Three-phase coupling circuit for carrier communication in power grid system

Abstract

The present application provides a three-phase coupling circuit for carrier communication of a power grid system, comprising: an isolation transformer, a bandpass filter, a driving circuit and a receiving circuit; the primary coil of the isolation transformer forms three connection ends through an intermediate tap; the bandpass filter includes the primary coil; the three connection ends are respectively connected to the phase lines of a three-phase three-wire power grid system through the bandpass filter; the secondary coil of the isolation transformer is connected to the driving circuit and the receiving circuit of the carrier signal. The present application realizes carrier communication between any two phases and three phases in a three-phase three-wire power grid system.

Description

Technical Field

[0001] The present application relates to the field of carrier communication technology, and in particular to a three-phase coupling circuit for carrier communication in a power grid system. Background Art

[0002] Power carrier communication is a type of power system communication that uses transmission lines as the transmission medium for carrier signals. Since transmission lines have good conductors and a solid supporting structure, they can be used to transmit carrier signals while transmitting industrial frequency current, which is both economical and very reliable. With the intelligent development of power systems, carrier communication has gradually become the main communication technology in smart grids.

[0003] In the application of carrier communication technology in smart grids, the use of single-phase carrier coupling circuits and three-phase carrier coupling circuits is often involved, among which the three-phase carrier coupling circuit is used for centralized acquisition equipment to realize communication with each single-phase carrier device. At present, most of the research on carrier communication technology is based on the research of single-phase or three-phase four-wire power grid systems. In the three-phase three-wire power grid system, the existing carrier communication scheme cannot realize carrier communication in any two phases.

[0004] Application Contents

[0005] In order to solve the above technical problems, the present application provides a three-phase coupling circuit for carrier communication in a power grid system.

[0006] In view of the above technical problems, the present application proposes a three-phase coupling circuit for carrier communication of a power grid system, comprising: an isolation transformer, a bandpass filter, a driving circuit and a receiving circuit;

[0007] The primary coil of the isolation transformer forms three connection ends through an intermediate tap; the bandpass filter includes the primary coil; the three connection ends are respectively connected to the phase lines of the three-phase three-wire power grid system through the bandpass filter; the secondary coil of the isolation transformer is connected to the driving circuit and the receiving circuit of the carrier signal.

[0008] Furthermore, the bandpass filter also includes a first filter circuit and a second filter circuit; the first filter circuit and the second filter circuit are respectively connected between one of the connection ends and the corresponding phase line.

[0009] Furthermore, the first filtering circuit includes a first capacitor and a first inductor connected in series; the second filtering circuit includes a second capacitor and a second inductor connected in series.

[0010] Furthermore, the three connection ends include a first connection end and a third connection end located at both ends of the primary coil, and a second connection end corresponding to the tap; the three-phase three-wire power grid system includes a first phase line, a second phase line, and a third phase line; the first end of the first inductor is connected to the first connection end, the second end of the first inductor is connected to the first end of the first capacitor, and the second end of the first capacitor is connected to the first phase line; the second connection end is connected to the second phase line; the first end of the second inductor is connected to the third connection end, the second end of the second inductor is connected to the first end of the second capacitor, and the second end of the second capacitor is connected to the third phase line.

[0011] Furthermore, the three-phase coupling circuit also includes a primary protection circuit, including a first transient absorption diode, a second transient absorption diode and a third transient absorption diode; the first end of the first transient absorption diode is connected to the first end of the first capacitor, and the second end of the first transient absorption diode is connected to the second phase line; the first end of the second transient absorption diode is connected to the second phase line, and the second end of the second transient absorption diode is connected to the first end of the second capacitor; the first end of the third transient absorption diode is connected to the first end of the first capacitor, and the second end of the third transient absorption diode is connected to the first end of the second capacitor.

[0012] Furthermore, the three-phase coupling circuit also includes a secondary protection circuit, including a first transient voltage suppression diode, a second transient voltage suppression diode and a third transient voltage suppression diode; the first end of the first transient voltage suppression diode is connected to the first connection end, and the second end of the first transient voltage suppression diode is connected to the second connection end; the first end of the second transient voltage suppression diode is connected to the second connection end, and the second end of the second transient voltage suppression diode is connected to the third connection end; the first end of the third transient voltage suppression diode is connected to the first connection end, and the second end of the third transient voltage suppression diode is connected to the third connection end.

