Characterization of a novel counter-rotating twin harmonic PM machine

Most machine topologies have two-ports, with one set of electrical connections and one mechanical shaft. Three-port machines having two rotors and mechanical shafts are able to drive two mechanical loads using one stator winding, fed by one power converter. In addition, it is possible to get the mechanical shafts to counter-rotate, which is promising for applications such as marine propulsion and hydraulic pumps. In this paper, a three-port radial flux permanent magnet machine is presented. A 2kW technology demonstrator based on this design is built, and its characteristics are presented, including the back-emf voltage waveforms. The phase sequence of the back-emf of each rotor shows that counter-rotation is possible using one stator winding. Next to that, a no-load motor test confirmed that when feeding a sinusoidal voltage to one stator winding, it is possible to have two mechanically counter-rotating rotors.