Research On Torque Performance Of Surface-Mounted Pm Torque Motor With Similar Number Of Poles And Slots

Numerical control (NC) direct drive rotary table solves the elastic distortion, friction, backlash and other problems resulted from previous indirect drive, and can improve the dynamic performance of the system. At the same time, higher requirement is proposed for rotating feed permanent magnet (PM) torque servo motor:one is that the motor must have enough torque output capability to meet the requirements of low-speed heavy cutting and fast response; the other is that the torque ripple must be small, especially still running smoothly at low speed, in order to satisfy the requirements of high machining accuracy and high precision positioning. Thus, the torque performance of the torque servo motor is directly related to the quality of the direct drive system. The researches as follows are performed to enhance the torque performance of surface-mounted PM torque servo motor with similar number of poles and slots in this dissertation.The electromagnetic torque expression based on the whole harmonic magnetic motive force (MMF) of stator and rotor is derived by analytical method. The quantitative relationship between the average torque, ripple torque and all the time and space harmonics of MMFs of stator and rotor is deduced by introducing the concept of virtual motor, in order to provide the theoretical basis for eliminating and weakening the torque ripple of surface-mounted PM torque motor with similar number of poles and slots. The torque performance is simulated and analyzed when the distribution of rotor magnetic field is sinusoidal and non-sinusoidal under sinusoidal current supply. The influences of the slot width size on the ripple torque and single and double layer winding on torque performance are studied.For the limitation of the easy-saturation magnetic circuit of PM torque motor with similar number of poles and slots when overload running, the structure of unequal teeth width and unequal teeth tops width is suitable for the motor with different phase windings wound on alternate teeth through analyzing the magnetic field distribution characteristics of the motor, in order to reduce the flux density of armature tooth and to enhance the torque output capability. The law of the influences of the pole-slot coordination rule and the different matching of teeth tops width and teeth width of the motor with different phase windings wound on alternate teeth on torque output is theoretically analyzed. A prototype of60-slot50-pole surface-mounted PM motor is designed through using the method. Test results and simulation results are consistent.The ripple torque caused by tooth top leakage flux and the cogging torque resulted from unequal teeth width are studied. The single zigzag leakage flux expression of PM motor with similar number of poles and slots is derived by analytical method, and the characteristics of whole zigzag leakage flux is analyzed. Also, the cycle zigzag leakage flux function is decomposed by Fourier series and the back electromotive force (EMF) harmonics of each phase winding are calculated by Faraday’s law to further analyse the ripple torque. Unequal teeth tops width motor modulates the air gap permeance in the different way with equal teeth tops width one. The analytical expression of cogging torque in unequal teeth tops width motor is derived from the simplified model of air gap relative permeance. The method that the cogging torque is reduced by adjusting the assistant teeth tops width is put forward.In order to further improve the torque output capability and to reduce the ripple torque of rotary table motor, the pole and slot number combining rule of dual three-phase unit motor with similar number of poles and slots and the validity of non-sinusoidal supply are studied. In each three-phase winding, the three windings are120°phase shifted with each other, and the two three-phase windings are30°phase shifted one from another. The average torques and ripple torques of96-slot88-pole motor and96-slot80-pole motor in two different situations are simulated and compared by using ANSOFT. One situation is that the motor windings are respectively connected to be three-phase winding and dual three-phase winding under sinusoidal current supply. The other is that the motor windings are connected to be dual three-phase winding under sinusoidal current and non-sinusoidal current supply respectively. The feasibility and validity of the dual three-phase motor under non-sinusoidal supply are verified.A60-slot50-pole PM torque servo motor with unequal teeth width and unequal teeth tops width is designed and manufactured to prove the correctness and effectiveness of the proposed theoretical analysis and method.