Foreign object detection in wireless power transmission systems

Abstract

The present disclosure provides systems, methods, and apparatus for foreign object detection (FOD) in wireless power transfer (WPT) systems. Some implementations generally relate to the use of a detection coil that is energized to measure and compare a differential current through a coil pair that includes at least two detection coils. A foreign object may cause a change in impedance of one or more detection coils compared to one or more other detection coils. By detecting the differential current of the coil pair, a detection device may determine that a foreign object is in proximity to one of the detection coils of the coil pair. The present disclosure provides several options for design, structure, layout, and operation of the detection coil to improve foreign object detection.

Claims

1. A detection device for a wireless power transmission (WPT) system (100), wherein the detection device is A plurality of detection coils (170) are configured as pairs of detection coils arranged symmetrically with respect to the primary magnetic field of the WPT system and within each foreign object detection zone covering the scanning area of ​​the wireless power transmission device, wherein the first pair of detection coils includes at least a first detection coil (171) and a second detection coil (172), and the plurality of detection coils (170) are configured as such. A first driver (305) configured to simultaneously energize the first detection coil and the second detection coil during the first foreign object detection (FOD) period, A differential current detection device configured to detect a first differential current associated with the difference between a first current in the first detection coil and a second current in the second detection coil while the first detection coil pair is actively excited during the FOD period, The system includes a control unit (155) configured to detect the presence of a foreign object (190) at least partially based on the first differential current exceeding a differential current threshold, Each pair of detection coils has at least two associated detection coils, and these detection coils are connected in parallel to the driver. The differential current detection device is A plurality of differential current sensing circuits configured to acquire a plurality of detection voltages, wherein each detection voltage corresponds to the differential current of a respective pair of detection coils, and the plurality of detection voltages include at least a first detection voltage whose magnitude is at least partially based on the first differential current of the first pair of detection coils, and a second detection voltage whose magnitude depends on the second differential current of the second pair of detection coils, The control unit (155) is For each detected voltage, multiple changes in detected voltages over a continuous FOD period are detected. The system is configured to determine a change count representing the amount of change in the plurality of detected voltages over the continuous FOD period for each detected voltage. The control unit (155) is configured to determine, at least in part, based on the change count, whether the change in the plurality of detected voltages was caused by movement of the wireless power receiving device in the WPT system. The control unit (155) further, (i) If the change count is equal to or greater than the count threshold, it is determined that the change in the plurality of detected voltages is due to the movement of the wireless power receiving device; if the change count is less than the count threshold, it is determined that the change in the plurality of detected voltages is due to the presence of a foreign object, or (ii) A detection device configured to determine the ratio between the change count and the total count of the plurality of detected voltages, and if the ratio is equal to or greater than a ratio threshold, to determine that the change in the plurality of detected voltages is due to the movement of the wireless power receiving device, and if the ratio is less than the ratio threshold, to determine that the change in the plurality of detected voltages is due to the presence of a foreign object.

2. The differential current detection device, The detection device according to claim 1, comprising at least a first magnetic core (510) through which the first current of the first detection coil (171) passes in a first direction and the second current of the second detection coil (172) passes in a second direction, wherein the difference between the first current and the second current generates a magnetic flux coupling within the first magnetic core that represents the first differential current.

3. The differential current detection device, The detection device according to claim 2, further comprising a first differential current detection circuit (501) including a first sensor coil wound around a first magnetic core, wherein the first magnetic core is configured to induce a first electrical signal in the first sensor coil at least partially based on the magnetic flux coupling, and the magnitude of the induced voltage of the first electrical signal is at least partially based on the magnitude of the first differential current.

4. The differential current detection circuit, A rectifier (530) configured to rectify the first electrical signal into a direct current (DC) signal having a first detection voltage, The detection device according to claim 3, further comprising a filter (540) configured to stabilize the first detection voltage of the DC signal.

5. The detection device according to claim 4, wherein the control unit (155) is configured to add or subtract a first offset to the first detection voltage in order to generate a first calibrated detection voltage.

6. The detection device according to claim 5, wherein the control unit (155) is configured to compare the absolute value of the first calibrated detection voltage with a detection threshold, and the foreign object detection signal indicates the presence of a foreign object when the first calibrated detection voltage exceeds the detection threshold, and the foreign object detection signal indicates the absence of a foreign object when the first calibrated detection voltage falls below the detection threshold.

7. The detection device according to any one of claims 1 to 6, wherein the control unit (155) is configured to adjust the plurality of detection voltages based on a set of offset values, and the set of offset values ​​includes at least a first offset value for the first detection voltage and a second offset value for the second detection voltage.

8. The control unit (155) The detection device according to claim 7, wherein the control unit is configured to change the set of offset values ​​based on the change in the plurality of detection voltages when it determines that the change in the plurality of detection voltages is due to movement of the wireless power receiving device in the WPT system.

9. The detection device according to claim 8, wherein the control unit (155) is configured to continuously calibrate the set of offset values ​​taking into account the movement of the wireless power receiving device within the WPT system.

10. A method for a detection device to be used in a wireless power transmission (WPT) system (100), wherein the method is: The plurality of detection coils are configured as pairs of detection coils arranged symmetrically with respect to the primary magnetic field of the WPT system and within each foreign object detection zone covering the scanning area of ​​the wireless power transmission device, wherein the first pair of detection coils includes at least a first detection coil (171) and a second detection coil (172). During the first foreign object detection (FOD) period, at least the first detection coil and the second detection coil are simultaneously energized (1710), The differential current detection device detects a first differential current associated with the difference between the first current of the first detection coil and the second current of the second detection coil while the first detection coil pair is actively excited during the FOD period (1720), The control unit detects the presence of a foreign object, at least in part, based on the first differential current exceeding a differential current threshold, wherein each detection coil pair has at least two associated detection coils, and these detection coils are connected in parallel to the driver, and the detection includes, The differential current detection device is A plurality of differential current sensing circuits configured to acquire a plurality of detection voltages, wherein each detection voltage corresponds to the differential current of a respective pair of detection coils, and the plurality of detection voltages include at least a first detection voltage whose magnitude is at least partially based on the first differential current of the first pair of detection coils, and a second detection voltage whose magnitude depends on the second differential current of the second pair of detection coils, The above method further, The control unit detects changes in multiple detection voltages over a continuous FOD period for each detection voltage, The control unit determines a change count representing the amount of change in the plurality of detected voltages over the continuous FOD period for each detected voltage, The control unit includes determining, at least in part, based on the change count, whether the change in the plurality of detected voltages was caused by movement of the wireless power receiving device in the WPT system. The above method further, (i) The control unit determines that if the change count is equal to or greater than the count threshold, the change in the plurality of detected voltages is due to the movement of the wireless power receiving device, and if the change count falls below the count threshold, the control unit determines that the change in the plurality of detected voltages is due to the presence of a foreign object, or (ii) A method comprising: (ii) determining the ratio of the change count to the total count of the plurality of detected voltages by the control unit; determining by the control unit that if the ratio is greater than or equal to a ratio threshold, the change in the plurality of detected voltages is due to the movement of the wireless power receiving device; and determining by the control unit that if the ratio is less than the ratio threshold, the change in the plurality of detected voltages is due to the presence of a foreign object.

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