I have a buck converter of 400 V input, 200 V output, 300 kHz switching frequency, power output 100 W. I am trying to put it into closed loop voltage mode control. It is working DCM mode. Modelling the open loop circuit in MATLAB, I got to know that a simple gain of 0.25 in the feedback path would meet the settling time, gain crossover frequency (one-tenth of 300 kHz) and Phase margin requirements (> 45°).
So I tried to simulate this using Pspice. But I am not getting this to work properly. I did add a shoot-through prevention circuitry, and later removed it as it did not switch on either MOSFET. In the below circuit, it is switching on, but it does so after some time. Why is this happening? The pulses are being produced after some time, but I cannot get why.
Also, these pulses produced are "shifted", please see the sawtooth waveform which is being compared to the OPAMP positive input, it looks shifted.
Although LM318 is a bipolar supply OPAMP, giving it a negative supply of -5V or -12V gives manny error messages in the simulation. So I grounded its negative supply terminal.
What is going wrong in my simulation?
This figure shows (red) Output voltage, (black) output voltage taken from the voltage divider.