Design Of Wound-Rotor Brushless Doubly-Fed Machine And Research On Its Torque Ripple Suppression

There are two fundamental magnetic fields with different pole pairs in wound-rotor Brushless Doubly-Fed Machine(BDFM).Compared with traditional motor,the causes of torque ripple are more complex.Wound-rotor BDFMs are mainly used in constant voltage speed adjustment with variable frequency and variable speed constant frequency power generation.The torque and speed change frequently.When designing the BDFM,it is very necessary to suppress the torque ripple.In this dissertation,the sources of torque ripple of wound-rotor BDFM are analyzed,and the corresponding measures are selected to reduce the torque ripple in the motor design.According to the characteristics of tooth standing wave magnetic field of the BDFM,in order to reduce the unbalanced magnetic pull and torque ripple,the condition of pole number combination is studied.The finite element models of motors with different pole pairs are established,the simulation results of radial and tangential air gap flux density and electromagnetic force of motors with different pole pairs are compared and analyzed,the electromagnetic torque and torque ripple of motors with different pole pairs are studied,and the condition of pole number combination with smaller torque ripple is given.According to the characteristics of flexible winding arrangement of stator and rotor in wound-rotor BDFM,the winding arrangements of stator and rotor in BDFM are studied based on the purpose of reducing the spatial harmonic of magnetic field and the torque ripple.According to the engineering practice of the flexible winding arrangements in 45 k W series small power motor,the rotor winding adopt the unequal-turn double-sinusoidal design method.By adjusting the turn-numbers of the winding coil in each slot,the fundamental winding coefficient and the content of the fundamental magnetomotive force are improved,the harmonic content is reduced,and the torque ripple is restrained.According to the engineering practice of high-power high-voltage forming winding motor,an equal-turn double-span rotor winding design method is proposed.Taking 450 KW high-power motor as an example,the design example is given.The equal-turn double-span method relies on the span adjustment of auxiliary winding to enhance the fundamental magnetomotive force of rotor winding,reduce spatial harmonic and suppress the torque ripple.Compared with unequal-turn winding,the equal-turn double-span method reduces the types of coil turns,the difficulties of manufacturing and installation of rotor winding are reduced.The slot size design of stator and rotor and opening of auxiliary slot in stator and rotor teeth are introduced into the optimization of the cogging structure of the BDFM.The finite element models of several schemes are established for comparative analysis,and the final optimization scheme is selected.The optimization scheme improves the slot size of the stator and rotor,and selects the scheme of opening the auxiliary slot of the rotor,which increases the absolute value of the electromagnetic torque,suppresses the torque ripple of the motor and improves the generation voltage waveform.