An AC zero-crossing detection circuit for the relay closing of an electric energy meter

Abstract

The present invention provides an AC zero-crossing detection circuit for the closing of a relay in an electric energy meter. The circuit includes: the live wire L and the neutral wire N of an AC power supply; a resistor R1, one end of which is connected to the live wire L and the other end is connected to the base of a PNP triode Q1; a PNP triode Q1, whose collector is connected to the neutral wire N and the emitter is connected to a resistor R2 and the pin 2 of an optocoupler U1; a capacitor C1, one end of which is connected to the collector of the PNP triode Q1 and the other end is connected to the resistor R2 and the pin 1 of the optocoupler U1; an optocoupler U1, whose pin 1 is connected to the resistor R2 and the capacitor C1, pin 2 is connected to the emitter of the PNP triode Q1, pin 3 is connected to the ground of the main control DC power supply, and pin 4 is connected to a resistor R3 and the input port of a main control CPU chip U2; the other end of the resistor R3 is connected to the main control power supply VCC; a main control CPU chip U2, whose output port is connected to the input port of a drive circuit U3, and the output port of the drive circuit U3 is connected to one end of a relay coil.

Description

Technical Field

[0001] The present invention relates to the technical field of electric energy meter detection circuits, and particularly to an AC zero-crossing detection circuit for relay closing of an electric energy meter. Background Art

[0002] In modern electric energy meters, the reliability and lifespan of relays are important factors affecting their overall performance and user experience. Especially in power systems, due to the diversity and complexity of user electrical equipment, relays are prone to current surges and arcs during frequent operations, resulting in contact welding, wear, or even failure of the contacts. The control methods of relays in traditional electric energy meters often cannot effectively avoid these problems, affecting the long-term stable operation of the electric energy meters.

[0003] Relays are one of the key components in electric energy meters, mainly used to control the on-off of current. With the development of smart grids, modern electric energy meters not only perform the function of electric energy metering but also need to have intelligent control functions such as remote power-off and power restoration. Therefore, the application of relays in electric energy meters has become more important and frequent. However, in electric energy meters, frequent operation of relays may cause the following problems:

[0004] Contact welding: When the relay closes, if the user's electrical equipment has a capacitive load, a large impact current will be generated instantaneously. This impact current will generate a strong arc between the relay contacts, causing the contact surface to melt and weld together at high temperature, resulting in the relay being unable to disconnect again.

[0005] Arc damage: During the operation of the relay, the generation of arcs is inevitable. This will not only cause ablation of the contact surface material but also may generate carbides or oxides, further increasing the contact resistance of the contacts and affecting the stable conduction of current.

[0006] Mechanical wear: The contacts of the relay will be subject to mechanical wear during frequent opening and closing, resulting in a decrease in the contact pressure of the contacts and poor contact, ultimately affecting the normal operation of the electric energy meter.

[0007] In the prior art, methods such as delay control and current-limiting protection are usually adopted to reduce the impact current and arcs of relay contacts. However, these methods have many limitations in practical applications:

[0008] Delay control: By delaying the closing time of the relay, it attempts to avoid the impact current generated by the load. However, this method is difficult to accurately control the time and cannot reflect the changes in AC voltage in real time, and the effect is limited.

[0009] Current-limiting protection: Adding a current-limiting resistor or using electronic components in the circuit to limit the current, but this increases the complexity and cost of the circuit, and may also affect the overall efficiency and reliability of the electric energy meter.

[0010] Mechanical improvement: By using highly wear-resistant materials and special structural designs to enhance the durability of the relay, although mechanical wear can be slowed down to a certain extent, the problems of arc and contact welding cannot be fundamentally solved.

[0011] With the development of smart grids and smart homes, electricity meters require a more intelligent and reliable relay control method. In this context, the AC zero-crossing detection technology has gradually received attention. The AC zero-crossing detection technology can significantly reduce the generation of inrush current and arc by controlling the closing of the relay at the zero-crossing point of the AC voltage (i.e., the moment when the voltage transitions from the positive half-cycle to the negative half-cycle or from the negative half-cycle to the positive half-cycle), thereby protecting the relay contacts.

[0012] Advantages of zero-crossing detection technology: Reducing inrush current: Closing the relay near the zero-crossing point of the AC voltage, the voltage is close to zero, and the current is small at this time, which can significantly reduce the inrush current generated by capacitive loads and protect the relay contacts.

