Björn Riemer

Rotor design of a high-speed Permanent Magnet Synchronous Machine rating 100,000 rpm at 10kW

Rotors of electrical high speed machines are subject to high stress, limiting the rated power of the machines. This paper describes the design process of a high-speed rotor of a Permanent Magnet Synchronous Machine (PMSM) for a rated power of 10kW at 100,000 rpm. Therefore, at the initial design the impact of the rotor radius to critical parameters is analyzed analytically. In particular, critical parameters are mechanical stress due to high centrifugal forces and natural bending frequencies. Furthermore, air friction losses, heating the rotor and the stator additionally, are no longer negligible compared to conventional machines and must be considered in the design process. These mechanical attributes are controversial to the electromagnetic design, increasing the effective magnetic air gap, for example. Thus, investigations are performed to achieve sufficient mechanical strength without a significant reduction of air gap flux density or causing thermal problems. After initial design by means of analytical estimations, an optimization of rotor geometry and materials is performed by means of the finite element method (FEM).

Calculation of the flux distribution of three phase five limb power transformers considering nonlinear material properties

Purpose – Depending on the load the flux‐density distribution inside power transformers core shows significant local variations due to stray fluxes which enter the transformer core. As saturation of the core has to be avoided the flux‐density distribution has to be determined early in the design stage of the transformer. This paper seeks to address these issues.Design/methodology/approach – To determine the load dependent flux‐density distribution the operating point of the transformer is calculated considering linear and non‐linear material properties. The operating point is determined using a linearised lumped parameter model of the transformer under various load conditions. Considering non‐linear material properties the inductance matrix depends on the operating point and will be extracted by means of the FEM whenever the magnetic energy within the transformer changes notably.Findings – This paper presents a numerical stable approach to calculate the operating point of a transformer by using the magnet...

The multi-slice method for the design of a tubular linear motor with a skewed reaction rail

A fundamental disadvantage of 3-dimensional finite-element simulations is high computational cost when compared to 2-dimensional models. However, for 3-dimensional specific features full models are essential, in principle. An approach to avoid this necessity is the multi-slice method. It is a well known procedure to determine the torque of electrical machines with a skewed rotor only deploying slices of the 3-dimensional full model. This paper presents the adoption of this method to a tubular linear motor and shows that it is applicable for this kind of machine as well. Furthermore, the number of slices and thereby computation time is minimised at the same accuracy of the simulation results.

Eddy Currents and Non-Conforming Sliding Interfaces for Motion in 3-D Finite Element Analysis of Electrical Machines

This paper presents non-conforming sliding interfaces for motion in 3-D finite element simulations. Sliding interfaces are favorable, especially for field circuit coupling in comparison to other approaches such as the Lockstep method because an arbitrary position of the rotor is possible. A previously presented approach by the authors is extended to take eddy-currents into account. The sliding interfaces approach utilizes specific Lagrange multiplier to handle the relative motion between stator and rotor which require a magnetic scalar potential formulation. The formulation is presented as well as methods to compute the mandatory cohomology basis functions.

The multi‐slice method for the design of a tubular linear motor with a skewed reaction rail

Purpose – A fundamental disadvantage of three‐dimensional finite element (FE) simulations is high computational cost when compared to two‐dimensional models. The purpose of this paper is to present an approach to minimize the computation time by achieving the same simulation accuracy.Design/methodology/approach – The applied approach for avoiding high computational cost is the multi‐slice method. This paper presents the adoption of this method to a tubular linear motor.Findings – It is demonstrated that the multi‐slice method is applicable for tubular linear motors. Furthermore, the number of slices and thereby computation time is minimized at the same accuracy of the simulation results.Practical implications – The results of this paper offer a faster computation of skewed linear motors. At this juncture, the results are independent from the deployed FE solver.Originality/value – The methods developed and proved permit a faster and more accurate design of tubular linear motors.