Total Harmonic Distortion fundamental frequency clarification
*My question is: if the input voltage frequency is 100Hz, would I use 100Hz as the fundamental frequency, or would I use 200Hz, since the power waveform would be P = IV = sin(100t)sin(100t) = sin(100t)^2, which has a frequency of 200Hz.
Use 100 Hz, since the 200 Hz rectified power signal is what you get from a 100 Hz sine input (and only a 100 Hz input). Consider that the first harmonic of 100 Hz is 200 Hz, but the power waveform is at 400 Hz. Each unique input frequency has a unique power frequency, so just reference everything to the input frequencies.