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NREL, Collaborators Complete Gearbox of Innovative Drivetrain

January 16, 2015

NREL researchers and industrial collaborators have completed the fabrication of a new gearbox and power converter software as a part of their ongoing project to create an innovative drivetrain. The innovative, medium speed, medium-voltage wind turbine drivetrain design was developed with CREE, DNV KEMA, Romax Technology, and Vattenfall Windpower. This new drivetrain can increase reliability, decrease mass, improve efficiency, and reduce the cost of wind energy. In addition, the design can scale up to ratings as high as 10 megawatts (MW) while maintaining the lowest possible costs.

The NWTC team’s design concept applies a system approach to improve the conventional 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 highspeed gearbox designs have been plagued with reliability issues caused by the large and unpredictable loads imparted on the gears and bearings by the wind acting on the rotor and by utility faults acting through the generator. Therefore, the team’s gearbox design consists of a single planetary stage that uses compliant flex-pins and journal bearings to support the planets, eliminating the lower-reliability, higher-speed stages. This new configuration improves the load distribution and increases the drivetrain’s overall reliability.

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 team’s power converter design incorporates innovative 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 exploring 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 January 2015, the team will assemble the new gearbox and power converter with the WindPACT medium speed generator. The completed drivetrain will be tested in the 2.5-MW dynamometer and with the newly commissioned controllable grid interface at the NWTC. Upon the successful completion of testing, technology readiness levels will be advanced and combined with a commercialization plan that will lead to global deployments of the drivetrain technologies. The team’s 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.

—Kelly Yaker