Faulty diagnosis and fault-tolerant operation of advanced electric machines

Abstract

Owing to the increasing concern on the environmental protection and the growing interest on the renewable energies, advanced electric machines are proposed for renewable energy applications, such as the advanced magnetless machine and the permanent-magnet hybrid brushless machine. The advanced magnetless machine, which equips with the field winding only to produce the magnetic field, has the advantages of flux controllability and cost effectiveness. The permanent-magnet hybrid brushless machines, which equip with both permanent-magnet and the field winding to produce the magnetic field, have the advantages of flexible flux control capability and high power density. Both of these two types of advanced electric machines have the merit of flexible flux controllability owing to the DC-field winding. However, this feature makes these machines become more vulnerable to the winding faults. Hence, it is of great significance to investigate the impacts of winding faults on these two types of advanced electric machines. In this thesis, the flux-switching DC-field machine and the permanent-magnet hybrid-excited machine are simulated and prototyped for the winding fault diagnosis and fault-tolerant operation investigations, respectively. First, the flux-switching DC-field machine is studied with its armature winding fault signatures, which emphasis on the single phase inter-turn (50%) short circuit faults and the one phase open circuit fault. In order to identify the machine fault signature as simple as possible, a fault diagnosis method is proposed by investigating its rectified current. With both simulation and experimentation, the results indicate that the rectified current under the winding faults can be distinctly distinguished from the one under the healthy operation from the magnitude and period. Second, a fault diagnosis approach is proposed for the machine winding inter-turn short circuit faults, which is capable of detecting and localizing the winding inter-turn short circuit fault by simply monitoring merely one signal. The proposed fault signal is generated based on the dq transformation of the three-phase voltages. The corresponding absolute value and phase angle are able to indicate winding inter-turn short circuit fault with severity level and localize the corresponding faulty phase. Both simulated and experimental results illustrate that the proposed fault signature indicator is able to indicate the winding inter-turn short circuit fault severity. And the proposed faulty phase localization indicator is able to localize the faulty phase. Third, the permanent-magnet hybrid-excited machine is utilized with a brushless DC (BLDC) fault-tolerant operation strategy under the 120 and 180 conduction angles. This strategy has the merit of readily be used for all types of BLDC machines. It is based on the reconfiguration of the phase currents to maintain the magnetomotive force (MMF) unchanged when the winding fault occurs. The one phase open circuit fault and inter-turn (50%) short circuit fault are studied. The average torque value and torque ripple are utilized as the key performance indicators to verify the proposed strategy. The results illustrate that the proposed BLDC fault-tolerant operations under both conduction angles can successfully maintain the generated torque output even under the winding faults.