High efficiency high frequency resonant power conversion

1. An apparatus comprising:

a resonant tank connected to a first switch network, wherein the resonant tank includes a coil and a first variable capacitance network comprising a first voltage shifting circuit and a plurality of adjustable capacitance circuits, and wherein the first variable capacitance network is configured to be adjustable for varying at least one operation parameter, and wherein the first voltage shifting circuit comprises a semiconductor diode, and a first terminal and a second terminal of each adjustable capacitance circuit of the plurality of adjustable capacitance circuits are directly connected to a first terminal and a second terminal of the semiconductor diode respectively, each adjustable capacitance circuit comprising a capacitor and a switch connected in series, and wherein the coil is magnetically coupled to a second coil, and wherein the coil and the second coil form a transformer.

2. The apparatus of claim 1 , wherein:

the coil is a transmitter coil, and the second coil is a receiver coil, and wherein:

the transmitter coil is coupled to a power source through the first switch network and the resonant tank; and

the receiver coil is coupled to an output capacitor of a receiver through a receiver network and a receiver resonant tank.

3. The apparatus of claim 2 , wherein:

the receiver resonant tank comprises a second variable capacitance network.

4. The apparatus of claim 1 , wherein the first voltage shifting circuit comprises:

a first capacitor and a second capacitor connected in series; and

the semiconductor diode and the second capacitor connected in parallel, wherein:

a cathode of the semiconductor diode is connected to a common node of the first capacitor and the second capacitor; and

the plurality of adjustable capacitance circuits is connected in parallel with the second capacitor.

5. A method comprising:

coupling a primary side circuit of a resonant power system to a secondary side circuit, wherein:

the primary side circuit comprises a first resonant tank comprising a first variable capacitance network having a first resonant frequency, wherein the first variable capacitance network comprises a first capacitor in parallel with an adjustable capacitance network comprising a second capacitor and a switch connected in series, and a semiconductor diode having a first terminal connected to a first terminal of the first capacitor directly, and a second terminal connected to a second terminal of the first capacitor directly; and

the secondary side circuit comprises a second resonant tank having a second resonant frequency;

configuring the resonant power system to operate in an idle mode by adjusting the first resonant frequency far away from a switching frequency of the resonant power system by modulating the capacitance of the first variable capacitance network; and

modulating a capacitance of the first variable capacitance network to adjust an operation parameter of the resonant power system.

6. The method of claim 5 , further comprising:

modulating the capacitance of the first variable capacitance network to minimize a current flowing through the primary side circuit.

7. The method of claim 5 , further comprising:

modulating the capacitance of the first variable capacitance network to reduce a voltage across a resonant capacitor of the first resonant tank.

8. The method of claim 5 , further comprising:

modulating the capacitance of the first variable capacitance network to regulate an output of the resonant power system.

9. The method of claim 5 , further comprising:

modulating a capacitance of a second variable capacitance network in the second resonant tank to regulate an output of the resonant power system.

10. The method of claim 5 , further comprising:

modulating the capacitance of the first variable capacitance network and a capacitance of a second variable capacitance network in the second resonant tank simultaneously to regulate an output of the resonant power system and adjust an operation parameter of the resonant power system.

11. The method of claim 5 , wherein:

the resonant power system is a wireless power transfer system.

12. The method of claim 5 , further comprising:

applying a feed-forward control mechanism to the resonant power system through modulating the capacitance of the first variable capacitance network in response to an input voltage or an output current change.