[0013] Furthermore, the first phase line is a phase A line of a three-phase three-wire power grid system, the second phase line is a phase B line of a three-phase three-wire power grid system, and the third phase line is a phase C line of a three-phase three-wire power grid system.

[0014] Furthermore, the tap is located in the middle of the primary coil of the isolation transformer.

[0015] Furthermore, the three-phase coupling circuit also includes a carrier chip connected to the driving circuit and the receiving circuit.

[0016] Furthermore, the three-phase coupling circuit also includes a third capacitor, a fourth capacitor, a fourth connection terminal and a fifth connection terminal located at both ends of the secondary coil; the first end of the third capacitor is connected to the fourth connection terminal, and the second end of the third capacitor is connected to the positive electrode of the drive circuit; the first end of the fourth capacitor is connected to the fifth connection terminal, and the second end of the fourth capacitor is connected to the negative electrode of the drive circuit.

[0017] The above-mentioned three-phase coupling circuit for carrier communication of the power grid system includes: an isolation transformer, a bandpass filter, a driving circuit and a receiving circuit; the primary coil of the isolation transformer forms three connection ends through the middle tap; the bandpass filter includes the primary coil; the three connection ends are respectively connected to the phase lines of the three-phase three-wire power grid system through the bandpass filter; and the secondary coil of the isolation transformer is connected to the driving circuit and the receiving circuit of the carrier signal. Furthermore, the three connection ends formed by the middle tap of the primary coil of the isolation transformer are respectively connected to the phase lines of the three-phase three-wire power grid system, so as to realize the path for signal transmission between the phase lines; and the bandpass filter includes the primary coil of the isolation transformer, so that bandpass filtering is formed between the phase lines and the three-phase paths, blocking the power frequency voltage of the power grid, so that the carrier signals of the phase paths and the three-phase paths in the power grid system can be effectively coupled to the receiving circuit, and at the same time, the carrier signal can be effectively coupled to the carrier devices of the phase paths and the three-phase paths in the power grid system, realizing the two-way coupling of the three-phase data in the three-phase three-wire power grid system. The problem of signal mutual cancellation in the traditional three-phase coupling circuit in the three-phase three-wire power grid system is solved. Furthermore, in the three-phase three-wire power grid system, the three-phase coupling circuit can be used to communicate with three-phase and three-phase carrier devices.

[0018] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0020] Figure 1 is a circuit diagram of a three-phase coupling circuit for carrier communication of a power grid system according to an embodiment;

[0021] Figure 2 is an application connection diagram of the three-phase coupling circuit of this embodiment; DETAILED DESCRIPTION

[0022] Typical implementations that embody the features and advantages of the present application will be described in detail in the following description. It should be understood that the present application can have various changes in different implementations without departing from the scope of the present application, and the descriptions and illustrations therein are essentially used for illustrative purposes rather than for limiting the present application.

[0023] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, "plurality" means two or more, unless otherwise clearly and specifically defined.

[0024] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be directly connected or indirectly connected through an intermediate medium. It can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this embodiment can be understood according to the specific circumstances.

[0025] In addition, the accompanying drawings are only schematic illustrations of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings represent the same or similar parts, and thus their repeated description will be omitted.

[0026] See also Figure 1 As shown, the three-phase coupling circuit for carrier communication of a power grid system provided in this embodiment includes: an isolation transformer S1, a bandpass filter S2, a driving circuit S3 and a receiving circuit S4;

[0027] The primary coil S11 of the isolation transformer S1 forms three connection terminals (such as Figure 1 The bandpass filter S2 includes the primary coil S11; the three connecting terminals are connected to the phase lines of the three-phase three-wire power grid system (such as Figure 1 The phase lines A, B and C shown are connected; the secondary coil S13 of the isolation transformer S1 is connected to the driving circuit S3 and the receiving circuit S4 of the carrier signal.

