RESONANT POWER SUPPLY WITH SELF TUNING

• US 20160226400A1
• Filed: 09/10/2014
• Published: 08/04/2016
• Est. Priority Date: 09/12/2013
• Status: Active Grant

• Current Assignee: Auckland UniServices Limited (Auckland University)
• Original Assignee: Auckland UniServices Limited (Auckland University)
• Inventors: Covic, Grant Anthony, Boys, John Talbot
• Granted Patent: US 10,305,393 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H02M 1/34 Snubber circuits
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 1/42 Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 7/4815 Resonant converters H02M7/4811 and H02M7/4826 take precedence
• CPC Class Codes: H02M 7/537 using semiconductor devices only, e.g. single switched pulse inverters
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

This invention relates to current-fed resonant inverters for electrical power applications to change direct current (DC) into alternating current (AC). One application of the invention is to power supplies for inductive power transfer (IPT) systems. There is provided a resonant inverter including an input for supply of current from a DC power source, a resonant circuit including two coupled inductive elements and a tuning capacitance, the inductive elements being arranged to split current from the power source; a first switching means comprising two switching devices operable in substantially opposite phase to alternately switch current from the power source into the inductive elements; and a second switching means to selectively switch one or more control capacitances into or out of the resonant circuit dependent on a power factor of the resonant circuit.

Claims

1. A resonant inverter including:

an input for supply of current from a DC power source, a resonant circuit including two coupled inductive elements and a tuning capacitance, the inductive elements being arranged to split current from the power source;

a first switching means comprising two switching devices operable in substantially opposite phase to alternately switch current from the power source into the inductive elements; and

a second switching means to selectively switch one or more control capacitances into or out of the resonant circuit dependent on a power factor of the resonant circuit.

2. The resonant inverter according to claim 1, wherein the second switching means comprises a switching device and a said control capacitance connected in parallel with each of the switching devices of the first switching means.

3. The resonant inverter according to claim 1, wherein the second switch means is arranged to switch the control capacitance into or out of the resonant circuit at zero current crossings of the tuning capacitance.

4. The resonant inverter according to claim 1, further comprising a power factor detection circuit arranged to determine the power factor by determining a phase difference between the current of the resonant circuit and a switching signal for driving the switching devices.

5. The resonant circuit according to claim 4, wherein the power factor detection circuit comprises a current transformer coupled to the resonant circuit and an integrating capacitor, a squarer coupled across the integrating capacitor, and a comparator for comparing the output of the squarer with the switching signal.

6. The resonant inverter according to claim 1, wherein individual or groups of control capacitances of a plurality of control capacitances are arranged to be selectively switched into or out of the resonant circuit in selected cycles of the resonant circuit to control the operation of the inverter.

7. The resonant inverter according to claim 1, further comprising a buck control circuit coupled between the input and the inductive elements, the buck control circuit having a diode and buck control switch having a duty cycle which is controlled in order to reduce the voltage across the tuning capacitor in response to an over voltage condition.

8. The resonant inverter according to claim 7, wherein the duty cycle is controlled in order to stop or start the resonant circuit.

9. The resonant inverter according to claim 7, wherein the duty cycle is controlled in order to reduce the voltage across the tuning capacitor in response to a power factor of the resonating current.

10. The resonant inverter according to claim 1, further comprising:

a third switching means arranged to selectively switch a control resistor into or out of the resonant circuit in order to start or stop the resonant circuit.

11. A method of operating a resonant inverter having an input for supply of current from a DC power source, a resonant circuit including two coupled inductive elements and a tuning capacitance, the inductive elements being arranged to split current from the power source, first switching means comprising two switching devices and second switching means;

the method comprising;

switching the two switching devices in substantially opposite phase to alternately switch current from the power source into the inductive elements; and

switching the second switching means to selectively switch one or more control capacitances into or out of the resonant circuit dependent on a power factor of the resonant circuit.

12. The method according to claim 11, wherein individual or groups of control capacitances of a plurality of control capacitances are selectively switched into or out of the resonant circuit in selected cycles of the resonant circuit to control the operation of the inverter.