Application board implements 3-phase energy meter

22nd January 2021
Mick Elliott

STMicroelectronics' EVALSTPM-3PHISO application board is based on ST metering analogue front end STPMS2, application processor STPM32f42143RH, and STISO621W, which provides the galvanic isolation among the three phases in the metering application.

The board is in stock at distributor Digi-Key Electronics.

The EVALSTPM-3PHISO evaluation board implements a complete 3-phase energy meter with low-cost shunt current sensors.

Based on the STPMS2 device, a dual-channel, 24-bit second order sigma-delta modulator, this solution measures voltage and current for each phase through a voltage divider and a shunt current sensor.

Sensing circuitry and PCB layout are optimised to maximise signal-to-noise ratio for optimal accuracy.

The STPMS2 oversamples the signal using a 4 MHz clock distributed in a synchronized way by the microcontroller and outputs voltage and current sigma-delta bitstreams, multiplexed on the same pin.

The two-wire communication between the STPMS2 modulator and the MCU is isolated by STISO621W, 6 kV galvanic isolated dual-channel bidirectional interface, allowing up to 100 Mbps rate and low pulse distortion (<3 ns) for safe and fast data transfer between isolated domains.

The FW embedded in the solution exploits the DFSDM filters of the STM32F413RH to convert the six bitstreams into 24-bits voltage and current data at a 200 µs rate.

All the metrology parameters are computed in real-time on a 200 µs basis.

Two LEDs are available for active and reactive pulses generation.

The FW also implements a virtual com port communication to easily access the internal parameters to read metrology data, modify the internal configuration for high flexibility of the application, and calibrate the board.

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