A new energy paradigm, consisting of greater reliance on renewable energy sources and increased concern for energy effi ciency in the total energy lifecycle, has accelerated research into energy-related technologies. Due to their ubiquity, magnetic materials play an important role in improving the effi ciency and performance of devices in electric power generation, conditioning, conversion, transportation, and other energy-use sectors of the economy. This review focuses on the state-of-the-art hard and soft magnets and magnetocaloric materials, with an emphasis on their optimization for energy applications. Specifi cally, the impact of hard magnets on electric motor and transportation technologies, of soft magnetic materials on electricity generation and conversion technologies, and of magnetocaloric materials for refrigeration technologies, are discussed. The synthesis, characterization, and property evaluation of the materials, with an emphasis on structure‐property relationships, are discussed in the context of their respective markets, as well as their potential impact on energy effi ciency. Finally, considering future bottlenecks in raw materials, options for the recycling of rare-earth intermetallics for hard magnets will be discussed.

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Magnetic materials and devices for the 21st century: Stronger, lighter, and more energy efficient

Fractional-slot concentrated-winding (FSCW) synchronous permanent magnet (PM) machines have been gaining interest over the last few years. This is mainly due to the several advantages that this type of windings provides. These include high-power density, high efficiency, short end turns, high slot fill factor particularly when coupled with segmented stator structures, low cogging torque, flux-weakening capability, and fault tolerance. This paper is going to provide a thorough analysis of FSCW synchronous PM machines in terms of opportunities and challenges. This paper will cover the theory and design of FSCW synchronous PM machines, achieving high-power density, flux-weakening capability, comparison of single- versus double-layer windings, fault-tolerance rotor losses, parasitic effects, comparison of interior versus surface PM machines, and various types of machines. This paper will also provide a summary of the commercial applications that involve FSCW synchronous PM machines.

Fractional-Slot Concentrated-Windings Synchronous Permanent Magnet Machines: Opportunities and Challenges

The influence of various design parameters on the cogging torque developed by permanent magnet machines is investigated. It is shown that the slot and pole number combination has a significant effect on the cogging torque, and influences the optimal value of both skew angle and magnet arc, as well as determining the optimal number of auxiliary teeth/slots. A simple factor, which is proportional to the slot number and the pole number and inversely proportional to their smallest common multiple, has been introduced to indicate the "goodness"/spl beta/ of the slot and pole number combination. In general, the higher the "goodness" factor the larger the cogging torque.

https://eprints.whiterose.ac.uk/889/1/zhuzq20.pdf

Influence of design parameters on cogging torque in permanent magnet machines

Energy is an essential ingredient of socio-economic development and economic growth. Renewable energy sources like wind energy is indigenous and can help in reducing the dependency on fossil fuels. Wind is the indirect form of solar energy and is always being replenished by the sun. Wind is caused by differential heating of the earth's surface by the sun. It has been estimated that roughly 10 million MW of energy are continuously available in the earth's wind. Wind energy provides a variable and environmental friendly option and national energy security at a time when decreasing global reserves of fossil fuels threatens the long-term sustainability of global economy. This paper reviews the wind resources assessment models, site selection models and aerodynamic models including wake effect. The different existing performance and reliability evaluation models, various problems related to wind turbine components (blade, gearbox, generator and transformer) and grid for wind energy system have been discussed. This paper also reviews different techniques and loads for design, control systems and economics of wind energy conversion system.

A review of wind energy technologies

Several techniques may be adopted in designing surface-mounted permanent-magnet motors in order to reduce the cogging torque. This paper describes various classical and innovative techniques, giving a theoretical justification for each of them. To this aim, a simple original model of the cogging torque mechanism and a Fourier analysis are introduced. As a result, it is highlighted that some techniques are not always utilizable, and some of them may even be deprecatory when not used correctly. In addition, effects of cogging torque elimination on back electromotive force are discussed.

Design techniques for reducing the cogging torque in surface-mounted PM motors

For the calculation of torque in brushless (BL) alternating current motors a local method is proposed, based on the Maxwell stress theory and the filtered contributions due to the harmonics of the magnetic vector potential in the motor air gap. By considering the space fundamental field only, the method can efficiently estimate the average synchronous torque for a variety or motor topologies, including concentrated winding designs. For BL direct current motor analysis a global method is introduced, based on the virtual work principle expressed in terms of energy components in various motor regions. The method leads to simplifications in the average torque calculation and enables the direct identification of the cogging and ripple components. The mathematical procedures have been validated against experiments and other numerical techniques.

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Assessment of torque components in brushless permanent magnet machines through numerical analysis of the electromagnetic field

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.

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

This paper describes an efficient calculating procedure for the steady-state operation of a single-phase line-start capacitor-run permanent-magnet motor. This class of motor is beginning to be applied in hermetic refrigerator compressors as a high-efficiency alternative to either a plain induction motor or a full inverter-fed drive. The calculation relies on a combination of reference-frame transformations including symmetrical components to cope with imbalance, and dq axes to cope with saliency. Computed results are compared with test data. The agreement is generally good, especially in describing the general properties of the motor. However, it is shown that certain important effects are beyond the limit of simple circuit analysis and require a more complex numerical analysis method.

/pdf/line-start-permanent-magnet-motor-single-phase-steady-state-364ofz4hu0.pdf

Line-start permanent magnet motor-single-phase steady-state performance analysis

The problem of choosing the firing angles within two average torque control schemes for switched reluctance motors, based on 'current control' and 'voltage control', respectively is examined. The primary goal is the maximisation of the energy conversion per stroke. Secondary goals of maximising efficiency (within current control) and obtaining approximately flat-topped current waveforms (within voltage control) are also considered. The main contribution is the development of a general theory of the optimal turn-off angle. When the theory is applied to a simple machine model. It leads to simple and explicit formulae for the optimal turn-off angle in the voltage and current control schemes. The model requires minimal machine data and the computational requirements are very modest. Comparison with experiment shows an accuracy that is believed to be more than adequate for practical purposes: greater accuracy would require an exhaustive search. It is believed that the method will be a valuable aid for the SR motor engineer in the field, and allow easier programming of variable-speed switched reluctance motor drives in the future.

Optimal commutation in average torque control of switched reluctance motors

This paper aims to define a minimum set of finite element solutions to be used in the design and analysis of saturated permanent-magnet motors. The choice of the finite element solutions belonging to this set is strictly associated with the classical d - q axis theory and it is described in terms of key points on the Flux-MMF diagram. When synchronous machine are considered, such a diagram has a regular shape, so that a huge reduction in finite element field solutions is possible with no loss of accuracy. It is also shown that the torque computed by using the d - q axis theory is almost independent of variation of the flux linkage with the rotor position. At last, the paper describes a technique in which few finite element solutions allow the identification not only of the average torque, but also the main torque harmonics. As a results, the torque behavior versus rotor position can be rapidly predicted.

T.J.E. Miller

Papers

Assessment of torque components in brushless permanent magnet machines through numerical analysis of the electromagnetic field

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

Line-start permanent magnet motor-single-phase steady-state performance analysis

Optimal commutation in average torque control of switched reluctance motors

MMF Harmonics Effect on the Embedded FE-Analytical Computation of PM Motors