US20170163100A1 - Foreign object detection in inductive power transfer field - Google Patents

Foreign object detection in inductive power transfer field Download PDF

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US20170163100A1
US20170163100A1 US15/320,606 US201515320606A US2017163100A1 US 20170163100 A1 US20170163100 A1 US 20170163100A1 US 201515320606 A US201515320606 A US 201515320606A US 2017163100 A1 US2017163100 A1 US 2017163100A1
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foreign object
current
power
transmitter coil
real
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Sander VOCKE
Tom VOCKE
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Apple Inc
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PowerbyProxi Ltd
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Priority to US16/372,299 priority Critical patent/US10879743B2/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/60—Circuit arrangements or systems for wireless supply or distribution of electric power responsive to the presence of foreign objects, e.g. detection of living beings
    • H02J5/005—
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/10—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling
    • H02J50/12—Circuit arrangements or systems for wireless supply or distribution of electric power using inductive coupling of the resonant type
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/90—Circuit arrangements or systems for wireless supply or distribution of electric power involving detection or optimisation of position, e.g. alignment
    • H02J7/0026—

Definitions

  • the present invention is in the field of inductive power transfer systems. More particularly, although not exclusively, the invention relates to a method and system for detecting foreign objects present on an inductive power transfer surface and in particular to foreign objects located between an inductive power transfer surface and a receiver.
  • Inductive power transfer systems are used to wirelessly provide power from a transmitter device to a receiver.
  • This technology is now being used in wireless charging pads for handheld devices.
  • a primary side or transmitter generates a time-varying magnetic field with a transmitting coil or coils. This magnetic field induces an alternating current in a suitable receiving coil or coils that can then be used to charge a battery, or power a device or other load.
  • the transmitter coil(s) or the receiver coil(s) may be connected to capacitors to create a resonant circuit, which can increase power throughput or efficiency at the corresponding resonant frequency.
  • a common problem with inductive power transfer systems is controlling when the transmitter should be powered and when the transmitter should be switched off.
  • a further problem arises when a non-receiver (a foreign object) is brought into the range of the transmitter, and an unwanted current (and therefore heat) is induced therein.
  • These non-receivers are typically known as parasitic loads.
  • a conducting foreign object may be located between the transmitter and a compatible receiver. Transmitting in this instance may result in damage to the transmitter and/or receiver.
  • a method for determining the presence of a foreign object in an inductive power transfer field in which control circuitry of an inductive power system performs the steps of: providing power to a direct current to alternating current converter, providing power from the converter to a transmitter coil in the inductive power transfer field, waiting for the current in the transmitter coil to stabilize, estimating the reactive power in the transmitter coil, estimating the real power in the transmitter coil, and using the estimated reactive power and estimated real power to determine whether a foreign object is present.
  • an inductive power transfer device comprising: a converter adapted to be electrically connected to a power supply and adapted to output alternating current to a transmitter coil, a controller for controlling the frequency of the converter output alternating current, at least one transmitter coil adapted to receive alternating current from the converter and further adapted to generate a time-varying magnetic field with predetermined frequency and strength, at least one sensor adapted to sense features of the inductive power transfer device voltage and current from which estimates of real and reactive power though the transmitter coil can be made and provide sensor output to the controller, said controller configured to: control the supply of power to the transmitter coil, receive signals from the sensor as to current flow through the transmitter coil, determine when the current in the transmitter coil has reached a steady state condition, receive sensor output from the sensor of features of the inductive power transfer device voltage and current, estimate the real and reactive power in the transmitter coil from the sensor output received from the sensor, and determine whether a foreign object is present based on the estimated real and reactive power.
  • FIG. 1 shows a block diagram of an inductive power transfer system
  • FIG. 2 shows the resulting shapes of four frequency sweeps with and without a foreign object and/or a receiver present
  • FIG. 3 shows the results gained when the centre of the shapes B, C and D depicted in FIG. 2 , weighted by the total area of the respective shapes, are plotted.
