Wireless Power Systems With Foreign Object Detection

Abstract

A wireless power system has a wireless power transmitting device and a wireless power receiving device. The wireless power transmitting device uses a wireless power transmitting coil to transmit wireless power signals to the wireless power receiving device. The wireless power transmitting device determines whether an external object is present. The external object may be a foreign object such as a coin or paperclip or may be a wireless power receiving device. External objects are detected using quality-factor measurements. Wireless communications are used to discriminate between foreign objects and wireless power receiving devices. Quality factor measurements may be compensated for aging and temperature effects using temperature measurements and compensation factors based on frequency and measured resistance.

What is claimed is: 
     
         1 . A wireless power transmitting device, comprising:
 wireless power transmitting circuitry having a wireless power transmitting coil configured to transmit wireless power signals; and   control circuitry coupled to the wireless power transmitting circuitry and configured to:
 measure a current quality factor of the wireless power transmitting coil; 
 compare the current quality factor to a baseline quality factor; and 
 determine whether a foreign object is present based at least partly on determining whether the current quality factor is lower than the baseline quality factor by at least a threshold amount. 
   
     
     
         2 . The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to:
 in response to determining that the current quality factor is lower than the baseline quality factor by at least the threshold amount, wirelessly transmit a wireless digital request that requests a corresponding wireless digital response from a wireless power receiving device; and 
 in response to receiving no wireless digital response from the wireless power receiving device corresponding to the wireless digital request, determine that the foreign object is present. 
 
     
     
         3 . The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to compare the current quality factor to the baseline quality factor at least partly by computing a difference between the current quality factor and the baseline quality factor. 
     
     
         4 . The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to compare the current quality factor to the baseline quality factor at least partly by computing a ratio between the current quality factor and the baseline quality factor. 
     
     
         5 . The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to measure the baseline quality factor at an initial time and is configured to save the measured baseline quality factor for later comparison to the current quality factor. 
     
     
         6 . The wireless power transmitting device of  claim 5  wherein the control circuitry is configured to periodically update the baseline quality factor using a filtering operation based on a history of measurements. 
     
     
         7 . The wireless power transmitting device of  claim 6  wherein the control circuitry is configured to perform the filtering operation upon determining that a wireless power receiving device is present and that no foreign object is present and is configured to perform the filtering operation using a current quality factor value measured without the wireless power receiving device present and without the foreign object present. 
     
     
         8 . The wireless power transmitting device of  claim 6  wherein the control circuitry is configured to periodically update the baseline quality factor using a filtering operation based on quality factor measurements made after the initial time. 
     
     
         9 . The wireless power transmitting device of  claim 1  wherein the threshold amount comprises a predetermined threshold amount. 
     
     
         10 . The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to update the threshold amount using a filtering operation based on a history of measurements. 
     
     
         11 . The wireless power transmitting device of  claim 10  wherein the control circuitry is configured to perform the filtering operation to update the threshold amount upon determining that a wireless power receiving device is present and that no foreign object is present and is configured to perform the filtering operation using a current quality factor value measured without the wireless power receiving device present and without the foreign object present. 
     
     
         12 . The wireless power transmitting device of  claim 10  wherein the control circuitry is configured to periodically update the threshold amount using a filtering operation based on quality factor measurements. 
     
     
         13 . The wireless power transmitting device of  claim 1  wherein the baseline quality factor is measured at a first frequency, wherein the current quality factor is measured at a second frequency, and wherein the control circuitry is configured to compensate the current quality factor measurement for a change of the second frequency from the first frequency. 
     
     
         14 . The wireless power transmitting device of  claim 1  wherein the wireless power transmitting coil has an inductive coil resistance that depends on frequency and wherein the control circuitry is configured to compensate the current quality factor measurement for a change in the inductive coil resistance due to a change in frequency. 
     
     
         15 . The wireless power transmitting device of  claim 1  further comprising a temperature sensor configured to measure a temperature, wherein the control circuitry is configured to compensate the current quality factor measurement based on the temperature. 
     
     
         16 . The wireless power transmitting device of  claim 1  wherein the wireless power transmitting coil has an entire inductive coil resistance with direct-current and alternating-current portions and wherein the control circuitry is configured to compensate for changes in the entire inductive coil resistance by:
 determining a compensated value of the entire inductive coil resistance from a sum of a baseline direct-current portion of the entire inductive coil resistance and a current alternating-current portion of the entire coil resistance; and 
 compensating the current quality factor using the compensated entire inductive coil resistance. 
 
     
     
         17 . The wireless power transmitting device of  claim 16  wherein the baseline direct-current portion is measured at an initial time and wherein the current measured alternating-current portion of the entire coil resistance is measured after the initial time. 
     
