Meeting Today’s Energy challenges – High-performance of Wind Turbine Pitch Systems depends on Pitch

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Published: 11th December 2012
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Wind power is increasingly being viewed as an important energy source by many nations. The key in wind turbine applications is reliability and efficiency, which means the wind turbine must be available to produce energy under varied wind conditions in a consistent manner. The challenge for wind turbine OEM’s is to make sure that components are reliable and robust to support these environmental conditions by balancing features, performance and cost.

Over the years, technology enhancements have led to more efficient, reliable, cost-effective and high-performance technology. In the wind energy space, one of the foremost technology advancements that allow wind turbine manufacturers improve operational effectiveness is the blade pitch control system. Pitch systems are responsible for the precise positioning of blades which enables wind turbines to operate at the optimum operation point to ensure the highest availability and power output. At lower wind speeds the blades are controlled at zero degrees, which allows maximum power to be harnessed from the wind. When the wind speed exceeds the nominal speed, the blade position is dynamically controlled in order to guarantee the maximum output power of the turbine. Beyond the maximum allowed wind speed, the blade pitch control moves the blades into the 90 degrees feathering position in order to stop the turbine. For modern turbines, the blade pitch control system is also responsible to halt the turbine – and therefore is part of the turbine’s safety system.

Given the harsh outdoor conditions that turbines operate in, the pitch system and its components face a variety of challenging conditions from offshore and onshore environments including low and unsteady wind speeds and ambient operating temperatures ranging from -30° C up to +50° C (-22 to +122° F). The pitch system components, specifically the Pitch Servo Motor, need to meet the performance requirements throughout the full temperature range.

Blade pitch control is implemented with either hydraulic or electromechanical actuation. However, electromechanical solutions are fast gaining ground and in due course, may become a norm.

Wind Turbine Pitch Servo Motors

The latest AC synchronous electromagnetic brushless servo motors designed specifically for the wind market combine high reliability, compactness, high power density and a unique capability that allows them to be controlled in sensorless mode.
The high-performance, reliability, safety and consistency of these servo motors are critical to the effectiveness of the wind turbine pitch system and the turbine performance.

Today, advanced wind turbine pitch motors are specifically designed as part of the pitch system to meet the demanding requirements of wind turbines. Even in extreme climates, these servo motors maintain high-performance while offering a compact design and reducing mechanical complexity. The brushless, permanent magnetic motor trumps induction-motor capabilities in dynamic performance as well as physical size and peak torque capability under field weakening condition. Due to their brushless design, they are smaller, lighter and more efficient than comparable brushed DC motors. Individual pitch control (being adopted in some of the latest turbine designs), places ever-higher demands on these servo motors, making AC servo the technology of choice for the future.

These motors are built to last very long, with low maintenance costs owing to minimum mechanical wear. Additionally, these servo motors offer protection in the event of grid loss and also combine safety features like sensorless control whereby the Pitch Servo Drive controls the motor in the event where position information is lost from the servo motor’s resolver. This feature offers wind turbine OEMs the ability to add an additional level of safety redundancy into the pitch system because a given motor (and the connected blade) can move to a safe position even in case of power loss, motor feedback loss and/or signal cable failure.

The wind power industry is undergoing significant transformation as wind farms grow from a few dozen megawatts capacity, to several hundred megawatts requiring locations in more remote areas. Wind turbines are also being designed to best match the wind and temperature profiles of the environment they are located in. The need for a competent pitch systems partner capable of harnessing cutting-edge technology is greater than ever today. The focus, very clearly, is on high-performance at reasonable costs, with absolutely no compromise on reliability and safety.

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