This paper introduces the design and implementation of a single-phase smart meter with reverse connection detection of live and neutral wires, analyzes the characteristics of the smart meter with reverse connection of live and neutral wires, and explains the software and hardware design and implementation scheme of the smart meter, especially the hardware and software design and implementation scheme of reverse connection detection of live and neutral wires.
Keywords： Single-phase smart meter; Reverse connection of live and neutral wires; G80F924
Content：
2. Meter hardware design
2.1 Metering circuit
3.Principle of reverse detection of live and neutral wires of smart meters
3.1 Adverse effects of reverse connection of live and neutral wires
1. Introduction
Although there are various single-phase smart meters on the market that can meet the various needs of customers, there is no related product that can alarm when the live and neutral wires are connected reversely. There is an urgent need for a meter that can alarm and prompt the installation technicians when the live and neutral wires are connected reversely. This article deals with such a single-phase smart meter that can detect the reverse connection of the live and neutral wires.
2. Meter hardware design
2.1 Metering circuit
The metering circuit realizes the acquisition of voltage and current metering signals. It consists of one voltage sampling circuit and two current sampling circuits. The live wire current is input to the differential AD input Ib+, Ib- of the main control chip through the manganese copper sampling shunt and the resistor and capacitor low-pass network; the neutral wire current is input to the differential AD input Ia+, Ia- of the main control chip through the current transformer and the resistor and capacitor low-pass network. The mains power is divided by the resistor network in front to realize the conversion from 220V to the voltage differential signal, and finally input to the AD differential input port of the main control chip.
2.2 Power supply circuit
The power supply circuit provides the various power supplies required by the smart meter, as shown in Figure 4. When the mains power is normally supplied, the power supply is output through a certain level conversion circuit to power the meter; when the neutral line is lost, the battery is used for power supply. After the software and hardware cooperate to handle low power consumption, the built-in lithium battery can be used for more than 15 years.
2.3 Pulse circuit
The pulse circuit realizes the output of pulses, which can calibrate the meter and detect errors. Q5 is the wireless output mode of pulse lamp; E4 is the optical coupling isolation wired output mode.
2.4 Storage circuit
The storage circuit realizes the measurement and time management of data and related events through EEPROM (Electrically Erasable Programmable Read Only Memory) and other storage chips, and realizes the storage of calibration parameters and power data.
2.5 Alarm circuit
The alarm circuit detects external signals and alarms. It includes the cover opening detection circuit and magnetic detection circuit. It will alarm when the cover is opened or an external magnetic field is detected.
3.Principle of reverse detection of live and neutral wires of smart meters
3.1 Adverse effects of reverse connection of live and neutral wires
1) There is a motto for the internal wiring of a three-pin wall socket: left neutral, right live, and middle ground. So after the three-pin plug is plugged in, the live, neutral, and ground wires are fixed. Moreover, the live wire of the three-pin plug is connected to the switch of the electrical appliance. Because the switch controls the live wire but not the neutral wire, it is best not to connect the live and neutral wires in reverse. Moreover, the ground wire is missing when the two-core plug is replaced, which poses a safety hazard.
2) There are two contact points on the screw-type lamp holder. The point with a small area in the middle is connected to the control line (live wire), and the point with a large screw-type area is connected to the neutral wire. If the live wire is connected to the screw-type position, the charged area is relatively large when the power is turned on, which poses a safety hazard.
3) The wiring of the single P leakage protection is also fixed with the live wire on the left and the neutral wire on the right, and the point corresponding to the N position is always in the on state. If the live wire is connected, the bottom of the switch is charged regardless of whether it is pushed or tripped, which is very dangerous.
4. Conclusion
The smart meter in this paper realizes the detection of reverse connection of live wire and neutral wire of single-phase smart meter. Through external hardware design and MCU's AD port to detect the voltage value under different wiring methods, to determine whether the reverse connection state of live wire and neutral wire occurs.