I am supposed to come up with some control schemes for the converter before understanding the standard PWM control scheme.
Isn't it just enough if the output of the converter is compared with a fixed reference voltage to drive the output to required voltage level? Although I'm not sure there is a lot more to it, this seems to work pretty well.
I've tried simulating this circuit with L,C and R values from an example.
The required output voltage is 6V. S2 is a voltage controlled switch, controlled by the output of comparator.
V2(green) is the output of comparator and V1(red) is the output of buck converter.