A safety system, a method of operating a safety system and a method of building a safety
system
The invention relates to a safety system for an inductive power transfer system, in
particular an inductive power transfer system for transferring electric energy to a vehicle
which is standing or travelling on a surface of a route. Furthermore, the invention relates
to a method of operating such a safety system and a method of building such a safety
system.
WO 201 2/047779 A 1 discloses a safety system for a charger to provide protection with
respect to an object that may become hot during operation of the charger, wherein the
safety system comprises a detection subsystem configured to detect presence of the
object and substantial proximity to the charger and a notification subsystem operatively
coupled to the detection subsystem and configured to provide an indication of the object.
The publication discloses that one or more inductive sensors can be integrated into a
source device, source housing, vehicle, or surrounding area to detect obstructions and
foreign objects and/or materials between the source and device resonators.
WO 2009/081 115 A 1 discloses a primary unit for use in an inductive power transfer
system, the primary unit being operable to transmit power wirelessly by electromagnetic
induction to at least one secondary unit of the system located in proximity to the primary
unit and/or to a foreign object located in set proximity, wherein the primary unit comprises
driving means operable to drive the primary unit so that in a driven state the magnitude of
an electrical drive signal supplied to one or more primary coils of the primary unit changes
from a first value to a second value. Furthermore, the primary unit comprises means for
assessing the effect of such driving on an electrical characteristic of the primary unit and
means for detecting in dependence upon the assessed effect the presence of said
secondary unit and/or foreign object located in proximity to said primary unit.
EP 231 7625 A2 discloses a primary device for inductive power transfer to a secondary
device, wherein the primary device comprises a primary coil, wherein the primary device
is being configured to (i) operate in a first mode during which the primary coil transfers
power to inductive coupling to the secondary device and (ii) operate in a second mode
during which a foreign object is detected. Furthermore, a primary control is configured to
operate the primary coil (i) using a first frequency during the first mode and (ii) using a
second frequency during the second mode.
It is an object of the present invention to provide the safety system for an inductive power
transfer system, a method of operating such a safety system and a method of building a
safety system which provide a reliable and fast detection of a foreign object, in particular a
metal object, located in proximity of a primary winding structure of the primary winding.
It a basic idea of the present invention that a foreign object located in the proximity of a
primary winding structure of the primary unit will cause a change electrical characteristics
of a detection structure, in particular a change of an inductance of the detection structure.
The present invention can be applied in particular to the field of energy transfer to any
land vehicle, in particular track bound vehicles, such as rail vehicles (e.g. trams), but also
to road automobiles, such as individual (private) passenger cars or public transport
vehicles (e.g. busses). A problem in such devices is that it is generally not possible to
mechanically prevent foreign objects, in particular objects made of metal, from being
placed into proximity of the primary unit of an inductive power transfer system. Such
foreign objects may e.g. comprise a coin, a can, a key, a tool and other objects. The
varying magnetic field generated by the primary unit and a secondary unit may induce
current in the foreign objects made of metal and in other objects or fluids. Such currents
may cause power losses and heating of the object. Heating of the foreign objects made be
dangerous for e.g. persons trying to touch and remove the foreign object and/or may
damage the surface the foreign object is placed on or parts of the primary unit. Also, a
heated object can cause fire.
A safety system for an inductive power transfer system is proposed. In particular, a safety
system for an inductive power transfer system for transferring electric energy to a vehicle
which is standing or travelling on a surface of a route, in particular for a primary system of
said power transfer system, is proposed. In general, the safety system can be part of the
primary unit and/or the secondary unit of the inductive power transfer system.
The inductive power transfer system comprises a route-sided primary unit with a primary
winding structure. The primary winding structure generates a primary electromagnetic field
which is received by a vehicle-sided secondary unit, which is also known as receiver or
pick-up. In between the primary winding structure and a secondary winding structure of
the secondary unit, there is an air gap through which the primary field extends. The
secondary winding structure can generate a secondary field, e.g. if a current flows in the
secondary winding structure. This current can e.g. be generated at least partially by the
mutual induction between the primary winding structure and the secondary winding
structure.
The inductive power transfer system can be a transfer system for so-called static energy
transfer or static charging, wherein the vehicle to which the energy is transferred to does
not move, i.e. is at a halt or rests. In this case, the primary unit can be designed as a socalled
charging pad, wherein the charging pad is integrated into the route or mounted on
the route surface (elevated charging pad).
The inductive power transfer system can also be a so-called dynamic transfer system,
wherein the vehicle to which the energy is transferred to travels along the driving surface
of the route.
A charging surface of the route is assigned to the primary winding. The charging surface
can be a subpart of the route surface through which the primary field or a predetermined
portion, e.g. a portion larger than 80%, 90% or 95%, of the primary field extends during
inductive power transfer, in particular during static charging. The charging surface can
have the same or larger dimensions, e.g. width and length, as an envelope of the primary
winding structure, e.g. a rectangle comprising the winding structure of the primary
winding. In case of a charging pad, the charging surface can correspond to the surface of
the charging pad.
The primary winding structure is usually arranged under a driving surface or standing
surface of the route or within such a driving or standing surface. The primary field
consequently extends through a part of the driving or standing surface. The foreign object
can heat up because of currents induced within the foreign object.
A total field, which can be also referred to as power system transfer field, at least partially
consists of the primary field. If no secondary winding structure is located within the
proximity, e.g. above, the primary winding structure, the total field will be equal or nearly
equal to the primary field. If a secondary winding structure is located within the proximity,
e.g. above, the primary winding structure, the total field results from the superposition of
the primary field and the secondary field, wherein the secondary field is generated by the
secondary winding structure.
The foreign object located within this part or charging surface can heat up because of
currents induced within the foreign object. The currents induced within the foreign object
can be caused by the total field.
The primary unit comprises the aforementioned primary winding for generating an
electromagnetic primary field for the inductive power transfer which can be received by
the aforementioned secondary unit. Furthermore, the safety system comprises at least
one inductive sensing system, wherein the inductive sensing system comprises multiple
detection windings.
According to the invention, the multiple detection windings are arranged in an array
structure. The array structure covers the charging surface at least partially, e.g. more than
80%, 90% or 95% of the charging surface. In this context, "covers" means that a least a
part of the, preferably the total, primary field or total field extends through the array
structure or a surface provided by the array structure. The array structure can be part of
the primary unit.
The term "covers" can also mean that in a common plane of projection, an area enclosed
by a minimal envelope of the array structure overlaps with the charging surface at least
partially.
An array structure can be a matrix-like structure providing multiple rows and columns,
wherein in each row/column-position a detection winding is arranged. Center points of the
detection windings can be arranged with respect to one another with predetermined
longitudinal and/or lateral distances, wherein a longitudinal direction is oriented parallel to
a direction of travel of the vehicle and the lateral direction is oriented perpendicular to the
longitudinal direction.
In other words, a sheet-like structure comprising multiple detection windings is provided.
The multiple detection windings can be located in an interspace provided by the primary
winding and the charging surface. The multiple detection windings can be part of the
route, e.g. located in a layer of the route which is arranged under the route surface or
located in a layer of the route which provides the route surface. The primary winding
structure can be covered by the array of the multiple detection windings.
Each of the detection windings provides a detection surface which is provided by the area
enclosed by the winding structure of the detection winding. During inductive energy
transfer, at least a part of the primary field or total field, preferably the total primary field or
total field, will extend through the array structure of the detection windings. In this case,
the primary field or total field will also extend through the detection surfaces provided by
the detection windings. It is possible that the dimension(s) of the detection winding(s)
is/are chosen depending on the dimension of the smallest object to be detected. In
particular, the detection winding can be designed such that a detection surface or area of
the detection winding is smaller than, equal to or, with a predetermined percentage, e.g.
10%, 20%, 50% or even more percent, larger than the smallest object to be detected.
The safety system can also comprise one or more evaluation units which are connected to
one, a predetermined number or all detection windings. The evaluation unit(s) is/are
designed such that electric characteristics and/or parameters, e.g. an output voltage, of
each detection winding can be determined.
For example, the evaluation unit(s) is/are designed such that an inductance of each
detection winding can be determined. If a foreign object, in particular a metal object, is
placed in the proximity of the primary winding, this object will also cause a change of
inductance of one or more detection windings. By determining the inductance and e.g.
comparing the inductance to a reference inductance, the presence of a foreign object can
be detected reliably.
Furthermore, it is possible to determine or estimate a position of the foreign object
depending on an output signal of the detection windings of the array of detection windings
with respect to the array of detection windings. For example, depending on the output
signal, e.g. an output voltage, of the detection windings, one or more detection winding(s)
can be determined, wherein the output signal(s) of this/these detection winding(s) is/are
altered or influenced by an object placed within the proximity of the detection winding(s),
e.g. above or under a detection surface of the detection winding(s). If a position of the
detection windings with respect to the primary unit is known, a position of the object with
respect to the primary unit, in particular the primary winding structure, can be determined.
The arrangement of detection windings in an array structure advantageously allows a
reliable detection of an object in a predetermined surface area, which can also be referred
to as surveillance area, of the route.
The surveillance surface can be assigned to the array structure. The surveillance surface
denotes a part of the route surface on which the object should be located in order to be
detectable with a predetermined reliability. The surveillance surface can be equal to the
charging surface. An object located on the surveillance surface will change an output
signal of the array of detection windings at least with a predetermined percentage, e.g.
with at least 10%, 20%, or 50%.
Thus, the invention is also related to an object detection system. If an object is detected, a
notification signal, e.g. an electric, acoustic, haptic, or acoustic notification signal can be
generated.
