Pitch control of a wind turbine is a challenging control problem to address for many reasons, including the need for high performance, ability to handle extreme environmental conditions, and accommodation of safety considerations. The motion control requirements of a wind turbine are complex, due to the need for precise control of the pitch on each of its three blades. Each blade has different and changing reaction forces depending on its orientation. Safety and reliability are also critical, due to the large size and height of wind turbines.

Moog Inc., East Aurora, N. Y., has developed a pitch control valve that uses digital technology for position control of wind turbines manufactured by MADE TecnologÌas Renovables S.A., Madrid, Spain. The intelligent servovalve has been enhanced with digital communication and embedded motion control capabilities that enable it to close the position loop within the valve itself. This axis-control functionality enables performance, reliability, remote diagnostics, and process control all in one device — functionality that could not be achieved with conventional servovalves. The intelligence embedded in this device also eliminates the cost and complexity of an external programmable logic controller (PLC).

The motion control system Moog developed in collaboration with MADE addressed a variety of technical challenges. Position control was a challenge because the reaction forces on the blades change depending on their position. In addition to the blade reaction forces changing with orientation, blades must return to a home position in the case of a serious fault. Also, motion control and data transmission must be reliable even in extreme vibration and temperature situations. Furthermore, MADE also required remote self-monitoring to reduce downtime and the need to climb the wind turbine tower to detect a fault.

The servovalve is part of Moog's new hydraulic valve platform, the Axis Control Valve with CAN-bus interface (D636 and D637 series). It is based on a proven servovalve design and enhanced with digital communication capabilities and the ability to close the position loop within the devices.

For the pitch control servovalve, Moog also developed flexible configuration software for axis control that was designed specifically for the MADE. Moog is also supplying prototypes of its RKP radial-piston pump, which will be in a dual pump arrangement on a common shaft to reduce cost.

Other features include a fail-safe system in the valve to synchronize the movement to a home position in case of a PLC fault. Moog's Valve Configuration Software was critical to MADE adjusting the pitch of the blades to reach the highest performance. This also enabled control strategies such as active dampening to reduce oscillation that could compromise integrity of the shaft. This will increase the power output, ensure the longevity of the system, and reduce maintenance costs.

Remote diagnostics and the ability to make adjustments on the fly were critical to improving operational effectiveness of the wind turbine. In addition, digital valves offer a plug-and-play benefit where every new valve can be identical to its predecessor with no need for the PID adjustments common with traditional valves. This makes startup easier, more predicable, and facilitates the development of new generation turbines.

Joseph Dyer, of Moog, added, "We are confident we will continue to work with [MADE] to achieve even higher performance and optimization of the process due to the flexibility and benefits of this new servovalve platform."

For more information call ( 800) 272- 6664 or ( 716) 652- 2000, e-mail jmarsh@moog.com, or visit www.moog.com/industrial.