A medium-voltage broadband PLC signal coupling system based on an inverted L-shaped matching attenuator

Abstract

The present invention provides a medium-voltage broadband PLC signal coupling system based on an inverted L-shaped matching attenuator. The coupling system includes a coupling module, an isolation module, an inverted L-shaped impedance matching module, a band-pass filtering module and a protection component. The coupling module is a coupling capacitor for signal coupling and blocking the 50Hz power frequency voltage; the isolation module is an isolation transformer for current isolation; the inverted L-shaped impedance matching module is used to match the impedance between the terminal carrier machine and the power line end to reduce signal reflection; the band-pass filtering module is a band-pass filter for signal frequency selection and filtering out-of-band interference; the protection component is a lightning arrester for sensing and suppressing instantaneous overvoltage surges on the circuit. The present invention can perform signal coupling in a wide frequency range of 1-30MHz. Using variable pure resistance elements to adjust the circuit can greatly simplify the matching process and improve the reliability of the circuit, providing a new basis for the practical application of broadband PLC coupling technology in intelligent distribution networks.

Description

Technical Field

[0001] The present invention relates to the field of power line carrier communication, and particularly to a medium-voltage broadband PLC signal coupling system based on an inverted L-shaped matching attenuator. Background Art

[0002] A power line communication (PLC) coupler is an interface circuit placed between a PLC transmitter / receiver and a power line channel, used to couple a high-frequency carrier signal to the power line or decouple it from the power line. In practical applications, electrical devices connected to the line will randomly access or remove, resulting in the input impedance of the power line channel having location and time-varying characteristics, which will cause impedance mismatch between the terminal carrier machine and the power line channel, resulting in reflection of PLC signals and affecting communication quality.

[0003] Currently, low-frequency narrowband power line communication technology has been widely applied to services such as intelligent meter reading, load management, and distribution automation. However, its bandwidth and communication rate are gradually at a disadvantage in the rapidly developing communication services, while the high-frequency broadband coupling method provides a new theoretical basis for the optimization of intelligent distribution networks. Summary of the Invention

[0004] The purpose of the present invention is to provide a medium-voltage broadband PLC signal coupling system based on an inverted L-shaped matching attenuator to solve the limitation problems of narrowband power line coupling technology in terms of signal bandwidth and impedance mismatch.

[0005] The present invention is implemented as follows:

[0006] A medium-voltage broadband PLC signal coupling system based on an inverted L-shaped matching attenuator includes a coupling module, an isolation module, an impedance matching module, a band-pass filtering module, and a protection component. The coupling module is a coupling capacitor, the high-voltage side of the coupling capacitor is connected to the power line, and the low-voltage side is connected to the isolation module, used for signal coupling and blocking the 50Hz power frequency voltage; the isolation module is an isolation transformer, the primary coil side of the isolation transformer is connected to the low-voltage side of the coupling capacitor, and the secondary coil side is connected to the impedance matching module, used for current isolation; the impedance matching module is an inverted L-shaped matching attenuator, connected to the isolation module and the band-pass filtering module, used for matching the impedance between the terminal carrier machine and the power line end to reduce signal reflection; the band-pass filtering module is a band-pass filter, connected to the impedance matching module and the carrier machine, having a bandwidth of 1 - 30MHz, used for signal frequency selection and filtering out out-of-band interference. The protection component is a lightning arrester, connected across the low-voltage side of the coupling capacitor and the ground wire, used for sensing and suppressing instantaneous overvoltage surges on the circuit and providing a low-impedance path for instantaneous phenomena.

[0007] Further, the turns ratio of the primary coil to the secondary coil of the isolation transformer is 1:1. There is a 10 KΩ unloading resistor in parallel with the primary coil side of the isolation transformer to form a loop. When the line voltage disappears, the unloading resistor is used to consume the magnetic field energy stored inside the primary coil of the transformer.

[0008] Further, the inverted L-shaped matching attenuator is connected to the secondary coil of the isolation transformer. The inverted L-shaped matching attenuator includes a first resistor R1 and a second resistor R2; the first resistor R1 and the second resistor R2 are placed in an inverted L-shaped structure. One end of the first resistor R1 is connected in series with the secondary coil of the isolation transformer, the other end of the first resistor R1 is connected to one end of the second resistor R2, and the other end of the second resistor R2 is grounded.

