PMP41081: difficult to understand SFRA

Part Number: PMP41081
Other Parts Discussed in Thread: SFRA

Hi,

I am working on LLC firmware using the PMP41081 reference design on C2000, and I am trying to understand the role of SFRA (Software Frequency Response Analyzer) in this project.

From my understanding, SFRA is used for loop analysis, but I am not clear on how it interacts with the control loop implementation in this example.

My Questions:

1. Role of SFRA in Control Loop

   • How exactly is SFRA integrated into the LLC control loop in this project?

   • Is it injecting perturbations into the reference or feedback signal?

2. Relation to Control Variables

   • The LLC control appears to be primarily frequency-controlled (PFM).

   • Does SFRA have any role in influencing:

     • Switching frequency (via TBPRD updates)?

     • Duty cycle?

     • Dead-time?

3. Injection and Measurement Points

   • Where in the code does SFRA inject the test signal?

   • What signals are used for plant output measurement in this example?

4. Practical Usage

   • When running SFRA on hardware:

     • What loop is being measured (voltage loop, current loop, or overall plant)?

     • How should the results be interpreted for compensator tuning?