Converting miRNA names
It seems there're no ids for a mature sequence. You better search for a parent sequence ids. You could check, but it also seems that HGNC ids are -miR-30E- part.
So you could try Ensemble search (you should input names in 'Filter'-'GENE' section) or use Genenames. As you see, it has API, and you could use it programmatically with HGNC ids.