[0009] Further, the inverted L-shaped matching attenuator achieves impedance matching on the left and right sides by adjusting the resistance values of the first resistor R1 and the second resistor R2. Due to the structural characteristics of the resistor elements of the inverted L-shaped matching attenuator, the input and output impedances seen from its left and right directions are not the same. Therefore, between two unequal impedances, only unidirectional matching can be performed. When matching to the smaller value of the two impedances, the following relationship exists between the first resistor R1 and the second resistor R2:

[0010]

[0011]

[0012]

[0013] When matching to the larger value of the two impedances, the following relationship exists between the first resistor R1 and the second resistor R2:

[0014]

[0015]

[0016]

[0017] Where: Z S 、Z L are the input and output impedances of the inverted L-shaped matching attenuator respectively, S is the square root of the ratio of the input and output impedances, The K value is the ratio of voltage or current corresponding to a given attenuation value in dB. In calculations, the K value is usually used to simplify the design process of complex attenuator circuits and can be obtained by looking up tables.

[0018] Further, the band-pass filter includes a first capacitor C1, a second capacitor C2, a first inductor L1 and a second inductor L2; one end of the first capacitor C1 is connected to the non-grounded end of the second resistor R2 in the inverted L-shaped matching attenuator, and the other end of the first capacitor C1 is connected in series with the first inductor L1; the first capacitor C1 is connected to one end of the second capacitor C2 through the first inductor L1, the other end of the second capacitor C2 is grounded, and the second inductor L2 is connected in parallel across the two ends of the second capacitor C2.

[0019] Further, the low-frequency cut-off frequency f of the band-pass filter circuit L = 1 MHz, and the high-frequency cut-off frequency f H = 30 MHz, with a characteristic impedance of 50 Ω.

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

[0021] A medium-voltage broadband PLC signal coupling system based on an inverted L-shaped matching attenuator proposed by the present invention overcomes the limitations of narrowband power line communication coupling technology in terms of signal bandwidth and impedance mismatch. The present invention can perform signal coupling in a wide frequency range of 1 - 30 MHz. At the same time, using variable pure resistance elements to adjust the circuit can greatly simplify the matching process and improve the reliability of the circuit, providing a new basis for the practical application of broadband PLC coupling technology in intelligent distribution networks. Description of the Drawings

[0022] Figure 1 is the circuit schematic diagram of the coupling system in a specific embodiment of the present invention.

[0023] Figure 2 is the circuit schematic diagram of the coupling capacitor in a specific embodiment of the present invention.

[0024] Figure 3 is the circuit schematic diagram of the isolation transformer and the unloading resistor in a specific embodiment of the present invention.

[0025] Figure 4 is the circuit schematic diagram of the impedance matching module in a specific embodiment of the present invention.

[0026] Figure 5 is the comparison diagram of the S11 parameters of the circuit when matched and unmatched in a specific embodiment of the present invention.

[0027] Figure 6 is the attenuation diagram of the S21 parameters of the circuit when impedance-matched and mismatched in a specific embodiment of the present invention.

[0028] Figure 7 is the circuit schematic diagram of the band-pass filter module in a specific embodiment of the present invention.

[0029] Figure 8 It is the attenuation diagram of the S21 parameter of the band-pass filter circuit in a specific embodiment of the present invention.

[0030] Figure 9 It is the input / output waveform diagram of the broadband PLC coupling system in a specific embodiment of the present invention. Specific Embodiment

[0031] As Figure 1 shown, the medium-voltage broadband PLC signal coupling system based on the inverted L-shaped matching attenuator provided by the present invention includes a coupling module, an isolation module, an impedance matching module, a band-pass filter module, and a protection element.

[0032] The coupling module is specifically a coupling capacitor. As Figure 2 shown, the two ends of the coupling capacitor C are the high-voltage side and the low-voltage side respectively. The high-voltage side is connected to the power line; the low-voltage side is connected to the isolation module, which is used for signal coupling and blocking the 50Hz power frequency voltage. The coupling capacitor is a high-voltage-resistant capacitor and should be able to withstand a maximum operating voltage of up to 11.5kV, a power frequency voltage of 42kV for 1 minute, and a lightning impulse voltage of 75kV without damage.

[0033] As Figure 3 shown, the isolation module is an isolation transformer. The primary coil side of the isolation transformer is connected to the low-voltage side of the coupling capacitor C, and the secondary coil side is connected to the impedance matching module, which is used for current isolation.

[0034] The turns ratio of the primary coil to the secondary coil of the isolation transformer is 1:1. There is a discharge resistor R with a capacity of 10KΩ in parallel with the primary coil side of the isolation transformer to form a loop. When the line voltage disappears, the loop can release the magnetic field energy stored in the primary coil.

