Environmental Engineering Reference
In-Depth Information
primary cable frequency can be reduced into the range of available high power
IGBT semiconductors. From (Ex12.3.1.5) it is clear that primary excitation fre-
quency,
f
p
, can be traded off against secondary turns in the CWT. It is not possible
on a single run of primary cable to have anything other than
N
p
¼
1, but the moving
secondary can have multiple turns.
12.3.2 Radiated near-field power transfer
The past two years have seen a substantial rise of interest in wireless power
delivery to a vehicle. Kurs
et al.
[15] discuss the case of single-turn coil, Helmholtz
type, transmitter and receiver side coils with intervening resonator coils. In the case
of this near-field inductive coupling type of energy transfer the efficiency is on the
order of only 40%, but the power transfer distances are substantial, on the order of a
couple metres. Figure 12.7 shows the configuration when the driving side coil has a
radius of 25 cm and is excited at
f
p
¼
10 MHz.
D
>> r
x
r
p
tc
r
s
L
pr
L
sr
C
pr
A
C
sr
f
p
~ 10 mHz
R
L
U
s
Figure 12.7 Near-field power transfer with intervening resonator coils
The wireless power transfer, augmented with slightly detuned primary and
secondary side resonators, that can also have angular displacement relative to their
adjacent coil are shown by Kurs
et al.
to be capable of delivering 60 W to the load
when 400 W is pulled from the wall plug. Given a 40% efficient wireless mode
over
D
¼
2.4 m (eight times the secondary coil radius), the total transmission
efficiency is 15%. For closer spacing, the efficiency will be higher.
McKeever
et al.
[16] expanded on the work of previous investigators, includ-
ing Kurs, to analyse, model, simulate and prototype a large evanescent wave power
transfer structure similar to Figure 12.7 but with large rectangular copper coils
separated by 17 cm without the intervening detuned resonators. The rectangular
coil geometry is meant to facilitate a variable overlap, such as when a vehicle
mounted coil moves over a road bed, or garage floor, mounted transmitting coil.
The prototype system exhibited 82% power transmission efficiency, exclusive of
the primary side amplifier at 58 kHz and secondary side power conversion stage.
More recently, Keeling
et al.
[17] described a guideway track primary con-
ductor of hairpin design that is excited via a utility side converter at 10-50 kHz and
300-400 A of primary current. Ferrite core secondary side inductors are placed
along the primary cable and designed for 300 V operation at 1 kW. The compen-
sating system demonstrated that power could be corrected over a
10% to
þ
15%
variation in compensating capacitor.
