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

Ocean waves are a huge, largely untapped energy resource, and the potential for extracting energy from waves is considerable. Research in this area is driven by the need to meet renewable energy targets, but is relatively immature compared to other renewable energy technologies. This review introduces the general status of wave energy and evaluates the device types that represent current wave energy converter (WEC) technology, particularly focusing on work being undertaken within the United Kingdom. The possible power take-off systems are identified, followed by a consideration of some of the control strategies to enhance the efficiency of point absorber-type WECs. There is a lack of convergence on the best method of extracting energy from the waves and, although previous innovation has generally focused on the concept and design of the primary interface, questions arise concerning how best to optimize the powertrain. This article concludes with some suggestions of future developments.

https://journals.sagepub.com/doi/pdf/10.1243/09576509JPE782

A review of wave energy converter technology

This paper reviews the trends in wind turbine generator systems. After discussing some important requirements and basic relations, it describes the currently used systems: the constant speed system with squirrel-cage induction generator, and the three variable speed systems with doubly fed induction generator (DFIG), with gearbox and fully rated converter, and direct drive (DD). Then, possible future generator systems are reviewed. Hydraulic transmissions are significantly lighter than gearboxes and enable continuously variable transmission, but their efficiency is lower. A brushless DFIG is a medium speed generator without brushes and with improved low-voltage ride-through characteristics compared with the DFIG. Magnetic pseudo DDs are smaller and lighter than DD generators, but need a sufficiently low and stable magnet price to be successful. In addition, superconducting generators can be smaller and lighter than normal DD generators, but both cost and reliability need experimental demonstration. In power electronics, there is a trend toward reliable modular multilevel topologies.

Trends in Wind Turbine Generator Systems

This paper investigates the cost-effective ranges of gearbox ratios and power ratings of multibrid permanent-magnet (PM) wind generator systems by using a design optimization method. First, the analytical model of a multibrid wind turbine concept consisting of a single-stage gearbox and a three-phase radial-flux PM synchronous generator with a back-to-back power converter is presented. The design optimization is adopted with a genetic algorithm for minimizing generator system cost. To demonstrate the effectiveness of the developed electromagnetic design model, the optimization results of a 500-kW direct-drive PM generator and a 1.5-MW multibrid PM generator with various gear ratios are, respectively, compared with those from other methods. Then, the optimal design approach is further employed for a range from 750 kW up to 10 MW. The optimization results of PM generator systems including direct-drive and multibrid wind turbine configurations are obtained, and the suitable ranges of gear ratios for different power ratings are investigated. Finally, the detailed comparisons of the most cost-effective multibrid PM generator system and the optimized direct-drive PM generator system are also presented and discussed. The comparative results have shown that the multibrid wind turbine concept appears more cost-effective than the direct-drive concept.

Optimization of Multibrid Permanent-Magnet Wind Generator Systems

The utilization of renewable energy sources is a vital aspect for development of sustainability. Currently, an unexploited energy source is ocean waves. Various types of wave energy converters (WECs) are able to transform the motion of the waves into electricity. During the last 30 years, a wide range of prototypes was presented with different rates of success. The aim of this survey is to give an overview of how WECs are categorized [operation principle and power takeoff (PTO) system] and show what are the most important criteria that have to be kept in mind when designing a WEC. A few important WECs are described and evaluated.

Wave Energy Converter Concepts : Design Challenges and Classification

The objective of this paper is to give an introduction into ocean wave energy converters and their impact on power systems. The potential of wave energy is very large. There are a lot of different methods and systems for converting this power into electrical power, such as oscillating water columns, hinged contour devices as the Pelamis, overtopping devices as the wave dragon and the Archimedes wave swing. The main characteristics of these wave energy converters are discussed. A lot of research, development and engineering work is necessary to develop the experimental systems into reliable and cost-effective power stations. The wide variety of systems makes it difficult to say general things about power quality. However, the large variations of output power are a common problem. Whether this can be solved by using wave farms has to be investigated further

Wave energy converters and their impact on power systems

Permanent magnet (PM) machines with concentrated fractional-pitch stator windings are increasingly used because of their cost-effectiveness. In this paper, the eddy-current losses in the solid back-iron of these machines are modeled. This model is applied to calculate the losses in the solid back-iron of the linear PM generator of the Archimedes wave swing (AWS) for different combinations of numbers of poles and numbers of teeth. In machines with fractional-pitch windings, these eddy-current losses are considerable and depend strongly on the combination of number of teeth and number of poles. In fractional pitch machines with a coil around very second tooth, these losses are excessive.

/pdf/eddy-current-losses-in-the-solid-back-iron-of-pm-machines-1dzsu10pnq.pdf

Eddy-Current Losses in the Solid Back-Iron of PM Machines for different Concentrated Fractional Pitch Windings

The objective of this paper is to calculate the eddy-current losses in the solid back-iron of permanent-magnet (PM) machines with concentrated fractional-pitch stator windings. PM machines with fractional-pitch stator windings are increasingly used a lot because of their cost-effectiveness. The paper derives a model for these eddy-current losses. Although the correlation between the model and the measurements is not perfect, some important conclusions can be drawn. In machines with full-pitch distributed windings, the eddy-current losses in the back-iron are negligible, while in machines with fractional-pitch windings, these losses are too high to be acceptable.

M. Scuotto

Papers

Wave energy converters and their impact on power systems

Eddy-Current Losses in the Solid Back-Iron of PM Machines for different Concentrated Fractional Pitch Windings

Eddy-Current Losses in the Solid Back-Iron of Permanent-Magnet Machines with Concentrated Fractional Pitch Windings