Search

Almost all electricity in the UK is generated by rotating electrical generators, and approximately half of it is used to drive electrical motors. This means that efficiency improvements to electrical machines can have a very large impact on energy consumption. The key challenges to increased efficiency in systems driven by electrical machines lie in three areas: to extend the application of variable-speed electric drives into new areas through reduction of power electronic and control costs; to integrate the drive and the driven load to maximise system efficiency; and to increase the efficiency of the electrical drive itself. In the short to medium term, efficiency gains within electrical machines will result from the development of new materials and construction techniques. Approximately a quarter of new electrical machines are driven by variable-speed drives. These are a less mature product than electrical machines and should see larger efficiency gains over the next 50 years. Advances will occur, with new types of power electronic devices that reduce switching and conduction loss. With variable-speed drives, there is complete freedom to vary the speed of the driven load. Replacing fixed-speed machines with variable-speed drives for a high proportion of industrial loads could mean a 15–30% energy saving. This could save the UK 15 billion kWh of electricity per year which, when combined with motor and drive efficiency gains, would amount to a total annual saving of 24 billion kWh.

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

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

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.

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.

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.

We have investigated the effects of processing variables and methods on the density, structure and magnetic properties of soft magnetic composite (SMC) materials primarily for use in low loss applications. Two commercially available SMC materials from Hoganas AB, Sweden were used throughout the study. The materials differed only in terms of the solid state lubricant incorporated in the powder. This was sufficient to affect the density of pressed samples. Both monotonic and cyclic pressing regimes were used to compact the materials, with pressures sufficiently large to control the bulk mechanical properties of the samples produced (Hardness typically 1.6 GPa). Samples were heat-treated to both relieve any stresses imposed during pressing, and to control the final composition through oxidation or non-oxidation processes. Magnetic properties were observed using a vibrating sample magnetometer and Barkhausen noise analyser and electrical properties determined using a micro-ohmmeter. Both magnetic and electrical properties were observed to be strongly dependent on sample density and heat treatment.

This paper compares various types of current controllers, including a novel method based on flux control. A proportional integral (PI) control method is used initially, to control the current in a high-speed permanent-magnet synchronous machine. The performance of this simple PI loop is presented, Various improvements to the PI controller are investigated, and the change in performance examined. A new current control scheme based on a flux-linkage model of the machine is introduced. The performance of the model-based control is demonstrated and compared with the performance of the PI current controller. Factors affecting the accuracy of the model-based control are given. By incorporating these factors into the model, the performance of the flux controller is further enhanced.

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.

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.

This paper presents a new topology for three-phase Modulated Pole Machines. This new topology the “Combined Phase Modulated Pole Machine” is analysed and compared to the more traditional technology of three separate single phase units stacked axially with a separation between phases. Three- dimensional Finite Element calculations are used to compare performance of the machines under the same conditions, it is shown that the new Combined Phase topology produces a greater torque whilst reducing the number of components required to assemble the machine and increasing its mechanical integrity. (6 pages)

Presented in this paper are the theoretical aspects of node addition to a non-convex, multiboundary mesh of tetrahedral elements as used in finite element modelling. The method used is derived from Watson1 and Shenton and Cendes2 and is extended to deal with node addition on inter-material boundaries. Several situations are identified that result in an illegal insertion polyhedron (IP), these could be caused by the ‘constrained’ nature of the mesh, adjacent objects with different material properties, or degenerate node configurations. A new Delaunay algorithm is described that checks for illegal cases of the IP and then corrects them, this checking relies on the consistent ordering of the element nodes. It is shown that a particular type of illegal IP can easily be identified and corrected using this technique. The Delaunay algorithm is then applied to automatic mesh generation, and modification to the basic Delaunay algorithm is described so that previously meshed edges and faces of the current object being meshed are not deleted during the addition of subsequent nodes. This ‘protection’ method only becomes viable by recognizing the node ordering sense of the IP faces.

This paper presents the toroidally wound induction machine and argues that such machines could have advantages compared to traditional concentrically wound machines. The paper emphasises the importance of attenuating harmonics in induction machines, which can be achieved using toroidal windings whilst reaping the benefits of non-overlapped windings. The paper also discusses possible construction methods and how these could result in a higher slot fill factor because the stator winding can be wound directly onto the stator structure.

The design of switched-reluctance motors (SRMs) requires the calculation of the phase flux linkage of the motor as a function of rotor position and exciting current. The authors describe a new method to establish this variation using finite element techniques. The mesh preparation, boundary source and material data, equation solution, and extraction of machine data from the solution are all done completely automatically. The designer is thus removed from the numerical analysis chores that, formerly, greatly reduced effectiveness. The method has also been applied to flux linkage against position determination in permanent magnet machines. >

Solar powered aircraft require electric drives for the main propulsion system. It is critical that these drives provide both very high efficiency and low mass. This paper describes a permanent magnet machine drive, developed specifically for this application. The machine uses 6% silicon steel laminations to achieve very low iron loss, combined with a high pole number to minimize mass. The system has been developed to maximize efficiency, taking into account both power electronic and motor losses.

