Note: Descriptions are shown in the official language in which they were submitted.
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WO 03/085797
PCT/EP03/01099
DEVICE FOR THE INDUCTIVE TRANSMISSION OF ELECTRIC POWER
The invention pertains to a device for the inductive transfer of electrical
energy in
accordance with the preamble of Claim 1.
Such a device serves for the transfer of electrical energy to a movable
consumer
without any mechanical or electrical contact. It comprises a primary and a
secondary part
that are electromagnetically coupled in a way that resembles the principle of
a
transformer. The primary part comprises a feed electronic system and a
conductive loop
that is installed along a certain stretch. One or more consumers and the
associated
consumer electronic systems form the secondary side. In contrast to the
transformer, in
the case of which the primary and the secondary parts are coupled as closely
as possible,
one is dealing here with a loosely coupled system. This is possible as a
result of a
relatively high operating frequency in the kiloHertz range. In this way, even
large air
gaps of up to several centimeters can be bridged. The operating frequency on
the
secondary side is hereby arranged to be the resonance frequency of a parallel
oscillatory
circuit that is formed by the parallel connection of a capacitor to the
consumer coil.
Freedom from wear and from maintenance and safety with regard to touching and
ready availability are included among the advantages of this type of energy
supply
system. Typical applications are automatic material transportation systems in
manufacturing technology, and also personal transportation systems such as
elevators and
electrically driven buses.
A basic circuit diagram of the consumer side is described in WO 92/17929, and
is
illustrated in simplified form in Figure 1. A rectifier 1 is connected
downstream of the
consumer inductance L1 and the capacitor C1 that is connected in parallel
thereto in order
to form an oscillatory circuit, and a switching regulator of known type
comprising an
inductance L2, a diode D1, a capacitor C2, and an electronic switch S as well
as a
regulator 2 are hooked up to the rectifier. The regulator 2 comprises, in
essence, a voltage
reference and a comparator, which closes the electronic switch S via the
control line 3
when the voltage across the capacitor C2 exceeds a first predetermined value,
and opens
it [the electronic switch] when it [the voltage] falls below a second value
that is only a
little below the first [value], as a result of which the voltage UL across the
capacitor C2
and the load 4, which is hooked up in parallel thereto at the terminals A and
B,
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approximately adopts a predetermined target value. The load 4 is typically an
electrical
drive system.
In many applications, a control electronic system has to be supplied with
electricity in addition to the main load 4 in the form of an electrical drive
unit, wherein
the necessary voltage levels differ considerably. Whereas a typical value for
the voltage
for the supply of electricity to the drive unit amounts to approximately 560
V, the
voltages in the control electronics region are more than one order of
magnitude lower,
e.g. 24 V. A possible route for the provision of a second, significantly lower
output
voltage is to connect a DC transformer to the terminals A and B in parallel to
the main
load 4. Such DC transformers that are being spoken of here for the conversion
ratio of,
e.g. 560 V to 24 V are, however, expensive [to manufacture] and are therefore
costly.
Another route is proposed in DE 100 14 954 A1 that forms the basis of the
preamble of Claim 1. A second secondary coil is provided on the consumer core
in order
to obtain a second, significantly lower DC voltage, and this secondary coil is
connected
to a second rectifier. Although this is not mentioned in the quoted
specification, a second
regulator will probably have to be connected downstream of the second
rectifier in order
to stabilize the voltage, as a result of which the consumer electronics system
is effectively
duplicated at the low voltage level. The necessity of applying a second
secondary coil on
the consumer [side] also limits design freedom in the construction of the
consumer [side].
A high voltage generator for the production of a high voltage in the kilovolt
range
for the anode of a cathode ray tube is known from US 6,005,435 in which an RC
parallel
component, which is needed on the output side for subdividing the output
voltage in the
form of a regulatory parameter with a high flank steepness, is formed by means
of the
serial connection of two individual RC parallel components. As a result of
this, less
stringent requirements arise for the electric strength of the capacitors that
are used as well
as a more compact assembly of the circuit.
