Flexible calculation method for air gap
and leakage flux reluctances
Introduction
Ex 1, 1-phase inductor
A method is presented to calculate air gap and leakage flux
reluctances. To this end, a program used for capacitance
calculations, FastCap, is used. From these capacitances, the
reluctances can be determined using the analogy between
electric capacitance and magnetic reluctance.
When using these reluctances in a
magnetic reluctance model of the core,
inductance
values
and
coupling
coefficients can be calculated more
accurately and/or faster. The method is
demonstrated and compared to other
methods in three examples.
For this simple example, the
proposed method using
FastCap is compared with the
finite element method (FEM)
and a method in which all
reluctances are determined
analytically(1).
Time [s]
Analytical
0,8
FastCap 109,5
FEM 1034,6
(1) J. Muhlethaler et al., "A novel approach for 3d air gap reluctance calculations," in
Power Electronics and ECCE Asia (ICPE & ECCE), Jeju, Korea, 2011, pp.446-452
Ex 2, 3-phase close-coupled inductor
Reluctance Model
Next to the inductance value,
the coupling between the
windings can be determined
more accurately using FastCap.
Time [s]
Analytical
0,6
FastCap
71,0
FEM 3080,4
FastCap Simulations
In the figures above, the complete
reluctance model is shown on the left. On
the right, the five FastCap simulations,
used in the proposed method to calculate
air gap and leakage flux reluctances, are
shown.
Ex 3, pot core
Coupling
coefficients
are
important for calculating the
generated DC flux in the core
when the inductor is used in a
3-phase interleaved DC-DC
converter as shown below.
Conclusion
Accurate inductance values and coupling coefficients can be
obtained using air gap and leakage flux reluctance calculations
with FastCap as shown in the examples. FastCap uses the 3D
method of moments (MoM) which is faster than the 3D finite
element method (FEM) for simple geometries. Furthermore,
only part of the geometry is taken into account for each FastCap
simulation. This leads the lower simulation times.
The air gaps of a pot core,
center air gap and outer air
gap, have a more complex
geometry compared to the
previous examples. Modeling
these with FastCap gives an
accurate estimate of the
inductance of the core with less
computational effort compared
to a full 3D FEM simulation.
Time [s]
FastCap
112,1
FEM 1018,2
The method presented in this poster is slower than analytical
methods but more widely applicable. It is still many times
faster than full 3D FEM simulations which can be of critical
importance in optimization of inductive components.
© K.U.Leuven – ESAT/Electa
Jeroen Zwysen, Johan Driesen
jeroen.zwysen@esat.kuleuven.be
EMF2013
68