This paper examines fault tolerant power converter topologies and develops a technique for producing data to compare the reliability of topologies. The various states of fault-tolerant systems are modelled, following which reliability curves and failure rate data is constructed.

In this paper, the finite element method (FEM) is used to design a spiral flexure bearing that suits a previously designed reciprocating linear motor. Stroke, maximum stress, axial and radial stiffness are the main parameters that have been taken into account in designing the flexure bearing. Moreover, stacks are designed taking into account the change in the system mass due to the part of the flexure bearings that is included. The design is then validated experimentally.

This paper reports on the design of a linear single phase permanent magnet oscillating motor aimed at application in a domestic refrigerator. An initial prototype has been designed and tested which has allowed the validation of the design techniques used. From this basis the effect of the various design parameters has been investigated. This investigation helps in optimising the cost and efficiency of the design. It is found in this paper that the mover SMC parts can be shaped to reduce their weight. Also the paper shows the influence of the length of the stator teeth on the stroke. Moreover, the simulations show that mover legs can be reduced in length significantly without affecting the force. Furthermore, it is found that changing length between magnets affects the stroke. Also, the paper investigates the effect of changing the length of the stator slot opening on inductance. Finally, the mover thickness effect and the distance between the axis of symmetry and the middle of air gap are investigated in this paper.

The integrated design of a high-speed brushless dc motor with a matched gearbox allows for a given output power to be achieved through the use of a lower torque-rated and thus lower volume, lightweight motor. This paper investigates the optimum speed for a brushless dc machine/gearbox combination and reports on the design, construction and testing of a transmission comprising a 100,000 revs per minute brushless dc motor and a gearbox with an output of 6Nm at 1,577 revs per minute.

This paper presents a case study. An existing PMSM design was moved to a new application with higher operating temperatures and higher peak currents. Substantial rotor demagnetisation was observed in the new application where no problem had been observed previously. The causes of the demagnetisation are presented, along with analysis of the magnetic circuit. The analysis is correlated with experimental results. The effects of machine design are considered. A solution to the problem is proposed and tested and again the analysis is correlated with the results. Finally some guidelines are proposed for the design of robust PM machines and the associated drive electronics.

The increasing number of distributed power generation systems, and more specifically wind farms, has led to electricity network companies laying down specifications as to how these power sources interact with the grid. The system described here is intended to act as a controllable grid to aid in the testing of these and other systems. The system is based on a voltage source inverter followed by a low pass filter. In order to achieve accurate output voltage control, high bandwidth closed loop control is required. A multi-level inverter was used to exploit the higher switching speeds available with low voltage rating devices. Also the lower switching harmonics in multi-level inverter allows the filter cut-off frequency to be increased in order to achieve a higher bandwidth response. A unit was constructed with a nominal continuous rating of 7.5 kW and experimental results are presented

This paper considers the electrical actuation of aircraft wing surfaces, with particular emphasis upon flap systems. It discusses existing electro-hydraulic systems and proposes an electrical alternative, examining the potential system benefits in terms of increased functionality, maintenance and life cycle costs. The paper then progresses to describe a full scale actuation demonstrator of the flap system, including the high speed electrical drive, step down gearbox and flaps. Detailed descriptions are given of the fault tolerant motor, power electronics, control architecture and position sensor systems, along with a range of test results, demonstrating the system in operation

The virtual power system is a real time, real power level, controllable sink/source used to emulate electrical machines and load systems connected to a system which requires testing. This can significantly aid in the development and testing of power systems. An earlier development, the virtual machine concentrated solely on the emulation of a low power (7.5 kW) induction machine. However, the concept of power system emulation is particularly appropriate to higher power level applications, such as renewable energy systems. Therefore, this paper considers the development of a 145 kW virtual power system. At higher power levels, however, semiconductor devices switch at slower rates. This has an impact upon the maximum pulse width modulation switching rate which may be applied to the power electronics, and in turn results in slower current control loop implementation. This paper investigates the performance achievable from a 145 kW power system emulator

The paper describes the design and construction of an axial flux permanent magnet machine in which the teeth are manufactured from compacted insulated iron powder and the core back is formed from a strip-punched lamination formed, into a circle to grip the teeth. This new method of construction overcomes the problems associated with punching and winding axial flux machines formed using index-punched spirally wound laminations (the current state of the art). The construction has been shown to be mechanically stable and rather simple to manufacture. As well as production advantages it offers very high fill factor coils which can significantly enhance the performance of this type of machine

