HK1194869A - Foreign object detection in wireless energy transfer systems - Google Patents

Description

Foreign object detection in wireless energy transfer systems

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application 61/532,785 filed 9 months 2011.

Technical Field

The present disclosure relates to wireless energy transfer and methods for detecting Foreign Object Debris (FOD) on a wireless power transfer system.

Background

Energy or power may be wirelessly transmitted using various known radiated, or far-field, and non-radiated, or near-field techniques, such as described in detail in, for example, commonly owned U.S. patent application 12/613,686 published as US2010/010909445 5/6 2010 and entitled "Wireless Energy Transfer systems," U.S. patent application 12/860,375 published as 2010/0308939 and entitled "Integrated reactor-Shield Structures" at 12/9 2010, U.S. patent application 13/222,915 published as 2012/0062345 and entitled "Low Resistance electric Conductor" at 3/15 2012, and U.S. patent application 13/283,811 published and entitled "Multi-receiver Wireless Energy Transfer for lighting," the contents of which are incorporated herein by reference.

Wireless charging systems that rely on an oscillating magnetic field between two coupled resonators can be efficient, non-radiative, and safe. Non-magnetic and/or non-metallic objects inserted between the resonators do not substantially interact with the magnetic field for wireless energy transfer. In some embodiments, a user of a wireless power transfer system may wish to detect the presence of these "foreign objects" and to control, reduce, shut down, alert, etc. the wireless power transfer system. Metal and/or other objects inserted between the resonators may interact with the magnetic field of the wireless power transfer system in a manner that causes the metal and/or other objects to disrupt the wireless energy transfer and/or substantially heat. In some embodiments, the user of the wireless power transfer system may wish to detect the presence of these "foreign objects" and may wish to control, reduce, shut down, warn, etc. the wireless power transfer system.

Foreign Object Debris (FOD) located near a wireless power transfer system may be benign and/or may interact with the field for energy transfer in a benign manner. Examples of benign FODs may include: dust, sand, leaves, twigs, snow, grease, oil, water, and other substances that do not significantly interact with the low frequency magnetic field. In an embodiment, a FOD may comprise an object that may interact with the field for wireless energy in a benign manner, but which is not restricted from being very close to the area of the resonator of the wireless transmission system due to perceived danger or due to prevailing caution. Common examples of this type of FOD are: for example, a cat may wish to sleep between the coils of a wireless EV charging system. In embodiments, some FODs may interact with magnetic fields in a manner that may disturb the characteristics of the resonator used for energy transfer, may obstruct or reduce the magnetic field used for energy transfer, or may create or burn hazards. In some applications, special precautions are necessary in order to avoid that flammable metal objects become hot enough to burn during high power charging. Some metal objects can heat and have sufficient heat capacity to cause burning or discomfort to a person picking up them while they are still hot. Examples include tools, coils, metal blocks, cans, steel wool, food (chewing gum, hamburger, etc.) wrappers, packets of cigarettes with metal foil, etc.

Therefore, what is needed are methods and designs for detecting or mitigating FOD effects in the vicinity of a wireless energy transfer system.

Disclosure of Invention

According to an exemplary and non-limiting embodiment, a foreign object debris detection system may use a magnetic field sensor and/or gradiometer to measure perturbations in a magnetic field surrounding a resonator of a wireless energy transfer system. The sensor and/or gradiometer may be placed in the magnetic field of the wireless energy sensing system. The sensor and/or gradiometer may comprise a loop of wire and/or a printed conductor track forming a loop, a figure 8 loop, and/or a structure comprising a loop or loops generating an electrical signal across its surface proportional to the amount of magnetic flux. The ring and/or rings may be connected to a high input impedance sensing circuit. The sensing circuit may measure the voltage and/or current in the loop, and/or the relative phase of the voltage and/or current. In an embodiment, the system can include a multi-layer ring for increasing the detection probability of FOD. In an embodiment, the loop may be designed to operate without significantly affecting the characteristics of the wireless power transfer system, such as the disturbance quality factor of the resonator, the efficiency of energy transfer, the amount of power transferred, the amount of heat generated by the system, etc.

