Hello everybody,

I am relative new to Fast and i am trying to simulate the behavior of a 2MW onshore turbine. I would be very grateful if someone could solve/help me with some issues. I am using FAST v7 (FAST_v70001a-bjj) and I want to simulate the behaviour of a 2MW onshore turbine, pitch regulated, under turbulent wind (from 3m/s to 25m/s) to get loads on the blades. I have run 12 *.wnd files with turbsim for a range of wind speed (3, 5, 7, …, 23, 25 m/s). I have obtain the power curve of the turbine from internet and I have the power values corresponding to the wind speed. Besides I know the range of the rotational speed of the rotor (9-19rpm) and the gearbox ratio. I have checked the Fast manual and an old post to try to understand how it works the control ("[url]http://forums.nrel.gov/t/torque-controller/675/1]") when I set the VSContrl=1.

My main doubts are relative to the parameters of the “Variable-speed control mode” (VS_RtGnSp, VS_RtTq, VS_Rgn2K, VS_SlPc) for each *.fst file. I have set the same VS_RtGnSp=(Generator rated speed) and VS_RtTq=(Generator torque constant) for the 12 *.fst files. For the VS_Rgn2K I have set the same value for the region 3 files (wind speed from 13 to 25 m/s) and for the region 2 files (wind speed from 3 to 11 m/s) I have set the value of each file so (HSS_Spd^2*VS_Rgn2K)*Rot_Spd is equal to the data of the power curve for each wind speed (HSS_Spd -Generator speed - in rpm and Rot_Spd - Rotor speed - in rad/s). I have supposed the rotor speed as a linear ramp from 9rpm to 16.8rpm for region 2 files and a constant of 16.8rpm for region 3 files.

Is this reasoning correct? Sure I am missing something but is this the correct way for a preliminary simulation?

Thank you in advance.

Regards,

Pablo

Dear Pablo,

You should be able to use the same values of VS_RtGnSp, VS_RtTq, VS_Rgn2K, VS_SlPc for each wind-speed bin for normal operation. Because the generator torque is calculated with respect to the high-speed shaft, the power in Region 2 should be (HSS_Spd^2*VS_Rgn2K)*Gen_Spd*GenEff/100, where HSS_Spd has units of rpm, Gen_Spd is the same speed in units of rad/s, and GenEff is the generator efficiency in percent.

I hope that helps.

Best regards,

Dear Jason,

Thank you a lot for your reply. As I suspected, I was defining these values wrong. Nevertheless I still have some doubts about how to calculate these values.

VS_RtGnSp: Equal to the generator rated speed. According to my synchronous generator data, it would be 1680 rpm. According to my data, the rotor speed range is [9-19 rpm].

VS_RtTq: If the turbine power is 2000KW, 2000000/(1680*pi/30)= 11368.2Nm

VS_Rgn2K: I have doubts with this parameter. How should I define a valid value for all wind-speed bins? How can I calculate it?

VS_SlPc: I have doubts with this parameter. I have checked the definition of this parameter on the Fast manual and I do not understand the “Equivalent synchronous generator speed (EsGnSp - I made up this parameter id)”. VS_SlPc=(VS_RtGnSp-EsGnSp)/EsGnSp, how can I define/calculate this parameter (EsGnSp)?

Thank you in advance!

Best regards,

Dear Pablo,

VS_Rgn2K should be set to equal the torque constant, “K”, such that the generator torque = K*omega^2 in Region 2 control (or generator power = K*omega^3, assuming 100% generator efficiency). The torque constant, “K”, can be derived from the surface of power coefficient as a function of tip-speed ratio and blade-pitch angle. This is documented in many wind turbine publications, e.g. see section 2.1 from the following report: nrel.gov/docs/fy04osti/36265.pdf.

In the absence of more specific information about the slope of Region 2.5, I would set VS_SlPc = 10%.

Best regards,

Dear Jason,

Thank you again for your answer. I will take a look to the report. I too wish to take this opportunity to congratulate you and your team for this forum. It really helps a lot.

Best regards,

Dear Jason,

I am trying to understand how Fast V7 calculates the RotSpeed. I have been doing some test trying to set the same torque constant “K” for different winds speed and depending on the value the Rotspeed changes a lot for low wind speeds. Could you explain to me the relation between these two factors?

Thank you

Best regards,

Dear Pablo,

The rotor speed in FAST is calculated by time-integration of the rotor acceleration, which itself is calculated by the difference in aerodynamic and generator torques divided by the drivetrain inertia.

Best regards,