WO2019206878A1

WO2019206878A1 - Adaptive sector trigger for doppler radar

Info

Publication number: WO2019206878A1
Application number: PCT/EP2019/060323
Authority: WO
Inventors: Friedbert Stuhlfelner; Michael Kausche
Original assignee: Continental Automotive Gmbh
Priority date: 2018-04-27
Filing date: 2019-04-23
Publication date: 2019-10-31
Also published as: DE102018206592A1

Abstract

An apparatus for detecting objects in a critical area of a wireless power transfer system is disclosed. The apparatus comprises a plurality of sensors, wherein the sensors are directional sensors, and at least one processor configured to receive sensor data from the plurality of sensors, detect an object in the critical area based on the received sensor data, and determine whether the object represents a living object based on a comparison of the received sensor data from multiple sensors of the plurality of sensors.

Description

Adaptive Sector Trigger for Doppler Radar

The instant disclosure relates to wireless power transfer, and more specifically to systems, methods and apparatuses for living object protection in wireless power transfer applications.

Background

Wireless power transfer (WPT) systems provide one example of wireless transfer of energy. For example, the SAE Recommended Practice J2954 entitled "Wireless Power Transfer for Light-Duty Plug-In/Electric Vehicles and Alignment Methodology" addresses the use of inductive charging in automotive applications. In WPT systems based on induction, a primary power device (or

"transmitter") transmits power wirelessly to a secondary power device (or "receiver") . Each of the transmitter and receiver comprises an inductive coupler, typically an arrangement of windings comprising electrically conductive materials, such as Litz wire. An alternating current passing through a primary or transmitter coupler produces an alternating magnetic field. A secondary or receiver coupler is placed in proximity to the primary coupler, and the alternating magnetic field induces an electromotive force (EMF) or current in the receiver coupler according to Faraday's law. The received current is used to wirelessly transfer power to the receiver.

Wireless power transfer to electrically powered vehicles at power levels of several kilowatts may require special protection to insure the safety of persons and other objects in proximity, especially living objects. Measures may include detection of moving objects in the so-called critical space of the WPT system. The critical space of a WPT system may be described as the space where electromagnetic field levels exceed certain critical levels. These levels may be based on regulatory limits for human exposure, magnetic flux density limits determined by eddy current heating effects in foreign metallic objects, or other limits such as those specified by a standard applicable to a particular product or to a particular use case.

The need for protection may be particularly acute for systems where the critical space is easily accessible. Typically the power transfer in automotive applications occurs between a ground-mounted primary transmitter, housed in a ground assembly, and a secondary receiver mounted underneath the vehicle. The critical space is thus generally between the vehicle and ground, and more specifically in a region defined by the electromagnetic fields between transmitter coupler and receiver coupler.

Corresponding protection measures may further include detection of living objects such as humans, extremities of humans such as hands or feet, or animals, to protect them from exposure to strong electromagnetic fields.

Sensors based on high-frequency radio waves may be used to monitor the critical space. This may be done with the well-known "radar" approach, where reflected high-frequency signals or pulses are captured by receivers and analyzed to identify objects.

The automotive undercarriage area is a particularly poor en vironment for radar. Challenges may include different metal objects in or on the underbody, as well as snow, rain, and foreign objects such as wet leaves, dirt, etc. There may be many re flections, and undesired cross-sections due to backscatter. To make matters worse, living objects may have particularly small radar signatures or cross-sections. Yet it is these living objects which must be reliably detected.

Doppler radar techniques may be used to identify objects which move, since motion is generally relevant for living objects such as persons or animals for which protection is desired. However, this motion may be very limited, for example in the case of a cat which is sleeping. Nevertheless, both regulations and the interest of car owners lead to a need for a fast reaction in the case of a living object being present, either by turning off the power transfer or by reducing the power. Particularly important is the area around the ground assembly of the transmitter coupler, up to the outer edge of the automotive underbody where the receiver coupler is located, with an ex tension to nearby areas if the electromagnetic field is also present outside this area. The challenge is to insure the reliable detection of living objects while still limiting the number of false alarms.

