System and method for detecting positive and negative connection of live line and null line of electric energy meter based on PCB capacitor

Abstract

The invention discloses an electric energy meter live and null line positive and negative connection detection system and method based on a PCB capacitor, and the system employs a coupling capacitor formed by reference ground laying copper and the ground to construct a signal backflow path, and outputs high and low level signals in combination with the conduction state change of a triode of a signal processing circuit. Signal isolation transmission is realized through an optocoupler device of the isolation circuit, and finally the MCU judges the connection state of the live line and the null line, thereby effectively detecting the reverse connection state of the live line and the null line of the electric energy meter, avoiding the fire hazard of electric appliances caused by manual missing detection, improving the safety performance of the circuit, and greatly facilitating the application and maintenance of the intelligent electric meter.

Description

A system and method for detecting the positive and negative connections of the live and neutral wires in an energy meter based on PCB capacitors. Technical Field

[0001] This invention relates to the field of power system metering equipment technology, and in particular to a system and method for detecting the positive and negative connection status of the live and neutral wires of an energy meter based on PCB capacitors. Background Technology

[0002] With the increasing sophistication of smart grids and electricity safety systems, electricity meters, as key metering and control nodes connecting the power supply system and end users, are directly related to the safety and reliability of the entire electricity circuit through standardized installation.

[0003] In actual installation and use, the live wire and neutral wire are often reversed, posing a significant safety hazard. From the perspective of electrical safety standards and equipment design principles, most household and similar appliances are designed to control and disconnect the live wire circuit. If the live and neutral wires are reversed, the internal control circuit of the appliance in standby mode actually disconnects the neutral wire, causing the equipment casing or critical internal components to remain at a high potential for an extended period. In this situation, if the equipment is in a dusty, humid environment or with an abnormal power supply system, the electrical clearance and creepage distance may decrease, potentially leading to localized electric arcs or even short-circuit sparks, ultimately increasing the risk of electrical fires and posing a serious threat to personal and property safety.

[0004] Currently, the detection of reversed live and neutral wires mainly relies on manual judgment during the installation of the electricity meter, and simple tools such as test pens are commonly used for verification. This method has a certain degree of subjectivity and the possibility of misjudgment.

[0005] Therefore, it is necessary to design a detection circuit that can effectively identify and prevent reverse connection of the live and neutral wires of the power supply in order to improve the safety and reliability of electrical equipment. Summary of the Invention

[0006] The purpose of this invention is to address the electrical safety issues caused by reversed connection of the live and neutral wires during the installation of electricity meters. A method based on PCB capacitors for detecting reversed connection of the live and neutral wires is designed to effectively detect the reversed connection state of the electricity meter and improve the safety performance of the circuit.

[0007] The technical solution of the present invention is as follows: Firstly, the present invention provides a power meter live / neutral wire positive / negative connection detection system based on PCB capacitors. This system includes a PCB capacitor coupling circuit, a signal processing circuit, an isolation circuit, and an MCU connected in series. The PCB capacitor coupling circuit includes a PCB reference ground DGND, a TVS diode D1, and capacitors C1 and C2. The entire bottom surface of the PCB is copper-plated as the reference ground DGND, connecting the live wire L and one end of the TVS diode D1. The other end of the TVS diode D1 is connected in series with capacitor C1 and then connected to the neutral wire N. The neutral wire N is connected to the ground behind the power meter's bottom casing. Using P... The CB board reference ground DGND is coupled to the ground behind the bottom shell of the energy meter. The capacitor C2 is connected in parallel across the two ends of the TVS diode D1, and the connection point of the capacitors C1 and C2 with the TVS diode D1 is connected to the input terminal of the signal processing circuit. The signal processing circuit is used to amplify the coupled signal, and its output terminal is electrically connected to the input terminal of the isolation circuit. The isolation circuit is used to isolate the amplified coupled signal and output the detection signal LN_CHECK to the MCU. The MCU analyzes the detection signal LN_CHECK, determines the positive and negative connection status of the live and neutral wires, and outputs the corresponding status flag according to the detection result.

