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Modelling And Control Of Inductive Power Transfer System
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Desktop peripherals and mobile phones
The first
inductive power transfer studies dedicated to mobile phones were
realized in the early 2000s. For example, the prototype of a small
platform allowing recharging a mobile phone battery is proposed in [33].
A picture of the prototype is given in Fig. 1.4(a). The coreless
transformer is made of printed circuit board (PCB) coils that have to be
precisely aligned to start the charging process.
The operating
frequency is ranged between 920 and 980 kHz, and the power transferred
to the battery is 3.3W, but the transformer has been tested to transfer
up to 24W.
More recently, many desktop applications have been
marketed. An example of existing inductive power transfer application is
the battery-free optical mouse from A4 Tech [8] (c.f.Fig. 1.4(b)).
Instead of batteries, the mouse uses inductive CET to provide energy via
the included mouse pad, which is connected to a computer USB port. Mice
are very low powered devices, generally the amount of transferred power
is less than 1W. In a similar way, the HP Touchstone is a small Dock
station powered by the USB port and can transfer the power (5W) to
recharge a phone or a Palm device [6].
Concerning systems involving
inductive power transfer to multiple devices, many products are
commercially available. They remain in this category of fixed position
charging because they do not offer the possibility to supply the devices
freely placed on the whole surface, but only at predefined places. For
example, the first inductive power transfer table developed by Fulton
Innovation under the denomination of eCoupledallows transferring power
to multiple but fixed devices [5]. This application has the ability to
communicate with the devices thanks to a process specifically developed
by Fulton, which allows transferring the exact amount of power required
by each load on the platform.
The common points to these applications
are the low power devices that they can supply (generally less than
5W), the predetermined position of the devices on the platform and the
integrated intelligence that detects and recognizes the devices.
Figure
1.4: (a) One of the first prototypes involving an inductive power
transfer system to charge a mobile phone [34]. (b) Inductively charged
mouse from A4 Tech [8]. (c) Portable Powermat station that allows to
charge up to three devices simultaneously.
Electric vehicles
A new
niche market that may explode in the future for fixed positioning
inductive power transfer systems is the electric vehicles charging. Many
researches are ongoing in this domain [49], prototypes are being tested
by Siemens or BMW [4], and some applications are on the verge to be
commercially available [19]. For instance, the typical specifications
for a prototype consist of transferring a power of 30 kW to the vehicle
battery. The operating frequency is 20 kHz. The main issue here comes
from the large airgap of 45mmwhichmakes the coupling low.
1.4 Thesis structure
The thesis presents the design and modeling of inductive power transfer system.
It
is divided into six main chapters in addition to the introduction and
conclusion. In the present chapter is given a general introduction on
inductive power transfer system with a state of the art of the field and
the main objectives of the thesis research.
Chapter 2 is dedicated
to the modeling of the coreless transformers. First the “magnetic†part
of the modeling allows to calculate resistances and inductances of the
coils based on the geometry of the coreless transformers. Then the
“electric†part allows to determine power magnitudes, current and
voltage intensities, based on the resolution of an equivalent electric
circuit of coreless transformers. Concepts of resonance and reactive
power compensation are introduced then.
Chapter 3 deals with the high
frequency effects in the coils. After defining the problem and
providing the main inherent hypotheses to resolve it, two methods to
compute the AC resistances that vary with the frequency are provided.
The first one is based on the resolution Of Maxwell’s equations in a
particular case, and the second one is derived from finite-element
method (FEM) simulations. The issue of losses in the coils is then
addressed and the impact of the high frequency is discussed.
Chapter 4
is probably the most important one because it provides innovative tools
to design and optimize different inductive power transfer systems. In
the first part, a sensitivity analyzis of the main parameters of
coreless transformers is presented. This allows to identify the ones
that need to be optimized, as well as their variation range. In the
second part, the optimization method itself is described. The main
concepts of genetic algorithms and, in particular, multi-objective
genetic algorithms are introduced. The implementation of a new algorithm
based on a very common one (called NSGA-II) is then presented. It
integrates notably several improvements that make it highly efficient.
It is then tested with some often-used functions for multi-objective
algorithms evaluation, and successfully applied to different inductive
power transfer system problems.
Chapter 5 presents the different
prototypes built during this thesis work. The design the electronics are
discussed in details. Notably, for the inductive power transfer system
table, the strategy used to control the detection and the local
activation of the table is thoroughly presented.
Chapter 6 ends with a
general overview of the results obtained in this thesis. The
perspectives and main contributions are also analyzed.
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