I am making a comparison between the perfomance of servo motors and stepper motors from the point of view of the presicion position control. I could make step response analysis of the dc servo motor using PID controller , but i don't know how to model a stepper motor nor how to make a simulation for it . i am using the MATLAB program , my concern is about high inertial loads. please help me for supplying me the stepper motor( HYBRID- VARIABLE RELUCTANCE - PERMENANT MAGNET )equations or the way to model or simulate it.