Active stall control

Active stall control achieves power limitation above rated wind speed by pitching the blades initially into stall, i.e., in the opposite direction to that employed for active pitch control, and is thus sometimes known as negative pitch control. At higher wind speeds, however, it is usually necessary to pitch the blades back towards feather in order to maintain power output at rated.

A significant advantage of active stall control is that the blade remains essentially stalled above the rated wind speed, so that gust slicing (see Section 6.7.2) results in much smaller cyclic fluctuations in blade loads and power output. It is found that only small changes of pitch angle are required to maintain the power output at rated, so pitch rates do not need to be as large as for positive pitch control. Moreover, full aerodynamic braking requires pitch angles of only about —20°, so the travel of the pitch mechanism is very much reduced compared with positive pitch control.

Figure 6.11 compares schedules of pitch angle against wind speed for active stall control and active pitch control for the same blade. The active stall control schedule is derived from the intersection of the family of power curves for different negative pitch angles with the 500 kW abscissa in Figure 6.12, while the active pitch control schedule is derived from Figure 6.7.

The principal disadvantage of active stall control is the difficulty in predicting aerodynamic behaviour accurately in stalled flow conditions. Active stall control is considered further in Section 8.2.1.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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  • MAKSYMILIAN
    What is active stall control?
    7 years ago

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