  • FIG. 1 is a block diagram shown a general representation of an inductive power transfer system 1 .
  • the inductive power transfer system includes a transmitter 2 and a receiver 3 .
  • the transmitter includes a DC-AC converter 4 that is electrically connected to an appropriate power supply 5 , such as Mains power. In FIG. 1 this is shown as converter 4 being connected to a DC-DC converter 6 that is in turn connected to the DC power supply 5 .
  • the converter 4 may be a non-resonant half bridge converter or other converter adapted for the particular inductive power transfer system, such as a push-pull converter.
  • the converter 4 is configured to output an alternating current of desired frequency and amplitude to one or more transmitting inductors 7 .
  • the voltage of the output of the converter may also be regulated by the converter 4 , the DC-DC converter or combination of both.
  • the transmitting inductor(s) 7 may be a suitable configuration of one or more coils or other electrically reactive components which provide an inductance, depending on the characteristics of the magnetic field that are required in a particular application and the particular geometry of the transmitter.
  • the transmitting inductors may be connected to reactive components, such as capacitors, (not shown) to create a resonant circuit.
  • the transmitting coil(s) receive alternating current from the converter 4 and generate a time-varying magnetic field. The frequency and strength of the magnetic field are controlled by the controller. Each transmitter coil may be individually operated.
  • FIG. 1 also shows control circuitry or a controller 8 of the transmitter 2 .
  • the controller can be directly or indirectly connected to the various components (blocks) of the transmitter.
  • the controller receives inputs from the connected parts of the transmitter and produces an output that controls the way those parts of the transmitter operate.
  • the controller may include or have access to electronic storage 9 .
  • the electronic storage is an on-board memory.
  • the controller may be a programmable logic controller that is programmed to perform different computational tasks depending on the requirements of the inductive power transfer system.
  • FIG. 1 further shows representations of sensors 10 a and 10 b for sensing particular operating characteristics of the transmitter 2 . It is understood that the sensors 10 a and 10 b may be connected to other or different parts of the transmitter than as depicted, be provided as a single integrated sensor, or as more than two distributed sensors, depending on the characteristics being sensed. The invention is not limited in this respect.
  • FIG. 1 shows representations of sensors 10 a and 10 b for sensing particular operating characteristics of the transmitter 2 . It is understood that the sensors 10 a and 10 b may be connected to other or different parts of the transmitter than as depicted, be provided as a single integrated sensor, or as more than two distributed sensors, depending on the characteristics being sensed. The invention is not limited in this respect.
  • FIG. 1 further shows representations of sensors 10 a and 10 b for sensing particular operating characteristics of the transmitter 2 . It is understood that the sensors 10 a and 10 b may be connected to other or different parts of the transmitter than as depicted, be provided as a single integrated sensor,
  • the sensor 10 a is shown connected to the junction between the DC-DC converter 6 and the DC-AC converter 4 , which is appropriate for measuring the current supplied to the converters, and the sensor 10 a is shown connected to the transmitting inductor(s) 7 , which is appropriate for measuring the current through, or voltage over, the inductor(s) 7 .
  • the sensors 10 a and 10 b may be alternatively or additionally adapted to sense the required characteristics elsewhere in the transmitter system.
  • the receiver 3 includes one or more receiving inductors 11 provided as a suitable configuration of one or more coils or other electrically reactive components which provide an inductance, that are suitably connected to receiver circuitry 12 that in turn supplies received power to a load 13 .
  • the load may be, for example, a rechargeable battery.
  • the receiver circuitry converts the induced current into a form that is appropriate for the load.
  • the receiving inductors may be connected to reactive components, such as capacitors, (not shown) to create a resonant circuit.
  • the receiver may also include control circuitry either as part of the receiver circuitry 12 or as one or more separate components (not shown) for disabling current to flow into the receiver load, effectively “disconnecting” the load from the system 1 .
