APPARATUS AND METHOD FOR DETERMINING A RESONANT FREQUENCY OF AN LC CIRCUIT IN SITU, BY COMPARING VOLTAGE AND CURRENT POLARITY CHANGES

摘要

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.

主权项

1. A device for determining the resonant frequency of a reactive circuit, the system 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.