Alasdair McDonald

10 MW Wind Turbine Direct-Drive Generator Design with Pitch or Active Speed Stall Control

The objectives of this paper are to investigate the feasibility of a 10 MW generator for a direct-drive wind turbine and to compare the generator systems for pitch control and for active speed stall control. The idea behind the active speed stall control concept is to make a rotor that is as simple as possible, and therefore very robust and suitable for offshore wind turbines. This is done by removing the pitch control of the blades. Above rated wind speed, the power is not controlled by controlling the pitch, but by controlling the rotor speed: the rotor speed is so much reduced that the aerodynamic power is limited to the rated value. A rough 10 MW permanent-magnet direct- drive generator design is presented, indicating that such a generator is feasible. It is shown that for a thorough evaluation of active speed stall control, more knowledge is required about changes in the wind speed. However, a considerable increase in generator system cost is necessary to enable active speed stall control.

Design and Testing of a Linear Generator for Wave-Energy Applications

A linear-generator topology is proposed for wave-energy applications. The main significance of the generator topology is that the relative position of the magnets, copper, and steels has been chosen so that there are no magnetic attraction forces between a stator and a permanent-magnet (PM) translator. The lack of magnetic forces and the modular nature of the generator topology make the manufacture and assembly of the generator easier than a conventional iron-cored PM linear generator. Analytical modeling techniques are described with a genetic-algorithm optimization method. The proposed topology is implemented to an Archimedes-wave-swing wave-energy converter. A 50-kW prototype has been built to prove the concept, and the no-load- and load-test results are presented.

Reliability Comparison of Wind Turbines With DFIG and PMG Drive Trains

Summary form only given. Modern wind turbines vary greatly in their drive train configurations. With the variety of options available it can be difficult to determine which type is most suitable for on and offshore applications. A large percentage of modern drive trains consist of either doubly fed induction generators with partially rated converters or permanent magnet generators with fully rated converters. These configurations are the focus of this empirical reliability comparison. The turbine population for this analysis contains over 1800 doubly fed induction generator, partially rated converter wind turbines and 400 permanent magnet generator, fully rated converter wind turbines. The turbines analyzed are identical except for their drive train configurations and are modern MW scale turbines making this population the largest and most modern encountered in the literature review. Results of the analysis include overall failure rates, failure rates per operational year, failure rates per failure mode and failure rates per failure cost category for the two drive train configurations. These results contribute towards deciding on the most suitable turbine type for a particular site as well as towards cost of energy comparisons for different drive train types. A comparison between failure rates from this analysis and failure rates from similar analyses is also shown in this paper.

A time series approach to design of a permanent magnet synchronous generator for a direct-drive wind turbine

The design of a permanent magnet generator for a wind turbine is studied. The best generator is chosen from a range of designs based on minimizing material cost and energy loss. The main loss mechanisms in an air-cored machine are copper and eddy current losses. The energy lost for each design is evaluated in the steady-state and then in the time domain so as to better take into account the thermal behavior of the machines.

The Ventilation Effect on Stator Convective Heat Transfer of an Axial-Flux Permanent-Magnet Machine

This paper investigates the effect of the inlet configuration on cooling for an air-cooled axial-flux permanent-magnet (AFPM) machine. Temperature rises in the stator were measured and compared with results predicted using computational fluid dynamic (CFD) methods linked to a detailed machine loss characterization. It is found that an improved inlet design can significantly reduce the stator temperature rises. Comparison between the validated CFD model results and the values obtained from heat transfer correlations addresses the suitability of those correlations proposed specifically for AFPM machines.

A direct drive permanent magnet generator design for a tidal current turbine(SeaGen)

In this study, the feasibility of a direct-drive permanent magnet generator for a tidal turbine power take-off system, namely MCTs SeaGen - the worlds first full scale commercial tidal turbine- has been investigated. The investigated PM generator topology is called C-GEN which is an air-cored axial-flux generator developed in the University of Edinburgh. The C-GEN is prior to conventional PM generators by absence of magnetic attraction forces between rotor and stator, absence of cogging torque, ease of manufacturing, modularity and high fault-toleration. Firstly, the integrated analytical design tool that couples electromagnetic, structural and thermal aspects of the generator has been introduced. Then, an optimization tool based on genetic algorithm has been used to maximize the annual electricity generation and to minimize the initial cost of the generator. The optimized generator is validated using FEA tools and the specifications of the generator has been presented.

A new concept for weight reduction of large direct drive machines

This paper looks into a new concept for reducing the structural weight of large direct drive generators used in wind turbines. The concept uses magnetic bearings to position the rotor of the machine. The weight of the rotor using the new concept is compared to a rotor designed with conventional methods. The comparison of a 5 MW generator rotor structural material shows about 45% reduction of weight of the rotor.

Integrated design of direct-drive linear generators for wave energy converters

Linear permanent magnet generators are a potentially useful technology for wave power applications. Typically, optimisation and comparison of these generators is based on an electromagnetic analysis with limited regard for the structural and thermal analysis. This paper presents a comparison of an air-cored synchronous machine and a double-sided iron-cored synchronous machine which includes the structural and bearing requirements for a more accurate cost comparison, and a discussion of the thermal issues. It is shown that both cost and feasibility depend heavily on these issues.

Linear generator for direct drive wave energy applications

A 50kW linear permanent magnet generator with a novel topology has been designed and built. The main significance of the generator topology is that there is no attractive force between the stator and permanent magnet translator. The magnetic force between the magnets is reacted within a self supporting structure. The lack of magnetic forces closing the airgap and the modular nature of the generator topology makes the manufacture and assembly of the generator easier than a conventional iron-cored permanent magnet linear generator. Photos of the manufacturing process are included in this paper. The modeling techniques used to design the generator are described and a summary of the design is presented.

Hydrodynamic and electromechanical simulation of a snapper based wave energy converter

A coupled electromechanical and hydrodynamic simulation of a novel generator connected to a heaving buoy for wave energy conversion has been developed. The simulation is based primarily in MATLAB using its built-in Ordinary Differential Equation (ODE) solvers. These solvers have acted on the data derived from an electromagnetic finite element analysis and from the WAMIT wave interaction simulation software, to simulate the full system in the time domain.