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36 results on '"Azar, Ziad"'

4. Electromagnetic performance of fractional slot interior permanent magnet and synchronous reluctance brushless AC machines having non-overlapping concentrated windings

Author

Azar, Ziad and Zhu, Zi-Qiang

Subjects
621.3
Abstract

This thesis investigates the electromagnetic performance of the fractional-slot interior permanent magnet (IPM) and salient-pole synchronous reluctance (SynR) brushless AC machines having non-overlapping concentrated windings, the SynR machines being excited by bipolar AC sinusoidal currents with and without DC bias. The analyses are validated by finite element calculations and measurements. The PM machines with modular stators are often employed to improve the electromagnetic performance and ease the manufacture process, particularly stator winding. The influence of uniform and non-uniform additional gaps between the stator teeth and back-iron segments on the electromagnetic performance of fractional-slot IPM machines having either un-skewed or step-skewed rotors and different slot openings, viz. open slot, closed slot and hybrid slot (sandwiched open and closed slots), is investigated. The influence of load conditions on cogging torque and back-emf waveforms and the effectiveness of rotor skew on the minimization of the cogging torque, thus the torque ripple, are also examined. It is found that the additional gaps have a negligible influence on the average output torque, but significantly increase the cogging torque magnitude, while their non-uniformity can cause a large increase in both the peak and periodicity of cogging torque waveform, which in turn makes the skew method ineffective. The magnetic cross-coupling level and the sensitivity of cogging torque to manufacturing limitations and tolerances strongly depend on the slot opening materials. The cogging torque magnitude is significantly increased by load, while its periodicity also changes with load which makes the rotor skew less effective unless the machine is skewed by one cogging torque period on load. The electromagnetic performance of the SynR machines under AC sinusoidal bipolar excitation with and without DC bias is investigated and compared for three different winding connections, such as asymmetric, symmetric and hybrid. In general, the SynR brushless AC machines with DC bias excitation exhibit significantly higher torque density than those without DC bias. Comparing with the asymmetric and symmetric winding connections, their hybrid counterpart results in significantly larger mutual inductance variations. Consequently, it results in significantly larger output torque, since such torque is produced by the variation of both the self and mutual inductances. In terms of torque ripple, the symmetric winding connection leads to the best performance. On the other hand, at significantly larger current densities, the hybrid winding connection become more suitable, since it exhibits large average output torque and relatively low torque ripple.

Published
2012

23. Comparison of Peak Armature and Field Winding Currents for Different Topologies of 10-MW Superconducting Generators Under Short-Circuit Conditions

Author

Vedreno-Santos, Francisco, Li, Guang J., Azar, Ziad, Thomas, Arwyn S., Li, Guang-Jin, Odavic, M., Zhu, Z. Q., and Guan, Yang

Subjects
621.3 Electrical & electronic engineering, superconducting machines, Air-cored, fault conditions, iron-cored, short-circuit, TK Electrical engineering. Electronics Nuclear engineering
Abstract

This paper studies the peak armature and peak field winding currents for three different topologies of 10 MW partial High Temperature Superconducting Generators (HTSGs) under Short-Circuit Conditions (SCC) by simulation. The investigated partial HTSGs employ copper armature windings and superconducting field windings with different armature and rotor topologies, i.e. iron cored armature and rotor, air cored armature and rotor, and iron cored armature and air cored rotor. For each HTSG topology, the investigation includes: (i) the field winding current control strategies, (ii) the influence of operating field current, and (iii) the ratings of circuit breakers for limiting the peak armature and peak field winding currents. The results can provide guidelines for determining the peak armature and peak field currents of HTSGs and also the possibility of limiting them by employing circuit breakers under SCC.

Published
2016

24. Comparison of Levelized Cost of Energy of Superconducting Direct Drive Generators for a 10-MW Offshore Wind Turbine

Author

Abrahamsen, Asger Bech, primary, Liu, Dong, additional, Magnusson, Niklas, additional, Thomas, Arwyn, additional, Azar, Ziad, additional, Stehouwer, Ewoud, additional, Hendriks, Ben, additional, Van Zinderen, Gerrit-Jan, additional, Deng, Fujin, additional, Chen, Zhe, additional, Karwatzki, Dennis, additional, Mertens, Axel, additional, Parker, Max, additional, Finney, Stephen, additional, and Polinder, Henk, additional

Published
2018
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