K Konstantin Boynov

Analysis of rotor eddy current losses in slotless high-speed permanent magnet machines

Rotor eddy current losses are one of the main reasons of permanent magnet demagnetization in high-speed permanent magnet machines. In this paper the rotor eddy current losses of high-speed permanent magnet machines with different slotless windings have been analysed. The analysis of the losses was performed using 2D and 3D analytical models. In the study, test machines with different windings and the same torque production capability have been analysed. Presented paper shows the dependency of rotor eddy current losses on sine- and square-wave PWM supply voltages and rotor sleeve properties. Several recommendations for reduction of rotor eddy current losses in high-speed permanent magnet machines are given.

Comparative analysis of the SRM as an alternative to the PM motor for automotive applications

Purpose – The purpose of this paper is to present comparative analysis of several configurations of the switched reluctance motor (SRM) for an in-wheel drive for a heavy-duty automotive series hybrid system. The SRM motor is regarded as one of the primary candidates for possible replacement of the permanent magnet (PM) motor. Design/methodology/approach – Three SRMs of 10/8, 12/10 and 12/8 configurations have been analysed, where the last two motors had the stator lamination profile taken from the existing PM motor. The analysis is performed using magnetostatic FEM and transient modelling techniques. Findings – The maximum developed electromagnetic torque of the two analysed motors of 12/10 and 12/8 SRM configurations with the stator lamination profile taken from the existing PM motor is limited due to saturation of the stator yoke. Both motor configurations are capable to provide the specified power within the same outer dimensions due to extended speed in the field-weakening region and position independ...

3-D Analytical Model of Helical Winding PM Machines Including Rotor Eddy Currents

Helical windings (or zigzag windings) are used in a number of applications, however, in electrical machines, mainly employed in low-power, high-speed permanent magnet (PM) brushless dc machines due to the cost effectiveness of the winding type while maintaining reasonable performance. Typically, helical windings are used for low-voltage applications due to their spiral form, which makes them most suitable for a small number of turns. In high-speed electrical machines, such a low number of turns are applicable. It is apparent that high-speed PM machines suffer from rotor eddy-current losses, which in some cases may lead to PM demagnetization due to overheating. The performance of the machine is compromised by these losses; hence, they have to be considered during the design procedure. There are many papers analyzing the magnetic field of these machines employing helical windings; however, none of them present a simple and precise electromagnetic model of a machine with the helical winding. This paper presents an analytical approach to model the resulting 3-D magnetic field of the helical winding, considering eddy currents in the conducting media of the rotor. The model is verified with the 3-D finite-element method by means of comparing magnetic field and rotor eddy-current losses.

Usage of the Inductive Energy Storage in the Field Winding for Driving the Variable Reluctance Motor

In automotive systems, reliability and cost are paramount for the success of electrical drive systems. Considering the switched reluctance motor (SRM), the power electronics cost dominates the total cost of the electrical drive. In this respect, especially the dc-link capacitor significantly contributes to the total bill of the material. This paper proposes the use of a dc-excited winding in an 8/6 SRM as a means of reducing the capacitor. The energy conversion of the motor is analyzed intensively. The control algorithm of the field winding is investigated and an active control algorithm is proposed to provide and absorb the energy in parallel with the dc-link capacitor. The effectiveness of this control method is confirmed by the cosimulation between the finite-element method and the Simulink.

The Effect of PWM on Rotor Eddy-Current Losses in High-Speed Permanent Magnet Machines

High-speed permanent magnet machines, supplied by pulsewidth modulation (PWM) voltage source inverters, operate with distorted stator currents. Harmonics present in these stator currents deteriorate the machine performance by generating losses. Mostly, these losses are following the machine design using a transient finite-element model. The precise measurement of these rotor eddy-current losses is extremely difficult, hence, only a few papers provide convincing comparisons between predictions and measurements. This paper presents a fast and precise analytical approach, verified with measurements, to consider rotor losses of machines, supplied by PWM voltages, already during the design procedure.

Torque ripple minimization of variable flux reluctance machines by rotor skewing

Variable flux reluctance machines (VFRM) are an interesting candidate to substitute permanent-magnet synchronous machines in many applications, mainly owing to the absence of rare-earth permanent magnets and improved field weakening capability.

Comparison of two Anisotropic Layer models applied to induction motors

A general description of the Anisotropic Layer Theory, which is derived in the polar coordinate system and applied to the analysis of squirrel-cage induction motors (IMs), is presented. The theory considers nonconductive layers, layers with predefined current density, and layers with induced current density. The electromagnetic field equations are solved by means of Fourier analysis. Furthermore, two different magnetic models for IMs are proposed, namely, the direct rotor current model and the indirect rotor current (IRC) model. The magnetic models are coupled to the single-phase equivalent circuit by means of an iterative algorithm, which also accounts for saturation of the main flux path. Finally, the calculation results are validated against results obtained from measurements on two benchmark motors. Comparison of the validation results shows that the IRC model is the more promising one.

Design and optimization tools for high-efficiency three-phase induction motors

An Expert System (ES) for the analysis and design optimization of low-power, three-phase induction motors (IMs) is presented. The ES is based on analytical models, which are carefully selected from literature, and coupled together to calculate motor performance characteristics. These performance characteristics are computed within a few seconds. Also, validation of the ES calculation results against measurements on four test motors shows that the analysis results are reasonably accurate. Additionally, the ES is applied to redesign a case study motor and a prototype of the new design is realized. The theoretical design results are validated against measurement performed on the prototype. This validation shows that the design optimization works, though a more accurate description of the lamination material B(H) characteristic is desirable to improve the accuracy of the ES.

Analysis and minimization of torque ripple for variable flux reluctance machines

Variable flux reluctance machines (VFRMs) are permanent-magnet-free three-phase machines and are promising candidates for applications requiring low cost and robustness. This paper studies the torque ripple and minimization methods for 12-stator VFRMs. Starting with the analysis of harmonics in the self and mutual inductances of field and armature windings, instantaneous torque equations are derived by virtual work method, which give a clear view on the dominated torque ripple components in VFRMs. Afterwards, the influences of motor topology on harmonics of the inductances as well as the torque ripple are investigated, such as number of rotor poles and tooth arc, etc. On the basis of the aforementioned analysis, harmonic injections in field current and armature current are analyzed for torque ripple reduction. The effectiveness of these two methods is investigated for non-saturated and saturated 12/10 VFRMs based on 2D finite element analysis. The results show good performance of torque ripple minimization by harmonic armature current injection.

Field weakening capability of 12-stator/10-rotor-pole variable flux reluctance machines

Variable flux reluctance machines (VFRMs) are viable candidates for automotive applications. This paper investigates the field weakening capability of a 12/10 VFRM. Starting with voltage and toque equations, the paper reveals the relationship between torque-speed characteristics and the current arrangement (slot division) of both DC-field and armature windings. The method for expanding the working envelope by tuning DC or AC currents is discussed for different slot divisions. The results are validated by 2D finite element analysis.