# US 2014/0191715 A1 · Method for detecting an electrically conductive foreign body and device for inductively transmitting electrical energy

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- Number: US 2014/0191715 A1
- Document ID: US20140191715A1
- Status: Published application
- Kind: A1
- Application number: 14/122,262
- Filed: 2012-05-24
- Published: 2014-07-10
- Earliest claimed: 2011-05-26
- Assignees: Conductix-Wampfler GmbH
- Inventors: Mathias Wechlin; Pascal Asselin
- Web page: https://patentgrep.com/patent/US20140191715A1

## CPC

- B60L 53/122: Circuits or methods for driving the primary coil, e.g. supplying electric power to the coil
- B60L 53/124: Detection or removal of foreign bodies
- B60L 53/38: specially adapted for charging by inductive energy transfer
- H02J 50/10: using inductive coupling
- H02J 50/12: of the resonant type
- H02J 50/60: responsive to the presence of foreign objects, e.g. detection of living beings
- B60L 2210/30: AC to DC converters
- B60L 2210/40: DC to AC converters
- B60L 2270/147: electro magnetic [EMI]
- Y02T 10/70: Energy storage systems for electromobility, e.g. batteries
- Y02T 10/7072: Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
- Y02T 10/72: Electric energy management in electromobility
- Y02T 90/12: Electric charging stations
- Y02T 90/14: Plug-in electric vehicles
- B60L: PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES (arrangements or mounting of electrical propulsion units or of plural diverse prime-movers for mutual or common propulsion in vehicles B60K1/00, B60K6/20; arrangements or mounting of electrical gearing in vehicles B60K17/12, B60K17/14; preventing wheel slip by reducing power in rail vehicles B61C15/08; dynamo-electric machines H02K; control or regulation of electric motors H02P); SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES (electric coupling devices combined with mechanical couplings of vehicles B60D1/64; electric heating for vehicles B60H1/00); ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL (control or regulation of electric motors H02P); MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION

## Abstract

In a method for detecting an electrically conductive foreign body at a device for inductively transmitting electrical energy from a stationary unit having an electrical power supply unit and a primary inductor to a mobile unit having a secondary inductor and an electric load, electrical power is initially fed from the electrical power supply unit into the primary inductor and the feed-in is interrupted. The curve over time of the resulting decay of an electrical operating variable of the primary inductor is measured and at least one parameter of the measured curve is compared with a corresponding parameter of a reference curve in the event of an interruption of the power feed-in into the primary inductor without the presence of an electrically conductive foreign body. The comparison is used to determine whether an electrically conductive foreign body is present in the region of the magnetic field produced by the primary inductor.

## Claims

### Claim 1

Method for the detection of an electrically conductive foreign body on a device for the inductive transmission of electrical energy from a stationary unit with a power supply unit and a primary coil to a mobile unit with a secondary coil and an electric consumer, in which, initially, electric power is fed from the power supply unit to the primary coil, this feed-in is interrupted, and the curve over time of the decay of an electric operating variable of the primary coil caused by this is measured, wherein at least one parameter of the measured curve is compared with a corresponding parameter of a reference curve, which was determined with an interruption of the power feed-in to the primary coil without the presence of an electrically conductive foreign body in the region of the magnetic field produced by the primary coil, in that with the aid of this comparison, a determination is made as to whether an electrically conductive foreign body is present in the region of the magnetic field produced by the primary coil, wherein with the determined presence of a foreign body from the curve over time of the decay of the measured electric operating variable, a measure is determined for the power that is consumed by the foreign body with the normal operation of the device, and in that with the aid of this determined measure, the power fed into the primary coil is reduced to such an extent that the power consumed by the foreign body remains below a predefined threshold.

### Claim 2 (depends on 1)

Method according to claim 1, wherein an electrically conductive foreign body is detected as being present if the difference between the parameter of the measured curve and the corresponding parameter of the reference curve exceeds a predefined threshold.

### Claim 3 (depends on 1)

Method according to claim 1, wherein the parameter is the relative change of the envelope curve of the curve over time or the effective value of the measured electric operating variable within a predefined time interval, which begins with or shortly after the interruption of the power feed-in, or in that the parameter is the length of a time interval, beginning with the interruption of the power feed-in or shortly afterwards, within which the envelope curve of the curve over time of the effective value of the measured electric operating variable attains a predefined relative change.

