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^2VS_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.
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_SpdGenEff/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.
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!
VS_Rgn2K should be set to equal the torque constant, “K”, such that the generator torque = Komega^2 in Region 2 control (or generator power = Komega^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%.
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.
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?
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.