[0035] The impedance matching module is an inverted L-shaped matching attenuator. The impedance matching module is respectively connected to the isolation transformer and the band-pass filter module, which is used to match the impedance between the terminal carrier communication machine and the power line end and reduce signal reflection.

[0036] As Figure 4 shown, the inverted L-shaped matching attenuator includes a first resistor R1 and a second resistor R2; the first resistor R1 and the second resistor R2 are placed in an inverted L-shaped structure. One end of the first resistor R1 is connected in series with the secondary coil of the isolation transformer, the other end of the first resistor R1 is connected to one end of the second resistor R2, and the other end of the second resistor R2 is grounded.

[0037] The inverted L-shaped matching attenuator can achieve impedance matching on both the left and right sides by adjusting the resistance values of the first resistor R1 and the second resistor R2. Due to the structural characteristics of the resistor elements of the inverted L-shaped matching attenuator, the input and output impedances seen from its left and right directions are not the same. Therefore, only unidirectional matching can be performed between two unequal impedances. When matching to the smaller value of the two impedances, the following relationship exists between the first resistor R1 and the second resistor R2:

[0038]

[0039]

[0040]

[0041] When matching to the larger value of the two impedances, the following relationship exists between the first resistor R1 and the second resistor R2:

[0042]

[0043]

[0044]

[0045] In the formula: Z S 、Z L are the input and output impedances of the inverted L-shaped matching attenuator respectively, S is the square root of the ratio of the input and output impedances, The K value is the ratio of voltage or current corresponding to a given attenuation value in dB. In calculations, the K value is usually used to simplify the design process of complex attenuator circuits. The K value can be determined by referring to Table 1 below, and then the attenuator loss can be calculated.

[0046] Table 1 Attenuator Loss Table

[0047]

[0048]

[0049] Figure 5 The shown S11 parameter curve shows the return loss of the circuit with and without impedance matching. It can be seen that the return loss of the circuit with matching by the present invention is much smaller than that of the unmatched circuit, and the matching circuit weakens the signal reflection caused by impedance discontinuity.

[0050] Figure 6It is the S21 parameter attenuation diagram of the circuit during impedance matching and mismatch in a specific embodiment of the present invention. Taking the measured input impedance data of a certain medium-voltage line and the port impedance of the carrier communication machine as the standard value of 50Ω as a reference, at a carrier frequency of 5MHz, the line impedance is 545Ω. On the premise of a 12dB attenuation in decibel loss, it can be seen from Table 1 that the K value is 3.9811, and the matching resistance values of the first resistor R1 and the second resistor R2 are calculated to be 503Ω and 242Ω respectively. At the same time, two sets of power line input impedance values of 200Ω and 120Ω are set respectively as a comparison to compare the circuit responses during impedance matching and mismatch. The top curve where the m1 marked point is located shows the passband characteristics of the correct impedance matching circuit. Compared with the impedance mismatch circuits where the m2 and m3 marked points are located, the correct matching has a gain of approximately 1dB and 2.2dB respectively.

[0051] The band-pass filtering module is a band-pass filter, which is connected to the impedance matching module and the carrier communication machine, has a bandwidth of 1 - 30MHz, and is used for signal frequency selection and filtering out of out-of-band interference. As Figure 7 shown, the band-pass filter includes a first capacitor C1, a second capacitor C2, a first inductor L1, and a second inductor L2; one end of the first capacitor C1 is connected to the non-grounded end of the second resistor R2 in the inverted L-shaped matching attenuator, the other end of the first capacitor C1 is connected in series with the first inductor L1, the first capacitor C1 is connected to one end of the second capacitor C2 through the first inductor L1, the other end of the second capacitor C2 is grounded, and the second inductor L2 is connected in parallel across the two ends of the second capacitor C2. The low-frequency cut-off frequency f L of the band-pass filtering circuit is 1MHz, the high-frequency cut-off frequency f H is 30MHz, and the characteristic impedance is 50Ω.

[0052] The protection component is a lightning arrester, which is connected across the low-voltage side of the coupling capacitor and the ground wire, and is used to sense and suppress the instantaneous overvoltage surge on the circuit, providing a low-impedance path for the instantaneous phenomenon.