  • This control circuitry may also generate a start-up sequence including a time delay prior to enabling current to flow into the load, or wait for a signal from the transmitter prior to enabling current to flow into the load.
  • This functionality may be implemented by any suitable means, such as a series electronic switching device between the load and the rest of the system.
  • ‘real power’ is defined as the total average power being dissipated in the system, plus any power flowing into the receiver's load
  • ‘reactive power’ is defined as the average power that is flowing back and forth between energy storage devices (such as capacitors and inductors) in the system, without being dissipated
  • ‘apparent power’ is defined as the product of the root mean square current going into the system and the root mean square voltage going into the system.
  • the “system” is anything after the point at which a measurement is being made, e.g., when measurement is at the input of the DC-AC converter, anything that comes before is not included in the “system”.
  • a non-resonant “hard-driven” inductive power transmitter circuit the voltage on the transmit coil is substantially a square wave and the current through the coil is substantially a triangular wave.
  • the difference between a non-resonant and a resonant inductive power transmitter circuit, as the terms are commonly used in the field of inductive power transfer (as opposed to their strict technical definitions), is as follows.
  • a series circuit having a transmitter conductor and a capacitor may be resonant or non-resonant depending on the values of the inductor and the capacitor, and the driving frequency.
  • the reactance of the inductor and capacitor are the same order of magnitude resulting in substantially sinusoidal waveforms with a variable phase difference.
  • the reactance of the capacitor is of a lower order of magnitude than that of the inductor, and the resulting waveforms resemble a square wave (voltage) and a triangular wave (current) with no fixed phase relationship.
  • FIG. 2 shows the results in curves or shapes (these terms are used synonymously and interchangeably herein) A, B, C and D of estimating real and reactive power at a plurality of frequencies with and without foreign objects present.
  • a calibration value for both real and reactive power is stored prior to obtaining measurements.
  • the origin of the graph represents a 0% offset from the calibration value for that frequency. If all frequencies measured have the same values as the respective calibration measurements then all the measurement points are at the origin.
  • the x axis is the percentile difference between the real power and its respective calibration measurement at that frequency.
  • the y axis is the percentile difference between the reactive power and its respective calibration measurement at that frequency.
  • a plurality of measurements can be made at a plurality of frequencies.
  • Each of the data sets are plotted with their points connected by a curve.
  • every curve is a data set of measurements at different frequencies. Every point in the curve is a measurement at a different frequency, but with the same placement of objects in the field.
  • the points are connected by a curve in ascending order of frequency.
  • D first and D last represent the lowest and highest measurement frequency for curve D, respectively.
  • Curve D corresponds to a bigger foreign object than curve C, resulting in bigger differences in average and size compared to curve B, than curve C.
  • the curves for foreign objects are offset from those for non-foreign objects in both spread size and average value.
  • the offset difference is in part dependent on the degree of overlap of the foreign object on the coil(s), for example, when the foreign object only partially overlaps a coil the difference is reduced.
  • FIG. 3 shows the results gained when characteristics of the shapes from FIG. 2 are used for foreign object determination.
  • the averages and sizes of the shapes can be evaluated. Averages are then the average percentile offset from the respective calibration. Sizes are the difference between maximum and minimum offset from the respective calibration. This is evaluated separately for the real and reactive parts so the results are plotted on separate axes in FIG. 3 . The averages are weighted by the sizes.
  • Curves B, C and D in FIG. 2 are each represented by a single point in FIG. 3 as points B, C and D, respectively. These points can then be compared to a threshold determined or pre-set for foreign object detection.
  • the dotted line in FIG. 3 is an example of a threshold that would, in the case presented, separate the foreign object situations (points C and D) from the non-foreign object situation (point B).
