Ironless axial flux permanent magnet motor control with multilevel cascaded H-bridge converter for electric vehicle applications

The Ironless Axial Flux Permanent Magnet (IAFPM) machine, also referred to as air-cored or coreless machine is a variant of the AFPM machine with the iron removed from the stator. This allows the efficiency and power density of the machine to be further improved [1]-[4]. However, IAFPM motors generally have very low inductance (< 50µH) due to their ironless nature [5], which increases the design complexity of the drive system as the motor currents becomes difficult to control. If neglected, the large current ripple will produce significant torque ripple. The Multilevel Cascaded H-bridge (MLCHB) converter topology could potentially address this issue. This paper first provides an analysis of the IAFPM motor characteristics and control method, then it provides a review of topologies currently used to control IAFPM motors. Lastly the application of a MLCHB converter for the control of low inductance motors is introduced. Simulation results of an IAFPM motor with 5µH line inductance driven by a MLCHB converter are presented with comparisons made to existing strategies.