In another embodiment, at least one detection winding is part of an LC oscillating circuit.
The LC oscillating circuit comprises at least one capacitive element, e.g. a capacitor.
Furthermore, the LC oscillating circuit comprises at least one inductive element, wherein
the inductive element is provided at least partially by the detection winding. Furthermore,
the LC oscillating circuit comprises a voltage generator which is able to provide an
alternating voltage with the resonant frequency of the oscillating circuit. Output terminals
of the voltage source are connected to a parallel connection of the capacitive element and
the inductive element. Furthermore, the oscillating circuit can comprise an element with a
predetermined impedance, wherein the element can be arranged such that the oscillating
circuit is decoupled from the voltage source.
The oscillating circuit is designed such that if a foreign object is placed within the proximity
of the detection winding, the oscillating circuit is detuned. In this case, the changed or
detuned resonant frequency of the oscillating circuit does not match the operating
frequency of the voltage source.
The resonant current can decrease significantly if the oscillating circuit is detuned. This
will, in turn, result in a voltage drop of the voltage falling across the aforementioned
parallel connection.
Depending on the voltage falling across the parallel connection of the inductive element
and the capacitive element, the presence of the foreign object in the proximity of the
detection winding can be detected. Such a design of a detection winding provides a high
detection sensitivity and an increased robustness of detection.
The detection winding being part of a LC oscillating circuit does not depend on the feature
that the inductive sensing system provides multiple detection windings, in particular in an
array structure. It is therefore possible that the inductive sensing system comprises at
least one detection winding, wherein the detection winding is part of a LC oscillating
circuit. Such a safety system constitutes an independent invention.
In another embodiment, a predetermined number of oscillating circuits are connected
parallel to each other, wherein the inductive elements of each of the oscillating circuits are
at least partially provided by a detection winding respectively. This advantageously allows
operating multiple oscillating circuits by one voltage source.
In this case, a voltage falling across the parallel connection of all oscillating circuits can be
measured, e.g. by one single voltage sensor. Alternatively, the voltages falling across
each of the oscillating circuits can be measured, e.g. by multiple voltage sensors.
The feature that multiple detection windings each provide an inductive element of LC
oscillating circuits connected in parallel to each other does not depend on the feature that
the inductive sensing system provides multiple detection windings in an array structure. It
is therefore possible that the inductive sensing system comprises multiple detection
windings, wherein each detection winding provides an inductive element of a LC
oscillating circuit. Such a safety system constitutes an independent invention.
In another embodiment, the inductive sensing system is designed as a primary field or
total field compensating sensing system. Alternatively or in addition, each detection
winding is designed and/or arranged as a primary field or total field compensating winding.
This means that the inductive sensing system and/or each of the detection windings is
designed such that a voltage induced by the primary field or total field is eliminated or
reduced due to the physical design of the inductive sensing system and/or the detection
windings.
In the case of an existing primary field, in particular in the case of inductive power transfer
to the vehicle, the inductive sensing system is exposed to the primary field or total field.
This exposure can influence the electrical characteristics or parameters determined by
e.g. the evaluation unit(s) and will therefore complicate the detection of foreign objects. If
the sensing system and/or the detection windings is/are physically designed and/or
arranged such that the effect of the primary field or total field on the determination of the
electrical characteristics or parameters is eliminated or reduced, this will advantageously
improve the reliability of detection during inductive power transfer.
In another embodiment, at least one of the detection windings comprises multiple, in
particular an even number, e.g. two, of counter-oriented subwindings. This means that the
subwindings are connected and/or arranged such that a current flowing through a first
subwinding of the detection winding flows e.g. in a clockwise direction, wherein the same
current flowing through a second subwinding of the detection winding flows in a counter
clockwise direction. The direction of current flow is defined with respect to an axis of
symmetry or central axis of each subwinding, wherein the axes of all subwindings are
oriented parallel to each other. In the case that the detection winding comprises more than
two subwindings, the central axes of all subwindings can be arranged along a common
axis with a predetermined distance, wherein the common axis can be oriented parallel to a
longitudinal direction (which corresponds to a direction of travel of vehicles driving on the
surface of the route) or a lateral direction (which corresponds to a direction perpendicular
to the longitudinal direction). In this case, the voltages induced by the primary field or total
field within the different subwinding will have different signs. Thus, the voltage induced by
the primary field or total field can be eliminated or, at least, reduced.
The inductive sensing system being designed as a primary field or total field
compensating sensing system or the detection winding being designed as a primary field
or total field compensating winding does not depend on the feature that the inductive
sensing system provides multiple detection windings, in particular in an array structure. A
safety system comprising at least one primary field or total field compensating sensing
system therefore constitutes an independent invention.
In another embodiment, the inductive sensing system comprises at least one excitation
winding. The at least one excitation winding generates an excitation field which can be
different from the primary field or total field. The excitation field can be received by the
detection winding(s). For example, the at least one excitation winding and the detection
windings can be arranged such that the total or at least a predetermined part, e.g. more
than 80%, 90%, or 95%, of a magnetic flux of the excitation field extends through the
detection surface of at least one detection winding. It is possible that a single detection
winding is assigned to a single excitation winding. This means that the excitation field or a
predetermined part of it generated by the excitation winding is exclusively received by the
single detection winding. Alternatively, multiple detection windings can be assigned to a
single or to multiple excitation winding(s). Furthermore, multiple excitation windings can
be assigned to a single or multiple detection winding(s).
The excitation field is an alternating electromagnetic field. A frequency of the excitation
field can be different from an operating frequency of the primary field. In particular, the
frequency of the excitation field can be higher, in particular many times higher, than the
operating frequency of the primary field, e.g. higher than 20 kHz, e.g. in the range of
200 kHz to 10000 kHz. The use of an excitation winding allows an active object detection,
wherein properties of the excitation field are monitored. In contrast, the embodiments
using no excitation winding allow a passive object detection, wherein only properties of a
winding structure are monitored.
The detection winding is different from the primary winding structure and different from the
secondary winding structure of the inductive power transfer system. Therefore, the at least
one detection winding is added to the existing primary and secondary winding structures
of the inductive power transfer system.
If a foreign object, in particular a metal object, is placed on the charging surface, the
magnetic flux provided by one or more excitation fields through the detection surface(s) of
one or more detection windings will change. This change will cause a change of (an)
output voltage(s) provided by one or more detection winding(s). Hence, the presence of a
foreign object can be detected. As each detection winding is assigned to a specific
subarea of the charging surface, the area of the location of the foreign object can also be
determined.
The safety system can also comprise a notification system which, in case a foreign object
is detected, notifies a user and/or activates a safe operation of the primary unit, e.g.
switches the primary unit off. The notification system can for instance generate a visual,
acoustic or any other type of warning signal.
The proposed safety system advantageously allows detection a foreign object placed in
proximity of a primary unit. The detection can be a quick, sensitive and robust detection.
In another embodiment, the excitation winding is part of a LC oscillating circuit. The
oscillating circuit can be designed as described above, wherein the inductive element is at
least partially provided by the excitation winding. The LC oscillating circuit comprises at
least one capacitive element, e.g. a capacitor. The oscillating circuit is designed such that
if a foreign object is placed within the proximity of the excitation winding, the oscillating
circuit is detuned. In this case, the changed or detuned resonant frequency of the
oscillating circuit does not match the operating frequency of the voltage source.
The resonant current can, inter alia as a result of the previously described decoupling of
the voltage source and the oscillating circuit, will decrease significantly if the oscillating
circuit is detuned. This will, in turn, result in a voltage drop in a detection winding which
receives the decreased magnetic field generated by the excitation winding.
Depending on the voltage falling across the terminals of the detection winding, the
presence of the foreign object in the proximity of the excitation winding can be detected.
Such a design provides a high detection sensitivity and an increased robustness of
detection.
In another embodiment, the excitation winding(s) and the detection windings are arranged
such that a foreign object located on or in the proximity of the charging surface is
arranged in between the excitation winding(s) and the detection windings. In this case, the
foreign object is located in an interspace between the excitation and the detection
windings. If a vertical direction is defined as a direction perpendicular to a driving or
standing surface of the route, the detection windings can be arranged above the excitation
winding with a predetermined distance, wherein the charging surface is located in
between the excitation and detection windings. It is possible to arrange the detection
windings on a secondary side of the power transfer system. It is, for instance, possible to
arrange the detection windings on a vehicle, e.g. at a bottom side of the vehicle. The
detection winding can, for instance, be arranged in proximity of a secondary unit. It is also
possible, that the secondary unit, e.g. a pick-up, comprises the detection unit. In this case,
the output voltage of the detection winding can be evaluated on a vehicle side. In this
case, the corresponding signals can additionally be transferred to the primary side.
This arrangement of the excitation and the detection windings advantageously provides a
high sensitivity as a foreign object placed in the interspace will cause a significant change
of the output voltage of the detection winding(s).
In an alternative embodiment, the excitation winding and the detection winding are
arranged such that a foreign object located on or in the proximity of the charging surface
is arranged above the excitation winding(s) and above the detection windings, e.g. with
respect to the aforementioned vertical direction.
In this case, the array structure of detection windings is located in between the primary
winding and the charging surface. Thus, the charging surface area is not located in
between the excitation and the detection windings. For example, the excitation and the
detection winding(s) can be located under the driving surface of the route. In this case, a
foreign object is located in an outer space with respect to the space between the
excitation and the detection windings. In this case, a sensitivity of detection is lower than
in the previously described case but it is advantageously possible to reduce an installation
space of the safety system. In this embodiment, the detection and the excitation windings
can be part of the primary unit.
