AC發電機和DC發電機的分別

兩者的主要分別是DC發電機有一個叫Commutator[換向器]的部件而AC發電機不須要。
http://sciencecity.oupchina.com.hk/npaw/student/chi/glossary/commutator.htm#topbar

The only difference is that there is a commutator in a d.c. generator that would reverse the polarity of the output voltage so as to make it (voltage) in a single direction.