Combined Permanent Magnet and Field Winding Result in Smaller, More Efficient Generators

July 05, 2019 by Scott McMahan

Researchers at Purdue University have devised a method of reducing the size and increasing the efficiency of the moderate- to low-power electric generators used in applications as diverse as automotive, microgrids, and aircraft. The researchers developed a parallel inner-magnet device which accomplishes both.

The system uses a unique combination of a permanent magnet and a field winding. This field winding is comprised of a group of insulated, current-carrying coils. A wound rotor synchronous machine incorporates a field winding on the rotor used to produce a rotating magnetic field and regulate the output voltage.

Losses are associated with this winding, which produces heat that has to be eliminated from the spinning rotor. Permanent magnets can also be utilized to generate the magnetic field with considerably less loss and heat generation, but this strategy does not aid in the regulation of output voltage.

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"The Purdue parallel inner-magnet device is a hybrid solution that creates some of the field with a permanent magnet and some of the field with a field winding," said Scott Sudhoff, the Michael and Katherine Birck Professor of Electrical and Computer Engineering in Purdue's College of Engineering, whose research focuses on power electronics and electromechanical devices. "This allows for regulation, but with lower losses than a conventional machine."

Omar Laldin, a former Ph.D. student of Sudhoff, lead the Purdue team that created the inner-magnet device. Sudhoff noted that the device could be used in a variety of ac and dc (with a rectifier) generator applications. Primary issues with the system include finding the best machine architecture in terms of merging the two field sources, electromagnetic damping, and fault performance.

The team employed finite element analysis based testing to validate the design code. The group worked with the Purdue Research Foundation Office of Technology Commercialization to patent the technology, and they are seeking commercialization partners. Sudhoff also worked with the same office on other technologies.