Power quality issues of 3MW direct-driven PMSG wind turbine

This paper presents power quality issues of a grid connected wind generation system with a MW-class direct-driven permanent magnet synchronous generator (PMSG). A variable speed wind turbine model was simulated and developed with the simulation tool of PSCAD/EMTDC. The model includes a wind turbine with one mass-model drive train model, a PMSG model and a full-scale voltage source back to back PWM converter. The converter controller model is employed in the dq-synchronous rotating reference frame and applied to both generator and grid sides. To achieve maximum power point tracking, a tip speed ratio method is applied in machine side, whereas DC voltage control is applied in grid side to achieve constant DC voltage. Due to wind fluctuation and power oscillation as a result of wind shear and tower shadow effects (3p), there will be a fluctuation in the output power and voltage. The concerned power quality issues in this work are Harmonics, power fluctuation and flicker emission. The measurements will be carried out under different wind speed and circumstances

Contra-rotating marine current turbines : single point tethered floating system - stabilty and performance

The Energy Systems Research Unit within the Department of Mechanical Engineering at the University of Strathclyde has developed a novel contra-rotating tidal turbine (CoRMaT). A series of tank and sea tests have led to the development and deployment of a small stand-alone next generation tidal turbine. Novel aspects of this turbine include its single point compliant mooring system, direct drive open to sea permanent magnet generator, and two contra-rotating sets of rotor blades. The sea testing of the turbine off the west coast of Scotland in the Sound of Islay is described; the resulting stability of a single-point tethered device and power quality from the direct drive generator is reported and evaluated. It is noted that reasonably good moored turbine stability within a real tidal stream can be achieved with careful design; however even quite small instabilities have an effect on the output electrical power quality. Finally, the power take-off and delivery options for a 250kW production prototype are described and assessed

The small wind turbine field lab extensive field tests for small wind turbines

This paper describes the research possibilities at the Small Wind Turbine Field Lab and the involved research groups of Ghent University, covering different aspects of a small wind energy system. In contrast to large and medium-sized wind turbines, small wind turbines are still plagued by relatively high production and purchase costs, and low reliability and energy yield. Furthermore, most of them have not been subjected to a field test program. Power-Link, the energy knowledge platform of Ghent University, has for three years operated a modest field test site for small wind turbines, that drew the attention of a lot of manufacturers of small wind turbines. In response, Ghent University decided to launch the Small Wind Turbine Field Lab (SWT Field Lab), to subject small wind turbines to more extensive field tests. Now not only the energy yield is tested, but also topics such as grid integration, structural strength, noise propagation, generator and drive train design and tower construction are studied. All of these parameters are correlated with meteorological data measured on-site

Influence of the amount of permanent-magnet material in fractional-slot permanent-magnet synchronous machines

The efficiency of permanent-magnet (PM) synchronous machines with outer rotor and concentrated windings is investigated as a function of the mass of magnets used, keeping the power, volume, and mechanical air-gap thickness constant. In order to be useful for electric vehicle motors and wind turbine generators, the efficiency is computed in wide speed and torque ranges, including overload. For a given type and amount of magnets, the geometry of the machine and the efficiency map are computed by analytical models and finite-element models, taken into account the iron loss, copper loss, magnet loss, and pulsewidth-modulation loss. The models are validated by experiments. Furthermore, the demagnetization risk and torque ripple are studied as functions of the mass of magnets in the machine. The effect of the mass of magnets is investigated for several soft magnetic materials, for several combinations of number of poles and number of stator slots, and for both rare earth (NdFeB) magnets and ferrite magnets. It is observed that the amount of PM material can vary in a wide range with a minor influence on the efficiency, torque density, and torque ripple and with a limited demagnetization risk

Directly driven, low-speed permanent-magnet generators for wind power applications

The rotor of a typical wind turbine rotates at a speed of 20-200 rpm. In conventional wind power plants the generator is coupled to the turbine via a gear so that it can typically rotate at a speed of 1000 or 1500 rpm. The wind power plant can be simplified by eliminating the gear and by using a low-speed generator, the rotor of which rotates at the same speed as the rotor of the turbine. The hypothesis in this work is that the typical generator-gear solution in the wind power plant can be replaced by a low-speed PM synchronous generator. This thesis deals with the electromagnetic design and the optimisation of two types of low-speed generators for gearless wind turbines. The generators designed are radial-flux permanent-magnet synchronous machines excited by NdFeB magnets. The machines have different kinds of stator windings. The first machine has a conventional three-phase, diamond winding. The second machine has a three-phase, unconventional single-coil winding consisting of coils which are placed in slots around every second tooth. The electromagnetic optimisation of the machine is done by the finite element method and by a genetic algorithm combined with the finite element method. The rated powers of the machines optimised are 500 kW, 10 kW and 5.5 kW. Two prototype machines were built and tested. The optimisation of the machines shows that the cost of active materials is smaller and the pull-out torque per the cost of active materials higher in the conventional machines than in the single-coil winding machines. The torque ripple can be reduced to a low level by choosing a suitable magnet and stator slot shape in both the designs. The demagnetisation of permanent magnets is easier to avoid in the single-coil winding machines than in the conventional designs. The investigation of various rotor designs shows that the rotor equipped with curved surface-mounted magnets has various advantages compared with the other rotor designs, for instance pole shoe versions. The analysis of the machines also shows that the load capacity of the machine is lower in a diode rectifier load than that when connected directly to a sinusoidal grid. According to the analysis, a typical generator-gear solution of the wind power plant can be replaced by a multipole radial-flux PM synchronous machine. The conventional diamond winding machine is a better choice for the design of a directly driven wind turbine generator but the single-coil winding machine is also suitable because of its simplicity.reviewe

