An overall six‐sigma process (SSP) that includes a novel process capability control (PCC) procedure is presented for satisfying a six‐sigma level for a Z‐value as well as a mean value of target performance. An example of this process is present for the efficiency and torque ripple in a spoke‐type permanent magnet motor considering the manufacturing tolerances of five rotor dimensions. In this context, six‐sigma means that the probability of failure of the product or system is 0.00034%. A novel SSP with a PCC procedure is suggested for designing electrical machines. In this procedure, three possible PCC methods were determined based on the definition of the Z‐value. Next, each method was carried out to achieve the target Z‐value and to illustrate the advantages and possible issues associated with each method. Finally, the authors showed that the suggested PCC procedure effectively achieves the target Z‐value of the motor and can be widely used for the design of electrical machines.

This study investigates the characteristics of a spoke-type permanent magnet (PM) motor with one of three magnet shapes, rectangular magnet (RM), trapezoidal magnet (TM), or inverted TM (ITM) in order to compare motor performance for the same magnet volume. The three magnet shapes vary in terms of upper thickness, lower thickness, and width of the magnet. Two-dimensional (2D) finite element method is performed to analyse torque, inductance, core loss, efficiency, and demagnetisation reliability. Advantages and disadvantages of each magnet shape are presented based on the analysis results. The ITM motor shows higher efficiency at its rated load due to the reduced core loss resulting from the decreased armature reaction field coupled with the increased magnetic reluctance circuit of the rotor near the airgap. However, the ITM motor shows lower maximum torque due to the reduced reluctance torque and demagnetisation reliability with a heavy over-current. ITM is thus suitable for applications that require low core loss with small starting torque, e.g. fans, TM is helpful for increasing maximum torque, and RM is appropriate for lowcost applications that require high demagnetisation reliability. Therefore, magnet shape should be carefully considered based on the required specifications of the motor application.

This paper presents a robust optimal design method using a hybrid response surface method (H-RSM) which directly finds an optimal point satisfying a target Z-value or a probability of failure. Through three steps, this paper achieves the goal that is to increase the open-circuit airgap flux (OCAF) in a surface-mounted permanent magnet motor and decrease its variation caused by variations of the airgap lengths including an additional one between permanent magnets and rotor back yoke. First, the OCAF equation is derived from the magnetic equivalent circuit (MEC) considering the additional airgap. Then, the equation is validated by comparing its results with those of the finite element method (FEM) modeled by the slotless stator. Next, the tolerance sensitivity analysis, using the partial derivative of the OCAF equation with respect to the airgap length, is performed to investigate the effects of design variables on the OCAF. It is shown that increasing the magnet thickness is effective for both increasing mean of the OCAF and reducing its variation. Finally, robust optimal design is performed using the H-RSM, in which all data are obtained from the FEM modeled by the slotted stator. The results of the robust optimal design are verified using the FEM.

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This paper proposes a rotating electronic billboard (REB) to save the cost of space required for its installation and a modular linear induction machine (M-LIM) to rotate the proposed REB. REBs are generally installed in public places such as subways and airports to display the advertisements. The proposed REB can be installed around a pillar since it is hollow inside, hence, no additional space is required which limits the cost of the space required for REBs. The proposed M-LIM for rotating the proposed REB has a short straight primary and a ring-shaped secondary. The secondary is installed on top of the light emitting diode (LED) display bars such that when secondary rotates, LED bars rotate along with it. To confirm the suitability of the M-LIM in proposed REB, an M-LIM is designed, and the initial results are examined using three-dimensional finite element analysis (3-D FEA) to consider the 3-D effects in the proposed design. A prototype of the proposed M-LIM along with the proposed REB is manufactured and their collective performance is evaluated experimentally. The results show good agreement with the simulation.

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The study compares the sensitivities of open-circuit airgap flux (OCAF) between a surfacemounted permanent magnet (SPM) machine and a spoke-type PM machine based on variations in airgap length including additional airgaps between permanent magnets and rotor core and between segmented stator cores to achieve high quality electric machines. Analytical equations deduced from magnetic equivalent circuits (MECs) are used to directly compare natural-born characteristics of the OCAF of the two machines. First, the MEC of each machine is modeled by considering two additional airgaps between the PMs and rotor core and between the segmented stator cores. Second, the OCAF equation of each machine is derived from the MEC to analyze the effects of the design variables on the OCAF. Subsequently, the partial derivative equation of the OCAF equation with respect to the airgap length is obtained for sensitivity analysis. A comparison of the equations of the two machines indicates that the spoke-type PM machine exhibits inherently higher sensitivity and average value of the OCAF when compared to that of the SPM machine. Finally, the results are validated via a two-dimensional finite element method (FEM) by considering the variations in airgap lengths.