In another embodiment, the sole excitation winding or at least one of the excitation
windings is provided by the primary winding. In this case, the detection windings can be
assigned to a sole excitation winding. In order to generate the excitation field, the primary
winding can be operated at a frequency different from the operating frequency during
inductive power transfer.
This embodiment advantageously provides a high integration of the safety system into the
power transfer system and therefore reduces the required installation space and building
costs.
In a preferred embodiment, the excitation winding is provided by a winding structure
different from the primary winding. If the safety system comprises multiple primary
windings, it is possible that all excitation windings are provided by windings different from
the primary windings. However, it is also possible that the primary winding provides a first
excitation winding, wherein at least one winding different from the primary winding
provides another excitation winding.
If the safety system comprises multiple excitation windings, these excitation windings can
be designed different from the primary winding which advantageously allows increasing a
sensitivity of detection. Also, the primary winding does not need to be operated at different
frequencies. This allows detecting a foreign object also during an operation of the primary
winding during inductive power transfer.
In another embodiment, an excitation winding or a group of multiple excitation windings
is/are designed and arranged such that an excitation field, in particular a field pattern of
the excitation field, is generated such that a magnetic flux based on the excitation field
received by (a) corresponding detection winding(s) is zero or minimal in a normal
operation mode. A normal operation mode means an operation mode wherein no foreign
object is placed in the proximity of the detection winding. In this case, a single detection
winding can be assigned to multiple excitation windings.
In this case, all or a predetermined percentage, e.g. 80%, 90% or 95%, of field lines of the
field pattern of the excitation field can extend through the surface provided by the
detection area of the detection winding such that the total magnetic flux which extends
through each of the detection surface(s) of the detection winding(s) is zero or minimal
through the normal operating mode.
This advantageously provides a high sensitivity concerning the placement of foreign
objects of the proximity of the detection winding. In the normal operating mode, the output
voltage of each of the detection windings will be zero or minimal as there is no magnetic
flux, and consequently also no change of the magnetic flux, through the detection surface
of each detection winding. A foreign object placed on the charging surface or in the
proximity of the charging surface will alter the magnetic flux such that the magnetic flux
received by at least one detection winding deviates from zero.
This, in turn, advantageously provides a high sensitivity of detection.
In another embodiment, the excitation winding is designed such that an even number of
poles is provided, wherein the excitation winding and a corresponding detection winding
are arranged and/or designed such that the magnetic flux generated by different poles, in
particular at least a part of the magnetic flux generated by at least two poles, extends
through the detection surface of the detection winding. A pole can e.g. be provided by a
subwinding of the excitation winding. It is possible that the total or a predetermined part,
e.g. 50%, of the magnetic flux of different poles extends through the detection surface.
This means that a current flowing through a first subwinding can generate a magnetic flux
with a first direction through an area enclosed by the first subwinding (first pole). Also, the
current can generate a magnetic flux with a direction opposite to the first direction through
an area enclosed by the second subwinding (second pole). However, each magnetic flux
generated by the current can have the same magnitude. If both magnetic fluxes extend
through the detection surface, the resulting magnetic flux extending through the detection
surface of the detection winding generated by such an excitation winding will be zero.
It is, however possible, to have more than two poles. It is also possible to provide the
magnetic flux with the first direction by a first excitation winding and the magnetic flux with
the second direction by a second separate excitation winding.
This advantageously allows a simple set up of an excitation winding providing a zero
magnetic flux through the detection surface of the detection winding.
The excitation winding can be designed as a primary field or total field compensating
excitation winding. For example, the excitation winding can comprise multiple, in particular
an even number, of counter-oriented subwindings. Each subwinding can comprise a
predetermined number of turns. The subwindings can be arranged and/or connected such
that a current flowing through a first subwinding of the excitation winding flows e.g. in a
clockwise direction, wherein the same current flowing through a second subwinding of the
detection winding flows in a counter-clockwise direction. The direction of current flow is
defined with respect to an axis of symmetry or central axis of each subwinding, wherein
the axes of all subwindings can be oriented parallel to each other. In the case that the
excitation winding comprises more than two subwindings, the central axes of all
subwindings can be arranged along a common axis with a predetermined distance,
wherein the common axis can be oriented parallel to a longitudinal direction (which
corresponds to a direction of travel of vehicles driving on the surface of the route) or a
lateral direction (which corresponds to a direction perpendicular to the longitudinal
direction).
In this case, the voltages induced by the primary field or total field within the first and the
second subwinding of the excitation will have different signs.
The inductive sensing system comprising at least one excitation winding does not depend
on the feature that the inductive sensing system provides multiple detection windings, in
particular in an array structure. It is therefore possible that the inductive sensing system
comprises at least one excitation winding and is designed according to one of the
previously described embodiments. Such a safety system constitutes an independent
invention.
In another embodiment, the primary unit comprises an acoustic sensor and a current
impulse generating means. By the current impulse generating means, a current impulse
can be generated and applied to e.g. an excitation winding. It is also possible to apply the
current impulse to one or multiple phase lines of the primary winding structure. In this
case, an impulse-like excitation field is generated. This excitation field will generate eddy
currents in a foreign metal object placed within the surveillance area. In an interaction of
such eddy currents with the excitation field or another electromagnetic field, a force, in
particular a Lorentz force, will act on the foreign metal object. As the force is an alternating
force, the metal object can start to vibrate. Oscillations of the air or of the route structure
providing the surface on which the object is placed can be caused by these vibrations,
wherein said oscillations can be detected by the acoustic sensor. Alternatively or in
addition, it is also possible that the object will be moved up, extended and/or deformed by
the Lorentz forces. If the impulse ends, the object will return to the original state, e.g. fall
down on the route surface or come back to the original shape. Because of small energy
absorption of the environment, the object starts to vibrate on the surface as a result of this
process.
This advantageously allows increasing a robustness of detection by providing an
additional detection method.
It is also possible to detect an electromagnetic field generated by the eddy current within
the foreign metal object. In this case, a permanent magnetic field can be generated, e.g.
by a permanent magnet or an electromagnet, and the back-induced voltage which is
induced by the magnetic field generated by the eddy current can be measured. This can
be done by using a separate winding structure or the structure of the excitation winding.
The safety system comprising an acoustic sensor and a current impulse generating
means does not depend on the feature that the inductive sensing system provides
multiple detection windings, in particular in an array structure. A safety system comprising
an acoustic sensor and a current impulse generating means therefore constitutes an
independent invention.
In another embodiment, the safety system comprises a microwave transmitting device and
a microwave receiving device. The transmitting device and receiving device can comprise
or be designed as an antenna.
The transmitting device can be designed and/or arranged such that radar waves or
microwaves can be emitted along the charging surface. In this case, the waves reflected
by the foreign object can be received by receiving device which is built as a radar or
microwave sensor. This allows an additional radar-based detection of foreign objects in
the proximity of the primary unit.
In particular, the microwave transmitting device can be operated by or comprise an LC
generator which generates the microwaves. The LC generator comprises at least one
inductive element, one capacitive element and one voltage source. The inductive and
capacitive element can be connected in parallel or in series. The voltage source provides
voltage with the resonant frequency of the parallel or series connection of the inductive
and capacitive element. The LC generator can be designed such that if a stationary, in
particular metal, object is located within the proximity of the LC generator, the operating
frequency of the LC generator is detuned because of the changed inductance of the
inductive element.
In this case, the waves received by the receiving device will have frequency depending on
the amount of detuning which, in turn, depends on the change of the inductivity of the LC
generator by the foreign object. Based on the changed frequency, a stationary object can
be detected.
In addition, it is also possible that the change of the frequency of the reflected microwaves
can be caused by a moving object. This allows detection of moving objects within a
detection range of the microwave transmitter-receiver configuration.
The transmitting device and the receiving device can be designed as elements separate
from the detection windings or excitation windings.
In particular, metal objects can be detected by the proposed safety system. Also, moving
objects, such as animals or the aforementioned vibrating metal object, can be detected by
the proposed safety system due to an evaluation according to the Doppler effect.
The embodiment comprising the transmitting device and receiving device presents an
independent invention. Thus, a safety system for an inductive power transfer system for
transferring power to a vehicle on a surface of a route is described. A primary unit
comprises at least one primary winding for generating an electromagnetic primary field for
the inductive power transfer, wherein a charging surface of the route is assigned to the
primary winding. The safety system comprises at least one microwave transmitting device
and at least one microwave receiving device. The transmitting device can be designed
and/or arranged such that radar waves or microwaves can be emitted along the charging
surface. The receiving device can be designed and/or arranged such that reflected radar
waves or microwaves emitted along the charging surface can be received.
In another embodiment, at least one of the detection windings is designed as the
microwave receiving device and/or one excitation winding is designed as the microwave
transmitting device. Designing at least one detection winding as a microwave receiving
and/or excitation winding as the microwave transmitting device does not depend on the
feature that the inductive sensing system provides multiple detection windings, in
particular in an array structure. A safety system comprising at least one of such a
detection winding or excitation winding therefore constitutes an independent invention.
In another embodiment, the detection windings are designed as circular detection
windings. The circular detection windings can be arranged such that detection surfaces of
the detection windings cover a predetermined part of the charging surface, e.g. in a
common plane of projection. A circular detection winding provides an optimal sensitivity
with respect to the circular detection surface of the detection winding. The sensitivity can
e.g. be constant for the total detection surface or 99% of the detection surface of the
detection winding.
This advantageously provides high detection sensitivity.
