| 摘要 |
PURPOSE:To enable to perform stable high speed operation by lowering the secondary frequency at the high speed time, thereby preventing the chopper current from decreasing irrespective of the decrease in the slip at the high speed time. CONSTITUTION:A motor speed (n) is detected by a speed detector 7, compared and calculated with a set speed n* by a speed controller 9, a current reference I1* is outputted, compared and calculated with the primary current I1 of a motor detected through a current transformer 6 and a current controller 11, and the output controls the ON/OFF ratio of a chopper 4 through a phase controller 12. A frequency controller 15 inputs a speed signal (n) from a speed detector 7, and the pulse frequency of the pulse generator 13 is stepwisely lowered in response to the rise of the n. Thus, the chopper frequency (f) at the high speed time is lowered to flow the sufficient secondary current I2 even at the high speed time, thereby obtaining stable high speed operation. |
