Object detection device for inductive charging system

Abstract

In an inductive charging system, energy is transferred via a magnetic field. An object detection device for an inductive charging system includes a transmitter for transmitting a signal and a directional receiver that receives a significant portion of the magnetic field within the directional spectrum to receive a reflection of the signal. A signal processing device examines the characteristics of the received signal and identifies a hazardous condition associated with the magnetic field. By converting the received signal into a frequency domain signal, the hazardous condition can be identified according to the form of the frequency domain signal. The object detection device of the present invention is suitable for use in an electric vehicle charging device.

Description

[Technical field]

[0001] An object detection device for an inductive charging system. An inductive charging system including an object detection device. A method for detecting a hazardous condition in an object detection device. Summary of the Invention

[0002] Wireless power transfer technologies are increasingly being used to deliver power from a power source to a wide range of devices, from small portable electronic devices such as cell phones and tablets that require a few watts of power, to electric vehicles that require several kilowatts of power. In addition to the convenience of not having to plug in devices for power or charging, the lack of wires and cables reduces clutter on desks and parking lots while reducing clutter, tripping hazards, and the risk of electric shock. Methods for wirelessly transferring power include capacitive and inductive coupling, both of which offer advantages over resistive (i.e., wired) coupling for powering devices.

[0003] Wireless power systems can be designed to deliver anything from a fraction of a watt, a few watts, or even several kilowatts of power from the source to the device or load. Typically, they use an air gap between magnetic coils, but other methods involve delivering power between the plates of a capacitor. They can also be designed to operate at a fixed or variable frequency, making them useful for varying load conditions.

[0004] The energy delivered in this way can be used, for example, to power electronic circuits and power devices. This includes powering consumer devices such as cell phones and tablets. It also includes driving electric motors in electric vehicles and charging batteries in circuits or vehicles. A few watts of power are needed to power a cell phone or charge a battery, and several kilowatts are needed to power a motor or charge a battery in an electric vehicle. The larger the battery circuit or motor, or the faster the battery is charged, the more power that must be transferred across the air gap.

[0005] Wireless power transfer technology has developed in different technology areas, leading to different terms being used to describe essentially the same thing. Common terms include "magnetic coupling," "magnetic induction," "inductive power transfer," "inductive charging," and "resonant inductive power transfer." Although there may be minor differences, these terms are generally used broadly and interchangeably to refer to systems that transfer power from a source to a load across an air gap by means of a magnetic field. In this document, we use the term "inductive charging system" or ICS to identify this type of system.

[0006] Similarly, different terms are used to refer to the various elements of an inductive charging system (ICS). Essentially, an ICS consists of power-related equipment and device-related equipment. The power supply consists of the circuitry that converts the energy from the power supply into a form suitable for driving the coil. Similarly, the device equipment converts the energy induced in the coil by the magnetic field into a form suitable for powering the device or charging the battery in the device.

[0007] Inductive charging systems can be used to charge the batteries of electric vehicles. The driver parks the car on a charging station placed on the ground, which magnetically couples with the vehicle's charging station and transfers energy to the battery. Vehicle inductive charging systems are known by several names, such as WEVC (Wireless Electric Vehicle Charging) systems, electric vehicle chargers, etc. The names are not meaningful and are a matter of commercial choice.

[0008] Inductive charging systems (ICS) used in electric vehicles use power devices with various names such as ground pads and ground pad modules (GPMs) that can be connected to a mains power source. The device is called a vehicle pad or car pad module (CPM) and can be mounted on a vehicle such as a car to provide energy to charge the vehicle's battery. The naming in many cases depends on the language used by the manufacturer. Of course, ICS for electric vehicles can be used for a variety of vehicles including large vehicles such as cars, trucks, buses, and streetcars, and is not limited to roadworthy vehicles. In this specification, we will use the terms GPM (Ground Pad Module) and CPM (Car Pad Module) to distinguish the two main parts of ICS for electric vehicles.

[0009] Other terminology that varies between different implementations of ICS includes "magnetic coil," "inductive coil," and "antenna." These terms are also used loosely and essentially interchangeably to describe the part of an inductive charging system that transfers energy across an air gap. Using these different terms doesn't change anything, but for the sake of accuracy, it should be noted that the element is actually a coil and not an antenna. This is because at typical operating frequencies, the element transfers energy in the near field where only a magnetic field exists.

[0010] Antennas are designed with consideration of the electromagnetic field that is formed when radiated energy passes beyond the near field and into the far field. Where the near field ends and the far field begins depends on the characteristics of the transmitting device (coil, antenna, etc.). In wireless power transfer applications, a precise definition is usually not necessary since the size of the air gap and the frequency at which the system operates will place it firmly in the near field. Nevertheless, the aforementioned "magnetic coil", "inductive coil" and "antenna" are used interchangeably by those working in the technical field of wireless power transfer as well.

