Sinusoidal vs. Unipolar Current Supply of Rolling Rotor Electrical Machine

Electrical machines with a reluctance torque generation principle have a relatively simple design, low cost, and high reliability. However, they have the disadvantage of relatively low torque density. To increase the torque density, a rolling rotor topology of a reluctance machine can be used. This topology is a combination of an electrical machine and a planetary mechanism, with the rotor being eccentrically positioned. Due to this arrangement, specific requirements are placed on the winding topology and the supply current. This paper compares sinusoidal and unipolar current supplies in rolling rotor electrical machine. A brief description of the machine's topology and operational principle is provided. The comparison is based on average output torque. To ensure that the parameters of the magnetic system are fitted for each type of excitation waveform, a multidimensional optimization study has been conducted. The results indicate that unipolar current supply provides 15 % higher torque, but with almost four times more torque ripple. The modelling also showed, that overlapping of unipolar current pulses should not be used since it reduces the average torque and increases torque pulsation