[0013] Reducing arc: Since the relay is closed at the zero-crossing point, the probability and intensity of arc generation are greatly reduced, thereby reducing the damage and wear of the arc to the contacts.

[0014] Improving the relay life: By reducing the influence of inrush current and arc, the service life of the relay can be significantly extended, and the long-term operation stability of the electricity meter can be improved. Summary of the Invention

[0015] The object of the present invention is to provide an AC zero-crossing detection circuit for the closing of a relay in an electricity meter, and the circuit includes:

[0016] The live wire (L) and the neutral wire (N) of the AC power supply;

[0017] A resistor (R1), one end of which is connected to the live wire (L), and the other end is connected to the base of a PNP transistor (Q1);

[0018] A PNP transistor (Q1), whose collector is connected to the neutral wire (N), and the emitter is connected to a resistor (R2) and the 2nd pin of an optocoupler (U1);

[0019] A capacitor (C1), one end of which is connected to the collector of the PNP transistor (Q1), and the other end is connected to the resistor (R2) and the 1st pin of the optocoupler (U1);

[0020] An optocoupler (U1), whose 1st pin is connected to the resistor (R2) and the capacitor (C1), the 2nd pin is connected to the emitter of the PNP transistor (Q1), the 3rd pin is connected to the ground of the main control DC power supply, and the 4th pin is connected to a resistor (R3) and the input port of the main control CPU chip (U2);

[0021] One end of the resistor (R3) is connected to pin 4 of the optocoupler (U1), and the other end is connected to the power supply VCC.

[0022] The main control CPU chip (U2), its output port is connected to the input port of the drive circuit (U3), and the output port of the drive circuit (U3) is connected to one end of the relay coil.

[0023] As a preferred technical solution of the present invention, the resistor (R1) functions as a current limiter to ensure that the current of the PNP transistor Q1 is within a suitable range. The capacitor (C1) is used to charge during the positive half cycle of the AC voltage and trigger the optocoupler (U1) to discharge when the voltage drops to the zero crossing point. The light-emitting diode of the optocoupler (U1) passes through current near the zero crossing point when the AC voltage drops during the positive half cycle, and transmits the zero crossing signal to the main control CPU chip (U2).

[0024] As a preferred technical solution of the present invention, the main control CPU chip (U2) calculates and issues a time point signal for closing the relay based on the zero crossing signal transmitted by the optocoupler (U1). The drive circuit (U3) receives the closing relay signal issued by the main control CPU chip (U2) and controls the relay to close near the zero crossing point of the AC voltage.

[0025] As a preferred technical solution of the present invention, the absolute value of the base-emitter breakdown voltage of the PNP transistor (Q1) is less than the absolute value of the base-collector breakdown voltage (conventional) to ensure the smooth completion of the charging process of the capacitor (C1) during the positive half cycle. The resistor (R3) serves as a pull-up resistor for the optocoupler (U1) to provide current for the optocoupler output signal.

[0026] As a preferred technical solution of the present invention, the main control CPU chip (U2) has an external interrupt function and can respond in real time to the zero crossing signal transmitted by the optocoupler (U1).

[0027] As a preferred technical solution of the present invention, the circuit is applied to an electric energy meter. By closing the relay near the zero crossing point, the phenomenon of relay contact welding is significantly reduced, and the operation stability of the electric energy meter is improved.

[0028] As a preferred technical solution of the present invention, the main control CPU chip (U2) calculates the next zero crossing point of the alternating current according to the power grid frequency and the action duration of the relay, and issues an instruction to close the relay at an appropriate moment, so that the relay contacts close just near the zero crossing point of the alternating current.

[0029] As a preferred technical solution of the present invention, the circuit includes a signal conditioning module for conditioning the zero crossing signal output from the optocoupler (U1) to ensure that the main control CPU chip (U2) can accurately identify the zero crossing point.

[0030] As a preferred technical solution of the present invention, the capacitance of the capacitor (C1) is optimized according to the voltage and frequency of the actual power grid to ensure the best charge and discharge effect.