[0053] Figure 8 It is the S21 parameter attenuation diagram of the band-pass filtering circuit in a specific embodiment of the present invention. The 3dB attenuation is used in the test to determine the bandwidth. It can be seen that at a frequency of 1.00MHz, the attenuation is 3.01dB, and similar attenuation points appear at a frequency of 30.00MHz with an attenuation of 3.01dB. The S21 parameter results demonstrate the good passband characteristics of the designed band-pass filtering circuit.

[0054] Figure 9It is the input / output waveform diagram of the broadband PLC coupling system in a specific embodiment of the present invention. Since the port impedance of the test equipment is 50 Ω, a resistor with a resistance value of 495 Ω is connected in series at the signal input end of the coupling system to simulate the actual line impedance. A sine wave with an amplitude of 2.5 V and a frequency of 5 MHz is transmitted on the power line as the signal waveform received by the broadband PLC coupling system from the power line. After being received by the broadband PLC coupling system, the signal amplitude drops to about 220 mV. The waveform comparison shows that the broadband PLC coupling system designed by the present invention can successfully receive the carrier signal sent by the signal source.

Claims

1. A medium-voltage broadband PLC signal coupling system based on an inverted L-shaped matching attenuator, characterized in that It includes a coupling module, an isolation module, an impedance matching module, and a band-pass filtering module connected in sequence; the coupling module is a coupling capacitor, the high-voltage side of the coupling capacitor is connected to the power line, and the low-voltage side is connected to the isolation module, which is used for signal coupling and blocking the 50Hz power frequency voltage; the isolation module is an isolation transformer, the primary coil side of the isolation transformer is connected to the low-voltage side of the coupling capacitor, and the secondary coil side is connected to the impedance matching module, which is used for current isolation; the impedance matching module is an inverted L-shaped matching attenuator, which is used to match the impedance between the carrier communication machine and the power line end and reduce signal reflection; the band-pass filtering module is a band-pass filter, connected between the impedance matching module and the carrier machine, with a bandwidth of 1 - 30MHz, which is used for signal frequency selection and filtering out of-band interference; a protection component is also provided between the low-voltage side of the coupling capacitor and the ground wire, which is used to sense and suppress the instantaneous overvoltage surge on the circuit and provide a low-impedance path for the instantaneous phenomenon; The inverted L-shaped matching attenuator includes a first resistor R1 and a second resistor R2; the first resistor R1 and the second resistor R2 are placed in an inverted L-shaped structure, one end of the first resistor R1 is connected in series with the secondary coil of the isolation transformer, the other end of the first resistor R1 is connected to one end of the second resistor R2, and the other end of the second resistor R2 is grounded; The inverted L-shaped matching attenuator realizes impedance matching on the left and right sides by adjusting the resistance values of the first resistor R1 and the second resistor R2; between two unequal input and output impedances, only one-way matching can be performed; when matching to the smaller value of the two impedances, the following relationship exists between the first resistor R1 and the second resistor R2: When matching to the larger value of the two impedances, the following relationship exists between the first resistor R1 and the second resistor R2: Where: Z S and Z L are the input and output impedances of the attenuator respectively, S is the square root of the ratio of the input and output impedances, and the K value is the ratio of voltage or current corresponding to a given attenuation value in dB.

2. The medium-voltage broadband PLC signal coupling system based on an inverted L-shaped matching attenuator according to claim 1, characterized in that The turns ratio of the primary coil to the secondary coil of the isolation transformer is 1:

1. There is a discharge resistor with a capacity of 10KΩ in parallel with the primary coil side of the transformer to form a loop. The discharge resistor is used to consume the magnetic field energy stored inside the primary coil of the transformer after the line voltage disappears.

3. The medium-voltage broadband PLC signal coupling system based on an inverted L-shaped matching attenuator according to claim 1, characterized in that, The band-pass filter includes a first capacitor C1, a second capacitor C2, a first inductor L1, and a second inductor L2; one end of the first capacitor C1 is connected to the non-grounded end of the second resistor R2 in the inverted L-shaped matching attenuator, and the other end of the first capacitor C1 is connected in series with the first inductor L1; the first capacitor C1 is connected to one end of the second capacitor C2 through the first inductor L1, the other end of the second capacitor C2 is grounded, and the second inductor L2 is connected in parallel across the two ends of the second capacitor C2.

4. The medium-voltage broadband PLC signal coupling system based on an inverted L-shaped matching attenuator according to claim 3, characterized in that, Low - pass cut - off frequency f of the band - pass filter circuit L = 1 MHz, high - pass cut - off frequency f H = 30 MHz, characteristic impedance 50 Ω.

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