Luming Cheng

The open-end winding multi-phase permanent-magnet (PM) machine driven by full-bridge inverter is a potential choice for safety-critical application fields. Based on the open-end winding multi-phase PM machine system, comparative investigations of the inverter short-circuit (ISC) fault and winding terminal short-circuit (WSC) fault are carried out to indicate the special characteristics of the ISC in aspects of short-circuit (SC) current characteristics and post-fault performances. The analytical prediction of the SC current under ISC fault is investigated based on the results of WSC conditions. The maximum SC current estimation, SC current rms value variation, and torque harmonic component distribution under the two fault conditions are further investigated. The results can be used for ISC fault diagnosis, PM demagnetization evaluation, and post-fault performance prediction of ISC fault. The post-fault hardware reconfiguration method is further provided to alleviate the effect of ISC fault and reduce the difficulty of compensation.

Based on rotating rhombus method (RRM), an equal-magnitude sinusoidal current compensation strategy is proposed to improve the post-fault performance of five-phase PMSM with short-circuit fault. RRM is a graphic method which is proposed to obtain optimal compensation currents, and the equal-magnitude phase currents are treated as rhombic current vectors. To maintain the same magnetomotive force (MMF) under fault condition, the geometric relations of rhombus are used to derive phase angles of the compensation currents. The effectiveness of the proposed strategy is verified by a 10-slot/8-pole five-phase PMSM, and the torque ripple caused by short-circuit fault is significantly reduced. Besides, the proposed strategy is compared with an existing strategy from aspects of toque, torque ripple, losses, and efficiency, and the proposed strategy has advantages of balanced copper loss of the healthy phases and lower inverter cost.

In this paper, 30-slot/24-pole five-phase PMSM with hybrid single/double layer (HL) fractional-slot concentrated winding (FSCW) is designed for wheel-driving application in electric vehicles (EVs). Third harmonic current injection in different operating stages of the machine is investigated, including normal operation and fault-tolerant operation. HL FSCW machine is validated to be suitable for injecting third harmonic current to enhance torque by both theoretical analysis and finite-element analysis (FEA), and compared with 20-slot/24-pole single-layer (SL) and double-layer (DL) FSCW machine under constant rms and peak harmonic injection. Besides, a novel flux weakening control method with third harmonic current injection is proposed, which improves torque and efficiency of HL FSCW machine. The influence of nonlinearity caused by stator core saturation and higher order harmonics contained in back electromotive force (EMF) is included in flux weakening operation with harmonic injection. Finally, fault-tolerant control of HL FSCW machine with one-phase open-circuit fault is investigated, and two compensatory strategies with and without third harmonic current injection are proposed. Torque ripple caused by one-phase open-circuit fault is suppressed effectively by the proposed strategies.

This paper proposes a multiphase modular fault-tolerant permanent-magnet (PM) machine with hybrid single/double-layer fractional-slot concentrated winding (FSCW). Comparisons between the proposed machine and conventional FSCW machines are made to indicate the special characteristics in aspects of armature magnetomotive force harmonic distribution, cogging torque, magnetic isolation ability, and torque capability. Then, influences of specific structural parameters, including the angle between single-layer slot (SLS) and double-layer slot (DLS) and the opening widths of SLS and DLS, on machine performances are investigated, and power density of the machine is improved by selecting the parameters appropriately. In addition, two stator modular design schemes are proposed. The influences of gaps between modules on machine performances, such as torque, losses, inductances, and short-circuit current, are investigated.

Electric vehicle (EV) is a promising technology for saving fossil energy and reducing pollution. Hybrid-permanent-magnet (PM) variable-flux machine is a competitive candidate for EV propulsion since it has wide speed range and high efficiency at high-speed region. A novel hybrid-PM variable-flux machine with magnetic barriers is proposed in this paper, and a new magnet material CeFeB is used. The structure and operating principle are introduced, and different magnetization states of the machine are analyzed. The equivalent magnetic circuit model of the machine is established considering the influence of magnetic barriers, and the model is proven with good precision for the calculation of air gap flux density and PM operating point. The electromagnetic performances are analyzed, and compared with a traditional variable-flux machine. It is verified that the added magnetic barriers improve the distribution of air gap flux and load magnetization performance of the machine. The no-load back electromotive force, electromagnetic torque, speed range, and load magnetization ratio of the proposed scheme are all improved.