In another embodiment, the circular detection surfaces of at least two circular detection
windings at least partly overlap, e.g. in a common plane of projection. If detection surfaces
of neighboring detection windings do not overlap, there are interspaces located outside
the detection surface in between the detection windings. These interspaces will decrease
the overall sensitivity of the safety system or will even make the detection impossible. By
having detection windings with overlapping detection surfaces, this disadvantage can be
advantageously overcome.
Designing the detection windings as circular detection windings does not depend on the
feature that the inductive sensing system provides multiple detection windings, in
particular in an array structure. A safety system comprising at least one of such a
detection winding therefore constitutes an independent invention.
In a preferred embodiment, the detection windings are designed as hexagonal-shaped or
rectangular-shaped detection windings. The multiple hexagonal-shaped detection
windings can be arranged in an array structure such that detection surfaces of the
detection windings cover a predetermined part of the charging surface, e.g. 80%, 90% or
95%, for example in a common plane of projection. It is also possible to use squareshaped
or rectangular-shaped detection windings. However, the proposed hexagonalshaped
detection windings advantageously provide a high sensitivity within the detection
surfaces enclosed by the detection windings and further advantageously allow arranging
multiple detection windings such that interspaces between the detection windings are
minimized.
In particular, the multiple hexagonal-shaped detection windings are arranged such that a
honeycomb structure is provided. This honeycomb structure advantageously provides a
high detection sensitivity for a large area of the route surface, i.e. an optimal detection
coverage. The shape of a hexagon is similar to a circle and has the advantage of having
the same response to a test object placed in an arbitrary position within the whole
detection surface and additional minimizes the interspaces between the detection
windings.
Designing the detection windings as hexagonal- or rectangular shaped detection windings
does not depend on the feature that the inductive sensing system provides multiple
detection windings, in particular in an array structure. A safety system comprising at least
one of such a detection winding therefore constitutes an independent invention.
A predetermined number of the detection windings within the array can provide the
previously described subwindings of one detection winding. In this case, the subwindings
can be arranged and/or connected such that the aforementioned primary field or total field
compensating detection winding is provided.
In a preferred embodiment, the primary unit comprises at least one total field cancellation
means for generating a cancellation field, wherein the cancellation means is designed
and/or arranged such that the total field can be at least partially cancelled by the
cancellation field. The total field is the electromagnetic field resulting from the primary field
generated by the primary winding structure and, if applicable, a secondary field generated
by the secondary winding structure.
The cancellation means can comprise one or more cancellation winding(s) which are
different from the excitation winding(s) and the detection winding(s). In particular, the
cancellation means can be assigned to a cancellation area of the route surface, in
particular of the surface of the surveillance area, wherein the cancellation field is designed
such that the total field extending through the cancellation area is cancelled or reduced by
the cancellation field.
Preferably, the cancellation means is provided by the excitation winding(s) and/or the
detection winding(s). This advantageously allows operating the detection and excitation
winding in a first operating mode to detect a foreign object and, in a different operating
mode, to cancel the total field in an area where the foreign object is located. It is possible
that the area of location or the object position is determined, e.g. depending on output
voltages of specific detection windings. Consequently, the cancellation means, e.g. the
detection windings and/or one or more excitation winding(s), which are assigned to the
area of location of the object position, can be operated such that the cancellation field is
generated. The cancellation area can be equal to or larger than the aforementioned
detection area. Thus, cancellation means have to be designed accordingly.
Such a safety system advantageously allows detecting a foreign object and furthermore
ensures a safe operation of the inductive power transfer system. If the total field within the
area of placement is cancelled or reduced, effects on, e.g. heating of, the object will be
prevented or reduced. This, in turn, reduces a risk of injuring a person or damaging e.g.
the primary unit.
Providing a safety system comprising at least one total field cancellation means does not
depend on the feature that the inductive sensing system provides multiple detection
windings, in particular in an array structure. A safety system comprising at least one total
field cancellation means therefore constitutes an independent invention.
Further proposed is a method of operating a safety system according to one of the
previously described embodiments. In such a method, an output signal of each of the the
multiple detection windings is measured and an electrical characteristic or parameter, e.g.
an inductance or output voltage of each detection winding, is determined depending on
the measured output signal and compared to a reference value. If the difference of the
electric characteristic or parameter to the reference value is higher than a predetermined
threshold value, the presence of a foreign object can be detected and a notification signal
can be generated. This advantageously allows a simple detection of a foreign object in the
proximity of the primary unit.
In another embodiment, an excitation field is generated by at least one excitation winding.
The excitation field or a part of the excitation field is received by at least one
corresponding detection winding. This means that at least a part of a magnetic flux of the
excitation field extends through a detection surface of the corresponding detection
winding(s). Then, an output voltage of the at least one detection winding is evaluated. If
the output voltage deviates from a predetermined output voltage, a notification signal can
be generated.
It is also possible, that a notification signal is generated, if a course and/or a magnitude of
the output voltage deviates from a predetermined course and/or magnitude of the output
voltage.
This advantageously provides a simple method to quickly and reliably detect a foreign
object in the proximity of a primary unit of an inductive power transfer system.
In another embodiment, an acoustic sensor captures sound waves in a surveillance area
of the primary unit after the excitation field has been generated. An output signal of the
acoustic sensor is evaluated. This advantageously increases a robustness of detection.
As explained previously, eddy current can cause a vibration of the foreign metal object
and therefore sound waves are being generated. By measuring these sound waves, a
presence of a foreign object can be (additionally) detected.
In another embodiment, a radar or microwave signal is emitted along the charging
surface, wherein the reflected signal is received by at least one microwave receiving
device, wherein a radar- or microwave based object detection based on the received
signal is conducted. This advantageously allows a detection robustness of the proposed
method.
In another embodiment, a cancellation field is generated by at least one total field
cancellation means if a foreign object has been detected. In particular, the cancellation
field can be generated such that the total field is only cancelled in an area of location,
wherein the area of location is the area where a detected foreign object is located on the
route surface. In this case, only a part, in particular a local part, of the total field is
cancelled or reduced. This advantageously provides a location specific cancellation or
reduction of the total field while an operation of the primary unit during inductive power
transfer does not need to be interrupted in total.
Further proposed is a method of building a safety system for a primary unit of an inductive
power transfer system, wherein the primary unit comprises at least one primary winding
for generating an electromagnetic primary field for the inductive power transfer, wherein a
charging surface of the route is assigned to the primary winding. The method comprises
the steps of
- providing multiple detection windings,
- arranging the detection windings in an array structure, wherein the array structure
covers the charging surface at least partially.
In particular, the detection windings can be arranged such that a foreign object located on
the charging surface changes a magnetic flux through (a) detection surface(s) of the
detection windings.
The method advantageously allows modifying existing primary units by providing
additional detection windings.
Furthermore, at least one excitation winding can be provided, wherein the at least one
excitation winding can be different from the primary winding. The excitation winding is
arranged such at least a predetermined part of a magnetic flux of an excitation field
extends through a detection surface of the at least one detection winding.
This advantageously provides a safety system, wherein the generation and detection of
the excitation field is independent from the primary winding.
Examples of the invention will be described with reference to the attached figures in the
following. The figures show:
Fig. 1 a schematic block diagram of an inductive detection system,
Fig. 2 a schematic diagram of the proposed safety system in a first embodiment,
Fig. 3 a schematic diagram of the proposed safety system in a second embodiment,
Fig. 4 a schematic diagram of the proposed safety system in a third embodiment,
Fig. 5 a schematic layout of an excitation winding and a detection winding,
Fig. 6a a schematic design of one detection winding and multiple excitation windings,
Fig. 6b another schematic design of one detection winding and multiple excitation
windings,
Fig. 7 another schematic design of one detection winding and multiple excitation
windings,
Fig. 8 an equivalent circuit of the system shown in Fig. 7,
Fig. 9 a schematic diagram of the proposed safety system in a fourth embodiment,
Fig. 10 an equivalent circuit of the system shown in Fig. 9,
Fig. 11 a schematic diagram of the proposed safety system in a fifth embodiment,
Fig. 12 a schematic diagram of the proposed safety system in a sixth embodiment,
Fig. 12a a schematic diagram of a proposed safety system in a seventh embodiment
Fig. 13 a schematic diagram of the proposed safety system in a eigth embodiment,
Fig. 14 an array structure of circular detection windings,
Fig. 15 another array structure of circular detection windings,
Fig. 16 a honeycomb array structure of hexagonal-shaped detection windings,
Fig. 17 a detailed view of hexagonal-shaped detection windings,
Fig. 18 a schematic diagram of the proposed safety system in a ninth embodiment,
Fig. 19 a schematic diagram of the proposed safety system in a tenth embodiment,
and
Fig. 20 a schematic diagram of a total field compensating winding.
Fig. 1 shows a schematic block diagram of an inductive sensing system 1. The inductive
sensing system 1 comprises a detection winding 2 having two turns. The detection
winding 2 is connected to an evaluation unit 3 which evaluates an inductance of the
detection winding 2.
An inductance can for instance be determined by one or more of the following methods:
a) measuring a current change at connecting terminals of the detection winding 2 with a
constant voltage falling across the connection terminals,
b) measuring a reactance with a constant current flowing through the connection
terminals of the detection winding 2 by evaluating a voltage change of a voltage
falling across the terminals,
c) measuring the so-called heterodyne frequency, e.g. by a direct digital frequency
measurement and/or
d) compare the resonant frequency of a resonant circuit provided by the detection
winding 2 and an additional capacitor with a reference frequency.
