Electric motors and generators, or more generally electric machines, are a fundamental building block of modern society. Electric machines convert electricity to motion (motor), or motion to electricity (generator). As of 2015, over 99% of all the electricity on the planet originates from an electric generator regardless of how it is spun (wind, coal, nuclear, etc.) and roughly 45% of that energy goes on to power electric motors in some application. In industry, motors account for two thirds of electricity usage. As electric energy consumption steadily increases annually, these ubiquitous workhorses continue to be mass-produced for performing the pumping, heating, cooling, drilling, pressing, cutting, grinding, and moving that occurs every minute of every day. Our group focuses on innovating to make electric machines more sustainable and higher performance, thus enabling emerging technologies in transportation, renewable energy, climate control and industrial automation.
Is it possible to build an electric machine that does not require copper windings, steel, or magnetic material? Could plastic, aluminum, or ceramics be used? The answer is yes. Electrostatic machines use coulomb forces that result from electric fields acting on charge to make torque, rather than magnetic fields acting on electric currents. Although dating as far back as Benjamin Franklin (~1750), Electrostatic machines are not commonly used today due to their low volumetric torque density compared to conventional magnetism-based electric machines. To produce more torque and transition to a competitive position, an electrostatic machine must possess a large rotor-stator surface area immersed in a dielectric medium to store electric charge under high potential. Our group uses dielectric liquids, 3D printed structures with high surface area, and medium voltage power electronics to develop high torque electrostatic machines for low speed direct drive applications. The voltage driven nature of an electrostatic machine allows the conduction or joule heating loss to be much lower than a magnetic machine. Additionally, electrostatic machines use little to no energy under stall conditions unlike their magnetic counterparts whose windings continuously heat up at zero speed.
Wound Field Synchronous Machines
Electric machines based on magnetic forces typically require three elements: 1) conductors to carry electric current (e.g. copper windings), 2) a magnetic field source (permanent magnets or electromagnets) and 3) a means to direct/channel the flux of the field source and support the windings (e.g. steel laminations). While there are many variations on this recipe, machines using rare-earthpermanent magnets (PMs) are especially popular for their high efficiency and power density. However, the rare earth materials can be relatively expensive and their extraction and refinement have serious environmental challenges. Our group is revisiting the PM machine’s predecessor that uses electromagnets, called the wound field synchronous machine (WFSM). With modern materials, optimization, and wireless power transfer to the rotor, WFSMs hold promise can rival their PM counterparts, but without the rare earth materials. The machine photos here are of a ~100 Hp WFSM prototype intended for electric vehicles.