| 摘要 |
1,166,695. Control of D.C. motors. GENERAL DYNAMICS CORP. 24 Aug, 1967 [2 Sept., 1966], No. 39113/67. Heading H2J. In a system in which a D.C. motor 16 is energized from a D.C. source 19 via a thyristor 20 which is turned off by a capacitor 30 when a second thyristor 28 conducts, the first thyristor 20 is triggered at a fixed frequency and, the motor speed is varied by adjustment of the time when the second thyristor 28 is triggered. The circuit for triggering commutating thyristor 28 comprises a capacitor 63 which is charged with positive potential from battery 19 through the thyristor 20 while it is conducting, the potential being kept constant by Zener diode 66 and the charging rate adjusted by speed control rheostat 64. When the charge on 63 is sufficient, unijunction transistor 62 conducts to produce a triggering pulse through transformer 58. As shown, the first thyristor 20 is triggered from a transistor oscillator 44, 45, whose output transformer 47 also supplies a rectifier bridge 40 by which the commutating capacitor 30 is charged, again through the thyristor 20 while it is conducting. This arrangement ensures correct commutation regardless of which thyristor is triggered first. Thyristor 28 is turned off when 20 is again triggered on by capacitor 30, which has been charged from battery 19 via thyristor 28; when 20 conducts this charge is reversed by resonance of the circuit 30, 20, 40 and choke 32, thus turning off 28. The transformer 47 is saturable so that if the thyristor 28 should fail to switch off the oscillator 44, 45 stops. A switch 34 is opened when continuous conduction of 20 is required for full speed, and a switch 24 provides for de-energizing the motor. In an alternative arrangement, (Fig. 3, not shown), the oscillator is replaced by an A.C. source which supplies the rectifiers 40 via a current limiting transformer. The A.C. source also powers a conventional unijunction transistor pulse generator for providing the triggering pulses to thyristor 20. |