[0031] As a preferred technical solution of the present invention, the optocoupler (U1) in the circuit uses a high-speed response optocoupler to ensure the timely transmission of the zero-crossing signal; the relay is a bistable relay to reduce the power consumption after the relay switches; the main control CPU chip (U2) includes a self-correction module for correcting the zero-crossing point offset caused by power grid fluctuations; the circuit includes a status indication module for displaying the current status of the relay and the working status of the circuit; the main control CPU chip (U2) can store and analyze multiple zero-crossing signals to optimize the closing moment of the relay; the circuit can adapt to different types of relays, including mechanical relays and solid-state relays. Beneficial effects

[0032] The present invention proposes an AC zero-crossing detection circuit for the closing of a relay in an electric energy meter, aiming to solve the problems of relay contact welding, arc damage, and mechanical wear in the prior art. By designing an AC voltage zero-crossing detection circuit, the relay is closed near the zero-crossing point of the AC voltage, effectively reducing the generation of impact current and arc, protecting the relay contacts, and improving the reliability and service life of the electric energy meter.

[0033] The present invention adopts the following technical solution: the capacitor is charged during the positive half-cycle of the alternating current, and the capacitor discharges through the light-emitting diode of the optocoupler when the zero-crossing point is triggered, and the zero-crossing point information of the AC voltage is isolated and transmitted to the main control CPU;

[0034] The main control CPU calculates and issues a time point signal for closing the relay according to the zero-crossing point information, so that the contacts of the relay are closed near the zero-crossing point of the AC voltage.

[0035] Through the above solution, the present invention realizes the closing of the relay near the zero-crossing point of the AC voltage, avoids the generation of impact current and arc, and significantly improves the operation stability of the electric energy meter and the service life of the relay. Description of the drawings

[0036] Figure 1 This is the circuit schematic diagram of the present invention, showing the specific connection and composition of the AC zero-crossing detection circuit for the closing of the relay in the electric energy meter. Specific implementation manners

[0037] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] Circuit Composition and Principle

[0039] The circuit of the present invention is as Figure 1 shown and includes the following key components:

[0040] The live wire (L) and neutral wire (N) of the AC power supply.

[0041] A resistor (R1), one end of which is connected to the live wire (L), and the other end is connected to the base of the PNP transistor (Q1).

[0042] A PNP transistor (Q1), whose collector is connected to the neutral wire (N), and the emitter is connected to the resistor (R2) and the 2nd pin of the optocoupler (U1).

[0043] A capacitor (C1), one end of which is connected to the collector of the PNP transistor (Q1), and the other end is connected to the resistor (R2) and the 1st pin of the optocoupler (U1).

[0044] An optocoupler (U1), whose 1st pin is connected to the resistor (R2) and the capacitor (C1), the 2nd pin is connected to the emitter of the PNP transistor (Q1), the 3rd pin is connected to the ground of the main control DC power supply, and the 4th pin is connected to the resistor (R3) and the input port of the main control CPU chip (U2).

[0045] A resistor (R3), one end of which is connected to the 4th pin of the optocoupler (U1), and the other end is connected to the power supply VCC.

[0046] The main control CPU chip (U2), whose output port is connected to the input port of the drive circuit (U3), and the output port of the drive circuit (U3) is connected to one end of the relay coil.

[0047] Circuit Operation Steps

[0048] Charging process during the positive half cycle of the alternating current:

[0049] When the live wire (L) of the AC power supply is in the positive half cycle, the live wire (L) provides current through the resistor (R1), causing the base-emitter voltage of the PNP transistor (Q1) to break down and conduct.

[0050] The current flows through the resistor (R2) to the capacitor (C1), charging the capacitor (C1). Positive charges accumulate on the right foot of the capacitor (C1), and negative charges accumulate on the left foot.

[0051] Zero-crossing detection process: When the AC power supply voltage transitions from the positive half-cycle to the negative half-cycle (i.e., the zero-crossing point), the positive charge on capacitor C1 enters the emitter-base of the PNP transistor (Q1) through resistor R2 and the light-emitting diode (LED) of the optocoupler, and then enters the live wire (L) and neutral wire (N) (the voltage between the live wire and the neutral wire is approximately 0 V) through resistor (R1), and returns to capacitor (C1). In this way, the transistor (Q1) has a base current, and the emitter and collector of the transistor (Q1) are turned on, providing a short pulse current for the light-emitting diode of the optocoupler (U1), and the optocoupler (U1) is turned on.

