As an important part of the smart grid, smart energy meters are constantly evolving, and the corresponding chip technology is also increasing. Taking the single-phase smart energy meter with the largest market demand as an example, its technical development is mainly reflected in the following aspects:
The measurement accuracy requirements are getting higher and higher, and the current range is getting wider and wider. From the previous 5 (20) A to the current 5 (60) A, and then to 1 (100) A, the early metering chip can not meet the current power. Table design requirements, high-precision, wide-range metering chips are widely used.
More and more data and event processing requirements make the MCU's computing power and program capacity continue to increase. Traditional 8-bit MCUs will gradually be replaced by 32-bit MCUs.
As the final node of the smart grid, the smart energy meter has more and more strong data communication requirements. The external communication methods include RS485, PLC and infrared, and each communication interface is required to be independent and can run at the same time; this requires the design of the energy meter. The MCU has a rich hardware communication interface.
IDT's 90E46 is the trend to comply with the smart energy meter, the industry's first integrated hardware high-precision wide-range metering module, ARM 32-bit Cortex M0 high-performance low-power MCU core, LCD driver and temperature compensation The high-precision real-time clock (RTC) is a true system-on-chip (SoC). In the measurement dynamic range of 5000:1, the active energy accuracy is better than 0.1%, the reactive energy accuracy is better than 0.2%, and only a single point calibration is required; the real-time clock error is less than ±0.5 seconds/day.
90E46 chip and hardware design
90E46 chip introduction
The 90E46 is the industry's most integrated high-precision, wide-range single-phase energy metering SoC. It integrates the ARM Cortex-M0 microprocessor, LCD driver and temperature compensation with IDT's existing wide-range metering analog front end (AFE). The functional high-precision real-time clock (RTC) reduces the number of components in a single-phase energy meter, simplifies design and production processes, and reduces material costs and inventory management.
The 90E46 has the following features:
32-bit ARM Cortex M0 core, 6KB RAM, 128KB Flash;
4 independent UARTs, UART0 supports infrared modulation (IR), UART3 supports hardware ISO7816 protocol;
Integrated hardware watchdog (WDT) with interrupt support;
2-way 25-bit general purpose PWM;
1 channel 14-bit low power PWM for infrared wake-up;
2-way 16-bit timer
Up to 45 GPIOs, 23 support 5V input;
4 external interrupt inputs for system wake-up;
2 12-bit GPADCs with integrated high precision reference voltage source and threshold comparison circuit;
1 low-power voltage comparator for chip power-down detection;
The chip supports an operation mode, a sleep mode, a standby mode, and an LCD display mode;
Built-in PLL circuit, the external only needs 32.768kHz crystal to work;
Comply with IEC and ANSIC standards; can be used for single-phase 1st, 2nd active energy meter and 2nd level reactive energy meter;
In the measurement dynamic range of 5000:1, the active energy accuracy is better than 0.1%, and the reactive energy accuracy is better than 0.2%;
The temperature coefficient of the on-chip reference voltage source is typically 6 ppm/ °C;
Electrical parameter measurement: voltage/current RMS, average power, frequency, power factor and phase angle reference error is less than 0.5%;
Only a single point calibration is required over the entire dynamic range for 50Hz and 60Hz grids;
The on-chip temperature sensor has an accuracy of ±1 °C in the range of -40 °C to +85 °C;
On-chip hardware RTC with frequency compensation. Compensation range: -3900ppm to 3900ppm, compensation accuracy ±0.12ppm;
Built-in 4Com & TImes; 34Seg / 6Com & TImes; 32Seg / 8Com & TImes; 30Seg LCD driver with bias voltage generation circuit;
Working temperature: -40 ° C ~ +85 ° C;
TQFP100 green package.
The functional block diagram of the 90E46 is shown in Figure 1:
Figure 1 90E46 functional block diagram
hardware design
The 90E46 uses a highly integrated chip design technology that requires only a small number of devices externally to achieve minimum system functionality. The entire MCU small system is shown in Figure 2:
Figure 2 90E46 small system circuit
Calibration and software design of wide-range energy meter
Measurement/metering calibration
With the 90E46 design of the single-phase energy meter, only a single point calibration at the Ib current point is required to ensure metering accuracy in the 5000:1 dynamic range. For the 1(100)A meter, it can be calibrated at 5A (or 10A), which also satisfies the measurement accuracy over the entire current range. The entire school process is shown in Figure 3:
Figure 3 90E46 calibration process
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