WARF: P00312US

Adjustable Speed Drive For Single-Phase Induction Motors


Thomas Lipo, Miroslav Chomat

The Wisconsin Alumni Research Foundation (WARF) is seeking commercial partners interested in developing a simple and inexpensive adjustable speed drive for use with single-phase induction motors.
OVERVIEWWidely used in applications such as HVAC, fans, pumps and home appliances, single-phase induction motors are manufactured in large volume and at low cost. These motors operate at a constant speed determined by the AC power line frequency and the load imposed on the motor; however, for many applications (e.g. fan motor drives), a single-phase induction motor that could operate at variable speeds would be advantageous.

Although simply reducing the AC voltage to the motor can easily and inexpensively decrease its operating speed, this approach lowers energy efficiency and generally does not allow close motor control. Another approach involves using a power conversion system to change motor speed; however, such power converters are expensive, especially when compared to the low cost of the motor itself.
THE INVENTIONUW-Madison researchers have developed a simple and inexpensive adjustable speed drive for use with low-cost, single-phase induction motors. The drive can operate in full-speed mode with high starting torque, and in at least one lower-speed mode suitable for applications such as fan motor drives.
  • HVAC
  • Fans
  • Pumps
  • Home appliances
  • Drive is simple and inexpensive
  • Allows motor operation at multiple, discrete speeds or in a continuously variable speed mode
  • Supplies power to the motor at higher efficiencies than can be obtained with conventional low-cost drives
  • Drive can be retrofitted to existing motors
For More Information About the Inventors
Contact Information
For current licensing status, please contact Emily Bauer at or 608-960-9842.
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Since its founding in 1925 as the patenting and licensing organization for the University of Wisconsin-Madison, WARF has been working with business and industry to transform university research into products that benefit society. WARF intellectual property managers and licensing staff members are leaders in the field of university-based technology transfer. They are familiar with the intricacies of patenting, have worked with researchers in relevant disciplines, understand industries and markets, and have negotiated innovative licensing strategies to meet the individual needs of business clients.