| 摘要 |
PURPOSE:To prevent an induction motor from running away even if the speed detected value is different from the actual speed due to the malfunction of a speed detector by variably setting the limit value of the primary frequency command. CONSTITUTION:A variable frequency limiter forms the absolute value omega0 of a speed command omega0 omega0 by an absolute value circuit 22, the sum of the set value omegasm of the maximum slip frequency is calculated by an adder 23 to generate the limit value omega10m of the primary frequency command value corresponding to the speed command omega0 at that time. A variable limiter 24 sets the output to omega10m if the absolute value ¦omega10¦ of the primary frequency command is higher than the generated control value omega10m, and retains omega10 as the output omega100 as it is if lower. Thus, the output omega100 of a variable frequency limiter 21 is limited not to exceed omega10m=omega0+omegasm in response to the speed command omega0. In other words, even if a speed feedback loop has a malfunction, the real speed is control to become equal to the speed command value omega0. |
