From erector set to integrated system-the evolution of MV variable frequency drives

Effective speed control of an electric motor has long been known to be key to improving process efficiency, product quality and plant system availability. To effectively use this key there are several implementation issues that need to be understood, and addressed. These include: motor compatibility, power quality impact, line side power system disturbance immunity, product availability and process control integration capability. As the issues, understanding and opportunities have become clear, and as technology has advanced, there has been a systematic evolution of medium voltage variable speed drive product and systems offerings. This paper follows the course of that evolution and reports on the status of current technology offerings including: thyristor DC drive; load commutated inverter; AC drive; filter commutated drive; GTO current source drive; diode rectifiers; GTO voltage source drive; and the distributed power circuit