Maintaining the synchronism of an AC adjustable speed drives during short supply interruptions for an optimal and automatic soft restart

Recent developments in power electronics technology have led to a significant market penetration of adjustable speed drives (ASDs), which are economical, reliable and highly flexible in their use. However, ASDs are particularly sensitive to short supply interruptions from the distribution network. These events may result in the total disconnection of the specific ASD load, thereby causing loss of revenue for the user. It may cause a loss of production capacity and may also incur significant restart costs depending on the specific industrial process in which the ASD is used. This paper presents a mitigation strategy which aims to maintain the inverter synchronized on the induction machine during short supply interruptions. This mitigation strategy allows an automatic soft restart right after the power system recovery. This technique has been validated using numerical simulations.