[0008] Furthermore, the signal processing circuit includes resistors R1, R2, and R3, and NPN transistors Q1 and Q2. The base of NPN transistor Q1 is connected to the output terminal of the PCB capacitor coupling circuit, the collector of NPN transistor Q1 is connected to one end of resistors R1 and R2, the emitter of NPN transistor Q1 is connected to the PCB reference ground DGND, the other end of resistor R1 is connected to the power supply VDD3V3, the other end of resistor R2 is connected to the base of NPN transistor Q2, the emitter of transistor Q2 is connected to the PCB reference ground DGND, the collector of transistor Q2 is connected to the input terminal of the isolation circuit and one end of resistor R3, and the other end of resistor R3 is connected to the power supply VDD3V3.

[0009] Furthermore, the isolation circuit includes an optocoupler U1, resistors R4 and R5, and a capacitor C3. The anode of the optocoupler U1 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the output terminal of the signal processing circuit. The cathode of the optocoupler U1 is connected to the PCB reference ground DGND. The collector of the optocoupler U1 is connected to the power supply VCC3V3. The emitter of the optocoupler U1 serves as the output terminal, outputting the detection signal LN_CHECK to the MCU. One end of resistor R5 is connected to the emitter of the optocoupler U1, and the other end is grounded to MGND. One end of capacitor C3 is connected to the power supply VDD3V3, and the other end is grounded to MGND.

[0010] Furthermore, the PCB board reference ground DGND is connected to the live wire L and the neutral wire N is connected to the ground behind the bottom shell of the energy meter. The coupling capacitance C is obtained using the following formula.

[0011] Where S represents the area of ​​the copper plating on the bottom surface of the PCB board, and d represents the distance between the PCB board reference ground DGND and the ground of the electricity meter casing. is the relative permittivity, and k is the electrostatic constant.

[0012] Furthermore, the range of d is 0-5cm, and the range of S is 10cm×10cm-15cm×20cm.

[0013] Furthermore, the MCU periodically samples the detection signal LN_CHECK. When the live wire and neutral wire are connected normally, the detection signal is a square wave; when the live wire and neutral wire are reversed, the detection signal is a continuous low level.

[0014] Secondly, this invention provides a method for detecting the positive and negative connections of the live and neutral wires of an energy meter based on PCB capacitance. Based on the system described, the method includes: S1, connecting the live wire to the copper plating on the entire bottom surface of the PCB board as a reference ground (DGND), and connecting the neutral wire to the wall behind the energy meter's bottom casing, thus forming a coupling capacitor between the PCB reference ground (DGND) and the ground behind the energy meter's bottom casing; when the live and neutral wires are normally connected, the coupling capacitor generates a potential difference and forms a PCB capacitor coupling loop; when the live and neutral wires are reversed, the copper plating area on the bottom surface of the PCB board has the same potential as the ground and cannot form a loop; S2, the signal processing circuit drives the conduction states of transistors Q1 and Q2 according to the capacitive reactance characteristics of the coupling capacitor during the positive and negative half-cycles of AC power; when the live and neutral wires are normally connected, transistor Q1 is turned off during the positive half-cycle of AC power to conduct. Transistor Q2 outputs a low level, and transistor Q1 conducts during the negative half-cycle of AC power to turn off transistor Q2, which outputs a high level. When the live and neutral wires are reversed, transistor Q1 turns off to turn on transistor Q2, which outputs a low level. S3: The isolation circuit receives the high and low levels output by the signal processing circuit to control the conduction of optocoupler U1. When the live and neutral wires are normally connected, optocoupler U1 turns off during the positive half-cycle of AC power to pull the detection signal down to a low level, and turns on during the negative half-cycle of AC power to pull the detection signal up to a high level. When the live and neutral wires are reversed, optocoupler U1 turns off to pull the detection signal down to a low level. S4: The MCU receives the detection signal output by the isolation circuit and determines the connection status of the live and neutral wires based on the waveform of the detection signal. When normally connected, the detection signal is a square wave signal; when reversed, the detection signal is a continuous low-level signal.

[0015] The beneficial effects of this invention are as follows: This invention utilizes the coupling capacitance formed by the reference ground copper and the ground to construct a signal return path. Combined with the change in the conduction state of the transistor in the signal processing circuit, high and low level signals are output. Signal isolation transmission is achieved through the optocoupler device in the isolation circuit. Finally, the MCU determines the connection status of the live and neutral wires, which effectively solves the accuracy and safety problems of live and neutral wire reverse connection detection. Especially in complex installation environments, it can stably identify the connection status and avoid electrical risks caused by reverse connection.

