Electrical generators for direct drive systems: a technology overview

Mueller, Markus; Zavvos, A.

doi:10.1533/9780857097491.1.3

Cited by 15 publications

(12 citation statements)

References 42 publications

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“…A linear generator can take advantage of the heave motion of the wave and therefore linear generators are used in several different wave energy converters [4][5][6][7]. Drawbacks with linear generators for wave power is that they become very large due to the high forces and low velocities [8,9] and that the induced voltage varies in both frequency and amplitude [10][11][12][13]. Another drawback with linear generators is the partial stator overlap that can occur depending on the design [14].…”

Section: Introductionmentioning

confidence: 99%

Partial Stator Overlap in a Linear Generator for Wave Power: An Experimental Study

Frost

Ulvgård

Sjökvist

et al. 2017

JMSE

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This paper presents a study on how the power absorption and damping in a linear generator for wave energy conversion are affected by partial overlap between stator and translator. The theoretical study shows that the electrical power as well as the damping coefficient change quadratically with partial stator overlap, if inductance, friction and iron losses are assumed independent of partial stator overlap or can be neglected. Results from onshore experiments on a linear generator for wave energy conversion cannot reject the quadratic relationship. Measurements were done on the inductance of the linear generator and no dependence on partial stator overlap could be found. Simulations of the wave energy converter's operation in high waves show that entirely neglecting partial stator overlap will overestimate the energy yield and underestimate the peak forces in the line between the buoy and the generator. The difference between assuming a linear relationship instead of a quadratic relationship is visible but small in the energy yield in the simulation. Since the theoretical deduction suggests a quadratic relationship, this is advisable to use during modeling. However, a linear assumption could be seen as an acceptable simplification when modeling since other relationships can be computationally costly.

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Section: Introductionmentioning

confidence: 99%

Partial Stator Overlap in a Linear Generator for Wave Power: An Experimental Study

Frost

Ulvgård

Sjökvist

et al. 2017

JMSE

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“…With the aim of increasing the efficiency of the wind turbines, variable speed systems are normally employed, which optimizes the rotor speed as a function of the wind speed [3,4]: In these systems, the turbine runs at a tip speed ratio that ensures the turbine has maximum efficiency over most of its working range. Further advantages in variable speed systems comes from the fact that the turbine can operate as a flywheel, smoothing the torque variations; they are less sensitive to the characteristics of the wind footprint of a given location; and they are quieter [3,5,6]. In currently developed variable speed turbines, an over gear is used to couple the turbine with an electric generator.…”

Section: Introductionmentioning

confidence: 99%

Power-Split Hydrostatic Transmissions for Wind Energy Systems

2018

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In a wind turbine, if a continuously variable transmission is placed between the turbine rotor and the generator, the speed ratio can be tuned to match the variable rotor speed to the constant speed of the electric generator, thus eliminating the need to adapt the frequency to the grid. In this paper, power-split hydrostatic transmission (PS-HTS) architecture is proposed as a suitable continuously variable transmission for application to wind turbine systems. The performance of PS-HTS is modelled and compared with that of previously proposed architectures in which the hydrostatic transmission is placed in-line with traditional drives (in-line HTS). It is shown here that the PS-HTS can improve the annual energy production of a 250 kW rated power wind turbine of about 10–11% by employing a hydrostatic transmission with one-seventh the size of the one requested by in-line HTS architecture.

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“…On the basis of the criteria such as torque density, cost per unit (pu) of torque, efficiency, mass of active materials, outer diameter, total length, size, costs, annual energy efficiency, and energy efficiency pu of cost, the permanent magnet (PM) synchronous generator systems with high pole number are the most appropriate option in comparison with other generator systems used in the direct-drive wind power generation applications [3][4][5][6][7][8][9]. Comparison of the PM generator systems including the radial-flux PM, axial-flux PM (AFPM), and transverse-flux PM generator systems, based on the criteria such as the torque density, mass of active materials, axial length, and efficiency has shown that the axial-flux internal stator (AFIS) generator system with a slotted stator and two outer disk rotors is the best option for use in the direct-drive wind turbines [8].…”

Section: Introductionmentioning

confidence: 99%

Multi‐objective design and prototyping of a low cogging torque axial‐flux PM generator with segmented stator for small‐scale direct‐drive wind turbines

Arand

Ardebili

2016

IET Electric Power Applications

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The multi-objective design of an axial-flux permanent magnet (PM) generator with the yokeless and segmented armature is done, for use in the small-scale direct-drive wind turbines. Using the multi-objective genetic algorithm technique, an optimisation process is performed for maximising the efficiency and minimising the cost, size, and mass of active materials, considering the practical constraints of the wind generator. The Pareto optimal fronts are used to find the best solutions. Also, a comparative study is performed to determine the most appropriate configuration among 12 configurations with the different combinations of poles and stator segments. Then, the selected optimal configuration is analysed using the three-dimensional (3D) finite element analysis (FEA). The inherent cogging torque of the PM wind generator affects the cut-in speed and start-up of the turbine. Thus, to improve the turbine performance, especially at low starting speeds, the generator cogging torque should be reduced to an acceptable level. In this study, using a new and practical approach, the peak-to-peak value of the cogging torque is reduced largely (81.4%), without notable reduction in the generator loadability. A prototype of the designed generator is fabricated and tested. The experimental results show good agreement with the 3D FEA simulation results.

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Electrical generators for direct drive systems: a technology overview

Cited by 15 publications

References 42 publications

Partial Stator Overlap in a Linear Generator for Wave Power: An Experimental Study

Partial Stator Overlap in a Linear Generator for Wave Power: An Experimental Study

Power-Split Hydrostatic Transmissions for Wind Energy Systems

Multi‐objective design and prototyping of a low cogging torque axial‐flux PM generator with segmented stator for small‐scale direct‐drive wind turbines

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