# design of compensator type 2 for current mode control of boost converter?

I have designed boost converter with Peak current mode control in PLECS. I have used the method of k factor approach to design the compensator. the bode plot transfer function of the power stage is used to select the crossover frequency of 40KHz as I am using a switching frequency of 2.2MHz and from this, I defined my compensator which shows a good bode plot( ). the bode plot of the complete system is perfectly matching my expectation as you can see in the figure. however, when I run the same circuit in PLECS with the compensator I get a huge oscillation and non-stable system and the compensator( ) is meant to stabilize my system ( I could not upload the file in stackoverflow). my question how can the frequency domain analysis works perfectly but when it comes to time domain( circuit) the system is completely wrong? I have used a crossover frequency of 5KHz and shows the good result which means that my control loop does not show good behavior when it comes to higher crossover frequency which goes against my understanding that says I Can choose any crossover frequency as long as it is tenth less than the switching frequency. the bode plot of the compensated circuit(circuit with the compensator) is : the circuit: the cross over freqquency where it is unstable is 40KHz, I have chosen phase margin 60 and with the k factor approach I calculated the pole zeros and gain of the comensator

• It's totally unclear from your bode plot what the compensated response is. Show the bode plot of only your compensated circuit. Also state what frequency the unstable system is oscillating at AND IMPORTANTLY show you circuit. May 22, 2018 at 10:08
• Hi Andy, i just edited it. I guess you mean the compensated circuit is the circuit with the compensator.thanks May 22, 2018 at 10:33
• For your bode plot where was your input and where was your output measured and how did you arrange the schematic so that the feedback was removed i.e. how did you measure the open-loop gain for your bode plot? May 22, 2018 at 10:39
• for the bode plot, the input is the Verr (Vref-Vout) to the voltage output Vout, I have used the goto/from signals(Vout and I_ind) instead of wires. I used Vout/Verr transfer function(mathematical transfer function given by Basso) and I used as well the analysis tools of PLECS to get the open loop (Vout/Verr) May 22, 2018 at 10:49
• The deal with the switching frequency is that it creates a peak in the response graph at 1/2 fsw so you want to have a good attenuation at that point. It's a bit simplistic to say 1/10th switching frequency for fco. You can try your PLECS model versus the one TI simulator provides, the latter is about as good as you can do without measurements. May 22, 2018 at 11:45