[0016] This invention achieves accurate detection of the live and neutral wire connection status of electricity meters through low-cost and high-reliability circuit design, improving the installation reliability and usage safety of electricity metering equipment, and providing important technical support for the stable operation of smart grids.

[0017] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0018] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0019] Figure 1 shows a schematic diagram of the principle of the live and neutral wire positive and negative connection detection system of the present invention based on PCB capacitor.

[0020] Figure 2 shows the circuit diagram of the present invention for detecting reverse connection of live and neutral wires based on PCB capacitor.

[0021] Figure 3 shows a schematic diagram of the positional relationship between the PCB board and the wall / ground.

[0022] In the diagram: 1. PCB board; 2. Bottom shell; 3. Wall. Detailed Implementation

[0023] Preferred embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0024] As shown in Figures 1-3, this invention provides a PCB capacitor-based system for detecting the positive and negative connections of the live and neutral wires in an energy meter. The system includes a PCB capacitor coupling circuit, a signal processing circuit, an isolation circuit, and an MCU connected in series. The PCB capacitor coupling circuit includes a PCB reference ground (DGND), a TVS diode (D1), and capacitors C1 and C2. The entire bottom surface of the PCB is copper-plated as the reference ground (DGND), connecting the live wire L and one end of the TVS diode D1. The other end of the TVS diode D1 is connected in series with capacitor C1 and then connected to the neutral wire N. The neutral wire N is connected to the energy meter... The meter's bottom casing is connected to the ground behind it, and is coupled to the ground behind the meter's bottom casing using the PCB reference ground DGND. Capacitor C2 is connected in parallel across TVS diode D1, and the connection point between capacitors C1 and C2 and TVS diode D1 is connected to the input terminal of the signal processing circuit. The signal processing circuit includes resistors R1, R2, and R3, and NPN transistors Q1 and Q2. The base of NPN transistor Q1 is connected to the output terminal of the PCB capacitor coupling circuit, and the collector of NPN transistor Q1 is connected to one end of resistors R1 and R2. The emitter of NPN transistor Q1 is connected to the PCB reference ground DGND. The other end of resistor R1 is connected to the power supply VDD3V3. The other end of resistor R2 is connected to the base of NPN transistor Q2. The emitter of transistor Q2 is connected to the PCB reference ground DGND. The collector of transistor Q2 is connected to the input of the isolation circuit and one end of resistor R3. The other end of resistor R3 is connected to the power supply VDD3V3. The isolation circuit includes an optocoupler U1, resistors R4 and R5, and capacitor C3. The anode of device U1 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the output terminal of the signal processing circuit. The cathode of optocoupler U1 is connected to the PCB reference ground DGND. The collector of optocoupler U1 is connected to the power supply VCC3V3. The emitter of optocoupler U1 serves as the output terminal, outputting the detection signal LN_CHECK to the MCU. One end of resistor R5 is connected to the emitter of optocoupler U1, and the other end is grounded to MGND. One end of capacitor C3 is connected to the power supply VDD3V3, and the other end is grounded to MGND.

[0025] This invention provides a method for detecting the reverse connection of the live and neutral wires in an energy meter based on PCB capacitance. The method can identify whether the live and neutral wires of the energy meter are reversed. The method includes the following steps: S1, using a single copper DGND plate on the back of the PCB board to connect the live wire and the neutral wire to the ground behind the meter's bottom case for signal coupling; based on the potential difference between parallel planes, a coupling capacitor will be formed. The capacitance calculation formula for a planar plate capacitor is:

[0026] Where S represents the area of ​​the copper plating on the bottom surface of the PCB board, and d represents the distance between the PCB board reference ground DGND and the ground of the electricity meter casing. is the relative permittivity, and k is the electrostatic constant.

[0027] Figure 3 shows a schematic diagram of the positional relationship between the PCB board and the wall / ground.

[0028] Where S represents the area of ​​the entire reference ground copper plating on the back of the PCB board, and d represents the distance between the reference ground copper plating on the back of the PCB board and the ground behind the meter's bottom case. These two are adjustable parameters. The PCB board should be as close as possible to the meter's bottom case, and the copper plating should be located on the back of the PCB board. The distance between the PCB board and the ground behind the meter's bottom case is considered to be between 0 and 5 cm. The area of ​​the entire reference ground copper plating DGND on the back of the PCB board is considered to be 10 cm * 10 cm. The required coupling capacitor value can be calculated according to the capacitance calculation formula of the planar plate capacitor. This coupling capacitor value is in the pF level. In general, the larger the planar area, the larger the coupling capacitor; the smaller the distance between the two planes, the larger the coupling capacitor.

