Abstract
The paper firstly summarizes a simple analytical model of the air gap flux-density distribution for isotropic permanent magnet (PM) synchronous machines, in the presence of static eccentricity. The model was proposed by the authors in a previous paper and is based on an efficacious analytical expression of the variable length of air gap magnetic field lines which occur in eccentric brushless machines with surface-mounted permanent magnets. The approximate expression of the air gap field makes it possible to achieve a mathematical model with concentrated parameters close to that of a PM machine without eccentricity. The expression of the armature voltages and electromagnetic torque are found, also with reference to steady-state operating conditions at fixed rotor speed and impressed currents. The differences introduced by the considered type of eccentricity are evaluated and highlighted especially with reference to the air gap inductance and to waveforms and frequency spectra of voltages and shaft torque. Numerical results in a case-study of an 8-pole, 110 kW PM motor are compared to those obtained by using finite element analysis.
Highlights
IntroductionEccentricity is one of the widely diffused unexpected working conditions in electrical machines
Eccentricity is one of the widely diffused unexpected working conditions in electrical machines.When an eccentricity anomaly occurs in a machine, the length of the air gap between rotor and stator has a non-uniform distribution
In order to evidence the variations introduced by static eccentricity, in Figure 10 the spectrum of the e.m.f. induced in a stator phase in the case of healthy is compared to the spectrum in presence of eccentricity, both obtained through finite element element method method (FEM) simulation; all harmonic amplitudes are in p.u. of the fundamental one in the healthy case
Summary
Eccentricity is one of the widely diffused unexpected working conditions in electrical machines. An analytical approach appears more useful for the diagnosis of eccentricity; different methodologies are applied in the literature [9,10,11,12] in order to develop an accurate mathematical model suitable for correctly taking eccentricity into account. With the the aim aim to to reduce reduce the the complexity complexity of of the the models, models, itit is ispossible possibleto tointroduce introducesome somesimplifying simplifying hypotheses hypotheses on on the the length length of of magnetic magnetic flux‐density flux-density in in the the air air gap gap and and on on the the magnetization magnetization law law of of the the permanent permanent magnets magnets [13,14]. Armature voltages and electromagnetic analysis in terms of no-load electromotive force and armature voltages and electromagnetic torque torque in in an an assigned assigned steady steady state condition with impressed armature currents
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