[0011] Inductive charging systems may use magnetic coils alone or in combination with other tunable or adjustable elements. In electric vehicle power transfer applications, the ground pad module may include a coil in combination with associated drive electronics, or it may include a coil with some or all of the associated electronics provided in a separate housing. In either case, the coil in the ground pad module is used to transmit power via a magnetic field. Similarly, the car pad module may include a coil in combination with associated control electronics, or it may include a coil with some or all of the associated electronics provided in a separate housing. In either case, the coil in the car pad module is used to receive power via a magnetic field.

[0012] A key design focus for inductive charging systems is maintaining a safe environment. When the system is operational, a magnetic field transfers significant energy into the space between the ground pad module and the vehicle pad module. Even a small domestic system can generate a magnetic field capable of transferring 2-3 kW of energy between the pads. Foreign objects such as coins, paperclips, and foil-covered pots of yogurt can heat up in the magnetic field and cause a fire. Also, living organisms such as people and animals can be at risk of injury when exposed to high-energy magnetic fields.

[0013] This has led to the design of inductive charging systems that can detect objects that are within the magnetic field or that enter the magnetic field. Inductive charging systems typically include object detection devices that identify such objects and shut down the system until the object is moved or removed from the magnetic field.

[0014] International Publication WO2016 / 060748 appears to describe a lifestyle item protection device that uses multiple radar modules to detect objects within a detection area. The radar modules are attached to the sides of the base pad facing away from the base pad to cover the entire surface of the base pad.

[0015] International Publication WO2019 / 086690 appears to describe a monitoring device for an inductive energy transmission device, which evaluates Doppler information and corrects it with a stored Doppler signature stored in the monitoring device.

[0016] In an inductive charging system, energy is transferred via a magnetic field. An object detection device for an inductive charging system comprises a transmitter for transmitting a signal and a receiver having a directionality that includes a substantial portion of the magnetic field for receiving a reflection of the signal within the directionality. A signal processing device examines a characteristic of the received signal and identifies a hazardous condition associated with the magnetic field. By converting the received signal to a frequency domain signal, the hazardous condition can be identified according to the form of the frequency domain signal. The object detection device of the present invention is suitably used in a charging device for an electric vehicle.

[0017] As defined in the claims, the present invention provides an object detection device for an inductive charging system, an inductive charging system including an object detection device, and a method for detecting a hazardous condition in an object detection device.

[0018] The invention and its features, as particularly set forth in the appended claims, together with its advantages, will become more apparent to those of ordinary skill in the art from a consideration of the following detailed description, given by way of example with reference to the accompanying drawings. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram showing the elements of an inductive charging system for electric vehicles. [Diagram 2] FIG. 2 is a schematic diagram showing elements of the object detection device. [Diagram 3] FIG. 3 is a schematic cross-sectional view of a car pad module. [Figure 4] FIG. 4 is a schematic cross-sectional view of another car pad module. [Diagram 5] FIG. 5 is a diagram showing the elements of the charging system. [Figure 6]FIG. 6 shows elements sharing a common antenna via a filter. [Figure 7] FIG. 7 shows elements sharing a common antenna via a multiplexer. [Figure 8] FIG. 8 is a schematic diagram showing further elements of the object detection device. [Figure 9] Figure 9 shows graphs of (a) a substantially symmetric signal, (b) a right-handed signal, and (c) a left-handed signal in the frequency domain. [Figure 10] FIG. 10 is a diagram showing a time domain signal and its corresponding frequency domain signal. [Figure 11] FIG. 11 shows a frequency domain signal with amplitude and distance components. [Figure 12] FIG. 12 shows a frequency domain signal corresponding to a hazard.

[0020] [Detailed Description] Turning now to Figure 1 of the accompanying drawings, an inductive charging system (ICS) 10 comprises a ground pad module (GPM) 12 which includes a coil 14, and a driver circuit 16 which is coupleable to a power source 18. A power signal from the power source 18 is conditioned by the driver circuit 16 into a suitable form for application to the coil 14. The coil 12 is driven by application of this power signal (represented as a current I and a voltage V) to generate a magnetic field 20.

[0021] The power source 18 may be a domestic voltage supply, for example 110V or 220V. In such domestic installations, 2-3kW is the limit, meaning that it would typically take several hours to charge the batteries. A larger power source, such as a 415 volt or higher multi-phase source, could complete charging more quickly. In commercial or industrial applications, more power is possible, and therefore faster charging.

