| 摘要 |
PURPOSE:To prevent stall of induction motor regardless of the characteristics thereof by making a decision of stall if the load current increases upon elapse of a predetermined time after finish of acceleration when the induction motor is accelerated over the basic frequency thereof. CONSTITUTION:A speed comparator 13 detects end of acceleration, a constant output state detector 14 detects a constant output region where maximum torque lowers, an AND circuit 15 detects that both a frequency comparator 8 and the constant output state detector 14 are in detecting state, and an acceleration end current detector 16 detects a current (I1) at the end of acceleration. A stall detector 19 compares the load current I1 detected through the acceleration end current detector 16 with a load current (I2) detected through a predetermined time later current detector 18. If I1, I2, a decision is made that an induction motor has stalled and a signal is delivered to a deceleration commander 21 so that the induction motor 6 is decelerated until it enters into regenerative state. According to the invention, the induction motor is prevented from stalling regardless of the characteristics thereof. |