[0028] Furthermore, the three connection ends formed by the intermediate tap S12 of the primary coil S11 of the isolation transformer S1 are respectively connected to the phase lines of the three-phase three-wire power grid system to achieve the connection between the phase lines (such as Figure 1 between the phases AB, BC and AC) and between the three phases (as shown Figure 1 The bandpass filter S2 includes a primary coil S11 of an isolation transformer S1. When the carrier signal is transmitted, the primary coil S11 is passed through the phase-to-phase path, so that bandpass filtering is formed between the phase lines and the paths between the three phases, thereby blocking the power frequency voltage of the power grid and making the power grid system phase-to-phase (such as Figure 1 Phase AB, BC and AC) and three phases (such as Figure 1 The carrier signal between the three phases ABC shown in the figure can be effectively coupled to the receiving circuit S4, and the carrier signal can also be effectively coupled to the carrier devices of each phase in the power grid system (such as Figure 2 Single-phase coupling equipment with phases AB, BC and AC as shown) and three-phase carrier equipment (such as Figure 2 The three-phase coupling device of the three-phase ABC shown in the figure realizes the bidirectional coupling of the three-phase data in the three-phase three-wire power grid system. At the same time, the primary coil S11 can sense the signals with opposite polarities between the phases through the middle tap S12 to avoid signal cancellation. For example, refer to Figure 1 In the implementation of this example, when the connection terminal 4 of the secondary coil is a positive signal and the connection terminal 5 is a negative signal, in the three-phase coupling circuit path corresponding to phase AB, the connection terminal 1 corresponding to A induces a positive signal, and the connection terminal 2 corresponding to B induces a negative signal, so as to realize the signal transmission between phases AB; at the same time, in the phase AC path, the connection terminal 1 corresponding to A induces a positive signal, and the connection terminal 3 corresponding to C induces a negative signal, so as to realize the signal transmission between phases AC; at the same time, in the phase BC path, the connection terminal 2 corresponding to B induces a positive signal, and the connection terminal 3 corresponding to C induces a negative signal, so as to realize the signal transmission between phases BC; thus, the signal transmission can be carried out normally in phases AB, BC and AC, which solves the problem of signal mutual cancellation in the traditional three-phase coupling circuit in the three-phase three-wire power grid system. Furthermore, in the three-phase three-wire power grid system, the three-phase coupling circuit can be used to realize two-way communication with the three-way phase-to-phase and three-phase carrier devices.

[0029] In particular, by locating the tap S12 in the middle of the primary coil S11 of the isolation transformer S1, the number of turns of the primary coils N1 and N2 on both sides of the tap S1 can be made equal, and further, by adjusting the number of turns of the secondary coil N3, a balanced distribution of the carrier communication signal quality between any two phases can be achieved.

[0030] Further, the bandpass filter S2 also includes a first filter circuit S21 and a second filter circuit S22; the first filter circuit S21 and the second filter circuit S22 are respectively connected between a connection terminal and the corresponding phase line. In any two of the three phases in the three-phase three-phase power grid system, a filter circuit is set between the phase line and the corresponding connection terminal, and then, filtering can be performed when the signal is transmitted in each phase path. In the implementation of this example, the first filter circuit S21 is connected between the first connection terminal 1 and the corresponding phase line A; the second filter circuit S22 is connected between the third connection terminal 3 and the corresponding phase line C. It can be understood that in other implementations, the first filter circuit S21 can also be connected between the second connection terminal 2 and the corresponding phase line B; the second filter circuit S22 is connected between the third connection terminal 3 and the corresponding phase line C. It is only necessary to set a filter circuit between any two phases and the corresponding connection terminal to realize the bandpass filtering between each phase based on the primary coil S11. It can be understood that in other embodiments, the bandpass filter S2 can also include a filter circuit that can be set between each phase line and the corresponding connection terminal in the three phases.

[0031] In the implementation of this example, the first filter circuit S21 includes a first capacitor C1 and a first inductor L1 connected in series; the second filter circuit S22 includes a second capacitor C2 and a second inductor L2 connected in series.

[0032] Furthermore, the three connection terminals of the primary of the isolation transformer include a first connection terminal 1 and a third connection terminal 3 located at both ends of the primary coil S11, and a second connection terminal 2 corresponding to the tap S12; the first filter circuit S21 is connected between the first connection terminal 1 and the corresponding phase line (such as the attached Figure 1 The second filter circuit S22 is connected between the third connection terminal 3 and the corresponding phase line (as shown in the attached Figure 1 The second connection terminal 2 is connected to the corresponding phase line (as shown in the attached Figure 1 The B phase line shown in FIG. 1 is directly connected to the

[0033] The first inductor L1 is connected to the first connection terminal 1 , and the first capacitor C1 is connected to the phase line corresponding to the first connection terminal 1 ; the second inductor L2 is connected to the third connection terminal 3 , and the second capacitor C2 is connected to the phase line corresponding to the third connection terminal 3 .

