Generator Systems for Marine Current Turbine Applications: A Comparative Study

Emerging technologies for marine current turbines are mainly related to works that have been carried out on wind turbines and ship propellers. It is then obvious that many electric generator topologies could be used for marine current turbines. As in the wind turbine context, doubly-fed induction generators and permanent magnet generators seem to be attractive solutions for harnessing the tidal current energy. In this paper, a comparative study between these two generator types is presented and fully analyzed in terms of generated power, maintenance, and operation constraints. This comparison is done for the Raz de Sein site (Brittany, France) using a multiphysics modeling simulation tool. This tool integrates, in a modular environment, the resource model, the turbine hydrodynamicmodel, and generator models. Experiments have also been carried out to confirm the simulation results.Financement de thèse de Brest Métropole Océan

Modeling and Control of a Marine Current Turbine Driven Doubly-Fed Induction Generator

This paper deals with the modeling and the control of a variable speed DFIG-based marine current turbine with and without tidal current speed sensor. The proposed MPPT control strategy relies on the resource and the marine turbine models that were validated by experimental data. The sensitivity of the proposed control strategy is analyzed regarding the swell effect as it is considered as the most disturbing one for the resource model. Tidal current data from the Raz de Sein (Brittany, France) are used to run simulations of a 7.5-kW prototype over various flow regimes. Simulation results are presented and fully analyzedThis work has been funded by Brest Métropole Océan

Modélisation et commande d’une hydrolienne équipée d’une génératrice asynchrone double alimentation

Cet article traite de la modélisation et de la commande d’un système de récupération de l’énergie des courants de marée ; à savoir une hydrolienne équipée d’une génératrice asynchrone double alimentation. Dans un premier temps et dans le but de pouvoir évaluer les performances et la dynamique de l’hydrolienne, dans différentes conditions de fonctionnement, un modèle multiphysique est implanté sous Matlab/Simulink®. Ensuite, une stratégie de commande MPPT sans capteur de vitesse de la génératrice asynchrone est proposée. Cette stratégie est éprouvée en regard de l’effet de la houle qui est considéré comme le plus à même de perturber le modèle de la ressource. La modélisation multi-physique et la commande à vitesse variable ont été testés sur une hydrolienne équipée d’une génératrice asynchrone double alimentation de 7,5 kW et en utilisant des données réelles du site du Raz-de-Sein (Bretagne) pour l’année 2007.Financement de thèse de Brest Métropole Océan

Power Extraction Strategy of a Robust kW Range Marine Tidal Turbine Based on Permanent Magnet Synchronous Generators and Passive Rectifiers

This paper presents a kW range marine tidal current power generation system consisting of a fixed pitch marine current turbine (MCT) with two permanent magnet synchronous generators in the turbine shaft, two diode rectifiers (each rectifier is associated with a permanent magnet synchronous generator) and a DC source voltage. This system is designed for a kW range robust power supply. The specificity of the proposed system is that the two generators have different numbers of turns in their windings and the two rectifiers are in parallel in the same DC source. It has been demonstrated that the proposed system is able to harness very efficiently the energy of the turbine in the whole tidal cycle. The proposed system is interesting because it does not need complex control system and it allows minimizing converter losses costs due to electronic devices as controlled IGBT PWM converters usually used in conventional power generation systems. The analytical results have been confirmed numerically using PSIM software for two kW range generators with the same magnetic circuit and different winding number of turns

General modeling of the windings for multi-phase ac machines

This paper, which deals with the winding modeling of ac multi-phase machines with a regular distribution of the stator slots, details an original matrix modeling of the stator winding. First, the properties of the balanced multi-phase windings (with integral-slot and fractional-slot patterns) are analysed. The winding function approach, one of the most common way to model the winding distribution effects on the stator rotating field, is then introduced. For multi-phase machines, it will be shown that the pole number generated by the winding distribution depends on a new parameter: the circularity index. The discrete nature of the winding, imposed by the stator slots, leads to the development of a discrete modeling of the winding obtained from sampling the winding function: two matrices, the winding function matrix and the distribution function matrix, are introduced to characterize the multi-phase winding. This matrix approach is thus a concise way to calculate the winding factors and to estimate the set of self and mutual stator inductances for smooth air gap multi-phase machines. A particularly original method of obtaining an analytical expression for the leakage mutual inductance is described. The results are validated with two experimental 5-phase PM machines by using experimental measurements and numerical simulations

DFIG versus PMSG for marine current turbine applications

Emerging technologies for marine current turbine are mainly relevant to works that have been carried out on wind turbines and ship propellers. It is then obvious that many electric generator topologies could be used for marine current turbines. As in the wind turbine context, doubly-fed induction generators and permanent magnet generators seems to be attractive solutions to be used to harness the tidal current energy. In this paper, a comparative study between these two generators type is presented and fully analyzed in terms of generated power, maintenance and operation constraints. This comparison is done for the Raz de Sein site (Brittany, France) using a multi physics modeling simulation tool. This tool integrates, in a modular environment, the resource model, the turbine hydrodynamic model and the generators models

