I have a MCU equipped with a single ADC and a single S&H (Sample and Hold) circuit. The board where the MCU is placed has several inputs (let's say 3 x currents, 3 x voltages). The MCU is programmed to sample each input at 1 kS/s. Since it has a single ADC, the ADC sampling frequency is at least 6 kS/s (due to the fact we have 6 inputs), and the ADC input is multiplexed on the various input signals sequentially.
I wish to calculate active power (single-phase and/or three-phases), but unfortunately the ADC has a single S/H, and hence the sample of the voltage and the sample of the current are not taken at the same time.
The best solution would be to use an MCU with several ADCs sampling simultaneously, or an MCU with one ADC but several S&H circuits.
Nevertheless is there some way to calculate active power accurately (multiplying the instantaneous voltage and current samples) with single ADC and single S&H, for instance through linear interpolation (to align the current and voltage samples to the same instant)?
Best Answer
You can do this digitally by retarding or advancing either voltage or current to make them align temporally. You just need a small buffer for holding values and calculate the in-between value you need. The more values you use in your interpolation routine the better the result. I'd start with trying two values and linearly interpolating to see what kind of error you get. Because voltage is more predictable than current (more sin wave ish) I'd interpolate that waveform to make it align with current.