[0034] Furthermore, the three-phase three-wire power grid system includes a first phase line, a second phase line, and a third phase line; the first end of the first inductor L1 is connected to the first connection terminal 1, the second end of the first inductor L1 is connected to the first end of the first capacitor C1, and the second end of the first capacitor C1 is connected to the first phase line; the second connection terminal 2 is connected to the second phase line; the first end of the second inductor L2 is connected to the third connection terminal 3, the second end of the second inductor L2 is connected to the first end of the second capacitor C2, and the second end of the second capacitor C2 is connected to the third phase line. In the implementation of this example, the first phase line, the second phase line, and the third phase line are respectively the A phase line, the B phase line, and the C phase line of the three-wire three-wire power grid system.

[0035] The bandpass filter S2 of the three-phase coupling circuit is formed by the first filter circuit S21 and the second filter circuit S22, as well as the primary coil S11 of the isolation transformer S1 and the transformer core T1. Bandpass filtering can be achieved when the signal is transmitted between each phase. For example, between phase AC, a bandpass filter composed of the first filter circuit S21, the second filter circuit S22, the primary coil S11 and the transformer core T1 is formed; between phase AB, another bandpass filter composed of the first filter circuit S21, the primary coil N1 between the first connection terminal 1 and the second connection terminal 2 is formed; between phase BC, another bandpass filter composed of the second filter circuit S22, the primary coil N2 between the third connection terminal 3 and the second connection terminal 2 is formed. Bandpass filtering is formed between AB, BC, and AC, blocking the power frequency voltage of the power grid, so that the carrier signal in the power grid system can be effectively coupled to the receiving circuit, and the carrier signal can also be effectively coupled to the power grid system.

[0036] Furthermore, the three-phase coupling circuit further includes a primary protection circuit S5, including a plurality of first diodes (such as Figure 1 The first diodes D1, D2 and D3 shown in the figure); multiple first diodes are connected in parallel between each phase line, and in a circuit with a capacitor and an inductor connected in series, the connection point between the first diode and the phase line is located between the capacitor and the inductor.

[0037] Specifically, in the implementation of this example, the primary protection circuit S5 includes a first transient absorption diode D1, a second transient absorption diode D2 and a third transient absorption diode D3; the first end of the first transient absorption diode D1 is connected to the first end of the first capacitor C1, and the second end of the first transient absorption diode D1 is connected to the second phase line (the B phase line in this example); the first end of the second transient absorption diode D2 is connected to the second phase line (the B phase line in this example), and the second end of the second transient absorption diode D2 is connected to the first end of the second capacitor C2; the first end of the third transient absorption diode D3 is connected to the first end of the first capacitor C1, and the second end of the third transient absorption diode D3 is connected to the first end of the second capacitor C2.

[0038] In this way, the first-level protection circuit can be set at the primary of the isolation transformer to absorb the noise of each phase separately. The influence of a certain noise on the communication of other phases can be avoided; the absorption distributed between phases can achieve stronger grid noise absorption. In particular, the first-level protection circuit uses a transient absorption diode, which has a fast response speed and high power, and can effectively absorb the instantaneous strong interference noise in the power grid system.

[0039] Furthermore, a secondary protection circuit S6 is included, including a plurality of second diodes (such as Figure 1 The first diodes D4, D5 and D6 shown in the figure); multiple second diodes are connected in parallel between each phase line, and the connection point between the first diode and each phase line is located at the primary of the transformer and is directly connected to each connection terminal.

[0040] Specifically, in the implementation of this example, the secondary protection circuit S6 includes a first transient voltage suppression diode D4, a second transient voltage suppression diode D5 and a third transient voltage suppression diode D6; the first end of the first transient voltage suppression diode D4 is connected to the first connection terminal 1, and the second end of the first transient voltage suppression diode D4 is connected to the second connection terminal 2; the first end of the second transient voltage suppression diode D5 is connected to the second connection terminal 2, and the second end of the second transient voltage suppression diode D5 is connected to the third connection terminal 3; the first end of the third transient voltage suppression diode D6 is connected to the first connection terminal 1, and the second end of the third transient voltage suppression diode D6 is connected to the third connection terminal 3.

[0041] In this way, the second-level protection circuit can be set at the primary of the isolation transformer, and the noise of each phase can be absorbed separately. The influence of a certain noise on the communication of other phases is avoided; the absorption distributed between phases can achieve stronger grid noise absorption. In particular, the second diode uses a transient voltage suppression diode, and its action voltage needs to exceed the amplitude of the maximum signal emission of the carrier, which can absorb continuous noise interference, so that the carrier signal coupled to the secondary can be within the normal working range of the carrier chip, ensuring that the secondary circuit will not be damaged due to excessive voltage.

