Re: [femm] AC and DC currents in FEMM? Is this possible?

[David Meeker <dmeeker@xxxxxxxx>]

daniel_handloser wrote:

> Hello
>
> Can I simulate both, AC and DC currents in one model? I've only found
> that I can describe the current with a phaser which turns with the
> frequency specified in "problem".
>
> We are three students and try to build a magnetic levitation vehicle
> like the transrapid (.de) with a linear motor. For the levitation we
> need DC-current in the rotor and for the propulsion we need a 3-phase-
> ac-current in the long-stator.
>
> thanks very much for answers, Dani
FEMM currently addresses only DC problems and AC problems in which the 
amplitude and phase of the fundamental only is considered. 

In many maglev systems, the suspension and propulsion are meant to be 
separate magnetic circuits, so there may be no need to analyze both in 
the same finite element simulation (although dynamics of the two systems 
may interact in funny ways, because they are both pushing on the same 
body). Rather than trying to model everything all at the same time via 
finite elements, it is better to start with an analytical or circuit 
model that captures the operation of the suspension and propulsion and 
the interatction between them. The finite element analysis is then used 
both as a design verification/optimization tool and/or to determine 
parameters and so forth in the analytical model that are hard to 
estimate via circuit theory. This analytical model can then be used for 
the purposes of controller design and dynamic simulation.

Dave.

P.S. -- beware of transverse edge effects that aren't captured by 2D 
models when you are thinking about the design of your motor. These can 
have a significant effect on performance, especially for linear 
induction motors (i.e. secondary resistance is a lot higher than you'd 
expect from a 2D model, and there's extra associated leakage inductance).

--
David Meeker
dmeeker@xxxxxxxx
http://femm.berlios.de/dmeeker