Design And Analysis Of Phase Winding Module Permanent Magnet Fault Tolerant Machine With Low Torque Ripple

The strategy of multi electrification and full electrification can significantly improve the energy utilization efficiency and performance of aircraft,achieving low energy consumption,low cost,and high efficiency operation of multi electric aircraft.It is an inevitable choice to promote the green and high-end development of the future aerospace industry.Because of its simple structure,high efficiency and high power density,the permanent magnet fault tolerant machine is particularly suitable for the propulsion system of electric aircraft.Its strong fault tolerance capability is the key to ensure the airworthiness safety of electric aircraft.However,conventional permanent magnet fault-tolerant machines have drawbacks such as high subharmonic content and large torque ripple,which seriously affect the operational quality of the machine.This paper proposes a phase winding module permanent magnet fault-tolerant machine.This machine not only overcomes the high subharmonic content of single-layer fractional slot concentrated winding,but also has better fault-tolerant performance than double-layer fractional slot concentrated winding.In addition,this structure also combines tooth shoes shift to achieve a balance between high fault tolerant performance and low torque ripple.The main contents of this paper include the following aspects:(1)Based on the power size equation and the performance law of slot-pole combination,determine the electromagnetic parameters of conventional permanent magnet machine.A strong fault-tolerant phase module winding structure is proposed by analyzing the magnetomotive force characteristics in single and double layer windings,besides,its design principle and optimization ideas are elaborated.According to the differences in stator topology and winding configuration between the two structures,the winding factors and winding functions of the two structures are derived.In addition,slot pole combinations suitable for the phase winding module structure have been expanded.(2)The inductance expressions of the conventional and phase winding module structure are analytically deduced according to the winding function theory,and then the calculation formulas of phase to phase coupling coefficient and short-circuit current are derived.Finite element models have been established for simulation verification,it has been found that the phase winding module structure is beneficial for improving self-inductance,suppressing short-circuit current and reducing phase to phase coupling.However,this structure has the disadvantage of high torque ripple.(3)The suppression of torque ripple in the phase winding module is achieved through reducing the amplitude of cogging torque.The generation mechanism of cogging torque is stated,and the representation of the cogging torque after tooth shoes shift is deduced according to the superposition principle,so as to the optimal shift angle is determined.On the basis of generation mechanism of cogging torque under different stator modules,two schemes are proposed: unit group tooth shoes shift and module tooth shoes shift.The module tooth shoes shift is determined as the optimal scheme by comparing the suppression of torque ripple between two schemes.(4)The prototypes of a conventional 18 slot 16 pole permanent magnet synchronous machine and the module tooth shoes shift structure are manufactured.Based on the experimental platform,the no-load back electromotive force,inductance,short circuit current,and torque of the two structures are tested.The correctness and rationality of the theoretical analysis are verified by comparing the finite element simulation and experimental data.