Soft restart of an adjustable speed drive after a short disconnection without any mechanical speed sensor

This high sensitivity of ASDs to power network disturbances is well known by ASD manufacturers. They offer some mitigation strategies against these disturbances. These strategies are based on `reducing as much as possible the effect of disturbances on the ASD behavior´ or having a `ride-through capability in regards to disturbances´ or a `soft restart´. Although some manufacturers seem to have mastered these mitigation techniques, they have published almost nothing on this subject to our knowledge. Therefore it is difficult to know which mitigation strategies are used and what is the real level of ASD reliability in regards to disturbances. EDF has performed some research in view of improving the reliability of ASDs under disturbances. Some results of this study are presented in this paper. The effects of voltage dips and short supply interruptions on ASD behavior are first examined, then some mitigation control strategies are proposed