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

This paper describes research aimed at producing a shaft-line-embedded starter/generator for an aircraft gas turbine. This machine needs to run in a very high ambient temperature of around 350 degC, whilst at the same time having a very high specific output. A review is made of possible designs that highlights potential mechanical and thermal problems and which eliminates the use of some machine topologies. The paper suggests that an outer rotating segmented rotor switched reluctance motor topology could satisfy all the thermal, mechanical and electromagnetic requirements. An initial prototype has been constructed to allow verification of the design and the design methods used. Preliminary results indicate that the performance, size and thermal requirements can be achieved using a fully developed version of this machine

In safety-critical applications fault-tolerant electric drives and motors can be used. To avoid compromising the reliability of the drives and isolated motor windings, the control hardware must also be fault tolerant. In this work control hardware is separated into lanes, each with a designated power supply, electric drive, motor phase winding and position feedback sensor, all packaged into a single assembly. For a system to operate with a faulted lane, lanes must be able to cross-compare data and determine whether a lane has failed. A demonstrator controller drive has been produced for a multiple lane actuator with the ability to detect a failed lane and continue operation. For the first time, current shaping is implemented on a working prototype to produce instantaneous torque control, even in the event of a fault. This permits rated torque at all rotor positions when stationary and when rotating slowly and rated mean torque at high speeds, when the inertia of the system lets the drive ride through torque dips caused by the faulted phase.

This paper is concerned with the development of low cost, brushless dc, high volume of production electrical machines, exploiting the special properties of compacted, insulated iron powder (or soft magnetic composite, SMC). The specific market for the application of this technology is the various electrical drives used in the automotive sector, but the technology is generic to any high volume application. Methods of construction of the SMC magnetic core are examined closely with the aim to reduce costs to make SMC competitive with well established electrical machines, which use lamination steel for the magnetic core. A base design has been developed and prototyped, costs established and a new and lower cost alternative designed. © 2004 University of Newcastle upon Tyne, UK.

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.

This paper examines the performance of switched reluctance machines which employ a segmental rotor construction in preference to the usual toothed structure. Two 3 phase designs are considered, one in which the windings span a number of teeth and one in which they spin a single tooth. Two demonstrators have been built - one for each design type, and their performance is compared with both conventional SRMs and rare earth permanent magnet machines. Both static parameter and running test results are presented. It is shown how these machines can operate from a standard SRM converter: there is discussion of general operating experience, ranging from measurement of mean torque, voltage and current controlled operation to general thermal performance.

The group of soft magnetic composites (SMCs) have expanded by the introduction of new materials with significantly improved low-medium frequency properties, which has made SMCs a viable alternative to steel laminations in a range of new applications, such as rotating machinery, sensors and fast switching solenoids. SMC components are successfully manufactured using the powder metallurgy compaction process. The isotropic nature of the SMC combined with the unique shaping possibilities opens up 3D-design solutions. If carefully implemented advantages such as better performance, reduced size and weight, fewer parts and lower cost can be obtained. In this paper the SMC concept is presented i.e. the materials, part manufacturing and electromagnetic design. Possibilities and also limitations for SMC's are highlighted, prototype motors are described and finally some examples of commercial products are presented.

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 more 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 generator with air-gap winding. The paper also proposes a new transverse-flux permanent-magnet generator topology that could be suitable for this application. This new double double-sided TFPM generator has flux concentrators, magnets, and conductors on the stator, while the translator only consists of iron.

The group of Soft Magnetic Composites (SMCs) have relatively recently expanded by the introduction of new materials with significantly improved low-medium frequency properties, which has made SMCs a viable alternative to steel laminations in a range of new applications, such as rotating machinery, sensors and fast switching solenoids. SMC components are successfully manufactured using the powder metallurgy compaction process. The isotropic nature of the SMC combined with the unique shaping possibilities opens up for 3D-design solutions. If carefully implemented advantages such as better performance, reduced size and weight, fewer parts and lower cost can be obtained. In this paper the SMC concept is presented i.e. the materials, part manufacturing and electromagnetic design. Possibilities and also limitations for SMC's are highlighted, prototype motors are described and finally some examples of commercial products are presented.

This paper presents a permanent magnet servo motor, built with a powdered iron stator, which has been designed to take full advantage of the properties of the material. There are a number of important design features which are not possible with laminated cores. For example, the core back is axially extended over the end windings, the armature core components are sub-divided and pre-formed stator coils are used. The coils are pre-pressed to form a solid component with an exceptionally high fill factor (78%). The prototype offers far superior performance to a conventionally laminated commercial machine, manufactured in the same frame.

