Phil Mellor

Design Considerations of a Direct Drive Brushless Machine With Concentrated Windings

This paper discusses the performance attributes of the open-slot, modular-wound, external-rotor, topology of electrical machine. Combinations of pole and slot numbers are presented for which the winding factor is maximal and torque ripple is minimal. An optimization of the magnetic circuit design of six promising pole-slot configurations is undertaken using a parametric finite element model (FEM) combined with a genetic algorithm (GA). These designs are benchmarked against a conventional 1.5 slots/pole external-rotor brushless dc machine. These candidate electrical machine versions are characterized by having the same external-rotor diameter, total slot area available for the winding and by equal volumes of permanent magnet (PM). Based on the analysis, the most promising motor structure was selected and a prototype wheel-hub motor has been built for application in a small electrical vehicle. Test data from the prototype is used to validate the findings of the initial analyses and practically demonstrate the attributes of the topology.

Application of fuzzy control algorithms for electric vehicle antilock braking/traction control systems

The application of fuzzy-based control strategies has gained enormous recognition as an approach for the rapid development of effective controllers for nonlinear time-variant systems. This paper describes the preliminary research and implementation of a fuzzy logic based controller to control the wheel slip for electric vehicle antilock braking systems (ABSs). As the dynamics of the braking systems are highly nonlinear and time variant, fuzzy control offers potential as an important tool for development of robust traction control. Simulation studies are employed to derive an initial rule base that is then tested on an experimental test facility representing the dynamics of a braking system. The test facility is composed of an induction machine load operating in the generating region. It is shown that the torque-slip characteristics of an induction motor provides a convenient platform for simulating a variety of tire/road /spl mu/-/spl sigma/ driving conditions, negating the initial requirement for skid-pan trials when developing algorithms. The fuzzy membership functions were subsequently refined by analysis of the data acquired from the test facility while simulating operation at a high coefficient of friction. The robustness of the fuzzy-logic slip regulator is further tested by applying the resulting controller over a wide range of operating conditions. The results indicate that ABS/traction control may substantially improve longitudinal performance and offer significant potential for optimal control of driven wheels, especially under icy conditions where classical ABS/traction control schemes are constrained to operate very conservatively.

Contribution of End-Winding Proximity Losses to Temperature Variation in Electromagnetic Devices

This paper presents an investigation into proximity losses in end-windings informed from 3-D finite-element analysis of an ac power inductor. The proximity effect in winding conductors is a result of circulating ac currents caused by magnetic fields generated by nearby conductors. The calculated results confirm that the effects within the end-winding while significant are lower compared to those with the active length of the conductors. The common approach of predicting proximity losses using 2-D field analyses accounts for active length of the conductors only, and therefore, an end-winding correction factor is needed to obtain a more accurate estimate of loss. The theoretical prediction of losses within the inductor has been validated experimentally on a prototype inductor. A simple method to account for the interdependence of ac loss and temperature is presented and is shown to differ significantly from the well-known dc variation of resistance with temperature.

Investigation of Proximity Losses in a High Speed Brushless Permanent Magnet Motor

This paper presents a finite element investigation into the proximity losses in brushless AC permanent magnet motors used in hybrid/electric vehicle applications. The proximity effect in winding conductors is as a result of eddy-currents caused by magnetic fields generated by nearby conductors. This paper considers the influence of the conductor shape and disposition on the losses for a given stator lamination. Several structures of the winding are analysed and compared in respect to the loss and AC resistance. The analysis shows that the proximity losses can be significantly reduced through an appropriate choice of conductor shape and winding technique. The calculated results have been validated experimentally on the machine prototype for three different winding arrangements

Estimation of Equivalent Thermal Parameters of Impregnated Electrical Windings

It is common practice to represent a composite electrical winding as an equivalent lumped anisotropic material as this greatly simplifies a thermal model and reduces computation times. Existing techniques for estimating the bulk thermal properties of such composite materials use either analytical, numerical, or experimental approaches; however, these methods exhibit a number of drawbacks and limitations regarding their applicability. In this paper, a numerical thermal conductivity and analytical specific heat capacity estimation technique is proposed. The method is validated experimentally against three winding samples with differing configuration. A procedure is presented which enables bulk thermal properties to be estimated with a minimal need for experimental measurement, thereby accelerating the thermal modeling process. The proposed procedure is illustrated by the modeling of three coil exemplars with differing windings. Experimental thermal transients obtained by dc test of the coils show close agreement with a lumped-parameter thermal model utilizing estimated material data.

Electrical generation and distribution for the more electric aircraft

The aircraft industry is developing the more electric aircraft (MEA) with an ultimate goal of distributing only electrical power across the airframe. The replacement of existing systems with electric equivalents has, and will continue to, significantly increase the electrical power requirement. This has created a need for the enhancement of generation capacity and changes to distribution systems. The higher powers will push distribution voltages higher in order to limit conduction losses and reduce cable size, and hence weight. A power electronic interface may be required to regulate generator output into the distributed power form.

A General Cuboidal Element for Three-Dimensional Thermal Modelling

This paper presents a lumped parameter approach for three-dimensional (3D) thermal modelling based upon the use of general 3D elements which are formulated to accurately cater for internal heat generation. Commonly used thermal networks tend not to account for an internal heat generation that is essential for accurate temperature predictions. In contrast, the general element proposed in this paper includes the internal heat generation as well as a material thermal anisotropy. To validate the technique, thermal models of an inductor using the equivalent circuit method based around a general cuboidal element and a full 3D finite element analysis was constructed and analyzed. The calculated results from the cuboidal element method show good agreement with the FEM predictions.

Comparison of passive cell balancing and active cell balancing for automotive batteries

This paper presents a quantitative performance analysis of a conventional passive cell balancing method and a proposed active cell balancing method for automotive batteries. The proposed active cell balancing method was designed to perform continuous cell balancing during charge and discharge with high balancing current. An experimentally validated model was used to simulate the balancing process of both balancing circuits for a high capacity battery module. The results suggest that the proposed method can improve the power loss and extend the discharge time of a battery module. Hence, a higher energy output can be yielded.

Derivation and Scaling of AC Copper Loss in Thermal Modeling of Electrical Machines

Accurate prediction of temperature-dependent ac winding loss effects is crucial in the design of electrical machinery. Average ac winding loss as a function of operating frequency is commonly characterized by the ratio of the equivalent ac and dc resistances (Rac/Rdc). However, as the ac and dc components of the winding loss scale differently with temperature, a single value of Rac/Rdc derived for one temperature can be inadequate when used in thermal modeling. In this paper, methods of deriving the Rac/Rdc ratio, together with scaling techniques of the ac winding loss accounting for thermal effects, are discussed. As an alternative to computationally intensive 3-D finite-element analysis, an experimental approach based on tests on full-scale stator assemblies is proposed. A previously proposed scaling technique of the ac winding loss is discussed and developed further. The proposed techniques of deriving the ac winding loss accounting for temperature variation are illustrated using both theoretical analysis and experimental data.

Design study of a three-phase brushless exciter for aircraft starter/generator

This paper presents a design study of a 3-phase AC main exciter (ME) for an aircraft starter-generator. A computationally efficient methodology for optimizing the design of the ME is presented. The optimisation is carried out using coupled two-dimensional (2D) magnetostatic finite element solver and particle swarm optimisation procedure (PSO). The ME design is then analysed using 3D FE to account for the end-winding effects, and the results are fed into a lumped-parameter circuit model of the ME. The circuit model allows for the operating modes of the ME being analysed in a computationally efficient manner also accounting for non-linearities. The theoretical findings are experimentally validated on a prototype generator.