Search results

Based on Fourier series theory, for almost periodic functions, the general as well as the specific harmonic‐balance model of induction machines is presented together with a brief derivation. Whereas the general model refers to both symmetrical and asymmetrical machines, the specific one is valid for only the former ones, with windings without parallel branches. The specific model permits classification of all symmetrical machines into three categories. The classification preserves its usefulness for machines not strictly fulfilling assumptions for the validity of the specific model. Expressions for the asynchronous and synchronous torque components are derived. Categories as well as frequencies of both the slot harmonics and the synchronous torques are listed in four tables referring to machines with one to four pole pairs.

Electrical machine slots cause an undesirable effect on the m.m.f. wave in the airgap. This effect consists of the occurrence of high frequency harmonics. When the rotor turns, the movement of rotor slots in relation to the stator slots produces cycle variations in the magnetic circuit reluctance. This effect results in high frequency harmonics in the current wave spectrum. Simultaneously high frequency harmonics torques appear. These are known as slot harmonics. To avoid slot harmonics, both in the rotor and in the stator slots, the slots are skewed. When this technique is used, the simplified hypothesis of the finite element model (FEM) in 2D cannot be employed, as it is based on the concept that the magnetic field possesses translational symmetry along the machine shaft. In this paper a method for analysing electrical machines with skewed slots is presented without using the 3D analysis.

The purpose of this paper is to present a detailed advanced dynamical model of induction machine (IM) with unskewed rotor bars, including rotor slot harmonics.

Procedure of IM modeling using results from finite element analysis (FEA). Series of magneto-static FEA simulations are used to obtain matrix of IM inductances as a function of rotor angular position and geometry. Each element in this matrix is represented by Fourier series (FS) and incorporated in proposed dynamical model. Using or neglecting various elements in FS of inductance matrix may be useful for determining which component of the series has dominant influence on harmonic content of stator currents, torque ripple or speed variation. The usefulness of application of presented model is verified comparing with time-stepping FEA simulations.

Although the model is not suitable for usage in on-line regulation of IM drives, but the results of simulations may be used to thoroughly explain origins of higher order harmonics in stator currents of IM and help improve sensorless speed estimation algorithms and fault diagnostics.

This paper shows an approach to the modeling of IM which includes effects of non-uniform air gap and non-sinusoidal distributions of magneto-motive forces. Inductance matrix elements are complex functions of rotor position, geometry and winding distributions and it gives an opportunity for detail analysis of IM behavior in numerous applications.

The purpose of this paper is to present a synthesis of the analysis and modeling of the rotor losses in high speed permanent magnets motors.

Three types of losses are as a result of eddy currents in the conductive parts of the rotor. The analysis includes their characterization and the setup of a numerical model using finite element method. The adopted methodology is based on the separation of the losses which allows a better understanding of the physical phenomena. Each type of losses will be modeled and computed separately.

It is possible to make a precise estimate of the different losses in the rotor while keeping a relatively short computing time.

The analysis is applied on a high-speed permanent magnet motor for avionic application. The model is validated with the commercial finite element model (FEM) software Flux2D.

The developed model allows an important save in terms of CPU-time compared to commercial FEM software while staying accurate. The separation of each losses and their sources is important for motor engineers and was requested for them to improve the designs more easily.

The purpose of this paper is to compare the study between two topologies of fractional-slot permanent-magnet machines such that: double-layer topology and single-layer one. The comparison considers the assessment of the iron loss in the laminated cores of the magnetic circuit as well as in the permanent magnets (PMs) for constant torque and flux weakening ranges.

The investigation of the hysteresis and eddy-current loss has been carried out using 2D transient FEA models.

It has been found that the stator iron losses are almost the same for both topologies. Whereas, the single-layer topology is penalized by higher iron loss especially the eddy-current ones taking place in the PMs. This is due to their denser harmonic content of the armature air gap MMF spatial repartition.

The analysis of the iron loss maps in different parts of each machine including stator and rotor laminations as well as the PMs, in one hand, and the investigation of their variation with respect to the speed, in the other hand, represent the major contribution of this work.

