Is it possible to inject generator speed as an input into OpenFAST during co-simulation (PHIL integration)

[FlavieDidier]

Hello OpenFAST community,

I'm currently working on a Power-Hardware-in-the-Loop (PHIL) setup where OpenFAST runs in co-simulation with a real-time controller (Beckhoff) and a hardware-based generator emulator. The generator speed is physically measured in real time.

My goal is to inject this measured generator speed into OpenFAST so that the aerodynamic torque is computed based on this externally provided generator speed, while OpenFAST continues to simulate the remaining turbine dynamics (e.g., aerodynamics, platform motion, etc.).

Question:
Is there a recommended or officially supported way to override or inject the generator speed as an input into OpenFAST (e.g., via Simulink or user-defined routines), so that aerodynamic torque is computed based on this value? Or is such a modification fundamentally unsupported within the OpenFAST architecture?

Any guidance, examples, or best practices would be greatly appreciated.

Thank you very much!

— Flavie

[dzalkind]

Hi Flavie,

Injecting generator speed into OpenFAST to recompute aerodynamic torque is not possible within the OpenFAST architecture.

To solve a similar problem to yours for a validation campaign, we used the ROSCO controller to add an offset to the generator torque signal for matching rotor azimuth position. Here is an example of that functionality. By matching the azimuth, you will also match the rotor speed.

I hope this helps.

Best, Dan

[FlavieDidier]

Hi Dan,

Thank you very much for your clear and helpful response.

That confirms what I suspected about the current limitations of the OpenFAST architecture. I really appreciate you pointing me toward the azimuth-matching workaround via ROSCO—it’s a clever approach, and the example you shared is very helpful. I'm currently implementing a similar strategy in my PHIL setup, using a PID controller to adjust generator torque based on the azimuth error. I hope it will perform as expected.

Thanks again for your guidance and for sharing your experience.

Best,
Flavie