DE 38 32 442 A1 teaches a device for the supply of electric current for a
traveling
towing car in which an alternating voltage, which is tapped off from the heavy
duty
towing and electrical connecting cable, is rectified and transformed into an
intermediate
circuit DC voltage of 600 V by a low voltage converter. 3 x 380 V sinusoidal
alternating
voltages are produced from this by means of two identical alternating current
inverse
rectifiers and LC filters that are connected downstream thereof. The low
voltage
converter hereby comprises two serially connected GTO thyristors that are
connected on
the input side and the output side via two identical capacitances that are
connected to one
another in series and whose connecting points are connected to one another.
This circuit
configuration for the low voltage converter serves for doubling its input
electric strength.
y
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Proceeding on the basis of this prior art, the problem for the invention
comprises
the indication of a route, which is as simple as possible, for making
available at least one
second output voltage in the case of a device of this general type with only
slight
incursions into the consumer [system] on the secondary side.
This problem is solved by a device with the features that are indicated in
Claim 1.
Advantageous further developments of the invention can be seen in the
dependent claims.
A significant advantage of the invention resides in the aspect that only a few
additional construction elements are needed and no great change in the circuit
topology is
required in order to obtain an additional output voltage. The incursion into
the consumer
[system] itself is minimal because it is limited to one tapping off point of
the secondary
coil. The efficiency of energy transfer also experiences no noteworthy
impairment as a
result of the modification of the consumer electronics. The subdivision of the
capacitances into serial circuits, which is necessary in order to realize the
invention, has
the positive side effect that a lower voltage drop occurs across each
individual
capacitance, whereby this signifies less stringent requirements in terms of
the electric
strength of the capacitors that are used.
As an additional special advantage, the invention permits the use of a DC
transformer with an input voltage of less than 300 V for supplying the control
electronics.
Such DC transformers are used in large numbers in items of apparatus that are
driven by
a mains supply voltage power supply, and they are therefore obtainable
inexpensively.
An especially preferred, inexpensive, and compact solution is the realization
of
the device in accordance with the invention in one single construction element
together
with a converter serving to actuate a drive unit, wherein the concept of such
a
combination is also applicable to conventional devices of this general type.
Embodiment of the invention are described below by means of drawings. The
following aspects are shown therein.
Figure 1 shows a basic circuit diagram of a consumer electronics system in
accordance with the prior art;
Figure 2 shows a circuit diagram of a consumer electronics system in
accordance
with the invention with a second output voltage;
Figure 3 shows the hooking up of a consumer electronics system in accordance
with the invention with a load in the form of a drive unit that is actuated by
a converter.
The embodiment of the invention that is illustrated in Figure 2 aims at making
available a second output voltage ULZ that is approximately half as large as
the voltage UL
that is needed for the main load 4 and that is still provided in unchanged
magnitude, e.g.
560 V, between the terminals A and B. Accordingly, the consumer inductance L1
is
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' " ' 4
subdivided into two equally large inductances L11 and L12 that are connected
to one
another in series and whose sum corresponds to the inductance L1. This
subdivision of
the inductance L1 is realized by means of a middle tapping off point C of the
coil without
other changes to the coil or to the core.
In the same way, the capacitors C1 and C2 are subdivided into serial
connections
of two equally large capacitors C11 and C12 or C21 and C22, wherein, as is
known, the
partial capacitances each must have twice the value of the total capacitance.
The
connecting point of the capacitors C 11 and C 12 is connected to the middle
tapping off
point C of the consumer coil, i.e. to the connecting point of the inductances
L11 and L12,
i.e. these two connecting points form a communal junction C. This procedure
does not
change anything in regard to the characteristics of the consumer oscillating
circuit in
terms of its outer connections that are connected to the rectifier 1.
The four diodes D 11 through D 14, which are connected downstream of the
consumer oscillatory circuit in Figure 2, form the rectifier 1, which is
illustrated only
schematically in Figure 1, in a known way . This part of the circuit does not
experience
any change. In the same way, the diode D1, the electronic switch S, and the
regulator 2,
which taps off the voltage UL across the load 4 between the terminals A and B
and holds
this voltage UL constant at a predetermined value as a result of suitable
actuation of the
switch S via the control line 3, remain unchanged. For the sake of clarity,
the regulator 2
is no longer illustrated in Figure 2.
