Hi
Currently, Power BI still performs a complete refresh of the data each time it refreshes.
What you describe is incremental refresh, this feature is not available in Power BI, an idea about this issue has been submitted in this link, please vote it up.
In your scenario, you can use other data source such as on-premises SQL Server database to host historic data, then append your new data. For more details, please review the following similar thread and blog.
https://community.powerbi.com/t5/Service/Question-Regarding-Data-Refresh-Frequency-and-History/td-p/75951
http://www.thebiccountant.com/2016/02/09/how-to-create-a-load-history-or-load-log-in-power-query-or-power-bi/
Thanks,
Lydia Zhang