GB1215217A - Exciter circuit for synchronous motors - Google Patents

Abstract

1,215,217. Starting brushless synchronous motors. BROWN, BOVERI & CO. Ltd. 24 May, 1968 [26 May, 1967; 3 Oct., 1967], No. 24978/68. Headings H2A, H2S. In a synchronous motor having a shaft without slip rings and supporting a rotor provided with a field coil 6 energizable during synchronous operation by unidirectional current fed via a rectifier bridge circuit 8 from an exciter alternator rotor mounted with the bridge circuit on the motor shaft, a plurality 21 of the bridge circuit rectifiers are controllable and are controlled by motor-speed-responsive circuitry which allows conduction thereof only when the motor is at the very near synchronous speed, and synchronous starting of the motor is attained by resistive circuitry which shunts the field coil during such periods and when the bridge circuit is non-conductive. In the embodiment shown, a resistance 7 forms the resistive circuit, and the speed-responsive circuitry comprises a pulse generator 37 whose output vector, projectional in frequency to the rotor speed, is compared with the mains voltage vector in a pole where angle instrument 35 which when a predetermined minimum slip is reached produces a synchronizing signal which opens a gate circuit of a H.F. A.C. generator 33 to energize the stationary primary coil 31 of a transformer 27 whose rotating secondary coils 27 fire the rectifiers 21. The stationary field coil 11 of the exciter alternator 9 is supplied from an A.C. supply via a rectifier 15 and voltage regulating variable resistance 13. In a modification, Fig. 2, a rectifier (39) is interposed to convert the H.F. A.C. applied to the control electrodes 25 of rectifiers 21. In other embodiments the rectifiers 21 are thryristors and the field coil is energized by a switch, and the resistive circuitry is arranged to avoid losses during continuous running.