Hi,
I think you meant 'Explain'. So the code you must be populating the ALV with the catalog control stucture of type lvc_t_fcat. This basically helps control Grid Functions that are processed during exit.
Say the Internal table that you pass to the ALV will have a field type for the WBS column. Try making that of domain PS_POSNR. the domain will link it to the associated conversion exit that SAP has for WBS.
Then clear the flag field CONVEXIT this would allow the associated Conversion exit for the domain to work and you get the external format of the WBS in the ALV.
Cheers,
Arindam