It may be particularly difficult in the underbody environment of a vehicle to use traditional or classic radar techniques, due to the problem of reflections. Vehicle underbodies are often made of metal or metallic components, and often with many edges, which yield a confused or "noisy" signal. Therefore, special techniques may need to be used in order to identify living objects in an underbody environment of a vehicle.

Depending on the configuration of the wireless power transfer system, it may be desirable that the sensors be mounted on the ground assembly together with the transmitter coupler. Multiple sensors may be used, each covering a different subset of the critical area to be protected. Directional sensors may be used, such that each sensor has a different perspective on the critical area. It may even be possible to identify living objects with high reliability if the living object approaches the critical area from outside the critical area, and therefore is detected by some sensors before being detected by other sensors.

Summary

Thus, in order to insure that the electromagnetic field levels are not exceeded, there is a need for systems, methods and apparatuses for improved living object protection in wireless power transfer applications.

Detection can be improved by using multiple independent sensors with a directional sensitivity, and coordinating the detection results of the multiple sensors. Brief description of the Figures

Figure 1 shows a Wireless Power Transfer system as a charging system for an electric vehicle.

Figure 2 shows an example of a critical area in relation to a ground assembly and a vehicle underbody.

Figure 3 shows the same critical area as covered by the sectors of increased sensitivity of multiple directional sensors.

Figure 4 shows one example of a directional sensor using a specific housing.

Figure 5 shows an example of a directional sensor using a phased array .

Figure 6 shows steps of an embodiment to determine the trajectory of an object.

Detailed Description

The detailed description set forth herein is meant to give the person of skill an understanding of certain implementations of the instant invention.

The invention is best understood in the context of wireless power transfer as might be used for an electric vehicle. Figure 1 gives an example of such a context. The electric vehicle 102 is charged with a wireless power transfer system 110 that uses induction to transfer power wirelessly between the wall box 114 and the battery BAT. Electrical power is provided to the transmit coupler LI in the ground assembly G1. The ground assembly may be flush with the floor as in this example, or it may be raised and closer to the undercarriage of the vehicle.

Power is transferred inductively from the transmit coupler LI to the receive coupler L2 located in or on the undercarriage of the vehicle 102. The electricity generated in the receive coupler is regulated and controlled by the charging controller 112, and supplied to the battery BAT.

The transfer power level may be on the order of several kilowatts . For example, the Recommended Practice SAE J2954 specifies charging power levels WPT1 (3.7 kW) and WPT2 (7.7 kW) . Charging may also be at a level of approximately 11 kW or at a different power level. At these power levels, the magnetic field in the vicinity of the transmit coupler and the receive coupler may reach levels which are considered too high for humans and other living beings. For example, a charging system may transfer 11 kW at an operating frequency of between 50 and 150 kHz. Different op erating frequencies may be used, for example a frequency of 85 kHz .

A charging system may generate magnetic or electromagnetic fields which exceed the limits specified by regulations or recom mendations. For example, the standard ICNIRP 1998 entitled "Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic and Electromagnetic Fields (up to 300 GHz)" provides recommendations for exposure to electromagnetic fields such as might be used for wireless power transfer. The critical area or areas for the strength of magnetic or electromagnetic fields is typically within or near the transmit coupler, or between the transmit and receive couplers. Because the recommended limits may easily be exceeded in the critical area, a protection system is needed to insure that either the transmit coupler is turned off, or that the power from the transmit coupler is reduced to a level which insures safety of living objects, or which ensures that recommended limits are not exceeded.

