Does someone have in depth info on this? Brief Google lookup did show some controversy around power factor on complex wfms.

Disclaimer: maybe ten years ago, I developed "Power Quality Measurement Instruments", aside from other things like Flicker, Harmonics, Transients, these things incorporate a power meter.

So usually you measure:

- Urms and Irms over an interval of 200ms, and display as Urms and Irms.

- "Real Power" (Wirkleistung) (Watt), as U(t)*I(t) integrated over an interval of 200ms.

- "Apparent Power" (Scheinleistung) (VA) is just Urms * Irms.

The above are independent of frequency and waveform, for a line frequency power meter, the integration (measurement) interval is supposed to be a multiple of the line period (10 * 20ms or 12 * 16.7ms).

Now it comes to call kinds of power factors:

Calculate (from a FFT or DFT) the displacement power factor: that's what we call cos(phi). Applicable for sinusoidal waveforms.

From the same FFT / DFT one calculates the fundamental real and reactive power. Also applicable for sinosoidal waveforms.

To add more complexity, one can calculate all these power values for each harmonic, but this is usually not so interesting.

Fundamental means the nominal line frequency here (50Hz or 60Hz). Use a reactangular window for your FFT or DFT and synchronize your sampling frequency to the line freqency, so there's a integer number of samples within a 10 / 12 line periods window. Sample U and I simultaneously. From the FFT / DFT you get complex numbers as result, representing the amplitudes and phase relationship, from this one can calculate the mentioned values.

From the above (waveform independent) apparent power and real power one calculates the "Power Factor" - this is not the same as the mentioned "displacement power factor".

So short form:

If one says "Power factor" this can mean both "Real Power / Apparent Power" (independent of the waveform) or displacement power factor / "cos(phi)" - (power factor caused by phase angle)

If one says cos(phi) or displacement power factor (DPF), this clearly means the power factor caused by phase angle. The "power factor" (PF) can be worse than the DPF in case of distorted waveforms.

Especially SMPS can have a near 1.0 DPF but a bad (<0.5) PF.

Don't expect this from a plugin-type power meter - the good ones display real power and maybe the PF (not the DPF), the bad ones might use the DPF to calculate the real power from Urms*Irms*DPF - but often quite unreliable and not suitable for distorted waveforms. And their Urms / Irms isn't a real rms but rather a simple rectifier and the form factor applied, so more crap for distorted waveforms.