According to an exemplary and non-limiting embodiment, a wireless energy transfer system is provided that may include a foreign object debris detection system. The system may include a wireless energy transfer source configured to generate an oscillating magnetic field. Foreign object debris can be detected by a field gradiometer placed in an oscillating magnetic field. A readout circuit can be used to measure the voltage and/or circuitry of the field gradiometer and a feedback loop based on readings from the gradiometer can be used to control parameters of the wireless energy source.

Drawings

Fig. 1 shows a side view of a resonator with a resonator cover providing passive FOD mitigation.

Fig. 2 is two coils that can be used as separate field sensors and can be made into gradiometers that detect differences in the magnetic flux captured by the two separate field sensors.

FIG. 3A shows a two-lobe configuration of two small conductor loops arranged with opposing magnetic dipoles (such a structure may be referred to as a magnetic quadrupole); 3B shows a 4-leaf configuration of aligned magnetic quadrupoles; 3C shows a 4-leaf configuration of opposite quadrupoles, sometimes referred to as octupoles; and 3D shows a 4-leaf configuration extended in the linear dimension. The "+" and "-" signs indicate the direction of the magnetic dipole of each loop with relative reference.

FIG. 4A shows a FOD detector array including loops with squares to achieve a higher area fill factor; and 4B shows an embodiment with two offset arrays that can be used to eliminate blind spots.

Figure 5 shows a FOD detector connected to a readout circuit.

Figure 6 shows an FOD detector array connected to a readout circuit.

FIG. 7 shows an FOD detector array connected to a readout circuit and a synchronization path.

FIG. 8 illustrates an exemplary embodiment of a FOD detector loop.

Fig. 9A-9C show exemplary voltage measurement curves from a digital 8-shaped gradiometer sensor.

Fig. 10 shows a block diagram of an exemplary EV charger system.

Detailed Description

Methods for mitigating FOD risk can be classified into passive mitigation techniques and active mitigation techniques. Passive mitigation techniques can be used to avoid FOD from entering or remaining in areas of high magnetic field. Passive mitigation techniques can reduce the likelihood of FOD interacting dangerously with magnetic fields. Active mitigation techniques can be used to detect and react to the presence of FOD.

Passive mitigation techniques

Passive mitigation techniques can be used to keep the FOD from entering areas between resonators or specific areas of high magnetic field, thereby avoiding interaction between the FOD and the magnetic field.

By way of additional exemplary embodiments, the design of a resonator cap in a wireless power transfer system can provide a passive FOD mitigation technique. In embodiments, the housing of the source and/or device and/or transponder resonator may be shaped to avoid FOD from coming close to areas of the resonator and/or resonator coil where the magnetic field may be large. The resonator housing may be designed to be curved, angled, or shaped to force any FOD on the cover to roll off the cover and away from the resonator and/or high magnetic field. The resonator housing may be shaped or placed to allow gravity to pull objects away from the resonator. In other embodiments, the housing and position of the resonator can be designed to use other natural or ubiquitous forces to move the FOD apart. For example, the force of water flow, wind, vibration, etc. may be used to avoid FOD from accumulating or staying in unwanted areas of the outer-wound resonator. In an embodiment, the resonator may be arranged substantially perpendicular to the ground, such that objects cannot naturally settle or accumulate on the resonator. In embodiments, the resonator housing can include an exclusion region that provides not only a minimum distance between the FOD and the resonator. The exclusion zone may be sufficiently large to ensure that the field outside the exclusion zone is sufficiently small so as not to pose a safety or performance hazard.

An exemplary resonator that provides a degree of passive FOD protection is shown in fig. 1. The magnetic resonator 104 of the wireless power transfer system may be enclosed by the shaped cover 102, or placed under the shaped cover 102. The shape of the cover 102 may force the FOD106 to roll down the cover 102 due to gravity. The shape of the cover 102 may avoid accumulation of the FOD106 on the top of the cover 102 and/or in the vicinity of the resonator 104 by forcing any FOD to the sides of the resonator and/or away from the area surrounding the resonator where the strength of the magnetic field is high enough to cause a hazardous condition due to heating of the FOD. In an embodiment, the FOD may be forced far enough away from the high field region to no longer pose a risk to being heated and/or ignited by the field.

