David A. Staton

Evolution and Modern Approaches for Thermal Analysis of Electrical Machines

In this paper, the authors present an extended survey on the evolution and the modern approaches in the thermal analysis of electrical machines. The improvements and the new techniques proposed in the last decade are analyzed in depth and compared in order to highlight the qualities and defects of each. In particular, thermal analysis based on lumped-parameter thermal network, finite-element analysis, and computational fluid dynamics are considered in this paper. In addition, an overview of the problems linked to the thermal parameter determination and computation is proposed and discussed. Taking into account the aims of this paper, a detailed list of books and papers is reported in the references to help researchers interested in these topics.

Convection Heat Transfer and Flow Calculations Suitable for Electric Machines Thermal Models

This paper deals with the formulations used to predict convection cooling and flow in electric machines. Empirical dimensionless analysis formulations are used to calculate convection heat transfer. The particular formulation used is selected to match the geometry of the surface under consideration and the cooling type used. Flow network analysis, which is used to study the ventilation inside the machine, is also presented. In order to focus the discussion using examples, a commercial software package dedicated to motor cooling optimization (Motor-CAD) is considered. This paper provides guidelines for choosing suitable thermal and flow network formulations and setting any calibration parameters used. It may also be considered a reference paper that brings together useful heat transfer and flow formulations that can be successfully applied to thermal analysis of electrical machines.

Design of a synchronous reluctance motor drive

A segmental-rotor synchronous reluctance motor is used in a variable-speed drive with current-regulated PWM control. The low-speed torque capability is compared with those of an induction motor, a switched reluctance motor, and a brushless DC permanent magnet (PM) motor of identical size and copper weight. The results suggest that many of the desirable properties of the switched reluctance motor can be realized with the synchronous reluctance motor, but using standard AC motor and control components. The torque capability is lower, but so is the noise level.<<ETX>>

A Review of the Design Issues and Techniques for Radial-Flux Brushless Surface and Internal Rare-Earth Permanent-Magnet Motors

This paper reviews many design issues and analysis techniques for the brushless permanent-magnet machine. It reviews the basic requirements for the use of both ac and dc machines and issues concerning the selection of pole number, winding layout, rotor topology, drive strategy, field weakening, and cooling. These are key issues in the design of a motor. Leading-edge design techniques are illustrated. This paper is aimed as a tutor for motor designers who may be unfamiliar with this particular type of machine.

Design of a new axially-laminated interior permanent magnet motor

The design of an axially-laminated interior permanent magnet motor drive optimised for its field-weakening performance is described. A 7.5 kW motor was built based on low-cost, flexible rubber-bonded ferrite magnet sheet. It achieved an extremely wide constant power speed range of greater than 7.5:1, in contrast to the 2.5:1 obtained both with an axially-laminated synchronous reluctance motor and a standard induction motor. The excellent field-weakening performance makes this type of motor a serious contender for applications such as machine-tool main spindle drives and traction.<<ETX>>

An Improved Subdomain Model for Predicting Magnetic Field of Surface-Mounted Permanent Magnet Machines Accounting for Tooth-Tips

The paper developed an improved analytical subdomain model for predicting the open-circuit magnetic field in surface-mounted permanent magnet machines accounting for the tooth-tips in the slots. The whole field domain is divided into four types of simple subdomains, viz. magnets, air-gap, slot openings, and slots. The analytical expression of each subdomain is derived and the field solution is obtained by applying the boundary conditions and interface conditions between subdomains. Compared with the conventional subdomain models, the subdomain model accounting for tooth-tips can accurately predict the flux density inside the slots. Based on the developed field model, the cogging torque is computed by the Maxwell stress tensor. The finite element analysis is carried out to validate the analytical model. It shows that the developed subdomain model accounting for tooth-tips is more accurate, especially for the machines having larger slot opening width compared with tooth-tip height.

Torque prediction using the flux-MMF diagram in AC, DC, and reluctance motors

This paper uses the flux-MMF diagram to compare and contrast the torque production mechanism in seven common types of electric motor. The flux-MMF diagram is a generalized version of the flux-linkage versus current (/spl psi/-i) diagram for switched-reluctance motors. It is illustrated for switched-reluctance, synchronous-reluctance, induction, brushless AC, brushless DC, interior PM and commutator motors. The calculated flux-MMF diagrams for motors with the same electromagnetic volume, airgap, slotfill, and total copper loss are shown and are used to compare the low-speed torque and torque ripple performance. The motor designs used were reasonably optimized using a combination of commercially available motor CAD packages and finite-element analysis.

Comparison of Analytical Models of Cogging Torque in Surface-Mounted PM Machines

This paper compares four analytical models for predicting the cogging torque in surface-mounted permanent-magnet machines, viz., lateral force (LF), complex permeance (CP), and exact subdomain (SD) models, together with an SD model based on a single slot/pole. The models are evaluated for the air-gap flux density, cogging torque, back electromotive force (EMF), electromagnetic torque, saturation effect, and computational complexity, with particular focus on the influence of design parameters, such as the slot-depth-to-slot-opening ratio and the optimal pole-arc-to-pole-pitch and slot-opening-to-slot-pitch ratios, on the cogging torque. It shows that all studied analytical models have similar high accuracy for the fundamental back EMF and average torque. However, their predictions are quite different for the ripples in the back EMF, cogging torque, and electromagnetic torque waveforms. Overall, the SD models have high accuracy, while the exact SD model is the most accurate among the studied models by accounting for mutual influence between slots, albeit with high computational complexity. The computation of the SD models is slower than that of the LF model but can be quicker than that of the CP model. The comparison is validated by the finite-element and experimental results.

Unified theory of torque production in switched reluctance and synchronous reluctance motors

A method is described for calculating the average and instantaneous torque of the synchronous reluctance motor from a knowledge of the trajectory of the phase flux-linkage versus phase current [i-/spl psi/] waveform, i.e., the same method as used with the switched reluctance motor. This allows a direct comparison between torque production in the two motors to be made. Analytical and finite-element analysis both show that the [i-/spl psi/] loci of the synchronous reluctance motor are ellipsoidal in shape and are not limited to the first and third quadrants as in the switched reluctance motor. The [i-/spl psi/] loci of the synchronous reluctance motor are not bounded by the magnetization curves in the same sense as in the switched reluctance motor and rely upon mutual coupling between phases for correct operation. >

Comparison of different motor design drives for hybrid electric vehicles

This paper describes an investigation into different motor designs for an application dictated by the performance of an existing hybrid electric vehicle drive (an internal permanent magnet motor). An induction motor and switched reluctance motor are studied. Torque over a wide speed range is required (base speed of 1500 rpm and maximum speed of 6000 rpm) and the total torque per volume is used as a key marker indicator. The efficiency is studied and efficiency plots are introduced; predicted losses are used to investigate thermal conditions and temperature rise, which affect the machines described in the paper. Results indicate that at 1500 rpm very high current density exists in all the machines whilst at 6000 rpm the iron loss dominates. The paper illustrates that the permanent magnet motor is not the sole solution to specifying a drive motor for this application.