This paper focuses on the modelling and parameter design of a period-controlled fully Digital Phase Locked Loop(DPLL).The reality that the zero crossing detection DPLL can be implemented easily and conveniently makes this DPLL prevailing in inverters' application in many situations.This paper gives an accurat modelling method of the zero-crossing time detection DPLL based on TMS320F240 and proposes one parameter design method base on the equivalent-model.The simulations and experiments verify the accuracy o...