In other exemplary and non-limiting embodiments, passive FOD techniques may include sizing resonators and/or resonator components to reduce the maximum magnetic field density anywhere in the wireless power exchange area below a desired limit. In embodiments, a relatively large resonator coil may be used to mitigate a subset of FOD risks. For a fixed level of power transfer, the use of a larger resonator coil can be used to reduce the magnetic field strength per unit area required to wirelessly transfer a certain amount of power. For example, the maximum magnetic field strength generated by the source may be reduced below a threshold at which heating or other hazards are known to occur. Passive mitigation techniques may not always be feasible or practical or sufficient. For example, it may not be practical to reduce FOD hazards by increasing the size of the resonator due to limitations in system cost or the desire to incorporate the resonator into a system of a given volume. However, even in applications where fully passive techniques are not possible, practical and/or sufficient, passive mitigation techniques may also be used, at least in part, to reduce FOD risk, and which may complement active mitigation techniques.

Active mitigation techniques

According to an exemplary and non-limiting embodiment, an active mitigation technique for FOD may include a detector system that may detect perturbations of metallic objects, thermal objects, resonator parameters, and/or perturbations in the magnetic field distribution.

According to an exemplary and non-limiting embodiment, FOD objects such as metal objects may be of sufficient size, extent, and/or metal composition to disrupt the efficiency or power transfer capability of a wireless energy transfer system. In such cases, the presence of the FOD object may be determined by detecting a change in one or more of voltage, current, and/or power associated with a source resonator and/or a device resonator and/or a repeater resonator of a wireless power system. Some FOD objects may disturb parameters of a resonator used for energy transfer and/or may disturb characteristics of the energy transfer. For example, FOD objects may change the impedance of a resonator. According to an exemplary and non-limiting embodiment, these disturbances may be detected by measuring the voltage, current, power, phase, frequency, etc. of the resonator and wireless energy transfer. Expected or predicted changes or deviations in values can be used to detect the presence of FOD. In an exemplary embodiment, a dedicated FOD sensor may not be needed in the wireless power system to detect or react to FOD.

According to an exemplary and non-limiting embodiment, a FOD object may only weakly disrupt wireless energy transfer and may be substantially undetectable by monitoring an electrical parameter of the resonator and/or a characteristic of the wireless energy transfer. However, such objects may still create a hazard. For example, FOD objects that interact only weakly with a magnetic field may still heat up significantly. Examples of FOD objects that may interact only weakly with a magnetic field, but may experience significant heating, are metal foils and wrapping paper, such as often found in the packaging of chewing gum and cigarettes, and such as often used for packaging food from fast food restaurants such as hamburgers and kentucky fried chicken. When placed between the resonators of a 3.3-Kw wireless energy vehicle charging system, the gum wrapper may not be detectable by detecting electrical parameters associated with the resonators and/or the energy transfer system. However, the wrapper may still absorb sufficient power to heat up quickly and cause the paper to eventually burn.

According to an exemplary and non-limiting embodiment, an activity mitigation system for a FOD may include a temperature sensor to detect hot spots, hot areas, and/or hot objects near a wireless energy transfer system. A system may include any number of temperature sensors, infrared detectors, cameras, etc. for detecting heat sources, thermal gradients, etc. surrounding an energy delivery system. In embodiments, thermal object sensing alone or in addition to other active and passive mitigation techniques may be used, and may be used to further improve the detectability of thermal FOD and/or reduce the false alarm rate of other active FOD systems.

According to an exemplary and non-limiting embodiment, an activity mitigation system for a FOD object that only weakly disrupts a magnetic field between two resonators may include: a sensor for measuring small changes in magnetic field in the vicinity of an FOD object. For example, a metal foil and paper gum packaging may not substantially alter the magnetic flux between the two resonators, but if it covers and/or blocks any portion of the coil or loop area, it may substantially alter the magnetic flux through a much smaller sensor coil or loop. In an embodiment, local disturbances in the magnetic field caused by the presence of the FOD can be detected by measuring magnetic field variations, vibrations, gradients, etc. in the vicinity of the FOD.

