Automatic switching circuit applied to three-phase three-wire and three-phase four-wire adaptive electric energy meters

Abstract

The invention discloses an automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive electric energy meter. The automatic switching circuit comprises an MCU, a phase detection circuit, a short circuit switch, a rectification step-down circuit and a step-down source, the phase detection circuit comprises a diode, a resistor, a capacitor and a photoelectric coupler, the phase detection circuit uses the diode, the resistor, the capacitor and the photoelectric coupler to detect the voltage difference between a phase B and a zero line (N line), and the hardware circuit and the MCU cooperate to realize the identification and switching of a wiring mode, namely, the wiring mode is automatically switched to a three-phase three-wire or three-phase four-wire mode. The electric energy meter can adapt to three-phase three-phase and three-phase four-line voltage specifications without replacing the electric energy meter, the universality is improved, and the operation and maintenance cost is reduced. The problem that hardware and software programs of a three-phase three-wire electric energy meter and a three-phase four-wire electric energy meter cannot be compatible is solved. Through the automatic switching circuit provided by the invention, the electric energy meter can automatically switch a three-phase three-wire or three-phase four-wire operation mode through self detection and judgment.

Description

Technical Field

[0001] The present invention relates to the technical field of electricity meter applications, and particularly to an automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive electricity meter. Background Art

[0002] In the power system, three-phase electricity meters are the core devices for electricity metering, and their wiring methods are mainly divided into three-phase three-wire system (3P3W) and three-phase four-wire system (3P4W). The three-phase three-wire system is mostly used in high-voltage industrial power distribution scenarios, and only transmits electric energy through three phase lines; while the three-phase four-wire system is widely used in low-voltage distribution networks (such as commercial or civil scenarios), including three phase lines and one neutral line to meet the current loop requirements of unbalanced loads. Due to the essential differences in the wiring methods and metering principles of electricity meters in different scenarios, traditional electricity meters usually need to select a specific type (three-wire or four-wire electricity meter) according to the on-site power grid topology structure, and rely on manual configuration of parameters or hardware jumper switching modes, resulting in complex installation and debugging and high operation and maintenance costs. Summary of the Invention

[0003] The purpose of this application is to provide an automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive electricity meter to solve the problem that traditional electricity meters usually need to select a specific type (three-wire or four-wire electricity meter) according to the on-site power grid topology structure, and rely on manual configuration of parameters or hardware jumper switching modes, resulting in complex installation and debugging and high operation and maintenance costs.

[0004] To solve the above technical problems, this application provides an automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive electricity meter, including:

[0005] MCU, phase detection circuit, short-circuit switch, rectification and buck circuit, and buck power supply;

[0006] The phase detection circuit includes a diode, a resistor, a capacitor, and an optocoupler. The negative electrode of the diode is connected to one end of the resistor, the other end of the resistor is connected to the positive electrode of the capacitor and the anode of the light-emitting diode in the optocoupler, the cathode of the light-emitting diode and the negative electrode of the capacitor are commonly connected to the rectification and buck circuit, the collector of the photosensitive triode in the optocoupler is connected to the VCC power supply of the buck power supply, and the emitter of the photosensitive triode is connected to the GND terminal of the buck power supply through a pull-down resistor;

[0007] The switch state detection interface of the MCU and the control interface of the short-circuit switch are commonly connected to the emitter of the photosensitive triode. The short-circuit switch is respectively connected to the positive electrode of the diode and the rectification and buck circuit, and the rectification and buck circuit is connected to the buck power supply.

[0008] As a preferred embodiment, an automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive watt-hour meter, wherein the rectifying and step-down circuit includes a full-wave rectifying circuit or a half-wave rectifying circuit.

