Introduction - ABB ACS800 Application Manual

Introduction

Connecting the DC buses of frequency converters together results in energy savings
and in some cases simplifies the connection to the main supply. With common DC
the braking energy of one converter can be used for the other converters and
motors.
Unequal current distribution and different charging methods cause difficulties to
common DC systems:
• Unequal current distribution is influenced by input cables, AC or DC chokes and
input bridges' forward characteristics. If the voltage reduction over the supply
components mentioned is not the same with all converters, more current will flow
through the converter which has a lower voltage reduction. Factors which
influence the current distribution include temperature, tolerances of components
and in DC choke cases the input cable's cross-sectional area and length.
• Charging methods vary depending on the converter size. Because of this in some
installations, the supplies of the frame sizes R2-R4 should be disconnected when
they are connected parallel with frame sizes R5-R8.
Note: The drive compliance with the EMC Directive on low voltage networks is
specified in the appropriate Hardware Manual. However, please notice that different
common DC configurations have not been tested according to the EMC
requirements of conducted and radiated emissions.
7
Introduction