| 摘要 |
1,202,919. Control of A.C. motors. SIEMENS A.G. 18 Dec., 1967 [28 Dec., 1966; 25 Feb., 1967], No. 57444/67. Heading H2J. The speeds of a plurality of three-phase synchronous or asynchronous motors, e.g. in textile machinery, are controlled in unison by a system in which a pulse train from a common speed setting device 10 is applied to digital counting stages 11, 12, or a common counting network, which control the output frequency of frequency changers 5, 6, individual to each motor or group of motors M1, M2. The counting stages are adjustable, or different counts may be selected from the common network. The speed device 10 may be adjusted, by a potentiometer 8, or it may be a piezo-electric resonator or an LC tank circuit operating at a fixed frequency The device 10 is connected to adjustable frequency dividers 14, 16 and to gating devices 15, 17 which produce an output equal to the difference between the frequencies from 10 and 14, and 10 and 16 respectively. In the event of supply failure the motors may be kept in step by reducing the set speed at 8 so that the motors run down as generators, as described in Specification 1,085,520. The frequency changers comprise thyristor rectifier/inverter combinations of variable output voltage. |
