Research On Topologies And Operational Characteristics Of Flux-switching Machines

The flux-switching permanent-magnet (FSPM) machine inherits the simple and robust rotor of theswitched reluctance machine (SRM) and high torque density and efficiency of the permanent magnetsynchronous machine (rotor-PM machine). As the magnets are on the stator, the temperature rise ofthe magnets may be more easily managed; moreover, the brushless hybrid excitation structure may bemore easily achieved. Furthermore, the armature field is in parallel with the PM field and there is norisk of PM demagnetization. Therefore, FSPM machines exhibit the potential in applications includingaerospace engineering, wind power systems and hybrid electric vehicles.This dissertation focuses on basic research of topologies and operational characteristics of theFSPM machines with emphasize on fault tolerant, electrical excitation and hybrid excitationtopologies and control strategies for both generator and motor operations, moreover, experiments arecarried out and analyzed.For the electro-mechanical actuator (EMA) in aircraft subsystems, a6/19multi-tooth fault-tolerantFSPM machine with twisted-rotor (MTFTFSPM-TR) is presented. Compared with the traditionalfault-tolerant FSPM machines, the MTFTFSPM-TR shows higher torque density, better capability ofinhibition short-circuit current and lower cogging torque. Meanwhile, the twisted-rotor structure canachieve a symmetric and high sinusoidal back-EMF in each armature coil without the magnitudereduction. Besides, the fault tolerant control methods are investigated to reduce the torque rippleswhen in fault operation, which has been verified on MTFTFSPM-TR machines.For low cost applications, the electrical excitation topologies of FSPM machines are analyzed:(1)compared with the12/8EEDS machine, the12/10EEFS machine shows bipolar excitation flux andrelatively higher torque density.(2) Compared with the12/10EEFS machine, the “E” core EEFSmachine, the “C” core EEFS machine and the multi-tooth EEFS machine shows higher torque density.Meanwhile, the “E” core EEFS machine, the “C” core EEFS machine and the multi-tooth EEFSmachine show wide constant-power capability even with constant excitation current. Besides，theexternal characteristics of the EEFS and the EEDS generators are compared based on differentrectifiers.For generation application field, a twisted-rotor parallel hybrid excitation flux-switching machine isproposed. Compared with the series hybrid excitation topology, the series hybrid excitation topologywith iron flux bridge and the parallel hybrid excitation topology with E core structure, the proposedtopology shows the following advantages:(1) the coupling problem of PM field and electrical excitation field can be solved.(2) high excitation current and high magnets utilization can be achievedsimultaneously. It can be found that the twisted-rotor parallel hybrid excitation flux-switchingmachine is suitable for applications that require high reliability (no PM demagnetization), high torquedensity (no PM magnetic short circuit), and high flux adjustment capability (small reluctance inelectrical field circuit).For the hybrid excitation flux-switching generator, a direct power linear control (DPLC) isproposed. This strategy shows similar excellent dynamic performance as that of the traditional directpower control (DPC), and further, it can reduce the ripples in stator flux-linkage and electromagnetictorque, which enhance the system steady performance. In terms of system cost, reliability, powerfactor and machine utilization, the DPLC, DPC, vector control (VC) and excitation current regulationstrategies are compared and their suitable applications are analyzed.Moreover, the direct torque linear control (DTLC) can also be employed for the motor operation. Inthe DTLC under motor operation, the abilities to control the torque angle by the motion vector and themaximum space vector, respectively, are compared. The DTLC and direct torque control (DTC) showabilities to control torque, which is verified. The concept of DTLC can also be extended to otherapplications using AC machines, which has been verified on FSPM machines.However, both DPLC and DTLC need accurate stator flux-liakage. Hence, a new integrationalgorithm, which can not only overcome the problems the pure integrator and LP filter produced butalso effectively solve the problems that estimation accuracy may be affected by closed-loop parameterin the closed-loop algorithms and adaptive filter algorithms, is proposed. This method has sameamplitude-frequency and phase-frequency characteristics as those of the pure integrator. Meanwhile,its dc gain is zero and the operation will not be affected by machine load and speed as well asclosed-loop parameters. The performance is verified by experiments.