This paper describes iron loss measurements in a permanent magnet servomotor, which has a stator constructed with soft magnetic composites (SMCs). It is shown that whilst the SMC has significantly greater iron loss density than silicon iron steel, it has many other advantages. The SMC machine is shown to outperform its conventional laminated equivalent.

Consideration is given to the design of small brushless DC drives for applications such as laser scanners or gyros in which high speeds are coupled with the requirement for precise speed stability. The design features of these drives are discussed with attention being given to minimization of torque ripple and the control strategies necessary to limit speed oscillations, inherent in this type of drive, to give speed stability to better than five parts per million. Experimental results for speed stability for a commercially available drive are presented and a prototype drive for the application is described. >

This paper compares various types of current controller, including a novel method based on flux control. A PI control method is used initially, to control the current in a permanent magnet machine. The performance of this simple PI loop is presented. Various improvements to the PI controller are investigated and the change in performance examined. A new current control scheme based on a flux linkage model of the machine is introduced. The performance of the model based control is demonstrated and compared with the performance of the PI current controller. Factors affecting the accuracy of the model based control are given. By incorporating these factors into the model, the performance of the flux controller is further enhanced.

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.

Design and test results are reported for a vacuum cleaner universal motor with the stator core manufactured from compacted iron powder. The isotropic magnetic properties allow freedom to create better-shaped windings and savings in copper. The core is separated into poles and half-yokes, split on the axial centreline, allowing bobbin winding of the field and easy assembly. The motor uses the existing production rotor, brushes and bearings. Tests show the new motor to be near identical electrically, but slightly better than the existing machine when placed in the vacuum cleaner.

Power hand tool applications typically require a high output torque at modest speed. The product must be light, small and ergonomically designed. Forced air cooled DC motors or universal motors are typically used in combination with a step down gear box to achieve the required torque. This paper reports on some research which is seeking to produce better systems by producing very high torque density electrical machines. The work has sought to achieve this by using a combination of new materials, including both rare earth magnets and powdered iron, and novel topologies of machine. Two machines have been built: one uses conventional laminated construction for a radial field machine, the other uses powdered iron for a claw pole armature machine. Both machines contain a number of novel features; this paper gives the rationale behind each design and comprehensive test results thereby comparing their performance.

This paper establishes a specification and compares the relative merits of switched reluctance and permanent magnet motors for electric vehicle drives. It is shown that permanent magnet machines offer size advantages, but that the high costs of magnets relative to steel and copper gives much greater material costs for the permanent magnet machine.

This paper is concerned with reporting the design, construction and testing of a permanent magnet machine which has both axial and radial magnets and is the drive motor for an electric bicycle. The armature of a machine with multiple axes of magnetisation must be capable of carrying alternating flux in all three coordinate directions. Bonded iron powder has isotropic properties and its use for the core makes the motor possible. The result is that a very large magnet surface area is possible within the machine envelope, leading to high specific output per unit volume or weight. Bonded iron powder has been used as a core material for a very long time but it is only recently that magnetic properties have improved to the extent that the inherent advantages are not outweighed by the inferior magnetic properties (in comparison to laminations). The improvement has come about by thinner and higher temperature powder coatings, improved compaction and improved post compaction heat treatment. The paper is mainly concerned with reporting the motor, but the bicycle application also imposes specific design constraints. The concept has far wider application however and an attempt is made to set the motor's design in a wider reference frame.

In many applications the failure of a drive has a serious impact on the operation of a system. In some cases the failure results in lost production, whilst in others it may jeopardize human safety. In such applications it is advantageous to use a drive capable of continuing to operate in the presence of any single point failure. Such a drive is termed fault tolerant and the development of a fault tolerant drive is the aim of the research presented. Previous work by B.C. Mecrow et al. (see Seventh International Conference on Electric Machines and Drives, Durham, UK, IEE, p.443-7, 1995) has introduced the concept of a fault tolerant permanent magnet (PM) machine drive for safety critical applications. This drive was based on a novel design of PM machine with a high per unit reactance to limit fault currents. It is shown by A.G. Jack et al. (see IEEE Trans. Ind. Appls., vol.32, no.4, p.889-95, 1996) that the torque and power densities of this PM drive exceed those possible with an SRM drive. This previous work was undertaken on a small prototype machine without a power electronic converter. A new drive has now been built and extensively tested. It uses a similar topology to the prototype machine and is designed to an aircraft fuel pump specification, requiring 16 kW at 13000 rpm. This paper reports the key design attributes and provides detailed measured parameters. The machine is controlled by a power electronic converter using a separate "H bridge" to drive each phase. The controller, implemented via a DSP, uses the measured machine flux linkage to provide robust current control with high dynamic performance.