[0052] After the optocoupler (U1) is turned on, it transmits the zero-crossing signal to the main control CPU chip (U2). After receiving the signal, the main control CPU chip triggers an external interrupt.

[0053] Relay control process: The main control CPU chip (U2) calculates the most suitable relay closing time point based on the received zero-crossing signal and the closing action time of the relay.

[0054] After calculating the closing time point, the main control CPU chip (U2) controls the drive circuit (U3) through an output signal. The drive circuit (U3) further controls the relay coil to make the relay close near the zero-crossing point of the AC voltage.

[0055] Current path in the negative half-cycle of alternating current:

[0056] When the live wire (L) of the AC power supply enters the negative half-cycle, the current flows from the neutral wire (N) through the PN junction of the collector-base of the PNP transistor (Q1) and resistor (R1) to the live wire (L), forming a current path.

[0057] Contact protection and stable operation: By closing the relay near the zero-crossing point, the generation of impact current and arc can be effectively reduced, protecting the relay contacts and extending the service life of the relay.

[0058] The circuit designed by the present invention operates stably, without complex control algorithms and high-cost components, and is applicable to various types of watt-hour meters.

[0059] Function description of circuit components

[0060] Resistor (R1): Plays a current-limiting role to ensure that the current of the PNP transistor (Q1) is within an appropriate range.

[0061] Capacitor (C1): Used to charge during the positive half-cycle of the AC voltage and trigger the optocoupler (U1) to discharge at the zero-crossing point, transmitting the zero-crossing information to the main control CPU chip (U2).

[0062] Optocoupler (U1): It is used to isolate the zero-crossing signal of the AC voltage from the main control CPU chip (U2) to ensure the safety of the circuit and the stable transmission of signals.

[0063] PNP Triode (Q1): During the positive half-cycle of the alternating current, through its base-emitter voltage breakdown characteristic, it controls the charging of the capacitor (C1) and the triggering process of the optocoupler (U1); during the negative half-cycle of the alternating current, through the conduction of the PN junction between its collector and base, it provides a current path for the negative half-cycle of the alternating current.

[0064] Main Control CPU Chip (U2): It is responsible for receiving the zero-crossing signal, calculating and sending the time point signal for closing the relay, and controlling the closing operation of the relay.

[0065] Driver Circuit (U3): According to the signal sent by the main control CPU chip (U2), it drives the relay coil to make the relay close near the zero-crossing point of the AC voltage.

[0066] Circuit Operation Example

[0067] In practical applications, this circuit can be integrated with the control system of the electric energy meter to achieve intelligent relay control. The specific steps are as follows:

[0068] When the electric energy meter is working normally, the circuit monitors the change of the AC voltage in real time and triggers the optocoupler at the zero-crossing point to transmit the zero-crossing signal.

[0069] The main control CPU chip accurately controls the closing time point of the relay according to the zero-crossing signal and user requirements to ensure that the contacts of the relay close near the zero-crossing point of the AC voltage.

[0070] In this way, the relay in the electric energy meter can still work stably under high load conditions, avoiding contact welding and arc damage, and extending the service life of the equipment.

[0071] Specific Example

[0072] In practical applications, the present invention has been tested and verified in a certain type of electric energy meter. The test results show that:

[0073] After adopting the AC zero-crossing detection circuit of the present invention, no contact welding phenomenon has occurred in the relay contacts, and the electric energy meter operates stably and has reliable performance.

[0074] Under long-term high-load conditions, the service life of the relay is significantly extended, the maintenance cost is reduced, and the user satisfaction is improved.

[0075] In summary, the present invention provides a simple, efficient and reliable AC zero-crossing detection circuit, which is particularly suitable for the control of relays in electric energy meters and has broad application prospects and market value.

[0076] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or apparatus.