Investigations on the performances of the electrical generator of a rim-driven marine current turbine”

In this paper, the electrical generator of a rim-driven horizontal-axis current turbine is modeled in detail. Its main characteristics and performances are evaluated (efficiency, mass, cost, etc). This generator is of permanent magnet direct-driven synchronous type and is connected to a variable speed power electronics drive. It is then compared to a more traditional technology (a pod generator) in terms of mass and cost for a common set of specification. In addition, due to the specific geometry of the machine, the use of low-cost ferrite magnets is investigated in place of NdFeB magnets

Génératrice à aimants permanents à flux axial à grand diamètre avec entrefer immergé

Cette étude propose une méthode de modélisation et de conception adaptée aux machines à flux axial et à Double Stator (poly-entrefer) destinée à être intégrée comme génératrice pour une hydrolienne RIM-DRIVEN de grande puissance. La particularité du concept RIM-DRIVEN ou à entrainement circonférentiel réside dans le fait que la machine électrique se situe sur la périphérie de l’hélice. De plus, dans cette étude, l’entrefer de la machine est considéré immergé dans l’eau de mer. Les particularités du système imposent de mettre au point des modèles de dimensionnement adaptés. Ainsi, un modèle électromagnétique analytique 2D inversé permettant le calcul des dimensions géométriques principales est présenté. De même, un modèle thermique spécifique aux machines à entrefer immergé est décrit. Ces modèles permettent d’estimer la masse et le coût des parties actives. Cette machine à flux axial est comparée en termes de coûts matières, masses et comportement thermique avec une machine à flux radial à aimants permanents dimensionnée pour un même cahier des charges. Il en ressort clairement que la machine à flux axial double stator est thermiquement moins contrainte que les machines à simple stator

Comparizon of Conventional and Unconventional 5-phase PM Motor Structures for Naval Applications

Multi-phase motors are widely used in marine propulsion. In this paper, a Multi-machine modeling of Surface Mounted PM motors is presented and applied to a 5-phase one. The latter is proved to be equivalent to a set of two-phase fictitious machines each ones being characterized by a set of specific harmonic rank. A simple control consists in supplying each fictitious machine by a current which contains only one harmonic. A five phase machine is then supplied by currents with only both first and third harmonics. Considering this kind of control, it is proved that for given stator resistance and average torque the Joule losses and the torque ripple are minimized if a simple criterion on the harmonics of electromotive force at constant speed is fullfilled. Different structures of rotor are then compared to examine numerically which improvements can be practically obtaine

Power Smoothing Control of a Grid-Connected Marine Current Turbine System Using Supercapacitors

Les variations de la vitesse des courants marins induisent généralement de grandes fluctuations de la puissance produite par une hydrolienne. La houle est considérée comme principale source de variation à très court terme des vitesses de courants. Une stratégie MPPT conventionnelle nécessiterait dans ces conditions d’accélérer ou de décélérer fréquemment la turbine entraînant ainsi de fortes fluctuations de la puissance générée. Cet article se propose alors d’étudier le lissage de la puissance produite par une hydrolienne équipée d’une génératrice synchrone à aimants permanents à laquelle sera associé un banc de supercondensateurs. Le système sera commandé au moyen de stratégies de contrôle appropriées. Pour ce faire un algorithme de MPPT modifié associé à une stratégie de filtrage est proposé. Il utilisera plus particulièrement l’inertie du système pour atténuer les fluctuations de la puissance. Le système de stockage supercapacitif est ensuite utilisé pour lisser les fluctuations résiduelles. Des simulations sur une hydrolienne à entraînement direct de 1.5 MW connectée au réseau montrent que l’association de la stratégie de contrôle proposée à un stockage supercapacitif permet d’injecter une puissance relativement lisse au réseau en présence de perturbations liées à la houle.Variations of marine current speed can lead to strong fluctuations in the power extracted by a marine current turbine (MCT). During short-time period, swell effect is the main cause for the current speed variations. Conventional tip speed ratio Maximum Power Point Tracking (MPPT) algorithm will require the MCT to accelerate or to decelerate frequently under swell effect, which can cause severe fluctuations in the generator power. This paper focuses on power smoothing control of a PMSG-Based MCT system. A modified MPPT algorithm with filter strategy is proposed in generator-side control to use the system inertia for smoothing the fluctuation of generator power. When the current speed is over rated value, the power limitation control will be applied. In the second step, Supercapacitor (SC) Energy Storage System (ESS) is added to compensate the residual power fluctuations. Simulations of a 1.5 MW directdriven grid-connected MCT system are carried out. The results demonstrate that the association of the generator-side filter strategy with the SC ESS system achieves a smoothed power injected to the grid in case of swell disturbances