IGBT Short Circuit Fault in 3 Phase invertor

Thread Starter

wahidbashir

Joined May 19, 2010
1
Dear Forum,
I have a 3 phase servo motor with seimens.
In its invertor stage, there are 3 IGBT modules each have two one for upper and the other is for low side.
The invertor out put phases are U,V and W
IGBT on low side for V phase has been shorted thrice a time.
On inspection I have found gate drives for these 6 IGBTs which are optically isolated from controller. 5 optocouplers give reading on diode test of 1.5 V
but the one for low side of V phase has a reading of 1.002V.
Motor insultation is OK with the help of Meggar.
Problem is inside drive. Is that could be the reason (optocoupler)
Please guide in this regard.

Wahid Bashir
 

t_n_k

Joined Mar 6, 2009
5,447
Why not contact the drive manufacturer or their representatives in your locality? Siemens would hopefully have a strong (helpful???) technical support department. There's a reasonable chance they might respond, particularly to questions with a specific query such as yours.
 

BillB3857

Joined Feb 28, 2009
2,516
What you have is a |-|-| configuration (3 phases with H bridges) and from your description, if the Low V opto is too sensitive, you could be seeing punch-through if the High side is still on when the low side erroneously triggers on. Since the high side would already be in saturation when the low side falsely triggers, the low side would take the heat (pun intended)

That's my theory but others may have other ideas.
 

t_n_k

Joined Mar 6, 2009
5,447
What you have is a |-|-| configuration (3 phases with H bridges) and from your description, if the Low V opto is too sensitive, you could be seeing punch-through if the High side is still on when the low side erroneously triggers on. Since the high side would already be in saturation when the low side falsely triggers, the low side would take the heat (pun intended)

That's my theory but others may have other ideas.
I would imagine if both the high and low side IGBT's were both being driven fully on then there is risk of an effective short circuit on the DC bus via the two IGBT's in series - so both devices would be equally at risk from over-current failure.

It is possible that if the lower IGBT is being driven marginally close to or just into conduction and is operating in a quasi-linear state this would subject that device to risk from excursions outside of its SOA.
 
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