Two equally large resistors R21 and R22, of relatively high ohmic value and in
the form of additional elements, are connected in parallel to the capacitors
C21 and C22
in the circuit in each case. In addition, the middle tapping off point C of
the consumer
[system] inductance, which is composed of L11 and L12, is connected via a
diode D2 to
the connecting point D of the capacitors C21 and C22 as well as the resistors
R21 and
R22, wherein the diode is connected such that it permits the flow of electric
current only
from C to D, i.e. from the consumer oscillatory circuit to the RC components
on the
output side.
The partial voltage U~ across the parallel circuit comprising C22 and R22,
which
voltage is approximately equal to the partial voltage ULZ [sic; ULl] across
the parallel
circuit comprising C21 and R21 and thus amounts to half of the output voltage
UL that is
applied across the main load 4, is fed to the inlet of a DC transformer S that
produces the
output voltage US therefrom. The additional output terminal for connecting the
transformer 5 is designated E in Figure 2. Typical values for the designated
voltages are
Ur.i = ULZ = 280 V, and Us = 24 V.
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The mode of functioning of the circuit proceeds, first of all, from the
halving of
the overall output voltage UL as a result of subdividing the original output
capacitor C2
into 2 mutually serially connected and equally large capacitors C21 and C22.
However, it
is not possible simply to connect a DC transformer to an appropriate low
nominal input
voltage across one of the capacitors C21 or C22 in order to produce a low
voltage Us,
which is required in addition to UL, since the load asymmetry that is caused
as a result of
this would allow the voltage across the capacitance in question to break down.
In order to avoid this, the invention provides for the feature that the
consumer
inductance L1 and the tuning capacitor C1, which is connected in parallel
thereto, are
appropriately subdivided into partial inductances L11 and L12 and [partial
capacitors]
C11 and C12, and the junction C, at which the two partial oscillatory circuits
that are
produced as a result are connected together, are connected to the connecting
junction D
of the two output capacitances. The breakdown of the voltage across the
capacitor C22,
which is provided in the present case for tapping off the partial voltage for
the additional
DC/DC transformer 5, can be avoided as a result of this measure, but a short
circuit on
the pathway via the partial inductance L12, the rectifier diode D13, the
inductance L2,
and the switch S would arise in the closed state of the switch S for the DC
voltage across
C22. The task for the additional diode D2 is to prevent the discharge of the
capacitor C22
via this short circuit pathway.
The circuit already functions satisfactorily solely with the measures that are
described above, i.e. one half of the voltage that is applied between the
terminals A and B
can additionally be tapped off across C22 and supplied to a DC/DC transformer
5.
However, if, for whatever reason, the main load 4 is separated from the
consumer
electronics system, then constancy of the voltage UL2 would no longer be
ensured since,
in this case, the only remaining ohmic load would be connected in parallel to
C22,
whereas the regulator 2, as shown in Figure 1, observes the overall voltage UL
= ULl +
Ur.2.
In order to ensure a stable partial voltage ULZ even in the case of separation
of the
main load 4, the two equally large resistors R21 and R22 are each connected in
parallel to
the capacitors C21 and C22, as a result of which the presence of an ohmic load
between
the terminals A and B is ensured. This load is not symmetrical in overall
terms, wherein
the extent of the asymmetry depends primarily on the magnitude of the power
that is
tapped off at the terminals F and G of the DC/DC transformer 5. This means
that the
power, which is capable of being tapped off from these terminals, is limited
especially in
the case of operating the consumer electronics system without a hooked up main
load 4.
As already mentioned at the beginning, the additional voltage Us is needed
only for
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operating a control electronics system that has only a low demand for power in
comparison to the main load 4. The additional resistors R21 and R22 can have a
relatively high ohmic value, i.e. on the order of 10-100 kS~ .
Although the embodiment described in the preceding section provides for the
symmetrical subdivision of the consumer oscillatory circuit and of the RC
components on
the output side, it would also be possible to select an asymmetrical
subdivision ratio in
order to be able to tap off an additional voltage that is greater than or
smaller than one
half of the output voltage UL.
