A T-type impedance matching coupler for power line communication

Abstract

The present invention discloses a T-type impedance matching coupler for power line communication, belonging to the technical field of power line communication. It includes a transmitting end, to which a first capacitor and a first inductor are connected, and then a second inductor, a Π-type structure, and a power line equivalent circuit connected in parallel are connected. A third inductor is connected between the Π-type structure and the power line equivalent circuit, and the transmitting end is connected to a ground wire; the first capacitor and the first inductor resonate at the center frequency. The present invention realizes the functions of impedance matching, signal coupling, and DC isolation between the transmitting end, the receiving end, and the power line by designing a T-type impedance matching coupling circuit with a simple circuit structure, with a low level of complexity. At the same time, a power line equivalent circuit is designed, taking into account the impedance caused by the equivalent resistance and equivalent inductance of the power line. Through simulation and physical tests, the designed T-type impedance matching coupling circuit can obtain a gain of 3 dB - 7 dB compared with the coupling circuit under impedance mismatch conditions.

Description

Technical Field

[0001] The present invention relates to a T-type impedance matching coupler for power line communication, belonging to the technical field of power line communication. Background Art

[0002] Power Line Communication (PLC) is a technology that uses existing power lines as communication media to simultaneously transmit electrical energy and electrical signals in the power lines, effectively reducing the usage cost because no additional signal cables need to be laid. Power line communication requires loading communication signals into the power lines or extracting communication signals from the power lines, which are usually completed by a signal coupling circuit. During signal transmission, if the impedances of the signal source and the signal sink do not match the impedance of the power line, serious signal reflection will occur, resulting in power loss. Therefore, in addition to having the functions of signal loading and extraction, it is expected that this signal coupling circuit can achieve impedance matching between the power line and the signal source and the signal sink, so as to maximize the transmission power of the signal.

[0003] In the past two or three decades, power line communication has been widely applied in the AC field. In AC-PLC, the coupling method is mainly transformer coupling, and its technology has gradually matured. In contrast, the application research of power line communication in the DC field has just begun. With the rise of industries such as wearable electronics, intelligent vehicles, and photovoltaic power generation, more and more scholars and engineers are attracted to conduct research on DC power line communication. It should be noted that when designing a coupling transformer in AC-PLC, parameters such as the leakage inductance, magnetization inductance, internal resistance of the signal source, and turns ratio of the transformer need to be considered simultaneously, and the design method is relatively complex. At the same time, the size of this kind of coupler is often relatively large. Considering the stringent requirements for miniaturization of device size in wearable electronics and intelligent vehicles, etc., it is very necessary to develop a coupling circuit with a small size and excellent performance in DC power line communication (DC-PLC).

[0004] So far, there have been a few literature reports on L-C band-pass matching couplers applicable to DC-PLC. SIBANDA M P et al. designed a T-type band-pass filter (BPF) to achieve the coupling and filtering of communication signals and at the same time isolate the power signals. However, this design did not take into account the impedance mismatch between the power line and the signal source and sink. In view of this, SIBANDA M P et al. designed an impedance matching circuit, which can achieve signal coupling and impedance matching after being cascaded with the previously designed BPF, but the circuit complexity is relatively high and the cost is increased. SWANA Z W et al. designed a coupler using the voltage division characteristic of resistors, but also did not take into account the impedance mismatch problem between the power line and the signal source and sink. In addition, WANG Bingting et al. designed a π-type band-pass matching coupler that only considered the equivalent inductance impedance of the power line, but did not consider the equivalent resistance impedance that cannot be completely ignored. Summary of the Invention

[0005] The purpose of the present invention is to provide a T-type impedance matching coupler for power line communication, which solves the problems of impedance caused by the equivalent resistance and equivalent inductance of the power line not being considered in the prior art, high complexity, impedance mismatch, etc.

[0006] To achieve the above purpose, the present invention is implemented by the following technical solutions:

[0007] The present invention provides a T-type impedance matching coupler for power line communication, including a transmitting end. At the transmitting end, a first capacitor and a first inductor are connected, and then a second inductor, a Π-type structure, and a power line equivalent circuit connected in parallel are connected. A third inductor is connected between the Π-type structure and the power line equivalent circuit, and the transmitting end is connected to a ground wire;

[0008] The first capacitor and the first inductor resonate at the center frequency.

[0009] Further, the transmitting end includes a signal source and an output resistor connected in sequence, and the output resistor is connected to the first capacitor.

[0010] Further, the Π-type structure is composed of a second capacitor, a third capacitor, and a fourth capacitor, where the second capacitor and the fourth capacitor are respectively the two legs of the Π-type structure.

[0011] Further, the power line equivalent circuit includes a power line equivalent inductor and a power line equivalent resistor connected in series, and its mathematical expression is:

[0012]

[0013] Z L =|Z0|*cos(θ)

[0014] Among them, L4 is the equivalent inductance of the power line, Z L is the equivalent resistance of the power line, Z0 is the characteristic impedance of the power line, θ is the impedance angle of the characteristic impedance of the power line, and f0 is the center frequency.