[0009] It should be detailed in the solution that an automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive watt-hour meter, wherein the full-wave rectifying circuit includes a first rectifier bridge, a second rectifier bridge and a third rectifier bridge. The positive poles of the output ends of the first rectifier bridge, the second rectifier bridge and the third rectifier bridge are connected to the positive pole of the step-down source, and the negative poles of the output ends of the first rectifier bridge, the second rectifier bridge and the third rectifier bridge are connected to the negative pole of the step-down source. The input end of the first rectifier bridge is respectively connected to the A-phase terminal and the neutral terminal of the three-phase power supply. The input end of the second rectifier bridge is respectively connected to the B-phase terminal and the neutral terminal of the three-phase power supply. The input end of the third rectifier bridge is respectively connected to the C-phase terminal and the neutral terminal of the three-phase power supply;

[0010] Wherein, the neutral terminal is respectively connected to the shorting switch, the cathode of the light-emitting diode and the negative pole of the capacitor, and the B-phase terminal of the three-phase power supply is respectively connected to the shorting switch and the positive pole of the diode.

[0011] It should be detailed in the solution that an automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive watt-hour meter, wherein the half-wave rectifying circuit includes a first rectifying diode, a second rectifying diode and a third rectifying diode. The output ends of the first rectifying diode, the second rectifying diode and the third rectifying diode are all connected to the positive pole of the step-down source, and the negative pole of the step-down source is connected to the neutral terminal. The positive pole of the first rectifying diode is connected to the A-phase terminal, the positive pole of the second rectifying diode is connected to the B-phase terminal, and the positive pole of the third rectifying diode is connected to the C-phase terminal;

[0012] Wherein, the neutral terminal is respectively connected to the shorting switch, the cathode of the light-emitting diode and the negative pole of the capacitor, and the B-phase terminal is respectively connected to the shorting switch and the positive pole of the diode.

[0013] As a preferred embodiment, an automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive watt-hour meter further includes:

[0014] A mutual inductance sampling circuit or a resistance step-down sampling circuit connected to the shorting switch.

[0015] It should be elaborated in detail in the solution that an automatic switching circuit for a three-phase three-wire and three-phase four-wire adaptive watt-hour meter. The mutual inductance sampling circuit includes three voltage transformers connected in parallel with each other. One end of the primary coil of the voltage transformer is respectively connected to the A-phase terminal, B-phase terminal, and C-phase terminal after passing through a current-limiting resistor, and the other end of the primary coil of the voltage transformer is connected to the neutral terminal. Both ends of the secondary coil of the voltage transformer are connected to a sampling resistor and then connected to the sampling chip;

[0016] Among them, the short-circuit switch is located between the B-phase terminal and the neutral terminal.

[0017] It should be elaborated in detail in the solution that an automatic switching circuit for a three-phase three-wire and three-phase four-wire adaptive watt-hour meter. The resistor step-down sampling circuit includes three groups of series-connected sampling resistors. Two of the series-connected sampling resistors form a group. The input ends of the series-connected sampling resistors are respectively connected to the A-phase terminal, B-phase terminal, and C-phase terminal, and the output ends of the series-connected sampling resistors are all connected to the neutral terminal. A sampling wire is led out from one end of the sampling resistor connected to the neutral terminal and connected to the sampling chip;

[0018] Among them, the short-circuit switch is located between the B-phase terminal and the neutral terminal.

[0019] Compared with the prior art, an automatic switching circuit for a three-phase three-wire and three-phase four-wire adaptive watt-hour meter provided by the present invention includes: an MCU, a phase detection circuit, a short-circuit switch, a rectification and step-down circuit, and a step-down power supply; the phase detection circuit includes a diode, a resistor, a capacitor, and an optocoupler. The negative electrode of the diode is connected to one end of the resistor, the other end of the resistor is connected to the positive electrode of the capacitor and the anode of the light-emitting diode in the optocoupler, and the cathode of the light-emitting diode and the negative electrode of the capacitor are jointly connected to the rectification and step-down circuit. The collector of the photosensitive triode in the optocoupler is connected to the VCC power supply of the step-down power supply, and the emitter of the photosensitive triode is grounded through a pull-down resistor; the switch state detection interface of the MCU and the control interface of the short-circuit switch are jointly connected to the emitter of the photosensitive triode. The short-circuit switch is respectively connected to the positive electrode of the diode and the rectification and step-down circuit, and the rectification and step-down circuit is connected to the step-down power supply.