  • This method could also be used for foreign object detection in the absence of a receiver. Based on these measured relationships and characteristics of foreign objects and IPT receivers, different measurement regimes may be used to detect the presence of foreign objects. Examples of such regimes are now described.
  • a transmitter may begin foreign object detection when the presence of a potential receiver is detected.
  • a receiver may be brought into proximity with the transmitter prior to commencing foreign object detection.
  • the detection of the presence of a potential receiver can be performed in a number of ways, for example, the various methods and systems described in PCT Publication No. WO 2013/165261, the entire contents of which are hereby incorporated by reference, may be used.
  • the receiver is configured to commence a charging start-up mode when the receiver detects the presence of a transmitter and prior to being charged by the transmitter. In this mode the receiver runs in a substantially no-load condition, as the receiver keeps the output load disconnected. In this condition there may still be the load of the receiver controller circuitry itself. This condition may continue for a set period or until a signal is received from the transmitter to cease the start-up mode.
  • the transmitter performs foreign object detection during the start-up mode. The transmitter may send the signal once foreign object detection is completed and if no foreign object is detected. Once the predetermined period expires, or a signal is received from the transmitter, the receiver begins charging and the load is connected to the receiver coil(s).
  • the controller controls the converter so that it supplies the inductor with alternating current at one or more test frequencies.
  • the test frequencies are of the same order of magnitude as (and may include) the power transfer frequency used by the inductive power transfer system.
  • the controller Upon supplying the current at the test frequency(s) the controller waits for a predetermined period for the current to stabilize within the transmitter coils in foreign object detection mode.
  • the controller may also wait for current to stabilize within the receiver.
  • the predetermined period is typically approximately 50 milliseconds.
  • the sensor 10 a is configured to sense the average direct current into the converter 4 (prior to DC to AC conversion). The output from the sensor is provided to the controller. The product of the average direct current into the DC to AC converter 4 with the power supply voltage provides an estimate of the average real power in the transmitter coil.
  • the controller controls one or more sensors (e.g., the sensor 10 b ) to sense the peak alternating current through the transmitter coils and the peak voltage across the transmitter coils.
  • the peak voltage may be fixed, and therefore the known peak voltage need not be sensed.
  • the controller combines these values into an estimate of the reactive power.
  • the reactive power in the transmitter coil is estimated as
  • the controller may be a microprocessor, an FPGA, other digital logic device or an analog discrete multiplier/integrator.
  • the estimated reactive power provides a close estimate of the reactive power as the current relating to reactive power is dominant over the current relating to real power through the transmitter coil where the current is measured. This holds as long as little or no real power is being drawn by the receiver.
  • the real and reactive power estimates may be performed at one test frequency or over a plurality or sweep of frequencies and combined into a data set for further analysis.
  • the plurality of frequencies are not limited to the charging or operating frequency of the transmitter.
  • the real and reactive power of the receiver will depend on the receiver's mechanical or material design (for example, proportionate use of ferromagnetic material, e.g., ferrite, metal, etc.), position (for example, distance from and degree of overlap with the transmitter coil), the receiver circuitry itself and the presence of any foreign object(s).
  • the real and reactive power are not substantially dependent on the receiver's load.
  • the controller determines whether a foreign object is present. This determination can be by any suitable means, including but not limited to: comparing estimated values to threshold values stored in electronic storage, comparing the estimated values to calibration values stored in electronic storage, determining a shape of the estimated values or a characteristic of the estimated values and comparing this to a threshold or expected value. While the data set may be viewed as a shape (see FIG. 2 ; discussed in detail later) the transmitter controller mathematically evaluates the data set to determine a characteristic of the data set. For example, average value and centre can be determined directly from the data set. Those skilled in the art will be aware that other characteristics can be determined directly from the data set.
  • calibration values of real and reactive power for each transmitter coil with no load and with no foreign object present are stored in the inductive power transfer system memory and accessed by the controller for comparison purposes.
