4. Special functions

4.1 On the fly

Short interruptions and voltage dips often result in tripping, followed by drive stoppage, and long restart times.

Increasing the availability of a variable speed drive means reducing the number of downtimes (reliability) and the time taken to repair it (maintainability).

To meet industrial requirements for continuity of service, control strategies have been developed to offer maximum immunity of asynchronous drives to network disturbances and, in particular, to voltage dips and short interruptions (see IEC 1000-2-1), with the aim of restarting the production process as soon as the disturbance is over. Following a power failure, the control unit stops sending control pulses to the voltage inverter. Speed deceleration depends...