Phase angle regulator for high frequency inverter

Claim 2

In a static inverter adapted to supply alternating current to a tank load, said inverting including means responsive to a control signal of variable magnitude for varying the frequency of said alternating current as a function thereof, improved means for supplying said control signal comprising: a. first means coupled to said inverter for sensing the actual phase displacement between said alternating current and the alternating voltage across the load and for developing a feedback signal representative thereof; b. second means for providing a reference signal representative of a desired phase displacement between said alternating current and voltage; c. third means energized by said feedback and reference signals for deriving said control signal therefrom, said third means being so arranged that the magnitude of said control reflects the difference between said actual and desired phase displacements, said third means including means for delaying changes in the magnitude of said control signal in response to any rapid change in said feedback signal; and d. means for supplying said control signal to the frequencyvarying means of said inverter which responds thereto by controlling the frequency of said alternating current as appropriate to keep said actual phase displacement approximately equal to said desired phase displacement.

Claim 3

The subject matter of claim 1 in which said tank load comprises a parallel RLC circuit which is tuned to have a leading power factor characteristic during normal load impedance and fundamental frequency conditions, and said control signal tends to cause said frequency-varying means to lower the frequency of said alternating current in response to an abnormal increase in the phase angle by which current leads voltage.

Claim 4

In a static inverter adapted to supply alternating current to a tank load, said inverter including means responsive to a control signal of variable magnitude for varying the frequency of said alternating current as a function thereof, improved means for supplying said control signal comprising: a. first means coupled to said inverter for sensing the actual Phase displacement between said alternating current and the alternating voltage across the load and for developing a feedback signal representative thereof, said first means being constructed and arranged to develop a feedback signal comprising a train of discrete signals which recur at a frequency proportional to the frequency of said alternating current and which individually have a duration corresponding to the electrical degrees by which said alternating current is phase displaced from said alternating voltage, whereby the ratio of the cumulative duration of said discrete signals per cycle of alternating current to the period of the same cycle is a fraction which varies with the amount of said actual phase displacement; b. second means for providing a reference signal representative of a desired phase displacement between said alternating current and voltage; c. third means energized by said feedback and reference signals for deriving said control signal therefrom, said third means being so arranged that the magnitude of said control signal reflects the difference between said actual and desired phase displacements; and d. means for supplying said control signal to the frequency-varying means of said inverter which responds thereto by controlling the frequency of said alternating current as appropriate to keep said actual phase displacement approximately equal to said desired phase displacement.

Claim 5

In a static inverter adapted to supply alternating current to a tank load, said inverter including means responsive to a control signal of variable magnitude for varying the frequency of said alternating current as a function thereof, improved means for supplying said control signal comprising: a. first means coupled to said inverter for sensing the actual Phase displacement between said alternating current and the alternating voltage across the load and for developing a feedback signal representative thereof, said first means being constructed and arranged to develop a feedback signal comprising a train of discrete signals which recur at a frequency proportional to the frequency of said alternating current and which individually have a duration corresponding to the electrical degrees by which said alternating current is phase displaced from said alternating voltage, whereby the ratio of the cumulative duration of said discrete signals per cycle of alternating current to the period of the same cycle is a fraction which varies with the amount of said actual phase displacement; b. second means for providing a reference signal representative of a desired phase displacement between said alternating current and voltage; c. third means energized by said feedback and reference signals for deriving said control signal therefrom, said third means being so arranged that the magnitude of said control signal reflects the difference between said actual and desired phase displacements; and d. means for supplying said control signal to the frequency-varying means of said inverter which responds thereto by controlling the frequency of said alternating current as appropriate to keep said actual phase displacement approximately equal to said desired phase displacement.

Claim 6

The subject matter of claim 3 in which the discrete signals of said feedback signal train have a first predetermined constant magnitude, said reference signal is a continuous signal having a second predetermined constant magnitude, said first magnitude being related to said second magnitude by a ratio which is substantially the reciprocal of said fraction whenever said actual phase displacement is approximately equal to said desired phase displacement, and said third means is so constructed and arranged that said control signal is proportional to the average magnitude of the difference between said feedback and reference signals.

Claim 7

The subject matter of claim 4 in which said third means comprises a relatively high gain amplifier having a time constant which is at least three times longer than the period of said alternating current, thereby delaying changes in said control signal in response to rapid changes in said feedback signal.