Fault-tolerant Design And Optimization Of Automotive Power Steering Motors

With the upgrading of China’s automotive industry structure,the electrification,intelligence and networking of vehicles are gradually deepening,which has also attracted high attention from the automotive steering industry to product reliability and steering safety.As a new type of fault-tolerant motor adapted to steering system,dual winding permanent magnet motor has become a research hotspot in current steering problems.Therefore,this thesis focuses on the design and optimization of the winding layout,stator and permanent magnet structure of a dual-winding permanent magnet fault-tolerant motor in three aspects: strong fault tolerance,low torque ripple,and fault operation ability and the motor fault control strategy is discussed according to the final obtained motor model.Firstly,based on the basic model characteristics and design elements of the double-winding permanent magnet fault-tolerant motor,this thesis introduces the basic working principle of the motor.Through research on design factors such as fault tolerance,number of motor phases,main dimensional structure,pole slot matching,etc,a preliminary design scheme for a double three-phase structure motor with high fault tolerance and low failure rate is established.Considering the difference in coupling effects caused by the spatial arrangement of the two sets of windings in the slot,a simplified mathematical model for dual three-phase windings was established to analyze the motor performance under different arrangement forms.The optimal arrangement method that minimizes the influence between windings is obtained,which provides the basis for the subsequent optimization design of the motor structure parameters.Secondly,due to the requirements of suppressing short-circuit current,reducing torque ripple and having high fault-tolerant capability for the motor studied in this thesis,based on the preliminary design model of the motor,the whole parameters of the stator slot structure and permanent magnet shape of the motor are optimized by the method of finite element simulation and analytical method.The thesis also analyzed the reasons for the impact of changes in the stator slot structure on the motor’s ability to suppress short-circuit currents,as well as the effect of magnetic shaping on the motor’s torque short-circuit currents,as well as the effect of magnetic shaping on the motor’s torque ripple.At the same time,on the basis of the above research results,the limit range of the output capacity of the motor due to the change of the volume of the magnet modification is proposed.Finally,an effective stator slot structure was obtained to improve the short-circuit resistance of the motor,and a magnet modification method was obtained to significantly reduce motor torque fluctuations,providing an effective fault-tolerant optimization design scheme for the steering system.Finally,considering that the motor should work closely with the power electronic control driver to complete the vehicle steering fault tolerance function,this thesis discusses the motor fault-tolerant control strategy for the motor performance problems under the motor winding open circuit and short circuit faults encountered during the operation of the steering system,a fault-tolerant method of using the non-faulty phase to compensate for the faulty phase is proposed to effectively solve the problem that the steering system cannot work normally due to the sharp increase of motor torque fluctuation after the failure of one phase.