Simulation problems of a classical PI controllers using operational amplifiers for buck converters

Sciebou

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.

Datsen Davies Tharakan

The pwm signal is having 400Hz as frequency which is completely wrong and Vd is also wrong as you have mentioned. To start investigation, you can try tstep = 1n and also check the feedback loop. I wonder if you could attach all design related
files in a zip file for further investigation. Also let me know if you are
using commercial version or student version of SaberRD.