  • Calibration values for real and reactive power for each transmitter coil may be stored in the electronic storage for a plurality of frequencies. Preferably these frequencies include the test frequencies.
  • the presence of a foreign object may be determined by comparing the estimated real and reactive power through the transmitter coil(s) to the calibration values.
  • the receiver ferrite At low receiver loads, the ferrite may cancel out the change in reactive and/or real power caused by foreign metal.
  • the influence for the receiver ferrite at low loads may be just as large, or larger than, that of the metal (foreign object) in between. It also means that the curve seen when multiple frequencies are measured is not always linear or close to linear.
  • Ferrite, or more generally ferromagnetic material is typically provided in the receiver in association with the receiver coil(s) in order to augment the induced magnetic field and increase the amount of power coupled from the transmitter coil(s).
  • the controller may evaluate the data set and find a characteristic of the shape to determine whether or not a foreign object is present. For example, the size, average value or centre of the shape as evaluated from the data set.
  • a transmitter may begin foreign object detection when the presence of a potential receiver is detected.
  • a receiver may be brought into proximity with the transmitter prior to commencing foreign object detection.
  • the receiver is configured to commence a charging start-up mode when the receiver detects the presence of a transmitter and prior to being charged by the transmitter. In this mode the receiver runs in a substantially no-load condition, as the receiver keeps the output load disconnected. In this condition there may still be the load of the receiver controller circuitry itself. This condition may continue for a set period or until a signal is received from the transmitter to cease the start-up mode.
  • the transmitter performs foreign object detection during the start-up mode. The transmitter may send the signal once foreign object detection is completed and if no foreign object is detected. Once the predetermined period expires, or a signal is received from the transmitter, the receiver begins charging and the load is connected to the receiver coil(s).
  • the controller controls the converter so that it supplies the inductor with alternating current at one or more test frequencies.
  • the test frequencies are of the same order of magnitude as (and may include) the power transfer frequency used by the inductive power transfer system.
  • the controller Upon supplying the current at the test frequency(s) the controller waits for a predetermined period for the current to stabilize within the transmitter coils in foreign object detection mode. The controller may also wait for current to stabilize within the receiver.
  • the predetermined period is typically approximately 50 milliseconds.
  • the controller controls one or more sensors (e.g., the sensor 10 b ) to sample the instantaneous voltage and current through the transmitter coil.
  • the output from the sensor(s) is provided to the controller.
  • Multiple samples of the instantaneous voltage over the transmitter coil(s) and the total instantaneous current through the transmitter coil(s) are taken for every cycle of their periodic waveforms, and stored. This process is referred to herein as “sampling the waveforms”. At least one entire period of the voltage waveform and one entire period of the current waveform are sampled by the sensor(s). Either an integer number of periods of the current and voltage waveforms is sampled or a large number of periods of the voltage and current waveforms are sampled so that an integer number of periods is not essential.
  • the controller multiplies the voltage and current waveforms together and the product of the multiplication is integrated.
  • the real power is estimated as the result of the integration divided by the time over which the waveform was sampled.
  • the controller To estimate the reactive power in the transmitter coil(s) the controller first determines an estimate of the apparent power.
  • the apparent power is the product of the root mean square (RMS) values of the current and voltage.
  • the controller calculates the root mean square values of the sampled voltage and current waveforms.
  • RMS root mean square
  • the estimated reactive power has a Pythagorean relationship with the estimated apparent power and the estimated real power, as in the following equation (with all powers in Watts):
  • P REACTIVE ⁇ square root over ( P APPARENT 2 ⁇ P REAL 2 ) ⁇ Equation (2).
  • the real and reactive power estimates are performed at one test frequency or over a plurality or sweep of frequencies and combined into a data set for further analysis.
  • the plurality of frequencies are not limited to the charging or operating frequency of the transmitter.
