Код:
[System.Runtime.Interopservices.Marshal]::ReleaseComObject($ex)
[System.Runtime.Interopservices.Marshal]::ReleaseComObject($wb)
Remove-Variable ex
Remove-Variable wb
Get-Process EXCEL | Stop-Process -Force
Get-Process EXCEL | Stop-Process -Force - Можно попробовать без нее для начала.