An object 4 is shown being placed in proximity of the detection winding 2. If no object 4 is
present within the proximity or detection area of the detection winding 2, a base
inductance L0 will be determined by the evaluation unit 3. If the object 4 is placed in the
proximity of detection area of the detection winding 2, the inductance will change from the
base inductance L0 to a changed inductance I_0+D I_. The presence of the object 4 can e.g.
be detected if the change of inductance AL is larger than a predetermined threshold value.
It is also possible that the type of object can be detected depending on the change of
inductance AL. In this case it can e.g. be detected if the object is a diamagnetic object,
e.g. consists of aluminum, copper, ferromagnetic iron and/or ferrite, etc.
Fig. 2 shows a proposed safety system 5 in a first embodiment. The safety system 5
comprises a detection winding 2, a voltage sensor 6 and a primary winding structure 7 of
a primary unit of a system for inductive power transfer to a vehicle (not shown). The
primary winding structure 7 consists of three individual phase lines which extend in a
meandering manner in a direction of travel of vehicles driving on the surface of the route
11 (longitudinal direction). In the embodiment shown, the primary winding structure 7
serves as an excitation winding which generates an alternating electromagnetic excitation
field which is symbolized by field lines 8. It is shown that a magnetic flux extends through
a detection surface 9 of the detection winding 2. The magnitude of the magnetic flux will
change depending on the presence of an object 4 in the proximity of the detection winding
2. It is shown that the detection winding 2 is arranged such that the object 4, which is
located on a charging surface 10 of the route 11 for the vehicle is located in between the
excitation winding and the detection winding 2. The charging surface 10 of the route 11 is
a subpart of the route surface. The primary winding structure 7 is located under the route
surface. If the object 4 is placed on the charging surface 10, an output voltage of the
detection winding 2 will change in comparison to a normal operating mode in which there
is no object 4 placed on the surveillance surface 10. The change of the output voltage
therefore indicates the presence of the object 4. The object 4 can be detected, if the
change of the output voltage is higher than a predetermined threshold value. In Fig. 2,
only one detection winding 2 of an array structure of detection windings 2 is shown for
illustration purposes.
It is possible that the primary winding structure 7 can be operated at two frequencies. A
first frequency can be an operating frequency if the primary winding structure 7 generates
an electromagnetic field in order to transfer energy to a secondary unit of a vehicle (not
shown). A second frequency can be a frequency in a detection mode, wherein the primary
winding structure 7 generates the excitation field 8.
In Fig. 3, another embodiment of a proposed safety system 5 is shown. The safety system
5 comprises a detection winding 2 and an excitation winding 12 which is different from the
primary winding structure 7 of the primary unit shown in Fig. 2. The excitation winding 12
is operated by a high frequency generator 13. Thus, the excitation winding 12 generates
an alternating excitation field which is symbolized by field lines 8. In Fig. 3, the detection
winding 2 is assigned to the excitation winding 12. This means that at least a part of a
magnetic flux provided by the excitation field 8 generated by the excitation winding 12
extends through a detection surface 9 of the detection winding 2. If an object 4 is placed
on a charging surface 10 of the route 11, an output voltage of the excitation winding 12
will change in comparison to a normal operating mode, where no object 4 is placed on the
charging surface 10. The voltage sensor 6 detects the voltage change. The presence of
the object 4 can therefore be detected depending on the change of the output voltage of
the detection winding 2.
In Fig. 3, the charging surface 10 and thus the object 4 placed on the charging surface 10
is located in an interspace between the excitation winding 12 and the detection winding 2.
The detection winding 2 can be arranged on a vehicle, in particular can be a part of a
vehicle-sided secondary unit (not shown). As in Fig. 2, only one of multiple detection
windings 2 and one excitation winding 12 is shown.
In Fig. 4, another embodiment of a proposed safety system 5 is shown. In contrast to the
safety system 5 shown in Fig. 3, the safety system 5 shown in Fig. 4 is designed such that
an object 4 located on a charging surface 10 of a route 11 is placed above an excitation
winding 12 and above a detection winding 2. Both, the excitation winding 12 and the
detection winding 2 are arranged under a surface of the route 11, wherein the object 4 is
placed above or on the surface of the route 11. This advantageously allows a compact
design of the safety system 5. As in Fig. 2, only one of multiple detection windings 2 and
only one excitation winding 12 is shown.
In Fig. 5, a schematic design of a detection winding 2 and an excitation winding 12 is
shown. The detection winding 2 is a circular winding with a circular-shaped detection
surface 9. The excitation winding 12 comprises a first half turn 14 and a second half turn
15. A radius of each of the half turns 14, 15 is smaller than the radius of the circularshaped
detection winding 2. The turning directions 16, 17 are opposite to each other.
Both, the first half turn 14 and second half turn 15 are arranged concentric to a common
central axis which is aligned with a central axis of the circular-shaped detection winding 2.
If a current I flows through the first and the second half turn 14, 15, an excitation field
symbolized by field lines 8 is generated. In particular, a flowing direction of the current I in
the first half turn 14 (indicated by an arrow 16) is oriented clockwise with respect to the
common central axis, wherein a flowing direction of the current in the second half turn 15
(indicated by arrow 17) is oriented counter-clockwise. In a normal operating mode, that
means if not foreign object 4 (see Fig. 3) is placed in the proximity of the detection winding
2 (i.e. the surveillance area), the total magnetic flux through the detection surface 9 of the
detection winding 2 is zero. The first and the second half turn 14, 15 are connected by a
connecting line 18. If an object 4 is placed in the proximity of the detection winding 2, the
magnetic flux extending through the detection surface 9 will deviate from zero. Thus, a
non-zero voltage will be generated by the detection winding 2 which can be measured by
a voltage sensor 6. Shown is also a high frequency generator 13 which generates the
alternating current I.
In Fig. 6a, a schematic design of a detection winding 2 and multiple excitation windings
12a, 12b is shown. The arrangement comprises a rectangular-shaped detection winding 2
enclosing a detection surface 9. A voltage sensor 6 is connected to connecting terminals
of the detection winding 2. Furthermore, the arrangement comprises a first excitation
winding 12a and a second excitation winding 12b which are operated by high frequency
generators 13, respectively. It is, however, possible that the detection winding 2 and the
excitation windings 12a, 12b can have another shape having an axis of symmetry.
The first excitation winding 12a comprises or provides an even number of consecutive,
counter-oriented rectangular-shaped subwindings with identical dimensions, in this case
four subwindings 36a, 36b, 36c, 36d, extending along a common central axis symbolized
by an arrow 19. In this case, each subwinding 36a, 36b, 36c, 36d provides a pole. The
consecutive subwindings 36a, 36b, 36c, 36d are connected such that a flowing direction
of a current 11 in the uneven-numbered subwindings 36a, 36c corresponds to a counter
clockwise direction, wherein a flowing direction of a current 11 in the even-numbered
subwindings 36b, 36d corresponds to a clockwise direction, wherein the clockwise
direction is determined with respect to an axis perpendicular to the plane of projection and
pointing towards a viewer.
The second excitation winding 12b is designed similar to the first excitation winding 12a
but arranged with a displacement A along the central longitudinal axis 19. This means that
also the second excitation winding 12b comprises or provides an even number of
consecutive rectangular-shaped subwindings, in this case four counter-oriented
subwindings 37a, 37b, 37c, 37d extending along the common central axis symbolized by
the arrow 19.
It can be seen that the detection winding 2 and the excitation windings 12a, 12b are
designed and arranged such that if the excitation windings 12a, 12b are projected into the
plane of the detection surface 9 of the detection winding 2, the detection winding 2
encloses the second and the third subwinding 36b, 36c of the first excitation winding 12a
and one half of the first subwinding 37a, the second subwinding 37b and one half of the
third subwinding 37c of the second excitation winding 12b. Thus, the detection winding 2
encloses two poles of each excitation winding 12a, 12b.
Thus, a magnetic flux, represented by field lines 8, generated by the first excitation
winding 12a extending through the detection surface 9 will be zero in a normal operating
mode (no foreign object 4). Also, the magnetic flux, represented by field lines 8, generated
by the second excitation winding 12b extending through the detection surface 9 will be
zero in a normal operating mode.
By using two excitation windings 12a, 12b which are displaced with a displacement A, a
higher detection sensitivity can be achieved. Considering the arrangement shown in Fig.
5, an object 4 placed symmetrically on the connecting line 18 will alter the magnetic flux
through the area enclosed by the first half turn 14 and the connecting line 18 in the same
way as the magnetic flux through the area enclosed by the second half turn 15 and the
connecting line 18. If a foreign object 4 is placed symmetrically on a connecting section
20b of e.g. the second subwinding 37b and the third subwinding 37c of the second
excitation winding 12b, the object 4 will alter the magnetic flux generated by a flow of a
current I2 through the two neighboring subwindings 37b, 37c of the second excitation
winding 12b in the same way. In such a configuration, the magnetic flux generated by the
second and the third subwinding 37b, 37c will be altered similarly.
Because of the displacement, however, the object 4 will alter the magnetic flux of the third
subwinding 36c of the first excitation winding 12a differently from the magnetic flux of the
second subwinding 36b, as these subwindings 36a, 36b are displaced with a
displacement A with respect to the subwindings 37b, 37c of the second excitation winding
12b. Such an arrangement increases the robustness of detection.
The displacement A can be chosen such that the first and the second excitation windings
12a, 12b are magnetically decoupled and their high frequency generators 13 can be
operated independently from each other. Another option is to operate the high frequency
generators 13 in a cyclic operating mode, wherein either the high frequency generator 13
of the first excitation winding 12a or the high frequency generator 13 of the second
excitation winding 12b is operated in order to ensure a magnetic decoupling. It is also
possible to connect the first and the second excitation winding 12a, 12b in series. The
decoupling would still help in that case to reduce the impedance of the excitation windings
12a, 12b to limit the generator voltage.