  • the real and reactive power of the receiver will depend on the receiver's mechanical or material design (for example, proportionate use of ferromagnetic material, e.g., ferrite, metal, etc.), position (for example, distance from and degree of overlap with the transmitter coil), receiver circuitry and presence of any foreign object(s).
  • the real and reactive power are not substantially dependent on the receiver's load.
  • the controller determines whether a foreign object is present. This determination can be by any suitable means, including but not limited to: comparing estimated values to threshold values stored in electronic storage, comparing the estimated values to calibration values stored in electronic storage, determining a shape of the estimated values or a characteristic of the estimated values and comparing this to a threshold or expected value. While the data set may be viewed as a shape (see FIG. 2 ) the transmitter controller mathematically evaluates the data set to determine a characteristic of the data set. For example, average value and centre can be determined directly from the data set. Those skilled in the art will be aware that other characteristics can be determined directly from the data set.
  • calibration values of real and reactive power for each transmitter coil with no load and with no foreign object present are stored in the inductive power transfer system memory and accessed by the controller for comparison purposes.
  • Calibration values for real and reactive power for each transmitter coil may be stored in the electronic storage for a plurality of frequencies. Preferably these frequencies include the test frequencies.
  • the presence of a foreign object may be determined by comparing the estimated real and reactive power through the transmitter coil(s) to the calibration values.
  • the receiver ferrite At low receiver loads, the ferrite may cancel out the change in the reactive and/or real power caused by foreign metal.
  • the influence of the ferrite at low loads may be just as large, or larger than, that of the metal (foreign object) in between. It also means that the curve seen when multiple frequencies are measured is not always linear or close to linear.
  • Ferrite, or more generally ferromagnetic material is typically provided in the receiver in association with the receiver coil(s) in order to augment the induced magnetic field and increase the amount of power coupled from the transmitter coil(s).
  • the controller may evaluate the data set and find a characteristic of the shape to determine whether or not a foreign object is present. For example the size, average value or centre of the shape as evaluated from the data set.
  • a transmitter may begin foreign object detection when the presence of a potential receiver is detected.
  • a receiver may be brought into proximity with the transmitter prior to commencing foreign object detection.
  • the receiver is configured to commence a start-up mode that commences when the receiver detects the presence of a transmitter and prior to being charged by the transmitter. In this mode the receiver runs in a substantially no-load condition, as the receiver keeps the output load disconnected. In this condition there may still be the load of the receiver controller circuitry itself. This condition may continue for a set period or until a signal is received from the transmitter to cease the start-up mode.
  • the transmitter performs foreign object detection during the start-up mode. The transmitter may send the signal once foreign object detection is completed and if no foreign object is detected. Once the predetermined period expires, or a signal is received from the transmitter, the receiver begins charging and the load is connected to the receiver coil(s).
  • the controller controls the converter so that it supplies the inductor with alternating current at one or more test frequencies.
  • the test frequencies are of the same order of magnitude as (and may include) the power transfer frequency used by the inductive power transfer system.
  • the controller Upon supplying the current at the test frequency(s) the controller waits for a predetermined period for the current to stabilize within the transmitter coils in foreign object detection mode. The controller may also wait for current to stabilize within the receiver.
  • the predetermined period is typically approximately 50 milliseconds.
  • the controller controls the sensor(s) to sense the amplitudes of the voltage and current through the transmitter coil(s) undergoing foreign object detection.
  • the controller further controls a (further) sensor to sense the phase difference between the voltage and current waveforms.
  • the controller can estimate the real power in Watts in the transmitter coil as:
  • V pk is the peak voltage over the transmitter coil(s) in Volts
  • I pk is the peak total current through the transmitter coil(s) in Amperes
  • ⁇ is the phase difference between the voltage and current waveforms in radians.
  • the reactive power in the transmitter coil in Watts can be estimated by the controller as:
  • Equations (3) and (4) for real and reactive power may require adjustment.
  • One skilled in the art will be able to make suitable adjustments to the given formulas to account for changes in waveforms.
