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

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

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

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

Energy Storage Technologies for Smoothing Power Fluctuations in Marine Current Turbines

With regard to marine renewable energies, significant electrical power can be extracted from marine tidal current. However, the power harnessed by a marine current turbine varies due to the periodicity of the tidal phenomenon and could be highly fluctuant caused by swell effect. To improve the power quality and make the marine current generation system more reliable, energy storage systems will play a crucial role. In this paper, the power fluctuation phenomenon is described and the state of art of energy storage technologies is presented. Characteristics of various energy storage technologies are analyzed and compared for marine application. The omparison shows that high-energy batteries like sodiumsulphur battery and flow battery are favorable for smoothing the long-period power fluctuation due to the tide phenomenon while supercapacitors and flywheels are suitable for eliminating short-period power disturbances due to swell or turbulence phenomena. It means that hybrid storage technologies are needed for achieving optimal performance in marine current energy systems

Inductances and back-emf harmonics influence on the Torque/Speed characteristic of five-phase SPM machine

In this paper, the study of torque/speed characteristic for five-phase Surface-mounted Permanent Magnet (SPM) machine is carried out. With considering several hypothesis (linear magnetic modelling, only first and third harmonic terms in the back-emf and current spectrums), an optimization problem that aims to maximize the torque for given maximum voltage and RMS current is formulated: the optimal torque sharing among the two virtual machines (the two dq-axis subspaces) that represent the real five-phase machine is thus calculated for any mechanical speed. For an inverter and a DC voltage sized with only considering the first harmonic of back-emf and current, the problem is solved with changing the ratio between the two virtual machine back-emfs and changing the ratio between the two virtual machine inductances. The results are examined by introducing particular speed points

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

A Comparative Study of Modular Axial Flux Podded Generators for Marine Current Turbines

International audienceThis research note deals with performance comparison of axial flux modular podded generators for marine current turbines (MCTs). Due to the submarine environment, maintenance operations are very hard, very costly, and strongly depending on sea conditions. In this context, the drive train reliability is a key feature for MCTs. For that purpose, a comparative study is proposed, to assess modular axial flux permanent magnet (AFPM) machines potential for reliability improvement. Thereby, designs of direct-drive modular AFPM generators for a given experimental MCT are performed. The proposed study shows that a pair number of spatially shifted AFPM machine modules, adequately associated, leads to the reduction of the electromagnetic torque ripples transmitted to the MCT shaft. Moreover, it is shown that the proposed module-based generator configuration achieves better thermal behavior. As the actives parts masses and costs are expected to be higher, compromises should be carried-out in terms of reliability and fault-tolerance

Design and Performance Analysis of Double Stator Axial Flux PM Generator for Rim Driven Marine Current Turbines

This paper deals with the design and performance analysis of double stator axial flux permanent magnet generators for rim-driven marine current turbines (MCT). Indeed for submarine applications, drive train reliability is a key feature to reduce maintenance requirements. Rim-driven direct-drive multi-stator generators can therefore be a very interesting solution to improve this reliability. In this context, the presented work focus on the design of a double-stator axial flux permanent magnets (PM) generator as a rim-driven direct-drive multi-stator generator. The paper details the models, specifications and an optimization procedure that allow to preliminary design these kind of generators for rim-driven marine turbines. Thereafter, validations with finite elements computations and performance analysis considering particular design of rimdriven generators are presented. The obtained results highlight some designs issues of PM generators for rim driven marine turbines. In order to assess the effectiveness of the double stator axial flux PM generator, a comparison with a designed surface mounted radial flux PM generator for rim marine turbines is carried out.. The comparison highlights that the double stator axial flux generator presents a better cooling and a reduced active parts cost and mass than the radial flux PM generator.International audienceThis paper deals with the design and performance analysis of double stator axial flux permanent magnet generators for rim-driven marine current turbines (MCT). Indeed for submarine applications, drive train reliability is a key feature to reduce maintenance requirements. Rim-driven direct-drive multi-stator generators can therefore be a very interesting solution to improve this reliability. In this context, the presented work focus on the design of a double-stator axial flux permanent magnets (PM) generator as a rim-driven direct-drive multi-stator generator. The paper details the models, specifications and an optimization procedure that allow to preliminary design these kind of generators for rim-driven marine turbines. Thereafter, validations with finite elements computations and performance analysis considering particular design of rimdriven generators are presented. The obtained results highlight some designs issues of PM generators for rim driven marine turbines. In order to assess the effectiveness of the double stator axial flux PM generator, a comparison with a designed surface mounted radial flux PM generator for rim marine turbines is carried out.. The comparison highlights that the double stator axial flux generator presents a better cooling and a reduced active parts cost and mass than the radial flux PM generator

Five-phase SPM machine with electronic pole changing effect for marine propulsion

In this paper, the possibility of designing a fivephase Surface-mounted Permanent Magnet (SPM) machine with 20 slots and 8 poles for a low power marine propulsion system is examined. Due to its particular winding and surface magnet design, the machine inherently offers an electronic pole changing effect from 3×4 pole pairs at low speed to 4 pole pairs at high speed. At high speed, in the constant power range, according to Finite Element Analysis, the Maximum Torque Per Ampere strategy appears not to be the right solution to minimize the whole machine losses (copper, iron and magnets). In particular, a strategy that favors the 4-pole rotating field at high speed allows to mitigate the magnet losses, thus limiting the risk of magnet overheating