (2), and the output voltage is proportional to the change rate of the common mode current to be measured, and the magnetic induction ring (2) and the externally wound coil winding (3) together form a Rogowski coil current sensor with a magnetic core; the input end of the integration circuit (4) is connected to the output of the coil winding (3), and is used to integrate the voltage signal output by the coil winding (3); and the noise alarm device (7) alarms based on the signal output by the coil winding (3).

2. The high-frequency common-mode interference online early warning device according to claim 1 is characterized in that: The relative magnetic permeability of the magnetic induction ring (2) is less than 1 / 2 of the relative magnetic permeability of the magnetic filter ring (1), and the height of the magnetic induction ring (2) is not higher than the height of the magnetic filter ring (1).

3. The high-frequency common-mode interference online early warning device according to claim 1 is characterized in that: The wire diameter of the coil winding (3) is determined based on the diameter of the conductor to be measured, ensuring that the gap range of the conductor passing through the magnetic filter ring (1) and the magnetic induction ring (2) is not affected.

4. The high-frequency common-mode interference online early warning device according to claim 1 is characterized in that: The device further comprises a high-pass filter (5) and an interference intensity detection circuit (6); the output end of the integration circuit (4) is connected to the high-pass filter (5), the interference intensity detection circuit (6) and the noise alarm device (7) in sequence; the high-pass filter (5) is used to filter out noise interference of other frequency components in the high-frequency common-mode current signal; and the interference intensity detection circuit (6) is used to output a signal representing the interference intensity.

5. The high-frequency common-mode interference online early warning device according to claim 1 is characterized in that: The number of turns of the coil winding (3) is determined according to the frequency range of the high-frequency signal to be collected, the sensitivity and the parameters of the subsequent integration circuit (4), and the sensitivity and the lower limit frequency are inversely proportional to the number of turns.

6. The high-frequency common-mode interference online early warning device according to claim 1, characterized in that: The output signal of the integration circuit (4) is in linear proportion to the common-mode current being measured, and the sensitivity and lower limit frequency of the output signal of the integration circuit (4) are proportional to the equivalent resistance value of the integration circuit (4).

7. The high-frequency common-mode interference online early warning device according to claim 4 is characterized in that: The bandwidth of the output signal of the high-pass filter (5) is greater than 500 kHz.

8. The high-frequency common-mode interference online early warning device according to claim 4 is characterized in that: The cut-off frequency of the high-pass filter (5) is greater than the switching frequency of the LED driver when it is operating normally, and is greater than 100 kHz.

9. The high-frequency common-mode interference online early warning device according to claim 4, characterized in that: The output signal of the interference intensity detection circuit (6) is a level signal, an analog signal or a PWM pulse signal. When the output is a level signal, the interference intensity detection circuit (6) uses a voltage comparator to compare the output signal of the high-pass filter (5) with a threshold voltage, and outputs a high level when the threshold voltage is exceeded, otherwise a low level is output; When the output signal is an analog signal, the interference intensity detection circuit (6) uses an envelope detection circuit to process the output signal of the high-pass filter (5) and output an envelope analog signal; When the output signal is a PWM pulse signal, the interference intensity detection circuit (6) uses a voltage comparator to compare the output signal of the high-pass filter (5) with a reference voltage, and connects a Schmitt trigger to output a PWM pulse signal representing the interference intensity.

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