Negative values from internal table are not properly saved to Excel

Hi ABAP Experts,

I wrote a report to extract condition value from billing documents.  One of condition is discount so the value is negative when displaying in ALV.

I used the function SAP_CONVERT_TO_XLS_FORMAT to download the internal table to an excel file.  However, the value and currency are not properly saved.

Would you please give me some advice ? How do I cleanse or format those data correctly before saving it to XLS ?

Thanks and regards,

Danny