Hi R.,
I have the same problem with my daughter. She is now 21 months, and this started about 5 months ago. I let her help out and that seems to distract her enough most of the time. She gets her own diaper, powder, and wipees when needed. She wants to do everything herself so this worked great for a while.
Sometimes, though, she is sooooo excited to be diaper free that she runs around when I try to change her - I use our king size bed to change her on and she LOVES to jump and bounce on the bed. So, I have gone with the motto, "If you cannot beat 'em, join 'em." I chase her around and say silly things like, "I'm gonna get that booty", etc. Once I 'catch' her, she has gotten rid of some of that energy and is still long enough so I can put on a clean diaper.
It can still be a challenge, but I have learned that fighting it only makes it worse. Let her think that she is winning, even when it is something that you chose to do.
Good luck,
L.