Dear all,
Having success with my latest topic (pitch sensitivity) I seek help for another issue/wonder I have had for quite a while. This relates to the VSVP turbines - specifically derating / curtailment of speed and power.
My design follows the NREL 5MW reference turbine i.e.:
*) Torque control with MPPT in zone 2, limited in zone 3 and linear transient regions 1.5 and 2.5 (So the following zones: 1, 1.5, 2, 2.5, 3)
Current power curtailment
- Limit max torque to the requested power at rated speed
- Also having considered the STSR method presented by Younes Oudich in his paper.
Question
To switch control zones and thereby schedule the torque, I utilize fixed generator speed thresholds.
- This presents an issue when the turbine is scheduled for generator speed derating due to high turbulence detection / cold lubrication etc - as the reference may lie between zones.
*) I suspect dynamic speed thresholds would resolve this matter. However, I am worried that some unwanted combination of speed inputs may create poor scheduling.
*) Having looked far and wide I have not come across any litterature with this classical torque control setup and speed derating issue.
Anyone with experience in this topic that can expand on the subject? I have had no luck looking through the forums.
Kind regards,
Hi Rasmus,
When I was a student, I developed a control scheme to change the generator speed set points like (I think) you suggest: https://onlinelibrary.wiley.com/doi/full/10.1002/we.2705. To make changing the set points simpler, this controller does not use the linear interpolation in region 2.5, but instead two parallel PI controllers for torque and pitch. I suspect this is why the “classical” torque control scheme is not used in modern turbines that change set points for the reasons you described.
ROSCO is close to a new release that will include curtailment and derating. Here is the example, documentation, and code.
Theoretically, it makes sense to re-schedule the pitch control gains for the new pitch operating points, but I suspect the change in sensitivity would be small because using the same gains when de-rated seems to work fine in practice.
I hope this helps.
Best, Dan
Hey Daniel,
Thank you for the thorough answer! I briefly looked at your paper and it is very intriguing, I am going to go through all the documentation you linked and hopefully decide on an approach!
I stumbled upon a sentence in a paper which presents another idea for derating speed. Maybe this is a more “standard” approach? Leaving it on the forum for future readers (and to encourage discussion!).
In short: (parafrasering)
Follow the standard torque-speed curve and constraint any torque-speed references to lie on the curve. So if a speed derating of 200 rpm is desired, the intersecting power at -200 rpm must be the reference.
It sounds simple and besides maybe some hysteresis / tolerance logic to seperate torque and pitch controller, it might require no changes to any logic.
Reference: Power train degradation modelling for multi-objective active power control of wind farms | Forschung im Ingenieurwesen p.17