Danfoss VLT Series Service Manual page 6

LOGIC TO POWER
INTERFACE
INPUT LINE DRIVER (ILD)
CARD
POWER SECTION
R
S
T
The logic to power interface isolates the high voltage components of the power
section from the low voltage signals of the logic section. This is accomplished by
use of the Interface/ILD Card*. All communication between the control logic and
the rest of the unit passes through the Interface/ILD Card. This communication
includes: DC Bus voltage monitoring, line voltage monitoring, feedback from the
current sensors, temperature sensing, and control of the gate drive firing signals.
The Interface Card contains a Switch Mode Power Supply (SMPS) which provides
the unit with 24VDC, ±13VDC, and 5VDC. The switch mode type supply is used
due to its efficiency and linearity. Another benefit of the SMPS is that it uses the
DC Bus voltage as a power source. In the event of a power loss the power supply
remains active for a longer period of time versus conventional power supplies.
During the troubleshooting process it is important to determine whether the
Interface Card is receiving or sending the signal that appears to be at fault. For
example, the gate-drive signals are generated by the Interface Card. Conversely
an over-temperature fault can result from the Interface Card receiving an "open"
from the heatsink thermal switch. If the fault could stem from a signal received by
the Interface Card, it is necessary to isolate the fault to either the signal source or
the Interface/ILD card. It is critical to check all possibilities to avoid costly errors
and long downtime. In any case, the Interface/ILD Card is relatively easy to change,
so if it is suspect, a quick exchange will confirm a faulty board.
* The Input Line Driver (ILD) Card is used on VLT 3002-3004, 230V; VLT 3502-
3504, 230V; VLT 3002-3008, 380V/460V, and VLT 3502-3511, 380V/460V.
All other units covered by this manual use the Interface Card.
The power section contains the Rectifier, the DC Capacitor Bank and the IGBT
power components. Also included in the power section are the DC Bus Coils and
the Motor Coils. During the troubleshooting process, extreme care is required
when probing into the power section components. The DC Bus voltage can rise
well over 700VDC on 460V units. Although this voltage begins to decrease upon
removal of input power, it can take up to fifteen minutes to discharge the DC
Capacitor Bank to safe levels.
A fault in the power section will usually result in at least one of the customer
provided line fuses being blown. Replacing fuses and re-apply power without
further investigation is not recommended. The tests listed under Static Test
Procedures in Section Three should be performed to insure that there are no
shorted components in the power section. It is recommended that the motor
leads be disconnected from the unit prior to re-applying power. This precaution
opens the path for short circuit currents through the motor in case a faulty
component remains.
RECTIFIER DC BUS
SIMPLFIED PWM POWER SECTION
Section One
INVERTER
M
3Ø
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