Rockwell Automation 7000 PowerFlex Medium Voltage (B Frame) Commissioning - ForGe (PanelView 550) - Manual (Page 14)

10 Rockwell Automation Publication 7000-IN006B-EN-P - May 2013
Chapter 2 PowerFlex 7000 Overview
Rectifier Designs
Active Front-end (AFE) Rectifier
An active front end (AFE rectifier) does not require an isolation transformer to
meet IEEE 519-1992. Depending on the topology, an isolation transformer can
have up to 15 sets of secondary windings.
The AFE rectifier requires a switching pattern that complies with similar rules as
the inverter. The pattern, used for the example shown in
Figure 2 , is a 42-pulse
selective harmonic elimination (SHE) pattern, which eliminates the 5th, 7th and
11th harmonics.
The filter resonant frequency is placed below 300 Hz (for a 60 Hz system) where
no residual harmonics exist. This prevents the excitation of system harmonic
frequencies. Other factors that are considered when designing the filter are the
input power factor and the requirement on Total Harmonic Distortion (THD)
of input current and voltage waveforms.
The small integral AC line reactor (see Figure 2 ) provides additional filtering and
current limiting features to a line side short circuit fault. The line current and
voltage waveforms are also shown in
Figure 2 . The line current THD is
approximately 4.5%, while line-to-line voltage THD is approximately 1.5%.
(THD of line voltage is a function of system impedance.) Input power factor
with the AFE rectifier is near unity throughout a typical operating speed range
for variable torque loads.
Use the AFE rectifier in conjunction with a rectifier duty isolation transformer or
with an AC line reactor (as shown in
Figure 2 ).
Available isolation transformer configurations:
• Integral to the drive (“A” Frame only)
• Remote indoor dry type,
• Outdoor oil-filled type
This allows for maximum flexibility in dealing with floor space, installation cost
and control room air conditioner loading.