A.G. Jack

A comparative study of permanent magnet and switched reluctance motors for high-performance fault-tolerant applications

Switched reluctance machines (SRMs) have been extensively researched for high performance aerospace applications because of their inherent fault tolerance. Recent work by the authors suggests that with careful design a similar degree of fault tolerance may be achieved with a permanent magnet machine (PM) at a significantly higher torque density than its SRM counterpart. This latter suggestion is of crucial importance in high performance applications, such as aerospace, where a low mass is essential. This paper is concerned with reporting measured results from a fault tolerant PM machine, and using these results to examine the relative merits of SR and PM technology for this application.

Conventional and TFPM linear generators for direct-drive wave energy conversion

The archimedes wave swing (AWS) is a system that converts ocean wave energy into electric energy. The goal of the research described in this paper is to identify the most suitable generator type for this application. Of the conventional generator types, the three-phase permanent-magnet synchronous generator with iron in both stator and translator is most suitable, because it is cheaper and more efficient than the induction generator, the switched reluctance generator, and the permanent-magnet (PM) generator with an air-gap winding. The paper also proposes a new transverse-flux PM (TFPM) generator topology that could be suitable for this application. This new double-sided moving-iron TFPM generator has flux concentrators, magnets, and conductors on the stator, while the translator only consists of iron.

Fault Ride-Through of Large Wind Farms Using Series Dynamic Braking Resistors (March 2007)

Fault ride-through (FRT) is required for large wind farms in most power systems. Fixed speed wind turbines (FSWTs) are a diminishing but significant sector in the fast-growing wind turbine (WT) market. State-of-art techniques applied to meet grid requirements for FSWT wind farms are blade pitching and dynamic reactive power compensation (RPC). Blade pitching is constrained by the onerous mechanical loads imposed on a wind turbine during rapid power restoration. Dynamic RPC is constrained by its high capital cost. These present technologies can therefore be limiting, especially when connecting to smaller power systems. A novel alternative technology is proposed that inserts series resistance into the generation circuit. The series dynamic braking resistor (SDBR) dissipates active power and boosts generator voltage, potentially displacing the need for pitch control and dynamic RPC. This paper uses a representative wind farm model to study the beneficial effect of SDBR compared to dynamic RPC. This is achieved by quasi-steady-state characterization and transient FRT stability simulations. The analysis shows that SDBR can substantially improve the FRT performance of a FSWT wind farm. It also shows that a small resistance, inserted for less than one

Design and testing of a four-phase fault-tolerant permanent-magnet machine for an engine fuel pump

This paper discusses the design and testing of an aircraft electric fuel pump drive. The drive is a modular, four-phase, fault-tolerant system which is designed to meet the specification with a fault in any one of the phases. The motor employed has a permanent-magnet rotor with the magnets arranged in a Halbach array to maximize the air-gap flux density. Exceptionally high electric loadings are obtained by flooding the entire motor with aircraft fuel, which acts as an excellent cooling agent. Theoretical results are compared with test results gained in conditions approaching those found in an aircraft. Tests are carried out on the unfaulted drive and with one of several fault scenarios imposed. The electrical and thermal performance of the drive is assessed, showing how the flooded fuel cooling has excellent performance without introducing significant drag on the rotor.

Operation of fault tolerant machines with winding failures

This paper examines winding faults in a demonstrator drive, based on a specification for an aircraft fuel pump. This drive has been designed with a degree of inherent fault tolerance and is capable of continued operation in the presence of a variety of faults. Some of the most severe faults arise from winding insulation failure within a phase of the machine. A method of detecting turn to turn short circuits which can result from winding insulation breakdown is presented, along with a strategy for continued post fault operation of the drive. The detection method operates in real time, requires no additional sensors and is sufficiently sensitive to detect even a single shorted turn.

The Analysis of Losses in High-Power Fault-Tolerant Machines for Aerospace Applications

This paper discusses the design of a fault-tolerant electric motor for an aircraft main engine fuel pump. The motor in question is a four-phase fault-tolerant motor with separated windings and a six-pole permanent magnet rotor. Methods of reducing machine losses in both the rotor and stator are introduced and discussed. The methods used to calculate rotor eddy current losses are examined. Full three-dimensional finite-element (FE) time stepping, two-dimensional (2-D) FE time stepping, and 2-D FE harmonic methods are discussed, and the differences between them and the results they produce were investigated. Conclusions are drawn about the accuracy of the results produced and how the methods in question will help the machine designer

Preliminary performance evaluation of switched reluctance motors with segmental rotors

This paper examines the performance of switched reluctance machines which employ a segmental rotor construction in preference to the usual toothed structure. Two three-phase designs are considered, one in which the windings span a number of teeth and one in which they span a single tooth. Two demonstrators have been built-one for each design type, and their performances are compared with both conventional switched reluctance motors (SRMs) and a rare earth permanent-magnet machine. It is shown how these machines can operate from a standard SRM converter: running test results are presented and there is a discussion of general operating experience, ranging from the measurement of mean torque, voltage, and current-controlled operation to general thermal performance.

The design of fault tolerant machines for aerospace applications

This paper discusses the design of a fault tolerant electric motor for an aircraft main engine fuel pump. The motor in question is a four phase fault tolerant motor with separated windings and a six pole permanent magnet rotor. Methods of reducing machine losses in both the rotor and stator are introduced and discussed. The methods used to calculate rotor eddy current losses are examined. 3D finite element, 2D finite element time-stepping and 2D finite element harmonic methods are discussed and the differences between them and the results they produce investigated. Conclusions are drawn about the accuracy of the results produced and how the methods in question helps the machine designer

Design and testing of a 4 phase fault tolerant permanent magnet machine for an engine fuel pump

This paper discusses the design and testing of an aircraft electric fuel pump drive. The drive is a modular, four phase, fault tolerant system which is designed to meet the specification with a fault in any one of the phases. The motor employed has a permanent magnet rotor with the magnets arranged in a Halbach array to maximise the air-gap flux density. Exceptionally high electric loadings are obtained by flooding the entire motor with aircraft fuel, which acts as an excellent cooling agent Theoretical results are compared with test results gained in conditions approaching those found In an aircraft Tests are carried out on the un-faulted drive and with one of several fault scenarios imposed. The electrical and thermal performance of the drive is assessed, showing how the flooded fuel cooling has excellent performance without introducing significant drag on the rotor.

Claw pole armature permanent magnet machines exploiting soft iron powder metallurgy

This paper describes a novel permanent magnet machine which uses a claw pole topology in the armature to produce a high performance machine. This machine is almost impossible to construct from laminated material, therefore a soft magnetic composite has been employed throughout the stator. The paper gives details of the constructional features and presents performance measurements for this machine.