regarding modelling of a boost converter in simulink

[vishnu3546]

I am trying to model ideal boost converter in voltage mode. I have tuned it for some Kp and Ki values which are giving good gain and phase margin in terms of bode plot. But in simulink model, it is taking more time to settle and producing some periodic oscillations. May i know how to fix this.

 

[BradtheRad]

But in simulink model, it is taking more time to settle and producing some periodic oscillations.

Have you tried fiddling with the timestep?

I like to experiment with simulations of switched coil converters. On powerup, boost converter output usually soars high for several cycles, then settles. There is little opportunity for periodic oscillations, due to a diode being inline with the inductor and capacitor.

A possible issue is that feedback may be 'loose', in the sense there is excessive delay to correct the duty cycle, after a change has occurred somewhere in the circuit. Could this be the case in your model?

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Because if feedback is 'loose', there is a tendency to overcorrect. Then the feedback signal (which is delayed) instructs 'correct in opposite direction.' Etc. Oscillations can develop.

 

[vishnu3546]

Have you tried fiddling with the timestep?

I like to experiment with simulations of switched coil converters. On powerup, boost converter output usually soars high for several cycles, then settles. There is little opportunity for periodic oscillations, due to a diode being inline with the inductor and capacitor.

A possible issue is that feedback may be 'loose', in the sense there is excessive delay to correct the duty cycle, after a change has occurred somewhere in the circuit. Could this be the case in your model?

- - - Updated - - -

Because if feedback is 'loose', there is a tendency to overcorrect. Then the feedback signal (which is delayed) instructs 'correct in opposite direction.' Etc. Oscillations can develop.

I don,t think so that is the issue because i have modeled everything as ideal once i am good with this i will go with the non ideal condition. please go through the model i made then u may be able to figure out the problem.

 

[BradtheRad]

I see it is a flowchart. It makes decisions and performs actions. (I am not familiar with Simulink.)

The first thing to suspect is the feedback loop, when operation does not settle quickly.

At left is a repeating sequence (sawtooth generator). A comparator looks at this waveform, and examines the points where it intersects the capacitor charge. That determines the length of duty cycle. That is how the feedback loop functions.

Normally feedback causes the duty cycle to settle eventually at some value.

However somewhere there could be opportunity for a component to overcorrect the duty cycle. It can occur by excessive amplification or excessive attenuation. Then you could get periodic oscillations.

This is only speculation on my part.

What happens when you apply a fixed duty cycle? Do you still get the same problem?

Do you have a load connected to the output stage? With no load, voltage will soar to unpredictable levels.

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Additionally, a boost converter is more difficult than a buck converter, in regard to control and feedback. Did you already get success with a buck converter?