WiTricity Corporation

Described herein are active rectification methods and systems for a rectifier of a wireless power system. Exemplary methods can include detecting, by a zero-crossing detector, one or more zero-crossings of a current at an input of the rectifier and determining a first delay time based on at least one wireless power system parameter and the zero-crossings. The methods can include generating first and second control signals for first and second switches of the rectifier, respectively, based on the first delay time; inserting a first dead time between the first control signal and the second control signal; and providing the first and second control signals to the first and second switches, respectively.

Systems and methods are described for extended foreign object detection (FOD) signal processing. In aspects, an oscillator reset is implemented in a FOD system to mitigate the effects of intermodulation products. In addition, dynamic frequency allocation is implemented to avoid high noise desensitizing the FOD system. Also, a slow sampling mode is implemented to increase a tolerance to transient foreign objects. Reference tracking and auto-recovery is implemented to bridge power outages. Additionally, the FOD system is configured to support position finding for determining an alignment between the vehicle pad and the base pad using a passive beacon transponder circuit and to perform beacon response cancellation as needed in concurrent FOD operation.

The disclosure features wireless energy transfer sources that include at least two source resonators and a power source, where: each of the at least two source resonators has a nominal impedance when a device resonator is not positioned on or near any of the at least two source resonators, the nominal impedances of each of the at least two source resonators varying by 10% or less from one another; and the at least two source resonators are configured so that during operation of the wireless energy transfer source, when a device resonator is positioned on or near a first one of the at least two source resonators: (a) the impedance of the first source resonator is reduced to a value smaller than the nominal impedances of each of the other resonators by a factor of 2 or more.

Methods, systems, and devices for controlling a variable capacitor. One aspect features a variable capacitance device that includes a capacitor, a first transistor, a second transistor, and control circuitry. The control circuitry is configured to adjust an effective capacitance of the capacitor by performing operations including detecting a zero-crossing of an input current at a first time. Switching off the first transistor. Estimating a first delay period for switching the first transistor on when a voltage across the capacitor is zero. Switching on the first transistor after the first delay period from the first time. Detecting a zero-crossing of the input current at a second time. Switching off the second transistor. Estimating a second delay period for switching the second transistor on when a voltage across the capacitor is zero. Switching on the second transistor after the second delay period from the second time.

A wireless power receiver includes one or more tunable capacitors in parallel with an inductor. The wireless power receiver adapted to receive an induced voltage input at the inductor due to a magnetic field generated by a wireless power transmitter. The rectifier has an output with a rectified voltage and a rectified current. A controller has a first input for receiving a signal representative of the rectified voltage and a first output for supplying an adjustment signal to the tunable capacitor. The controller includes a processor coupled to the first input and is configured to operate on the signal representative of rectified voltage to produce a desired capacitance value for capacitor and provide the adjustment signal determined so as to adjust a capacitance value of capacitor to the desired capacitance value.

Certain aspects of the present disclosure provide methods and apparatus for multi-phase coil control in power transfer systems. One example power transfer device generally includes a plurality of coils configured to generate at least one charging field, the plurality of coils comprising a first coil and a second coil, and a controller configured to identify that a coupling factor between the first coil and a third coil, which is external to the power transfer device, is at or below a threshold, and to adjust, based on the identification, one or more parameters associated with a current applied to the first coil to transfer power from the first coil to the second coil.