[0042] Furthermore, in the implementation of this example, capacitors C1 and C2 are connected to the corresponding phase lines A and C, and a primary protection circuit S5 and a secondary protection circuit S6 are simultaneously provided to form a protection circuit of the three-phase coupling circuit, which includes components D1, D2, D3, D4, D5, and D6, wherein transient absorption diodes D1, D2, and D3 are connected in parallel between each phase after passing through capacitors C1 and C2, forming a first-level protection, wherein transient voltage suppression diodes D4, D5, and D6 are connected in parallel between each phase at the primary of the isolation transformer, forming a second-level protection. The two-level protection circuit first absorbs the instantaneous strong interference noise in the power grid system when the carrier signal is coupled and transmitted, and then absorbs the continuous noise interference, which can realize the absorption of continuous power grid noise and effectively ensure the normal operation of the circuit.

[0043] Furthermore, the three-phase coupling circuit also includes a carrier chip S7, which is connected to the drive circuit S3 and the receiving circuit S4. The primary coil S11 of the isolation transformer S1 has a central tap S12, forming the N1 and N2 primary coils on both sides of the tap S12, which can centrally couple the carrier signals between the AB, BC, and AC phases of the three-phase three-wire power grid system to the secondary N3 coil, and enter the carrier chip S7 through the receiving circuit S4; the carrier signal emitted by the carrier chip S7 through the drive circuit S3 can also be coupled to each phase AB, BC, AC power grid system by the isolation transformer at the same time.

[0044] Further, the three-phase coupling circuit also includes a third capacitor C3, a fourth capacitor C4, a fourth connection terminal 4 and a fifth connection terminal 5 located at both ends of the secondary coil S13; the fourth connection terminal 4 is connected to the positive electrode PA+ of the drive circuit S13 through the third capacitor C3, and the fifth connection terminal 5 is connected to the negative electrode PA- of the drive circuit through the fourth capacitor C4. In this way, the third capacitor C3 and the fourth capacitor C4 can pass high frequency and block the effect of low frequency, wherein the low frequency is the grid frequency and the high frequency is the carrier signal, so as to ensure the normal operation of the drive circuit S3. Specifically, in the implementation of this example, the first end of the third capacitor C3 is connected to the fourth connection terminal 4, and the second end of the third capacitor C3 is connected to the positive electrode PA+ of the drive circuit S13; the first end of the fourth capacitor C4 is connected to the fifth connection terminal 5, and the second end of the fourth capacitor C4 is connected to the negative electrode PA- of the drive circuit S13.

[0045] refer to Figure 2 , which is a connection diagram of an application of a three-phase coupling circuit according to an embodiment of the present application in a three-phase three-wire power grid system.

[0046] By connecting the three ports of the three-phase coupling circuit (centralized acquisition device) using the embodiment of the present application to each phase line (A, B, C) in the three-phase three-wire power grid system, carrier communication can be carried out with the single-phase coupling device distributed between the AB, BC, and AC phases on the right and the three-phase coupling device of the three-phase ABC.

[0047] In summary, relative to the prior art, some embodiments of the present application can respectively connect the phase lines of the three-phase three-wire power grid system through the three connection ends formed by the middle tap of the primary coil of the isolation transformer, so as to realize the path for signal transmission between the phase lines; and the bandpass filter includes the primary coil of the isolation transformer, so that the bandpass filter is formed between the phase lines and the three-phase paths, blocking the power frequency voltage of the power grid, so that the carrier signals of the phase paths and the three-phase paths in the power grid system can be effectively coupled to the receiving circuit, and at the same time, the carrier signal can be effectively coupled to the carrier devices of the phase paths and the three-phase paths in the power grid system, realizing the bidirectional coupling of the three-phase data in the three-phase three-wire power grid system. The problem of signal mutual cancellation in the traditional three-phase coupling circuit in the three-phase three-wire power grid system is solved. Furthermore, in the three-phase three-wire power grid system, the three-phase coupling circuit can be used to realize communication with the three-phase phases and the three-phase carrier devices. In some embodiments, the balanced distribution of the quality of the carrier communication signal between any two phases can be achieved.

[0048] Although the present application has been described with reference to the above typical embodiments, it should be understood that the terms used are illustrative and exemplary, rather than restrictive terms. Since the present application can be implemented in a variety of forms without departing from the spirit or essence of the application, it should be understood that the above embodiments are not limited to any of the aforementioned details, but should be widely interpreted within the spirit and scope defined by the attached claims, so all changes and modifications falling within the claims or their equivalents should be covered by the attached claims.

