Parameter Estimation and Control of Axial Flux Permanent Magnet Motors for Electric Aircraft: Evaluating Axial Force Implications in Field-Oriented Control Methods

Axial flux permanent magnet (AFPM) motors are emerging as a promising technology for electrifying transportation due to their high specific power, torque, and efficiency. A model of a motor is developed, demonstrating that the inductance matrix of this AFPM motor differs from typical machines primarily due to the fractional slot concentrated winding (FSCW). This article provides a comprehensive parameter estimation of the ASCEND motor utilizing finite element analysis (FEA) for parameter estimation across a wide range of operating conditions and a field-oriented control (FOC) algorithm based on the motor model derived from FEA parameter estimation, utilizing two three-level active neutral point clamped (ANPC) inverters with half-bridge silicon carbide (SiC) modules. A tailored approach to current trajectory, incorporating maximum torque per amp (MTPA) and maximum torque per loss (MTPL) strategies, is developed to optimize torque acquisition and assess the impact of current variations on axial forces imposed on the rotor. The application of the negative d-axis current reduces axial forces by approximately 11% with MTPA and 24% with MTPL at speed of 5000 r/min and peak torque. Implementing the control system with a similar motor topology shows that the model aligns well with experimental results, with speed and torque discrepancies of less than 3%.