generating sine pwm in orcad pspice
Have you read this: http://homepages.which.net/~paul.hills/Circuits/PwmGenerators/PwmGenerators.html

Basically what you need is a comparator and a triangular shaped waveform. You feed the triangle to one input of the comparator and your sine wave to the other input. Then the output of the comparator will be the PWM signal you desire.