Fault-tolerant Flux-switching Permanent-magnet Research Articles

Analysis of PM Eddy Current Loss in Four-Phase Fault-Tolerant Flux-Switching Permanent-Magnet Machines by Air-Gap Magnetic Field Modulation Theory

In this article, the permanent-magnet (PM) eddy current loss in a four-phase fault-tolerant flux-switching PM (FT-FSPM) machine is investigated from the perspective of air-gap magnetic field modulation. It can be found that the PM eddy current loss in FT-FSPM machines results from the relative motion between air-gap field space harmonics and PMs. Some effective working harmonics produce the major PM eddy current loss. The proportion of PM eddy current loss generated by each working harmonic is studied in detail, revealing that the low-order (third) harmonic is the main factor. Then, two new structures are proposed to reduce PM eddy current loss, in which magnetic flux barriers are designed by reducing low-order harmonics from the aspect of magnetic field modulation theory. Electromagnetic performance is investigated by finite element analysis. The results show that the proposed structure is effective to suppress PM eddy current loss. Finally, an experimental test platform is established to verify the theoretical analysis results.

Improved Control Strategy for Fault-Tolerant Flux-Switching Permanent-Magnet Machine Under Short-Circuit Condition

Fault-tolerant flux-switching permanent magnet (FTFSPM) machines are suitable for high-reliability applications owing to their good fault-tolerant capability and relatively high torque density. Under a short-circuit fault, the torque ripple caused by the short-circuit current of the FTFSPM machine affects the steady-state performance of the system; in addition, the traditional proportional–integral (PI) controller of the speed loop can hardly guarantee the optimal dynamic performance of the speed. In this study, to solve these two problems, an improved control strategy that can offer two improvements for the FTFSPM machine under the short-circuit condition is investigated. As the first improvement, on the basis of analysis of the torque ripple caused by the short-circuit current, the feed-forward control is employed to reduce the torque ripple. As the second improvement, on the basis of analysis of the influence of the speed loop PI parameters on the system dynamic performance, a torque integral balance-control method is proposed. This algorithm can make the speed and the electromagnetic torque converge simultaneously after only one adjustment of the speed. Thus, the best possible dynamic response for the speed can be achieved. Experimental results verify the correctness and effectiveness of the improved control strategy.

Field-oriented control and direct torque control for a five-phase fault-tolerant flux-switching permanent-magnet motor

This paper presents a comparative performance analysis of a new five-phase fault-tolerant flux-switching permanent-magnet(FT-FSPM) motor for high-reliability applications under the two most popular control schemes, namely, field-oriented control(FOC) and direct torque control(DTC) based on stator-flux orientation. Firstly, the new motor topology and structural characteristics are briefly presented. Secondly, the d- and q-axis for the FT-FSPM motor are defined, which is crucial to the mathematical model and control scheme, and the mathematical models are derived. Then, two control schemes, i.e., FOC and DTC, and the main system are proposed. The operational principles of the two control schemes are presented, and space vector pulse width modulation(SVPWM) based on four neighboring vectors is adopted to reduce current harmonics and torque ripples. Finally, the simulated and experimental results are given, and performance analysis of the two control schemes are compared and discussed. The results reveal that FOC scheme has the sinusoidal phase current and low torque ripples, while the DTC scheme has fast dynamic response, verifying the effectiveness of the two proposed control schemes. This paper is a primary investigation for more possible improvements in the control schemes of the five-phase FS-FTPM motor.

Low‐noise design of fault‐tolerant flux‐switching permanent‐magnet machines

The high variable flux density in the air-gap of fault-tolerant flux-switching permanent-magnet (FT-FSPM) machine results in rich harmonics of the magnetic field, thus generating large vibration and noise. This study proposes two novel FT-FSPM machines which can effectively reduce the radial pressure, thus reducing the vibration and noise. First, the radial pressure of the initial FT-FSPM machine is analysed. Second, the novel proposed FT-FSPM machines are introduced and analysed. Third, the electromagnetic performance, including back electromotive force, output torque, inductance, and radial pressure harmonics, of the initial and the two proposed machines are compared by finite element method. Then, the vibration modes with corresponding natural frequencies are predicted. The vibration and noise are simulated by boundary element method. Finally, the effectiveness of the low-noise design is verified by measurement results.

Vibration prediction in fault‐tolerant flux‐switching permanent‐magnet machine under healthy and faulty conditions

This study investigates the vibration behaviour of a fault-tolerant flux-switching permanent-magnet (FT-FSPM) machine due to electromagnetic origins. The FT-FSPM machine adopts fault-tolerant teeth and odd rotor pole to obtain more symmetric back electromotive force and reduced cogging torque. However, this topology suffers from high local magnetic force and unbalanced radial force, thus producing significant vibration and noise. In order to predict the vibration characteristic generated by the structure, electromagnetic and structural models are developed. First, the air-gap field is qualitatively analysed by using the rotor permeance to modulate the magnetomotive force. Second, the radial forces during healthy and faulty operations are compared by using finite element method. Then, the most significant vibration modes are calculated to determine how the machine is excited. Furthermore, the vibration behaviour of the FT-FSPM machine under healthy and faulty conditions is predicted by structural analysis. Finally, the experimental measurements are given for verification.

