Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C Frame) - Classic Control - Manual (Page 330)

5-22 Functional Description
7000L-UM300I-EN-P – June 2013 7000 “C” Frame

SCR Rectifier Active Off-Line Diagnostics
In the active diagnostic test, each device is gated at maximum
blocking voltage. For a healthy SCR, the feedback will normally
change from high to low when gated. However the drive will
receive a high state both before and after gating if the device is
open-circuited, there is an incomplete gating fiber-optic path or a
damaged gate driver. When this occurs the drive will issue an
Offline OC fault for the device. If the drive receives a low signal
in both states, there may be shorted device or an incomplete
feedback fiber optic. If this occurs drive will issue an Offline SC
fault for the device. Failed or open-circuited snubber connections
will shift the device blocking voltage (when not running) which
may case either fault to appear. It should be noted that during the
active diagnostics stage a dc link voltage which is close to rated
voltage will appear due to interaction with the snubber circuit.

PWM Rectifier Active Off-Line Diagnostics
For the PWM rectifier, the active diagnostic test can differentiate
between a failed device and a broken fiber-optic path because the
gate driver toggles the feedback differently when gated as shown
in Figure 5.10. As in the SCR rectifier active offline diagnostics,
each device is gated at peak blocking voltage (if MV is
available). Devices which could cause a line to line short circuit
are not gated. If the drive detects a failed device a Device Flt is
issued for the device. A weak gate power supply may also cause
a device fault. If the drive receives no light signal both before
and after gating, then there may be an incomplete feedback fiber-
optic and an Fbk FO Loss fault will be issued. A completely
failed or unplugged power supply will also cause this fault. If the
drive always receives feedback both before and after gating, the
device may not have received the gating signal and a Gat FO
Loss fault will be issued. From 4.001 onwards, the drive will not
allow the contactor to be closed if it detects enough failed
devices to cause a line to line short circuit.
• Machine Converter off line diagnostics
The inverter diagnostics are performed when the drive control is
powered up and when the drive receives a start command. From
4.001 onwards, the drive also performs off line diagnostics when
a drive reset command is issued. These diagnostics are capable
of detecting a bad device, loss of feedback fiber optic and loss of
gating fiber optic.
The inverter off-line diagnostics are similar to the PWM rectifier
diagnostics except that: no passive diagnostic is done, no
consideration is given to line-to-line short-circuits and the input
contactor is not involved. The inverter off-line diagnostics will
generate Device Flt Fbk FO Loss and Gat FO Loss faults.
Power Semiconductor
Diagnostics (cont.)