This paper introduces the composition and principle of a high-current single-phase three-wire smart meter, analyzes the characteristics of its control chip, and explains the implementation scheme of the high-current single-phase three-wire smart meter.
Keywords: high current; single-phase three-wire; smart meter
Content：
1. Overview of the electric meter solution
2. Electricity meter module
2.1 Voltage divider and voltage signal sampling circuit module
2.2 Current transformer current signal sampling circuit 1 module
2.3 Current transformer current signal sampling circuit 2 module
3. Meter function realization
3.1 Electricity accumulation function
3.2 High current metering function
3.3 Wiring method
4. Conclusion
1. Overview of the electric meter solution
This solution adopts a modular and platform-based design, and single-phase and three-phase share a development platform. It overcomes the shortcomings of only one integrated chip, the need to redesign and develop software and hardware, the long cycle, and the need to spend a long time to verify the reliability and stability. This solution has higher accuracy, reaching 0.5S level; the error is 50% of the level 1 meter. It has better fairness and input-output for power sales companies. The error consistency is better and the anti-interference ability is strong. Under various influencing quantities: including ambient temperature, voltage, frequency, and magnetic field, the error is small. The maximum current specification can reach 200A.
2. Electricity meter module
2.1 Voltage divider and voltage signal sampling circuit module
The voltage divider circuit converts the external 220V mains into a differential voltage input signal through the front resistor network R27,R28, R1, R2, R3, R9, R5, R6, R7, and inputs it to the AD port of the SOC through V3P and V3N.
2.2 Current transformer current signal sampling circuit 1 module
Specific implementation principle: The external current signal passes through the current transformer CT1 to generate a millivolt signal, which passes through the resistor voltage divider network and enters the AD sampling port 1 of the metering chip as a voltage differential signal.Among them, R37 and R39 are voltage dividers, R40 and R41 are voltage dividers, and C41 and C44 play a filtering role.
2.3 Current transformer current signal sampling circuit 2 module
Specific implementation principle: The external current signal passes through the current transformer CT2 to generate a millivolt signal, which enters the AD sampling port 2 of the metering chip as a voltage differential signal through the resistor voltage divider network. Among them, R43 and R45 are voltage dividers, R46 and R48 are voltage dividers, and C47 and C49 play a filtering role.
2.4 Power module
The power module provides various power supply voltages for each functional module. Its circuit is shown in Figure 5. The mains power is introduced from N and L and converted into a voltage of about 15V +DC_IN through the circuit. Then, after being stabilized by V3, MVDD is provided for analog power and DVDD is provided for digital power.
2.5 Pulse output module
Specific working principle: The output signal pin of the main control chip is SEC/PULSE, and the signal is isolated by the optical coupler and output to AP1 and AP2. E1 is the role of optical coupler to achieve isolation, and C24 is the role of interference removal and filtering. AP1 and AP2 can be connected to an external calibration table to achieve error calibration and detection.
Specific working principle: Y1 LCD driver chip is connected to the corresponding pins of the main control chip through 4 COM ports and other SEG segment control ports. Output control segment code data to control the display content on the LCD screen.
2.7 Storage Module
The data storage module includes storage chips U2 and U3, which store and manage data such as power. The calibration data is stored in U2, and the power data is stored in U3.
3. Meter function realization
Through modular design, the main chip and metering chip are single-phase and three-phase unified hardware design platforms. The meter functions that need to be realized are already ready for mass production. Only certain
cutting is required to achieve the output requirements of sample meters and small batch verification meters. The calibration process is a mature design solution.
3.1 Electricity accumulation function
Hardware design: The hardware design is a metering chip and a main control chip to realize metering accumulation and other functions. Directly connect the analog signal to the three analog differential input terminals of the metering chip.
Software design: The software design is to realize the software accumulation of electricity and the management function of pulse output by reading the corresponding metering data in the metering module.
3.2 High current metering function
The high current metering function means that the metering can be realized when the current is 200A, because the high current CT current transformer is used to convert the high current signal into the analog voltage differential signal allowed to be input by the metering chip, realizing the sampling function of the instantaneous current.
3.3 Wiring method
Through the coordination of specific wiring methods, structural parts and hardware,
the wiring function of single-phase three-wire is realized.
4. Conclusion
On the basis of unified software and hardware platform, through the modular design of single-phase and three-phase, the combination of two-way current sampling circuit and other circuit modules, the single-phase smart meter design with large current single-phase three-wire measurement function is realized. Only after certain cutting, the output requirements of sample meter and small batch meter can be achieved. In the design of single-phase and three-phase smart meters, it has great promotion value. The platform-based and modular design ideas can be applied in the development process of other meter products.