[0022] The size and form of the ground pad module 12 will vary depending on the technical requirements of the system. The coil 14 is depicted in FIG. 1 as being circular, but may be any polygonal or elliptical shape. The coil 14 may be configured as a solenoid, arranged in a double-D configuration, or any other of the widely available coil topologies. The exact form will be determined by the technical requirements of the system and routine design choices. To give an idea of ​​size, the ground pad module 12 is typically around 600mm wide. The height of the GPM should be as low as possible to ensure that the GPM does not pose a snag hazard with the underside of the vehicle or a tripping hazard.

[0023] The inductive charging system 10 also includes a car pad module (CPM) 22. In use, the CPM 22 is located on the vehicle (not shown) at a location dictated by design considerations, for example, under the chassis or floor pan. As the vehicle moves over the GPM 12 and the CPM 22 located thereon, energy is transferred from the GPM to the CPM. The magnetic field 20 is converted by a coil 24 into a power signal (represented as a current I and a voltage V) and conditioned by a drive circuit 26 to deliver energy to a battery 28, so that it is in a suitable form for charging.

[0024] As with the ground pad module (GPM) 12, the size and shape of the CPM 22 is dictated by technical requirements and design choices made in designing the inductive charging system 10. The car pad module (CPM) 22 is similarly provided as a package. Again, the exact form of the coil 24, and therefore the shape and size of the CPM 22, is determined in large part by technical requirements and design choices. The coil 24 does not need to be circular as depicted, and in fact does not even need to have the same shape or topology as the coil 14 in the ground pad module 12. Space within a vehicle is limited. Typically, the goal is to make the CPM 22 as small as possible, for example around 300 mm in width.

[0025] One convenience of the ICS 10 is that the battery 28 on the vehicle may be charged simply by parking the vehicle on the ground pad module 12 in a position where the car pad module 22 and the ground pad module 12 are aligned. A vehicle guidance and alignment device (not shown) is provided to assist the driver in properly positioning the vehicle, and thus the car pad module 22, relative to the ground pad module 12.

[0026] The inductive charging system 10 includes an object detection device 30, shown in Figure 2 of the accompanying drawings. The object detection device 30 may be included in or collocated with the ICS system 10 of Figure 1. The object detection device 30 is comprised of a transmitter 32 for transmitting a signal via an antenna 34, and an antenna 36 coupled to a receiver 38. The antennas 34, 36 are aimed at the volume of space between the coils 14, 24 of the GPM 12 and the CPM 22. The receiving antenna 36 serves to receive a reflection of the signal from the transmitting antenna 34. The object detection thus uses a form of radar to detect objects in the magnetic field 20 in the volume between the car pad module (CPM) 22 and the ground pad module (GPM) 12.

[0027] The characteristics of the transmitted signal can be used as a criterion. At the very least, a change in the signal received by the receiver 38 indicates a change in the operating conditions. Typically, the presence of a reflection indicates the presence of an object. And a change in frequency indicates the movement of the object, i.e., the Doppler effect. Thus, the object detection device 30 can be configured to detect vehicle movement caused, for example, by passengers getting on and off the vehicle, or by a cat or other animal jumping on the vehicle.

[0028] Such a change may indicate an unwanted or unexpected object in the magnetic field 20. The signal from the receiver 38 is passed to a signal processor 40, which processes characteristics of the received signal to determine what caused the change. The processor outputs a corresponding signal δ, and the ICS 10 responds by shutting off the magnetic field 20 (or reducing it to a safe level) until the danger has passed.

[0029] The antennas 34, 36, like all antennas, have a radiation pattern including a beamwidth that may be considered the antenna's directivity. For any antenna, the radiation pattern applies to both the transmission and reception of signals. The object detection device 30 is located in or near the car pad module (CPM) 22 or ground pad module (GPM) 12.

[0030] The exact relationship between the magnetic field 20 and the antenna directivity (i.e., beamwidth) depends on the specific design of the ICS 10. The ground pad module 12 and car pad module 22 are designed so that the magnetic field 20 is contained as much as possible within the volume of space between the GPM and the CPM. The directivity of the object detection antennas 34, 36 must be selected and positioned such that any object within the magnetic field will be "picked up" by the antennas.

[0031] In reality, there will be leakage of the magnetic field beyond the volume of space between the GPM and CPM. To the extent that the magnetic field 20 exceeds prescribed safe levels in areas outside that volume, the directivity of the antennas 34, 36 should include those areas as well. Typically, the antennas 34, 36 are positioned side-by-side with one another or are provided as a single antenna shared between the transmitter 32 and receiver 38.

[0032] Radar equipment is widely available as off-the-shelf units. Thus, although shown as separate elements, the antennas 34 and 36, the transmitter 32 and receiver 38, and the processor 40 or various subcombinations thereof may be provided as a single off-the-shelf unit. The two antennas 34 and 36 may be combined into a single antenna or single unit. Reflections of the signal transmitted from the antenna 34 are received by the antenna 36 and the receiver 38. The received signal is analyzed by a signal processor 40 to detect the presence of objects within the magnetic field 20.