Figure 2 shows one possible constellation of a wireless power transfer system 210 for inductive charging of a vehicle 220, as seen from above. The critical area for a potentially dangerous magnetic field strength is shown as a circle 230; it is this area which must be watched and protected so that living objects do not enter a potentially dangerous magnetic or electromagnetic field. In this example the boundary is drawn as a circle, but the critical area may have any shape, and the boundary may not be a hard boundary but rather represent an indication of ever-increasing concern. The critical area may also in turn be divided by levels of criticality. For example, in an outer critical zone the response to a living object may be to reduce the power, while in an inner critical zone the response may be to turn off all or almost all power.

The critical zone 230 in this example extends a bit beyond the ground assembly 240, which assembly contains the transmit coupler. The critical area may or may not extend beyond the limits of the vehicle undercarriage 220.

Figure 3 shows an example system 310 similar to that in Figure 2, with the vehicle 320, a critical area 330, and a ground assembly 340. Directional sensors 341 and 342 are placed in the corners of the ground assembly 340. The sensors have a directional sensitivity pattern 351, 352. The sensors may receive sensor data from all directions, but in one sector the sensors have a significantly higher sensitivity. For example the sensor 341 in the lower right-hand corner of the ground assembly 340 has a sector with higher sensitivity 351 going towards the upper left-hand corner of the ground assembly. The sector may have an angle of roughly 60 degrees, or between 45 and 90 degrees.

The sector may also not have a sharp boundary 351, as is shown here for convenience, but rather pass from high sensitivity to the normal sensitivity more or less gradually. In fact the sensitivity may be a continuum, whereby the sensitivity is generally highest in the middle of the sector of high sensitivity and lowest in the middle of the sector of lower sensitivity, and the boundary represents a figurative separation between the two zones. Objects are detected more readily and particularly at a greater distance in the sector with higher sensitivity.

Figure 3 also shows how objects at different positions relative to the critical area 330 may be detected by different numbers of sensors. The object A, 375, is outside the critical area in this example. The object A is detected only by sensor 344 with its sector of higher sensitivity 354. The object B, 376, is near or at the edge of the critical area. The object B is detected by both sensor 343 and sensor 344 with respective sectors of higher sensitivity 353 and 354. The object C, 377, is well inside the critical area. In a system with different zones of criticality, this might be an especially critical zone. The object C is detected by multiple sensors 341, 342, 343, 344 with respective sectors of higher sensitivity 351, 352, 353 and 354. In this example, the object is detected by all sensors, but in other systems the object may be detected by a different number of sensors. The objects 375, 376, 377 may correspond to the same object at different points in time. The movement of this object may be derived from the sequence of positions 375, 376, 377. These positions over time may be used to determine the trajectory of the object.

The directional sensors detect objects in the sector of sen sitivity at a greater distance than in other directions. This characteristic may be used by the inventive system or method to allow better differentiation than can be done by measuring distance per se. For example, with radar sensors a metal object may have a much bigger reflective signature in the received sensor data than living objects do, and may therefore be detected at a much greater distance than is a living object. By using multiple sensors with different orientations and coverage sectors, it is possible to detect objects with a small signature, such as living objects, more reliably and consistently.

A processor may apply additional processing of some sort to the received sensor data. This may be needed to distinguish between living objects and irrelevant sensor input. The sensors may be positioned such that when only one sensor detects an object, the object may be present and in the vicinity of the charging system, but when multiple sensors detect an object, it is an indication that the object is in or is entering the critical area, and response actions are needed. The processor may be a central processing unit (CPU) . Likewise, with the information from multiple sensors, it is possible to set or adjust thresholds for detection. Thresholds cannot be set too high - or sensitivity too low - as living objects may be difficult to detect, and in particular may be more difficult to detect than metal objects or other solid objects. The use of received sensor data from multiple sensors can allow thresholds to be set better, so that false detection is avoided while still detecting hard-to-detect objects such as living objects.

The processor may use signals from the sensors to do dynamic threshold adaption, or "tuning" of the sensitivity of sensors in the sensor system. If the information from one sensor indicates that a living object may be entering the critical area, then the sensitivity of one or more sensors may be increased based on the information from sensors. In this way, living objects can be detected well before they enter the critical area, or before they enter the critical area, or at or near the boundary of the critical area .

