IEEE Power Electronics Magazine - June 2023 - 41

oltage controlled magnetic components,
which consist of dynamically controllable
inductances and transformers, are a promising
yet understudied technology of growing
interest. In fact, these components offer circuit
designers an additional degree of freedom to achieve
multi-objective optimization with improved Pareto fronts.
This article provides a review of some technologies that
can be used to create controlled magnetics, including
emerging technologies with high potential. Furthermore, a
list of possible applications are proposed, where these
components can provide a significant advantage in terms
of efficiency, size reduction, or controllability. Special
emphasis is laid on a use case: a 20 kW multiport dc-dc
converter in which power flow control is achieved using
voltage-controlled inductors based on partially saturable
magnetic cores.
V
Introduction
Magnetic components constitute one of the basic devices in
power electronics systems. As a matter of fact, inductors
and transformers can be used for short-term energy storage,
filtering, and to transfer power while providing galvanic isolation
between circuits [1].
Nonetheless, they remain amongst the bulkiest parts
and account for a significant share of the losses [2], [3].
Magnetic component design results from trade-offs
between a variety of parameters. For instance, in a filter,
a higher inductance value will improve the filtering,
which is related to pulse width modulation choice, but
also increases the response time and, often, the losses [4].
In some power converter topologies, inductance values
result from a trade-off between power lost in the active
and reactive devices. Capability to bear higher currents,
which are dictated by fault conditions, will also translate
to higher volume [5]. In general, inductance and conduction
losses are positively correlated. Furthermore, magnetic
component selection, either custom or off-the-shelf,
results from trade-offs between several variables such as
cost, losses, and size.
Dynamically controlled magnetics [6], which have
the capability to change their values online based on an
external control signal, constitute an opportunity for
power electronics, by bringing an additional degree of
freedom in finding a compromise among minimal size,
minimal losses, maximum filtering, limiting current rise
without compromising dynamic response, etc. After a
brief introduction on magnetics and reluctance modeling,
this article gives an overview of technologies and
physical phenomena used to create tunable magnetics. In
addition, it also provides a list of relevant possible applications,
while a use case is also detailed later on. Finally,
a conclusion closes the article.
Basis of Magnetics Design
Figure 1(a) shows a schematic of a generic inductor, composed
of the winding, a magnetic core, and an air gap. Its
equivalent reluctant model, analyzed using basic circuit
theory, can be derived by replacing the core and the air
gap by reluctances R . The winding is replaced by a magnetomotive
force (MMF) source-calculated as shown in
Figure 1(b). lg is the length of the air-gap, l is the average
length of the magnetic core, A its cross-sectional area, N
the number of turns, and the magnetic material has a relative
permeability µr -which characterises its ability to
increase or channel the magnetic flux φ .
FIG 1 (a) Physical schematics of an inductor, (b) equivalent reluctant model, and (c) inductance calculation.
June 2023 z IEEE POWER ELECTRONICS MAGAZINE 41

IEEE Power Electronics Magazine - June 2023

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