# Phase shift in blade root flap wise bending moment

Dear sir,
I am trying to implement individual pitch controller on a linearized model. I have a doubt that, If we apply base line(PI) controller to fast linearized model , and regulate the generator speed using collective blade pitch control , can we expect to get 120 degree phase shift in between the three blade root out of plane bending moments ? thank you in advance.

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Dear @Suresh.Nakkala,

I’m not sure I understand your question. Is your linearized model periodic or azimuth averaged? Are you referring to a 120-degree phase shift due to gravity loads, shear, skew, etc and are these effects captured by your linear model?

Best regards,

Dear sir
I have linearized the model from the bladed 4.10 .
I have given the azimuth step 10 degree .so it generated linearized model for each (360/10 =36) .
I am applying collective pitch controller for one out of the 36 models using simple pi controller (with help of generator speed regulation).I have doubt that which one i can consider out of 36 linearized models. but any way i chose one and i applied collective pitch controller but i am not getting the 120 degree phase shift in between the blade bending moments when the wind shear effect is present. Yes sir, I have captured linearized models with wind shear present. thank you in advance.
than and regards

Dear @Suresh.Nakkala,

To design a pitch controller for a 3-bladed rotor, I would normally expect that you’d:

1. Extract a periodic linearized model from OpenFAST (e.g., as you said, in 36 increments of 10 degrees)
2. Apply MBC3 to each of these linear models
3. Azimuth average the MBC3-transformed linear models, resulting in a linear time-invariant (LTI) model
4. Eliminate the generator azimuth state from the LTI model