| 摘要 |
PROBLEM TO BE SOLVED: To permit an AC motor to be controlled until its speed reaches zero by inhibiting the operation of a trip detecting means over a prescribed time, when the detected DC intermediate voltage of a power converter drops to an undervoltage trip level, thereby preventing the interrupt of an output regardless of whether a load is heavy or light in the event of power failure. SOLUTION: If power failure occurs, a DC intermediate voltage detecting value Edc is reduced transiently due to delayed operation of a PI investigator 22 and reaches a trip level E2 or lower after prescribed time elapses. After a prescribed time has elapsed, undervoltage recovers to a higher value than the trip level E2 . If power supply voltage during power failure becomes lower than an instantaneous level E1 , the output of a voltage detector 20 changes from a high level into a low level. When it reaches the low level, a time counter 26 is started, the output reaches the high level during a prescribed time, and a switch 29 is released to inhibit a trip circuit 27 from operating. Thus output of an electric power converter 11 can be prevented from being interrupted. |
