David G. Dorrell

Analysis of airgap flux, current and vibration signals as a function of the combination of static and dynamic airgap eccentricity in 3-phase induction motors

This paper provides new information for the online diagnosis of airgap eccentricity in three-phase induction motors. A new theoretical analysis of the interaction between harmonic field components due to static and dynamic rotor eccentricity which previous research has not considered is put forward. The resultant harmonic current components produced in the supply current which are highlighted by the analysis are found to exist experimentally and indeed shown to be a function of the combined effect of both dynamic and static eccentricity. Further vibration analysis is put forward to identify which particular form of rotor eccentricity is dominant; hence illustrating how faults can be identified in a motor using condition monitoring techniques.

Automotive Electric Propulsion Systems With Reduced or No Permanent Magnets: An Overview

Hybrid and electric vehicle technology has seen rapid development in recent years. The motor and the generator are at the heart of the vehicle drive and energy system and often utilize expensive rare-earth permanent magnet (PM) material. This paper reviews and addresses the research work that has been carried out to reduce the amount of rare-earth material that is used while maintaining the high efficiency and performance that rare-earth PM machines offer. These new machines can use either less rare-earth PM material, weaker ferrite magnets, or no magnets; and they need to meet the high performance that the more usual interior PM synchronous motor with sintered neodymium-iron-boron magnets provides. These machines can take the form of PM-assisted synchronous reluctance machines, induction machines, switched reluctance machines, wound rotor synchronous machines (claw pole or biaxially excited), double-saliency machines with ac or dc stator current control, or brushless dc multiple-phase reluctance machines.

An Improved Direct Torque Control for Three-Level Inverter-Fed Induction Motor Sensorless Drive

A sensorless three-level neutral-point-clamped inverter-fed induction motor drive is proposed in this paper. The conventional direct torque control (DTC) switching table fails to consider the circuit limitations, such as neutral-point-balance and smooth vector switching, caused by the topology of a three-level inverter. Two kinds of modified schemes for three-level DTC are proposed to solve these problems. They also provide performance enhancement while maintaining robustness and simplicity. Fuzzy logic control and the speed-adaptive flux observer (with novel gain and load toque observation) are introduced to enhance the performance of the system. The issue of large starting current is investigated and solved by introducing the technique of preexcitation. A 32-bit fixed-point DSP-based motor drive is developed to achieve high-performance sensorless control over a wide speed range. The effectiveness of the proposed schemes is confirmed by simulation implementation and experimental validation.

Development of a Magnetic Planetary Gearbox

In this paper, we describe a new design for a magnetic planetary gearbox. We discuss the theory of operation and a simulated design. We constructed and verified the simulation by measuring the transmitted torque and cogging torque. A magnetic planetary gearbox operates like a mechanical planetary gearbox, except that it is contact-free and needs no gear lubrication. Hence, it has the same characteristics of three transmission modes, a high-speed-reduction ratio, and high durability. The starting point for the design procedure is to avoid possible sliding (i.e., pole-slipping), and we propose three steps to obtain the maximum number of magnetic planet gears. We show that using more planetary gears is a way to increase the transmission torque. Cogging torque can be high in this design. We assessed this potential by using finite-element analysis and then measuring performance of the fabricated gearbox. While the simulation overestimates the cogging torque (for various reasons), we propose a method to reduce the cogging torque to a very low value. We present a literature review to illustrate the development of magnetic gearing and highlight the innovation of this design.

On-line current monitoring to diagnose airgap eccentricity in large three-phase induction motors-industrial case histories verify the predictions

An appraisal of on-line monitoring techniques to detect airgap eccentricity in three-phase induction motors is presented. On-line current monitoring is proposed as the most applicable method in the industrial environment and a novel analysis strategy is explained. The practical details of on-site case histories and analysis of the current spectra for each motor are presented. The results verify that the interpretation of the current spectrum proposed in this paper was successful in diagnosing airgap eccentricity problems in large, high voltage, three-phase induction motors.

Combined Thermal and Electromagnetic Analysis of Permanent-Magnet and Induction Machines to Aid Calculation

This paper reports on methods for the analysis of electrical machines by combined electromagnetic and thermal models using commercial software which can be an aid to the design of these machines. Examples using a brushless permanent-magnet motor and an induction motor illustrate the available tools and possible techniques. It reviews the different loss calculations, particularly iron losses, and also the thermal models that can be used, including steady state and transient (where thermal capacitances have to be included). This paper will be useful to an engineer in an industrial design office to illustrate the possibilities that are now possible.

Analysis and Design Techniques Applied to Hybrid Vehicle Drive Machines—Assessment of Alternative IPM and Induction Motor Topologies

In this paper, different analysis and design techniques are used to analyze the drive motor in the 2004 Prius hybrid vehicle and to examine alternative spoke-type magnet rotor (buried magnets with magnetization which is orthogonal to the radial direction) and induction motor arrangements. These machines are characterized by high transient torque requirement, compactness, and forced cooling. While rare-earth magnet machines are commonly used in these applications, there is an increasing interest in motors without magnets, hence the investigation of an induction motor. This paper illustrates that the machines operate under highly saturated conditions at high torque and that care should be taken when selecting the correct analysis technique. This is illustrated by divergent results when using I-Psi loops and dq techniques to calculate the torque.

Unbalanced Magnetic Pull Due to Asymmetry and Low-Level Static Rotor Eccentricity in Fractional-Slot Brushless Permanent-Magnet Motors With Surface-Magnet and Consequent-Pole Rotors

We report on an investigation into the unbalanced magnetic pull (UMP) in ferrite-magnet fractional-slot brushless permanent-magnet motors due to either magnetic asymmetry or static rotor eccentricity. We justify the work in terms of the establishment of total indicated runout (TIR) tolerance and use 10% eccentricity as the nominal tolerance. The UMP will generate force and vibration, which causes wear. We investigated several machines with different pole numbers, slot numbers, and winding arrangements. Some of the windings contain sub-harmonics, and we found these to be more susceptible to UMP when there is rotor eccentricity and also to produce vibrating UMP. We found that consequent rotor poles produce high UMP under centered and rotor eccentricity conditions. We conducted detailed finite-element studies to calculate the UMP.

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 and Analysis of Brushless Doubly Fed Reluctance Machines

Brushless doubly fed reluctance machines (BDFRMs) are a class of machines that may be controlled using a power converter that has a rating lower than the total power rating of the machine. The attractive properties of these machines have, in the past, been offset by low power density and efficiency when compared to other types of machines. Recent advances have shown that, when well designed, these machines are, in fact, capable of operation at high torque density and efficiency. However, little guidance on how to design these machines is available in the literature. This paper presents analytical approaches to design a BDFRM with desirable qualities and the use of time-stepped finite-element analysis to validate the results of the design process.