Ti energy library msp430 phase to phase voltage calculation

Hi Anand,

We don't have a library to do phase to phase that I am aware of, but I can walk you through the changes you need to make to the library to implement phase to phase measurements.  I've also notified some of our metering experts to help assist if necessary.

In the metrology-background.c file, there is a function called per_sample_dsp() that runs inside of the ADC ISR for every sample.  In this function, the sample gets saved to V_sample with this line of code (where 'ph' is the phase that is being manipulated at that time):

V_sample = adc_v_buffer[ph];

Then a few lines later, the value gets squared as part of the root-mean-square calculation:

#if defined(SAG_SWELL_SUPPORT)
    sqac_voltage(phase->metrology.V_sq_cycle, V_sample);
#else
    sqac_voltage(phase_dot_products->V_sq, V_sample);
#endif

In between these lines, you should add the modification that compares V_sample to the sample for the next phase by subtracting it out.  E.g., for phase 0, you should subtract phase 1; for phase 1, subtract phase 2; and for phase 2 subtract phase 0.  Then that this difference and square it, then continue the rest of the library.

Mike

The next version of the energy library will have the option to measure phase-to-phase voltages using the differencing technique Mike described. It works well, but it does assume time alignment between the ADCs. If there are significant differences between the phase shifts caused by the three voltage ADC input filters, due to component tolerances, this might compromise accuracy. It shouldn't be too serious an issue, but it is something to be aware of, and check.