[0029] When the live and neutral wires are connected normally, there is a potential difference between the PCB copper plate connected to the live wire and the ground connected to the neutral wire, forming a PCB coupling capacitor. Under the action of alternating current, the capacitor exhibits capacitive reactance characteristics. A circuit is formed between the coupling capacitor formed between the parallel planes and capacitors C1 and C2. At this time, a voltage is distributed across capacitor C2. During the positive half-cycle of the alternating current, the TVS diode clamps the transistor Q1, preventing it from conducting. During the negative half-cycle of the alternating current, the voltage across capacitor C2 enables transistor Q1 to conduct. When the live and neutral wires are reversed, the PCB copper plate is connected to the neutral wire, which is connected to ground. Since both the PCB copper plate and ground are connected to the neutral wire, there is no potential difference between their parallel planes, thus preventing the formation of a circuit, and transistor Q1 cannot conduct. The signal processing circuit (S2) drives transistor Q1 to conduct based on the PCB capacitor coupling circuit. When the live and neutral wires are connected normally, transistor Q1 is not conducting during the positive half-cycle of the AC current, while transistor Q2 is conducting, thus providing a low-level input to the isolation circuit. During the negative half-cycle of the AC current, transistor Q1 conducts, causing transistor Q2 to be off-circuit, providing a high-level input to the isolation circuit. When the live and neutral wires are reversed, since there is no potential difference between the parallel planes of the PCB copper and ground, a loop cannot be formed, so transistor Q1 is not conducting, while transistor Q2 is conducting, thus providing a low-level input to the isolation circuit. S3: The isolation circuit receives the high and low levels from the signal processing circuit to determine whether optocoupler U1 is conducting. When the live and neutral wires are connected normally, during the positive half-cycle of the AC current, the isolation... When the circuit receives a low level, it does not conduct. However, during the negative half-cycle of the AC current, the isolation circuit receives a high level. At this time, the anode of the optocoupler U1 is pulled high, and after the optocoupler conducts, the detection signal LN_CHECK is pulled high by the power supply VCC3V3. When the live and neutral wires are reversed, the isolation circuit receives a low level, the optocoupler U1 does not conduct, and the detection signal LN_CHECK is pulled low by the resistor R5. S4 and the MCU receive the waveform of the isolated detection signal to determine whether the live and neutral wires are reversed. When the live and neutral wires are normally connected, the MCU detects a square wave signal. When the live and neutral wires are reversed, the MCU continuously detects a low-level signal, thereby identifying whether the live and neutral wires are reversed.

[0030] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A power meter live / neutral wire positive / negative connection detection system based on PCB capacitors, characterized in that, The system includes a PCB capacitive coupling circuit, a signal processing circuit, an isolation circuit, and an MCU connected in series. The PCB capacitive coupling circuit includes a PCB reference ground (DGND), a TVS diode (D1), and capacitors C1 and C2. The entire bottom surface of the PCB is copper-plated as the reference ground (DGND), connecting the live wire (L) and one end of the TVS diode (D1). The other end of the TVS diode (D1) is connected in series with capacitor C1 and then connected to the neutral wire (N). The neutral wire (N) is connected to the ground behind the power meter casing. The system utilizes the connection between the PCB reference ground (DGND) and the ground behind the power meter casing... The coupling is performed by connecting capacitor C2 in parallel across TVS diode D1, and the connection point between capacitors C1 and C2 and TVS diode D1 is connected to the input terminal of the signal processing circuit. The signal processing circuit amplifies the coupled signal, and its output terminal is electrically connected to the input terminal of the isolation circuit. The isolation circuit isolates the amplified coupled signal and outputs a detection signal LN_CHECK to the MCU. The MCU analyzes the detection signal LN_CHECK, determines the positive or negative connection status of the live and neutral wires, and outputs the corresponding status flag based on the detection result.

