Showing papers by "Georges Barakat published in 2018"

Large wind turbine generators: State-of-the-art review

Abstract: This paper presents a broad overview of wind energy conversion generators in muti-megawatts wind turbines. Both technological and economic advantages and drawbacks of each generator system technology (geared and gearless) are detailed. Moreover, comparison based on weight, diameter, cost, energy yield and axial length between different electrical generators is discussed. This comparison helps us to find the suitable structure of generator system for high-power wind turbines. Additionally, recent developments on generators are introduced including some examples of their implementation in ultra-large operational wind turbines. Finally, this review could help to understand the potential future choices in the design of wind turbine energy conversion systems.

Global Quantities Computation Using Mesh-Based Generated Reluctance Networks

Abstract: Numerical methods and mostly finite element analysis (FEA) are popular in electromagnetic modeling because they are standardized methods and because of the availability of a large number of commercial software. However, the computation time may be prohibitive, especially for 3D models. Analytical models are fast but restricted in terms of magnetic saturation evaluation and geometry complexity. Magnetic Equivalent Circuits (MEC) are an excellent compromise as they are fast and take into account magnetic saturation. They are not as generic as FEA and if parameters vary, MEC models have to be readjusted [1–6]. Thus, model development durations are longer for MEC than for FEA. For more genericity, authors in [7–9] have demonstrated the equivalence between the equations of reluctance network (RN) and FEA method and the possibility to form RN matrix system by means of FEA. This paper presents the load analysis of a Permanent Magnet Linear Machine (PMLM) as a case study for a direct flux tube MEC method using an automatic Mesh Based Generated Reluctance Network (MGRN). The aim is to show that it is possible to quickly build a semi-numerical model of studied structures with an automatically generated MEC with accurate results on global and local quantities. Comparisons of iron losses evaluated by the use of the MGRN model show that results are in a very good agreement with those obtained byAnsys-Maxwell FEA [10] used as a reference. This approach can be used in a tool that allows the automated processing of an arbitrary geometry providing an accurate model in a shorter amount of time than needed for building a dedicated model. MESH BASED GENERATED RELUCTANCE NETWORK Geometry is discretized in a number of bidirectional elementary reluctance blocks (Fig. 1). The model is divided into zones according to geometry and material proprieties. Discretization can be made finer or coarser according to the desired precision. Central nodes of element blocks are connected via their branches. The advantage of using bidirectional block elements is that no previous knowledge of flux paths is necessary. Each mesh of the network of the final MEC will describe a possible path for flux to go through. The second advantage is to have access to normal and tangential components of local quantities such as flux density and magnetic field. Thus, forces can be evaluated using the Maxwell stress tensor and iron losses by means of Bertotti model [11]. Scalar magnetic potential is used to formulate and solve the nodal based matrix equation: $[\mathrm{U}] =[\mathrm{P}] ^{-1} [\Phi_{s}][\mathrm{P}]$ Permeance matrix [U] Scalar magnetic potential in each node $[\Phi_{s}]$ Sum of flux sources for each node n Total number of nodes The approach for solving the equation system as well as PMLM proprieties are given in [12]. A non-linear B-H curve is used for the ferromagnetic material and saturation is addressed with an iterative method as the value of permeability is adjusted in every ferromagnetic block element till convergence of the algorithm. The framework for space discretization, boundary conditions and PM sources assignment are explained in [13]. The PMLM is supplied with a 3-phase sinewave current and distribution of sources of magneto-motive force (MMF) due to coil currents is determined at each step. Fig 1 illustrates the geometry of the PMLM and the MMF distribution.Sources distribution MMF sources due to PM need to be placed on the branches of the magnetization direction (y axis) in the elements through all layers of the PM zones. Similarly, MMF sources due to coil currents are distributed on all elements of the teeth and slots. Total MMF according to position (along the x axis) is the sum of the MMF created by each coil. The ratio (height of element block to height of coil zone) is used to weight the MMF sources on each branch in each block of the winding zone (Fig. 1): mmf elem =(1/ 2)×E h Z h )× e(x node )e Total mmf according to position $\mathrm{x}_{node}$ Position of the central node of block mmf $_{elem}$: MMF on the branch of the block E h Element height Z h Zone height Saturation The permeability in the reluctances of the blocks in the ferromagnetic parts is initialized with the linear part of the B-H curve. Convergence criteria is magnetic energy in each block as a product of flux density and magnetic field at each step is compared to the one of the previous iteration till the difference no longer exceeds a pre-defined value. At each displacement step, the magnetic permeability value of the block elements are those of the previous magnetic state in the whole model i.e. the previous displacement step. \textit{Motion} A relative moving zone is defined including mover, PM and lower airgap region. The airgap is discretized in a way that the desired movement step is equal to the size of an element block in the airgap. This avoids non-conformal meshing problems and makes it easier to handle changes in matrix topology. \textit{Iron losses} The total iron losses In the MGRN model are calculated in post-processing and are the sum of hysteresis losses, eddy current and excess losses as shown in the equation: $\mathrm{P}= \mathrm{k}_{h} \quad f \mathrm{B}_{m}^{2} \quad + (\pi \sigma \mathrm{d}^{2}f^{2}/ 6 ) \int($ dB$/ \mathrm{d}\unicode{0x03B8} ) ^{2} \mathrm{d}\unicode{0x03B8} + (\pi \sigma \mathrm{d}^{2}f^{2}/ 6 ) \int\vert$ dB$/ \mathrm{d}\unicode{0x03B8} \vert ^{1.5} \mathrm{d}\unicode{0x03B8}$ Flux density values in each node of each reluctance block element are evaluated in the MGRN model using the same B(H) curve and material proprieties as implemented in the Ansys-Maxwell FEA model. Fig 2 shows comparisons of total iron losses (in all ferromagnetic parts i.e. stator and mover) vs frequency for the MGRN and the FEA models used as a reference at $\mathrm{I}_{max}=5\mathrm{A}$. It is shown that the results are in very good agreement.

