Understanding Motor Speed Control: Fixed and Variable Speed Technologies Two primary types of speed control govern electric motors : fixed speed and variable speed. Fixed speed involves constant motor operation, while variable speed, facilitated by Variable Frequency Drives (VFDs), adjusts the motor speed based on load or demand. VFDs are particularly beneficial in applications prioritising energy efficiency. In both oil-lubricated and oil-free compressor models, variable frequency drives find common use in Rotary Screw Air Compressors. Fixed speed control methods include start/stop control, load/unload control, and modulation. Each method caters to specific compressed air system requirements, offering choices based on energy efficiency and maintenance needs.