Frequency inverters produce high frequency spikes on the side of the power input. This is relevant when designing an emergency power supply for a site with lots of VFD, apparantly it is advised to install far bigger alternators so the alternators don't get damaged by these spikes (So if for 100 kW worth of VFDs you would install a 200kW alternator on a 100kW engine). These spikes are explained by how an FI works:
Image source, instead of physical switches there are thyristors or similar.
The "switches" switch with the output frequency or far faster, to create the desired frequency and output voltage via pulse width modulation. This rectangular wave form of course creates hih frequency signals.
Now here are my questions:
The DC Bus is mostly a capacitor, so it should essentially short circuit high frequency signals. Why, then, do we have high frequency signals on the input side?
Should it not be relatively easy to either separate the FI from the power supply with a band pass (50 or 60Hz) to block high frequencies, or protect the alternator in a similar fashion?
