A number of grants ask for personal statements as part of the application. However, what they mean by the term can vary widely. “Personal statement” in some applications might refer to a hybrid research narrative-personal background format, while in others it might refer to a more strictly personal, i.e., autobiographical, essay. Be sure to pay close attention to how the funder defines the personal statement.
If an application requires a personal statement in addition to a more traditional proposal narrative, one productive way to go about writing the personal statement is to think of it as an intellectual biography and piece of creative non-fiction, which serves to connect where you are now (interested in a particular area of research) to your past (an event or context that brought you to the present) while also projecting into the future (where you see yourself going after having completed this research).
This blog post from UMass Amherst gives a good overview to different things you will want to keep in mind as you prepare a personal statement.