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Modelling And Control Of Inductive Power Transfer System
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1.2.2 Technical and industrial background
More and more electric applications require an energy transfer without wires and contacts.
Especially
in the domain of desktop applications such as computer peripherals,
wireless technologies (Bluetooth, ZigBee, RF, IR,WiFi) that allow
transfer of information are very trendy, while the supplying process
uses massively wires or batteries. In a desktop environment, removing
the cables between the power source and electronic devices would be
convenient. It would allow to gain a certain amount of place and to
clean the surface from wires pollution.
In this context, the
contactless energy transfer by inductive coupling meets more and more
success. Some products are already available for a few applications,
such as mice or mobile phones. However, a full platform enabling to
supply simultaneously several consumers is still not to be reported.
In
the framework of collaboration between Logitech SA and the Laboratory
of Integrated Actuators (LAI), inductive power transfer systems are
studied for notebook and desktop applications. This collaboration is
divided into two different practical applications:
1. The inductive
notebook charger is aiming to realize the prototype of a inductive power
transfer system from a platform to a static notebook. The said platform
is a product already available on the market under the commercial name
Alto (Fig. 1.2);
2. The Inductive Power Transfer table is aiming to
realize a prototype of a inductive power transfer system embedded in a
table in order to supply multiple desktop peripherals.
Logitech [9]
is a Swiss company developing and marketing products such as peripheral
devices for PCs, including mice, keyboards, loudspeakers, microphones
and webcams. They are responsible in the above-mentioned projects for
providing the equipment and sharing their know-how on hardware and
manufacturing of electronic peripherals.
Figure 1.2: Pictures of the Alto platform. (a) Without notebook [1]. (b) With notebook [2].
1.2 Problem of Statement
Inductive
power transfer systems can be classified into two categories. The first
one concerns fixed position systems wherein the devices to be supplied
are static. The second one concerns the free position systems involving
devices that can be freely moved on the charging surface. With such a
definition, it is obvious that the inductive notebook charger belongs to
the first one and the Inductive power transfer table to the second one.
1.3.1 Fixed position systems
The
fixed position system is the simplest inductive Inductive power
transfer method. Nowadays, it involves almost all the existing
industrial applications. It usually charges one load and the energy is
transferred from a single primary coil to a single secondary coil.
Furthermore, both coils have to be approximatively the same size and
well aligned to ensure a good mutual coupling, a sufficient amount of
transferred energy and a good efficiency.
Induction cookers
Fixed
Inductive power transfer is traditionally the method used in induction
cookers, except that the secondary coil is replaced by the cooking
vessel made of ferromagnetic and conductive metal. The initial
researches and patents date from the early 1900s, but the first
production of induction cookers was performed in the 1970s by the
Westinghouse Electric Corporation[15].
The principle of the induction
heating is shown in Fig. 1.3. The magnetic field generated by the
primary coil creates Eddy currents in the pot that cause the heating
Joule effect. The wires of the primary coils generally exhibit a flat
and spread geometry in order to enhance the distribution of the magnetic
field that reaches the cooking vessel. The transferred power is in the
order of 1 to 2 kW and the operating frequency is situated in a range
from 20 kHz to 50 kHz.
Figure 1.3: Principle of an induction cooker
Electric toothbrushes
Inductive
power transfer is interesting for applications that require no exposed
electrical contacts, such as devices that are used in a moist
environment or even immersed in water. Since the early 1990s,
rechargeable toothbrushes (for example from the Oral-B brand [7]) use
this technology that allows to enclose and therefore fully insulate the
wires. It gives the advantage to protect the user against electric
shocks due to apparent contacts and to prevent short-circuits that could
damage electronics. The system generally includes a ferromagnetic core
that increases the coupling between the coils. The operating frequency
is around 10 kHz or more, and the transferred power is between 10 and
15W. Similar inductive power transfer systems are also integrated into
electric shavers.
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