Analysis of features of magnetic field of a synchronous electric machine with a multi-phase fractional slot winding in a polyharmonic mode of operation

An analytical model has been developed for calculating magnetic field in a multiphase synchronous electric machine with fractional toothed windings. For this, a harmonic analysis of the distribution functions of the magnetic field of excitation and the magnetic field of the armature reaction was carried out, taking into account the presence of higher harmonic components in the function of the magnetomotive force of permanent magnets, variable magnetic conductivity of the air gap, polyharmonic mode of operation of a multiphase electric machine and a non-sinusoidal law of variation of spatial winding functions. As a result of the analysis, the substantiation is given that in the investigated electric machine a nine-phase winding can extract with the greatest efficiency the harmonic components of the first and third order of a rotating magnetic field to create flux linkage and induce an electromotive force (as well as create a magnetomotive force with prevailing spatial harmonics of the first and third order). In the investigated electric machine, the amplitudes of the working harmonics of the induction of the modulated magnetic field of the armature reaction can be increased due to the modulation of the inoperative harmonics of the magnetomotive force of the armature response by the stator teeth to the first and third order. To check the developed provisions, a magnetostatic vector model of the magnetic field of the investigated electric machine was created. The simulation results confirmed the high efficiency of the developed analytical model for calculating the magnetic field in a synchronous electric machine with fractional toothed windings. The use of such a model will make it possible to reveal most reliably the influence of the geometricparameters of the magnetic circuit and the multiphase winding circuit on the nature of the change in the functions of the magnetic field in the air gap with the lowest time costs in the process of optimizing an electric machine.

Research on Self-exciting Air-core Pulsed Alternator Considering Armature Reaction

Compared with the traditional synchronous generator with iron core structure, air-core pulse alternator usually adopts self-excitation to establish a higher field current to meet its demand for high flux density. In this paper, the topology of the self-exciting rectifier is determined to be the full bridge rectifier by discussing the respective application scope of the full bridge and the half wave rectifier. Considering the armature reaction, the self-excitation process and the coupling relationship between the field winding and the armature winding are analyzed. According to the commutation overlap angle, the equivalent circuits of different states are carried out, and the instantaneous expressions of field current and armature current are deduced, which lays a foundation for the following phase control research.

The Armature Reaction Inductive Reactances of Synchronous Machines with Permanent Magnets Nonmagnetic Holder

The most widely used design scheme of synchronous machines with radially magnetized permanent magnets and a nonmagnetic magnet holder is considered. To calculate the armature reaction inductive reactances in these machines, it is proposed to use the conventional approach and the expressions obtained on its basis for the armature reaction inductive reactances of synchronous machines with electromagnetic excitation. The features of permanent magnet machines can be taken into account by special calculated coefficients included in these expressions. On the basis of the magnetic field analytical solution of the armature reaction, the special calculated coefficient for the design scheme with a cylindrical yoke of the inductor was determined taking into account the increased nonmagnetic gap between the armature magnetic core and inductor yoke core. By applying the Schwartz method with the use of a scalar magnetic potential, a new magnetic field analytical solution of the armature reaction with a polyhedral yoke of the inductor is obtained. On the basis of this solution, the field form factors of the longitudinal and transverse armature reaction were determined, which take into account the real geometry of this design scheme. Graphical dependences of the special calculated coefficients on the active zone geometric parameters are given.

2D Analytical Model of Armature Reaction Magnetic Field Distribution in Slotless Permanent-Magnet Linear Tubular Machines

This paper presents a 2D analytical model for predicting the magnetic flux density distribution in slotless permanent-magnet (PM) linear tubular (PMLT) motors due to armature reaction effects based on the sub-domain method. According to this method, the machine cross-section is divided into the six sub-regions and Maxwell partial differential equations (PDEs) are formed in each sub-region. Solving these PDEs leads to defining the magnetic vector potential in each sub-region and applying curl on the calculated magnetic vector potential results in determining the magnetic flux density components. Eventually, the extracted results are compared with those of the finite-element method (FEM) to confirm the accuracy of the described analytical model. The results reveal that the presented analytical model is a suitable candidate for predicting the magnetic flux density components of the slotless PMLT motors in a shorter time.

Improvement of Electric Propulsion System Model for Performance Analysis of Large-Size Multicopter UAVs

In this study, an improved model of the electric propulsion system is proposed in order to analyze the performance of large-size multicopter unmanned aerial vehicles. The main improvement of the proposed model is to reflect the armature reaction of the motor, which effectively explains the significant performance degradation in high-power operation. The armature reaction is a phenomenon, in which the main field flux is interfered by a magnetic flux and, as the size and output of the motor increase, the effect of armature reaction also rapidly increases. Therefore, the armature reaction must be considered for the optimal design and performance analysis of large-size multicopter platforms. The model proposed in this study includes several mathematical models for propellers, motors, electric speed controllers, and batteries, which are key components of the electric propulsion system, and they can calculate key performance data, such as thrust and torque and power consumption, according to given product specifications and input conditions. However, estimates of the armature reaction constants and heat profiles of motors need to be obtained in advance through experimental methods, since there is not yet enough data available in order to derive an estimation model. In conclusion, a comparison with the static thrust test of some commercial products confirmed that the proposed model could predict performance in the high-power operation of electric propulsion systems for large multicopter platforms, although some errors were noted.

Modular Permanent Magnet Synchronous Machine with Low Space Harmonic Content

Modularity technique is desirable in large permanent magnet synchronous machines (PMSMs) because it facilitates manufacture, assembly, and maintenance. Although the PMSMs with fractional-slot concentrated windings (FSCWs) allow their stators to be modularized, they usually suffer from high nonworking space harmonic content. The PMSMs with various reported two-slot pitch windings (TSPWs) show much lower nonworking space harmonic content, but they do not support stator modularity. This paper proposes a modular PMSM with a special dual three-phase (DTP) TSPW, which exhibits quite low nonworking space harmonic content. First, the topology of the proposed machine is described in detail. Then, the mechanism of reducing the nonworking space harmonic content of the machine is expounded through winding magnetomotive force (MMF) analysis. Finally, the electromagnetic characteristics of a specific proposed modular PMSM and a conventional modular PMSM with DTP-FSCW are compared by finite element method (FEM), in terms of electromotive force (EMF), armature reaction field, torque performance, efficiency and power factor. The FEM results demonstrate that the proposed machine can realize low space harmonic content while retaining stator modularity.