The hybrid variable-flux permanent-magnet synchronous machine (VF-PMSM) is an alternative candidate for adjustable speed applications. The series magnet and parallel magnet configurations are the two existing topologies for hybrid VF-PMSMs. However, they both have drawbacks that have not been fully resolved. A premium topology with high power density and magnetization regulation using acceptable current pulses is highly desired. This paper proposes a new hybrid VF-PMSM with a quasi-series magnet configuration and a passive flux barrier. After introducing the proposed topology and its operating principles, the results of a comparative study are presented comparing the magnetization characteristics and torque capabilities of the three configurations. The influences of key design variables on the machine’s performance are investigated, showing that the proposed machine can achieve a relatively high power density comparable to the series configuration, and the required magnetization current amplitude falls within acceptable limits.

To overcome the inherent demerit of low power factor existing in transverse‐flux permanent‐magnet (TFPM) machines, a tubular staggered‐teeth TFPM linear machine is presented here. Linear alternator integrated with free‐piston Stirling engines could offer a great potential in a wide variety of applications ranging from solar energy generation to space power supply. The thermal behaviour of the machine is studied using a three‐terminal lumped‐parameter thermal network (LPTN) to solve the problem of temperature overestimation of the traditional LPTN. The determination of thermal resistances and thermal parameters are introduced in detail. The temperatures of various components of the machine under different load conditions are calculated by both the three‐terminal LPTN model and the numerical thermal model. Sensitivity analysis is carried out to study the influence of critical thermal parameters on the temperature rise of the machine. On this basis, the effectiveness of the forced air cooling is investigated. A prototype is fabricated and temperature experiment indicates that there is a good agreement between measurement and calculation.

Although fractional-slot concentrated winding (FSCW) offers many significant advantages, such as short end-turn windings, high slot filling factor, and low cogging torque, it is frequently limited by excessive stator magnetomotive force (MMF) harmonics which will induce high eddy losses in the permanent magnets (PMs). What is more, in the literature, it can be observed that the reluctance torque of the salient-pole machine with FSCW is usually much lower than that obtained with integral slot winding. To explore the underlying reason why the reluctance torque in a salient machine with FSCW significantly decreases, a new six-phase FSCW with 24 slots and 10 poles, which can significantly reduce the undesirable stator MMF harmonics, is obtained by using the concept of stator shifting. Then, two permanent-magnet-assisted synchronous reluctance machines (PMA-SynRMs) with the proposed winding layout and conventional asymmetric 12-slot/10-pole six-phase winding layout are designed and simulated by the finite-element method (FEM). The reluctance torque, total torque, and d/q-axis inductances with different current phase angles are also compared under different loaded conditions. The results show that a reduction in stator MMF harmonics can indeed lead to a significant enhancement in reluctance torque under heavy loaded conditions, while the dominance will diminish under light loaded conditions.

The multiphase machine is a competitive candidate for applications where uninterrupted operation is demanded under post-fault conditions. In this paper, the decoupling vector control for a surface mounted five-phase permanent-magnet (PM) synchronous machine (PMSM) under single-phase open-circuit fault is investigated. The decoupled mathematical model of the five-phase PMSM under single-phase open-circuit fault is derived. Then, two post-fault control strategies are obtained, which are based on the principles of minimum copper loss and equal amplitudes of currents, respectively. The post-fault control strategy based on the feed-forward compensation is proposed in order to eliminate the influences of certain factors and decrease the current ripple. The validity of the post-fault control strategies is proved by experiments.