A METHOD FOR A FOREIGN OBJECT DETECTION IN A CONTACTLESS CHARGING SYSTEM

A contactless power supply device (10) for a contactless charging system comprising a high frequency generator (11) for generating a high frequency waveform, an oscillation unit (12) with a primary coil (13) for generating an alternating flux and a control unit (14) for controlling operation of the high frequency generator (11). The output of the high frequency generator (11) is connected to the primary coil (13) of the oscillation unit (12) and the output of the control unit (14) is connected to the input of the high frequency generator (11). Furthermore, the contactless power supply device (10) comprises a measuring unit (15) configured to measure instantaneous values Imeas of alternating current of the primary coil (13) during a charging state of a contactless charging system, or to measure the RMS values IRMS of alternating current of the primary coil (13) during a charging state of a contactless charging system, or the contactless power supply device (10) comprises a measuring unit (15) configured to measure instantaneous values Imeas of alternating current of the primary coil (13) during a charging state of a contactless charging system and the control unit (14) is configured to calculate the RMS values IRMS of the measured instantaneous values Imeas of alternating current, or to calculate the change rate didt of the measured instantaneous values Imeas of alternating current, wherein di - a first degree differential of the measured instantaneous values Imeas of alternating current of the primary coil (13), dt - a first degree differential of measurement time of the instantaneous values Imeas of alternating current of the primary coil (13), or to calculate a second derivative d2idt2 of the measured instantaneous values Imeas of alternating current, wherein d2i - a second degree differential of the measured instantaneous values Imeas of alternating current of the primary coil (13), dt2 - a second degree differential of measurement time of the instantaneous values Imeas of alternating current of the primary coil (13), or the control unit (14) is configured to measure instantaneous values Imeasof alternating current of the primary coil (13) during a charging state of a contactless charging system, or to measure the RMS values IRMS of alternating current of the primary coil (13) during a charging state of a contactless charging system, or to measure instantaneous values Imeas of alternating current of the primary coil (13) during a charging state of a con