L.B.
I just converted my son's crib to a toddler bed and had the same problem. The best advice given to me was to not make it in to a big deal. it turns nap time into a game. We also will just let him stay up in his room during nap time. sometimes he plays the whole time and more often than not he plays for about 45 minutes then curls up in his bed and sleeps.
Good luck cause there are some days that are more trying than others.