2. The energy meter live / neutral wire positive / negative connection detection system based on PCB capacitors according to claim 1, characterized in that, The signal processing circuit includes resistors R1, R2, and R3, and NPN transistors Q1 and Q2. The base of NPN transistor Q1 is connected to the output terminal of the PCB capacitor coupling circuit. The collector of NPN transistor Q1 is connected to one end of resistors R1 and R2. The emitter of NPN transistor Q1 is connected to the PCB reference ground DGND. The other end of resistor R1 is connected to the power supply VDD3V3. The other end of resistor R2 is connected to the base of NPN transistor Q2. The emitter of transistor Q2 is connected to the PCB reference ground DGND. The collector of transistor Q2 is connected to the input terminal of the isolation circuit and one end of resistor R3. The other end of resistor R3 is connected to the power supply VDD3V3.

3. The energy meter live / neutral wire positive / negative connection detection system based on PCB capacitors according to claim 1, characterized in that, The isolation circuit includes an optocoupler U1, resistors R4 and R5, and a capacitor C3. The anode of the optocoupler U1 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the output terminal of the signal processing circuit. The cathode of the optocoupler U1 is connected to the PCB reference ground DGND. The collector of the optocoupler U1 is connected to the power supply VCC3V3. The emitter of the optocoupler U1 serves as the output terminal, outputting the detection signal LN_CHECK to the MCU. One end of resistor R5 is connected to the emitter of the optocoupler U1, and the other end is grounded to MGND. One end of capacitor C3 is connected to the power supply VDD3V3, and the other end is grounded to MGND.

4. The energy meter live / neutral wire positive / negative connection detection system based on PCB capacitors according to claim 1, characterized in that, The PCB reference ground DGND is connected to the live wire L and coupled to the ground behind the energy meter's bottom casing, which is connected to the neutral wire N. The coupling capacitance C is obtained using the following formula: C=ε r S / 4πkd, where S is the area of ​​the copper plating on the bottom surface of the PCB board, d is the distance between the PCB board reference ground DGND and the ground of the power meter casing, and ε r is the relative permittivity, and k is the electrostatic constant.

5. The energy meter live / neutral wire positive / negative connection detection system based on PCB capacitors according to claim 4, characterized in that, The range of d is 0-5cm, and the range of S is 10cm×10cm-15cm×20cm.

6. The energy meter live / neutral wire positive / negative connection detection system based on PCB capacitors according to claim 1, characterized in that, The MCU periodically samples the detection signal LN_CHECK. When the live wire and neutral wire are connected normally, the detection signal is a square wave; when the live wire and neutral wire are reversed, the detection signal is a continuous low level.

7. A method for detecting the positive and negative connections of the live and neutral wires in an energy meter based on PCB capacitors, wherein the system described in any one of claims 1 to 6 is characterized in that, The method includes: S1, using copper plating on the entire bottom surface of the PCB board as a reference ground (DGND) connected to the live wire, and connecting the wall behind the power meter's bottom casing to the neutral wire, so that a coupling capacitor is formed between the PCB board's reference ground (DGND) and the ground behind the power meter's bottom casing; when the live wire and neutral wire are normally connected, the coupling capacitor generates a potential difference and forms a PCB capacitor coupling loop; when the live wire and neutral wire are reversed, the copper plating area on the bottom surface of the PCB board has the same potential as the ground and cannot form a loop; S2, the signal processing circuit drives the conduction state of transistors Q1 and Q2 according to the capacitive reactance characteristics of the coupling capacitor during the positive and negative half-cycles of AC power; when the live and neutral wires are normally connected, transistor Q1 is turned off during the positive half-cycle of AC power to turn on transistor Q2 to output a low level, and transistor Q2 outputs a low level during the negative half-cycle of AC power. During the first half-cycle, transistor Q1 is turned off to turn off the high-level output of transistor Q2; when the live and neutral wires are reversed, transistor Q1 is turned off to turn on transistor Q2 to output a low-level output; S3, the isolation circuit receives the high and low levels output by the signal processing circuit to control the conduction of optocoupler U1; when the live and neutral wires are normally connected, optocoupler U1 is turned off during the positive half-cycle of AC power to pull the detection signal down to a low level, and optocoupler U1 is turned on during the negative half-cycle of AC power to pull the detection signal up to a high level; when the live and neutral wires are reversed, optocoupler U1 is turned off to pull the detection signal down to a low level; S4, the MCU receives the detection signal output by the isolation circuit and determines the connection status of the live and neutral wires based on the waveform of the detection signal. When normally connected, the detection signal is a square wave signal, and when reversed, the detection signal is a continuous low-level signal.

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