| 摘要 |
<p>992,014. Control of A.C. motors; electric converting systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. July 13, 1962 [July 19, 1961], No. 26180/61. Headings H2F and H2J. The speed of an induction motor M is varied by injecting a variable A.C. voltage at slip frequency into its secondary winding, using static electronic switching devices, to buck or boost the slip voltage. By increasing a bucking voltage the motor is slowed, and by increasing a boosting voltage the motor speed can be increased above synchronism. The voltage is derived from a variable transformer T connected to the three-phase supply to the motor primary which may be the rotor. The switching devices X, preferably transistors or semi-conductor controlled rectifiers, are triggered to connect each end of each secondary winding S1 . . . S3 to the three-phase output of T in a sequence which results in the windings receiving effectively a six-phase supply, which it is stated improves the wave shape of the injected voltage. The triggering is effected by a timing unit U, coupled to the motor shaft, which provides pulses at a frequency such that the resultant frequency of the injected voltage is that of slip. Details are given (Fig. 2, not shown) of the manner in which the semi-conductor devices are used to switch A.C. (using a rectifier bridge) and the way in which they are automatically " extinguished. It is stated that the secondary windings could be in star formation, and that the power factor can be controlled by adjusting the phase angle of the triggering pulses. Specification 926,099 is referred to.</p> |
