| 摘要 |
PURPOSE:To detect a situation necessary for brake-off quickly and avoid the overcurrent of an induction motor by a method wherein the lowest value of the outputs of the respective speed detectors of the induction motors is obtained and inputted to a comparing circuit as a speed output. CONSTITUTION:The output fMmin of a lowest value detecting circuit 65 which outputs the lowest value of the outputs of speed detectors 41 and 42 is inputted to a comparing circuit 64. If the speed of one shaft is fixed to a speed a little higher than a predetermined lower limit speed fo, the output of the speed detector of the fixed shaft declines rapidly and, as a result, the lowest speed value fMmin of the output of the lowest value detecting circuit 65 is reduced rapidly. Then the comparing circuit 64 is operated and outputs a brake-off instruction S1 to stop an inverter. |
