| 摘要 |
An asynchronous motor 4 is supplied by a static frequency changer 1, 2, 3 whose inverter 3 is controlled, over an upper frequency range, by pulses derived from the motor voltage and, over a lower frequency range when a sufficiently high voltage is not available, by external pulses. The latter are derived from the desired value voltage of potentiometer 5 feeding voltage/frequency converter 18 controlling inverter 3 through one position of a changeover switch 22. Firing unit 12 controls the inverter through the other switch position in accordance with pulses derived by members 13-16. Controller 19 receives the pulse trains from members 12, 18 and controls unit 12 to reduce to a minimum the phase difference between the pulse trains. Stage 21 responds to this condition and to trigger stages 20, 23 operable when the motor voltage and frequency exceed preset values, to change over switch 22 and ensure smooth transition from external to motor pulsed operation. Signals from members 8, 17 are compared with the potentiometer voltage to produce control signals for controllers 6, 7, whose outputs are summed to determine the phase of pulses from firing unit 10 for rectifier 1 and from unit 12. Further control is provided by signals from current sensor 11 and optionally from torque controller 25 if the motor is operated at a constant voltage/frequency ratio. <IMAGE> |