### Claim 4 (depends on 1)

Method according to claim 1, wherein the parameter is the value of an ohmic resistance RF, lying as a model for a conductive foreign body in series with the primary coil, which is calculated according to the following formula:
RF=[2LP/(Δt)]·ln[(Iref·I0f)/(I1·I0)],
wherein LP is the value of the inductance of the primary coil, Δt the length of a predefined time interval, I0 and I0F the amplitude or the effective value of the primary current IP before or shortly after the interruption of the power feed-in without the presence of a foreign body or with the presence of the foreign body, and Iref and I1 the values at which the envelope curve or the effective value of the primary current IP decay within the time interval Δt, after interruption of the power feed-in without the presence of a foreign body or with the presence of the foreign body.

### Claim 5 (depends on 1)

Method according to claim 1, wherein the electric operating variable is the current IP through the primary coil or the voltage UP across the primary coil.

### Claim 6 (depends on 1)

Method according to claim 1, wherein with the detected presence of a foreign body, a display unit is activated and/or a defect report is sent to a higher level unit and/or a user of the device.

### Claim 7 (depends on 6)

Method according to claim 6, wherein with a detected presence of a foreign body, the entry of an acknowledgement signal, which indicates a foreign body-free state of the device, is expected by a user of the device on an input unit; after the entry of the acknowledgement signal, a renewed foreign body detection is carried out; and in the case of a renewed detection of the presence of a foreign body, a display unit is activated and/or a defect report is sent to a higher level unit and/or a user of the device, wherein a defective state of the device is indicated on the display unit and/or by the defect report, instead of a foreign body.

### Claim 8 (depends on 1)

Method according to claim 1, wherein the feed-in of electric power to the primary coil remains interrupted, if the measure for the power consumed by the foreign body exceeds a predefined threshold with a normal operation of the device.

### Claim 9 (depends on 1)

Method according to claim 1, wherein the current feed into the primary inductance is adjusted to a value that is smaller or, at most, equal to a value IPmax, which is calculated in accordance with the following formula:
I
P


max
=
P
F


max
2

L
P
Δ


t

ln

(
I
ref
·
I
0


F
I
1
·
I
0
)
;
wherein PFmax is the maximum permissible value of the power consumed by the foreign body; LP the value of the inductance of the primary coil; Δt the length of a predefined time interval; I0 and I0F the amplitude or the effective value of the primary current IP, before or shortly after the interruption of the power feed-in, without the presence of a foreign body or with the presence of the foreign body and Iref and I1 are the values at which the envelope curve or the effective value of the primary current IP decay within the time interval Δt, after the interruption of the power feed-in without the presence of a foreign body or with the presence of the foreign body.

### Claim 10 (depends on 1)

Method according to claim 1, wherein in the presence of a mobile unit with a secondary coil and an electric consumer, before the interruption of the power feed-in into the primary coil, the power supply from the secondary coil to the consumer is interrupted.

### Claim 11 (depends on 10)

Method according to claim 10, wherein the secondary coil is short-circuited and/or the current circuit between the secondary coil and the consumer is interrupted.

### Claim 12 (depends on 1)

Method according to claim 1, wherein due to the interruption of the power feed-in into the primary coil, an electric oscillating circuit is produced without an external stimulus, which contains the primary coil, and wherein the curve of the measured electric operating variable has the form of a decaying oscillation of this oscillating circuit.

### Claim 13 (depends on 1)

Method according to claim 1, wherein the measurement of the curve over time of the decay of an electric operating variable of the primary coil, caused by the interruption of the feed-in electric power into the primary coil, is carried out by means of at least one measurement coil located next to the primary coil.

### Claim 14

Device for the inductive transmission of electric energy from a stationary unit with a power supply unit and a primary coil to a mobile unit with a secondary coil and an electric consumer, wherein the device has a means for the feed-in of electric power from the power supply unit into the primary coil and for the subsequent interruption of this feed-in and has a means for the measurement of the curve over time of the decay of an electric operating variable of the primary coil caused in this way, comprising means for the comparison of at least one parameter of the measured curve with a corresponding parameter of a reference curve, which was determined with an interruption of the power feed-in into the primary coil, without the presence of an electrically conductive foreign body, in the region of the magnetic field produced by the primary coil, means for the determination, with the aid of this comparison, as to whether an electrically conductive foreign body is present in the region of the magnetic field produced by the primary coil, means for the determination of a measure for the power consumed by the foreign body, with the normal operation of the device, from the curve over time of the decay of the measured electric operating variable, with the detected presence of a foreign body, and a means for the reduction of the power fed into the primary coil, with the aid of the determined measure, to the lowering of the power consumed by the foreign body below a predefined threshold.

### Claim 15 (depends on 1)

Device for the inductive transmission of electric energy from a stationary unit with a power supply unit and a primary coil to a mobile unit with a secondary coil and an electric consumer, wherein the device is set up for the execution of the method according to claim 1.