  • the real and reactive power estimates are performed at one test frequency or over a plurality or sweep of frequencies and combined into a data set for further analysis.
  • the plurality of frequencies are not limited to the charging or operating frequency of the transmitter.
  • the real and reactive power of the receiver will depend on the receiver's mechanical or material design (for example, proportionate use of ferromagnetic material, e.g., ferrite, metal, etc.), position (for example, distance from and degree of overlap with the transmitter coil), receiver circuitry and presence of any foreign object(s).
  • the real and reactive power are now not substantially dependent on the receiver's load.
  • the controller determines whether a foreign object is present. This determination can be by any suitable means, including but not limited to: comparing estimated values to threshold values stored in electronic storage, comparing the estimated values to calibration values stored in electronic storage, determining a shape of the estimated values or a characteristic of the estimated values and comparing this to a threshold or expected value. While the data set may be viewed as a shape (see FIG. 2 ) the transmitter controller mathematically evaluates the data set to determine a characteristic of the data set. For example, average value and centre can be determined directly from the data set. Those skilled in the art will be aware that other characteristics can be determined directly from the data set.
  • calibration values of real and reactive power for each transmitter coil with no load and with no foreign object present are stored in the inductive power transfer system memory and accessed by the controller for comparison purposes.
  • Calibration values for real and reactive power for each transmitter coil may be stored in the electronic storage for a plurality of frequencies. Preferably these frequencies include the test frequencies.
  • the presence of a foreign object may be determined by comparing the estimated real and reactive power through the transmitter coil(s) to the calibration values.
  • the receiver ferrite At low receiver loads, the ferrite may cancel out the change in reactive and/or real power caused by foreign metal.
  • the influence of the receiver ferrite at low loads may be just as large, or larger than, that of the metal (foreign object) in between. It also means that the curve seen when multiple frequencies are measured is not always linear or close to linear.
  • Ferrite, or more generally ferromagnetic material is typically provided in the receiver in association with the receiver coil(s) in order to augment the induced magnetic field and increase the amount of power coupled from the transmitter coil(s).
  • the controller may evaluate the data set and find a characteristic of the shape to determine whether or not a foreign object is present. For example the size, average value or centre of the shape as evaluated from the data set.
  • the foreign object detection can be equally performed by control circuitry of the IPT receiver.
  • the control circuitry of either or both of the IPT transmitter and receiver may be configured to ensure that inductive power transfer is only performed if no foreign object is detected, or if the type or location of foreign object detected is determined to not cause a potential problem in the inductive power transfer.
  • the foreign object or non-IPT receiver detection is performed during a start-up or otherwise non-charging or power transfer stage of the operation of the IPT system or receiver.
  • the various methods described could be adapted to be performed at a particular time or times (e.g., intermittently) during charging or power transfer through temporary entry into a non-charging or power transfer stage so as to ensure that foreign object conditions have not changes since charging or power transfer has begun.
  • the methods described may be adapted to be performed during charging or power transfer.
  • the different exemplary methods of foreign object or non-receiver detection described may be performed singularly or in combination, either as a standalone foreign object detection test regime or in conjunction with one or more other foreign object detection tests in the applicable IPT system.
  • Such singular or expanded foreign object detection test regimes could be performed in IPT systems using inductive coupling of single transmitter and receiver coils, so-called 1:1 systems or using inductive coupling of plural transmitter and receiver coils, so-called N:N systems.

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  • Computer Networks & Wireless Communication (AREA)
  • Power Engineering (AREA)
  • Charge And Discharge Circuits For Batteries Or The Like (AREA)
US15/320,606 2014-06-20 2015-06-11 Foreign object detection in inductive power transfer field Abandoned US20170163100A1 (en)

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PCT/NZ2015/050072 WO2015194969A1 (en) 2014-06-20 2015-06-11 Foreign object detection in inductive power transfer field

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