PWM Capacitor Control

A variable capacitance device comprising:

• a capacitor;
• a first transistor comprising a first-transistor first terminal, a first-transistor second terminal, and a first-transistor gate terminal, the first-transistor first terminal electrically connected to a first terminal of the capacitor;
• a second transistor comprising a second-transistor first terminal, a second-transistor second terminal, and a second-transistor a gate terminal, the second-transistor first terminal electrically connected to a second terminal of the capacitor, and the second-transistor second terminal electrically connected to the first-transistor second terminal;
• and
• control circuitry coupled to the first-transistor gate terminal and the second-transistor gate terminal, wherein the control circuitry is configured to adjust an effective capacitance of the capacitor by performing operations comprising:
• generating an alternating ramp signal having peaks and troughs that are timed to correspond with zero-crossings of an input current, and
• switching off the first transistor in response to the ramp signal crossing a first reference value.

A high-power wireless energy transfer system comprising:

• a variable capacitance device comprising:
• a capacitor;
• a first transistor comprising a first-transistor first terminal, a first-transistor second terminal, and a first-transistor gate terminal, the first-transistor first terminal electrically connected to a first terminal of the capacitor;
• a second transistor comprising a second-transistor first terminal, a second-transistor second terminal, and a second-transistor a gate terminal, the second-transistor first terminal electrically connected to a second terminal of the capacitor, and the second-transistor second terminal electrically connected to the first-transistor second terminal;
• and
• control circuitry coupled to the first-transistor gate terminal and the second-transistor gate terminal, wherein the control circuitry is configured to adjust an effective capacitance of the capacitor by performing operations comprising:
• generating an alternating ramp signal having peaks and troughs that are timed to correspond with zero-crossings of an input current, and
• switching off the first transistor in response to the ramp signal crossing a first reference value;
• and
• an inductive coil electrically coupled to the variable capacitance.

An impedance matching network of a wireless power transmission system, comprising:

• first and second transistor switching elements having internal body diodes or external antiparallel diodes associated therewith;
• a PWM-switched capacitor coupled across the first and second switching elements;
• and
• a controller coupled to the first and second transistor switching elements and configured to control the first and second switching elements by steering current flow away from body diodes into the channels of the first and second transistor switching elements.