This paper deals with the numerical modelling of electromagnetic losses in electrical machines, using electromagnetic field computations, combined with advanced material characterisations. The paper gradually proceeds to the actual reasons why the building factor, defined as the ratio of the measured iron losses in the machine and the losses obtained under standard conditions, exceeds the value of 1.

Velomobiles or bicycles cars are human-powered vehicles, enclosed for improving aerodynamic performance and protection from weather and collisions. The purpose of this paper is to design and develop a three-wheeled velomobile equipped with a hybrid human-electric propulsion system.

The mechanical layout has been developed in order to improve safety, a CAD code has been used for the design and the dynamic performances have been studied by means of specific multi-body codes. The electric propulsion system has been designed both with analytical and FEM methods.

A special three-wheeled tilting vehicle layout equipped with a four-bar linkage connection has been developed. A particular synchronous reluctance machine has been developed, which is very suitable for human-electric hybrid propulsion. A MATLAB code for integrated mechanical and electrical analysis has been developed.

A new kind of light vehicle has been conceived. A new synchronous reluctance machine with high efficiency has been developed. A performance analysis in electric, human and hybrid working modes has been presented, which takes into account the specific features of both the electric motor and the pedaling legs. A prototype of the vehicle has been built.

The purpose of this paper is to present the distribution of the magnetic field and additional losses analysis of the induction motors (IM) with opened and closed rotor slots.

In the field-circuit approach the distribution and changes of magnetic flux density in the motor are computed using a time-stepping finite element method. The additional losses in each element are evaluated at different frequencies.

An approximate analytical formulation is derived for rapid losses computation confirmed by the results of field-circuit method. For high-voltage motors due to the size ratios of the core and relatively deep stator and rotor slots major role in causing loss of higher harmonics play a fundamental slot harmonics. Higher harmonics order bigger than 100 cause only small part of total higher harmonics core losses. Closed rotor slots construction influenced significantly on no-load losses mainly due to reduction of losses at slot upper part. For nominal load condition that influence is not so strong according to the saturation of slot tips by rotor leakage flux. Nevertheless, core losses at load are several times higher as at no-load.

In future research authors will take into account motors feed from PWM inverter, working in the frequency range up to 400 Hz.

The results of investigation will be used in more detailed design of IMs especially for motors with closed rotor slots.

The methods presented in the paper was not used before. Also results of additional losses in the motor core calculation, especially according motors with closed slots at no load and load conditions are new.

The development of electrical machines is nowadays closely related to the knowledge of the electromagnetic fields throughout the different parts of a machine. Although a machine is often of complicated geometrical structure and of different, mostly nonlinear materials, modern numerical methods and the related software allow calculation of the fields in 2D models and several 3D cases precisely enough in order to derivate from them quantities like energy density distribution, the torque behaviour and characteristics like load and no load. The paper will at first compare numerical methods suited for electromagnetic field calculation in electrical machines. The following topic deals with adaptive mesh generation playing an important role to save computer memory and cpu time. Then examples like a Switched Reluctance Machine, an Asynchronous Machine and a Stepping Motor are shown concerning the results of field calculation. It is shown that anisotropy may have to be taken into account, and finally it is shown that field calculation enables the shape optimization of a machine.

This study involves the development of a PSPICE 5.4 package oriented model for the dynamic behaviour of a series excited synchronised slip ring induction motor including the bridge rectifier for rotor circuit excitation. Furthermore, in this study is aimed at investigating the synchronising behaviour for various rotor connections of a series excited synchronous motor formed by connecting a bridge rectifier input in series with the stator winding of a slip‐ring induction motor whereas the rectifier output feeds the rotor winding. The steady state behaviour of such a scheme in comparison to a separately excited one is well known, but the behaviour during synchronisation requires further study. Presentation of results obtained by a PSPICE based simulation and comparison with experimental results acquired during this study points to a model to account for design variations and additional circuitry. It is convenient to use this model in a drive system. The advantage of this simulation method over the others is that it does not involve the utilisation of specialised programs and mathematical difficulties such as the solution of stiff differential equations. Furthermore, steady state behaviour of the scheme is explained by means of a simple analysis and illustrated by test results.