There are a number of authors who have discussed whether a variable frequency drives (VFDs) are helpful in limiting the amount of inrush current to motors and thereby extending motor life.

Joe Kimbrell, product manager for Automation Direct, in his article published in march of 2014 states that “Controlling starting current can also extend motor life because across-the-line inrush current shortens life expectancy of ac motors.  Shortened lifecycles are particularly prominent in applications that require frequent starting and stopping.  VFDs substantially reduce starting current, which extends motor life, and minimizes the necessity of motor rewinds.”

http://www.plantengineering.com/single-article/determine-if-a-vfd-is-right-for-your-application/f2aa2b60ab12540a38e18d52b4b090b9.html

WEG’s publication “Choosing a Variable Frequency Drive or Soft Starter based on your application need” also discussed this issue in the first paragraph:

http://www.weg.net/files/products/WEG-vfds-vs-soft-starters-white-paper-vfdsvssoftstarters-technical-article-english.pdf

“When accelerating an AC motor to full speed using a full voltage connection, a large inrush current may be required. Additionally, the torque of the AC motor is mostly uncontrolled and can shock the connected equipment, potentially causing damage. Variable Frequency Drives and Reduced Voltage Soft Starters and can both be used to reduce inrush currents and limit torque; thereby protecting expensive equipment and extending the life of the motor and coupling devices. Choosing between a variable frequency drive and soft starter often depends on the type of application, the mechanical system requirements, and cost (both for initial installation and over the lifecycle of the system).”