Thus, an arrangement of at least two excitation windings 12a, 12b is shown, wherein each
excitation winding 12a, 12b comprises at least two subwindings extending along a
common central axis 19, wherein the subwindings are designed and connected such that
a direction of a current flowing through a subwinding is oppositely oriented to a direction of
a current flowing through a consecutive subwinding, wherein corresponding subwindings
of the two excitation windings 12a, 12b are spaced apart with a displacement A along the
common central axis 19. The common central axis 19 is perpendicular to the central axes
of the subwindings. The displacement A can be chosen equal to or larger than a
dimension, i.e. a diameter of the smallest object 4 which is to be detected. Alternatively or
in addition, the displacement A can be chosen such that a magnetic coupling between the
excitation windings 12a, 12b is smaller than a predetermined value, preferably zero and/or
such that a minimal mutual inductance between the excitation windings 12a, 12b is
provided. This means that there is no or only a minimal energy transfer between the
respective excitation windings 12a, 12b.
In Fig. 6b, another schematic design of a detection winding 2 and multiple excitation
windings 12a, 12b, 12c, 2d is shown. In contrast to the design shown in Fig. 6a, two
additional excitation windings 12c, 2d are provided. These additional excitation windings
12c, 12d are designed similar to the excitation windings 12a, 12b, in particular with a
displacement B along a common central axis 19b. The displacement B can be equal to or
different from the displacement A. The common central axis 19b, however, is oriented with
a predetermined angle with respect to the common central axis 19 of the excitations
windings 12a, 12b, in particular perpendicular to the common central axis 19 of the
excitations windings 12a, 12b. This further increases a detection sensitivity.
Thus, an arrangement of at least four excitation windings 12a, 12b, 12c, 2d is shown,
wherein each excitation winding 12a, 12b, 12c, 2d comprises at least two subwindings.
The subwindings of a set of two excitations windings 12a, 12b extend along a first
common central axis 19, wherein the subwindings are designed and connected such that
a direction of a current flowing through a subwinding is oppositely oriented to a direction of
a current flowing through a consecutive subwinding, wherein corresponding subwindings
of the two excitation windings 12a, 12b are spaced apart with a first displacement A along
the first common central axis 19. The subwindings of another set of two excitations
windings 12c, 2d extend along a second common central axis 19b, wherein the
subwindings are designed and connected such that a direction of a current flowing
through a subwinding is oppositely oriented to a direction of a current flowing through a
consecutive subwinding, wherein corresponding subwindings of the two excitation
windings 12c, 2d are spaced apart with a second displacement B along the second
common central axis 19b which encloses a predetermined angle with the first common
central axis 19.
Thus, a configuration is provided, wherein the number of balanced configurations is
minimized. In this context, "balanced configuration" means that a magnetic flux generated
by the excitation windings 12a, 12b, 12c, 2d which extends through the detection surface
9 of the detection winding 2 is zero although a foreign object 4 is located in the
surveillance area, e.g. in the proximity of the detection winding 2 and/or the excitation
windings 12a, 12b, 12c, 2d.
It is, of course, possible to provide more than two subwindings per excitation winding
and/or more than two excitation windings extending along a common central axis and/or
more than two sets of excitation windings which extend along different common central
axes.
In Fig. 5, in Fig. 6a and in Fig. 6b it is shown, that a diameter or a geometric size of the
detection winding 2 is larger than a diameter or geometric size of the subwindings 36a,
36b, 36c, 36d, 37a, 37b, 37c, 37d provided by the excitation windings 12a, 12b, 12c, 2d
or sections of the excitation windings 12a, 12b. However, it is possible that a diameter or
geometric size of the subwindings 36a, 36b, 36c, 36d, 37a, 37b, 37b, 37c, 37d provided
by the excitation winding(s) 12a, 12b, 12c, 12d is larger than a diameter or geometric size
of the detection winding 2. In this case, only a part of the magnetic flux generated by the
excitation winding(s) 12a, 12b will extend through the detection surface 9. This will
decrease a detection sensitivity. In this case, the detection sensitivity can be increased by
increasing the number of subwindings 36a, 36b, 36c, 36d, 37a, 37b, 37c, 37d of the
detection winding 2.
In another embodiment it is also possible that only one excitation winding with one
subwinding is used, wherein a diameter or geometric size of the subwinding is larger than
a diameter or geometric size of the detection winding 2. This will lead to a smaller voltage
induced in the detection winding. In this case, a winding number of the detection winding 2
can be chosen higher than a predetermined value in order to increase the sensitivity of
detection.
In Fig. 7, another schematic design of a detection winding 2 and multiple excitation
windings 12a, 12b is shown. The difference to the design shown in Fig. 6a is that the first
excitation winding 12a is connected in series to the second excitation winding 12b. Also,
the first excitation winding 12a comprises only two consecutive, counter-oriented
subwindings 36a, 36b wherein the second excitation winding 12b comprises four
consecutive counter-oriented subwindings 37a, 37b, 37c, 37d. The currents 11 , I2 which
are fed to the excitation windings 12a, 12b are provided by a constant current source. The
constant current source comprises the voltage source 13, a first inductive element L 1, a
second inductive element L2, and a capacitive element C 1. The first and the second
inductive elements L 1, L2 are connected in series to the voltage source 13, wherein the
capacitive element C 1 is connected in parallel to the series connection of the first
inductive element L 1 and the voltage source 13.
Due to the even number of poles of the excitation windings 12, 12a, 12b which are
provided by the even number of subwindings 36a, 36b, 37a, 37b, 37c, 37d, the previously
described total field 24 (see Fig. 10) will not alter or influence the operational
characteristics of the constant current source. If no metal object 4 is located in the
proximity of the excitation windings 12, 12a, 12b, the voltage induced in the detection
winding 2 will be zero due to the design and arrangement of the excitation windings 12,
12a, 12b (as explained with respect to Fig. 6a).
In Fig. 7 it is shown that a second capacitive element C2 is connected in parallel to the
detection winding 2. If a voltage is induced in the detection winding 2, a relatively high
resonant current will flow through the detection winding 2 as the second capacitive
element C2 provides a low impedance at the frequency of the induced voltage. This
resonant current generates a voltage falling across the second capacitive element C2,
wherein an amplitude of said voltage is proportional to the resonant current. This provides
a high detection sensitivity of the shown design.
In the embodiments shown in Figs. 6a, 6b, 7, the number of turns of each subwinding 36a,
36b, 36c, 36d, 37a, 37b, 37c, 37d can be equal to one or larger than one.
Fig. 8 shows an equivalent circuit of the design shown in Fig. 7. The design shown in Fig.
8 provides a current transformer, wherein an input current 11 is constant and the output
circuit provides a current source. The detection winding 2 is operated in a parallel
resonant mode.
Fig. 9 shows a schematic diagram of the proposed safety system 5 in a fourth
embodiment. A voltage generator 13 is operated at the resonant frequency of an
oscillating circuit, wherein losses of the oscillating circuit are compensated by the voltage
source 13. The oscillating circuit is provided by a resonant capacitive element Cres and
an excitation winding 12. The elements of the oscillating circuit are designed such that the
oscillating circuit provides an infinite impedance with respect to the voltage source 13.
Within the oscillating circuit, a resonant current Ires flows. This resonant current Ires
generates an excitation field which is received by the detection winding 2, wherein the
detection winding 2 generates a relatively high voltage which can be detected by a voltage
sensor 6. If a foreign object (not shown) is placed within the proximity of the excitation
winding 12, the oscillating circuit is detuned. In this case, the resonant frequency of the
oscillating circuit does not match the operating frequency of the voltage source 13.
As seen in Fig. 10, which shows an equivalent circuit of the design shown in Fig. 9, the
oscillating circuit is coupled to the voltage generator 13 by an element Z, wherein an
impedance of the element Z is higher, e.g. 10OOtimes higher, than the impedance
provided by the oscillating circuit or the impedance of the excitation winding 12. Thus, the
oscillating circuit is decoupled from the voltage source 13.
As a result of the decoupling, the resonant current Ires will decrease significantly if the
oscillating circuit is detuned. This will decrease a magnitude of the excitation field which,
in turn, will result in a voltage drop of the voltage induced in the detection winding 2.
Depending on the voltage course detected by the voltage sensor 6, the presence of the
foreign object in the proximity of the excitation winding 12 can be detected. Such a design
provides a high detection sensitivity and an increased robustness of detection.
The decoupling of the detection from the primary field or total field can be achieved by
choosing the resonant frequency of the oscillating circuit different from the operating
frequency of the primary field or total field.
To enhance stability of the operation of the oscillating circuit, a temperature can be
measured by a temperature sensor 38, wherein the operating frequency of the voltage
generator 13 is adapted to the measured temperature.
The excitation winding 12 and/or the detection winding 2 can have an arbitrary design or
shape. It is, however, of advantage that the excitation winding 12 and/or the detection
winding 2 provide a single pole, e.g. provide only one subwinding. In this case, the
excitation winding 12 and the detection winding 2 can be designed equally and arranged
such that their axes of symmetry correspond to each other. A number of turns of the
excitation winding 12 can be chosen different from, in particular smaller than, a number of
turns of the detection winding 2.
