3phase PI filter inductors and caps

The aim of the input filter is normally to reduce conducted emissions passing to the source, although it also acts in transient suppression. A three-phase delta version will require impedance consideration also between source V6 and V8 in your model.

If your source is captive, this filter convention may not apply, but check your generator's reaction to HF ripple (increased losses) and any resulting radiated emissions.

The relevant conducted interference frequencies are 150KHz and up - you can assume, as a starting point, that the interference is maximum at the peak AC input, as this likely corresponds with peak input ripple and worst-case inductor droop.

The conventional relevant radiated emissions are 30MHz and up - these are poor subjects for this modelling method.

What ARE you trying to do?

I think you need to do a first-order approximation of ripple current amplitudes requiring suppression (to meet your unstated aims), before assuming that inductors in the microhenry range will serve any useful purpose.

RL

Hi,

I am mainly trying to decrease the RMS current in the generator as well as decrease audible noise from the pulsed current being extracted from the generator. Also evening out the current draw as much as possible will create a smoother running generator. With the simple voltage source model for the generator in ltspice, the generator phase RMS current goes from 10.39Arms (no cap/coil filtering) to 8.87Arms when the filter is used.

I would like to add a more realistic generator model to ltspice, I know the phase DC resistance and inductance, is it realistic to just add a series inductor with DC resistance to each of the phase voltage sources?

In the future I would like to use 3phase active power factor correction to change this phase current waveform:

into a true 3phase sine wave and reduce the RMS current so that more power can be extracted from the generator. What would be the difference in the RMS currents in this case, is that proportional to the amount of power able to be extracted without overheating?

cheers, Jamie

If you're trying to get a ballpark justification of whether to use PFC or not, your RMS current reports from the PFC-free situation should tell you what you need to know. I advise you to experiment with more realistic (larger?) values of L8 and C10, to observe effects of I2 waveform, and to pay more attention to controlling power delivered to the load (for consistency between iterations).

When similar (larger) L values show up in L7, 9 and 11 positions, they will benefit from the flux reversal produced by the AC source.

There is a 3ph transformer in Ltspice that might make generator modeling easier (see the yahoo group circuits collection), but the generator characteristics could be represented as simply as you want to make them - the presence of more effective filters will make these characteristics more increasingly irrelevant. Rs and Ls of each phase winding can be extracted from simple regulation tests (into static loads), if not stated in the part spec or manual. Use the actual generator winding arrangement - don't substitute wye for delta if the source is delta, and don't ignore the common wye terminal, if present.

RMS calculations may be affected by the min time step (and speed) of the simulation - be sure you have a simulation that has reached equilibrium and that all start-up transient effects are passed. This may take many line cycle periods.

RL