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NWTC and Industry Partners Design a Leading-Edge Drivetrain

December 2, 2013

Illustration of a next-generation drivetrain. The image reveals the three major components.

The new drivetrain applies a system approach to improve all three major components: a single-stage gearbox, a medium-speed permanent-magnet generator, and a high-efficiency power converter. Illustration by Josh Bauer, NREL

The National Wind Technology Center (NWTC) at the National Renewable Energy Laboratory (NREL), along with CREE, DNV GL, Oak Ridge National Laboratory, GE Wind, Romax Technology, and Vattenfall Windpower, are developing an innovative, medium-speed, medium-voltage wind turbine drivetrain design. Tapping into unparalleled expertise, the team created a drivetrain that can increase reliability, decrease mass, improve efficiency, and reduce the cost of wind energy. In addition, the drivetrain design can scale up to ratings as high as 10 megawatts (MW) while maintaining the lowest possible cost of energy.

In 2011, six teams were awarded by DOE to conduct a phase one study of advanced drivetrain technologies that could be scaled to larger turbines and significantly reduce the cost of wind energy. From these studies, the NWTC-led team was one of two selected for phase two awards, which are intended to demonstrate the technologies’ commercialization potential.

The team’s design applies a system approach to improve the wind turbine drivetrain, focusing on all three of its major components: a single-stage gearbox, a medium-speed permanent-magnet generator, and a high-efficiency power converter. Traditional three-stage high-speed gearbox designs have been plagued with reliability issues caused by the large loads imparted on the gears and bearings by the wind acting on the rotor and by utility faults acting through the generator. Therefore, the new gearbox design consists of a single planetary stage that eliminates the lower-reliability, higher-speed stages and uses compliant flex-pins and journal bearings to support the planets, improving gear alignment under all conditions. This new configuration improves the load distribution and increases the drivetrain’s overall reliability. In addition, the single-stage gearbox connects to a medium-speed generator that uses a fraction of the rare-earth magnets typically used in direct-drive permanent-magnet generators of similar power.

Historically, wind plants have been subjected to less stringent utility interconnection requirements than fossil-fuel plants. However, because of the success and substantial growth of wind energy in recent years, wind plant interconnection requirements are now the same as fossil-fuel plants. As a result, these requirements drive the design of new power converters. The new power converter design incorporates advanced software algorithms that are grid-friendly, compliant with emerging requirements, and support the continued growth of wind power as a large contributor to power generation. The team will also be developing and testing medium-voltage, wide-band gap, silicon-carbide power modules. These state-of-the-art power modules are expected to significantly reduce the losses within the power converter, leading to increased efficiency, energy capture, and revenue.

In phase two, a test article that incorporates these advancements will be designed and fabricated. The drivetrain elements will be tested in the 2.5-MW dynamometer and newly commissioned controllable grid interface at the NWTC, and the silicon-carbide power modules will be tested on a specialized, medium-voltage test rig. Upon the successful completion of testing, technology readiness levels will be advanced. A commercialization plan will be developed to guide global deployments of the new drivetrain technologies. The designs will further reduce the cost of wind energy and ensure that U.S. companies are at the forefront of technical innovation within the global wind energy industry.