This is a typical electrical configuration for a VFD...
Figure 1. A typical electrical conections in VFD
The Input power is a three-phase input (208V,440V/60Hz), the rectifier circuit converts the input in a DC input (this rectifier is a 6 pulsations rectifier), the fixed DC voltage is a Capacitor whose mission is to establish the DC reference, and now the Inverter Circuit... remember that the IGBT is a semiconductor device with characteristics of mosfest (the controls gate) and BJT (the current output), often the IGBT have a Diode for protection in the current discharges.
How can you probe if the IGBT is fine or not? easy... If the diode of each IGBT is fine the IGBT is fine, if the diode fail, probably the IGBT is damaged.
Figure 2. Connection terminals VFD
Procedure
1. Attention -Turn OFF disconnect the VFD system from Three phase input.2. Using the figure 1, and figure 2... measure with a multimeter "diode mode" at terminals DC+ (red terminal) and U, V and W (black terminal). See the figure 3.
Figure 3. First Measurement
if the Diode is fine each measured is OL... the diode is polarized negative way.3. Using the figure 1, and figure 2... measure with a multimeter "diode mode" at terminals DC+ (black terminal) and U,V and W (red terminal). See the figure 4.
Figure 4. Second Measurement
if the Diode is fine each measured is 04V-0.6V.4. Using the figure 1, and figure 2... measure with a multimeter "diode mode" at terminals DC- (red terminal) and U, V, and W (black terminal). See the figure 5.
Figure 5. Third Measurement
if the Diode is fine each measured is 04V-0.6V.5. Using the figure 1, and figure 2... measure with a multimeter "diode mode" at terminals DC- (black terminal) and U, V, and W (red terminal). See the figure 6.
Figure 6. Fourth Measurement
if the Diode is fine each measured is OL.End of this tutorial.