A New Adaptive Control for Five-Phase Fault-Tolerant Flux-Switching Permanent Magnet Motor

The five-phase fault-tolerant flux-switching permanent magnet (FT-FSPM) motor can offer high efficiency and high fault-tolerant capability. In this paper, its operation principle is presented briefly and its mathematical model is derived. Further, a new adaptive control for an FT-FSPM motor, based on the backstepping method and the sliding mode control strategy, is proposed. According to the backstepping method, the current controllers and voltage control laws are designed to track the speed and minimize the current static error, which enhance the dynamic response and the ability to suppress external disturbances. In order to overcome the influence of parameter variations, according to sliding mode control theory, the virtual control variables and the adaptive algorithm are utilized to approach uncertainty terms. Three Lyapunov functions are designed, and the stability of the closed-loop system is analyzed in detail. Finally, both simulation and experimental results are presented to verify the proposed control method.

A Novel Dual-Rotor, Axial Field, Fault-Tolerant Flux-Switching Permanent Magnet Machine With High-Torque Performance

This paper proposes a novel dual-rotor, axial field, fault-tolerant flux-switching permanent magnet machine (FSPMM) with high-torque performance for direct-drive applications, in which the phase-group concentrated-coil windings and the unaligned arrangement of the two rotors are used. The adoption of the phase-group concentrated-coil windings is made to obtain a unity displacement winding factor, and to enhance the flux-focusing effects together with the use of a spoke-type PM configuration. The unaligned arrangement of the two rotors will help to achieve increased flux magnification and also to suppress the cogging torque and the torque ripple. In particular, the proposed configuration for FSPMMs exhibits the advantage of fault tolerance, benefiting from the electromagnetic isolation of phases and a dual three-phase channel of supply. The operating principle and the design criteria of the proposed FSPMM are discussed in detail. To highlight the advantages of the proposed FSPMM, two conventional FSPMMs are adopted for comparison under the same operating conditions based on a 3-D finite-element method. As a result, it is demonstrated that the proposed FSPMM exhibits significantly improved performance with not only higher torque (power) density but also lower cogging torque and torque ripple, compared with the conventional FSPMMs.

A Multi-Tooth Fault-Tolerant Flux-Switching Permanent-Magnet Machine With Twisted-Rotor

Flux-switching permanent-magnet (FSPM) machines have high torque density, high efficiency, and robust rotor structure. In order to achieve a high level of fault-tolerant capability and torque capability simultaneously, a multi-tooth 6-stator pole, 19-rotor pole fault-tolerant FSPM machine with twisted-rotor (MTFTFSPM-TR) is investigated and its design specifications including rotor pole numbers and gap width between the stator tooth and the fault-tolerant tooth are analyzed in this paper. Compared with a 12-stator pole, 14-rotor pole alternate poles wound fault-tolerant FSPM (FTFSPM) machine, the MTFTFSPM-TR shows higher torque density, better capability to inhibit short-circuit current, and lower cogging torque. Moreover, the twisted-rotor structure can achieve a symmetric and high sinusoidal back-electromotive force in each armature coil without the value reduction. Electromagnetic performance of the MTFTFSPM-TR has been verified experimentally on a prototype machine.

Control and operation of fault-tolerant flux-switching permanent-magnet motor drive with second harmonic current injection

This study investigates the operations of a recently developed fault-tolerant flux-switching permanent-magnet (FT-FSPM) brushless motor, in which the concentrated coils of each stator phase are wound on alternate teeth and permanent-magnets (PMs) are located in the stator, offering a number of significant advantages over conventional PM brushless machines, such as simpler rotor structure, easier cooling in PMs and independence of phases. The control strategy of the FT-FSPM motor is proposed for torque ripple minimisation, in which the key is to introduce harmonic currents to compensate for non-ideal sinusoidal back-electromotive force (EMF). Both simulation and experimental results confirm that the proposed control algorithms can reduce torque ripple and offer good dynamic performance under normal and fault conditions. Hence, it can be concluded that the developed motor drive system is suitable for applications where reliability, efficiency and power density are of importance in such applications as electric and hybrid electric vehicles.

A Novel Multi-Tooth Fault-Tolerant Flux-Switching Machine

Fault tolerant flux-switching permanent magnet (FTFSPM) machine is a novel fault tolerant machine having magnet in the stator, which not only has the advantages such as excellent physical, mechanical and magnet insulation abilities, but also overcomes the disadvantages in conventional rotor-PM topology like magnets are subjected to centrifugal force and difficult to dispel heat. However, the ability to inhibit short circuit current of FTFSPM has a great impact on the machine torque (power) density. In this paper, a novel multi-tooth fault-tolerant flux-switching permanent magnet (MTFTFSPM) machine which has big self inductance is proposed. Finite element analyses (FEA) are employed to compare the electromagnetic performance of three types of fault-tolerant topology including flux-linkage, back-EMF, torque density and inductances. The results show that the MTFTFSPM machine can reach higher torque density than traditional FTFSPM due to the multi-tooth structure.