Optimal Design Of External Rotor Switched Reluctance Motor For Electric Bicycle

The demand for electric bicycle(E-bike)has greatly increased,owning to its health,friendly environment and low cost.The motor with high performance is key parts that affect the overall performance and cost of e-Bike.The switched reluctance motor(SRM)has low cost,simple structure,good fault tolerance,wide speed range and large starting torque.The SRM with external rotor can directly drive hub which reduce transmission loss,therefore it is very suitable for e-Bike.However,the high magnetic saturation,non-linear flux,and switched power supply result in poor torque performance.The output torque can be increased,and the torque ripple can be reduced by optimizing the structural parameters of the SRM.So,the structure optimization of SRM with external rotor for e-Bike is very important to practical engineering.Firstly,the basic working principle of SRM is introduced in this paper,the output torque characteristics of SRM and the reasons for the generation of torque ripple are analyzed.The finite element simulation is used to further analyze torque,magnetic flux,the distribution of magnetic field lines and magnetic flux density.Secondly,the structure of SRM is optimized.The structure with multiple teeth per pole is used according to the design requirements and initial prototype parameters for e-Bike.The torque performance of each stator pole is analyzed by the equivalent magnetic circuit(EMC)method,and the pole arc angle and the number of rotor pole is also given.In addition,the condintional winding connection methods in SRM are analyzed,and the windings of each phase are connected in series forward and then in parallel in this paper.Then the torque performance and loss are analyzed and calculated by using the finite element(FE)method.The results show that the new improved motor has better torque performance and higher energy density at different excitation currents and different speeds,and the motor loss is also reduced,which is more suitable for e-Bike driven by inwheel motors compared with the conditional motor.Then,the parameters of SRM are optimized.The objective function,variables,and constraints are determined,and the dimensionality is reduced through sensitivity analysis.The sample points are selected by D-optimal design,and the torque and ripple data of the sample points are obtained by FE simulation.A third-order polynomial regression(PR)response surface model is built to obtain the response surface function of the average torque and torque ripple.Moreover,the multi-objective optimization of the motor parameters based on the improved NSGA-II isperformed to achieve the maximum average torque and minimize the torque ripple.A fuzzy set theory is used to obtaind the best compromise solution upon the Pareto-optimal set of nondominated solution.The FE simulation is used to analyze SRM models before and after optimization.The results show that the output torque characteristics in the optimized SRM are improved to a certain extent,and the average torque output is increased while suppressing the torque ripple as much as possible.Finally,the segmented PWM current chopping control is used for the speed control of the SRM in the low speed section,the PWM control signal adjustment module is designed,and the SRM model is simulated through Simulink.