High-power AC voltage stabilizer

Apparatus for stabilizing an AC voltage at high-power levels, comprising:

• first and second input terminals adapted for connection to a source of AC voltage;
• first and second output terminals adapted for connection to an input voltage-sensitive load, one of said output terminals being connected to one of said input terminals;
• an injection transformer having first and second windings, said second winding producing an injection voltage having a fundamental frequency and harmonic frequencies thereof, said second winding being connected between the other one of said input terminals and the other one of said output terminals;
• bidirectional switching means, said bidirectional switching means being serially connected with said first winding between said first and second input terminals;
• control means responsive to the voltage across said first and second output terminals, said control means providing control signals for said bidirectional switching means;
• and
• filter means, said filter means having a first portion which presents a relatively high impedance to said harmonic frequencies of said injection voltage and a relatively low impedance to said fundamental frequency, and a second portion which presents a relatively high impedance to said fundamental frequency of said injection voltage and a relatively low impedance to said harmonic frequencies, said first portion of said filter means being serially connected with a predetermined one of said first and second windings of said injection transformer, said second portion of said filter means including components connected across at least one of said first and second windings of said injection transformer, and wherein said filter means and said injection transformer cooperatively produce a voltage representative of said fundamental frequency of said injection voltage which is vectorially added with said AC source voltage to provide a filtered, regulated AC voltage across said output terminals.