Parallel multicell converters (often referred to as interleaved converters) allow reducing the total current ripple
by summing n phase-shifted phase current ripples. InterCell Transformers are special magnetic devices allowing to
obtain the ripple reduction in each phase. To obtain this result, they combine two main functions:
- they smooth the current ripple and, to this extent, behave as inductors,
- they couple the phase currents and, to this extent, behave as transformers.
Because of this inherent hybrid nature, their design is different from both the design of an inductor and the design of a transformer,
so that a specific design method needs to be established for such devices.
The main difficulties of this design is that parameters that are generally of lesser importance are key parameters for ICT:
- the leakage inductance is governed by flux lines flowing along a complex 3D air path, so it is difficult to evaluate it accurately;
underestimation of this parameter is dangerous because it implies underestimation of the peak induction,
and overestimation implies underestimation of the current ripple,
- the current ripple at n times the switching frequency may generate uneven current densities in the conductor and the equivalent
resistance of the windings needs to be accounted for to evaluate the copper losses,
- the triangular fluxes generated by each phase can combine into complex waveforms in the different parts of the core and
these complex waveforms must be accounted for when evaluating the core losses.
For all these reasons, specific design methods need to be developed for the design of ICTs. An example of such a design tool using
constrained optimization routines is described here.
Main Design Interface
Graphic User Interface for ICT Design using constrained optimization routines
Refinement of conductor losses using FEMM
Automatic connection to 2-D finite element software to check inductances and resistances
at the different relevant frequencies and obtain a better evaluation of the conductor losses
Refinement of Core losses using iGSE (improved General Steinmetz Equations)
Determination of real flux waveforms in the different core legs and evaluation of core losses with iGSE
to account for non-sinusoidal waveforms
The simplified conductor and core loss models used in the analytic model are tuned to match FEMM and BvsT results;
a second optimization is run with this refined model.
Optimisation with parameter sweep
This automatic desgn can be processed for different sets of parameters, which can especially be usefull
to evaluate the influence of some discrete parameters: core material, for example, but even more important,
the orientation of the winding (vertical | horizontal), or the type of ICT (Cyclic cascade | monolithic | linear), etc.
Looking for a skilled volunteer !
We would like to make these routines available and
we are looking for a volunteer to make this matlab model available on-line.
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We can also run this model for you to match your specifications.
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