According to an exemplary and non-limiting embodiment, as shown in FIG. 2, a FOD sensor may be implemented using two small coils 202, 204. Such sensors may be placed on or near the resonator for wireless energy transfer. During operation, the wireless energy transfer system generates a magnetic field that passes through both wire loops. Each individual ring develops a voltage proportional to the amount of magnetic flux passing through the interior of each ring 206, 208. For the first order, the difference between the voltages formed by the two loops is proportional to the gradient of the magnetic field near the loops. If the two rings are placed in the region of a uniform field and the rings are substantially similar, the difference between the voltages formed by the two rings may be very small. For example, if the gum packaging is placed such that it partially covers one of the rings but not the other, the difference in voltage formed by the two rings will be greater than when the packaging is not present, because the metal foil of the gum packaging can divert or absorb some of the magnetic flux that would normally pass through the rings. In an embodiment, the outputs from the two loops may be subtracted from each other such that when the sensed field is substantially uniform, the combination of the loops produces a small signal and when there is a gradient in the field between the two loops, the combination of the loops produces a measurably larger signal. When the loop and/or coil is configured to generate a signal in the presence of a field gradient, it may be referred to as being arranged as a gradiometer. Note that the signals from the loops may be subtracted using analog circuitry, digital circuitry, and/or by connecting the loops together in a particular configuration. The sensitivity of the sensor and/or gradiometer may be related to the magnitude and/or phase of the voltage difference between the two rings.

According to an exemplary and non-limiting embodiment, the sensitivity of the sensor and/or gradiometer may be adjusted to preferentially detect objects of a given size or greater than a given size. The sensitivity may be adjusted to reduce false detection rates, reduce noise of the detection system, and/or operate over a range of frequencies. In an embodiment, the size and shape of the ring may be adjusted to adjust the sensitivity of the sensor. The rings may be adjusted to include more turns and or to include additional rings, such as four rings or 8 rings, for example. In embodiments, the rings may be placed to have rotational symmetry or may be arranged in a line or shaped to fill an area of any size and shape.

In embodiments where field density may be non-uniform in locations where gradiometers may be placed and/or other gradiometer and/or loop designs may be implemented, the presence of metallic objects may cause a change in the amplitude and/or phase of the waveform corresponding to the difference between the two loop voltages. In an embodiment, the loop may have a plurality of turns. According to an exemplary and non-limiting embodiment, the loop regions 206, 208 may be sized according to the magnetic field length of the wireless energy transfer system, the desired sensitivity of the detection method, the complexity of the system, and the like. If the metallic FOD is substantially smaller than the loop area, only a weak signal may be present when the FOD is present. This weak signal may risk being swamped by noise or interfering signals. If the size of the ring is of the order of the minimum FOD size to be detected (e.g., within a factor of 3), the signal may be large enough for detection at a lower false alarm rate. In embodiments, the FOD sensor and/or gradiometer may comprise one or more rings of different size, shape and/or arrangement. In embodiments, a FOD sensor may include an area with one sensor, more than one sensor, or no sensors.

According to an exemplary and non-limiting embodiment, another approach for measuring the field gradient in the vicinity of a metallic object is to create a coil (also referred to as a loop) in a manner that directly outputs a voltage proportional to the local gradient in the magnetic field. Such a coil serves the purpose of the two coils depicted in fig. 2, but only requires voltage measurement. For example, if one were to double the area of one of the rings depicted in fig. 2 and then twist it into a digital 8-shaped shape in which each leaf of 8 has approximately equal area, but the current induced in each ring by the local magnetic field is transmitted in a different direction, the voltage developed across its two ends would be proportional to the difference in magnetic flux between the two leaves. Fig. 3A-3D depict some exemplary configurations of a twisted loop that can directly output a voltage proportional to the local gradient in the magnetic field.

The two rings shown in fig. 2 may be referred to as magnetic dipoles, the ring in fig. 3A may be referred to as gradiometers and/or magnetic quadrupoles, and the ring in fig. 3B may be referred to as gradiometers and/or octupoles, respectively. A quadrupole configuration can develop a voltage proportional to the magnetic field gradient in the left-to-right direction. The 4-leaf configuration may be configured to measure field gradients (fig. 3B), as well as gradients of field gradients (fig. 3C). Fig. 3D represents an embodiment in which multiple leaves may extend along a linear dimension. In an embodiment, higher order multipoles with an even number of leaves may also be configured to measure spatial perturbations to the magnetic field. In an embodiment, the leaves depicted in fig. 3A-3D may use multiple turns of the conductor.

