TIDUEM8B March   2019  – February 2021

 

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2.3.2.3.1.1 Voltage and Current Signals

For a one-voltage configuration, reverse the orientation for the line B current measurement with respect to the line-to-line voltage measurement for the power readings to have the proper sign. Instead of reversing the CT connections to switch the orientation of the line B current measurement, line B raw current samples are negated for the one-voltage configuration, which allows switching between two-voltage configuration and one-voltage configurations in software without having to rewire the CT to board connections. The test software of the design has support for storing the raw voltage and current ADC values for phase A or phase B, regardless if the one-voltage configuration or two-voltage configuration is selected.

The raw ADS131M04 samples are signed integers and any stray DC or offset value on these converters are removed using a DC tracking filter. A separate DC estimate for all voltages and currents is obtained using the filter, voltage, and current samples, respectively. This estimate is then subtracted from each voltage and current raw ADC sample.

The resulting instantaneous voltage and current samples are used to generate the following intermediate results:

  • Accumulated squared values of voltages and currents, which is used for VRMS and IRMS calculations, respectively
  • Accumulated energy samples to calculate active energy
  • Accumulated energy samples using current and 90° phase-shifted voltage to calculate reactive energy

The foreground process processes these accumulated values.