Large variable speed drives for energy efficiency

Variable frequency asynchronous drives (with an increasing market share) and DC drives (with a reducing market share) dominate the variable speed drives market below 1 MW. However the situation for larger powers is different and there are several different systems available and viable for large variable speed drives. The different systems have different benefits and disadvantages and so are likely to endure as they meet different market needs although a long-term trend is likely to be an increasing use of asynchronous motors with voltage source inverters. This paper describes the characteristics of the different systems followed by consideration of specific topics relevant to the use of these drives