This paper presents a comprehensive study on the state-of-the-art and emerging wind energy technologies from the electrical engineering perspective. In an attempt to decrease cost of energy, increase the wind energy conversion efficiency, reliability, power density, and comply with the stringent grid codes, the electric generators and power electronic converters have emerged in a rigorous manner. From the market based survey, the most successful generator-converter configurations are addressed along with few promising topologies available in the literature. The back-to-back connected converters, passive generator-side converters, converters for multiphase generators, and converters without intermediate dc-link are investigated for high-power wind energy conversion systems (WECS), and presented in low and medium voltage category. The onshore and offshore wind farm configurations are analyzed with respect to the series/parallel connection of wind turbine ac/dc output terminals, and high voltage ac/dc transmission. The fault-ride through compliance methods used in the induction and synchronous generator based WECS are also discussed. The past, present and future trends in megawatt WECS are reviewed in terms of mechanical and electrical technologies, integration to power systems, and control theory. The important survey results, and technical merits and demerits of various WECS electrical systems are summarized by tables. The list of current and future wind turbines are also provided along with technical details.

High-Power Wind Energy Conversion Systems: State-of-the-Art and Emerging Technologies

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

https://www.mikalsen.eu/papers/FPEreview.pdf

A review of free-piston engine history and applications

Data-driven design of robust fault detection system for wind turbines

Recently, automotive original equipment manufacturers have focused their efforts on developing greener propulsion solutions in order to meet the societal demand and ecological need for clean transportation, so the development of new energy vehicle (NEV) has become a consensus among governments and automotive enterprises. Efficient electrical energy storage system (EESS) appears to be very promising for meeting the rapidly increased requirements of vehicular applications. It is necessary to understand performances of electrical energy storage technologies. Therefore, this paper reviews the various electrical energy storage technologies and their latest applications in vehicle, such as battery energy storage (BES), superconducting magnetic energy storage (SMES), flywheel energy storage (FES), ultra-capacitor (UC) energy storage (UCES) and hybrid energy storage (HES). The research priorities and difficulties of each electrical energy storage technology are also presented and compared. Afterwards, the key technologies of EESS design for vehicles are presented. In addition, several conventional EESSs for vehicle applications are also analyzed; the comparison on advantages and disadvantages of various conventional EESSs is highlighted. From the rigorous review, it is observed that almost all current conventional EESSs for vehicles cannot meet a high-efficiency of power flow over the full operation range; optimization of EESS and improved control strategies will become an important research topic. Finally, this paper especially focuses on a type of linear engine, a brand new automotive propulsion system used for NEV; the guiding principle of EESS design for the new type of linear engine is proposed, an overview of a novel hybrid EESS based on hybrid power source and series–parallel switchover of UC with high efficiency under wide power flow range for the type of linear engine is presented, and advanced features of the novel hybrid EESS are highlighted.

Review of electrical energy storage system for vehicular applications

This paper analyzes rotor eddy-current loss in permanent-magnet brushless ac machines. It is shown that analytical or finite-element techniques published in literature for predicting rotor eddy-current loss using space harmonic based approaches may not yield correct results in each magnet segment when one magnet-pole is circumferentially segmented into more than two pieces. It is also shown that the eddy-current loss in each equally segmented piece may differ by a large margin, which implies that the temperature distribution in the magnets will be uneven and the risk of demagnetization has to be carefully assessed. The theoretical derivation is validated by time-stepped transient finite-element analysis.

/pdf/rotor-eddy-current-loss-in-permanent-magnet-brushless-ac-zu5a4m0cwj.pdf

Rotor Eddy-Current Loss in Permanent-Magnet Brushless AC Machines

This paper discusses issues that are pertinent to the design of a linear permanent magnet generator for application in a free-piston energy converter. To achieve the required high power density, high efficiency, and low moving mass, a tubular machine equipped with a modular stator winding and a quasi-Halbach magnetized armature is employed. It is shown that the machine design can be optimized with respect to three key dimensional ratios while satisfying other performance requirements. It is also shown that, when the generator is interfaced to an electrical system via a power electronic converter, both the converter volt-amps rating and the converter loss should be taken into account when optimizing the machine design. The performance of such a tubular generator is demonstrated by measurements on a 10-pole/9-slot prototype machine.

Design and Experimental Verification of a Linear Permanent Magnet Generator for a Free-Piston Energy Converter

A transverse flux machine (TFM) offers a higher specific torque and power density than a conventional radial flux machine, though at a cost of a poorer power factor. This paper provides an analytical approach to dimension an application-specific TFM and analyse its performance for first order calculations. Important features of TFMs are also outlined to facilitate an understanding of its operation and design. The design is explained with reference to an arbitrarily chosen application; a TFM wind generator. Only a surface mounted, single sided, outer rotor TFM generator design is treated. The method can however be equally applied to other types of TFMs, with proper adjustments of the analytical models.

Analytical design and analysis procedure for a transverse flux machine

The presented work is about a new low-leakage lineartransverse-flux electrical machine.The machine is dimensionedfor a free-piston generator. The intended application is inseries-hybrid vehicles. T ...

A Low-Leakage Linear Transverse-Flux Machine for a Free-Piston Generator

The objective of this paper is to review the possibilities of applying fault tolerance in generator systems for wind turbines based on what has been presented in the literature. In order to make generator systems fault tolerant in a suitable way, it is necessary to gain insight into the probability of different failures, so that suitable measures can be taken. Therefore, a literature survey of reliability of wind turbines, electrical machines and power electronic converters is given. Five different ways of achieving fault tolerance identified in the literature are discussed together with their applicability for wind turbines: (1) converters with redundant semiconductors, (2) fault tolerant converter topologies, (3) fault tolerance by increasing the number of phases, (4) fault tolerance of switched reluctance machines, and (5) design for fault tolerance of PM machines and converters. Because converters fail more often than machines, it makes sense to use of fault tolerant converter topologies. Increasing the number of phases is a useful form of fault tolerance because it can be achieved without increasing the cost significantly.

Fault tolerant generator systems for wind turbines

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