Dear Jason.
I am comparing the blade pitch control natural frequency(BPCNF) to platform pitch natural frequency(PPNF). In the report of OC3 wind turbine system (nrel.gov/wind/pdfs/47535.pdf), the BPCNF is 2rad/sec and the PPNF is 2.1rad/sec. BPCNF is less than PPNF, but BPCNF is very close to PPNF. Doesn’t BPCNF need to be decreased more in order to reduce the resonance effect between PPNF and BPCNF?
Thank you.
Daniel Kim.
Dear Daniel,
I think you mean 0.21 rad/s and 0.2 rad/s for the PPNF and BPCNF, respectively. The BPCNF of 0.2 rad/s was found to be a sufficient compromise between preserving damping of the platform-pitch mode and regulating rotor speed, but you could always perform a sensitivity of BPCNF yourself to see the influence.
Best regards,
Dear Jason
I am sorry for my mistake. You are right. BPCNF 0.2rad/sec and PPNF is 0.21 rad/sec
Regarding compromise between preserving damping of the platform-pitch mode and regulating rotor speed, I have some questions.
Preserving damping means that Kp has a large number, so that damping ratio also have a large value, doesn’t it? Then, what does regulating rotor speed mean? Which values must be adjusted in order to regulate rotor speed well? If KP decreases, is it worse in terms of damping, and is it better in terms of the regulating rotor speed? I don’t know how I can make the better rotor speed regulating ability.
Also, is not the resonance between BPCNF and PPNF considered in that compromising?
Please understand that blade pitch control part is not accustomed to me.
Sincerely,
Daniel Kim.
Dear Daniel,
The goal of the pitch controller is to regulate rotor speed. The higher the controller gains, the better the speed regulation. But if the gains are too high, the platform-pitch mode can be driven unstable. See the following paper for further information: nrel.gov/docs/fy08osti/42589.pdf.
Best regards,
Dear Jason.
Thank you for your help. nrel.gov/docs/fy08osti/42589.pdf is very helpful to me.
Sincerely,
Daniel Kim