# Pitch and Torque Cntrl (Region 3)

Dear Dr. Jonkman,

One document in Fast 7 (A wind turbine with 600KW) explains that to have the maximum generator torque in region 3, we should have a fixed generator torque like this:

While, in another document related to 5MW for offshore wind turbines, the maximum generator torque in region 3 is decreasing. The below picture shows this:

May I know what is the underlying reason behind this difference?

Thanks

Best Regards,
Sina

Dear Sina,

There are two torque strategies in Region 3 (above rated): constant torque or constant power. In the former, the generator torque is held constant regardless of speed variations, which means the generator power (equaling torque times speed times efficiency loss) is variable. In the latter, the generator torque is inversely proportional to the speed variations, which means the generator power is constant. In the latter, the pitch controller must work a bit harder to regulate generator speed (to counteract the generator torque variations).

Best regards,

Dear Dr. Jonkman,

Thanks for clarifying the issue. If the pitch controller must work harder, may I know why the latter method (constant power) is used? In other words, what are the pros and cons of each approach?

Thanks

Best Regards,
Sina

Dear Sina,

With the constant power strategy, the generator torque varies and the pitch-control system must work a bit harder, but the generator power is constant. With the constant torque strategy, the pitch-control system does not have to work as hard, but the generator power is variable, which means the generator is overloaded for periods of time. Either way, the control strategy must be considered in the detailed design of the turbine components.

Best regards,

Dear Dr. Jonkman,
Thanks again for clarifying the issue. I got these results:

My question is that, are those figures are correct? If they are not, what is the reason? because my figures in region 3 are different from the above figures I placed!

Thanks

Best Regards,
Sina

Dear Sina,

No, these do not look correct e.g. I don’t see any 1.5 or 2.5 regions in your torque-speed curve. How were these curves made?

Best regards,

Hello jason,

``````              I am working on Krogmann 15/50 Wind turbine. With Power of 50kW and Generator speed of 1500 rpm. So i have calculated Generator Torque of 318.31 N-m. I am trying to build Torque controller. i am confused about the omega1 and omega2 values for my system and how do i achieve Variable-speed regions. As attached in picture do i have to suppose my omega1 and omega2 values. Will my rated Torque be 318.31?
``````

Thank you
best regards
Muddassir Nawaz

Dear Muddassir,

I would guess your rated generator torque would be more than 318.31 Nm because normally the electrical power output is less than the mechanical power output due to electrical efficiency losses.

I’m not sure what you mean by omega1 and omega2; are you referring to the transition generator speeds between regions 1 and 2 and between regions 2 and 3?

The constant (K) in the standard variable-speed torque control law (T=K*omega^2) can be calculated from the power coefficient surface…you’ll need to know the peak power coefficient and the tip-speed ratio where this peak occurs.

Best regards,

Dear jason,

``````             Thank you for your response. Generator Torque calculated in my case as (GenTq = Rotor Torque/Gearbox ratio), here  Rotor Torque = 7.3477kNm and Gearbox ratio = 23.23. So my GenTq = 316.5Nm. And Maximum Generator Power obtains at toruqe 318.31Nm. So i assume Rated Torque to be 318.31Nm.
``````

The Omega1 and Omega2 are where region 21/2 starts and end. In “Advanced Control Design for Wind Turbines” Omega1 is 1691.98rpm and Omega2 is 1781.98rpm. These values are frictional or calculated? As i wanted to find out region 21/2 for Krogmann 15/50 wind turbine.

Thank you
best regards
Muddassir Nawaz

Dear Muddassir,

I believe the values of omega1 and omega2 you are reporting are appropriate for the CART2 wind turbine.

Best regards,

Hello jason,

``````             Thank you for your response. Sorry you misunderstood, I am not reporting Omega1 and Omega2 values, just describing that Omega1 and Omega2 are where region 21/2 start and end. In my first Post on this page you asked what Omga1 and Omega2 are?
``````

My Question still remains, Omega1 and Omega2 values are calculated or supposed?

I supposed values for , Omega1 = 1436.498rpm , Omega2 = 1461.963rpm. After running Simulation as shown in picture, i got rated Torque at 2700 rpm. This is incorrect. At GenSpeed 1500 rpm, i should have a constant Rated Torque.

[/code]
Can you please let me know what is going wrong in my case.

I would appreciate any help.
Thank you
Best regards
Muddassir Nawaz

Dear Muddassir,

I don’t know how to answer your question because I don’t know anything about the Krogmann 15/50 wind turbine. In general, you should set the values to match the properties of the actual wind turbine you are modeling.

Does this wind turbine have a variable speed torque controller? Does it operate with a region 2.5? How did you make your generator torque versus generator speed plot?