[0033] Current thinking in the design of inductive charging systems is to place the object detection device in or on the ground device. To enable the object detection device to "see" objects in a position where a hazard may occur, multiple sensors (e.g. radar modules) are placed around the periphery of the base pad. See, for example, the above-mentioned International Publication WO2016 / 060748.

[0034] In the ICS 10, the object detection device 30 is preferably, but not necessarily, located in the car pad module (CPM) 22. As a practical matter, it will usually be easier to locate the radar module within or alongside the CPM 22, where the antenna, in use, can "see" the volume occupied by the magnetic field from above towards the ground pad 12 and beyond. Locating the antenna in the center of the CPM 22 will usually be the optimal approach.

[0035] The use of a single unit (e.g., a radar module) is preferred, though not required, and is more cost-effective. Careful selection during the design phase of the signal antenna or transmit / receive antenna pair can provide comprehensive directivity, including the space between the ground pad module and the car pad module that contains the magnetic field, and other areas beyond that volume where the magnetic field may be a risk, without adding significant weight or volume to the car pad module.

[0036] Turning now to the schematic cross-section of the car pad module 22 in Figure 3, the CPM 22 comprises a printed circuit board (PCB) 42 or other support on which are mounted the coil driver circuitry 26 and other electrical and electronic elements associated with the operation of the pad 22. This includes the object detector 30 and its antennas 34, 36. The object detector 30 is mounted in a space 44 bounded by the windings 46, 48 of the coil 24. The crosses and dots here merely represent cross-sections of the coil windings, with current in use conceptually flowing into (crosses) or out (dots) of the page.

[0037] The directionality of the antennas 34, 36 is away from the printed circuit board PCB 42 in the direction represented by arrow 50. If the car pad module (CPM) 22 is installed under a car, the direction of arrow 50 corresponds to a direction away from the car and toward the GPM (not shown in FIG. 3). The combination of positioning the antennas 34, 36 on the CPM 22 and selecting antennas having appropriate radiation patterns enables the object detection device to "see" or detect objects in the magnetic field 20 between the GPM 12 and the CPM 22.

[0038] 4 of the drawings, in an alternative car pad module 22, the circuitry associated with the object detection device 30 is located above a printed circuit board (PCB) 42 (i.e., when in use located on the vehicle side). The antennas 34, 36 "grab" onto the underside of the PCB (as shown, when in use) again pointing downwards in the direction of arrow 50 towards a ground pad (not shown).

[0039] In consideration of Figures 3, 4 and the foregoing discussion, it will be appreciated that the placement of detector circuitry and antennas is a matter of design choice driven by technical requirements.

[0040] Currently, inductive charging systems are provided to customers as a combined system consisting of a ground pad module and a car pad module. However, this situation may change as inductive charging systems become more widespread. OEMs may supply only the car pad module, with the ground pad being supplied by a different company. In that case, OEMs may specify that the car pad module be as light and inexpensive as possible. In that case, the ICS elements would be transferred from the car pad to the ground pad.

[0041] For at least these design reasons, it may be necessary in some inductive charging systems to place the object detection device 30 on or within the ground pad 12. If this is done, the antennas 34, 36 will typically be located below and centrally located on the top surface of the ground pad 12. The antennas will "look down" through the ground pad 12 toward the car pad 22. It may be desirable, or even necessary, to be able to see objects on the surface of the ground pad 12. This requires an antenna radiation pattern that is essentially omnidirectional, at least within a hemisphere above the surface of the ground pad.

[0042] Similarly, while desirable from a weight and space standpoint, some systems may require the use of two or more antennas for transmitting and / or receiving object detection signals. A vehicle layout may include "blind spots," i.e. areas or spaces under the vehicle that are not captured by a single optimal location for an object detection antenna. In these situations, a second antenna for transmitting and / or receiving may be a suitable solution.

[0043] The inductive charging system includes a control device that allows data to be transferred between the ground pad module 12 and the car pad module 22 to control the operation of the system 10. The control device typically includes a wireless link that conforms to existing standards such as Wi-Fi or Bluetooth or a combination thereof. Both Figures 3 and 4 show a Wi-Fi unit 60 located in the space 44 together with the object detection device 30. The Wi-Fi unit 60 has its own antennas 62, 63 for transmitting and receiving signals to a similar Wi-Fi unit (not shown) located on the ground pad.

[0044] There are many ways to place the Wi-Fi and object detectors on the ICS pad. One approach is shown in Figure 5, which treats the object detector 30 and the Wi-Fi unit 60 as completely separate elements, each with its own antenna 36, ​​62. Although the object detector 30 operates in one frequency band and the wireless control link (Wi-Fi unit 60) operates in a different frequency band, it may be necessary to add bandpass filters 66, 68 to each of the object detector 30 and the Wi-Fi 60 to avoid interference from harmonics or other sources.

