Читать книгу Wind Energy Handbook - Michael Barton Graham - Страница 103

Many of the shortcomings of fixed‐pitch/passive stall regulation can be overcome by providing active pitch angle control. Figure 3.58 shows the sensitivity of power output to pitch angle changes.

The most important application of pitch control is for power regulation, but pitch control has other advantages. By adopting a large positive pitch angle, a large starting torque can be generated as a rotor begins to turn. A 90° pitch angle is usually used when the rotor is stationary because this will minimise forces on the blades such that they will not sustain damage in high winds. At 90° of positive pitch the blade is said to be ‘feathered’. The blades need not be as strong, therefore, as for a stall‐regulated turbine, which reduces blade costs. Only a small change of pitch angle is needed to provide an assisted start‐up.

The principal disadvantages of pitch control are lower reliability and cost, but the latter is offset by lower blade costs.

Power regulation can be achieved either by pitching to promote stalling or pitching to feather, which reduces the lift force on the blades by reducing the angle of attack.