I am reading papers and books about control method of WTG and confused by comparison between active stall control and pitch control.
What is power-wind speed curve with active stall and passive stall control? I attach two graphs I found from internet below. The first one is from “control of wind turbines - Mragheb”. The second one is from book “power conversion and control of wind energy systems”. The stall part of these two graphs are very different, so I am curious which one is right?
Considering we have already had “pitch-control” method which works very well, why do we still need “active-stall control”? Since the biggest difference between them is just the direction to pitch blade when wind speed is above rated value and “active-stall control” is not much simpler than “pitch control”. Is there any obvious advantage of introducing “turbulence” than just “reducing angle of attack”?
Regarding (1), my guess is the difference in the two “active stall regulation” curves are just two different examples i.e. Figure 2-13b has better power regulation than Figure 4. Active stall regulation is not very common in practice.
Regarding (2), while the power regulation can be quite similar between active pitch-to-feather and active pitch-to-stall control, the resulting thrust can be quite different. I looked at this once when looking at control of floating wind turbines–see my ASME Wind Energy Symposium paper from 2008 (sectrion III.B) for more information: nrel.gov/docs/fy08osti/42589.pdf.