The information from one or more sensors may be used to establish or estimate a trajectory of a living or potentially living object. This might be as shown in Fig. 3, where an object might first be detected at position 375, being in the sector of higher sen sitivity 354 of the sensor 344. At position 376 the object enters the sector of higher sensitivity 353 of the sensor 343, and may therefore be identified as being in two sectors of higher sensitivity. At position 377 the object is in the critical area, and is in the sectors of higher sensitivity 351, 352, 353, 354 of all four sensors. Thus it is possible for a processor which receives information from the sensors 341, 342, 343, 344 to perform a sort of tracking or trajectory estimation of the object. Likewise, when information from one sensor or from several sensors or from all sensors indicates that there are no objects in or near the critical area, then the sensitivity of one or more sensors may be reduced to reduce the risk or number of false alarms or false positive detections. In another system, when information from one sensor or from several sensors or from all sensors indicates that there are no living objects in or near the critical area, then the sensitivity of all sensors may be reduced to reduce the risk or number of false alarms or false positive detections.

The directional sensors 341, 342, 343, 344 may be radar sensors. The directional sensors 341, 342, 343, 344 may be doppler radar sensors. The directional sensors may be transceivers, i.e. configured to both send and receive signals high-frequency (HF) signals. The directional sensors may be doppler radar trans ceivers. Other types of radar sensors may be used, such as those for ultra-wide-band radar. In addition, other sensors such as ultrasound, light or infrared sensors are also contemplated for the instant invention. An example of a directional sensor configured for doppler radar is shown in Figure 4. An antenna 430 is mounted on a base plate 410, in this example via a socket 420. The two straight sides 441 and 442 of the housing form a back and sides of the housing and are opposite a curved "front" side 443. The walls 461, 462 along the straight sides 441, 442 are substantially thicker than the wall 463 along the curved side 443. As a result of this difference, high-frequency signals from the antenna 430 are significantly damped outside of the straight edges 441, 442, whereas outside of the curved edge 463 they are only slightly damped. The housing may be of a carbonized plastic or a hard foam or any other non-metallic material which allows radar signals to pass, especially in conjunction with a certain amount of damping. The damping of the edges may act to form sectors of higher and lower sensitivity. The sensor may exhibit higher or much higher sensitivity in the sector of the curved side 443 than it does elsewhere.

Another example of a directional sensor is shown in Figure 5. The directional sensor 570 comprises multiple phased-array antenna elements 561. In this example there are 3 such elements. The signals sent by the respective antenna elements and received by the respective elements are shifted in phase such that signals in one direction experience constructive interference, and signals in other directions experience destructive interference. In this way, a directional sensor may be constructed. It may be necessary to add a housing 560 to damp signals which are at 180 degrees from the desired direction, as would be understood by the person skilled in sensor design. The resulting array would allow 360° sensitivity while providing sectors of higher and lower sensitivity. Due to the problem of reflections, the directional sensor may have limited accuracy and/or may need to be swept slowly in order to obtain a usable signal.

The directional sensor of Figure 5 may also be dynamic, in the sense that the phased-array antenna sweeps across the sector of higher sensitivity.

Due to the problem of reflections, especially in the underbody area of a vehicle, a living object may seem to move when it is not moving, or seem not to move when it is moving. This must be taken into account for determining the trajectory of a living object, as shown in one embodiment in Figure 6.

Object movement may be determined to start a trajectory de termination 610, or the steps may be taken regularly or starting with some other event.

When measuring the radial distances of the object to the sensors 620 given their geometric arrangement to each other, there is the possibility of an undetermined position determination of the observed object, such as would be needed for step 625, which is to determine the trajectory of the base object. This can be improved for example via triangulation or determining a radial movement relative to the sensor at step 630.

