I am having some problems with an active rectifier (AFE unit) that produces a 8 kHz and a 50 Hz component on my DC.
We have bult in a normal standard Low-pass filter that deals with the 8 kHz, so no problems there.
But we still have the 50 Hz problem (its a software issue in the AFE inverter itself, and therefore not easily solved fast).
Its not much, 600mA rms when charging with 50A@600VDC but apparently still enough to mess up the battery that it is charging.
The problem is that the battery that the AFE is charging can be considered a capacitive load. So the dampening effect on the low pass filter for it to take care of the 50Hz is quite much.
We solved it with putting in a standard power resistor in series before the load, so with a normal power resistor on 1 ohm we can filter the 50Hz signal also. But that is not so economical, just burning off a cupple of hundreds of watt.
So the the next step is to get a 3,2 mH inductor to create 1 ohm of resistance@50Hz and that will we test this week.
But what I am thinking about is the voltage spike from this inductor,
we have capacitors that is sitting between + and – before and after the inductor. Approx 1 mF on each side.
Since a capacitor is a low inductance on rapid voltage changes, they should take care of the voltage spike.
The voltage spike can be simply calculated with E=I x R.
Since the capacitor is the resistance here, it is frequency dependent of course but we can still say that the spike will se the capacitor as a low resistance.
But am I correct in my thoughts here, that capacitors between + and – will take care of the spike?
And how do i calculate the amount of current/energy, that will go into the capacitor?