| 摘要 |
1,021,088. Control of A.C. motors. ALLMANNA SVENSKA ELEKTRISKE A.B. Dec. 11, 1962 [Dec. 11, 1961], No. 46653/62. Heading H2J. The driving system of an asynchronous motor comprises primary winding 5 supplied from network 9 through slip-rings 10, and secondary winding 4 associated with rectifier 1 and inverter 2 whereby power is fed back from the winding 4 to the network 9. Speed regulation is effected by means of the inverter 2. The motor also has a braking system comprising short-circuited rotor winding 6, and stator winding 8 which is supplied from variable voltage source 7 connected to network 11. The windings 6, 8 have a different pole-number from the windings 4, 5. When the inverter 2 is adjusted to reduce the speed of the motor, the secondary current falls to a low value whereby a control signal is applied to source 7 to render the braking system effective. The braking torque is reduced when the speed approaches the desired value by regulating source 7 in accordance with the secondary current or other speed-responsive factor. The winding 8 may be connected for providing a reverse torque, and a resistor may be connected in series with winding 6. Reversal of the winding 5 is prevented until braking has taken place. In another arrangement, the primary winding 12 of the driving system is placed on the stator and is formed as a double star-connected winding. The braking field is produced by controlled rectifier 15. Secondary winding 13 of the driving system has two parallel groups per phase to form a short-circuited winding for the braking system having a pole-number different from that of the driving system. The winding 13 is connected to frequency changer 14, Fig. 2 (not shown). In a further embodiment the motor has a squirrel-cage rotor 21, the stator winding having phase coils 20 supplied with direct-current from source 18 for braking. An inverter 19 is supplied from rectifier 17. Source 18 is controlled from rectifier 17 to provide braking current when the power of the driving system drops to a low value, Fig. 3 (not shown). |