[0020] The phase detection circuit uses a diode, a resistor, a capacitor, and an optocoupler to detect the voltage difference between phase B and the neutral line (N line). When three-phase four-wire power is connected, the output terminal of the optocoupler conducts, the short-circuit switch opens, and the phase B wiring terminal and the neutral line wiring terminal will not be short-circuited. At this time, the output level of the phase detection circuit is high, and the level state detected by the MCU detection port is also high. At the same time, the MCU control system switches the operation mode to the three-phase four-wire mode state. When three-phase three-wire power is connected, the output terminal of the optocoupler disconnects, the short-circuit switch closes, and the phase B wiring terminal and the neutral line wiring terminal are short-circuited together. At this time, the output level of the phase detection circuit is low, and the level state detected by the MCU detection port is also low. At the same time, the MCU control system switches the operation mode to the three-phase three-wire mode state. The recognition and switching of the wiring mode are realized by the cooperation of the hardware circuit and the MCU, that is, it automatically switches to the three-phase three-wire or three-phase four-wire mode. It can adapt to the three-phase three-wire and three-phase four-wire voltage specifications without replacing the electricity meter, improving the versatility and reducing the operation and maintenance costs. Moreover, a rectifier step-down circuit is used to convert alternating current into direct current and reduce the voltage, and the voltage is further reduced to the system working voltage VCC through a step-down source.

[0021] The present invention overcomes the problem that the hardware and software programs of three-phase three-wire and three-phase four-wire electricity meters cannot be compatible. Through the automatic switching circuit of the present invention, the electricity meter can automatically switch the operation mode between three-phase three-wire and three-phase four-wire through its own detection and judgment. Brief Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0023] Figure 1 Schematic diagram of an automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive electricity meter provided by an embodiment of the present application;

[0024] Figure 2 Schematic diagram of another automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive electricity meter provided by an embodiment of the present application;

[0025] Figure 3 Schematic diagram of a mutual inductance sampling circuit provided by an embodiment of the present application;

[0026] Figure 4 Schematic diagram of a resistance step-down sampling circuit provided by an embodiment of the present application;

[0027] In the figure: 1. MCU; 2. Short - circuit switch; 3. Step - down power source; 4. Diode; 5. Resistor; 6. Capacitor; 70. Light - emitting diode; 71. Photo - sensitive triode; 72. Pull - down resistor; 8. First rectifier bridge; 9. Second rectifier bridge; 10. Third rectifier bridge; 11. First rectifier diode; 12. Second rectifier diode; 13. Third rectifier diode; 14. Voltage transformer; 15. Current - limiting resistor; 16. Sampling resistor; 17. Sampling chip; 18. Sampling resistor string. Specific embodiments

[0028] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0029] The core of this application is to provide an automatic switching circuit applied to a three - phase three - wire and three - phase four - wire adaptive energy meter, which solves the problem that traditional energy meters usually need to select a specific type (three - wire or four - wire energy meter) according to the on - site power grid topology structure and rely on manual configuration of parameters or hardware jumper to switch modes, resulting in complex installation and debugging and high operation and maintenance costs.

[0030] Figure 1 The following is a schematic diagram of an automatic switching circuit applied to a three - phase three - wire and three - phase four - wire adaptive energy meter provided by an embodiment of this application. Figure 2 The following is another schematic diagram of an automatic switching circuit applied to a three - phase three - wire and three - phase four - wire adaptive energy meter provided by an embodiment of this application. Figure 3 The following is a schematic diagram of a mutual - inductance sampling circuit provided by an embodiment of this application. Figure 4 The following is a schematic diagram of a resistor step - down sampling circuit provided by an embodiment of this application. See Figures 1 to 4 as shown. Figure 1 The rectifier step - down circuit shown is a full - wave rectifier circuit. Figure 2 The rectifier step - down circuit shown is a half - wave rectifier circuit.

[0031] Embodiment 1

[0032] An automatic switching circuit applied to a three - phase three - wire and three - phase four - wire adaptive energy meter includes an MCU 1, a phase - detection circuit, a short - circuit switch 2, a rectifier step - down circuit, and a step - down power source 3. The purpose of the phase - detection circuit is to detect whether there is a voltage difference between the B - phase connection and the N - line (neutral line). If there is a relatively high voltage difference, the voltage access mode is three - phase four - wire; otherwise, it is three - phase three - wire. The step - down power source 3 can reduce the rectified voltage to the system operating voltage VCC. In the accompanying drawings, UA represents the A - phase connection, UB represents the B - phase connection, and UC represents the C - phase connection.

