1. Field of the Invention
The present invention relates generally to stall controlling features for a wind turbine that is capable of varying torque via an alternator to cause or induce aerodynamic stall in coupled wind turbine blades. In particular, the wind turbine controller of the present invention includes stall controlling features that enable generation of stall torque under both normal conditions and upon certain triggering conditions occurring, so that in the event of a failure in the windings of the alternator or connectors thereto, or to the controller, sufficient torque remains available in the alternator to control the wind turbine.
2. Background of the Related Art
It is known in the art to provide small scale wind turbines for commercial and residential use. Problems with these existing turbines include, but are not limited to, the need to control power, especially in low and high wind conditions, and to provide features to address regulatory and other requirements and needs for stopping or slowing turbine blade rotation under certain triggering conditions, such as in the event of high winds combined with control system failure and/or failure of at least some portion of alternator windings.
To meet the need to control power output, it is known to provide stall control through the use of control electronics, which adjust the torque of the alternator in differing wind conditions. Such control electronics and operation is described further in applicant's U.S. Pat. No. 6,703,718 titled “WIND TURBINE CONTROLLER,” the entirety of which is incorporated herein by reference.
Prior art solutions to the problem of stopping turbine blade rotation in emergency conditions have included use of blade furling to reduce blade rotation speed in extreme winds and mechanical braking or other use of mechanical backup devices that operate in the event of control system failure and other emergency conditions.
Problems with such prior art mechanical approaches to stopping or reducing blade rotation speed in such conditions have included increased noise (e.g., due to blade “fluttering” or excess noise when furling is used), and increased complexity and cost for such devices and systems. These devices increase complexity and decrease reliability. Among other things, there remains an unmet need in the art for systems, methods, and devices for operation in such triggering conditions, which meet regulatory and other needs and requirements, but which minimize noise and do not add significant complexity, loss of reliability, or cost to wind turbines. There is a further need for wind turbines that meet such triggering condition needs, and that also include features to allow efficient operation over a range of wind conditions.