Each of these configurations can accomplish the goal of measuring magnetic field perturbations due to the presence of a metallic FOD. A configuration with multiple leaves may be advantageous in covering more area without substantially reducing the likelihood of detecting FODs with similar features to the leaves.

The ring configurations depicted in fig. 2 and 3A-3D are depicted as circles to illustrate the direction of current flow induced in the presence of an oscillating magnetic field. Plus and minus indicates that the resulting current is mostly counter-clockwise or clockwise. Shapes other than circles may be more suitable for arrays with higher area fill factors. Examples include square, rectangular, hexagonal, and other shapes laid out with little interstitial space therebetween. Fig. 4A shows an example of a square coil, where it is assumed that the array extends further than shown, and has an equal number of plus and minus rings. The windings of the coil may be connected so that the resulting circuit flows in the direction indicated by the plus and minus signs.

For the configuration shown in fig. 4A, a piece of symmetric FOD may be placed in a location between adjacent rings so that field perturbations do not produce detectable magnetic field gradients. Such a "blind spot" is depicted in fig. 4A. According to an exemplary and non-limiting embodiment, the second layer of the ring array may be placed on top of the first layer, and as shown in fig. 4B, and may be offset laterally. The offset may be selected such that the "blind spot" of the first layer sensor corresponds to the location of maximum detectability for the second layer. In embodiments, the offset may be any offset that increases the likelihood of FOD detection relative to the likelihood of single array detection. In this way, the likelihood of having a large number of blind spots, where a single FOD may not be detectable, may be reduced. Similar schemes of one or more offset arrays may achieve substantially the same advantages in reducing blind spots. The orientation of the rings in the plurality of arrays may also be changed to handle non-uniform magnetic fields.

In embodiments, the leaves in a single ring or dipole, quadrupole, octupole, etc. may have multiple sizes or have non-uniform sizes. In embodiments where the gradiometer may cover regions of non-uniform magnetic field, the loop size may be designed to ensure that the voltage at the output of the gradiometer loop is minimal when the FOD is not present. The loops may be sized such that larger loops are placed in a weaker magnetic field and smaller loops are placed in a higher magnetic field. In an embodiment, the loops may be sized such that larger loops are placed in areas of more uniform magnetic field and smaller loops are placed in areas of more non-uniform magnetic field.

According to an exemplary and non-limiting embodiment, a FOD sensor array may include multiple types of sensors. In embodiments, the FOD sensor may comprise a single loop sensor and/or a dipole gradiometer and/or a quadrupole gradiometer and/or an octapole gradiometer, or the like. Some regions of a FOD sensor may not include gradiometers. The FOD sensor may include a temperature sensor, an organic material sensor, an electric field sensor, a magnetic field sensor, a capacitance sensor, a magnetic sensor, a motion sensor, a weight sensor, a pressure sensor, a water sensor, a vibration sensor, an optical sensor, and any combination of sensors.

Active FOD detection processing

The coil configurations described above (fig. 2-5) may develop oscillating voltages in the presence of non-uniform oscillating magnetic fields, due to, for example, the presence of FOD. According to an exemplary and non-limiting embodiment, a sense amplifier connected to a given coil may have a high input impedance. This arrangement may avoid substantial circulating currents in the sensor coil that would disrupt the Q-factor of the resonator for wireless energy transfer. In an embodiment, the loops, coils, gradiometers, etc. may be connected to amplifiers and/or filters and/or analog-to-digital converters and/or operational amplifiers, and or any electronic components which may be arranged to have a high input impedance. In an embodiment, a FOD sensor may include a conductive loop and high input impedance electronic components.

According to an exemplary and non-limiting embodiment, each conductor pair from each coil (loop, sensor, gradiometer) in the array may be connected to a sense amplifier and/or an analog-to-digital converter, as shown in fig. 5. Each loop conductor 502 may be connected to an amplifier 506 and/or an analog-to-digital converter 508, and may produce an output 504, which output 504 may be used by other elements of the wireless energy transfer system or as an input to a processing element (not shown), such as a microprocessor, for storing and analyzing the output of the coils, loops, sensors, and/or gradiometers.