[0045] The arrangement of Figure 5 requires additional antennas to enable the wireless link, adding additional weight and cost to the ICS 10. The arrangements of Figures 6 and 7 address this problem.

[0046] As shown in Figure 6, a single antenna 70 may be shared between the object detection device 30 and the Wi-Fi element 60. Each of the object detection device 30 and the Wi-Fi element 60 has an associated filter 66, 68 coupled to the antenna. The filter 66 passes the object detection signal between the antenna 70 and the object detection device while blocking the signal from the control device 60. The filter 68 passes the control signal between the antenna 70 and the control device 60 while blocking the object detection signal.

[0047] Alternatively, as shown in FIG. 7, a multiplexer (M) 72 may be disposed between a single antenna 70 and the OD device 30 and the Wi-Fi element 60, so that access to the antenna 70 can be switched at different times.

[0048] In an ideal world, the difference between the signal transmitted by the object detection device's antenna 34 and the signal received by the antenna 36 would clearly indicate the presence of an object in the magnetic field. In reality, there are various situations where external influences can cause a signal difference. If we focus too much on the side of safety, the result is that the system frequently enters a safe operating mode where the magnetic field is blocked or reduced to a safe level. Also, in the event of a false alarm, the ICS will not be able to charge the battery in the expected time.

[0049] It is clearly desirable to be able to distinguish between the true presence of an object in the magnetic field and a false positive. One way to achieve this is to have a definition of a signal difference that corresponds (or may correspond) to a known false positive.

[0050] Returning to FIG. 2, in the object detection device 30, the characteristics of the transmitted signal are used as a criterion and input to the signal processing device 40. This enables the object detection device 30 to detect movement, including a change in the position of an object within its directivity, i.e., the intrusion of an object. The transmitter 32 provides the signal processing device 40 with either the transmitted signal itself or digital data representing the characteristics of the transmitted signal. The receiver 38 similarly provides either the signal or the characteristics of the received signal to the signal processing device 40. If there is a difference in frequency and / or phase between the transmitted and received signals, the processor 40 identifies any such difference as an output δ.

[0051] The detection device 30 of Figure 2 includes a reference store 74 that is used to hold data representing operating characteristics associated with these external events. The operating characteristics may represent waveforms associated with changes caused by the external events.

[0052] The relevant components of the detection apparatus are also shown in Figure 8. The reference store 74 holds a library of data representing the characteristics of reference signals or waveforms 76. The characteristics of each reference signal (which may be in the time or frequency domain) correspond to the properties of the received signal under known operating conditions.

[0053] In this manner, the reference store 74 can hold data representing different waveforms for different events. A person getting into a car might produce a relatively low frequency, high amplitude waveform, whereas a cat jumping into a car might produce a short pulse waveform. The reference store 74 holds enough data to allow the processor 40 to distinguish between multiple different external events.

[0054] When there is a short-term change due to an external event, the processor 40 compares the data representing the signal 58 from the receiver 38 with the data in the reference store 74. The signals 58, 74 may not be identical, but they will be similar. The processor compares characteristics of the waveform of the received signal 58 with characteristics of the reference waveform 76. If there is substantial equivalence between the received waveform and the reference waveform, the processor 40 outputs an indication δ (delta) that there is no or little difference (e.g., δ=0). If there is a difference between the two waveforms, the processor 40 indicates the difference by outputting a value δ≠0.

[0055] It will be appreciated that in practice there will of course be some differences between the signal from the receiver and the signal represented by the data in the reference store 47. These differences are due to different operating conditions and ambient noise. Therefore, the value of δ will never be truly zero. However, it will be close enough to zero so that substantial equality can be determined between the received signal and the represented signal.

[0056] For simplicity, an output value of δ=0 is used herein, but this can be understood to mean sufficiently close to zero to indicate that the two signals are essentially the same. Similarly, the expression δ≠0 does not mean any non-zero value, but rather a value of δ (delta) substantially greater than zero to indicate a lack of equality between the characteristics of the received signal waveform and the characteristics of the reference waveform 76.

[0057] An output of δ=0 means that the change may be caused by a known activity, e.g., a foreign object or living organism entering the magnetic field. This value is therefore a bona fide indication caused by an event, i.e., a foreign object or living organism entering the magnetic field. The ICS 10 must therefore shut off the magnetic field 20, e.g., by turning off or significantly reducing the voltage and current supplied to the coil 14 in the ground pad 12, thereby stopping the magnetic field 20. An output of δ≠0 means that the change is not a known activity, and is likely a false positive. There is no need for the ICS 10 to move.