An object position repeatedly determined over several time steps or measurement instants corresponds to the movement trajectory of the object. Since all relevant objects can show only a moderate acceleration, trajectories in which jumps occur are not possible. This can be checked as a Plausibility of an Object Trajectory at step 635. Nevertheless, if jumps occur, it can be assumed with a certain probability that the cause of the measured signals is of a different nature. Depending on the assumed probability, therefore, the detection thresholds can be increased dynamically at the step Dynamic Threshold Adaption 655 to avoid misdetections . In the opposite case (consistent trajectory), correspondingly lowered values can be used to increase the sensitivity of the detection device.

The adaption at 655 may be with reference to a base threshold which is calibrated at step 650. The base calibration may happen occasionally or regularly or may be done e.g. during or after manufacture. Certain embodiments may not calibrate the base threshold .

Since the sensors used also have the ability to determine the direction of motion of the object, an additional plausibility check can be made. If, for example, a movement is detected on the respective sensor while the movement trajectory corresponds to an increasing distance, this can be regarded as implausible. Increasing the thresholds would again be the logical consequence.

Therefore, it may be necessary to treat the living object as an object doing at least partially a random walk, and use prob abilistic analysis and functions such as are appropriate for a stochastic process. The analysis may include determining the maximum likelihood of a position at a given time. In turn, the results of this analysis can be used to determine a trajectory.

The signal intensity of the sensors can also be used to contribute to detecting movement and determining a trajectory. In step 640 the intensity may be determined.

In an alternative embodiment, the intensity of the signal from the sensors may be used to determine directly the trajectory of an object.

The results of both methods of detecting movement, and of other methods which might also be used, can then be brought together as a last step 660, where the different results are compared, and a living object detected.

Claims

Claims :

1. An apparatus for detecting objects in a critical area of a wireless power transfer system, the apparatus com prising :

a plurality of sensors, wherein the sensors are di rectional sensors; and

at least one processor configured to:

receive sensor data from the plurality of sensors, detect an object in the critical area based on the received sensor data, and determine whether the object represents a living object based on a comparison of the received sensor data from multiple sensors of the plurality of sensors, and wherein the information from the sensors is used to identify the trajectory of an object.

2. The apparatus of claim 1 wherein a sensitivity of at least one of the plurality of sensors is adapted during op eration

3. The apparatus of claim 1 or 2 wherein the sensors are radar sensors .

4. The apparatus of any previous claim wherein the sensors are doppler radar sensors and doppler techniques are used to identify objects which move.

5. The apparatus of any previous claim wherein at least one directional sensor has a coverage area with sensitivity in all directions and a sector with higher sensitivity in one direction than in the other directions.

6. The apparatus of claim 4 in which the sensor has a sector with higher sensitivity over a range of less than 90 degrees .

7. The apparatus of any previous claim wherein the di

rectional sensors are oriented such that the sector with higher sensitivity of one sensor overlaps with the sectors with higher sensitivity of other sensors.

8. The apparatus of any previous claim wherein the plurality of sensors have overlapping sectors with higher sen sitivity, which overlapping sectors comprise the critical area .

9. The apparatus of any previous claim wherein an object inside the critical area is detected by more sensors than is an object outside the critical area.

10. The apparatus of any previous claim wherein the plurality of sensors comprises four sensors located at the four corners of a quadrilateral.

11. The apparatus of any previous claim wherein the sensors are co-located with a transmitter coupler.

12. The apparatus of any previous claim wherein the de

termination includes comparing received sensor data with previously received sensor data.

13. The apparatus of any previous claim wherein the trajectory of an object is determined using a probabilistic function.

14. A method for protecting a critical area from the presence of living objects wherein a processor receives sensor data from a plurality of sensors, detects an object in the critical area based on the received sensor data, and determines whether the object represents a living object, characterized in that

the sensors are directional sensors, and

the information from the sensors is used to identify the trajectory of an object.

15. The method of claim 14 wherein the processor dynamically adapts the sensitivity of one or more sensors of the plurality of sensors during operation.