In other embodiments, as shown in FIG. 6, the voltages on each coil in the array may be measured sequentially or may be multiplexed in a manner that allows fewer sense amplifiers or analog-to-digital converters to sample the array. The ring arrays 602, 604, 606 of gradiometers may be connected to a multiplexed amplifier 608 and to one or more digital to analogue converters 610. The output of the digital to analog converter 612 may be used by other elements of the wireless energy transfer system or as an input to a processing element (not shown), such as a microprocessor, for storing and analyzing the output of the gradiometer.

In an embodiment, each conductor pair of the sensor and/or gradiometer loop may be connected to an active or passive filter circuit to provide a high termination impedance at very high or very low frequencies.

The voltage on a given coil may be sampled in increments that allow the processor to determine the amplitude and phase of the resulting waveform relative to a reference waveform. In an embodiment, the voltage on a given coil may be sampled at least twice per oscillation period (i.e., at or above the nyquist rate). In an embodiment, the voltage on a given coil may be sampled less frequently (i.e., in the higher order nyquist band). The voltage waveform may be analog filtered or conditioned prior to sampling to improve the signal-to-noise ratio or to reduce the harmonic content of the signal to be sampled. After sampling, the voltage waveform may be digitally filtered or conditioned.

The time-sampled electrical signal from the FOD detector coil can be processed to determine the amplitude and phase relative to a reference signal. The reference signal may be derived from the same clock used to excite the resonator for wireless energy transfer.

As shown in fig. 7, in some embodiments, the FOD detection system may include a separate frequency, field strength, and/or phase sampling loop 704 and electronics 702 for synchronizing sensor and/or gradiometer readings to the oscillating magnetic field of the wireless energy transfer system.

In an embodiment, the reference signals may be from different oscillators at different frequencies.

An example of processing a digital 8-shaped octupole configuration (FIG. 3A) for FOD detection may be as follows:

1. collecting a time-sampled voltage waveform from one of the digital 8-rings without FOD

2. Calculating amplitude and phase (or harmonics thereof) of fundamental frequency components

3. Storing amplitude and phase as reference

4. Absent FOD, collecting voltage waveforms from the same figure 8 ring

5. Calculating fundamental wave amplitude and phase (or harmonic thereof)

6. Comparing the amplitude and phase with a reference

7. On a polar plot (or in amplitude and phase space), a FOD is declared detected if the distance between the signal and the reference exceeds a predetermined threshold.

In embodiments, the processing of the signals may be performed using analog electronic circuitry, digital electronics, or both. In an embodiment, signals from multiple sensors may be compared and processed. In embodiments, the FOD sensor may be located on only one, or all, or some of the resonators in the wireless power transfer system. In embodiments, signals from FOD sensors on different resonators may be processed to determine the presence of FOD and/or to impart control information to the wireless power system. In an embodiment, FOD detection can be controllably turned on or off. In embodiments, FOD detection and processing may be used to control the frequency of the wireless power transfer system, the power level transferred by the wireless power system, and/or the time period during which wireless power transfer is enabled and/or disabled. In an embodiment, the FOD detector may be part of a reporting system that may report the presence of FOD to a system user and/or may report the presence or absence of FOD to a higher level system. In embodiments, a FOD detection system may include a "learning capability" that may be used to identify a certain type of FOD, and it may include a system and/or system feedback for classifying the type of FOD as harmless, dangerous to heat, not allowed for other reasons, and the like.

According to an exemplary and non-limiting embodiment, the processing may be embedded in the FOD detection subsystem or the data may be returned to the central processor. The process may compare the collected voltage waveforms to a reference waveform and look for statistically significant changes. Those of ordinary skill in the art will appreciate that the waveforms may be compared in terms of amplitude and phase, I or Q components, sine or cosine components, in the complex plane, and the like.

Exemplary active FOD detection embodiments

Two specific and non-limiting embodiments of FOD detection systems constructed are described below. Data has been collected from both of these examples and shows that they are working as FOD detectors.

