Abstract
A new harmonic field excitation technique for the brushless operation of wound field synchronous machines (WFSMs) is proposed in this paper. The proposed scheme involves conventional three-phase and single-phase inverters operating at different frequencies and supply input current to the armature winding simultaneously. This results in a composite output current of the inverters, which contains fundamental as well as the third harmonic current components. The fundamental is utilized to develop the stator field, on the other hand, the third harmonic is used for developing the pulsating magnetomotive force (MMF) in the airgap. This MMF produces a harmonic current in the harmonic winding of the rotor which is later rectified to inject field current to the rotor field winding. The theoretical analysis of the proposed technique is supported using 2-D finite element analysis (FEA).
Highlights
Permanent magnet (PM) machines have a vast range of applications owing to their high efficiency, power density, power factor, and torque density capabilities [1,2,3,4,5,6]
They do not require any extra exciter, brushes, or slip rings for their field excitation. This makes PM machines compact as compared to the classical synchronous machines which require complex and bulky field excitation mechanisms that involve exciters installed on the shaft of the machine
There are a few fundamental deficiencies such as unadjustable flux and risk of loss excitation associated with PM machines
Summary
Permanent magnet (PM) machines have a vast range of applications owing to their high efficiency, power density, power factor, and torque density capabilities [1,2,3,4,5,6]. In [8,9,10], the authors proposed brushless techniques in which a sub-harmonic MMF component is produced besides the fundamental by injecting currents into the two different sections of the armature winding In one of such studies, two inverters were used for this purpose. The generated harmonic current is rectified for rotor field excitation This technique achieves brushless operation for WFSM, the usage of thyristor switches with both inverters makes the system bulky and costly. The provided thyristor switches were operating at near zero-crossing of each phase current This arrangement generated a zero-sequence third harmonic for the armature winding, which was induced in the harmonic winding to achieve the brushless operation of WFSM. The generated rotor field as it interacts with the stator field develops torque
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