Cyclic behavior during switching below D = 0.67 in Quadratic Buck-Boost Converter

PLECS
1

Hello,

I am having a persistent “Cyclic behavior during switching” error in my Quadratic Buck-Boost Converter simulation in PLECS, specifically when the duty cycle falls below 0.67. Above this value, the simulation runs perfectly and reaches steady-state.

I checked the solution on the Plexim website at What does the error message "cyclic behavior during switching" mean? | Plexim but I couldn’t find a solution for my case.

I have attached my .plecs file to this post. Thanks in advance.

versatile-QBBC-switching2026.plecs (49.1 KB)

2

Check your topology and the PWM pattern. If S1 and S2 are turned on and C3 is negatively charged, the capacitor is basically short-circuted through RC3, D3, S1 and S2.

4

Thanks for your answer.

The topology and switching strategies is based on paper (doi: 10.1109/TPEL.2026.3686299), and the simulation works fine with simscape components on MATLAB/Simulink. Did the state you’ve mentioned occur during the transient region? Because I don’t expect the capacitor C3 to be negatively charged while S1 and S2 are turned on.

5

For the purposes of debugging you can connect a small capacitor (e.g. 10 pF) between the node connected to D1 and D2 anodes and ground to stabilize the node voltage. This eliminates the cyclic switching error, such that you can investigate the topological transitions that should be happening in more detail and compare them against the expected sequences illustrated in the paper.