Optimization of Airgap Profile in Electric Machines for Torque Pulsation Mitigation
Electric machines are essential in daily life for industrial applications, transportation, medical equipment, and office/home appliances. Performance of electric machines directly influences the quality of product experience. Torque pulsation is one of the most important design considerations in electric machine design, since it can cause unwanted byproducts such as vibrations and acoustic noise, which poses a significant shortcoming in vibration and noise sensitive applications (i.e. office/home appliances, automotive). There are mainly two categories of torque pulsation mitigation techniques studied by scholars, namely control technique and optimal design technique. However, a thorough investigation and a practical method of torque pulsation mitigation without punishing other machine performances is of high importance. In this dissertation, a 3-phase interior permanent magnet synchronous motor (IPMSM) and a 4-phase 8/6 switched reluctance motor (SRM) have been studied for torque pulsation mitigation by focusing on optimizing airgap profile. The main purpose of airgap optimization is to redistribute the flux density and force components on the rotor surface to obtain a smoother force profile while maintaining/slightly increasing the average torque. A grid on/off search method is proposed for optimizing the shape of rotor such that an optimal design is selected by searching the best combination of different materials. Genetic algorithm (GA) is applied to assist this method in order to reduce the simulation time. Finite element method (FEM) in ANSYS Maxwell is coupled with Matlab to automate the process. Optimal designs are obtained for both motors and proved to be superior by finite element analysis (FEA) simulation results and experimental results in reducing torque pulsation while maintaining/increasing the average torque. Complete structural analysis has been done to verify the feasibility of the optimal designs. Simulation results indicate that not only torque pulsation is reduced while maintaining average torque, but other machine performances such as vibration has also been improved. Prototype manufacturing cost by proposed technique remains the same as producing the original design.