Foreign object detection in inductive power transfer field

Abstract

A method for determining the presence of a foreign object in an inductive power transfer field in which control circuitry of an inductive power system performs the steps of: providing power to a direct current to alternating current converter; providing power from the converter to a transmitter coil in the inductive power transfer field; waiting for the current in the transmitter coil to stabilize; estimating the reactive power in the transmitter coil; estimating the real power in the transmitter coil; and using the estimated reactive power and estimated real power to determine whether a foreign object is present.

1 .- 44 . (canceled) 
     
     
         45 . A method for determining the presence of a foreign object in an inductive power transfer field in which control circuitry of an inductive power system performs the steps of:
 providing power to a direct current to alternating current converter;   providing power from the converter to a transmitter coil in the inductive power transfer field;   waiting for the current in the transmitter coil to stabilize;   estimating the reactive power in the transmitter coil;   estimating the real power in the transmitter coil; and   using the estimated reactive power and estimated real power to determine whether a foreign object is present.   
     
     
         46 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 45  further comprising the steps of:
 estimating the real power by sensing the direct current into the converter and combining this value with the value of the power supply voltage; and/or 
 estimating the reactive power by sensing the peak alternating current through the transmitter coil. 
 
     
     
         47 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 46  further comprising the step of estimating the reactive power as the sensed alternating current through the transmitter coil combined with the peak voltage on the transmitter coil. 
     
     
         48 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 45  further comprising the steps of:
 sampling the instantaneous current and voltage waveforms through the transmitter coil; 
 multiplying the sampled instantaneous current and voltage waveforms, integrating the product of the multiplication and estimating the real power as the result of the integration divided by the time sampled; and 
 calculating the root mean square values of the sampled voltage and current waveforms and estimating apparent power as the product of the root mean square current and root mean square voltage, and estimating the reactive power based on the estimated real power and estimated apparent power. 
 
     
     
         49 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 45  further comprising the steps of:
 sensing the amplitude of the voltage through the transmitter coil, sensing the amplitude of the current through the transmitter coil, and sensing the phase difference between the voltage and current waveforms; and/or 
 estimating the real power from the amplitude of the voltage and current through the transmitter coil and the cosine of the phase difference between the voltage and current; and/or 
 estimating the reactive power from the amplitude of the voltage and current through the transmitter coil and the sine of the phase difference between the voltage and current waveforms. 
 
     
     
         50 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 45  further comprising the step of sensing the real and reactive powers at a plurality of frequencies. 
     
     
         51 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 50  further comprising the steps of combining the estimates into a data set and determining at least one characteristic of the data set. 
     
     
         52 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 51 , wherein the characteristic is one of centre, size or average value. 
     
     
         53 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 51  further comprising the step of classifying whether the measurement relates to a foreign object depending on the data set. 
     
     
         54 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 45 , further comprising the steps of:
 storing calibration values of real and reactive power for each transmitter coil when no receiver is present and no foreign object is present; and/or   storing calibration values of real and reactive power for each transmitter coil at a plurality of frequencies; and/or   comparing the estimated real and reactive power to the calibration values.   
     
     
         55 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 45  further comprising the step of bringing a receiver into proximity with the inductive power transfer field prior to the step of providing power to a transmitter coil. 
     
     
         56 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 55  wherein the receiver is adapted to run a start-up sequence in which no current is drawn for a predetermined period or until a signal is sent from the transmitter. 
     
     
         57 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 55  further comprising the step of waiting for the receiver current and/or voltage to reach a steady state prior to estimating the real and reactive power. 
     
     
         58 . A method for determining the presence of a foreign object in an inductive power transfer field as claimed in  claim 56  further comprising the step of estimating the real and reactive power when the receiver is drawing substantially no current. 
     
     
         59 . An inductive power transfer device configured to execute the method of  claim 45 .