[0015] Furthermore, the expression of the center frequency is:

[0016]

[0017] Among them, f H is the upper cut-off frequency, and f L is the lower cut-off frequency.

[0018] Furthermore, the expression and value range of the first capacitor are:

[0019]

[0020]

[0021] Among them, C1 is the first capacitor, f H is the upper cut-off frequency, f L is the lower cut-off frequency, represents the impedance transformation multiple and Z L <50;

[0022] The expression and value range of the first inductor are:

[0023]

[0024]

[0025] Among them, L1 is the first inductor;

[0026] The expression and value range of the second inductor are:

[0027]

[0028]

[0029] Among them, L2 is the second inductor;

[0030] The expression and value range of the third inductor are:

[0031]

[0032] Furthermore, the expression of the second capacitor is:

[0033]

[0034] wherein The expression and value range of the third capacitor are as follows:

[0035]

[0036]

[0037] The expression and value range of the fourth capacitor are as follows:

[0038]

[0039]

[0040] wherein, C1 is the first capacitor, f H is the upper cut-off frequency, f L is the lower cut-off frequency, represents the impedance transformation multiple and Z L <50.

[0041] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0042] A T-type impedance matching coupler for power line communication provided by the present invention realizes the functions of impedance matching, signal coupling, and DC isolation between the transmitting end, the receiving end, and the power line by designing a T-type impedance matching coupling circuit with a simple circuit structure. Specifically, after impedance transformation, the transmitting end and the receiving end are impedance-matched with the power line. The circuit of the matching coupler can superimpose the signal onto the power line or extract the signal from the power line to achieve signal coupling. The Π-type structure is used to prevent the DC power signal from contacting the transmitting end or the receiving end, thereby realizing DC isolation. The complexity is low. At the same time, an equivalent circuit of the power line is designed, considering the impedance caused by the equivalent resistance and equivalent inductance of the power line. Through simulation and physical testing, the designed T-type impedance matching coupling circuit can obtain a gain of 3 dB - 7 dB compared with the coupling circuit under the condition of impedance mismatch. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a schematic structural diagram of a T-type impedance matching coupler for power line communication provided by an embodiment of the present invention;

[0044] Figure 2 is a simulation circuit built in the Multisim simulation software according to the solution of the present invention provided by an embodiment of the present invention;

[0045] Figure 3It is a comparison diagram of output responses when connecting different circuits with an output impedance of 22.14Ω provided by an embodiment of the present invention;

[0046] Figure 4 It is a comparison diagram of output responses with or without matching when the output terminal impedances provided by an embodiment of the present invention are 22.14Ω, 11.07Ω, and 5.535Ω respectively;

[0047] Figure 5 It is a performance comparison diagram of a 22.14Ω impedance matching coupler and a 50Ω BPF provided by an embodiment of the present invention under different load conditions. Detailed implementation manners

[0048] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and should not be used to limit the protection scope of the present invention.

[0049] As Figure 1 shown, a T-shaped impedance matching coupler for power line communication provided by an embodiment of the present invention includes a transmitting end, a first capacitor, a second capacitor, a third capacitor, a fourth capacitor, a first inductor, a second inductor, a third inductor, a power line equivalent inductor, and a power line equivalent resistor.

[0050] The transmitting end includes a signal source V connected in series S and an output resistor Z S , generally 50Ω. The output resistor is connected to a first capacitor C1 and a first inductor L1, and then connected to a parallel second inductor L2, a Π-shaped structure, and a power line equivalent circuit. A third inductor L3 is connected between the Π-shaped structure and the power line equivalent circuit. The transmitting end is connected to a ground wire.

[0051] The first capacitor and the first inductor resonate at the center frequency .

[0052] The Π-shaped structure is composed of a second capacitor C2, a third capacitor C3, and a fourth capacitor C4, where the second capacitor and the fourth capacitor are the two legs of the Π-shaped structure respectively.

[0053] The power line equivalent circuit includes a power line equivalent inductor and a power line equivalent resistor connected in series, and its mathematical expression is:

[0054]

[0055] Z L = |Z0| * cos(θ)

[0056] where L4 is the power line equivalent inductor, Z L is the power line equivalent resistor, Z0 is the power line characteristic impedance, θ is the impedance angle of the power line characteristic impedance, and f0 is the center frequency.

[0057] f H The ratio with f L is set to The range of k is which represents the impedance transformation multiple and Z L < 50.

[0058] The expressions and value ranges of the above components are as follows:

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] To verify the performance of the designed T-type impedance matching coupler, according to Figure 1 the circuit shown, a simulation circuit is built in the Multisim simulation software, and the structure is as Figure 2 shown, where the input impedance is 50 Ω and the impedance at the output end is the equivalent resistance impedance of the characteristic impedance, 22.14 Ω.