[0077] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An AC zero-crossing detection circuit for the relay closing of an electric energy meter, characterized in that, The circuit includes: the live wire L and the neutral wire N of the AC power supply; A resistor R1, one end of which is connected to the live wire L and the other end is connected to the base of the PNP transistor Q1; A PNP transistor Q1, whose collector is connected to the neutral wire N and whose emitter is connected to pin 1 of the resistor R2 and pin 2 of the optocoupler U1; A capacitor C1, one end of which is connected to the collector of the PNP transistor Q1 and the other end is connected to pin 2 of the resistor R2 and pin 1 of the optocoupler U1; An optocoupler U1, whose pin 1 is connected to the resistor R2 and the capacitor C1, pin 2 is connected to the emitter of the PNP transistor Q1, pin 3 is connected to the ground of the main control DC power supply, and pin 4 is connected to the resistor R3 and the input port of the main control CPU chip U2; A resistor R3, one end of which is connected to pin 4 of the optocoupler U1 and the other end is connected to the power supply VCC; A main control CPU chip U2, whose output port is connected to the input port of the drive circuit U3, and the output port of the drive circuit U3 is connected to one end of the relay coil.

2. The AC zero-crossing detection circuit for the relay closing of the electric energy meter according to claim 1, characterized in that, The resistor R1 plays a current-limiting role to ensure that the current of the PNP transistor Q1 is within a suitable range. The capacitor C1 is used to charge during the positive half-cycle of the AC voltage and trigger the optocoupler U1 to discharge when the voltage drops to the zero-crossing point. The light-emitting diode of the optocoupler U1 flows through current near the zero-crossing point when the AC voltage drops in the positive half-cycle, and transmits the zero-crossing signal to the main control CPU chip U2.

3. The AC zero-crossing detection circuit for the relay closing of the electric energy meter according to claim 2, characterized in that, Based on the zero-crossing signal transmitted by the optocoupler U1, the main control CPU chip U2 calculates and issues a time-point signal for closing the relay. The drive circuit U3 receives the closing-relay signal issued by the main control CPU chip U2 and controls the relay to close near the zero-crossing point of the AC voltage.

4. The AC zero-crossing detection circuit for the relay closing of the electric energy meter according to claim 1, characterized in that, The absolute value of the base-emitter breakdown voltage of the PNP transistor Q1 is less than the absolute value of the base-collector breakdown voltage to ensure the smooth completion of the charging process of the capacitor C1 during the positive half-cycle. The resistor R3 serves as the pull-up resistor of the optocoupler U1 to provide current for the optocoupler output signal.

5. The AC zero-crossing detection circuit for the relay closing of the electric energy meter according to claim 1, wherein, The main control CPU chip U2 has an external interrupt function and can respond in real time to the zero-crossing signal transmitted by the optocoupler U1.

6. The alternating current zero-crossing detection circuit for the electric energy meter relay closing according to claim 1, characterized in that, The circuit is applied to an electric energy meter. By closing the relay near the zero-crossing point of the alternating current, the phenomenon of relay contact welding caused by capacitive load is significantly reduced, and the operation stability of the electric energy meter is improved.

7. The alternating current zero-crossing detection circuit for the relay closing of the electric energy meter according to claim 1, characterized in that, The main control CPU chip U2 calculates the next zero-crossing point of the alternating current according to the power grid frequency and the action duration of the relay, and issues an instruction to close the relay at an appropriate moment, so that the relay contacts close just near the zero-crossing point of the alternating current.

8. The alternating current zero-crossing detection circuit for the relay closing of the electric energy meter according to claim 1, wherein, The circuit includes a signal conditioning module for conditioning the zero-crossing signal output from the optocoupler U1 to ensure that the main control CPU chip U2 can accurately identify the zero-crossing point.

9. The alternating current zero-crossing detection circuit for the relay closing of the electric energy meter according to claim 1, characterized in that The capacitance of the capacitor C1 is optimized according to the voltage and frequency of the actual power grid to ensure the best charge and discharge effect.

10. The alternating current zero-crossing detection circuit for the relay closing of the electric energy meter according to claim 1, characterized in that, The optocoupler U1 in the circuit uses a high-speed response optocoupler to ensure the timely transmission of the zero-crossing signal; the relay is a bistable relay to reduce the power consumption after the relay is closed; the main control CPU chip U2 includes a self-correction module for correcting the zero-crossing point offset caused by power grid fluctuations; the circuit includes a status indication module for displaying the current status of the relay and the working status of the circuit; the main control CPU chip U2 can store and analyze multiple zero-crossing signals to optimize the closing moment of the relay; the circuit can adapt to different types of relays, including mechanical relays and solid-state relays.

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