Pitch drives can be electric or hydraulic, although hydraulic units are prevalent on utility-sized wind turbines.
Hydraulic pitch controls would use servovalves along with microprocessor-based electronics and one of several network connections, such as CANopen, Profibus, or Ethernet fieldbus interfaces. These allow digital communication for improved performance, enhanced remote diagnostics, and greater process control.
A hydraulic pitch control could also include software, actuators, and pumps along with hoses, reservoirs, and brakes for precise control of each blade’s position. Actuators with digital servovalves allow changing pitch angles with a resolution of less than 1° at a response time of less than 100 ms. A fail-safe system moves the blades to a safety position in case of a fault. Temperatures in the hub where a lot of pitch equipment is mounted ranges from -30 to 70°C.
The latest generation of CANbus compatible valve controllers operating under the CANopen protocol have the bandwidth to accommodate almost any practical load of control signals plus inputs from sensors that monitor valve and actuator performance. By identifying small degradations in performance, sensors and software in today’s systems can schedule preventive maintenance and even component replacement during scheduled downtime.
Electric pitch actuators often consist of a gearbox and either an ac or dc motor. Backup systems often give designers the choice of lead acid, or lithium ion batteries, or capacitors.
Pitch controls provide other possibilities with inputs from load sensors molded into the blades. For instance, load sensing would allow adjusting the pitch of each blade as needed for best rotor loading and to avoid overloads.
Yaw drives are generally electric motors mounted on a gear-reduction set and equipped with an electric release, spring-activated brake. One 2.3-MW turbine uses about eight motors to control yaw.
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