[0058] There are further measures to mitigate false positives. These measures may be used alone or in combination with each other and in combination with the monitoring of the energy transfer (operation) parameters mentioned above. For the purpose of identifying false positives, the signal can be characterized as either motion or vibration / noise. Motion corresponds to an object within the directivity of the object detection device 30. If motion is detected, it is desirable for the magnetic field 20 to be shut off or at least reduced to a safe level.

[0059] The Fast Fourier Transform (FFT) converts a time domain signal into a frequency domain signal. After the FFT transformation of a signal, we get a frequency domain signal with positive (+f) and negative (-f) frequency components, where f=frequency. The positive and negative frequency components result from the use of complex numbers in the FFT, which are made up of real and imaginary components. Usually, negative frequencies contain the same information as positive frequencies and can be ignored.

[0060] Taking a simple sine wave signal and applying an FFT transform to it, we get a frequency domain signal with positive frequency components at +f and negative frequency components at -f. In comparison, the sound of a musical instrument is more complex, since it is made up of the sound itself and its overtones. In addition to the frequency of the sound itself, the FFT also produces multiple components at the overtone frequencies. In the frequency domain, the sound has elements at +f and -f on either side of f=0.

[0061] FIG. 9(a) of the drawings shows a graph 90 representing a frequency domain signal consisting of essentially symmetrical -f elements 91 and +f elements 92 on either side of a vertical line 94 at f=0. The graph in FIG. 9(a) is presented merely for illustrative purposes and does not correspond to any particular signal or event. However, it is the kind of graph that one would expect to capture when a signal is received by the receiver 38 of the object detection device 30. It contains information that the signal from the transmitter 32 has been reflected by something within the directivity of the detection device 30. Processing of that signal may reveal more information about the object, for example whether it is moving or stationary.

[0062] Systems such as communications and radar often use complex signals to convey information in the time domain. The complex components of these signals are known as in-phase (I) and quadrature (Q) components. Each of these is used to transmit different information. Some radar receivers can represent the received signal as a complex number. The complex form is sometimes shown in rectangular notation with real and imaginary components as previously described in this specification. Complex signals may alternatively be shown in polar notation with magnitude and phase components.

[0063] This means that the complex representation contains more information about the received signal, and therefore the object, that can be used to distinguish between false positives and true events. That information can be extracted by converting the received complex signal in the time domain to an equivalent signal in the frequency domain, for example by FFT.

[0064] Transforming the complex signal into the frequency domain gives a result that contains information about the position and movement of the detected object. Positive frequencies can be thought of as meaning that the object is moving towards the detector, i.e. towards the magnetic field, and negative frequencies as meaning that the object is moving away from the space between the GPM and CPM, i.e. away from the magnetic field. In other words, the signal in the frequency domain contains the following frequencies (left or right): Handedness This means that there will be a bias.

[0065] The graph 90 in FIG. 9(a) described above is Handedness The plots on either side of the vertical line (f=0) 94 are substantially similar, if not identical. The reflected signal is from a moving object, and if the signal is not new, it suggests that the reflection is from a stationary object, which may well be a false positive.

[0066] In contrast, in the frequency domain, Fig. 9(b) and (c) show that Handedness , (c) left Handedness The terms "left" and "right" are arbitrary, with "right" being chosen because the plot in graph (b) has a peak to the right of vertical line 94, and "left" being chosen because the plot in graph (c) has a peak to the left of vertical line 94.

[0067] 9(b) and (c) represent signals (b) and (c) that may be generated, for example, by an object moving (b) toward and (c) away from the object detection device 30. FIG. 9(b) may represent signals generated by a person walking toward a car, and FIG. 9(c) may represent signals generated as the person walks past a car and continues walking away from the car. Thus, the object may be a living human or animal, and may be exposed to the magnetic field if it gets too close to the car. This is a dangerous condition, and the signal needs to be identified as a potentially dangerous event.

[0068] In each of the graphs of Figures 9(a), (b), and (c), any position on the line or curve is related to the energy of the signal received by the receiver 38 at a particular frequency. The area under each curve is therefore related to power. The area under the curve is therefore related to something energetic, such as motion or noise. Object detection, in the antenna 36 and receiver 38, has to do with sensing moving objects (true positives) and ignoring other energy sources (false positives) (see Figure 2).

[0069] In the frequency domain of FIG. 9, motion tends to produce curves that are low in height and therefore cover small areas, while false positives tend to produce plots with large amplitudes that cover large areas.

[0070] The noise is random and tends to cancel out over time. If the energy (represented by the area under the curve) is less than a predefined threshold, no detection occurs. If the area under the curve is greater than a predefined threshold, the detected activity is either identified as an actual detection of motion or a false positive, i.e., unrelated to the motion of a living or inanimate object within the directionality of the object detection device.

