Siemens AC electric drive system

Anyone familiar with AC systems drives? Specifically Siemens, Liebherr and G.E. electric drive systems. My knowledge of AC drivers and DC conversion is extremely limited. I was hoping someone could include a basic layman's term explanation of AC drive systems. My current search is for an electrical support engineer to perform system analysis, training and troubleshooting. Basic technical knowledge on the subject would help me out greatly. I appreciate any assistance. Thank you again.

Jason Bowles
jason.bowles at mriyorktown. com