You could fit another rcd in the workshop and I would recommend that you have one. The best idea may be to get the installation for your workshop changed to a TT installation and fitted with rcd protection. This should prevent any faults in the workshop from tripping the protection in the D.B.
Do you a split consumer unit in the house? Does it have one side protected by and rcd and the other side not? If so then supply the workshop from the non rcd side via an mcb then fit an rcd at the workshop D.B.
There are a few options for this and if your aren't competent in wiring then get someone who is to look into it. If the wiring is already in place and suitable for the job then its not a big change.