IEEE Power Electronics Magazine - June 2023 - 44

significant improvements in the operation
of a wide set of circuits and applications.
This section describes some
of these, summarized in Table I.
Magnetic designs are constrained
by trade-offs, making it impossible
to achieve optimal operation over
a wide range of operating points
with conventional components.
For instance,
in phase-shifted fullbridge
(PSFB) and dual active bridge
(DAB) converters, a high inductance
is required to achieve soft switching-and
thereby high efficiency-at
low load, but this increases the copper
loss and limits power transfer.
Dynamically adjusting
the inductance
therefore offers an additional degree of freedom
to track the maximum efficiency point. For example, the
energy saving considering a lithium-ion battery charging
cycle using a PSFB would reach 10%.
Although, switching energies of wide-bandgap semiconductor-based
devices can fall to a few percent of
their silicon counterparts, full potential of SiC and GaN
is achieved in resonant topologies, owing to the loss
Table 1. Summary of the gain expected from the use
of tunable magnetics for some applications.
-
HVDC circuit breaker
Wind generator inverter
Battery charger
−45% breaking current
−20% inverter loss
−10% loss
Magnetic designs are
constrained by tradeoffs,
making it
impossible to achieve
optimal operation over
a wide range of
operating points with
conventional
components.
reduction offered by soft switching.
However, LC-circuits have resonant
frequencies with low initial accuracy,
and possibly significant shift
due to ageing and temperature. This
is an issue when matching tanks are
required, such as in multiport converters
or wireless power transfer.
The ability to dynamically tune tanks
is then of great interest to maximize
power delivery and efficiency-as
showcased in section " use case. "
New topologies of power converter
could further benefit from
controllable magnetics. For instance,
critical conduction mode converters,
and more generally hysteretic controllers,
suffer from complex control and EMI management
due to their variable switching frequency. Online
tunable inductors would solve this issue by enabling such
converters to run at constant frequency.
The output filtering inductance of an inverter is limited
by the voltage drop across it at fundamental frequency
and nominal load. However, under reduced loading, the
inductance could be increased to keep the voltage-drop
constant. This would allow the switching frequency to be
reduced proportionally without power quality degradation,
resulting in a proportional reduction in switching
power loss. Under this control strategy, the analysis of
the annual production profile of a wind turbine located
in northern France and equipped with an IGBT inverter
shows that the potential average power loss reduction
reaches 20%, assuming a tunability of ±30%.
FIG 5 Current rise after load-side short-circuit of a HVDC transmission line: constant versus tunable line inductance. Simulation
performed with V=400 kV,I =2kA,L =20mH
DC 00 .
44 IEEE POWER ELECTRONICS MAGAZINE z June 2023

IEEE Power Electronics Magazine - June 2023

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