Torque-versus-speed response of the variable-speed controller

Marwa.Mohamed · September 20, 2024, 5:18am

Hello All,
I tried to draw the relation between Generator torque and generator speed for both DISCON and ROSCO controllers for NREL 5 MW monopile wind turbine, it looks fine until region 3, instead of having generator torque is inversely proportional to the generator speed in DISCON, in my results the generator torque is increased proportional to the generator speed not inversly as shown here.
what is the error in my calculation? is there a specific reason for that?

Regards,
Marwa

Jason.Jonkman · September 20, 2024, 12:38pm

Dear @Marwa.Mohamed,

Can you clarify the source of the DISCON and ROSCO controllers for the NREL 5-MW baseline wind turbine? I presume you obtained the DISCON from the OpenFAST r-test, but where did you obtain the ROSCO controller?

How did you derive these torque-speed curves from both controllers?

Best regards,

Marwa.Mohamed · September 20, 2024, 12:55pm

Dear Dr. Jason,
Thanks for your reply. For DISCON, yes it is from OpenFASST r-test.
for ROSCO, I got it from

github.com

NREL/ROSCO/blob/main/Examples/example_inputs/minimal_DISCON.IN

! Controller parameter input file for the NREL-5MW wind turbine
!    - File written using ROSCO version 2.7.0 controller tuning logic on 02/27/23

!------- DEBUG ------------------------------------------------------------
0                   ! LoggingLevel		- (0: write no debug files, 1: write standard output .dbg-file, 2: LoggingLevel 1 + ROSCO LocalVars (.dbg2) 3: LoggingLevel 2 + complete avrSWAP-array (.dbg3))
0                   ! Echo		        - (0 - no Echo, 1 - Echo input data to <RootName>.echo)

!------- CONTROLLER FLAGS -------------------------------------------------
1                   ! F_LPFType			- (1: first-order low-pass filter, 2: second-order low-pass filter), [rad/s] (currently filters generator speed and pitch control signals
2                   ! VS_ControlMode	- Generator torque control mode in above rated conditions {0: constant torque, 1: constant power, 2: TSR tracking PI control with constant torque, 3: TSR tracking PI control with constant power}
1                   ! VS_ConstPower  	- Do constant power torque control, where above rated torque varies, 0 for constant torque}
1                   ! PC_ControlMode    - Blade pitch control mode {0: No pitch, fix to fine pitch, 1: active PI blade pitch control}
1                   ! SS_Mode           - Setpoint Smoother mode {0: no setpoint smoothing, 1: introduce setpoint smoothing}
2                   ! WE_Mode           - Wind speed estimator mode {0: One-second low pass filtered hub height wind speed, 1: Immersion and Invariance Estimator, 2: Extended Kalman Filter}
1                   ! PS_Mode           - Pitch saturation mode {0: no pitch saturation, 1: implement pitch saturation}

Extra lines that ROSCO doesn't care about anymore

!------- FILTERS ----------------------------------------------------------
1.57080             ! F_LPFCornerFreq	- Corner frequency (-3dB point) in the low-pass filters, [rad/s]

This file has been truncated. show original

I tested both turbines under DLC 1.1 under wind speed range from cut in to cut out with intervals 2 m/s .

Regards,
Marwa

Jason.Jonkman · September 20, 2024, 1:02pm

Dear @Marwa.Mohamed,

Thanks for clarifying the source of the ROSCO controller.

How did you derive the torque-speed curve from simulations of DLC 1.1?

Best regards,

Marwa.Mohamed · September 20, 2024, 1:09pm

I request the output of GenTq [kN-m] and GenSpeed [rpm] for every wind speed from cut in to cut out and got the (min, mean, max) from pyDatView. then I plot the curve between the Max of GenTq and Max of GenSpeed.
when I plot the mean value of the 2 outputs in Region 3, they almost have the same value
I attached my results

Regards,
Marwa

Jason.Jonkman · September 20, 2024, 1:16pm

Dear @Marwa.Mohamed,

I would guess you are biasing your results by not pairing GenTq and GenSpeed at the same time steps. What does the torque-speed curve look like if you simply plot GenTq and GenSpeed at each time step for a given load case simulation (and how do these plots compare between simulations)?

Best regards,

Marwa.Mohamed · September 20, 2024, 1:41pm

Dear Dr, Jason,
Do you mean that? Am I understand right?
DISCON, but why there is backword portion of the curve?

ROSCO

Am I understand right? and How to got a smooth line for the plots like your thesis please?

Regards,
Marwa

Jason.Jonkman · September 20, 2024, 2:43pm

Dear @Marwa.Mohamed,

Indeed, these results are making more sense to me now, although I’m not sure why ROSCO has a wider spread (must be different control logic than implemented in DISCON).

The negative slope in Region 3 ensures constant power in Region 3 (as speed increases, torque must decrease to maintain constant power).

The figure from my thesis (and NREL 5-MW specifications report) shows an analytical expression for the torque-speed curve. I would expect that the parametric plot of GenTq and GenSpeed from different time steps that you are showing to match the analytical expression “on average”, which it seems to do.

Best regards,

Marwa.Mohamed · September 20, 2024, 2:53pm

Thanks Dr. Jason for your time and detailed answer.

Regards,
Marwa

Topic		Replies	Views
OpenFast Controller Modelling Computer-Aided Engineering Software Tools	5	1893	June 28, 2022
Baseline NREL 5MW controller on simulink Controls	15	10868	November 26, 2021
Controlof 5MW Offshore WT Controls	7	3204	December 14, 2021
15MW control behaviour rated wind Controls	2	2820	January 29, 2021
IEA 15MW Thrust mismatch between libdiscon.dll and Discon.dll Rotor Aerodynamics	3	45	September 3, 2024

Torque-versus-speed response of the variable-speed controller

Related topics