Inductive Power Transmitter
An inductive power transmitter comprising an power transfer circuit which includes a transmitter coil; and a power inverter including a plurality of control devices configured to drive the power transfer circuit; a controller configured to provide drive signals for the control devices, wherein the controller is programmed to estimate the power in the power transfer circuit; compare the estimated power to a predetermined power level; and calculate an adjustment to the drive signals based on the comparison, to adjust the power in the power transfer circuit to the predetermined power level.
1 . An inductive power transmitter comprising:
a power transfer circuit which includes a transmitter coil;
a power inverter including a plurality of control devices configured to drive the power transfer circuit; and
a controller configured to provide drive signals for the control devices,
wherein the controller is programmed to:
estimate the power in the power transfer circuit;
compare the estimated power to a predetermined power level; and
calculate an adjustment to the drive signals based on the comparison, to adjust the power in the power transfer circuit to the predetermined power level.
2 . The transmitter according to claim 1 , wherein estimated power is an estimate of the real power in the power transfer circuit.
3 . The transmitter according to claim 1 , wherein predetermined power level includes the rated output power of a receiver together with an estimate of a power loss.
4 . The transmitter according to claim 1 wherein the power transfer circuit is selected from the group consisting of
a LCL circuit,
a parallel tuned circuit,
a series tuned circuit,
a non resonant circuit.
5 . The transmitter according to claim 4 wherein the power transfer circuit is a LCL circuit, and the estimated power is based on the current through the transmitter coil and the imaginary component of the voltage across a parallel tuning capacitor.
6 . The transmitter according to claim 5 wherein the power estimate is based on the formula P in.Rx =|I p ·Im[V p ]|.
7 . The transmitter according to claim 6 wherein the current through the transmitter coil is determined based on the formula
I
p
→
=
-
j
4
V
in
π
2
(
ω
L
t
1
)
sin
(
π
D
p
)
.
8 . The transmitter according to claim 1 wherein the power transfer circuit is a series tuned circuit or a parallel tuned circuit, and the power estimate is based on current through the transmitter coil, the real component of the current through the transmitter coil, the imaginary component of the current through the transmitter coil and the RMS output voltage of the transmitter drive circuit.
9 . The transmitter according to claim 8 wherein the power estimate is based on the formula
P
in
.
Rx
=
I
p
2
·
R
r
=
I
p
2
·
V
1.
rms
3
Re
[
I
p
]
1
+
(
Im
[
I
p
]
·
V
1.
rms
Re
[
I
p
]
)
2
.
10 . The transmitter according to claim 1 wherein the power transfer circuit is a non-resonant circuit, the power estimate is based on the current through the transmitter coil and the RMS output voltage of the transmitter drive circuit.
11 . The transmitter according to claim 1 wherein the current through the power transfer coil is controlled according to a methodology selected from the group consisting of
amplitude control,
duty cycle control,
frequency control, and
phase shift control.
12 . The transmitter according to claim 1 wherein the current through the transmitter coil is decreased if the estimated power is more than the predetermined power level.
13 . The transmitter according to claim 12 , wherein the current through the transmitter coil is calculated according to the formula
I
p
.
new
=
I
p
(
P
o
+
P
loss
.
Rx
)
P
in
.
Rx
.
14 . The transmitter according to claim 1 wherein the current through the transmitter coil is increased if the estimated power is less than the predetermined power level.
15 . The transmitter according to claim 14 , wherein the current through the transmitter coil is calculated according to the formula
I
p
.
new
=
I
p
P
in
.
Rx
(
P
o
+
P
loss
.
Rx
)
.
16 . The transmitter according to claim 3 , wherein the estimated loss is: a proportion of the rated output power of a receiver, approximately 10 W, or approximately 5 W.
17 . The transmitter according to claim 1 wherein the controller determines there is a partial load present if the estimated power is below a threshold and adjusts the predetermined power level.