Environmental Engineering Reference
In-Depth Information
periodically. When the RLC circuit is set to operate at its resonant frequency,
the complex part of the circuit's impedance, which is expressed as
j
1
Z
=
R
+
L
−
(6.3)
C
becomes zero, so the impedance of the electrical circuit is at its minimum,
Z
R
.Assuch, it is desirable to design the RLC circuit to operate at its
resonant frequency, as expressed by
Equation 6.2
, by selecting the appropriate
L
and
C
based on the construction of the coils and the capacitors.
In this WPT research work, the objective was to explore different ways
to improve the efficiency of the WPT technique operating in the strongly
coupled regime. The efficiency
=
of the WPT system with magnetic resonance
in accordance to the coupled-mode theory is a function of the coupling-to-loss
ratio
/
, where
is the coupling coefficient of the coils and
is the intrinsic
loss rate, and it is expressed [163] as
W
D
2
S
D
=
1
D
2
(6.4)
1
D
S
D
+
W
+
W
2
+
where the source and device are identified by subscript
S
and
D
,respectively,
and an external load (subscript
W
) acts as a circuit resistance to the connected
device. Referring to [163], Kurs et al. state that the efficiency of the WPT
system is maximized when
2
/
S
D
)]
1
/
2
.Inaddition, for two
W
/
D
=
[1
+
(
identical coils,
S
=
D
=
, the efficiency of the WPT system can thus be
expressed as
2
1
2
2
+
2
=
1
2
(6.5)
1
1
1
+
2
2
+
2
+
+
+
2
2
2
For the WPT system to be efficient, the magnetic fields of the coils must be
strongly coupled such that the coupling coefficient of the coils
is high and
the intrinsic loss rate
1, and the efficiency
of the WPT system with magnetic resonance expressed in
Equation 6.5
can
be further deduced as follows:
is low. If that is the case,
/
=
1
≈
1
(6.6)
+
Hence, to maximize the efficiency of the WPT system, one important factor
to be considered is the coupling coefficient
of the coils [163], which is given
by
M
2
√
L
1
L
2
=
(6.7)
Search WWH ::
Custom Search