Comparative study of dual-rotor permanent magnet machines with series and parallel magnetic circuits

This paper compares the electromagnetic performances of radial-flux, dual-rotor, permanent magnet (DRPM) machines with series (S) and parallel (P) magnetic circuits for two rotors, i.e., SDRPM and PDRPM, accounting for different slot/pole number combinations, stator winding configurations, and machine sizes. The machines are optimized using the finite element analysis (FEA) based on the genetic algorithm. It shows that the PDRPM machine with the tooth coil (TC) configuration has the highest permanent magnet (PM) utilisation compared to the PDRPM with toroidal winding (TW) configuration and the SDRPM machine with the TC configuration under different slot/pole number combinations. The scaling effects of the machine size on the torque have been investigated. The TW-PDRPM machine is suitable for large-radius and short-axial length applications due to the short end-winding length of the TW configuration, while the TC-PDRPM is better for small-radius and long-axial length applications. The TC-SDRPM performs well when both the machine outer radius and axial length increase. Finally, the TC-SDRPM and TW-PDRPM machines are prototyped and validated experimentally.