GB964255A - Improvements relating to alternating current power supply circuits - Google Patents

Abstract

964,255. Frequency controlled circuits. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. July 2, 1962 [July 7, 1961], No. 24605/61. Heading H3A. In an inverter circuit for supplying alternating current to a resonant load circuit connected across terminals A, B, means are provided for altering the frequency of operation of the circuit when a change occurs in the load impedance to maintain the frequency of the supply at resonance with the load circuit. The D.C. supply is converted to A.C. by a controlled rectifier TR1 and the output developed across terminals A, B is also applied via transformer T1 to a first phase-shifting circuit comprising C1, R1 which provides across points C, D and E, D a voltage shifted in phase from that appearing at terminals A, B. The voltage across C, D is applied to a second phase-shifting circuit R2, C2, R3, C3 and the negative halfcycles of the output of this circuit (positive half-cycles removed by rectifier Dl) are applied to point E where they combine with the output of the first circuit to provide a waveform with positive portions of duration shorter than a half-cycle and subsequent long duration negative portions. The positive portions cut-off transistors S1, S2, and during this period the rectifier TR1 is triggered from the positive voltage source G. During the negative portions of each cycle transistors S1, S2 are conducting and connect point H to the negative supply terminal F and during this period the rectifier TR1 is rendered non-conducting by the resonant action of the load. Alterations in the resonant frequency of the load advances or retards the positive portions of the derived waveform which trigger the rectifier and hence bring the supply frequency into agreement with the resonant frequency of the load.