Because of my companys' policies, we are not allowed to use to PowerBI.com and we don't have an on-premise SharePoint server either. In other words, we use Power BI Desktop (PBD) and share the PBIX files using a shared network drive.
Given the above scenario:
I don't think that is a built in, out of the box feature but you could try PowerUpdate. Here is a link:
1. unfortunately i don't think there is any way to refresh pbix files automatically.
2. PBD has data modelling feature where you can use DAX to be able to do data transformations.
Apart from Power Update, given your constrains, see if either of the below is an option for you
a) Pyramid Analytics Server is an option of you.
b) Alternately, if the data set is not too large, see if you can get the data into some dierct queriable database and use direct query.