Efficient Finite Element Computation of Circulating Currents in Thin Parallel Strands

Electrical machines often utilize stranded parallel conductors to reduce the skin-effect losses. This practice can lead to uneven total current distribution among the strands, increasing the resistive losses. Direct finite-element (FE) analysis of circulating current problems can be computationally costly due to the large number of nodal unknowns in the FE mesh in the conductor domains. Methods to reduce the computational burden exist for special problems only. This paper proposes two efficient FE formulations to solve the circulating current problems with arbitrary winding configurations. According to simulations, the proposed methods yield reasonably accurate results significantly faster than the traditional brute-force approach.Peer reviewe

Reduced basis finite element modelling of electrical machines with multi-conductor windings

Finite element analysis of electrical machines withmulti-conductor windings can be computationally costly. Thispaper proposes a solution to this problem, using a reducedbasis approach. The field-circuit problem is first solved in asingle slot only, with a set of different boundary conditions.These pre-computed solutions are then used as shape functionsto approximate the solution in all slots of the full problem. Apolynomial interpolation method is also proposed for couplingthe slot domains with the rest of the geometry, even if thegeometries or meshes do not fully conform on the boundary. The method is evaluated on several test problems. Accordingto the simulations, accurate solutions are obtained. Furthermore,a speed-up factor of 30 is observed when analysing asix-slot phase belt of a high-speed induction machine.Peer reviewe

Reduced Basis Finite Element Modeling of Electrical Machines with Multiconductor Windings

Finite element analysis of electrical machines withmulti-conductor windings can be computationally costly. Thispaper proposes a solution to this problem, using a reducedbasis approach. The field-circuit problem is first solved in asingle slot only, with a set of different boundary conditions.These pre-computed solutions are then used as shape functionsto approximate the solution in all slots of the full problem. Apolynomial interpolation method is also proposed for couplingthe slot domains with the rest of the geometry, even if thegeometries or meshes do not fully conform on the boundary.The method is evaluated on several test problems both inthe frequency- and time-domains. According to the simulations,accurate solutions are obtained, 54-90 times faster compared tothe established finite element approach.Peer reviewe

Homogenization Technique for Axially Laminated Rotors of Synchronous Reluctance Machines

In this paper, we propose a homogenization technique to model the axially laminated rotor of synchronous reluctance machines. Thus, the computational effort can be significantly reduced by replacing the laminated parts of the rotor by some equivalent anisotropic media. The proposed method is validated in terms of flux density and electromagnetic torque. Some small discrepancies can be noticed due to the air-gap fluctuations caused by the steel sheets and the interlaminar insulation sheets of the rotor. With the test machine, the homogenization method reduces by the number of elements to one fourth and the computation time to one third.Peer reviewe

Domain Decomposition Approach for Efficient Time-Domain Finite-Element Computation of Winding Losses in Electrical Machines

Finite element analysis of winding losses in electrical machines can be computationally uneconomical. Computationally lightermethods often place restrictions on the winding configuration or have been used for time-harmonic problems only. This paperproposes a domain decomposition type approach for solving this problem. The slots of the machine are modelled by their impulseresponse functions and coupled together with the rest of the problem. The method places no restrictions on the winding and naturallyincludes all resistive AC loss components. The method is then evaluated on a 500 kW induction motor. According to the simulations,the method yields precise results 70–100 faster compared to the established finite element approach.Peer reviewe

Monte Carlo Analysis of Circulating Currents in Random-Wound Electrical Machines

Electrical machines with stranded random windings often suffer from considerable circulating current losses. These losses have been poorly studied because of the difficulty and computational cost of modelling stranded windings, and the stochastic nature of the problem due to the uncertain positions of the strands. This paper proposes two methods to model random stranded windings of arbitrary complexity. Firstly, a circuit model considering the entire main flux path is presented, and some practical implementation considerations are discussed. Secondly, a computationally efficient finite element approach based on non-conforming meshing is presented. Finally, a method is proposed to model the random packing process of strands within a slot, without any re-meshing or inductance re-calculation required. The proposed methods are then compared to special no-rotor measurement data of a large number of high-speed induction machines, and a good agreement is observed.Peer reviewe

Coupled Magneto-Mechanical Analysis of Iron Sheets Under Biaxial Stress

A novel single sheet tester design is proposed and a directly coupled magneto-mechanical model is used to numerically analyze the behavior of iron sheets under biaxial magneto-mechanical loading applied by the tester device. magneto-mechanically coupled constitutive equations of the material derived using an energy-based approach are integrated into a finite element model of the single sheet tester device, and simulations are performed to solve for the displacement field and the magnetic vector potential in the sample. The obtained numerical results of magnetostriction evolution due to uniaxial stress and stress-induced anisotropies due to permeability variation under different magneto-mechanical loadings are presented. The simulation results are compared with the results published in the literature for the purpose of validation.Peer reviewe