Analysis and Optimization of Unbalanced Electromagnetic Force on the Rotor of Dual-Parallel Rotor Permanent Magnet Direct-Driven Motor

Most parallel synchronous drive equipment, such as the two-roll mill and twin-screw pump, are driven by an induction motor with synchronous mechanical gear. Such drive systems have large volumes, poor synchronization of master and slave shafts, requiring regular maintenance. A dual-parallel rotor permanent magnet direct-driven motor has gradually come into view. Due to the distance limitation between rotating shafts, part of the stator core and windings are cut off in the design of a dual-parallel rotor permanent magnet direct-driven motor, resulting in unbalanced rotor electromagnetic force. Therefore, this paper analyzes the inductance parameter asymmetry of the motor windings. Inductance parameters of the motor with windings pitch of 4 and 3 are calculated. On this basis, a mathematical model for the total electromagnetic force on the rotor is constructed, and the influence of each component force on the rotor’s total electromagnetic force is studied. Five optimization methods are proposed to optimize the electromagnetic force on the rotor: optimizing the duty angle, optimizing the coupling distance, adopting the asymmetric stator end structure, adopting the eccentric rotor structure, and eliminating part of the unit motors. Finally, the optimization effects of different methods on torque ripple are discussed. The advantages and disadvantages of different optimization methods are summarized, laying a foundation for studying dual-parallel rotor permanent magnet direct-driven motors. The following conclusions can be drawn: (1) The long-pitch coil of the modular structure may cause asymmetric three-phase inductance parameters. Three-phase inductance can be effectively balanced by reasonably selecting the winding pitch and the head end of the A-phase winding. (2) The electromagnetic force Ftotal on the rotor includes the electromagnetic force F1 between the stator with windings and the corresponding rotor, the magnetic force Fmag between two permanent magnet rotors in the coupling area, the force Fend between the core end and the rotor outside the duty area in the coupling area, and the magnetic resistance force Fend,cog of the rotor against the core end in the coupling area and additional electromagnetic force Fad. The X direction force of Ftotal is related to the above forces, while the Y direction force of Ftotal is only relevant to F1. F1, Fmag, and Fend are the most important components of Ftotal. (3) According to the analysis of the Ftotal, five methods are proposed to weaken the Ftotal. The influence of the five optimization methods on the electromagnetic force is given, and the advantages and disadvantages of the five optimization methods are discussed. The method with a rotor eccentric structure has the best optimization effect but requires higher processing technology. The method of eliminating partial unit motors is the most practical. (4) The motor can output rated electromagnetic torque using five optimization methods. In practical application, the combination of various optimization methods can be considered. © 2024 China Machine Press. All rights reserved.