[0073] Figure 3 represents the output response when connecting different circuits with an output impedance of 22.14 Ω; when correctly matched (22.14 Ω coupler @ 22.14 Ω), the passband response is the flattest, and a gain of approximately 0.8 dB can be obtained compared to when not matched (50 Ω BPF @ 22.14 Ω).

[0074] Considering that the power line impedance is dynamically changing, it is necessary to evaluate the output response of the band-pass matching coupler when the power line impedance is lower than 22.14 Ω. Figure 4 Shows the output response of the impedance matching coupler with a matched impedance of 22.14 Ω compared to the output response of the BPF circuit without impedance matching when the output impedance is 22.14 Ω, 11.07 Ω, and 5.535 Ω respectively. From Figure 4 It can be seen that when the terminal impedance becomes 11.07 Ω, the 22.14 Ω impedance matching coupler (22.14 Ω coupler@11.07 Ω) can obtain a 2 dB gain compared to the BPF circuit without impedance matching (50 Ω BPF@11.07 Ω); when the terminal impedance becomes 5.535 Ω, the 22.14 Ω impedance matching coupler (22.14 Ω coupler@5.535 Ω) can obtain a 2.5 dB gain compared to the circuit without impedance matching (50 Ω BPF@5.535 Ω). At the same time, the 22.14 Ω matching coupler has the flattest passband response when correctly matched (22.14 Ω coupler@22.14 Ω) compared to when mismatched (22.14 Ω coupler@11.07 Ω, 22.14 Ω coupler@5.535 Ω), and can obtain gains of 3.5 dB and 8 dB respectively.

[0075] To verify the actual performance of the designed T-type impedance matching coupler, two sets of T-type impedance matching couplers were fabricated and placed on the transmitter side and the receiver side as the transmitter-receiver coupler respectively. Since the imaginary impedance of the power line (inductive reactance caused by inductance) needs to be considered during actual testing, it is necessary to build the circuit according to Figure 5 the circuit shown. At this time, the inductance of the power line characteristic impedance is in series with the inductance in the circuit, so the total inductance value at the output end remains unchanged.

[0076] Figure 5 Shows the performance comparison between the 22.14 Ω impedance matching coupler and the 50 Ω BPF under different load conditions. It can be seen from the figure that the 22.14 Ω impedance matching coupler has the best band-pass response when correctly matched (22.14 Ω coupler@22.14 Ω), and can obtain gains of 3 dB and 7 dB respectively compared to when mismatched (22.14 Ω coupler@11.07 Ω and 22.14 Ω coupler@5.505 Ω). When the loads are the same (22.14 Ω, 11.07 Ω, 5.505 Ω), the 22.14 Ω impedance matching coupler can obtain gains of 0.3 dB, 1.5 dB, and 4 dB respectively compared to the 50 Ω BPF, and the worse the load condition, the more gain the 22.14 Ω impedance matching coupler can obtain compared to the 50 Ω BPF.

[0077] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A T-type impedance matching coupler for power line communication, characterized in that, It includes a transmitting end. At the transmitting end, a first capacitor and a first inductor are connected, and then a second inductor, a Π-shaped structure, and a power line equivalent circuit connected in parallel are connected. A third inductor is connected between the Π-shaped structure and the power line equivalent circuit, and the transmitting end is connected to a ground wire; The first capacitor and the first inductor resonate at the center frequency; The Π-shaped structure is composed of a second capacitor, a third capacitor, and a fourth capacitor, where the second capacitor and the fourth capacitor are respectively the two legs of the Π-shaped structure; The expression and value range of the first capacitor are: ； ； Among them, is the first capacitor, is the upper cut-off frequency, is the lower cut-off frequency, , (1, , represents the impedance transformation multiple and ; The expression and value range of the first inductor are: ； ； Among them, is the first inductor; The expression and value range of the second inductor are: ； ； Among them, is the second inductor; The expression and value range of the third inductor are: ； ； The expression of the second capacitor is: ； Among them ; The expression and value range of the third capacitor are: ； ； The expression and value range of the fourth capacitor are: ； ； Among them, is the first capacitor, is the upper cut-off frequency, is the lower cut-off frequency, , (1, , represents the impedance transformation multiple and .

2. The T-type impedance matching coupler for power line communication according to claim 1, characterized in that, The transmitting end includes a signal source and an output resistor connected in sequence, and the output resistor is connected to the first capacitor.

3. The T-type impedance matching coupler for power line communication according to claim 1, characterized in that, The power line equivalent circuit includes a power line equivalent inductor and a power line equivalent resistor connected in series, and its mathematical expression is: ； ； Among them, is the equivalent inductance of the power line, is the equivalent resistance of the power line, is the characteristic impedance of the power line, is the impedance angle of the characteristic impedance of the power line, is the center frequency mentioned above.

4. A T-type impedance matching coupler for power line communication according to claim 1, characterized in that, The expression of the center frequency is: ； Among them, is the upper cut-off frequency, is the lower cut-off frequency.

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