Apparatus and method for determining a resonant frequency of an LC circuit in situ, by comparing voltage and current polarity changes

Patent metadata

Field	Value
Publication number	US-9733288-B2
Application number	US-201514874110-A
Country	US
Kind code	B2
Filing date	Oct 2, 2015
Priority date	Oct 2, 2015
Publication date	Aug 15, 2017
Grant date	Aug 15, 2017

Abstract

The resonant frequency of a reactive circuit is determined in situ by determining phase angle differences between an A.C. driving voltage applied to a transformer primary winding and an induced alternating current in the transformer secondary winding. The phase angle is determined indirectly by detecting when the driving voltage applied to the primary changes its polarity and when an induced current in the secondary changes its polarity. The time difference between those polarity changes indicates whether the voltage leads or lags the current or is in phase. A driving voltage frequency is adjusted in real time until the phase angle differences disappear. A duty cycle of the driving signal applied to the primary is also adjusted to change the voltage induced in the secondary winding. The duty cycle is adjusted by changing either a phase of primary driving voltages or the duty cycle of primary driving voltages.

First claim

What is claimed is:

1. A device for determining a resonant frequency of a reactive circuit, the device comprising:
a transformer having a primary coil and a secondary coil, the primary coil having first and second input terminals, the secondary coil having first and second output terminals, at least one of which is configured to be coupled in series with a reactive circuit;
a voltage source configured to provide an alternating current (A.C.) to the primary coil of the transformer;
a voltage polarity determiner coupled to the primary coil;
a current polarity determiner, coupled to the reactive circuit;
a high-speed, multi-pole switch (switch) coupled to the voltage source and to the first and second terminals of the primary coil, the switch being configured to periodically connect the voltage source to the first input terminal at a frequency and alternately connect the voltage source to the second input terminal at the same frequency; and
a phase angle determiner coupled to: the switch, the voltage polarity determiner and the current polarity determiner, the phase angle determiner being configured to receive a voltage polarity signal and receive a current polarity signal and determine therefrom, a time between when voltage applied between the terminals of the primary coil and current passing through the reactive circuit change polarity, the phase angle determiner being additionally configured to change the frequency at which the voltage source is connected to the first and second input terminals responsive to whether voltage on the primary coil leads or lags voltage flowing through the reactive circuit, said frequency being changed to eliminate a phase angle difference between voltage applied between the terminals of the primary coil and current through the reactive circuit.

2. The device of claim 1 ,
wherein the voltage polarity determiner comprises a first voltage comparator coupled to the primary winding and to a reference potential, the first comparator configured to determine when voltage on the primary coil changes its polarity relative to the reference potential; and
wherein the current polarity determiner comprises a second comparator configured to determine when current flowing through the reactive circuit changes its polarity relative to the reference potential, and
wherein the phase angle determiner is configured to receive signals from the first and second comparators and determine whether the current through the reactive circuit leads or lags voltage across the reactive circuit.

3. The device of claim 2 , wherein the phase angle determiner is configured to determine a phase angle difference between voltage on the primary winding and current through the reactive circuit by determining an elapsed time between when voltage on the primary coil changes its polarity and current flowing through the reactive circuit changes its polarity.

4. The device of claim 1 , wherein the voltage source is obtained from a battery.

5. The device of claim 1 , wherein the voltage source comprises a battery and wherein the phase angle determiner is configured to adjust a duty cycle of the battery voltage applied to the primary winding responsive to a magnitude of a voltage output from the secondary winding.

6. The device of claim 1 , wherein the phase angle determiner comprises a computer and an associated memory device, the memory device storing program instructions, which when executed by the computer cause the computer to receive the voltage polarity signal and the current polarity signal and determine a phase angle between them, the computer being additionally configured to send control signals to the switch, the control signal to the switch changing the frequency at which the voltage source is coupled to the first and second input terminals, the frequency being changed by the program instructions in order to reduce a phase angle difference between voltage on the primary and current through the reactive circuit.

7. The device of claim 1 , wherein the reactive circuit is an inductance connected in series with a capacitance.

8. The device of claim 7 , wherein the capacitance has an associated, frequency-dependent parallel resistance.

9. The device of claim 1 , wherein the reactive circuit is an inductance connected in parallel with a capacitance.

10. The device of claim 1 , wherein the high-speed, multi-pole switch comprises at least four transistors connected to form an H-bridge having first and second parallel legs, the first leg and second legs comprising first and second transistors connected in series to each other at a central node, the central node of the first leg being connected to the first input of the primary coil, the central node of the second leg being connected to the second input of the primary coil.

11. The device of claim 1 , wherein the voltage polarity determiner comprises a first voltage comparator configured to detect a zero crossing of voltage signals on one of the first and second input terminals.

12. The device of claim 1 , wherein the current polarity determiner comprises a current-to-voltage converter coupled to a second voltage comparator, the current-to-voltage converter and second voltage comparator configured to detect the polarity of current flowing through the reactive circuit responsive to voltage signals provided to the primary coil.

13. The device of claim 1 , wherein the phase angle determiner is configured to determine both positive and negative phase angle differences.

14. A method of determining a resonant frequency of a reactive circuit coupled to a secondary winding of a transformer having a primary winding with first and second opposing ends, the method comprising:
connecting an alternating current (A.C.) source at a first frequency to the primary winding;
increasing and decreasing the first frequency, responsive to a determination that voltage on the primary coil leads or lags current flowing through the reactive circuit, said first frequency being changed to eliminate a phase angle difference between voltage on the primary coil and current through the reactive circuit;
determining a phase angle of a voltage on the primary;
determining a phase angle of a current through the reactive circuit;
determining a difference between the phase angle of the voltage and the phase angle of the current; and
changing the frequency of the A.C. source to reduce the phase angle difference.

15. The method of claim 14 , wherein the A.C. source is a square wave signal.

16. The method of claim 14 , further comprising: determining a phase angle of voltage applied to the primary winding and determining a phase angle of current passing through the reactive circuit.

17. The method of claim 14 , wherein voltage induced in the secondary winding has magnitude, the method further comprising changing the magnitude of a voltage induced in the secondary winding by adjusting a duty cycle of the A.C. source provided to the primary winding.

18. The method of claim 17 , wherein adjusting the duty cycle of the A.C. source provided to the primary winding comprises changing a relative phase of voltages applied to the first and second opposing ends of the primary winding.

19. The method of claim 17 , wherein adjusting the duty cycle of the A.C. source provided to the primary winding comprises change a duty cycle of voltages applied to the first and second opposing ends of the primary winding.

20. A method of determining a resonant frequency of a reactive circuit coupled to a secondary winding of a transformer having a p

Assignees

• Continental automotive systems inc

Inventors

• Stephens Dennis L
• O'Gorman Patrick A

Classifications

• G01R19/175

  Indicating the instants of passage of current or voltage through a given value, e.g. passage through zero · CPC title

• G01R25/04

  involving adjustment of a phase shifter to produce a predetermined phase difference, e.g. zero difference · CPC title

• G01R27/02 Primary

  Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant (by measuring phase angle only G01R25/00) · CPC title

• G01R27/26 Primary

  Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants {; Measuring impedance or related variables} · CPC title

• H02M3/3385 Primary

  with automatic control of output voltage or current (H02M3/33561 takes precedence) · CPC title