Claims

1. A three-phase coupling circuit for carrier communication of a power grid system, characterized in that: include: Isolation transformer, bandpass filter, drive circuit and receiving circuit; The primary coil of the isolation transformer forms three connection ends through a middle tap; The bandpass filter includes the primary coil; the three connection ends are respectively connected to the phase lines of the three-phase three-wire power grid system through the bandpass filter; the secondary coil of the isolation transformer is connected to the driving circuit and the receiving circuit of the carrier signal; The bandpass filter further comprises a first filter circuit and a second filter circuit; the first filter circuit and the second filter circuit are respectively connected between one of the connection terminals and the corresponding phase line; The first filter circuit includes a first capacitor and a first inductor connected in series; the second filter circuit includes a second capacitor and a second inductor connected in series; The three-phase coupling circuit further includes a primary protection circuit, which includes a plurality of first diodes; the plurality of first diodes are respectively connected in parallel between each phase line, and in a circuit in which a capacitor and an inductor connected in series are arranged, a connection point between the first diode and the phase line is located between the capacitor and the inductor; The three-phase coupling circuit also includes a secondary protection circuit, which includes multiple second diodes; the multiple second diodes are respectively connected in parallel between each phase line, and the connection point between the second diode and each phase line is located at the primary of the isolation transformer and is directly connected to each connection end.

2. The three-phase coupling circuit for carrier communication of a power grid system according to claim 1, characterized in that: The three connection ends include a first connection end and a third connection end located at both ends of the primary coil, and a second connection end corresponding to the tap; the three-phase three-wire power grid system includes a first phase line, a second phase line, and a third phase line; the first end of the first inductor is connected to the first connection end, the second end of the first inductor is connected to the first end of the first capacitor, and the second end of the first capacitor is connected to the first phase line; the second connection end is connected to the second phase line; the first end of the second inductor is connected to the third connection end, the second end of the second inductor is connected to the first end of the second capacitor, and the second end of the second capacitor is connected to the third phase line.

3. The three-phase coupling circuit for carrier communication of a power grid system according to claim 2, characterized in that: The primary protection circuit includes a first transient absorption diode, a second transient absorption diode and a third transient absorption diode; the first end of the first transient absorption diode is connected to the first end of the first capacitor, and the second end of the first transient absorption diode is connected to the second phase line; the first end of the second transient absorption diode is connected to the second phase line, and the second end of the second transient absorption diode is connected to the first end of the second capacitor; the first end of the third transient absorption diode is connected to the first end of the first capacitor, and the second end of the third transient absorption diode is connected to the first end of the second capacitor.

4. The three-phase coupling circuit for carrier communication of a power grid system according to claim 2, characterized in that: The secondary protection circuit includes a first transient voltage suppression diode, a second transient voltage suppression diode and a third transient voltage suppression diode; the first end of the first transient voltage suppression diode is connected to the first connection end, and the second end of the first transient voltage suppression diode is connected to the second connection end; the first end of the second transient voltage suppression diode is connected to the second connection end, and the second end of the second transient voltage suppression diode is connected to the third connection end; the first end of the third transient voltage suppression diode is connected to the first connection end, and the second end of the third transient voltage suppression diode is connected to the third connection end.

5. The three-phase coupling circuit for carrier communication of a power grid system according to any one of claims 2 to 4, characterized in that: The first phase line is a phase A line of a three-phase three-wire power grid system, the second phase line is a phase B line of a three-phase three-wire power grid system, and the third phase line is a phase C line of a three-phase three-wire power grid system.

6. The three-phase coupling circuit for carrier communication of a power grid system according to claim 1 or 2, characterized in that: The tap is located in the middle of the primary coil of the isolation transformer.

7. The three-phase coupling circuit for carrier communication of a power grid system according to claim 1, characterized in that: The three-phase coupling circuit also includes a carrier chip connected to the driving circuit and the receiving circuit.

8. The three-phase coupling circuit for carrier communication of a power grid system according to claim 1, characterized in that: The three-phase coupling circuit also includes a third capacitor, a fourth capacitor, a fourth connection terminal and a fifth connection terminal located at both ends of the secondary coil; the first end of the third capacitor is connected to the fourth connection terminal, and the second end of the third capacitor is connected to the positive electrode of the drive circuit; the first end of the fourth capacitor is connected to the fifth connection terminal, and the second end of the fourth capacitor is connected to the negative electrode of the drive circuit.

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