## Search found 16 matches

Sat Dec 28, 2019 10:13 am
Forum: Controls
Topic: is pitch control decided by power output or wind speed
Replies: 4
Views: 2192

### Re: is pitch control decided by power output or wind speed

Jason.Jonkman wrote:Dear Yanda,

There are multiple uses for a power curve, but what you state is one of them. The power curve you show is really an averaged quantity.

Best regards,

Thx, Jason. I appreciate your help on weekends.
Sat Dec 28, 2019 9:09 am
Forum: Controls
Topic: is pitch control decided by power output or wind speed
Replies: 4
Views: 2192

### Re: is pitch control decided by power output or wind speed

Dear Yanda, It is rare for the pitch controller to use a direct wind speed measurement in its feedback loop. Using the generator speed and/or electrical power is more common. The wind at hub height does not determine the control region. Best regards, Thx, Jason. That makes sense. So the ideal power...
Fri Dec 27, 2019 10:13 pm
Forum: Controls
Topic: is pitch control decided by power output or wind speed
Replies: 4
Views: 2192

### is pitch control decided by power output or wind speed

Hi guys, When we talk about pitch control, we assume only if wind speed is larger than rated wind speed then mechanical power output could be larger than rated power output. Capture.PNG However, considering wind speed is measured at hub height and wind speed at top and bottom of blade differ in dire...
Fri Oct 11, 2019 10:24 am
Forum: General
Topic: what is thrust force?
Replies: 2
Views: 2143

### Re: what is thrust force?

Dear Yanda, There are not different thrust forces at the inlet and outlet of the control volume. Instead, the thrust force of the rotor can be written as the difference in linear momentum between the inlet and outlet, i.e., T = rho*S_1*V_1^2 - rho*S_2*V_2^2, or equivalently from Bernoulli's equatio...
Thu Oct 10, 2019 6:25 pm
Forum: General
Topic: what is thrust force?
Replies: 2
Views: 2143

### what is thrust force?

Hi guys, While learning betz's law, I notice thrust forces at the inlet and outlet of control volume are both represented as density*area*velocity^2, which is different from thrust force caused by air pressure difference at the two sides of turbine itself, since air pressure at inlet and outlet of c...
Thu Oct 10, 2019 4:03 pm
Forum: General
Topic: question about assumption of inlet and outlet pressure in betz's law
Replies: 2
Views: 2182

### Re: question about assumption of inlet and outlet pressure in betz's law

Dear Yanda, I think the answer to your question is scale. The pressure-gradient zone around the rotor is fairly small scale...perhaps encompassing a couple rotor diameters upwind and downwind of the rotor. The pressure gradient driving wind in the first place tends to be a much larger scale (mesosc...
Wed Oct 09, 2019 9:28 pm
Forum: General
Topic: question about assumption of inlet and outlet pressure in betz's law
Replies: 2
Views: 2182

### question about assumption of inlet and outlet pressure in betz's law

Hi guys, I have a question about assumption of inlet and outlet pressure in betz's law. The upper diagram below is a control volume of one-dimensional air flow. The lower one is its pressure at corresponding places. Wind blows from left to right. And it is assumed air pressures at the far left and t...
Sat Jul 27, 2019 10:11 am
Forum: WIND Toolkit
Topic: About the WIND Toolkit Forum
Replies: 1
Views: 18313

### Re: About the WIND Toolkit Forum

Hi Jason,

Is it possible we can download solar irradiation data of wind toolkit? Since we need pair of solar/wind data from same model, NSRDB won't be a choice for us. Waiting for your reply.

Best,
Yanda
Tue Apr 30, 2019 6:30 pm
Forum: General
Topic: Active stall control VS pitch control
Replies: 2
Views: 5491

### Re: Active stall control VS pitch control

Dear Yanda, 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 ...
Mon Apr 29, 2019 11:12 am
Forum: General
Topic: Active stall control VS pitch control
Replies: 2
Views: 5491

### Active stall control VS pitch control

Hi guys, I am reading papers and books about control method of WTG and confused by comparison between active stall control and pitch control. 1) 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 "co...
Tue Apr 16, 2019 2:04 pm
Forum: General
Replies: 2
Views: 2845

### Re: Question about Betz limit

Dear Yanda, It is common practice to use the swept area of the rotor (A_t) as the reference in the Betz limit because if the rotor was absent, the flow would not slow down and would pass through that area unaffected. The area A_u is smaller than swept area because the wind slows down due to the pre...
Tue Apr 16, 2019 11:20 am
Forum: General
Replies: 2
Views: 2845

Hi guys, I just started to learn betz's law and wanna ask a question about it. Capture.PNG Capture2.PNG In betz's law, the "1/2*rho*At*Uu^3" is regarded as wind power input , but why don't we use "1/2*rho*Au*Uu^3" instead? I suppose this is the real wind power input at the very b...
Mon Mar 11, 2019 11:35 am
Forum: General
Topic: FIXED and VARIABLE wind turbines, help pls!
Replies: 12
Views: 27526

### Re: FIXED and VARIABLE wind turbines, help pls!

Dear Yanda, The power grid operates at a "fixed frequency", so, coupling a fixed-speed turbine to the grid is straightforward. Coupling a variable-speed turbine to the grid requires a fancy power electronics i.e. AC-to-DC-to-AC conversion. Best regards, Dear Jason, Thx very much for your ...
Mon Mar 11, 2019 10:48 am
Forum: General
Topic: FIXED and VARIABLE wind turbines, help pls!
Replies: 12
Views: 27526

### Re: FIXED and VARIABLE wind turbines, help pls!

Dear Yanda, The point is that the fixed-speed turbine actually has a small variation in generator speed, so that large variations in wind speed result in small variations in generator speed and large variations in torque / power i.e. the torque-speed curve is steep. Best regards, Dear Jason, Thx so...
Mon Mar 11, 2019 10:19 am
Forum: General
Topic: FIXED and VARIABLE wind turbines, help pls!
Replies: 12
Views: 27526

### Re: FIXED and VARIABLE wind turbines, help pls!

Dear Yanda, Yes, small changes in rotor speed together with a steep torque-speed curve will result in large variations in torque and power. The fixed rotor speed will be selected to maximize aerodynamic efficiency at a given wind speed together with structural design decisions of the wind turbine. ...