It would also basically be conceivable to undertake subdivision into more than
two voltages in the event that several different additional voltages were
needed. Such
modifications or expansions are easily accessible to the technical expert, who
is skilled
in the art, with knowledge of the example that is described above, and they
are a
component of the present invention.
Figure 3 shows an expedient form of interconnection of the consumer
electronics
system, which is described above, with a main load 4 in the form of a
nonsynchronous
motor 6 that is actuated by a three phase converter 7. The consumer
electronics system is
illustrated in Figure 3 in the form of a block 8 that is to contain all the
components of the
circuit, which is elucidated by means of Figure 2, with the exception of the
consumer
inductance L11 + L12, the DC transformer S, and the main load 4. The
configuration that
is shown in Figure 3 with a motor 6, which is actuated by a converter 7, is a
typical form
of main load 4 that is provided for connection to the terminals A and B of a
consumer
electronics system 8 in accordance with the invention.
The problem that arises hereby is that in the event of generator operation of
the
motor 6, such as occurs during a braking procedure, power can flow back via
the
converter 7 in the direction of the consumer electronics system 8. In the case
of a
consumer electronics system in accordance with the prior art, as shown in
Figure 1, this
would lead to an increase in voltage across the output capacitor C2, which
would cause
the regulator 2 to close the switch S in order that no contribution be made to
any further
increase in output voltage UL from the side of the consumer. The voltage
increase would
not be disruptive as long as the regulator 2 can cope with it.
In the case of a circuit in accordance with the invention as shown in Figure
2,
however, no such increase in the output voltage UL = ULl + U~ can be permitted
in the
event of generator operation of the motor 6 since it would ruin the stability
of the input
voltage UL2 of the DC transformer 5. A marked increase in the output voltage
could even
lead to damage of the inlet of the DC transformer 5 as a result of the
corresponding
marked increase in the partial voltage ULZ.
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v
For this reason, the interconnection in Figure 3 of an additional diode D3
between
the output terminal A of the consumer electronics system 8 and the converter
7, as well as
the parallel connection of an additional capacitance, which comprises two
capacitors C31
and C32 in series with one another, is provided in parallel to the inlet of
the converter 7.
An increase in voltage at the inlet of the converter 7 as a consequence of
operating the
motor 6 in the braking mode leads, in this case, to the charging up of the
capacitors C31
and C32, whereas a reverse current to the outlet of the consumer electronics
system 8,
which reverse current would increase the voltage there with accompanying
charging up
of the capacitors C21 and C22 on the output side, is prevented by the diode
D3. The
capacitors C31 and C32 are needed for accommodating the energy that flows back
from
the converter 7, wherein the subdivision of the capacitance into two serially
connected
capacitors is not essential but is expedient for realizing [the invention]
with capacitors
with lower electrical strength.
It is especially expedient if the consumer electronics system 8, the converter
7,
and the elements which are connected between them, namely the diode D3 and the
capacitors C31 and C32 in the example of Figure 3, are combined into one
construction
unit. This means that they are at least accommodated in one shared housing. In
addition,
they can also advantageously be arranged on one shared board. As a result of
this, space,
weight, and components are saved, and thus a more compact and less expensive
solution
is created in contrast to the prior art in which the consumer electronics
system 8 and the
converter 7 are separate units each with its own housing, whereby these first
have to be
connected to one another by means of a cable and plug.
This applies not only to the case in which the consumer electronics system 8
permits the tapping off of a second output voltage, but also to the
combination of a
conventional consumer electronic system as illustrated in Figure 1 with a
converter 7 that
is provided for actuating a drive unit 6. The combination of the
aforementioned system
components to give one shared construction component always brings about the
saving of
space, weight and costs relative to the embodiment in the form of separate
construction
units. A special advantage arises in the case of a consumer electronics system
8 in
accordance with Figure 2 with two output voltages as a result of the fact that
the
additional elements D3, C31, and C32, which are needed in this case for de-
coupling the
consumer electronics system 8 from the converter 7 in the event of a reverse
power flow,
can be integrated into the shared construction unit without great expense.
