Combined Optimal Torque and Modal Current Control for Low Inductance PM Motor

Abstract

Innovative extreme lightweight electric motor designs exploiting the advantages of air-gap windings depend on a B-field with higher harmonics and have only very small phase inductances in the range of several $\\mu \\mathbf{H}$. Besides the advantages of a very small electrical time constant and the opportunity of very fast current control, the demands on sampling time and PWM switching frequency are very high, which leads to increased losses and higher hardware cost. This paper proposes an optimal torque control method reducing motor losses combined with a very robust and computation efficient modal current control. Compared to well-known DQ control methods, proposed strategy reduces motor losses significantly and offers a very fast implementation on a standard microcontroller. The accuracy of the control method was tested experimentally on a wheel-hub motor built with a slotless air-gap winding and low inductance using a standard microcontroller and GaN Power Devices. The proposed method was validated by comparison of simulation and experimental results on one hand and by comparison to conventional DQ control on the other.