Can you be more specific when you say tuning is not working?
PID Tuner works by linearizing a Simulink model from controller output (plant input) to controller input (plant output). PID Tuner then uses the resulting linear model to come up with the PID gains. If the model linearizes to zero, then PID Tuner cannot calculate PID gains for you.
As you model has strong discontinuities like switching and diodes, that's most likely the issue you are experiencing.
The workaround is to find a linear representation of Simulink model in some other way than exact linearization.
