Please, are there any standards for DC microgrids? For example, what should be the maximum percentage of DC bus voltage transient dip, the accepted duration of a transient etc.
Yes IEEE 2030.10 it is. As part of the World bank's Lighting Global program, we are in the process of implementing many of these standards (https://www.lightingglobal.org/wp-content/uploads/2017/12/Quality-Standards-Test-Methods.pdf). I also found the following YouTube video useful: https://www.youtube.com/watch?v=DvCXsgrwqzE