Research On Torque Ripple Suppression For Permanent Magnet Synchronous Servo Machine

Fractional-slot permanent magnet synchronous motors (PMSMs) for servo drive are selected as the objects for this study. The generating mechanism of the torque ripple is thoroughly investigated, and some novel and practical technologies are presented. This paper focuses on design optimization, manufacturing process, experimental testing of the machine, and so forth. Many aspects have gained innovation and improvement. The main work of this paper includes the following aspects:Firstly, the background and significance of the research are expounded, and the basic structures of PM servo motors are introduced. We systematically summarize the methods for minimizing cogging torque and suppressing torque ripple, and analyze their application characteristics and existing problems. The manufacturing errors of segmented-stator PM motors are thoroughly analyze. This paper fully summarizes design of experiments (DOEs) and robust design, and analyzes their application actuality and characteristics, along with existing problems in the motor design.Secondly, three sources for torque ripple of PM motor are deeply studied, including the cogging torque, field harmonic torque and reluctance harmonic torque. The generation mechanisms are respectively analyzed. The analytical expression of the cogging torque is derived based on energy method. The expressions of electromagnetic torque and reluctance torque are also derived. Offset-elimination method is systematically analyzed to achieve cogging torque minimization, which includes the coefficient of offset elimination and direct torque of offset elimination. The constraints to offset elimination are determined. We study on application of offset-elimination method to reduce the instantaneous torque harmonic.Thirdly, we focus on the influence of design parameters on cogging torque, summarize the characteristics of design parameters and determine their primary and secondary orders. A complete design flow based on an integrated parameter is established. Two asymmetrical V rotor structures are presented to reduce cogging torque. Design principle is expounded and design reasonableness is verified with finite element method. The rotor structure is optimized based on the Taguchi design method, and main performance are compared and analyzed. The influence of the different rotation directions on the torque is finally evaluated. The prototypes are manufactured for test.Fourthly, we study on the offset-elimination method to suppress the torque ripple of the interior PM motors. The axial two-stepped rotor structure composed of one lamination is adopted to suppress torque ripple. Three practical rotor structures are presented, which include the asymmetric "I" type, "V" type and "spoke" type. The optimal parameters of each analysis model are determined with optimization. Finite element method is used to verify the reasonableness of the analysis model. Main performance are compared with those of the stepped skewing models. Three engineering prototype are developed, and design method is fully validated. On the basis of the axial two-stepped rotor structure, an integral asymmetric rotor structures are presented this the paper, involving quarter-circular 2-pole alternating structure and semi-circular 4 pole alternating structure. The realization of rotor structure is analyzed, and the reasonableness of the offset-elimination method is validated from the two aspects of the air gap flux density and cogging torque. Finite element method is utilized to predict main torque characteristics of the motor, and the feasibility of design method is verified.Fifthly, the influence of manufacturing errors on the segmented-stator PM motors are fully studied, involving seven kinds of manufacturing errors, which are roundness error of stator inner surface, nouniform stator slot opening, stator axial bending, additional gap of the jointed section of the segmented stator, magnet offset, rotor eccentricity and magnetic conductivity variation of core edge. We analyze their causes and establish a unified finite element model based on the actual domestic manufacturing level. The cogging torque and instantaneous torque of each error model are predicted with finite element method, and the primary and secondary orders of manufacturing errors are determined. Two kinds of the assembly toolings are designed to improve the effect of manufacturing error on the cogging torque. The effect of process improvement is verified by experiment.Finally, robustness design considering the influence of manufacturing errors is deeply studied. Variance analysis is added to Taguchi robust design for a unified evaluation system. Uniform design (UD) and response surface method (RSM) are combined to achieve the dual-response-surface-model robust design. A comprehensive robustness experiment design process is established based on the characteristics of these two robust design methods,.