[0033] The phase detection circuit includes a diode 4, a resistor 5, a capacitor 6, and an optocoupler. The start of the line is connected to the positive electrode of the diode 4 through the B-phase wiring. The negative electrode of the diode 4 is connected to one end of the resistor 5. The other end of the resistor 5 is connected to the positive electrode of the capacitor 6 and the anode (forward input terminal) of the light-emitting diode 70 in the optocoupler. The cathode (reverse input terminal) of the light-emitting diode 70 and the negative electrode of the capacitor 6 are jointly connected to the rectifier and buck circuit through the N line. The collector of the photosensitive triode 71 in the optocoupler is connected to the VCC power supply of the buck source 3, and the emitter of the photosensitive triode 71 is connected to the GND terminal of the buck source 3 through a pull-down resistor 72.

[0034] The switch state detection interface of the MCU 1 and the control interface of the short-circuit switch 2 are jointly connected to the emitter of the photosensitive triode 71. The short-circuit switch 2 is respectively connected to the positive electrode of the diode 4 and the rectifier and buck circuit. The rectifier and buck circuit is connected to the buck source 3.

[0035] As Figure 1 shown and Figure 2 illustrated, the short-circuit switch 2 is controlled by the detection result of the phase detection circuit. The short-circuit switch 2 is a single-pole double-throw electronic switch. The N line is connected to the common terminal of the switch 2. One fixed terminal of the switch 2 is connected to the B-phase wiring terminal, and the other fixed terminal is left floating. When the input voltage is three-phase four-wire, the short-circuit switch 2 connects the common terminal and the floating terminal. When the input voltage is three-phase three-wire, the short-circuit switch 2 connects the common terminal and the B-phase wiring terminal.

[0036] The device for judging the wiring mode of the electric energy meter includes an optocoupler. When three-phase four-wire electricity is connected, the output terminal of the optocoupler conducts, and the short-circuit switch 2 will open and will not short-circuit the B-phase wiring terminal and the zero-line wiring terminal. After the B-phase voltage passes through the diode 4, the resistor 5, and the capacitor 6, the anode (forward input terminal) of the light-emitting diode 70 in the optocoupler will be 2V higher than the cathode (reverse input terminal) of the light-emitting diode 70, causing the light-emitting diode 70 to conduct. When three-phase three-wire electricity is connected, the output terminal of the optocoupler disconnects, the short-circuit switch 2 will close, and the B-phase wiring terminal and the zero-line wiring terminal will be short-circuited together. There will be no large voltage difference between the B phase and the N line, and thus there will be no large voltage difference between the anode and the cathode of the light-emitting diode 70, so that the light-emitting diode 70 will not conduct.

[0037] After the MCU 1 is powered on, it delays detecting the switch state of the short - circuit switch 2. When the wiring mode is three - phase four - wire, the output level of the phase - detection circuit is high, and the level state detected by the detection port of the MCU 1 is also high. At the same time, the MCU 1 switches the system operation mode to the three - phase four - wire mode state. When the wiring mode is three - phase three - wire, the output level of the phase - detection circuit is low, and the level state detected by the detection port of the MCU 1 is also low. At the same time, the MCU 1 switches the system operation mode to the three - phase three - wire mode state. Setting this circuit inside the watt - hour meter can judge and automatically switch the wiring mode, and then judge the output state of the phase - detection circuit through the MCU, enabling the watt - hour meter to operate normally whether it is connected to three - phase three - wire or three - phase four - wire.

[0038] Embodiment 2

[0039] Based on Embodiment 1, an automatic switching circuit applied to a three - phase three - wire and three - phase four - wire adaptive watt - hour meter. The rectifier and step - down circuit includes a full - wave rectifier circuit or a half - wave rectifier circuit. The rectifier and step - down circuit adopts full - wave or half - wave rectification methods, which can adapt to different wiring scenarios.

