The authors would like to extend their apologies for the inadvertent inclusion of an erroneous index of the matrix <inline-formula> <tex-math notation="LaTeX">{M} </tex-math></inline-formula> for ...DIZY-80 in <xref ref-type="bibr" rid="ref1">1 . We sincerely regret any inconvenience caused by this typographical error and appreciate the chance to rectify it.
Flywheel energy and power storage systems Bolund, Björn; Bernhoff, Hans; Leijon, Mats
Renewable & sustainable energy reviews,
02/2007, Volume:
11, Issue:
2
Journal Article
Peer reviewed
For ages flywheels have been used to achieve smooth operation of machines. The early models where purely mechanical consisting of only a stone wheel attached to an axle. Nowadays flywheels are ...complex constructions where energy is stored mechanically and transferred to and from the flywheel by an integrated motor/generator. The stone wheel has been replaced by a steel or composite rotor and magnetic bearings have been introduced. Today flywheels are used as supplementary UPS storage at several industries world over. Future applications span a wide range including electric vehicles, intermediate storage for renewable energy generation and direct grid applications from power quality issues to offering an alternative to strengthening transmission.
One of the key issues for viable flywheel construction is a high overall efficiency, hence a reduction of the total losses. By increasing the voltage, current losses are decreased and otherwise necessary transformer steps become redundant. So far flywheels over 10
kV have not been constructed, mainly due to isolation problems associated with high voltage, but also because of limitations in the power electronics. Recent progress in semi-conductor technology enables faster switching and lower costs. The predominant part of prior studies have been directed towards optimising mechanical issues whereas the electro technical part now seem to show great potential for improvement. An overview of flywheel technology and previous projects are presented and moreover a 200
kW flywheel using high voltage technology is simulated.
Variable speed generator systems (VSGs) are at work in the now 600 GW installed wind power plants (parks). Also, they are used as vehicular and on ground stand-alone generators. VSGs imply full kVA ...rating PWM converters in permanent magnet (PM) or in electrically excited synchronous or in cage rotor inductance generators. But, to reduce cost in absence of PMs at a reasonable initial cost (weight) and efficiency, the fractional kVA PWM converter doubly fed induction generators (DFIG) cover now about 50% of all installed power in wind generators. The present paper reviews recent progress in DFIG and various forms of brushless DFGs (doubly fed generators) characterized in terms of topology, design, performance and advanced control for healthy and faulty load conditions in the hope of inspiring new, hopefully ground breakings, progress for wind and hydro energy conversion and in vehicular and on the ground stand-alone generator applications.
This study presents a wind energy conversion system (WECS) with a diesel generator (DG). The proposed system with its control regulates the loading of DG to achieve a low-specific fuel consumption. ...The generator used in WECS is a doubly fed induction generator (DFIG). It consists of two voltage-source converters for the system control. The rotor-side converter helps in achieving the maximum power-point tracking of the wind turbine. The generator-side converter (GSC) helps in regulating the DG generation, while maintaining DFIG as well as DG currents balanced and harmonics within the requirement of the IEEE-519 standard for variety of loads. The system envisages an energy storage by connecting a battery bank at the dc bus of DFIG. The battery bank provides a buffer storage. The GSC also provides a path for the surplus or deficient power through the battery bank. The proposed system is modeled using Sim-power-system tool box of MATLAB and its performance results are presented for conditions such as synchronisation of the wind generator, variation of nonlinear and unbalanced loads, and varying wind speeds. Under all these scenarios, the currents flowing through both the generators are balanced. Finally, the effectiveness of the system is demonstrated experimentally on a prototype developed in the laboratory.
Trends in Wind Turbine Generator Systems Polinder, Henk; Ferreira, Jan Abraham; Jensen, Bogi Bech ...
IEEE journal of emerging and selected topics in power electronics,
09/2013, Volume:
1, Issue:
3
Journal Article
Peer reviewed
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.
Ocean waves are an abundant source of energy. This energy of the ocean can be converted into useful electrical energy using electrical generators. Linear generators have received tremendous attention ...in energy harvesting technology due to its unique ability to convert the energy without any intermediate converter. The principal objective of this study is to present the various types of linear electrical generators which have been investigated so far for direct drive ocean wave energy conversion and describe the working principle of each type with the difference. In this study, after a brief description of the basic electrical generator, various types of generators, including the linear and flat generators available in the literature are reviewed and discussed based on the design configuration of different types of magnet arrangements. Linear generators have been compared in terms of core type, flux path, the location of PMs, etc. The research gaps have been identified and future research directions have been suggested.
Properties of a class of groups on Z m Huang, Benwen; Zhang, Li; Wu, Xiaotao
Wuhan University journal of natural sciences,
2/2017, Volume:
22, Issue:
1
Journal Article
Peer reviewed
In this paper, we obtain the factorization of direct production and order of group GL(n, Zm) in a simple method. Then we generalize some properties of GL(2, Zp) proposed by Huppert, and prove that ...the group G L ( 2 , Z z λ ) is solvable. We also prove that group GL(n, Zp) is solvable if and only if GL(n, Zp) is solvable, and list the generators of groups GL(n, Zp) and SL(n, Zp). At last, we prove that PSL(2, Zp)(p > 3) and PSL(n, Zp)(n > 3) are simple.
The wind power generation is a rapidly growing grid integrated renewable energy (RE) technology with an installed capacity of 539.291 GW. The capability of the wind energy conversion system (WECS) to ...remain integrated into the utility network in the case of low voltage events is called low-voltage ride-through (LVRT) capability. This paper offers a comprehensive overview of improvement techniques of the LVRT capability in WECS to increase the wind energy penetration level in the utility grid. Exhibited portrait manifests a broad spectrum of 1) wind turbines, 2) electrical generators used for wind power applications, 3) international grid codes applicable for grid integration of WECS, 4) LVRT fundamentals in WECS, 5) wind turbines LVRT methods by doubly fed induction generator (DFIG), 6) wind turbines LVRT methods by permanent magnet synchronous generators (PMSG), and 7) LVRT methods of wind turbines using squirrel cage induction generator (SCIG). This ready-reckoner paper critically reviews and classifies more than 190 research papers on LVRT issues, practices, and available technologies for grid integration in wind energy systems, and it aims to be a quick reference for the researchers, designers, manufacturers, and engineers working in the same field.
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