Linyuan Xiao

Cogging Torque Analysis and Minimization of Axial Flux PM Machines With Combined Rectangle-Shaped Magnet

This paper introduces three indexes for the cogging torque waveform and analyzes the influence of machine parameters on these three indexes in the theory. The phase of cogging torque under different combinations of slot opening ratio and pole-arc ratio is analyzed. Based on this analysis, two techniques to minimize cogging torque of the axial-flux permanent-magnet (AFPM) machines are proposed and discussed. Using the quasi-3-D analysis method, the mechanism of cogging torque minimization for AFPM machines equipped with several special magnet shapes is revealed by elaborating the results of each slice. Then, a novel rectangle-shaped magnet arrangement is proposed and investigated for cogging torque minimization. Comparing with other cogging torque minimization techniques such as conventional skew on PM edges, this method is able to decrease cogging torque without comprising torque output. Finally, a prototype is built and the experiment is performed to validate the finite-element analysis results.

Reduction of unbalanced axial magnetic force in post-fault operation of a novel six-phase double-stator axial flux PM machine using model predictrive control

This paper investigated the post-fault operation of a novel six-phase double-stator axial flux permanent magnet machine with detached winding configuration, which was found to be superior to existing winding configuration in previous study. However, the unbalanced magnetic force problem still remains unsolved. In this paper, the axial force balancing control principle is proposed and a group of specific current waveforms are deduced. When applying these currents under post-fault condition, magnetic torque, axial magnetic force and rotor losses of the machine are calculated in finite element analysis. The results are compared with normal condition and commonly-used post-fault current waveforms. It is verified that this method reduced the unbalanced axial magnetic force immensely and the torque ripple was also kept at a low level. In order to achieve the proposed current waveform, finite control set model predictive control (FCS-MPC) is adopted. This paper proposed the post-fault model of dual three-phase permanent magnet machines and designed a cost function to track the desired current waveforms. The model of the machine is used to predict the future behavior of the controlled variables and the cost function decides the next step of the inverter by evaluating all the predictions. At last, it is verified by simulation results that the control strategy performs well in both dynamic and steady-state situations.

Six-phase double-stator inner-rotor axial flux PM machines with novel detached winding

This paper proposes a novel detached winding configuration for asymmetric six-phase double-stator axial flux permanent magnet machines aiming at fault-tolerant applications. Due to the machine unique double-stator structure, the six-phase winding can be separated into two three-phase windings with 30 electrical degree angle shift and arranged in different stators, which is the basic idea of the detached winding. In this paper, the connection of detached six-phase winding is first given, followed by a comprehensive comparison of the conventional six-phase winding and the detached winding in aspect such as the winding factor, electromotive force, inductances, rotor eddy current loss, and torque in normal condition. Performance under fault-tolerant operation is investigated by the copper loss minimization control strategy. The results show that by applying the detached winding instead of the conventional winding, rotor eddy current losses could be reduced by 25% and 70% under normal and fault-tolerant operation, respectively, without sacrificing torque output. This implies that under fault operation, the excess heating in rotor could be reduced and the machine durability can be enhanced. A prototype machine is built to validate the performance of the detached winding design. The experimental results match well with simulation analysis.

Six-Phase Double-Stator Inner-Rotor Axial Flux PM Machines With Novel Detached Winding

This paper proposes a novel detached winding for 6-phase double-stator inner-rotor axial flux PM machines. The connection of detached 6-phase winding is firstly given, followed by a comprehensive comparison with the conventional 6-phase winding in aspect of the winding factor, EMF and inductance, et al. Comparison of performance including rotor eddy current loss, torque ripple and rotor unbalanced axial force under fault tolerance operation is also mentioned in this paper.

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

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.

Cogging torque analysis and minimization of axial flux PM machines

This paper defines three indexes for the cogging torque waveform and analyzes the effect of slot opening ratio and pole-arc ratio on the three indexes of cogging torque waveform in theory. Two measures to reduce cogging torque of the axial flux PM machines are discussed and analyzed. Using the quasi-3D analysis method, the mechanism of cogging torque minimization for axial flux PM machines equipped with several special magnet shapes is explained by detailed sector results. Finally, a novel method based on magnet shape prediction is proposed for cogging torque minimization.

Improved Overmodulation Technique with Limited Switching Frequency of Integrated Starter-Generator for Hybrid Electric Bus

Axial flux PM machines, featured by compact size and high performance, are suitable for powertrains of electric vehicles. This paper studies the design and control of a totally enclosed axial flux PM integrated- starter-generator system. Torque density and volume benefits from large number of pole pairs when designing PM machines. However, the increased pole pair number decreases the switching-frequency-to-electrical-period ratio, and large power drives are troubled with limited switching frequency. To improve this situation, a control strategy named overmodulation technique with variable sampling frequency is proposed to improve the system performance in the nonlinear region. The heat dissipation potential of the inverter is fully utilized and the DC bus voltage utilization ratio is enhanced with this control strategy. Simulation results are carried out in which the current waveform is also improved.

Vernier reluctance dual-stator inner-rotor machines with semi-closed slot

This paper proposes vernier reluctance dual-stator machines with semi-closed slot. The structure of vernier reluctance dual-stator machines with semi-closed slot is firstly given, followed by a comprehensive comparison with the conventional structure in aspects of no load flux linkage, cogging torque and torque. The effect of inner stator shift on the performance of vernier reluctance dual-stator machines with semi-closed slot is also analyzed.

Windings configurations for vernier reluctance dual-stator inner-rotor axial flux machines

This paper analyzes the conventional windings, detached windings and alternative windings for vernier reluctance dual-stator axial flux machines. The connection of winding configurations is firstly given, followed by a comprehensive comparison in aspects of no load flux linkage, cogging torque, rotor unbalanced axial force, torque, torque ripple and iron loss.

Research on main insulation temperature field for open-type high energy density permanent magnet motor

According to the fluid-solid heat transfer theory, taking the Main Propulsion Motor(MPM) of Unmanned Aerial Vehicle (UAV) as the object of study, the fluid-solid coupled physical and mathematical models were established under the strong cooling condition combining the ventilation and structure characteristics of MPM. The finite element method was used in coupling calculation of 3D fluid field and temperature field. The heat transfer characteristic and winding temperature distribution are analyzed. Using embedded temperature detector method (ETD) to winding insulation test, the distribution of winding insulation of the highest temperature rise has measured, which provides a theoretical basis for optimal design for MPM of UAV.