[0040] Based on Embodiment 2, an automatic switching circuit applied to a three - phase three - wire and three - phase four - wire adaptive watt - hour meter. The full - wave rectifier circuit includes a first rectifier bridge 8, a second rectifier bridge 9, and a third rectifier bridge 10. The positive poles of the output ends of the first rectifier bridge 8, the second rectifier bridge 9, and the third rectifier bridge 10 are connected to the positive pole of the step - down source 3, and the negative poles of the output ends of the first rectifier bridge 8, the second rectifier bridge 9, and the third rectifier bridge 10 are connected to the negative pole of the step - down source 3. The input end of the first rectifier bridge 8 is respectively connected to the A - phase terminal and the neutral - line terminal of the three - phase power supply. The input end of the second rectifier bridge 9 is respectively connected to the B - phase terminal and the neutral - line terminal of the three - phase power supply. The input end of the third rectifier bridge 10 is respectively connected to the C - phase terminal and the neutral - line terminal of the three - phase power supply;

[0041] Among them, the neutral - line terminal is respectively connected to the short - circuit switch 2, the cathode of the light - emitting diode 70, and the negative pole of the capacitor 6. The B - phase terminal of the three - phase power supply is respectively connected to the short - circuit switch 2 and the positive pole of the diode 4.

[0042] Based on Embodiment 2, an automatic switching circuit applied to a three - phase three - wire and three - phase four - wire adaptive watt - hour meter. The half - wave rectifier circuit includes a first rectifier diode 11, a second rectifier diode 12, and a third rectifier diode 13. The output ends of the first rectifier diode 11, the second rectifier diode 12, and the third rectifier diode 13 are all connected to the positive pole of the step - down source 3. The negative pole of the step - down source 3 is connected to the neutral - line terminal. The positive pole of the first rectifier diode 11 is connected to the A - phase terminal, the positive pole of the second rectifier diode 12 is connected to the B - phase terminal, and the positive pole of the third rectifier diode 13 is connected to the C - phase terminal;

[0043] Among them, the neutral wire terminal is respectively connected to the short - circuit switch 2, the cathode of the light - emitting diode 70 and the negative electrode of the capacitor 6, and the B - phase wiring terminal is respectively connected to the short - circuit switch 2 and the positive electrode of the diode 4.

[0044] Embodiment 3

[0045] Based on Embodiment 1, an automatic switching circuit applied to a three - phase three - wire and three - phase four - wire adaptive watt - hour meter further includes:

[0046] A mutual - inductance sampling circuit or a resistance - step - down sampling circuit connected to the short - circuit switch 2.

[0047] When the wiring mode is three - phase three - wire, the reference plane of the sampling circuit is the N - wire at this time. When the MCU 1 switches the system operation mode to the three - phase three - wire mode state, the reference plane of the sampling circuit is the B - phase at this time. The on - off of the short - circuit switch 2 determines whether the neutral potential of the sampling circuit is the B - phase, thereby affecting the voltage sampling of the watt - hour meter.

[0048] Based on Embodiment 3, an automatic switching circuit applied to a three - phase three - wire and three - phase four - wire adaptive watt - hour meter, the mutual - inductance sampling circuit includes three voltage transformers 14 connected in parallel with each other. One end of the primary coil of the voltage transformer 14 is respectively connected to the A - phase wiring terminal, the B - phase wiring terminal, and the C - phase wiring terminal after passing through the current - limiting resistor 15, and the other end of the primary coil of the voltage transformer 14 is connected to the neutral wire terminal. The two ends of the secondary coil of the voltage transformer 14 are connected to the sampling resistor 16 and then connected to the sampling chip 17;

[0049] Among them, the short - circuit switch 2 is located between the B - phase wiring terminal and the neutral wire terminal.

[0050] Based on Embodiment 3, an automatic switching circuit applied to a three - phase three - wire and three - phase four - wire adaptive watt - hour meter, the resistance - step - down sampling circuit includes three groups of sampling resistor strings 18. Two sampling resistor strings 18 are in a group. The input ends of the sampling resistor strings 18 are respectively connected to the A - phase wiring terminal, the B - phase wiring terminal, and the C - phase wiring terminal, and the output ends of the sampling resistor strings 18 are all connected to the neutral wire terminal. One end of the sampling resistor 16 connected to the neutral wire terminal leads out a sampling line and is connected to the sampling chip 17; at this time, after the sampling voltage passes through the sampling resistor string 18 and is divided by the last resistor at the end of the N - wire connection, the peak value of the input voltage will be converted into the highest value that does not exceed the ADC sampling range requirements of the sampling chip 17 or the MCU 1. Among them, the short - circuit switch 2 is located between the B - phase wiring terminal and the neutral wire terminal.

