| 摘要 |
1,242,099. Control of D.C. motors. ALLMANNA SVENSKA ELEKTRISKA A.B. 24 Dec., 1968 [27 Dec., 1967; 29 April. 1968], No. 61308/68. Heading H2.T. A traction motor is supplied with D.C. pulses having a variable frequency, and means are provided to prevent the development of an A.C. component of a given frequency (f). This avoids disturbances in other equipment, when rails are used both as return conductors for the load current and parts of a signal system, for example. The motor may be supplied with pulses arranged in groups of two, the time-lag between pulses in a group being 1/2 f, and the periods between the groups being variable from 1/2 f upwardly. As shown, a thyristor 1 is connected in series with motor 2 and a D.C. source 4, a pulse generator 6 delivering triggering pulses to the thyristor. An extinguishing thyristor is fired a predetermined period after the thyristor 1 by means of a delay circuit 11. The average value of motor current is determined by signal Ur applied through diode 16 to the pulse generator 6 so that a higher signal produces a higher frequency. A signal Uk determines a pulse frequency at which the period between two pulses is 1/2 f, this signal being applied to the pulse generator 6 through switch 14 and diode 15. The switch 14 is controlled by a bi-stable circuit 20 responsive to pulses from generator 6. When Ur is less than Uk, a pulse from generator 6 closes the switch 14 and the signal Uk is selected to pass to the pulse generator. After an interval 1/2 f an ignition pulse is delivered to the thyristor 1 and switch 14 opens The signal Ur is then supplied to the pulse generator which, after a longer time interval, again delivers an ignition pulse to the thyristor 1. When Ur equals Uk, all the pulse intervals equal 1/2 f, and if Ur is increased still further the pulse frequency will increase but with the same interval between pulses. At a maximum pulse frequency, a signal is transmitted through Zener diode 19 to the unit 11 whereby the pulse length increases until the motor current becomes continuous. At low values of Ur, a selector circuit 21, 22, 23 becomes effective to increase the interval between pulses in each group and so reduce the intervals between each group of pulses for smoother running of the motor. In another arrangement, the system comprises two groups of motors each group including a pair in parallel. Each group is associated with a main thyristor, and ignition pulses are directed alternately to the thyristors, Fig. 5 (not shown). |
