| With the increasing demands for reliability and fault-tolerant capability of machines in the fields of new energy vehicles and aerospace applications,the multi-phase fault-tolerant permanent magnet(PM)synchronous machines(PMSMs)have become a promising research focus.In order to achieve good electrical,magnetic,thermal and physical isolations between phases,the fractional-slot concentrated winding(FSCW)is usually adopted in the multi-phase fault-tolerant PMSMs.At the same time,the adoption of FSCW brings the problem of high space harmonic contents of the armature magnetic field,which further reduces the efficiency and increase the thermal stress of rotor.The low-space-harmonic six-phase fault-tolerant PMSMs(LSHSP-FTPMSMs)are proposed in this paper,which can fix the problem of high space harmonic contents of the armature magnetic field for the FSCWs,and serve as a high reliability machine scheme in the fields of new energy vehicles and aerospace applications.The main research work of this paper is as follows:Firstly,investigations on the topologies of the LSHSP-FTPMSMs are carried out.The harmonic distributions of the main components of the armature magnetic field in the conventional FSCWs are analyzed.Based on this,the modular-stator-based and stator-winding-shifting-based topology schemes of LSHSP-FTPMSM are proposed to restrain the fundamental component and the harmonic component concomitant with the working harmonic,respectively.The suppression mechanism for the space harmonic components of the armature magnetic field is investigated for the two LSHSP-FTPMSMs.By comparing the influence of different modular stator schemes and different st ator winding shifting schemes on the harmonic components of the armature magnetic field,the barrier in non-wound teeth(BNWT)scheme and the scheme with double six-phase shifted by15° are selected as the final schemes.Secondly,the torque characteristics and loss distributions of LSHSP-FTPMSMs are investigated.The cogging torque,permanent magnet torque and reluctance torque of the two proposed LSHSP-FTPMSM schemes and the six-phase PMSM using the conventional FSCW are analyzed,and the associations between the harmonic components of the armature magnetic field and the torque components are obtained.On this basis,the mechanisms of PM torque improvement in the modular stator BNWT scheme and reluctance torque improvement in the scheme with double six-phase shifted by 15° are investigated.The distribution laws of magnetic flux density at different parts of the low-space-harmonic scheme and the conventional scheme with only the armature excitation or with both the PM excitation and the armature excitation are analyzed.The mapping relations between the harmonic components of the armature magnetic field and the alternating magnetic flux density at different parts of the machine are obtained.Moreover,the distributions of core loss and PM eddy current loss in different six-phase PMSM schemes are analyzed and compared.Thirdly,the open-circuit fault and the corresponding fault-tolerant control strategy of the LSHSP-FTPMSM are investigated.The type of open-circuit fault,the distributions of armature magnetic field and PM eddy current after the open-circuit fault in the LSHSP-FTPMSM are analyzed.And the ability of the low-space-harmonic scheme to suppress the space harmonic components of armature magnetic field under open-circuit fault is evaluated.The application effects of two conventional open-circuit fault-tolerant control strategies used in the low-space-harmonic schemes are analyzed.Aiming at the problem of the excessive reduction of average torque due to the excessive pursuit of low torque ripple usin g the conventional open-circuit fault-tolerant control strategies,an open-circuit fault-tolerant control strategy with adjustable negative MMF sequence is proposed.The proposed control strategy is analyzed and evaluated by finite element analysis(FEA).Fourthly,the winding terminal short-circuit fault and the corresponding fault-tolerant control strategy of the LSHSP-FTPMSM are investigated.The influence of short-circuit initial angle and internal power factor angle on the transient short-circuit current is analyzed.Based on the results of the trajectories of short-circuit current in the d-q plane,the magnetization sate of magnets at the moment that the negative d-axis short-current reaches the peak,and the influence laws of the armature magnetic field harmonic components on the anti-demagnetization ability under the short-circuit fault are obtained.The steady-state short-circuit current and corresponding electromagnetic torque adopting different rotor structures are analyzed.Aiming at the torque ri pple caused by the phase failure and steady-state short-circuit current under the short-circuit fault,a self-compensation short-circuit fault-tolerant control strategy is proposed.The proposed control strategy is analyzed and evaluated by FEA.Finally,the prototype machines of the modular BNWT and the scheme with double six-phase shifted by 15° schemes are manufactured respectively.The test bench is established.The relevant experimental research of the two low-space-harmonic prototype machines are carried out.The experimental research includes the test of no-load back-electromotive force(back-EMF),the test of torque capabilities under healthy conditions,the test of torque capabilities under the open-circuit fault and winding terminal short-circuit fault without or with the corresponding fault-tolerant control strategies.The experimental results show that the tested no-load back-EMFs,output torques under healthy conditions and the performances of the proposed fault-tolerant strategies are in good agreement with the FEA results. |