In a first embodiment, a strand forms a figure 8 loop, as shown in fig. 8, the figure 8 loop forming a quadrupole (gradiometer 1) with a longer wire between the two loops. The second embodiment is designed as shown by gradiometer 2 in figure 8. The figure 8 ring is approximately 5cm long. Figures 9A-9C show voltage waveforms collected from two sensors placed on top of a wireless energy source between resonators for a 3.3-kW wireless energy transfer system when the system is transferring 3.3kW to a load. FIG. 9A shows a small residual voltage (-30 mVrms) on the two gradiometers depicted in FIG. 8. The residual voltage is caused by a combination of a non-uniform magnetic field, slight variations in the leaf area, and electrical interference. The results from gradiometers #1 and #2 are plotted as curve 904 and curve 902, respectively. When the metal chewing gum foil was placed on the right lobe of gradiometer #2, some flow was prevented and a substantial increase in amplitude and slight phase shift was observed in fig. 9B, curve 902. Conversely, when the foil is moved into the left lobe of gradiometer #2, as shown in fig. 9C, the amplitude remains the same, but the phase is changed by 180 °. These changes in phase and amplitude readings can be used to detect the presence of FOD on the sensor.

Embodiments of the digital 8-shaped sensor are also constructed using Printed Circuit Board (PCB) technology to implement the sensor coil or ring. This embodiment may have advantages including low cost, higher fill factor (since the ring can be made into any shape and laid down easily using standard PCB processing techniques), higher uniformity, higher reproducibility, small size, etc. For a 16-channel array of single digital 8-shaped sensors, a higher fill factor is obtained using laid-down rectangular rings. The printed rings are uniform in height, resulting in a smaller (and flatter) reference reading from the sensor when no FOD is present.

OTHER EMBODIMENTS

In embodiments, the sensors and gradiometers described above may be combined with other types of FODs to increase the detection probability and lower false alarms (when no FOD is present, the system detects a FOD). For example, an array of temperature sensors may be combinatorially integrated into the resonator. If a FOD begins to heat up, it will interfere with the normal expected spatial temperature distribution. The deviation may be used to send an alert to the system controller. In embodiments, a temperature sensor may be used alone or in combination with a metal object sensor and/or may be used as a backup or confirmation sensor for the metal object sensor.

A living being such as a pet may be difficult to detect. Generally, they may not interact with the magnetic field in a substantial manner. Furthermore, the organisms do not heat up significantly when exposed to a magnetic field. However, if a living being invades a magnetic field of a certain field strength, it may be necessary to shut down the wireless power system. The field strength limit may be frequency dependent and may be based on standard limits, safety limits, public awareness limits, and the like. In an embodiment, a non-conductive sensor, such as a long wire, that measures changes in fringe capacitance from a conductor may detect the proximity of a living being. In embodiments, this type of sensor may be used during diagnostic testing, prior to and during wireless energy transfer.

Application to charging of vehicles

In many types of wireless energy transfer systems, detection of FOD can be an important safety precaution. An example of an embodiment for an example of a 3.3-kW car charging system is as follows.

A block diagram of an exemplary EV charger system is shown in fig. 10. The system may be divided into a source module and a device module. The source module may be part of a charging station and the device module may be mounted to an electric vehicle. Power is wirelessly transferred from a source to a device via a resonator. Closed loop control of the transmitted power may be performed over in-band and/or out-of-band RF communication links between the source module and the device module.

The FOD detection system (not shown) may be integrated into the system in various places. In embodiments, the FOD system may be integrated into a source module, a source resonator, a housing or enclosure of a source resonator, or the like. In other embodiments, the FOD system may be integrated onto the device side of the system. In other embodiments, the FOD system may be implemented on both the source and device sides of the wireless power transfer system. In an embodiment, a FOD detection system may include a plurality of sensors and a processor having a discrimination algorithm. The processor may be connected to an interface that acts as an interlock for the source control electronics. Other FOD detection systems may be connected to the charger system through additional interfaces or through an external interface. Local I/O at each module may provide an interface for system level management and control functions in a wireless power system using FOD detection.

The source resonator in a high power (3.3 + kW) vehicle charging system may have the highest magnetic field density near the boundary of the winding, and optionally any magnetic material. In this region, an array of multiple channels containing two figure 8 coils with rectangular lobes can avoid inadvertent heating of the metal FOD. The array may be fabricated on a PCB and may contain integrated filtering and signal conditioning on the board. The second PCB of equivalent design can be placed slightly higher than the first PCB and it is translated sideways in the manner in fig. 4B. The algorithm as described above may be run in an on-board processor, where the output of the processor may be sent to a system controller. The system controller may compare the output of the metal FOD detector with the output of another FOD detector, such as a FOD detector that measures a temperature profile or a non-conductivity change. Then, if FOD is detected, the system can decide whether to turn the system down or off.