Best regards,

Hello Jason,

``````             I checked Krogmann 15/50 deosn't have region 2.5 (it has four regions 1, 2, 3 ,4). but it has a torque controller. Can you tell me how to apply Wind as Input signal in FAST7 to check Wind turbine Performance(as i have my own wind calculation .wnd file). I tried with Test01_SIG.mdl {Since i don't have any idea how controller will look like without 2.5 region, as all document to controller on internet are related region 2.5. if you could link me to controller document, that will be helpful}. But How to apply wind as input? do i use "TotWindV" in simulink?
``````

Thanks
best regards
Muddassir Nawaz

Dear Muddassir,

TotWindV is an output from the FAST S-Function in Simulink, not an input.

Instead, in FAST v7 (both with and without the Simulink interface), wind is specified via the WindFile input parameter in the AeroDyn v13 input file–see the old FAST v7 and AeroDyn related documentation for more information:
nwtc.nrel.gov/system/files/FAST.pdf
nwtc.nrel.gov/system/files/AeroDyn.pdf
nwtc.nrel.gov/system/files/User … erface.pdf

I’m not sure what you controller document you are asking for a link to.

Best regards,

Dear jason,

``````               I am trying to get "GenPwr" with Torque controller
``````

``` 1 VSContrl - Variable-speed control mode {0: none, 1: simple VS, 2: user-defined from routine UserVSCont, 3: user-defined from Simulink/Labview} (switch) 1500 VS_RtGnSp - Rated generator speed for simple variable-speed generator control (HSS side) (rpm) [used only when VSContrl=1] 318.31 VS_RtTq - Rated generator torque/constant generator torque in Region 3 for simple variable-speed generator control (HSS side) (N-m) [used only when VSContrl=1] 0.0001414 VS_Rgn2K - Generator torque constant in Region 2 for simple variable-speed generator control (HSS side) (N-m/rpm^2) [used only when VSContrl=1] 9999.9e-9 VS_SlPc - Rated generator slip percentage in Region 2 1/2 for simple variable-speed generator control (%) [used only when VSContrl=1]```

i followed Control section of FAST User’s guide, neglecting 21/2 region. But problem is, i am getting GenPwr around 80kW which should be 50kW.
My GBoxEff =98% , GenEff = 92.8% following [url]http://forums.nrel.gov/t/resistant-moment-of-the-rotor-and-of-the-electric-generator/408/1] if i calculate my GenPwr is around 45-50kW, but output show 80kW.

Also HSShfV goes to 2500 rpm and LSSGagV goes to 120 rpm {even though RotSpeed =64.5 rpm is mentioned in “initial Conditions”} Why is generator and rotor speed so high?

Thank you
best regards
Muddassir Nawaz

Dear Muddassir,

Your power is likely going so high because:

• the generator torque in your model is constant for speeds higher than rated speed (Region 3 control),
• the aerodynamic torque is higher than the rated generator torque, and
• you don’t have active blade-pitch control to reduce the aerodynamic torque at high winds to regulate the speed,

which means that the rotor will overspeed (and generator power will exceed rated) until the aerodynamic torque balances with the generator torque.

You’ll need another means of control to operate in Region 3 e.g. active blade pitch control.

Best regards,

Dear Jason,

If I am well understood, there are 2 methods to get generator torque, (considering the turbine working in region 3)
first, constant torque: fix it at its rated value;
second, constant power: get the generator torque by calculating T = P_rated/Omega;

And I’m working on the floating wind turbine control in region 3. The control objectives are keep rated power output and reduce the platform pitch motion. Currently, the generator torque was fixed at rated, the single control input is the collective blade pitch (CBP) angle.

My question is:
Is it possible to use generator torque as the second input? i.e. do not use the constant torque and the constant power strategy. Then, I will get two control inputs, it might improve the controller performance.

Best regards,
Cheng

Dear Cheng.Zhang.

Yes, what you propose has certainly been done before. Varying the torque in Region 3 can be effective to mitigate vibrations of the drivetrain-torsion and/or tower side-to-side modes.

Best regards,

Dear Jason,

Thank you!

I’m confused that,
1). Do a high vibration of the drivetrain-torsion means a high variation of the rotor speed?
2). In my opinion, performance is highly related to the control algorithm.

If I introduce additional control input (generator torque), the control is different from the one only have a single input (blade pitch angle). Recall that in my case, the objectives are to keep rated power output and to reduce the platform pitch motion. I can compare the performance of power and platform pitch motion of the two controllers.
As for the vibrations of the drivetrain-torsion and/or tower side-to-side modes, since they are not my control objectives, I can only check it rather than controlling it. Hence, why it is effective to mitigate vibrations of the drivetrain-torsion and/or tower side-to-side modes.

Best regards,
Cheng

Dear Cheng,

My previous comment simply stated that I have seen combined blade-pitch and generator-torque controllers, but that the generator-torque is often used to mitigate drivetrain-torsion and tower-side-to-side vibrations. I would not expect control of the generator torque to have a strong influence on platform-pitch, but it may be useful to regulate rotor speed and power in Region 3 if the pitch controller is also tasked with mitigating platform pitch. I would suggest reviewing the literature on these matters. The work of Namik and Stol from around 2010 comes to mind, but there are likely many others as well.

Best regards,