Abstract
By developing a simple permeance-magnetomotive force (MMF) model of switched-flux permanent magnet (SFPM) machines, the air-gap flux density produced by both PMs and armature current can be derived, in which harmonics with the same order and rotational speed are called an effective harmonic pair (EHP). By investigating the influences of armature current angle $\delta $ on both the phase and amplitude of each EHP, it is found that the amplitudes of both PM and armature reaction flux-density harmonics maintain fixed, whereas the space phase shift between them changes accordingly with armature current angle. Specifically, the PM and armature reaction flux-density harmonics are orthogonal in space if zero ${d}$ -axis current is fed. Therefore, the maximal torque is realized for each EHP. As the total torque of SFPM machines is the superposition of the contributions by each EHP, the zero ${d}$ -axis current control method turns out to be the optimum for maximal torque per ampere, thus verifying analytically that the ${d}$ - and ${q}$ -axes inductances are equal according to the general torque equation for the investigated machine topology. In addition, the torque adjustment mechanism of each EHP in SFPM machines has also been analytically demonstrated to be resemble that of the surface-mounted PM synchronous machine (PMSM). Finally, the finite-element analysis (FEA) has been performed to validate the previous analytical predictions.
Highlights
SWITCHED-FLUX permanent magnets (PM) (SFPM) machines have obtained increasing attention in industrial applications, such as new energy automobiles and domestic appliances for the merits of high torque density, high efficiency, robust rotor, good thermal management, etc [1,2,3,4]
This paper focuses on the analysis of harmonic components for PM and armature reaction fluxdensities and their relationship with the current angle δ, which is defined as the armature current space vector preceding angle with respect to the d-axis in this paper
By using a simple permeance-magnetomotive forces (MMFs) model, air-gap flux-density harmonics produced by PMs and armature currents of SWITCHED-FLUX PM (SFPM) machines are derived
Summary
SWITCHED-FLUX PM (SFPM) machines have obtained increasing attention in industrial applications, such as new energy automobiles and domestic appliances for the merits of high torque density, high efficiency, robust rotor, good thermal management, etc [1,2,3,4]. The periodic variation of induced phase Back-EMF due to rotor movement, typically addressed from a generator-oriented perspective [5] This approach can be easyunderstanding to some extent, it cannot reveal the operating mechanism of SFPM machines in depth. Identifying the torque production and adjusting principle analytically from a motor-oriented perspective, analyzing electrical machines through the interaction between armature reaction and excitation fields rather than open-circuit phase flux-linkages, gives more meaningful insight, which helps to reveal the nature of SFPM machines in further depth [6]. The purpose of this paper is to analytically verify identical d- and q-axis inductances for SFPM machines through air-gap flux-density harmonic analysis for different current angles δ from the motor-oriented perspective.
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