GB1309034A - Variable speed drive arrangements - Google Patents

Abstract

1309034 Control of synchronous motors SIEMENS AG 25 June 1971 [25 June 1970] 29996/71 Heading H2J A speed control, e.g. starting circuit for a synchronous motor has a frequency converter, e.g. thyristors 5 to 10 fed from a three phase supply RST, and connected via two parallel arms to the supply neutral Mp, one arm comprising star connected stator windings 1, 2, 3 in series with rotor windings 4, the other arm having star connected diodes 11, 12, 13 in series with a single-pole switch 14 (or thyristor 16) and the secondary of transformer 15. To start the motor, switch 14 is closed (or thyristor 16 turned on). For negative half cycles of the supply, one thyristor of each set of thyristors comprising the frequency converter, i.e. 5, 6, 7 and 8, 9, 10 is turned on, e.g. thyristors 7 and 10, so that current flows from the neutral Mp through the rotor winding 4 and stator winding 3. For positive half cycles of the supply, thyristors 5 to 10 block, and the current through windings 3, 4 is maintained, through the parallel path, by transformer 15, whose secondary voltage is in phase with the supply.. As the rotor turns, stator windings 1, 2 or 3 are excited in turn by firing thyristors 5, 6 or 7 resp. until natural commutation of the motor occurs, when switch 14 is opened (or thyristor 16 turned off), and thyristors 8, 9 and 10 turned on.