GB1396784A - Brushless synchronous dynamo-electric machines - Google Patents

Abstract

1396784 A.C. machines with D.C. excitation; control of A.C. motors LAURENCE SCOTT & ELECTROMOTORS Ltd D M PAYNE I SWAN and K W G BURCHAM 10 May 1972 21901/72 Headings H2A and H2J In a brushless synchronous dynamo-electric machine, e.g. a motor, as shown, or a generator, wherein in operation the field winding 14 is energized by a field supply circuit comprising rectifying means, e.g. a bridge 12 and an A.C. exciter winding 11 across which the bridge is connected the field winding, bridge, and exciter winding being mounted for rotation with the rotor of the machine and power being supplied to the exciter winding by rotation in a stationary exciter field, the field supply circuit comprises a field control circuit 18 mounted for rotation with the rotor and semi-conductor switching means, e.g. a thyristor 13 in the path between the exciter winding and the field winding, and the control circuit is responsive to a voltage generated on the rotor independently of the field winding and having a frequency which is proportional to the rotor speed to render the thyristor conducting in dependence on the frequency of the voltage thereby to connect the exciter winding to the field winding when the rotor speed exceeds a predetermined value. This voltage is derived, via a transformer 31 and a bridge rectifier 32, from a part of the exciter winding 11, and is created by a pulse shaping circuit formed by resistors 33, 35 and a Zener diode 34 whose rectangular output pulses are proportional in length to the period of the exciter voltage which as the motor speeds up become shorter until at a predetermined speed, depending on the setting of a variable resistor 53, will fail to charge a capacitor 38 to a level sufficient to initiate a discharge through a PUT 37; above this predetermined speed pulses are developed across a resistor 42 which renders conducting a transistor 55 which in turn renders conducting a transistor 57 whereby a charge on a capacitor 47 develops a series of pulses across a resistor 59 to render conducting the thyristor 13; the motor will now pull into synchronism. Field winding shunting resistors 22, 23 progressively limit the field slip voltage during initial starting, and in Fig. 2 a further stage of shunting resistor (60) is added, whilst in Fig. 3 the resistor 23 is replaced by a resistor (71) shunting the thyristor 13, and an oppositely poled field shunting thyristor (72). In Fig. 4 the supply to the motor stator winding is monitored by a current transformer (81) whose rectified output is added to an independent supply to a stator exciter winding (15). The pulse shaping circuit may be replaced by a transistor switch/Zener diode combination.