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STMicroelectronics EVALSTPM-3PHISO Evaluation Board implements a complete three-phase energy meter with low-cost shunt current sensors. The solution is based on the STPMS2 device, a double channel, 24-bits second-order sigma-delta modulator, measuring voltage and current for each phase through a voltage divider and a shunt current sensor. Sensing circuitry and PCB layout are optimized to maximize the signal-to-noise ratio for optimal accuracy. The STMicroelectronics STPMS2 oversamples the signal using a 4MHz 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 STPMS2 modulator and MCU is isolated by STISO621W, a 6kV galvanic isolated interface, allowing up to 100Mbps rate and low pulse distortion (< 3ns) 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 200µs rate. All the metrology parameters are computed in real-time on a 200µs 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, to modify the internal configuration for high flexibility of the application, and to calibrate the board.
