Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - Classic Control - Manual (Page 23)

1-6 Overview of Drive
7000-UM150I-EN-P – June 2013 7000 “B” Frame
Rather than use an Isolation Transformer, the “Direct-to-Drive”
Active Front End uses the semi-conductor switching pattern to
reduce line current harmonics to levels that comply to the world’s
most accepted harmonic standards. The Active Front End is the best
method of harmonic cancellation because it does not suffer from
complexity and high component count like multi-pulse drive
topologies do.
“Direct-to-Drive” technology produces almost no common mode
voltage so it is suitable for new or existing motors and imposes no
stress on the drive input. The advantage of “Direct-to-Drive”
technology over an Isolation Transformer is that no extra insulation
is required in the motor, in the motor cables or in the line cables.
In addition to mitigating Common Mode Voltage, “Direct-to-Drive”
technology does not generate dv/dt or Reflected Wave Voltage Stress
on Motors.
The simplicity of its design results in a lower initial capital
investment, lower operating cost, lower installation cost and lower
maintenance cost relative to drives that require isolation
transformers.
The PowerFlex 7000 with “Direct-to-Drive” technology is typically
smaller and lighter than drive technologies that use Isolation
Transformers. Isolation Transformers represent 30 to 50% of a drive
system size and 50 to 70% of the system’s weight. This means that
there is no interwiring between drive and transformer (for external
transformer configurations), and no shipping splits in the drive (for
integral transformer configurations). This makes the PowerFlex 7000
the simplest to install.
“Direct-to-Drive” Technology
(cont.)