Optimal design and implementation of a drivetrain for an ultra-light electric vehicle

This paper presents an integrated design of a drivetrain for a single-person ultra-light electric vehicle (ULEV). To calculate losses and efficiency of the inverter, the permanent magnet synchronous machines (PMSMs) and the gearbox, parameterised analytical models are used. For the gearbox - which has a single gear ratio - the studied parameters are the gear ratio, the number of stages, the number of teeth and the module of each spur gear combination. The novelty of the paper is that it learns how the total average efficiency and the total mass of the drivetrain depend on the gear ratio, on the number of stages in the gearbox, on the motor parameters and on the chosen several driving cycles including the new European driving cycle (NEDC). On the basis of the presented results, it is possible to choose the right configuration of power electronics, PMSM and gearbox in order to have a good trade-off between high efficiency and low mass

PM wind generator topologies\ud

The objective of this paper is to provide a comparison among permanent magnet (PM) wind generators of different topologies. Seven configurations are chosen for the comparison, consisting of both radial-flux and axial-flux machines. The comparison is done at seven power levels ranging from 1 to 200 kW. The basis for the comparison is discussed and implemented in detail in the design procedure. The criteria used for comparison are considered to be critical for the efficient deployment of PM wind generators. The design data are optimized and verified by finite-element analysis and commercial generator test results. For a given application, the results provide an indication of the best-suited machine.\u

Design and Characteristic Investigation of Novel Dual Stator Pseudo-Pole Five-Phase Permanent Magnet Synchronous Generator for Wind Power Application

The main focus of this paper is to design and assess the characteristics investigation of Novel Dual Stator Pseudo-Pole Five Phase Permanent Magnet Synchronous Generator (NDSPPFP-PMSG) for wind power application. The proposed generator has a dual stator and two sets of five phase windings which enhance its power density and fault tolerant capability. The novelty of this generator is based on the fact that, eight magnetic poles are formed using only four poles of actual magnets on both the surfaces of the rotor. For the designing and optimal electromagnetic performance of the proposed generator, a Dynamic Magnetic Circuit Model (DMCM) is reported. To validate the results obtained from DMCM, Finite Element Method (FEM) has been opted owing to its high accuracy. For showing the performance superiority, the proposed generator is compared with two conventional generators namely, Dual Stator Embedded-Pole Five Phase (DSEPFP) and Single Stator Single Rotor Five Phase (SSSRFP) PMSG. To compare their performances, FEM results are considered. The electromagnetic performance namely, generated Electromotive Force(EMF), percentage(%) Total Harmonic Distortion(THD) of generated EMF, generated EMF vs speed, terminal voltage vs load current, electromagnetic torque developed on rotor vs time, %ripple content in the torque, and %efficiency vs load current are investigated for all the three generators. From these investigations, it is found that the power density (power to weight ratio) of the proposed generator is maximum.publishedVersio

Improved Design of Permanent Magnet Generators for Large Scale Wind Turbines

Direct-drive permanent magnet generators (DDPMGs) offer many benefits over traditional geared doubly-fed induction generators for large and offshore wind turbines. However, DDPMGs are used in less than 1% of utility scale wind turbines (\u3e100 kW) in the U.S. wind industry due to two major barriers: significant scaling of size and mass with rated torque and power, and the use of rare earth NdFeB permanent magnets. The former is due to the need to generate high torque at low speeds by increasing the volume of the PMG, while the latter is a concern due to the high cost of the critical rare earth materials. In this work, finite element methods were used to investigate methods to increase magnetic contribution to torque and allow for significant reduction in the PMG volume, or the use of hard ferrite permanent magnets that do not contain critical rare earth materials. To achieve these goals, the magnetic loading, or average magnetic flux density over the rotor surface of the PMG, must be increased to compensate for torque not generated from either the PMG volume or high energy density NdFeB permanent magnets. The magnetic properties of permanent magnets needed to achieve significant size reduction in a 10 MW PMG were calculated to provide insight into suitable material developments, and mechanisms by which permanent magnets contribute to torque and power were investigated. Practical approaches to concentrating the magnetic flux over the rotor surface were also investigated. The use of Halbach arrays and a novel rotor design incorporating electrical steel flux collectors in a 3.5 kW PMG were found to allow for up to 35% or 46% reduction in the outer diameter and axial length respectively compared to a PMG with surface mounted permanent magnets, or the use of hard ferrite, strontium iron oxide permanent magnets. Existing permanent magnet topologies were also investigated to determine which provided the highest magnetic loading and torque density to allow for size reduction. Finally, the political, environmental and social barriers to the lack of U.S. legislative action to secure a long-term, sustainable supply of rare earths were investigated

Harmonic effects on induction and line start permanent magnet machines

Power Electronics (PE) are implemented in a wide variety of appliances, either to increase its controllability or energy efficiency, or simply because a DC supply is needed. The massive integration of rectifiers has resulted in a decrease of the supply voltage quality. Although PE have enabled the end user to control electrical machines, the resulting distortion inversely affects Direct On-Line (DOL) machines. In this paper a review is presented of the influence of these supply anomalies on Induction Motors (IM). The suggested problems have already been subject of much study. However, as new DOL technologies are emerging, for example Line Start Permanent Magnet Machines or Induction Generator systems, the influence of supply distortion on these systems should also be considered. This paper will present a comprehensive overview of the loss mechanisms, the magnitude of the losses and the impact of these losses on operation of IM, LSPMM and IG