Reduction of Unbalanced Axial Magnetic Force in Postfault Operation of a Novel Six-Phase Double-Stator Axial-Flux PM Machine Using Model Predictive Control

Abstract

This paper investigates the postfault operation of a novel six-phase double-stator axial-flux permanent-magnet machine with detached winding connection. In previous research, this configuration was found to be superior to existing winding connection except that its unbalanced magnetic force in the postfault operation cannot be ignored. In this paper, an axial magnetic force balancing method (AMFBM) is proposed to reduce unbalanced magnetic force by deducing a set of special winding current. By comparing electromagnetic torque and axial magnetic force of the traditional winding current and the proposed method in postfault operations through a finite-element analysis, it is verified that AMFBM can reduce most of the unbalanced axial magnetic force as well as keeping torque ripple at a low level. In order to realize the AMFBM, finite control set model predictive control is adopted. A postfault model of dual-three-phase permanent-magnet machines with modified vector space decomposition method is first brought forward to predict the future behavior of the controlled variables with various voltage inputs. After that, a cost function is designed to track the desired winding current by evaluating all the predictions to decide the next step of the inverter. Experimental results show that the control scheme performs well in both dynamic and steady-state situations.