Apparatus for automatic tuning and control of series resonant circuits

• US 6,570,370 B2
• Filed: 08/21/2001
• Issued: 05/27/2003
• Est. Priority Date: 08/21/2001
• Status: Expired due to Term

• Current Assignee: Raven Technology LLC
• Original Assignee: Raven Technology LLC
• Inventors: Wood, Duncan G., Tupper, Christopher N.
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US09/934,165
• Publication Number:
  US 20030038613A1
• Time in Patent Office: 644 Days
• Field of Search: 323/207, 323/208, 323/209, 323/222, 323/293, 323/352, 323/364
• US Class Current: 323/293
• CPC Class Codes: H02M 7/4818 with means for adaptation of resonance frequency, e.g. by modification of capacitance or inductance of resonance circuits
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• 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

An arrangement is disclosed to automatically match the resonant frequency of a series resonant circuit to an imposed operating frequency. A series resonant circuit is used to store or modulate magnetic energy or to generate high voltages. The circuit includes a capacitive element in series with an inductive element and voltage driving source. The capacitive element includes a base capacitance in parallel with a switch circuit that is in series with a trim capacitance. The switch circuit regulates the timing and direction of current through the trim capacitance. The capacitance of the capacitive element may be tightly controlled so that the resonant frequency may be closely regulated. A controller regulates the operation of the switch circuit and the voltage driving source as a function of sensed current through the resonant circuit and the driving frequency and amplitude to be matched.

Claims

1. A series resonant circuit for storing or modulating magnetic field energy, the circuit comprising:

a. an inductive element;

b. a driving voltage source coupled in series with said inductive element;

c. a series capacitive element coupled in series with said inductive element and said driving voltage source, wherein said series capacitive element includes a base capacitive element and a trim capacitive element; and

d. a switch circuit coupled in series with said trim capacitive element such that said switch circuit and said trim capacitive element are coupled in parallel with said base capacitive element, wherein said switch circuit regulates the timing and direction of current through said trim capacitive element to tune a resonant response, or to control a natural frequency, of the resonant circuit.

2. The resonant circuit as claimed in claim 1 further comprising a controller coupled to said switch circuit such that a driving voltage supplied by said driving voltage source and a resulting current through the resonant circuit are in phase.

3. The resonant circuit as claimed in claim 2 wherein said controller regulates operation of said switch circuit to adjust a natural frequency of the resonant circuit to match an excitation frequency of said driving voltage source.

4. The resonant circuit as claimed in claim 3 wherein said controller regulates operation of said switch circuit by providing a tuning signal at said excitation frequency and wherein said tuning signal is phase modulated with respect to said driving voltage or said resultant current in a manner to:

a. allow initiation of the discharging and charging of said trim capacitor element by natural commutation processes,

b. prevent sudden discharge between said base capacitive element and said trim capacitive element, and

c. change the effective capacitance of said series capacitive element in order to adjust a natural frequency of the resonant circuit to match an excitation frequency of said driving voltage source.

5. The resonant circuit as claimed in claim 3 further comprising a current sensor for sensing a resonant current of the resonant circuit, wherein said current sensor includes an output coupled to said controller.

6. The resonant circuit as claimed in claim 5 further comprising a resonant performance sensor for sensing one or more resonant performance parameters of a device associated with the resonant circuit, wherein said resonant performance sensor includes an output coupled to said controller, and wherein said controller operates to maintain the amplitudes of said performance parameters at given levels.

7. The resonant circuit as claimed in claim 6 wherein the one or more resonant performance parameters include stored energy, magnetic field strength, and electrostatic potential.

8. The resonant circuit as claimed in claim 1 wherein said driving voltage source includes a DC power source and an H-bridge commutation circuit.

9. The resonant circuit as claimed in claim 8 wherein said H-bridge commutation circuit includes a plurality of controllable solid-state switches.

10. The resonant circuit as claimed in claim 1 wherein said switch circuit includes a first terminal coupled to said driving voltage source and a second terminal coupled to said trim capacitive element, said switch circuit further comprising a first unidirectional conduction path and a second unidirectional conduction path coupled in anti-parallel between said terminals, wherein said first conduction path is supplied by a first enabling voltage source and said second conduction path is coupled to a second enabling voltage source.

11. The resonant circuit as claimed in claim 10 wherein said first conduction path includes a first diode device coupled in series with a first solid-state switch and said second conduction path includes a second diode device coupled in series with a second solid-state switch.

