- Preprint
(1504 KB) - Metadata XML
22 Jan 2021
22 Jan 2021
Abstract. Individual Pitch Control (IPC) is a well-known approach to reduce blade loads on wind turbines. Although very effective, IPC usually requires high levels of actuator activities, which significantly increases the pitch Actuator Duty Cycle (ADC). This will subsequently result in an increase of the wear on the bearings of the blades and make the current IPC design not economical viable. An alternative approach to this issue is to reduce the actuator activities by incorporating the output constraints in IPC. In this paper, a fully data driven IPC approach, which is called constrained Subspace Predictive Repetitive Control (cSPRC) is introduced. The output constraints can be explicitly considered in the control problem formulation via a Model Predictive Control (MPC) approach. The cSPRC approach will actively produce the IPC action for the necessary load reduction when the blade loads violate the output constraints. In this way, actuator activities can be significantly reduced. Two kinds of scenarios are simulated to illustrate the unique applications of the proposed method: wake-rotor overlap and turbulent wind conditions. Simulation results show that the developed cSPRC is able to account for the output constraints into the control problem formulation. Since the IPC action from cSPRC is only triggered to prevent violating the output constraints, the actuator activities are significantly reduced. This will help to reduce the pitch ADC, thus leading to an economical viable load control strategy. In addition, this approach allows the wind farm operator to design conservative bounds to guarantee the safety of the wind turbine control system.
Yichao Liu et al.
Status: open (until 01 Apr 2021)
The aim is good, to restrict IPC to the times when it is most needed, and the control theory is impressive. However, I feel that similar results should be easily achievable using simple pragmatic extensions to the traditional PI-based IPC without all the complexity of this type of advanced control theory. For example, a deadband could be used to prevent unnecessary small control actions, and the input to the IPC could be just the excess of the asymmetric moments over a selected threshold, rather than the full asymmetric moments, so that pitch action is targeted to reducing the highest loads. This may not have the same mathematical rigour but might be more likely to be adopted because it preserves the simplicity, transparency and robustness of the traditional approach.
Dear Ervin,
Thank you for your compliments and comment. We agree that with traditional PI-based IPC, augmented with some deadbands, you might be able to achieve something similar. However, we have not found something like this in literature and most likely it would be cumbersome to tune. If you have done something like this in industry, we would love to challenge you to write a paper about this and include the tuning procedure in the paper. We would like to stress that the proposed method: 1) can directly minimize a cost function, 2) is predictive 3) can be used directly in a MIMO setting (no need for decoupling) 4) has more degrees of freedom than a PID controller (depending on the windows used) 5) can directly be made adaptive without increasing the complexity. To conclude, we agree that many control-engineering challenges can (still) be solved with PID controllers but we are approaching an era in which we have to go beyond PID and the method proposed is a candidate that can take over the role of PID control in the near future.
With kind regards,
Jan-Willem (also on behalf of the other authors)
Such simple extensions to PI-based control are generally quick and easy to tune manually with the help of a suitable simulation model. The process is not mathematically rigorous, but simple, effective, and highly practical to implement, and given that the IPC pitch travel issue has been known for years it is very likely that something like this is already implemented somewhere. It is also very likely that it has not been reported in the literature, because the methodology is not particularly interesting academically, and because an engineer implementing something like this has little incentive to publish it and might not even think of doing so. There must be a huge number of similar examples. However, I do not mean to say that researchers should not publish papers like this one, because it is important to explore new frontiers and showcase possibilities to the industry. Somewhere in the middle, academics developing new solutions looking for applications will meet practical engineers searching for better ways to solve their problems, and progress will ensue. A full appreciation of the possibilities and limitations of existing methods is important for identifying suitable applications for new advanced methods.
Yichao Liu et al.
Output Constrained, Subspace Predictive Repetitive Control Approach for Wind Turbine Load Reduction Yichao Liu https://doi.org/10.5446/50771
Yichao Liu et al.
HTML | XML | Total | Supplement | BibTeX | EndNote | |
---|---|---|---|---|---|---|
240 | 80 | 13 | 333 | 69 | 2 | 2 |
Country | # | Views | % |
---|
Total: | 0 |
HTML: | 0 |
PDF: | 0 |
XML: | 0 |
The interactive open-access journal of the European Academy of Wind Energy