SaberRD Design Example: Stability Analysis of DC-DC Converters

Balaji Siva Prasad Emandi

Introduction:

This design example demonstrates a method of determining whether a system consisting of DC-DC converters is stable or not. This method is based on the traditional small-signal AC analysis and the use of averaged nonlinear and non-switching models for the converters.

For investigating the stability of the system, the Middlebrook criterion is used. The stability of the system is determined by measuring the source (zsource) and load (zload) impedances. According to this method, if the |zload|>|zsource|, the system would be stable and if |zload|<|zsource|, the system is unstable.

SaberRD’s capability to model systems using generic component library and the availability of various relevant analyses to investigate on stability of a system are demonstrated in this example. The use of MAST language for implementing required functionality such as measuring impedances comes handy unlike other simulation software. The use of Experiment Analyzer allows for automating the simulation process and creating results in a user friendly format.

There are two topologies tested in this example

1. Single DC-DC power supply connected to a DC bus through input LC filter.
   
   
   
2. DC distribution system with multiple DC-DC converters working as "constant power loads" (CPL).
   
   
   

How to Run the Experiment:

Download the attached Stability_Analysis_Demo.zip and unzip the contents to a local folder.
To run the experiments for Single DC-DC power supply connected to a DC bus through input LC filter design:

1. Open the Stability_DCDCconverter_avg.ai_dsn design from the Single_DCDCconverter_stability_analysis folder in the design files.
2. Go to Simulate Tab. Select “Experiment” in the Analysis and stability analysis in the experiments list. Click the GO Button.
3. Once the experiment progress is 100%, go to SaberRD Tab and enter the following command to plot the graphs.
   
   source stability_analysis.aim
   
   
4. To simulate the next experiment, go to Simulate Tab. Select “Experiment” in the Analysis and stability analysis feedback gain in the experiments list and click the GO Button.
5. Once the progress is 100%, go to SaberRD Tab and enter the command given in point 3) above, to plot the graphs.

To run the experiments for DC distribution system with multiple DC-DC converters working as "constant power loads" (CPL):

1. Open the Stability_DC_distribution_system.ai_dsn design from the Stability_analysis_DC_distribution_system folder in the design files.
2. Go to Simulate Tab. Select “Experiment” in the Analysis and stability analysis in the experiments list.
3. Click the GO Button.
4. Once the experiment progress is 100%, graphs are plotted by the AIM script which is part of the experiment to investigate the stability of the system.

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

Note:

1. The Single DC-DC power supply connected to a DC bus through input LC filter design example works in SaberRD Commercial Edition as well as in SaberRD Student / Demo Edition (2018.09 and Above).
2. The DC distribution system with multiple DC-DC converters working as "constant power loads" (CPL) design works only in SaberRD Commercial Edition 2018.09 and above.