Some possible modes of operation of the FOD detection system are as follows:

low power diagnostic tests can be performed with the vehicle absent to check the health and status of the charging station (rare) and to check the FOD before the vehicle is driven by the source (more common).

After the vehicle arrives and is on the source module, but before high power charging, the FOD detector may prove that the source is still free of FOD.

During high power charging, the FOD detector may demonstrate that no additional FOD is moving onto the coil.

While the present invention has been described in connection with certain preferred embodiments, one of ordinary skill in the art will understand that other embodiments are intended to fall within the scope of the present disclosure, which is to be construed in the broadest sense permitted under the law. For example, designs, methods, configurations of components, etc., related to transmitting wireless power have been described above with various specific applications and examples thereof. Those of ordinary skill in the art will appreciate that the designs, components, configurations, or assemblies described in this application may be used in combination, or interchangeably, and the above description does not limit such interchangeability or combination of components to only those described in this application.

It is also noted that the techniques described herein may be applied to any wireless power system that uses electromagnetic fields to transmit power. Where we have described the source and device resonators of a highly resonant wireless power system, one of ordinary skill in the art will appreciate that the same sensors, detectors, algorithms, subsystems, etc. may be described for an inductive system using primary and secondary coils.

All documents referred to in this application are hereby incorporated by reference.

Claims (19)

1. A foreign object debris detection system for a wireless energy transfer system, comprising:

at least one magnetic field sensor, and

at least one readout circuit for measuring an electrical parameter of the at least one magnetic field sensor,

wherein the at least one magnetic field sensor is placed in the magnetic field of the wireless energy transfer system.

2. The system of claim 1, wherein the at least one magnetic field sensor comprises a magnetic field gradiometer.

3. The system of claim 2, wherein the at least one magnetic field gradiometer comprises a digital 8-shaped quadrupole conductor loop.

4. The system of claim 2, wherein the at least one magnetic field gradiometer comprises an octapole conductor loop.

5. The system of claim 2, wherein the readout circuit has an input impedance sufficient to substantially prevent circulating currents in the gradiometer loop.

6. The system of claim 3, wherein the digital 8-shaped quadrupole conductor loop is printed on a circuit board.

7. The system of claim 6, wherein the digital 8-shaped quadrupole conductor loop is rectangular.

8. The system of claim 3, wherein the system comprises an array of gradiometer loops placed in the magnetic field of the wireless energy transfer.

9. The system of claim 8, wherein the system comprises multiple layers of offset and overlapping gradiometer loops.

10. The system of claim 5, wherein the readout circuit is multiplexed between multiple gradiometer loops.

11. The system of claim, further comprising:

a feedback loop for adjusting the parameter of the wireless energy transfer based on a reading from the foreign object debris detection system.

12. The system of claim 2, wherein the gradiometer is at least twice the size of the smallest Foreign Object Debris (FOD) to be detected.

13. A wireless energy transfer system utilizing foreign object debris detection, the system comprising:

at least one wireless energy transfer source configured to generate an oscillating magnetic field;

at least one magnetic field gradiometer positioned in the oscillating magnetic field;

a readout circuit for measuring an electrical parameter of the field gradiometer; and

a feedback loop for controlling the parameter of the wireless energy transfer source in response to the measured electrical parameter of the field gradiometer.

14. The system of claim 13, further comprising:

at least one temperature sensor, wherein the temperature sensor is positioned to measure a temperature in a vicinity of the wireless energy transfer source.

15. The system of claim 13, wherein the energy transfer of the at least one wireless energy transfer source is turned off using readings from the gradiometer.

16. The system of claim 13, wherein the system further comprises: a field gradiometer array connected to a high input impedance readout circuit.

17. The system of claim 16, wherein the high impedance readout circuit monitors the voltage of the gradiometer loop.

18. The system of claim 17, wherein the high impedance readout circuit monitors a phase of a voltage signal of the gradiometer loop.

19. The system of claim 18, further comprising:

a field sensing loop for synchronizing the readout circuit with a frequency of the oscillating magnetic field of the at least one wireless energy transfer source.