Fig. 11 shows a schematic diagram of the proposed safety system 5 in a fifth
embodiment. In this case, the detection winding 2 is part of an LC oscillating circuit. As
shown in Fig. 9, a voltage generator 13 is operated at the resonant frequency of the
oscillating circuit, wherein losses of the oscillating circuit are compensated by the voltage
source 13. The oscillating circuit is provided by a resonant capacitive element Cres and
the detection winding 2. Again, the elements of the oscillating circuit are designed such
that the oscillating circuit provides an infinite impedance with respect to the voltage source
13. Within the oscillating circuit, a resonant current Ires flows. This resonant current Ires
generates a voltage falling across the parallel connection of the capacitive element Cres
and the detection winding 2. If a foreign object (not shown) is placed within the proximity
of the detection winding 2, the oscillating circuit is detuned. In this case, the resonant
frequency of the oscillating circuit does not match the operating frequency of the voltage
source 13.
The oscillating circuit is coupled to the voltage generator 13 by an element Z, wherein an
impedance of the element Z is higher, e.g. 10OOtimes higher, than the impedance
provided by the oscillating circuit or the impedance of the detection winding 2. Thus, the
oscillating circuit is decoupled from the voltage source 13.
As a result of the decoupling, the resonant current Ires will decrease significantly if the
oscillating circuit is detuned. This will, in turn, result in a voltage drop of the voltage falling
across the aforementioned parallel connection. Depending on the voltage course detected
by the voltage sensor 6, the presence of the foreign object in the proximity of the detection
winding 2 can be detected. Such a design provides a high detection sensitivity and an
increased robustness of detection.
Fig. 12 shows a schematic diagram of the proposed safety system 5 in a sixth
embodiment. The safety system 5 comprises n oscillating circuits which are connected in
parallel, wherein only one voltage sensor 6 is used in order to measure the voltage falling
across the parallel connection of all oscillating circuits. Each oscillating circuit comprises a
capacitive element Cres_1 , Cres_2, Cres_n and a detection winding 2 1, 2 2, 2_n which
provides the inductive element. The detection sensitivity of the shown safety system 5
depends on the number n of parallel connected oscillating circuits. A higher number n of
oscillating circuits decreases the detection sensitivity. It is, however, possible to adjust the
detection sensitivity by tuning the impedance of the element Z. The impedance of the
element Z, for example, can be increased until a voltage falling across the parallel
connection of all LC oscillating circuits reaches a minimal value, wherein the minimal
value represents a voltage value which can be measured with a desired precision.
An important property of the safety system 5 shown in Fig. 12 is a self-surveillance
function. If one element of one oscillating circuit, e.g. a capacitive element Cres_1 ,
Cres_2, Cres_n or a detection winding 2 1, 2 2, 2_n, is defective, e.g. provides a short
circuit, the voltage measured by the voltage sensor 6 will break down.
Fig. 12a shows a schematic diagram of the proposed safety system 5 in a seventh
embodiment. The safety system 5 is designed as the safety system 5 shown in Fig. 12,
wherein, the safety system 5 comprises n series connections of a an element Z 1, Z2,...,
Zn with a predetermined impedance and an oscillating circuit, wherein said series
connections are connected in parallel. However, the safety system 5 comprises n voltage
sensors 6_1 , 6_2, 6_n, wherein each voltage sensor 6_1 , 6_2, 6_n measures the
voltage falling across one oscillating circuit. In this case, the safety system 5 comprises
only one single voltage source 13 per array of parallel connections. Using n voltage
sensors 6_1 , 6_2, 6_n advantageously allows, however, detecting or estimating a
position where a foreign object 4 (see e.g. Fig. 1) is located as the object will only detune
one or a small number of oscillating circuits. Consequently, the resulting voltage drop will
be detected by the corresponding voltage sensor(s) 6_1 , 6_2, 6_n. Each voltage
sensor 6_1 , 6_2, 6_n can be provided by a individual measurement channel of a
common voltage sensor.
In Fig. 13, another embodiment of the proposed safety system 5 is shown. The safety
system 5 comprises multiple detection windings 2 and an excitation winding, which is not
shown in Fig. 13. Further, the safety system 5 comprises at least one cancellation winding
22. Also shown is a voltage source 23 which operates the cancellation winding 22. Also
shown is an object 4 placed in the proximity of the detection winding 2 on the surface of a
route 11. For illustration purposes, only one detection winding 2 is shown. The
cancellation winding 22 is designed and arranged such that a total field shown by field
lines 24 is cancelled by a cancellation field shown by field lines 25 generated by the
cancellation winding 22 in a subarea of the surface of the route 11. After the object 4 is
detected by means of the detection winding 2, an area of location can be determined
based e.g. on a specific identifier of the detection winding 2. Then, a cancellation winding
22 assigned to the entire charging surface 10 (see Fig. 2) or to the respective detection
winding 2 can be operated by the voltage source 23 such that the total field 24 can be
cancelled or reduced at least within the area of location, preferably only within the area of
location. In particular, the voltage source 23 operates the cancellation winding 22 such
that an alternating electromagnetic field is generated which has the magnitude of the total
field but is oriented in a direction opposite to a direction of the total field 24. This
advantageously allows local cancellation or reduction of the total field 24 and thus reduces
heating of the object 4.
In Fig. 14, an array structure 27 of detection windings 2 is shown. The detection windings
2 are all circular-shaped, each providing a detection surface 9. It is shown that the
detection windings 2 next to each other have no overlap of the detection areas 9. In this
case, interspaces 26 between the circular-shaped detection windings exist. Such an
arrangement provides a high sensitivity of detection if an object 4 (see Fig. 2) is placed at
least partly over a detection area 9 of a detection winding 2. If, however, an object 4 is
placed over an interspace 26, such an object may not be detected or a sensitivity of
detection is decreased.
In Fig. 15, another array structure 27 of circular-shaped detection windings 2 having a
circular-shaped detection area 9 is shown. In this case it is shown that the detection
windings 2 are arranged such that detection areas 9 of different detection windings 2, in
particular neighboring detection windings 2, overlap such that there are no interspaces 26
(see Fig. 14). This increases a coverage of a desired surveillance area while providing a
high sensitivity. However, a large number of detection windings 2 have to be used.
In Fig. 16, an array structure 27 of hexagonal-shaped detection windings 2 is shown. Also
shown is a primary winding structure 7 which is arranged underneath the array structure
27 of hexagonal-shaped detection windings 2. These detection windings 2 also provide
detection surfaces 9 which are hexagonal-shaped. For illustration purposes, only one
hexagonal-shaped detection winding 2 and one detection surface 9 is denoted by a
reference numeral. The shown array structure 27 advantageously provides a high
coverage of a desired charging surface or surveillance area located above or over the
primary winding structure 7 with a high sensitivity while an amount of detection windings 2
is reduced. To achieve this, the hexagonal-shaped detection windings 2 are arranged
such that a honeycomb arrangement is provided. This means, that an edge of hexagonalshaped
detection winding 2 is arranged parallel to an edge of a neighboring hexagonalshaped
detection winding 2, wherein a displacement between the two neighboring edges
is minimized. The hexagonal-shaped detection winding 2 advantageously provides a
constant or nearly constant detection sensitivity across the total detection surface 9 of
such a detection winding 2.
Multiple detection windings 2 of the array structure 27 can form a group of detection
windings 2. Thus, multiple detection windings 2 can be arranged in subgroups, wherein
the safety system 5 comprises one connecting means per subgroup, wherein each
detection winding 2 of a subgroup is connectable to an evaluation unit, e.g. a voltage
sensor 6, via the respective connecting means. The connecting means can be e.g. a d e
multiplexing unit 3. Via such a unit 3, each detection winding 2 of a subgroup can be
connected to one evaluation unit. This advantageously allows using only one evaluation
unit for the array structure 27 of detection windings 2.
Another option is shown in Fig. 17. Fig. 17 shows a detailed view of an arrangement 27 of
hexagonal-shaped detection windings 2 with a hexagonal-shaped detection surface 9.
The detection windings 2 are arranged in a matrix-like structure, wherein the safety
system comprises a first connecting means which is assigned to the sequence of rows of
the matrix-like structure, and a second connecting means, which is assigned to the
sequence of columns of the matrix-like structure. The first and second connecting means
can be provided by a de-multiplexing unit 3. Via the first and the second connecting
means, each of the detection windings 2 of the array structure 27 is connectable to an
evaluation unit, e.g. a voltage sensor 6. In this case, a first connecting terminal of a
detection winding 2 can be connectable to the first connecting means, wherein a second
connecting terminal of the detection winding 2 can be connectable to the second
connecting means.
In Fig. 18, another embodiment of a proposed safety system 5 is shown. The safety
system 5 comprises a wayside power converter 29, an impulse generator 30, a primary
winding structure 7 and a detection winding 2 (see Fig. 2), which is not shown in Fig. 18.
Furthermore, the safety system 5 comprises an acoustic sensor 3 1, e.g. a microphone.
The impulse generator 30 is electrically connected to the primary winding structure 7.
Also, the wayside power converter 29 is electrically connected to the primary winding
structure 7. The impulse generator 30 can generate an impulse 32 which, in turn,
generates an electromagnetic field via the primary winding structure 7. The
electromagnetic field generated by the impulses 32 can create eddy currents in a metallic
object 4 placed on the charging surface 10 of the route 11. These eddy currents interact
with an electromagnetic field, which can either be the electromagnetic field generated by
the impulses 32 or another electromagnetic field generated by signals of the wayside
power converter 29. The resulting Lorentz forces will cause the metallic object 4 to vibrate
and to create sound waves symbolized by wave lines 33. The sound waves 33 will be
received by the acoustic sensor 3 1. An evaluation unit 34 evaluates the sound waves 33
and depending on the received sound waves 33, the presence of the object 4 can be
detected. This advantageously provides a redundancy of detection.
