Frequency Analysis of Buck Converter

This PLECS demo model uses a basic buck converter to demonstrate the use of the Analysis Tools. The user can learn how to perform a steady-state simulation and obtain the loop gain of a voltage-regulated buck converter with a resistive load and extend the use of these tools to more complicated circuits. There is also a demo model in PLECS that shows how to perform several small-signal analyses for the same model with open-loop control, including control-to-output transfer functions.


The buck converter uses a basic PID control scheme to produce a DC output voltage of approximately 15 VDC from an input of 28 VDC. A transient simulation is easily done, although this isn't the focus of this example.

Analysis Tools

There are three pre-saved analyses in the demo model: a steady-state simulation, an output impedance analysis, and a closed loop gain. With the small-signal analyses, the transfer function that is generated is based on the location of the perturbation source and response or gain blocks used to measure how the system responds to the perturbation.

To run an analysis, choose Analysis tools... from the Simulation menu, then select an option from the list and click Start analysis. The steady-state analysis will produce the steady-state operating point traces for the load voltage and inductor currents in the scope. Both the output impedance and closed loop gain analyses will produce Bode plots of the respective transfer function upon completion, as shown below:

Output impedance
Loop gain analysis

Try it

This model is available in the PLECS Demo Model library provided in both versions of PLECS.