SaberRD Design Example: AC analysis of DC-DC Boost Converter

Balaji Siva Prasad Emandi

Introduction:

This design example provides a method to perform frequency domain analysis of a closed-loop DC-DC boost converter using the Multi-tone PAC (MPAC) analysis in SaberRD. The MPAC analysis is used to produce Bode plots of switching and periodic systems. Transfer functions and Bode plots are useful to assess the stability of closed-loop circuits, using criteria like gain and phase margins, or the Middlebrook criterion.
The Bode plot of the overall open-loop transfer function which aids in assessing stability is commonly measured by breaking the feedback loop and inserting the perturbation source between the output and the feedback node. The ratio of the frequency response of this feedback signal where the perturbation source is connected and that of the output gives the Bode plot of the overall open-loop transfer function as shown in Figure 1.

Figure 1: Block diagram for measurement of overall open-loop transfer function
Performing a PAC analysis on this system will help to plot the Bode plot of the overall open-loop transfer function and assess its stability. In SaberRD, the MPAC analysis allows you to produce frequency plots quickly. After performing PAC analysis, the voltage at the input node of the perturbation source (for example, vfb) is divided by the same at the output node (for example, vout) to get the Bode plot of the overall open-loop transfer function.

Schematic:

The closed-loop DC-DC boost converter used to assess stability by performing MPAC analysis in SaberRD is shown in Figure 2.

Figure 2: Closed-loop DC-DC boost converter

How to Run the Experiment:

1. Open the design boost_cl_pac.ai_dsn from the attached design files.
   
2. Go to the Simulate Tab. Select Experiment in the Analysis and performance_testing in the experiments list.
   
3. Click the GO button.
   
4. Once the experiment progress is 100%, the results pane shows the graphs “bode_plot” and “phase_margin”.
   
5. Double-click graph “bode_plot” and the Bode plot of the overall open-loop transfer function and “phase_margin” for the phase margin measurements at different operating conditions simulated.
   

For more details of the design, how to run the experiments, etc., refer to the README.pdf file in the attachments.

Note:

This design example can be simulated only in SaberRD commercial edition 2020.03 and above.