[0051] An automatic switching circuit applied to a three-phase three-wire and three-phase four-wire adaptive watt-hour meter provided by the present invention. The phase detection circuit uses diode 4, resistor 5, capacitor 6 and an optocoupler to detect the voltage difference between phase B and the neutral line N. When three-phase four-wire power is connected, the output terminal of the optocoupler conducts, the short-circuit switch 2 opens, and the phase B wiring terminal and the neutral line wiring terminal will not be short-circuited. At this time, the output level of the phase detection circuit is high, and the level state detected by the detection port of MCU 1 is also high. At the same time, the control system of MCU 1 switches the operation mode to the three-phase four-wire mode state. When three-phase three-wire power is connected, the output terminal of the optocoupler disconnects, the short-circuit switch 2 closes, and the phase B wiring terminal and the neutral line wiring terminal are short-circuited together. At this time, the output level of the phase detection circuit is low, and the level state detected by the detection port of MCU 1 is also low. At the same time, the control system of MCU 1 switches the operation mode to the three-phase three-wire mode state. The recognition and switching of the wiring mode are realized in cooperation with the hardware circuit and MCU 1, that is, automatically switch to the three-phase three-wire or three-phase four-wire mode. It is not necessary to replace the watt-hour meter to adapt to the three-phase three-wire and three-phase four-wire voltage specifications, improving the versatility and reducing the operation and maintenance costs. Moreover, a rectifying and step-down circuit is used to convert alternating current into direct current and reduce the voltage, and the voltage is further reduced to the system operating voltage VCC through the step-down source 3.

[0052] The present invention overcomes the problem that the hardware and software programs of three-phase three-wire and three-phase four-wire watt-hour meters cannot be compatible. Through the automatic switching circuit of the present invention, the watt-hour meter can automatically switch the operation mode between three-phase three-wire and three-phase four-wire through its own detection and judgment. The present invention solves the problem that the three-phase three-wire and three-phase four-wire adaptive watt-hour meters cannot sample due to the difference in the reference neutral line in current and voltage sampling. The present invention can be freely switched with the change of the power grid load, and due to the power-on delay detection setting of MCU 1, there will be no incorrect metering and chaotic metering due to power grid fluctuations.

[0053] Those skilled in the art will readily think of other embodiments of the present application after considering the specification and the practice of the application disclosed herein. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include the common general knowledge or conventional technical means in the technical field disclosed in the present application. The specification and the embodiments are only regarded as exemplary, and the true scope of the present application is pointed out by the claims.

[0054] It should be understood that the present application is not limited to the exact structure already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The above-described embodiments of the present application do not constitute a limitation on the protection scope of the present application.

Claims

1. An automatic switching circuit for three-phase three-wire and three-phase four-wire adaptive electric energy meters, characterized in that: include: MCU (1), phase detection circuit, short switch (2), rectifier and step-down circuit and step-down source (3); The phase detection circuit comprises a diode (4), a resistor (5), a capacitor (6) and a photoelectric coupler, wherein the cathode of the diode (4) is connected to one end of the resistor (5), the other end of the resistor (5) is connected to the anode of the capacitor (6) and the anode of a light-emitting diode (70) in the photoelectric coupler, the cathode of the light-emitting diode (70) and the cathode of the capacitor (6) are connected to the rectifier and step-down circuit, the collector of the phototransistor (71) in the photoelectric coupler is connected to the VCC power supply of the step-down source (3), and the emitter of the phototransistor (71) is connected to the GND terminal of the step-down source (3) through a pull-down resistor (72); The switch state detection interface of the MCU (1) and the control interface of the short-circuit switch (2) are commonly connected to the emitter of the phototransistor (71); the short-circuit switch (2) is respectively connected to the positive electrode of the diode (4) and the rectifier-step-down circuit; and the rectifier-step-down circuit is connected to the step-down source (3).

