Rockwell Automation 7000A PowerFlex Medium Voltage Drive (A-Frame) - Classic Control - Manual (Page 22)

1-4 Overview of Drive
7000A-UM150F-EN-P – June 2013 7000 “A” Frame
Rectifier Designs
There are two offered designs for the front-end rectifier of the
PowerFlex 7000 “A” Frame drive.
6-Pulse Rectifier
A 6-pulse thyristor phase controlled rectifier (with optional passive
tuned filters) is shown in Figure 1.2. The line current before and after
the filter is shown. It can be seen that the current before the filter
contains the 5
th , 7 th and 11 th harmonics, however, the current after the
filter is more sinusoidal since these harmonics are redirected through
the tuned filters. The tuned filters also serve to improve input power
factor to near unity. The total harmonic distortion (THD) of line
current with the 6-pulse rectifier and tuned filters is approximately
5.2%. The THD of line voltage (line-to-line) is approximately 2.6%.
(THD of line voltage is a function of system impedance.)
The 6-pulse rectifier can be used in conjunction with a rectifier duty
isolation transformer as shown or with an AC line reactor. A rectifier
duty isolation transformer is required when the supply voltage is
higher than the drive rated voltage. (Refer to Specification 80001-
005, Rectifier Duty Transformers for more details on transformer
requirements and features.)
An AC line reactor can be used in front of the 6-pulse rectifier when
the drive is being applied to new motors. (Refer to Specification
80001-004, Stator Insulation Requirements for MV Motors Without
Common Mode Voltage Elimination). Elimination of the isolation
transformer reduces capital and installation costs, saves on valuable
floor space, and increases overall system efficiency.
Figure 1.2 – 6-pulse Rectifier with input waveforms
a) Line current without filter
b) Line current with filter
c) Line-to-line voltage at point of common coupling (PCC)
a)
b)
c)