It is possible, that the proposed sound-based system prevents an independent invention.
In this case, the safety system comprises an impulse generator, means for generating an
excitation field, e.g. an excitation winding, and an acoustic sensor and an evaluation unit.
In Fig. 19, a further extension of the proposed safety system 5 is shown. In this case, the
safety system 5 comprises a microwave transmitter 35 and a detection winding 2
designed as a microwave receiver. The microwave receiver 35 and the receiver 2 are
arranged with respect to the surface of the route 11 such that an object 4 placed on the
charging surface 10 of the route 11 can be detected. By using a microwave-based
approach, moving objects 37 can be detected. It is shown that the microwave transmitter
35 generates signals with the operating frequency f0. If a moving object 37 moves on the
surface of the route 11, the reflected wave signals will have a frequency depending on the
velocity v of the moving object 37. Based on the Doppler effect, a moving object 37 can be
detected. If the microwave transmitter is operated by or comprises an LC generator which
generates the microwaves, the operating frequency of the LC generator can be detuned
due to a stationary metal object 4 located within the proximity of the LC generator. In this
case, the waves received by the detection winding 2 will have frequency depending on the
amount of detuning which, in turn, depends on the change of the inductivity of the LC
generator by the foreign metal object 4. Based on the changed frequency, a stationary
metal object 4 can be detected. It is possible that the change of the frequency caused by
a moving object 37 is similar to the change of frequency due to a stationary metal object
4. In this case, an additional criterion needs to be evaluated in order to identify a moving
or a stationary object 37, 4. For example it can be determined if the change of frequency
is constant or almost constant for a predetermined time period. If this is the case, a
stationary object 4 can be identified since a moving object 37 will most preferably have left
the detection range of the microwave transmitter-receiver configuration within the time
period.
In Fig. 20, a schematic diagram of a detection winding 2 designed as a primary field or
total field compensating winding 2 is shown. The detection winding 2 is designed such
that a total field shown by arrows 24 is compensated for. The detection winding 2
comprises a first subwinding 2a, and a second subwinding 2b. In general, the detection
winding 2 should be designed such that an even number of poles, which can e.g. be
provided by one subwinding 2a, 2b, is provided. The first and the second subwinding 2a,
2b are arranged and connected such that a current I , which flows through the subwindings
2a, 2b, flows in a first turning direction, e.g. a counter-clockwise direction, through
subwinding 2a and in a second turning direction, e.g. a clockwise direction, through the
second subwinding 2b, wherein the first turning direction is opposite to the second turning
direction. In total, the detection winding 2 is 8-shaped. If the total field 24 is almost
homogeneous and extends through areas enclosed by the first and the second
subwinding 2a, 2b, the voltages induced in the first subwinding 2a and the second
subwinding 2b have the same magnitude but an opposite sign. Thus, the total voltage
induced in the detection winding 2 by the total field 24 is zero or nearly zero, at least at the
operating frequency of the total field. Thus, the effect of the total field on the inductive
sensing system and on the detection sensitivity is minimized. An object 4 (see Fig. 1)
placed in the proximity of either the first or the second subwinding 2a, 2b can therefore be
detected depending on the change of the base inductance L0 of the detection winding 2
even if a total field 24 exists. Shown is also an evaluation unit 3 which is able to evaluate
an inductance of the detection winding 2. As described previously, this design can also be
applied to an excitation winding 12a, 12b (see e.g. Fig. 6a).

Claims
1. Safety system for an inductive power transfer system for transferring power to a
vehicle on a surface of a route ( 1 1),
wherein the primary unit comprises at least one primary winding (7) for generating an
electromagnetic primary field for the inductive power transfer, wherein a charging
surface ( 10) of the route ( 1 1) is assigned to the primary winding,
wherein the safety system (5) comprises at least one inductive sensing system,
wherein the inductive sensing system comprises multiple detection windings (2)
characterized in that
the multiple detection windings (2) are arranged in an array structure (27), wherein the
array structure (27) covers the charging surface ( 10) at least partially.
2. The safety system of claim 1, wherein a detection winding (2) is part of an LC
oscillating circuit.
3. The safety system of claim 2, wherein a predetermined number of oscillating circuits
are connected parallel to each other, wherein the inductive elements of each of the
oscillating circuits are at least partially provided by one detection winding.
4. The safety system of claim 1 to 3, wherein the inductive sensing is designed as a
primary field or total field compensating sensing system and/or each detection winding
(2) is designed and/or arranged as a primary field or total field compensating winding.
5. The safety system of claim 4, wherein at least one of the detection windings (2)
comprises an even number of counter-oriented subwindings (2a, 2b).
6. The safety system according to one of the claims 1 to 5, wherein the inductive sensing
system comprises at least one excitation winding ( 12, 12a, 12b).
7. The safety system according to claim 6, wherein the excitation winding ( 1 2a, 12b, 12)
is part of a LC oscillating circuit.
8. The safety system according to one of the claims 6 or 7, wherein the excitation
winding(s) ( 12, 12a, 12b) and the detection windings (2) are arranged such that a
foreign object (4) located on or in a proximity of the charging surface ( 1 1) is arranged
in between the excitation winding(s) ( 12, 12a, 12b) and the detection windings (2).
9. The safety system according to one of the claims 6 or 7, wherein the excitation
winding(s) ( 12, 12a, 12b) and the detection windings (2) are arranged such that a
foreign object (4) located on or in a proximity of the charging surface ( 1 1) is arranged
above the excitation winding(s) ( 12, 12a, 12b) and above the detection windings (2).
10. The safety system according to one of the claims 6 to 9, wherein at least one
excitation winding ( 12) is provided by the primary winding (7).
11. The safety system according to one of the claims 6 to 9, wherein the excitation
winding (12, 12a, 12b) is provided by a winding structure different from the primary
winding (7).
12. The safety system according to claim 11, wherein an excitation winding (12, 12a, 12b)
or a group of excitation windings (12, 12a, 12b) is/are designed and arranged such
that an excitation field (8) is generated such that a magnetic flux received by (a)
corresponding detection winding(s) (2) is zero in a normal operating mode.
13. The safety system according to claim 12, wherein the excitation winding (12, 12a, 12b)
is designed such that an even number of poles is provided, wherein the excitation
winding (12, 12a, 12b) and a corresponding detection winding (2) are arranged and/or
designed such that the magnetic flux generated by different poles extends through the
detection surface of the detection winding (2).
14. The safety system according to one of the claims 1 to 13, characterized in that the
safety system (5) comprises an acoustic sensor (31 ) and a current impulse generating
means.
15. The safety system according to one of the claims 1 to 14, wherein the safety system
(5) comprises a microwave transmitting device and a microwave receiving device.
16. The safety system according to claim 15, wherein at least one of the detection
windings (2) is designed as the microwave receiving device and/or one excitation
winding (12, 12a, 12b) is designed as the microwave transmitting device.
17. The safety system according to one of the claims 1 to 16, wherein the detection
windings (2) are designed as circular detection windings.
18. The safety system according to claim 17, wherein the circular detection surfaces (9) of
at least two circular detection windings (2) at least partly overlap.
19. The safety system according to one of the claims 1 to 16, the detection windings (2)
are designed as hexagonal-shaped or rectangular-shaped detection windings.
20. The safety system according to one of the claims 1 to 19, wherein the safety system
(5) comprises at least one primary field or total field cancellation means for generating
a cancellation field (25), wherein the cancellation means is designed and/or arranged
such that the primary field or total field (24) can be at least partially cancelled by the
cancellation field (25).
2 1 . Method of operating a safety system (5) of an inductive power transfer system for
transferring power to a vehicle on a surface of a route ( 1 1),
wherein the primary unit comprises at least one primary winding (7) for generating an
electromagnetic primary field for the inductive power transfer, wherein a charging
surface ( 10) of the route is assigned to the primary winding (7),
wherein the safety system (5) comprises at least one inductive sensing system,
wherein the inductive sensing system comprises multiple detection windings (2)
arranged in an array structure (27) covering the charging surface ( 10) at least partially,
wherein
- an output signal of each of the the multiple detection windings (2) is measured,
- an electrical characteristic or parameter is determined depending on the measured
output signal and
- the electrical characteristic or parameter is compared to a reference value.
22. The method of claim 2 1, wherein
- an excitation field (8) is generated by at least one excitation winding (12, 12a,
12b),
- the excitation field (8) is received by at least one corresponding detection winding
(2) and
- an output voltage of the at least one detection winding (2) is evaluated.
23. The method according to one of the claims 2 1 to 22, wherein
- an acoustic sensor (31) captures sound waves after the excitation field (8) has
been generated and
- an output signal of the acoustic sensor (31) is evaluated.
24. The method according to claim 2 1 to 23, wherein a radar or microwave signal is
emitted along the charging surface ( 1 0), wherein the reflected radar or microwave
signal is received by at least one microwave receiving device, wherein a radar- or
microwave-based object detection based on the received signal is conducted.
25. The method according to claim 2 1 to 24, wherein a cancellation field (25) is generated
by at least one primary field or total field cancellation means if a foreign object (4) has
been detected.
26. Method of building a safety system (5) for an inductive power transfer for transferring
power to a vehicle on a surface of a route ( 1 1), wherein the primary unit comprises at
least one primary winding (7) for generating an electromagnetic primary field for the
inductive power transfer, wherein a charging surface (10) of the route is assigned to
the primary winding (7), wherein
- multiple detection windings (2) are provided,
- the detection windings (2) are arranged in an array structure (27), wherein the
array structure (27) covers the charging surface ( 10) at least partially.