12. The resonant circuit as claimed in claim 11 wherein said first and second diode devices are diodes and said first and second solid-state switches are transistors, wherein the anode of said first diode is coupled to said second terminal and the anode of said second diode is coupled to said first terminal, and wherein a low-potential node of said second transistor is coupled to said second terminal a low-potential node of said first transistor is coupled to said first terminal.

13. The resonant circuit as claimed in claim 12 wherein said first enabling voltage source includes a first floating voltage source coupled in series with a first optically operated switch and a first resistance, and said second enabling voltage source includes a second floating voltage source coupled in series with a second optically operated switch and a second resistance, wherein a high-potential node of said first resistance is coupled to a gate or base of said first transistor and a low-potential node of said first resistance is connected to said first terminal, and wherein a high-potential node of said second resistance is coupled to a gate or base of said second transistor and a low-potential node of said second resistance is connected to said second terminal.

14. The resonant circuit as claimed in claim 13 wherein said first and second optically operated switch are phototransistors.

15. The resonant circuit as claimed in claim 1 wherein said switch circuit includes a first terminal coupled to said driving voltage source and a second terminal coupled to said trim capacitive element, said switch circuit further comprising a first unidirectional conduction path and a second unidirectional conduction path coupled in anti-parallel between said terminals, and wherein said first conduction path is supplied by a first enabling voltage source and said second conduction path is coupled to a second enabling voltage source.

16. The resonant circuit as claimed in claim 15 wherein said first conduction path includes a first diode device coupled in series with a first solid-state switch and said second conduction path includes a second diode device coupled in series with a second solid-state switch.

17. The resonant circuit as claimed in claim 16 wherein said first and second diode devices are diodes, said first solid-state switch is a transistor and said second solid-state switch is a complementary transistor, wherein the anode of said first diode and the cathode of said second diode are coupled to said second terminal, and wherein a low-potential node of said first transistor and a high-potential node of second transistors are coupled to said first terminal.

18. The resonant circuit as claimed in claim 17 wherein said first and second enabling voltage sources are arranged to be naturally charged by said driving voltage source during some portions of a driving voltage operational cycle and wherein said first and second enabling voltage sources can provide continuous enabling voltage to said paths.

19. The resonant circuit as claimed in claim 18 wherein:

a. said first enabling voltage source includes a first supply capacitor coupled at a low-potential node to said first terminal, and connected at a high-potential node to the anode of a first supply diode, and wherein the cathode of said first supply diode is connected in series with a first current limiting resistor, and wherein said first enabling voltage source is connected in parallel across said driving voltage source, and wherein said high-potential node of said first supply capacitor is also coupled with a first optically operated switch in series with a first series resistance, and wherein a high-potential node of said first series resistance is coupled to a gate or base of said first transistor and a low-potential node of said first series resistance is connected to said first terminal,

wherein said second enabling voltage source includes a second supply capacitor coupled at a high potential end to said first terminal and connected at a low-potential node to the cathode of a second supply diode, and wherein the anode of said second supply diode is connected in series with a second current limiting resistor; and

wherein said second enabling voltage source is connected in parallel across said driving voltage source; and

wherein said low-potential node of said second supply capacitor is also connected with a second optically operated switch in series with a second series resistance, and wherein a low-potential node of said second series resistance is coupled to a gate or base of said second transistor and a high-potential node of said second series resistance is connected to said first terminal.

20. The resonant circuit as claimed in claim 2 wherein said controller includes means for receiving a reference frequency signal to establish the desired operating frequency of the resonant circuit.

21. The resonant circuit as claimed in claim 20 wherein said controller further includes means to generate a corrective square wave signal and its complement for input to said switch controller.

22. The resonant circuit as claimed in claim 21 wherein said controller further includes means for generating a square wave of desired frequency and its complement for input to said driving voltage source, and wherein said controller further includes means to transmit a modulated pulse width train and its complement to said driving voltage source.

23. The resonant circuit as claimed in claim 6 wherein said inductive element is a field winding of a high frequency alternator and wherein said resonant performance parameter is an output voltage of said alternator modulated at said excitation frequency.

24. The resonant circuit as claimed in claim 6 wherein said inductive element is a field coil of an induction heater and wherein said resonant performance parameter is a temperature response of a heated target piece.