     
         18 . The wireless power transmitting device of  claim 1  wherein the control circuitry is configured to measure the current quality factor by a selected one of: a) applying an impulse to the wireless power transmitting coil and measuring a decay envelope associated with a ringing signal produced in the wireless power transmitting coil due to the applied impulse and b) measuring the impedance of the wireless power transmitting coil using an alternating-current source coupled to the wireless power transmitting coil and determining the current quality factor from the measured impedance. 
     
     
         19 . A wireless power transmitting device, comprising:
 wireless power transmitting circuitry having a wireless power transmitting coil configured to transmit wireless power signals; and   control circuitry coupled to the wireless power transmitting coil and configured to:
 measure a quality factor for the wireless power transmitting coil by applying an impulse to the wireless power transmitting coil and measuring a decay envelope associated with a ringing signal produced in the wireless power transmitting coil due to the applied impulse; 
 compensate the measured quality factor for a frequency-induced change; 
 compare the compensated measured quality factor to a baseline quality factor; and 
 determine whether a foreign object is present based at least partly on determining that the measured quality factor is lower than the baseline quality factor by at least a threshold amount. 
   
     
     
         20 . A wireless power transmitting device, comprising:
 wireless power transmitting circuitry having a wireless power transmitting coil configured to transmit wireless power signals; and   control circuitry coupled to the wireless power transmitting coil and configured to:
 measure a quality factor for the wireless power transmitting coil by measuring the impedance of the wireless power transmitting coil using an alternating-current current source coupled to the wireless power transmitting coil and determining the quality factor from the measured impedance; 
 compare the measured quality factor to a baseline quality factor; and 
 determine whether a foreign object is present based at least partly on determining that the measured quality factor is lower than the baseline quality factor by at least a threshold amount. 
   
     
     
         21 . A wireless power transmitting device, comprising:
 wireless power transmitting circuitry having a wireless power transmitting coil configured to transmit wireless power signals; and   control circuitry coupled to the wireless power transmitting circuitry and configured to:
 measure a current quality factor of the wireless power transmitting coil; 
 compare the current quality factor to a baseline quality factor; 
 determine, based at least partly on comparing a difference between the current quality factor and a baseline quality factor to at least one threshold, whether a foreign object is present; 
 in response to determining that no foreign object is present, use the wireless power transmitting circuitry to wirelessly transmit the wireless power signals at a first power level; and 
 in response to determining that a foreign object is present, use the wireless power transmitting circuitry to wirelessly transmit the wireless power signals at a second power level that is lower than the first power level. 
   
     
     
         22 . The wireless power transmitting device of  claim 21  wherein the at least one threshold comprises first and second thresholds and wherein the control circuitry is configured to:
 in response to determining that the difference between the current quality factor and the baseline quality factor is below the first threshold, determine that no foreign object is present; 
 in response to determining that the difference between the current quality factor and the baseline quality factor is between the first and second thresholds, determine that a moderate foreign object is present; and 
 in response to determining that the difference between the current quality factor and the baseline quality factor is above the second threshold, determine that a strong foreign object is present. 
 
     
     
         23 . The wireless power transmitting device of  claim 22  wherein the control circuitry is configured to:
 in response to determining that no foreign object is present by determining that the difference between the current quality factor and the baseline quality factor is below the first threshold, use the wireless power transmitting circuitry to transmit the wireless power signals at the first wireless power level. 
 
     
     
         24 . The wireless power transmitting device of  claim 23  wherein the control circuitry is configured to:
 in response to determining that the moderate foreign object is present, use the wireless power transmitting circuitry to transmit the wireless power signals at the second wireless power level. 
 
     
     
         25 . The wireless power transmitting device of  claim 24  wherein the control circuitry is configured to:
 in response to determining that the strong foreign object is present, forgo use of the wireless power transmitting circuitry to transmit wireless power signals. 
 
     
     
         26 . The wireless power transmitting device of  claim 21  wherein the baseline quality factor is measured at a first frequency, wherein the current quality factor is measured at a second frequency, and wherein the control circuitry is configured to compensate the current quality factor measurement for a change of the second frequency from the first frequency. 
     
     
         27 . The wireless power transmitting device of  claim 21  wherein the wireless power transmitting coil has an inductive coil resistance that depends on frequency and wherein the control circuitry is configured to compensate the current quality factor measurement for a change in the inductive coil resistance due to a change in frequency. 
     
     
         28 . The wireless power transmitting device of  claim 21  further comprising a temperature sensor configured to measure a temperature, wherein the control circuitry is configured to compensate the current quality factor measurement based on the temperature.