Document Type : Original Research Paper

Authors

• Pouria Nadri ¹
• Behrooz Rezaeealam ¹
• Morteza Mikhak-Beyranvand ²

¹ Department of Electrical Engineering, Lorestan University, Lorestan, Khorramabad, Iran.

² Department of Electrical Engineering, Faculty of Electrical and Computer Engineering, Technical and Vocational University (TVU), Tehran, Iran.

Abstract

Background and Objectives: Dual-rotor synchronous motors with counter-rotation are of significant interest for electric machine design due to their high performance and specific applications. In this study, a new Counter-Rotating Dual-Rotor Synchronous Motor (CRDRSM) is presented, with the permanent magnet (PM) rotor as the outer rotor and the reluctance rotor as the inner rotor.
Methods: To identify the optimal structure, the effects of distributed and fractional-pitch windings are first compared. Then, various PM and reluctance rotor topologies are examined in order to select the optimal combination. Despite high output torque, cogging torque significantly affects motor performance; therefore, reducing cogging torque is the main concern of this research. Dimensional optimization is conducted using the Taguchi method to minimize cogging torque in the PM rotor. Four key design parameters, including the PM arc, PM thickness, stator opening slot, and stator tooth width, are selected as optimization variables, while other parameters are kept constant. The minimum and maximum ranges of these variables are determined using parametric scanning and ANSYS Maxwell finite element software. Briefly, the optimization process proceeds in three stages: (1) winding configuration comparison, (2) selection of optimal inner and outer rotor structures, and (3) dimensional optimization using the Taguchi method.
Results: Analysis of the results demonstrates that the cogging torque of the proposed motor is reduced by up to 62.36%, the output power and efficiency are increased, and the voltage THD is also reduced. Other performance characteristics, including output torque and electromagnetic stability, are improved compared to the initial design or remain at a desirable level.
Conclusion: Finite Element Analysis (FEA) demonstrated that the distributed winding configuration delivers the best performance among all tested options. Model C, featuring a hyperbolic-line reluctance inner rotor combined with a surface-mounted PM outer rotor, was identified as the best configuration. This model offers an excellent balance of high torque, low torque ripple, minimized back-EMF harmonics, and satisfactory efficiency, making it highly suitable for submarine propulsion systems. To further reduce cogging torque (one of the primary sources of torque ripple and acoustic noise), the motor geometry was optimized using the Taguchi method and FEA. Overall, the electromagnetic performance of the proposed CRDRSM was validated in terms of flux density distribution, output torque, and cogging torque.

Keywords

• Counter-Rotating Dual-Rotor Synchronous Motor
• Cogging Torque
• Taguchi Method
• Finite Element Analysis (FEA)
• Torque Ripple

Main Subjects

• Electrical Machines

Open Access

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Publisher

Shahid Rajaee Teacher Training University