[0071] Of course, if there are no reflections received by the object detection unit, the receiver will output a null signal, and there will be a corresponding null in the frequency domain. This null is not zero, and there may be a component of noise, i.e. a noise floor.

[0072] Returning briefly to FIG. 2, the processor 40 processes the signal to determine regions in the frequency domain in order to distinguish between detected events and false positives. Handedness , the ICS 10 outputs a signal (δ) to the processor corresponding to the hazardous condition. The ICS 10 is arranged to respond to the object detection device 30 by ceasing to generate a magnetic field, or at least reducing the magnetic field to a safe level, until the hazard has been eliminated.

[0073] If the left and right are substantially equal, as in the graph of FIG. 9(a), this indicates that the signal may not be due to an object and may be a false positive. In the case of a false positive, the processor 40 outputs a signal indicating that there is no object hazard. Obviously, if there is no hazard, the ICS 10 takes no action related to the hazard and continues to generate the magnetic field 20 to transfer power and thus charge the battery 28 in the vehicle.

[0074] The two time domain signals 100, 102 shown in Figure 10 are converted by the processor 40 into equivalent signals 104, 106 in the frequency domain. This can be done using any of the well-known techniques for converting from the time domain to the frequency domain, for example a Fast Fourier Transform (FFT). In either case, the frequency domain signal will have elements on either side of zero (f=0), as in Figure 9(c). This is an indication of a false positive.

[0075] This frequency domain view of the received signal also allows the detection of multiple objects. This is clearly an advantage, since multiple objects may be in the receiver's directivity substantially at the same time. Furthermore, in many situations, the movement of multiple objects may be related to movement in the form of vibrations of parts of the vehicle or of the ground on which the vehicle is parked. Detecting the vibrations reduces the chance of false detections and improves confidence in the accuracy of the object detection device.

[0076] Automobiles (and other vehicles) are essentially one unitary structure. The car's parts cannot move independently except under limited circumstances, such as when the car is vibrating. The vibrations are caused by external stimuli, such as a heavy vehicle driving in front of the car while it is being charged, or something hitting the car body. Therefore, the detection of vibrations by the object detection device 30 will be a false positive.

[0077] Since each moving object has a characteristic frequency, vibrations usually exhibit a wide frequency spectrum, making it possible to detect vibration-related activity. If different parts of the car are captured moving, the signal is likely vibration-related activity and not due to an object entering the electromagnetic field.

[0078] In Fig. 11, signal 110 represents both the amplitude of the movement and its distance. This signal 110 is obtained by processing the received signal by the processor 40 using well-known techniques such as FFT to generate a frequency domain equivalent signal. Fig. 11 shows an example of a situation where the object detection device 30 detects different parts under the vehicle, which are detected moving at different speeds and in different directions, represented by positive and negative position values. This combination of signals in the frequency domain therefore represents a false positive. There is no safety risk and the WEVC system does not need to stop transmitting energy through the magnetic field.

[0079] Another result of the FFT may be to generate spikes 116 corresponding to a single frequency or a narrow band of frequencies and a single or narrow range of distances, as shown in Figure 12. Figure 12 depicts a situation where an object moving at a well-defined distance at a given speed from the car pad module can be identified, thus indicating a potential danger to objects in the magnetic field. The inductive charging system 10 should be arranged to respond by blocking the magnetic field 20 or at least reducing it to a safe level.

[0080] When an inductive charging system starts up, there is an initial period where the operating parameters change relatively quickly as current flows through the coil, a magnetic field is formed, and energy is delivered to the battery. After this initial change, the ICS settles into a substantially stable state. I say "substantially" because the operating conditions change as the battery is charged. Simply put, the more charge the battery has, the greater the voltage and current required to charge it.

[0081] These behavioral changes occur gradually over minutes or hours. In contrast, a dangerous event, such as a person putting their foot or hand under a car into the magnetic field or a coin being dropped on a ground pad, can occur suddenly. Vibrations, on the other hand, are most likely false positives and are harmless. Vibrations do not indicate a dangerous situation and charging can begin or continue uninterrupted.

[0082] When passengers get on and off the vehicle, the position of the vehicle pad relative to the ground pad, and therefore the position of the ground, can change rapidly. Such an external event can cause a sudden change in operation within a matter of seconds. The change in the relative position between the two pads immediately affects the operating characteristics of the inductive charging system. In particular, the voltage and current can rise or fall, and the transfer efficiency η changes. This change in operating characteristics can be measured.

[0083] Moreover, the way in which the transfer efficiency η changes is repeatable. If the efficiency is represented by a line on a graph, the shape of the line will be the same whether a person gets in or an animal jumps in. Comparing the detected changes to known changes in the operating characteristics helps to reduce false positives, i.e., events that do not correspond to a dangerous situation. Thus, the processor 40, alone or in combination with other control circuits (not shown) in the ICS 10, can mitigate object detection in response to changes corresponding to events such as changes in the height of the vehicle relative to the ground (false positives) and objects in or near the magnetic field (true positives / events).