2. The automatic switching circuit for three-phase three-wire and three-phase four-wire adaptive electric energy meters according to claim 1, characterized in that: The rectifier and voltage-step-down circuit includes a full-wave rectifier circuit or a half-wave rectifier circuit.

3. The automatic switching circuit for three-phase three-wire and three-phase four-wire adaptive electric energy meters according to claim 2 is characterized in that: The full-wave rectifier circuit comprises a first rectifier bridge stack (8), a second rectifier bridge stack (9) and a third rectifier bridge stack (10); the positive electrodes of the output ends of the first rectifier bridge stack (8), the second rectifier bridge stack (9) and the third rectifier bridge stack (10) are connected to the positive electrode of the step-down source (3); the negative electrodes of the output ends of the first rectifier bridge stack (8), the second rectifier bridge stack (9) and the third rectifier bridge stack (10) are connected to the negative electrode of the step-down source (3); the input end of the first rectifier bridge stack (8) is respectively connected to the A-phase wiring terminal and the neutral terminal of the three-phase power supply; the input end of the second rectifier bridge stack (9) is respectively connected to the B-phase wiring terminal and the neutral terminal of the three-phase power supply; and the input end of the third rectifier bridge stack (10) is respectively connected to the C-phase wiring terminal and the neutral terminal of the three-phase power supply; The neutral terminal is respectively connected to the short-circuiting switch (2), the cathode of the light-emitting diode (70) and the negative electrode of the capacitor (6), and the B-phase connection terminal of the three-phase power supply is respectively connected to the short-circuiting switch (2) and the positive electrode of the diode (4).

4. The automatic switching circuit for three-phase three-wire and three-phase four-wire adaptive electric energy meters according to claim 2, characterized in that: The half-wave rectifier circuit comprises a first rectifier diode (11), a second rectifier diode (12) and a third rectifier diode (13); the output ends of the first rectifier diode (11), the second rectifier diode (12) and the third rectifier diode (13) are all connected to the positive electrode of the step-down source (3); the negative electrode of the step-down source (3) is connected to the neutral terminal; the positive electrode of the first rectifier diode (11) is connected to the A-phase terminal; the positive electrode of the second rectifier diode (12) is connected to the B-phase terminal; and the positive electrode of the third rectifier diode (13) is connected to the C-phase terminal; The neutral terminal is respectively connected to the short-circuiting switch (2), the cathode of the light-emitting diode (70) and the negative electrode of the capacitor (6), and the B-phase terminal is respectively connected to the short-circuiting switch (2) and the positive electrode of the diode (4).

5. The automatic switching circuit for three-phase three-wire and three-phase four-wire adaptive electric energy meters according to claim 1, characterized in that: Also includes: A mutual inductance sampling circuit or a resistance step-down sampling circuit connected to the short-circuit switch (2).

6. The automatic switching circuit for three-phase three-wire and three-phase four-wire adaptive electric energy meters according to claim 5, characterized in that: The mutual inductance sampling circuit comprises three voltage transformers (14) connected in parallel with each other, one end of the primary coil of the voltage transformer (14) is respectively connected to the A-phase wiring terminal, the B-phase wiring terminal and the C-phase wiring terminal after passing through a current limiting resistor (15), the other end of the primary coil of the voltage transformer (14) is connected to a neutral terminal, and both ends of the secondary coil of the voltage transformer (14) are connected to a sampling resistor (16) and then connected to a sampling chip (17); Wherein, the short-circuit switch (2) is located between the B-phase terminal and the neutral terminal.

7. The automatic switching circuit for three-phase three-wire and three-phase four-wire adaptive electric energy meters according to claim 5, characterized in that: The resistor step-down sampling circuit comprises three groups of sampling resistor strings (18), two of the sampling resistor strings (18) form one group, the input ends of the sampling resistor strings (18) are respectively connected to the A-phase wiring terminal, the B-phase wiring terminal, and the C-phase wiring terminal, the output ends of the sampling resistor strings (18) are all connected to the neutral line terminal, and a sampling line is led out from one end of the sampling resistor (16) connected to the neutral line terminal and connected to the sampling chip (17); Wherein, the short-circuit switch (2) is located between the B-phase terminal and the neutral terminal.

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