I am attempting to extract and run a linear model of a full wind turbine system. I have had success already linearizing and running a model that did not include the turbine (just floater and dummy tower/nacelle mass). I am having issues running the turbine model. For reference I am using OpenFAST v3.5.1.
To be specific, running the turbine model in a wave-only environment works fine, but trying to run in a wind environment the linear model accelerates to infinity. I have attached an image that shows what I mean. Running the linear model with the same wind input as the linearization point, the linear model does not regulate.
The OpenFAST simulation for linearizing was done with a fixed pitch angle so I am running the linear model the same. My linearization process is:
- Enable linearization settings to linearize at 36 time steps during steady-state conditions. (ran simulation, computed steady-state, and prepared time steps to get 1 full rotation)
- Run MBC3 to perform rotor averaging of the system matrices (note that the code indicates no rotating frame states found (there are only outputs) so sets blades to 0 and does not do transform)
3)Store A,B,C,D as matlab files for use.
The inputs to my linear model are:
IFW Wind Speed: Constant value
ED Collective Pitch Command: Constant value (0.02967 rads/ 1.7 deg)
All other inputs (AD User Props, IFW power law/propogation, Yaw moment, individual pitch commands, & generator torque) are set to zero.
Also of note is that my radiation and excitation modes are set to 0 in HydroDyn to avoid the hydrodynamic states. I have also tried with these set to 2 with no change.
When linearizing, all control modes were set to zero to allow linearization. Here is what I have tried to get the model to perform:
- Feed GenTq from OpenFAST output as linear model input
- Fed different wind inputs.
- Changed operating point of linearization.
- Run linearization with all inputs and selected only the ones above.
- Changed pitch input to 0, to 2,3,5 times original (only saw change in 5x but just delayed taking off to infinity)
- Set constant (high) value for generator torque (just makes performance a little uneven.
The result is always the same, I am unable to achieve a steady-state response of the system.
The only thing I have not messed with yet is the DISCON input file for the controller. Is the linearization impacted by the DISCON input file for the controller (full model uses a bladed-style DLL for controller setup).