Engineers at Moog Inc. and wind turbine maker Made Tecnologías Renovables SA have produced a pitch control servo valve that governs blade pitch while eliminating external controls. The valve provides precise blade feathering in response to fluctuating winds. It controls pitch on each blade as they arc through a full rotation and the loading changes due to the wind velocity gradient. The valves add a measure of safety too, explains Shih Pin Tan, Moog's power generation marketing manager in Shanghai.
Wind turbines are built to match a site's prevailing wind speeds, Tan explains. They're classified as low, medium, and high speed types. The blades have to turn at nearly constant rpm to keep the ac power frequency steady. Some fluctuation is managed by electronics down the line, Tan says, but maintaining consistent blade speed remains a goal that is accomplished by varying pitch and, to a lesser degree, yaw.
Older digital valves had to communicate with a PLC located in the wind turbine's stationary housing, or nacelle. There, feedback from the LVDTs or other devices on the pitch control cylinders would close the loop with the servo valves. The new design brings intelligence directly onto the valve, dispensing with a separate PLC, Tan says.
Reliability and remote monitoring also take on major roles for the new valves. Because wind turbines often work remotely and in severe cold, Made wanted the valve to be self-monitoring to keep technicians out of the towers. The valves also will synchronize the safe return of the blades to home position if a control fails, the wind turns severe, or some other disaster strikes. The system can be configured to actively dampen blade oscillations for increased reliability.
A digital servo valve from Moog helps Spanish turbine builder Made control blade pitch.
Electric motors could accomplish the same feat as the new hydraulic systems, Tan agrees. A windmill maker choosing to use hydraulics over electrics sometimes bases the decision on whether its engineers came from aerospace. Aerospace engineers prefer fluid power, it seems.
For more information:
Made's line of turbines and turnkey wind farms
Moog's new hydraulic valve platform, the Axis Control Valve with CAN-bus interface