Losses such as rotor iron and stator iron losses, magnet eddy current loss, as well as efficiency of a double stator permanent magnet machine having varying rotor pole numbers is estimated and presented in this study. This current investigation would be vital for electrical machine designers in quantifying the amount of losses in the various sections of a given double stator electric machine and as well provide better insight on resulting output efficiency of the machine. Time-stepping finite element analysis (TS-FEA) procedure is adopted in the calculations using ANSYS-MAXWELL simulation software. The compared machines having the same stator teeth/pole number (Ps) and different rotor pole (Pr) numbers are designated as: 6Ps/10Pr, 6Ps/11Pr, 6Ps/13Pr and 6Ps/14Pr. The predicted total loss values at rated current and operating base speed is 13.02 Watts, 13.13 Watts, 13.539 Watts, 13.537 Watts, from the 6Ps/10Pr, 6Ps/11Pr, 6Ps/13Pr and 6Ps/14Pr machine types, respectively. The corresponding efficiency of the machine types at rated working conditions is: 81.76%, 88.17%, 86.95% and 78.61%, respectively. The results show that magnitude of losses in a given machine would largely depend upon factors such as number of rotor poles and hence, the machine’s operating speed, electric loading and angular rotor position of the machine, etc. It is also found that the number of loss waveform cycles (Nc) in an electric revolution of the investigated machine would depend upon its stator and rotor arrangements. The most performing compared machine types are the ones that have 11- and 13-rotor pole numbers, while the least amount of efficiency is obtained from the machine type that has 14-rotor pole number. Above all, the 6Ps/10Pr and 6Ps/14Pr are characterized with high amount of pulsations or ripples and this is detrimental to the overall performance of the machines.

The impact of structural dimensions and rotor pole numbers on the load and no-load torques of dual stator permanent magnet machine is investigated and presented in this work. Finite element analysis (FEA) is adopted in the prediction, since it exhibits higher computation accuracy compared to other methods such as analytical modelling and techniques, etc. Version 15.0 of MAXWELL/ANSYS-2D software is implemented in the entire computations. The considered structural dimensions include: rotor centrifugal size (Rth), aspect ratio (Sr), permanent magnet width (Mth), outer stator tooth width (Tth), rotor outer pole arc/pitch ratio (ϒ1) and rotor inner pole arc/pitch ratio (ϒ2). Also, model topologies having stator pole (S) and rotor pole (P) numbers i.e. 6S/10P, 6S/11P, 6S/13P and 6S/14P, are compared. The results show that the shaft torque and no-load torque would reasonably depend on the adopted machine’s structural dimensions; in addition to the impact of rotor pole number. More so, it is observed that the optimal output torque of a given machine may not necessarily occur at the same operating structural point with that of the required least no-load torque. Implementation of the optimum structural dimensions would result to largest average output electromagnetic torque from the machine. Moreover, practically all the most optimum results are obtained from the 6S/11P machine type. The useable average shaft torque from the simulated models is approximately: 2.33 Nm, 4.16 Nm, 3.75 Nm and 2.31 Nm, for the 6S/10P, 6S/11P, 6S/13P and 6S/14P categories, respectively. Similarly, least values of the no-load torque in the compared machine types are 1.2 Nm, 0.08 Nm, 0.04 Nm and 0.68 Nm i.e. for the 6S/10P, 6S/11P, 6S/13P and 6S/14P machine topologies.