For M580 PLC, the WEEK_OF_YEAR EF is not available and the system word %SW70 is giving the week of the year in UTC Time format. To get it in Local time you can import the attached DFB the output is giving the week of the year  in the Local Time (defined by the Project Settings->General->Time (Time Zone)).
The value is decimal from 1 to 52.

DFB in attachment

Released for: Schneider Electric USA