Mfj Maarten Kremers

Relative Permeability in a 3D Analytical Surface Charge Model of Permanent Magnets

The analytical surface charge model is used to calculate the magnetic field of magnets in 3D in an unbounded domain. The method combines high accuracy with a short calculation time. However, in the classical method the relative permeability of the magnet is assumed to be equal to air. This introduces an error in the resulting magnetic field strength. In this paper the permeability of the magnet is taken into account in the form of a redistribution of magnetic surface charge. As such, an exact solution for the magnetic field at low relative permeability is obtained. The interaction force between two magnets is calculated using the newly obtained expressions for the magnetic field and compared with FEM and measurements.

Spatial Discretization Methods for Air Gap Permeance Calculations in Double Salient Traction Motors

Weight limitations in electric/hybrid cars demand the highest possible power-to-weight ratio from the traction motor, as in double salient permanent magnet (PM) machines. Their high flux densities in the air gap result in nonlinear analytical models, which need to be time optimized. The incorporated reluctance networks are sensitive to the correctness of air gap permeances. Conventionally, in these networks, air gap permeances are calculated by approximating flux paths; however, it is time inefficient. For an improved simulation time, spatial discretization techniques are presented to calculate air gap permeances in double salient PM machines. The spatial techniques discussed here cover the tooth contour method and Schwarz-Christoffel (SC) mapping as semidiscrete methods, which are used to discretize only the air gap region. Their results are verified by the spatial discrete method and finite element method, which discretizes the whole machine geometry. For consistency in this paper, all methods are explained on a three-phase 12/10 flux-switching PM motor. Obtained air gap permeances show a very good agreement with only 0.8% difference. Further on, machine characteristics such as phase flux linkage and cogging torque are also compared to show the impact of the modeling techniques. The total machine simulation time is improved by 20% using the SC method. Although methods are explained particularly for double salient PM machines, formulas are generalizable for other machine types as well.

Analytical flux linkage and EMF calculation of a Transverse Flux Machine

Transverse Flux Machines (TFM) exhibit 3-D flux patterns. Their analysis and design are generally based on 3-D Finite Element Methods (FEM). Previous analytical models were mostly limited to Magnetic Equivalent Circuits (MEC). The analytical model presented in this paper is used to perform extremely fast calculation of the flux linkage and EMF of a TFM. The analytical model uses a combination of the magnetic charge and magnetic imaging techniques to represent magnetic flux distribution within the air gap of a TFM. Furthermore, a suitable method to calculate the flux linkage of the TFM had to be determined to allow EMF calculation. This resulted in an analytical model which obtains a magnetic flux distribution with less than 10% error in the air gap. The calculated EMF, and therefore the flux linkage, is within 15% accuracy compared to the EMF measured for two prototypes.

Toward Accurate Design of a Transverse Flux Machine Using an Analytical 3-D Magnetic Charge Model

Low-speed high-torque applications, e.g., wind energy generation, favor high number of pole solutions. This usually results in a dominating leakage flux in traditionally radial or axial field machines, while the output power remains constant. Within transverse flux machines (TFMs), an increase in output power proportional to the number of poles is achieved by traversing the flux direction. However, TFMs still suffer from a relatively large leakage, reducing their application in present industries. In order to research this leakage, fast and relatively accurate 3-D models are essential. To date, finite-element models (FEMs) have been dominantly used to calculate these 3-D magnetic fields. However, the FEM requires a large number of elements, hence it is very time consuming (hours for a single solution). A fast and more accurate parameterized model is essential to maximize the power factor while maintaining a high torque density. In this paper, the validity of a 3-D analytical magnetic charge model is used to investigate its applicability to model TFM topologies. As such, an automated parametric search has been undertaken to minimize machine volume, i.e., without considering power factor although with fixed constraints on magnetic flux density and slot leakage. Although this does not provide a global optimized minimum, it is surely interesting for the experienced machine designer who wants to further understand the physics of this machine. To illustrate the accuracy of the magnetic charge model, the error of the final result of such a parametric search is compared with a 3-D FEM, which shows an error in force prediction of only 8.9%.

Design Considerations for Coreless Linear Actuators

Linear permanent magnet synchronous motors are often used in applications where a high accuracy is needed. This paper investigates the influence of the key design parameters on the performance of a linear actuator with vertically magnetized magnets and a magnet array with quasi-Halbach magnetization. The performance is modeled by means of analytical expressions of the three-dimensional magnetic field components and optimal design ratios and guidelines are established.

Semi-analytical 3-D magnetic charge model for force calculation of a Transverse Flux Machine

Modeling the 3-D flux patterns within Transverse Flux Machines (TFM) is one of the main challenges during their design. The analysis and design are often based on 3-D Finite Element Methods (FEM). Analytical models of TFMs are mostly limited to Magnetic Equivalent Circuits (MEC). This paper uses an analytical magnetic charge model to calculate the 3-D flux density in the air gap. An iterative approach allows for the modeling of flux focussing, resulting in a semi-analytical solution. Including flux focussing in the magnetic charge model results in a highly accurate prediction of the magnetic flux density in the air gap with less than 10% error. Furthermore, the cogging and attraction force of the machine are calculated for four topologies.

Reluctance network model for the in-wheel motor of a series-hybrid truck using Tooth Contour Method

Recently, series-hybrid drivetrains are given more emphasis over parallel-hybrid drivetrains due to their simplicity, freedom in implementation and higher efficiency. However, the modeling phase of such machines takes either long calculation time with numerical methods such as Finite Element Analysis (FEA) or produces low accurate results with Magnetic Equivalent Circuit (MEC) models. In this paper a method is used to build a reluctance network where high accuracy is obtained yet still with acceptable calculation time.

Design and optimization of a transverse flux machine using an analytical 3-D magnetic charge model

Offshore wind farms are gaining more attention in the development of new renewable energy sources at the expense of onshore wind farms. The higher energy yield of an offshore wind farm is the main advantage. The reliability and efficiency of the wind turbine is of great significance as the capital costs for installation and maintenance as well as the repair time are increased over onshore wind turbines. The reliability of the commonly used gearbox is low and when reliability is considered besides efficiency, the direct drive permanent magnet generator is favorable. Energy produced from renewable sources by direct drive generators requires operation at low speeds in the range of 10 to 90 rpm. A machine topology with a high number of poles and high force density is needed in order to keep losses, mass and size limited. The Transverse Flux Machine (TFM) makes it possible to have a high pole number and high power density as the space for the winding is independent of the space for the poles and magnet flux. A segment of a TFM is shown in Fig. 1.