| 摘要 |
PURPOSE:To prevent the jump of an output current and a traction force at the time when switching is made by a speed range wherein a voltage control is conducted to a speed range in which a voltage becomes constant, by restricting a slip frequency temporarily at this time, and releasing it thereafter at a prescribed time constant. CONSTITUTION:An instruction converting circuit 10 resolves a motor torque instruction into a slip frequency instruction 102 and a primary current instruction 103. A slip frequency restricting circuit 12 generates a slip frequency instruction 112 containing a pattern which is restricted to a low level when the speed of the main motor 80 reaches a prescribed value and thereby a one-pulse mode signal 111 is given and which is returned thereafter to its original value at a prescribed time constant. A modulation circuit 60 receives a deviation signal 104 of the slip frequency instruction 112 from a motor speed signal 110 and a deviation signal 105 thereof from a primary current signal 109, and supplies an arc-igniting and arc-extinguishing signal 106. |
