Testing The Inverter Section - Danfoss VLT 3032 Service Manual

TESTING THE
INVERTER SECTION
The purpose of statically testing the inverter section is to rule out failures of the IGBT power devices
and the snubber diodes. If a short circuit is discovered during the testing, the particular devices can
be pinpointed by noting the output terminal indicating the short circuit. The output terminals are
designated with a letter corresponding to the phase that feeds that terminal. When looking in the unit,
the "U" phase is on the top, "V" phase in the middle and the "W" phase on the bottom. In each phase
the negative half of the phase in on the right and the positive half is on the left.
96 97 98
AC LINE AND MOTOR WIRING
SNUBBER DIODES D1 - D6
Anode (+)
Cathode (–)
1. Prior to making the test, it is necessary to disconnect the motor
leads from the unit. By not doing so, the low resistance windings
of the motor will make a short circuit on one terminal also appear
on the other terminals.
2. Connect the positive (+) meter lead to terminal 89 (+VDC).
89 88
Connect the negative (–) meter lead to terminals 96 (U), 97 (V),
and 98 (W) in turn. Each reading should show open.
3. Reverse the meter leads connecting the (–) lead to terminal 89
(+VDC) and the (+) meter lead to terminals 96 (U), 97 (V), and
98 (W) in turn. Each reading should show a diode drop.
4. Connect the positive (+) meter lead to terminal 88 (–VDC).
Connect the negative (–) meter lead to terminals 96 (U), 97 (V),
and 98 (W) in turn. Each reading should show a diode drop.
5. Reverse the meter leads connecting the (–) lead to terminal 88
(–VDC) and the (+) meter lead to terminals 96 (U), 97 (V), and 98
(W) in turn. Each reading should show open. Test is complete.
Incorrect readings indicate a faulty IGBT and/or Snubber Diode. To
further identify the faulty component the IGBT Snubber Board must be
removed. The Snubber Diodes on the IGBT Snubber Board and the
IGBT's can then be tested individually. See Removing and Replacing
Gate Card and IGBT on page 32.
Once the IGBT Snubber Board is removed the Inverter Section can be
retested, using the same tests as above, to verify the condition of the
IGBT's.
Testing Snubber Diodes
To test the Snubber Diodes connect the positive (+) meter lead to the
Anode (+) and the negative (–) meter lead to the Cathode (–) of each
diode. Each reading should show a diode drop.
Reverse the meter leads connecting, the (–) lead to the Anode (+) and
the (+) meter lead to the Cathode (–) of each diode. Each reading
should show open.
Incorrect readings indicate a faulty Snubber Diode. Replace the Snubber
Board.
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