Low Wind Speed Technology Phase II: Investigation of the Application of Medium-Voltage Variable-Speed 

Drive Technology to Improve the Cost of Energy from Low Wind Speed Turbines

Behnke, Erdman and Whitaker Engineering, Inc.

Project Description: As wind turbines grow in size, variable-speed operation becomes 

an absolute necessity to manage machine loads in turbulent wind conditions and to 

provide increased rotor efficiency in lower wind speed operations. Until now, wind 

turbines have been able to take advantage of readily available, low-cost low-voltage 

power converters and components. But economies of scale for low-voltage equipment 

begin to evaporate with the increased amperages of multimegawatt machines. It is 

clear that, at some point in the evolution of wind turbine technology, low-voltage 

components will be poorly suited for power distribution within the turbine. The new 

larger machines will depend more on full power handling through power electronics 

interface to control output frequency to the electrical grid. This study investigates the 

feasibility of applying medium-voltage variable-speed drive technology to low wind 

speed turbines with multi-megawatt ratings. The primary objective of this effort is to 

obtain a lower cost of energy from these machines by reducing the barriers to achieving lower capital cost and improved efficiency that simply paralleling additional low 

voltage components (generators, cabling, converters, switchgear, transformers) will 

allow. Areas of investigation include:

• Applications requirements—power and ride through capability

• Commercial availability of components

• Maintenance personnel requirements

• Power electronics topologies

• Existing intellectual property

• Special design and protection requirements.

Preliminary designs of power handling systems and operating costs for conceptual 

designs in the 3-, 5-, and 7.5-MW class will be developed. Based on this data, impact 

on turbine COE due to implementation of medium-voltage devices will be determined.

Total Project Budget: Conceptual Design Study

Total Project Budget: $197,656

Industry Cost Share: $0

DOE Cost Share: $197,656 

Planned Project Duration: July 2004–March 2005

Contacts: 

NREL/Sandia: Behnke, Erdman and Whitaker Engineering, Inc.: 

Alan Laxson, NREL Mike Behnke, BEW

1617 Cole Blvd. 2303 Camino Ramon, #220

Golden, Colorado 80401 San Ramon, California 94583

303-384-6944 925-867-3330

alan_laxson@nrel.gov mike.behnke@bewengineering.com

Current Status: Project Complete

Alternative power converter schematic.

Alternative power converter schematic.

A Strong Portfolio for a Strong America • Energy efficiency and clean, renewable energy will mean a stronger economy, a cleaner environment, and greater energy 

independence for America. Working with a wide array of state, community, industry, and university partners, the U.S. Department of Energy’s Office of Energy Efficiency 

and Renewable Energy invests in a diverse portfolio of energy technologies.

For more information contact EERE Information Center • 1-877-EERE-INF (1-877-337-3463) • www.eere.energy.gov

Produced for the U.S. Department of Energy by the National Renewable Energy Laboratory, a DOE national laboratory

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 10% post consumer waste.

DOE/GO-102006-2208

March 2006