Hello,
I would like to simulate a buck converter in closed-loop with SABER. Here is the schematic:

Classically, there are two loops with PI controllers: external voltage loop, and internal current loop. The output of the current loop's PI controller is compared to a sawtooth signal in order to generate PWM signals for gate drive. Vin = 270V
Vout_setpoint = 30V
Rload = 1.8ohms
fsw = 400k
time step = 0.5u However, I obtained the following strange results:
Output voltage:

The two op amp are both saturated. (Vcc and Vee are increased to ±30V, which is very big, but if not Vout is very small).

The MOSFET's and diode's current are strange, the PWM signals as well:


Finally, the diode cathode voltage is not as expected. Its maximum is normally Vin = 270V, but is limited here to 28V:

PI parameters are carefully calculated with these two transfert functions:

Do you have some ideas to troubleshoot my problem?
Many thanks for your help.
Comments
files in a zip file for further investigation. Also let me know if you are
using commercial version or student version of SaberRD.