Integrated Torque Ripple Analysis Method for Multi-Phase Motors

Multi-phase motors are widely used in large scale traction and propulsion applications because of their high torque generation capability, reliability, efficiency, power density, and reduced maintenance requirements. Torque ripple is a crucial factor in the performance and operation of these multi-phase motors because it determines the magnitude of the machine's vibration and acoustic noise, two important performance parameters. Torque ripple analysis is generally performed simply by examining the motor input currents from an inverter in a circuit simulator such as PSIM or MATLAB Simulink. This paper presents a torque ripple analysis method that combines inverter circuit simulation with FEA (Finite Element Analysis) motor modeling to perform an integrated transient study of the entire system. Output currents from a system of 12 full-bridge single-phase inverters are used as the source for a 12-phase SPMSM (Surface Permanent Magnet Synchronous Motor), modeled independently in an FEA software tool. The inverter circuit simulation uses a motor load model that accounts for armature reaction and contains a multi-phase inductance matrix for improved accuracy. Experimentally obtained inverter output currents are also presented for comparison with the simulated current results to verify the validity and accuracy of the proposed analysis method.