Controlling inductive power transfer systems

  • US 7,554,316 B2
  • Filed: 05/11/2005
  • Issued: 06/30/2009
  • Est. Priority Date: 05/11/2004
  • Status: Active Grant
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First Claim
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1. An inductive power transfer system comprising a primary unit, having a primary coil and electrical drive circuitry connected to the primary coil for applying electrical drive signals thereto so as to generate an electromagnetic field, and the system also comprising at least one secondary device, separable from the primary unit and having a secondary coil adapted to couple with said field when the secondary device is in proximity to the primary unit so that power can be transferred inductively from the primary unit to the secondary device without direct electrical conductive contacts therebetween, wherein the primary unit further comprises:

  • a control unit operable to cause a circuit including said primary coil to operate, during a measurement period, in an undriven resonating condition in which the application of said drive signals to said primary coil by said electrical drive circuitry is suspended so that energy stored in said circuit decays over the course of said period; and

    a decay measurement unit operable to take one or more measures of such energy decay during said period;

    wherein said control unit is further operable, in dependence upon said one or more energy decay measures, to control the electrical drive circuitry so as to restrict or stop inductive power transfer from the primary unit.

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