A basic drive is "6 pulse" meaning there are 6 diodes on the front end bridge rectifier used to convert the AC to DC. If you want to reduce the current harmonics imposed on the line side supply, you can have 2x6 Pulse front ends in parallel (12 pulse), one supplied by a Delta-Y transformer to create a phase shift on the AC side between the 2 rectifiers, which makes a large percentage of the current harmonics cancel each other out. If you want even further reduction of harmonics, you can do it again and have 18 pulse, even 24 pulse in extreme cases.
Jeff Raefield
Jraef Consulting
www.jraef.com [This message has been edited by jraef (edited 07-27-2006).]
