Soft start vs AC drives-understand the differences

Many view soft starters and AC variable frequency drives as the same or similar technologies. And why not? Reading literature and articles the same or similar terms are used. The list of possible applications are virtually identical. But they are very different and these differences need to be understood if they are to be applied properly. This paper reviews the basic operating principles of soft starters and AC variable frequency drives (VFD). A further analysis of these technologies reviews how motor performance is affected. These affects are compared in order to provide insight into proper selection of either soft starters or VFDs