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

Inductive power transfer is a practical method for recharging electric vehicles because it is safe, convenient, and reliable. The performance of the magnetic couplers that transfer power determines the overall feasibility of a complete system. Circular couplers are the most common topology in the literature; however, they have fundamentally limited coupling. Their flux patterns necessarily limit the operational air gap as well as tolerance to horizontal misalignment. A new polarized coupler topology [referred to as a double D (DD)] is presented, which overcomes these difficulties. DDs provide a charge zone five times larger than that possible with circular pads for a similar material cost and are smaller. A 0.31-m2 DD enables 2 kW of power transfer over an oval area measuring 540 mm × 800 mm with a 200-mm air gap. Leakage magnetic fields have been investigated and show that circular and DD couplers operating under similar power transfer conditions produce similar levels. Both topologies can be designed and operated to ensure compliance with international guidelines.

Development of a Single-Sided Flux Magnetic Coupler for Electric Vehicle IPT Charging Systems

With rapid development of wind power technologies and significant growth of wind power capacity installed worldwide, various wind turbine concepts have been developed. The wind energy conversion system is demanded to be more cost-competitive, so that comparisons of different wind generator systems are necessary. An overview of different wind generator systems and their comparisons are presented. First, the contemporary wind turbines are classified with respect to both their control features and drive train types, and their strengths and weaknesses are described. The promising permanent magnet generator types are also investigated. Then, the quantitative comparison and market penetration of different wind generator systems are presented. Finally, the developing trends of wind generator systems and appropriate comparison criteria are discussed. It is shown that variable speed concepts with power electronics will continue to dominate and be very promising technologies for large wind farms. The future success of different wind turbine concepts may strongly depend on their ability of complying with both market expectations and the requirements of grid utility companies.

Overview of different wind generator systems and their comparisons

A detection method for use in a primary unit of an inductive power transfer system, the primary unit being operable to transmit power wirelessly by electromagnetic induction to at least one secondary unit of the system located in proximity to the primary unit and/or to a foreign object located in said proximity, the method comprising: driving the primary unit so that in a driven state the magnitude of an electrical drive signal supplied to one or more primary coils of the primary unit changes from a first value to a second value; assessing the effect of such driving on an electrical characteristic of the primary unit; and detecting in dependence upon the assessed effect the presence of a said secondary unit and/or a foreign object located in proximity to said primary unit.

Inductive power transfer

Inductive power transfer (IPT) was an engineering curiosity less than 30 years ago, but, at that time, it has grown to be an important technology in a variety of applications. The paper looks at the background to IPT and how its development was based on sound engineering principles leading on to factory automation and growing to a $1 billion industry in the process. Since then applications for the technology have diversified and at the same time become more technically challenging, especially for the static and dynamic charging of electric vehicles (EVs), where IPT offers possibilities that no other technology can match. Here, systems that are ten times more powerful, more tolerant of misalignment, safer, and more efficient may be achievable, and if they are, IPT can transform our society. The challenges are significant but the technology is promising.

Inductive Power Transfer

The objective of this paper is to compare five different generator systems for wind turbines, namely the doubly-fed induction generator with three-stage gearbox (DFIG3G), the direct-drive synchronous generator with electrical excitation (DDSG), the direct-drive permanent-megnet generator (DDPMG), the permanent-magnet generator with single stage gearbox (PMG1G), and the doubly-fed induction generator with single-stage gearbox (DFIG1G). The comparison is based on cost and annual energy yield for a given wind climate. The DFIG3G is a cheap solution using standard components. The DFIG1G seems the most attractive in terms of energy yield divided by cost. The DDPMG has the highest energy yield, but although it is cheaper than the DDSG, it is more expensive than the generator systems with gearbox

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Comparison of direct-drive and geared generator concepts for wind turbines

The objective of this paper is to compare five different generator systems for wind turbines, namely the electrically-excited and the permanent-magnet excited direct-drive generator system, the permanent-magnet and the doubly-fed induction generator system with single-stage gearbox and the doubly-fed induction generator system with three-stage gearbox. The comparison is based on cost and annual energy yield for a given wind climate. The doubly-fed induction generator with single-stage gearbox seems the most attractive in terms of energy yield divided by cost. The doubly-fed induction generator with three-stage gearbox is a cheap solution using standard components. The permanent-magnet direct-drive generator has the highest energy yield, but although it is cheaper than the electrically-excited direct-drive generator, it is more expensive than the generator systems with gearbox

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A complicating aspect in the control design of resonant inductive power transfer systems is the absence of a direct communication link between primary and (multiple) secondary system sides. This paper introduces a new adaptive sliding-mode control surface, which continuously adapts the inductive system's input power to the required, but unknown, variable load power. As a result, an indirect communication link is redundant. Furthermore, due to matching input and output power, optimum relative system efficiency is automatically guaranteed in the entire system's output power range. The controller design, which has a simple analog implementation, has been verified with a dual-load experimental contactless system.

Adaptive Sliding-Mode Control for a Multiple-User Inductive Power Transfer System Without Need for Communication

Recent improvements in semiconductor technology make efficient switching possible at higher frequencies, which benefits the application of wireless inductive energy transfer. However, a higher frequency does not alter the magnetic coupling between energy transmitter and receiver. Due to the still weak magnetic coupling between transmitting and receiving sides that are separated by a substantial air gap, energy circulates in the primary transmitting side without being transferred to the secondary receiving side. This paper introduces an energy control method that reduces energy circulation in the primary to zero. The method makes use of the fact that energy can be stored in a magnetic field by the primary side and absorbed by the secondary side. Furthermore, the secondary side converter topology is modified in order to boost the damping as seen by the primary converter at required times. Essentially, the control method realizes an energetic coupling factor of one between the air coils of the wireless transformer. The working principle of the control method has been verified with an experimental setup.

Control Method for Wireless Inductive Energy Transfer Systems With Relatively Large Air Gap

The technique of inductive contactless energy transfer (CET) has found its application in specific industrial applications where an (air) gap between energy source and load is preferable or even required. A relative new application area of CET is where CET is part of a general energy distribution network. As an example, electrical sockets might give problems in bathrooms for safety reasons: CET provides a solution because of inherent electrical isolation between source (grid) and loads (e.g. hair dryer or electrical shaver). For such application this paper reports on the design of a contactless power system that is able to supply to multiple users simultaneously, analogously to the regular plug-and-socket network. The proposed contactless system consists of a special energy supply cable where clamps (each maximum 240 W) can be mounted on at arbitrary locations along the cable while electrical isolation is maintained between cable and clamps. Result is a supply cable design and a prototype with 2 clamps, which are compared by means of analytical calculations, simulations and experimental results.

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F.F.A. Van der Pijl

Papers

Comparison of direct-drive and geared generator concepts for wind turbines

Comparison of direct-drive and geared generator concepts for wind turbines

Adaptive Sliding-Mode Control for a Multiple-User Inductive Power Transfer System Without Need for Communication

Control Method for Wireless Inductive Energy Transfer Systems With Relatively Large Air Gap

Design of an Inductive Contactless Power System for Multiple Users