Three-Dimensional Modeling of Permanents Magnets Synchronous Machines Using a 3D Reluctance Network

Abstract: For electromagnetic actuators whose magnetic fields are three-dimensional, the use of the 3D finite element (FE) method is required. On the other hand, 3D FE analysis is expensive in computation time, especially for high power machines involving potentially high numbers of nodes. In this paper, a 3D reluctance network (RN) modeling approach is proposed for the pre-design of permanents magnets synchronous machines (PMSM). The RN model developed is used to model three types of electrical machines (linear machine, radial field rotating machine and axial field rotating machine). Our goal is to establish lightweight models for the pre-design of electrical machines. The performances (local and global quantities) of these machines are evaluated using this 3D RN modeling. The results obtained from this approach are validated by comparison with results issued from the 3D FE analyses.

Reluctance network lumped mechanical & thermal models for the modeling and predesign of concentrated flux synchronous machine

Abstract: Abstract The aim of this paper is the multi-physical modeling of synchronous permanent magnet machines, dedicated to hybrid electrical vehicles application, using reluctance network lumped mechanical and thermal models. The modeling approaches are presented and validated by comparing the obtained results to those of finite element method with a close look to the airgap modeling and the consideration of soft magnetic materials non-linearity in the electromagnetic modeling. As well as a close look also on the conduction and convection heat coefficients for the machine different regions in the thermal modeling. Finally a focus on the mass, damping and stiffness matrix computation in lumped mechanical modeling taking into account the temperature influence on the materials mechanical properties. In addition a simplified rotating electrical machine is described and multiple coupled analysis were done in order to derive the structure magneto-vibroacoustic performances.

Computation of Cogging Force of a Linear Tubular Flux-Switching Permanent Magnet Machine Using a Hybrid Analytical Modeling

Abstract: Permanent magnet flux switching machines are gaining more and more interest due to their relatively good characteristics. Indeed, the presence of all magnetic field sources in the stator (armature windings, permanent magnets and/or field windings), which implies a completely passive rotor, makes it suitable for a large variety of applications [1] [2]. Different flux switching machines topologies have been studied in scientific literature. In this contribution, a relatively new modeling approach [3] based on the coupling of mesh based generated reluctance networks (MBGRN) and analytical models (AM), based on the formal solution of Maxwell’s equations, is used for the accurate prediction of cogging force of a linear tubular flux switching machine. This type of machines could be favorably used in oceanic renewable energy conversion. Figure 1(a) illustrates how the two approaches are combined for the case of a tubular linear flux switching structure. In this example the analytical solution is used for modeling the mechanical air-gap, and inner and outer airs, and the RN method is used to model the moving and static armatures. In order to have a more generic approach, the stator and moving armatures are modeled using mesh based generated reluctance network (MBGRN) technique [3]. This technique, as classical RN method, can be used with a minimum number of reluctances for regions where flux tubes are not highly affected by topology changes. As for finite elements analyses (FEA), the studied domain in MBGRN should be finely meshed in some regions (air-gap for example) and coarsely meshed in other regions. However, in contrast to FEA, the mesh relaxation in MBGRN can be done more easily conducting to reduced system matrix dimensions, and consequently reduced computation time. Indeed, while in FEA two adjacent elements should share an edge, it is no more necessary for RN method, as illustrated in Fig. 1(b). This new modeling approach has been used to analyze the performance of different electromagnetics devices (2D and 3D) [3]–[7]. In this contribution, this technique is used for the computation of cogging force of a linear tubular flux switching permanent magnet structure, something which has never been reported yet, to the best of our knowledge, in scientific literature. The goal is to further extend the investigation of this technique for the computation of relatively sensitive quantities, such as the cogging force, in more complex structures. Another goal is to highlight advantages of HAM as compared to other modeling techniques, and more particularly FEA, in order to obtain reduced order equations system [8] [9].