[0084] While the invention has been described with reference to an object detection device for an inductive charging system and an inductive charging system including an object detection device, it will be understood that this has been described by way of example only and that such modifications and variations as occur to those of ordinary skill in the art may be made without departing from the spirit and scope of the invention as defined in the appended claims and equivalents thereof.

Claims

1. a transmitter for transmitting a signal; a receiver having a directivity including a large portion of a magnetic field for receiving reflections of a transmitted signal within the directivity; a signal processor that characterizes the received reflected signals and identifies hazardous conditions associated with the magnetic field; an object detection device for an inductive charging system in which energy is transferred via a magnetic field comprising: a ground pad module including a coil for generating a magnetic field and a drive circuit coupleable to a power source; a car pad module including a coil for receiving energy from the magnetic field and a drive circuit coupleable to power a battery in the vehicle; a wireless data link between the ground pad module and the car pad module for transmitting data relating to the operation thereof, the wireless data link comprising an antenna associated with the ground pad module and an antenna associated with the car pad module; the object detection device is coupled to one or the other of the antennas associated with the ground pad module or the car pad module; Inductive charging system.

2. The inductive charging system of claim 1 , wherein the signal processor is operable to convert a received signal into an equivalent frequency domain signal and to examine the frequency domain signal to identify a hazardous condition.

3. The inductive charging system of claim 2 , wherein the signal processor is operable to determine handedness in the frequency domain signal to identify a hazardous condition.

4. 4. An inductive charging system according to claim 2 or 3, wherein the signal processor is operable to determine a position and / or a direction of movement of an object within the magnetic field in response to the handedness of the frequency domain signal.

5. the received signal includes a waveform; and 5. The inductive charging system of claim 2, wherein the signal processor further comprises a reference store for holding data representative of characteristics of a reference waveform, the reference store being operable to compare data representative of characteristics of a waveform of the received signal with characteristics of a reference waveform and to identify a hazardous condition responsive to equivalence between the received waveform and the reference waveform.

6. The inductive charging system of claim 5 , wherein the characteristic of the reference waveform comprises a characteristic of the transmitted signal.

7. 7. An inductive charging system as claimed in claim 5 or 6, wherein the reference waveform characteristics comprise frequency and / or phase of the transmitted and received signals, respectively.

8. 8. The inductive charging system of claim 1, wherein the reference characteristic relates to an operational characteristic related to magnetic field energy transfer.

9. The inductive charging system of claim 8 , wherein the reference characteristic relates to energy transfer efficiency.

10. 10. An inductive charging system according to claim 1, wherein the reference characteristic is determined by a voltage signal and / or a current signal associated with the magnetic field energy transfer.

11. 11. An inductive charging system according to any preceding claim, wherein the signal processor is operable to mitigate detection of an object in response to changes corresponding to changes in height of the vehicle relative to the ground.

12. 2. The inductive charging system of claim 1, wherein the object detection device and wireless link are coupled to the antenna via a multiplexer operable to switch access to the antenna between the object detection device and the wireless data link.

13. the object detection device is operable at a first frequency; the wireless data link is operable at a second, different frequency; and the object detection device and wireless link are coupled to the antenna via respective filters associated with the first and second frequencies, respectively; 2. The inductive charging system of claim 1 .

14. the object detection device is coupled to an antenna in the car pad module; and The antenna has a directivity that includes a volume of space between the ground pad module and the car pad module.

10. The inductive charging system of claim 1.

15. Transmitting a signal; receiving a reflection of the transmitted signal from within the magnetic field; and examining a characteristic of the received reflected signal to identify a hazardous condition associated with the magnetic field. An object detection device for an inductive charging system in which energy is transferred via a magnetic field, a ground pad module including a coil for generating a magnetic field and a drive circuit coupleable to a power source; a car pad module including a coil for receiving energy from the magnetic field and a drive circuit coupleable to power a battery in the vehicle; a wireless data link between the ground pad module and the car pad module for transmitting data relating to the operation thereof, the wireless data link comprising an antenna associated with the ground pad module and an antenna associated with the car pad module; the object detection device is coupled to one or the other of the antennas associated with the ground pad module or the car pad module; A method for detecting an unsafe condition in an inductive charging system.

16. Transforming the received signal into an equivalent frequency domain signal; and examining the frequency domain signals to identify a hazardous condition; The method of claim 15 further comprising:

17. 20. The method of claim 16, further comprising determining handedness in the frequency domain signal to identify the hazardous condition.

18. 18. The method of claim 16 or 17, further comprising determining a position and / or a direction of movement of an object in a magnetic field depending on the handedness of the frequency domain signal.

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