Voltage
The voltage signal has both a dc offset and ac component. In electricity measurement, the dc offset is filtered out, and the ac signal is extracted.
There is a phase difference between the current sample and the voltage sample. This is mainly caused by the current transformer, the analog front end circuit, and the sequential sampling process. A simple finite impulse response (FIR) filter is used to remove this phase difference by adding a fractional delay on the voltage signal. Because the current sample is delayed by one sample, by adding the right amount of delay, the phase compensation can be both positive and negative.
The voltage signal is selected for this fractional phase adjustment function, because it is normally a
large-amplitude signal and has little harmonics content. These features make it easy to design a single-tap delay filter.