Cogging force reduction in linear tubular flux switching permanent-magnet machines

Abstract: Abstract The aim of this paper is to explore the possibility of using linear tubular flux switching permanent magnet machines in a free piston energy conversion (FPEC) system. In FPEC systems, acceleration and therefore speed are often relatively high, which impose to have a reduced number of poles, meanwhile the cogging force will be relatively high. In order to reduce the cogging force two techniques are combined. The analysis is done using finite element method.

3D Finite Element Analysis of Eccentricity in a Tubular Linear Permanent Magnet Machine

Abstract: In this paper, the translator eccentricity of a tubular linear permanent magnet (TLPM) machine is studied using a 3D finite element analyses. Translator eccentricity in linear machines, as rotor eccentricity in rotating machines, is inevitable. It should then be evaluated and studied during the design stage to avoid performance degradation and life time reduction. Apart from few publications, translator eccentricity in tubular linear machines has been rarely addressed in scientific literature. The aim of this study is to contribute to filling this gap. The effect of static eccentricity of the translator is studied for a surface mounted TLPM motor. While the novelty may seem limited, this study should be regarded as a step toward the development of modeling approaches allowing a good “accuracy/computation time” ratios.

Permanent magnet linear induction heating device: new topology enhancing performances

Abstract: Purpose This work aims to study a new design of linear permanent magnet transverse flux induction heating devices of nonmagnetic parallelepipedic workpiece. In these topologies, the permanent magnet inductor produces a static magnetic field, and the workpiece to be heated is subjected to a linear movement. To study the magnetothermal process, a new analytical coupling method between the magnetic and thermal phenomena is developed. This analytical model described in this study takes into account the variation of the physical properties of the heated workpiece. The analytical results are compared with good agreement to those issued from finite elements simulations, as well as those issued from measurements on an actual prototype. Design/methodology/approach The research methodology is based on analytical development of coupled problem, including the electromagnetic and thermal boundary problems. A strongly coupled magneto-thermal analytical model is developed; the time dependent magnetic problem is first solved by using the separation of variables method to evaluate the induced currents in the nonmagnetic plate and the resulting power density loss distribution. The plate temperature profile is then obtained, thanks to strong involvement of this magnetic model in a new analytical thermal model based on a synergy of separation of variables method and Green’s function transient regime analysis method. Findings The results show that an efficient transient magneto-thermal analytical model was developed allowing fast analysis of permanent magnet induction heater for deep heating of parallelepipedic workpieces. Developed model allows also fast and precise simulations of nonlinear and transient magneto-thermal phenomena for different types of permanent magnet induction heating devices. Practical implications The developed magneto-thermal analytical model can be used for fast designing of permanent magnet linear induction heating devices for moving parallelepipedic nonmagnetic workpiece. Originality/value A new analytical coupled model, including the electromagnetic and transient thermal boundary problem with additional algebraic equations and taking into account the nonlinearity, has been developed. The developed model accuracy was validated with a permanent magnet linear induction heating device. Developed coupled analytical model allows fast analysis and designing of such permanent magnet linear induction heating devices.

Performance Comparison of Different Winding Configurations of a Novel Wound-Field Flux-Switching Linear Machine

Abstract: This paper presents a study on a novel design of a Wound- Field Flux -Switching Linear Machine. Inspired by the rotating Wound-Field Switched Flux machine 18/10 topology, the concept has never been explotied in the case of a linear motor. Different armature winding configurations (double-layer and simple-layer configurations) are studied and compared with regards to open-circuit flux-linkage, force and force ripple. A non-linear Magnetic Equivalent Circuit model founded on Mesh Based Reluctance Network is developed with the purpose of addressing pre-design studies. The mesh based generated reluctance network model gives the possibility to make rapid changes in model proprieties and winding configurations. This semi-analytical model is validated using 2D Finite Element Analysis.

Fault Tolerant Performances of a Double Star PM Synchronous Machine under an IGBT Fault

Abstract: In this paper, the performances of a double star permanent magnet synchronous machine fed by two independent voltage source inverters are investigated in presence of an IGBT short circuit. The differential equations system governing the machine is based on equivalent magnetic circuit theory where inductances are calculated thanks to winding functions technique. The impact of the mechanical shift angle β between the two stars on the stator currents and the produced torque is then performed and discussed in both healthy and faulty cases. Simulation and experimental results are compared in a special case.