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 manifested 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 measurement chip can no longer meet the current energy Table design requirements, high-precision, wide-range measurement chips are widely used.
Data and event processing requirements are increasing, which makes the MCU's computing power and program capacity continue to increase, and the traditional 8-bit MCU will gradually be replaced by 32-bit MCU.
As the final node of the smart grid, the smart energy meter has increasingly stronger data communication requirements. The external communication methods include RS485, PLC, and infrared, and each communication interface is required to be independent of each other and can operate simultaneously; this requires MCU has rich hardware communication interface.
IDT's 90E46 is in line with this development trend of smart energy meters. The industry's first integrated hardware high-precision wide-range measurement module, ARM 32-bit Cortex M0 high-performance low-power MCU core, LCD driver and temperature compensation function The high-precision real-time clock (RTC) in a true system-on-a-chip (SoC). In the measurement dynamic range of 5000: 1, the accuracy of active energy is better than 0.1%, and the accuracy of reactive energy is better than 0.2%, and only one-point calibration is required; the real-time clock error is less than ± 0.5 seconds / day.
90E46 chip and hardware design
90E46 chip introduction
90E46 is the industry's most integrated high-precision wide-range single-phase energy measurement SoC, based on IDT's existing wide-range measurement analog front end (AFE), integrated ARM Cortex-M0 microprocessor, LCD driver and temperature compensation The functional high-precision real-time clock (RTC) can reduce the number of components of single-phase energy meters, simplify the design and production process, and reduce the cost of materials and the difficulty of inventory management.
90E46 has the following characteristics:
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), support interrupt function;
2-channel 25-bit general-purpose PWM;
One 14-bit low-power PWM for infrared wake-up;
2 16-bit timers
Up to 45 GPIOs, 23 support 5V input;
4 external interrupt inputs can be used for system wake-up;
2-channel 12-bit GPADC, integrated high-precision reference voltage source and threshold comparison circuit;
1 way low power consumption voltage comparator, used for chip power down detection;
The chip supports running mode, sleep mode, standby mode and LCD display mode;
Built-in PLL circuit, external only need 32.768kHz crystal to work;
Comply with IEC and ANSIC standards; can be used for single-phase Class 1, Class 2 active energy meters and Class 2 reactive energy meters;
The accuracy of active energy is better than 0.1% and the accuracy of reactive energy is better than 0.2% in the dynamic range of measurement of 5000: 1;
Typical temperature coefficient of on-chip reference voltage source is 6 ppm / ℃;
Electrical parameter measurement: the reference error of voltage / current effective value, average power, frequency, power factor and phase angle is less than 0.5%;
Only one-point calibration is needed in the entire dynamic range, which can be used in 50Hz and 60Hz power grids;
The on-chip temperature sensor has an accuracy of ± 1 ℃ in the range of -40 ℃ ~ +85 ℃;
On-chip hardware RTC with frequency compensation function. Compensation range: -3900ppm to 3900ppm, compensation accuracy ± 0.12ppm;
Built-in 4Com & TImes; 34Seg / 6Com & TImes; 32Seg / 8Com & TImes; 30Seg LCD driver, including bias voltage generation circuit;
Working temperature: -40 ℃ ~ + 85 ℃;
TQFP100 green package.
The functional block diagram of 90E46 is shown in Figure 1:
Figure 1 90E46 functional block diagram
hardware design
90E46 uses a highly integrated chip design technology, and only a small number of devices are needed to achieve the minimum system function. The entire MCU small system is shown in Figure 2:
Figure 2 90E46 small system circuit
Calibration and software design of wide-range energy meters
Measurement / metrology calibration
The single-phase energy meter designed with 90E46 only needs to be calibrated at the Ib current point to ensure the measurement accuracy in the dynamic range of 5000: 1. For 1 (100) A energy meters, the meter can be calibrated at 5A (or 10A) current, which can also meet the measurement accuracy in the entire current range. The entire calibration process is shown in Figure 3:
Figure 3 90E46 calibration process
Description
-Contact Resistance:≤50mΩ
-Insulation Resistance:≥100mΩ
-Dielectric Strength:1,500V,
-1min Electronic Life:10,000 cycles
-Operating temperature:T120
-Rating current/voltage:6A 250V AC
Features
â—† Small Compact Size, high reliability
â—† Micro contact gap,high speed operation,high sensitirity,Micro operatizon travel.
â—† Long life & high reliability
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