D. Andessner

Analytical and experimental loss examination of a high speed bearingless drive

Bearingless drives have been intensely researched for over a decade since they represent a compact motor-bearing system fulfilling very special requirements. They provide all advantages of a typical magnetically levitated system, including the absence of mechanical wear and bearing friction. Therefore, an application for high-speed processes seems tempting. Nevertheless, there are no high-speed bearingless drives in industry so far and even in scientific research, their rated speed hardly exceeds 20krpm. One of the main obstacles on the way to rotational speeds of up to 100krpm are the occurring losses in stator, winding and air gap. This work deals with their analytical description, appropriate design steps of the drive system and a concluding experimental verification.

Measurement of the magnetic characteristics of soft magnetic materials with the use of an iterative learning control algorithm

The quality of finite elements simulations is depending on the used magnetic characteristic curves and material coefficients on a high degree. Especially in the automotive industry the power density of electric machines are tending to increase. Thereby the quality of a whole design optimization process for highly saturated magnetic circuits is depending on the accuracy of the material data. To measure the magnetic characteristics of materials at high field strengths and high frequencies, the losses in the coil and the material has to be reduced because of thermal influences. On the one hand the influence of the heating itself is unwanted and on the other hand, especially when small test specimen are used, the maximum measuring time is limited to the temperature and sometimes leads to bad control accuracies. To overcome this problem an iterative measurement cycle is introduced in this paper.

Development of a compact and low cost axial flux machine using soft magnetic composite and hard ferrite

Especially for automotive applications, the request for small, lightweight, powerful and cheap electrical machines is tremendous - not only for the drivetrain in electrical vehicles but also for ancillary components like air conditioning compressors, starters/generators or pumps. In terms of small size and high power to weight ratio, the use of permanent magnets, especially rare earth magnets is essential. However, rare earth permanent magnets(PMs) have several concerns caused by a very concentrated resource market, which has already caused unpredictable price increase or export restrictions. Therefore, it is the goal to avoid rare earth magnets on the one hand but, on the other hand, keep the characteristics of a machine for the automotive industry. The combination of hard-ferrite magnets and soft magnetic composites, combined in an axial flux motor topology is a promising approach to fulfill the requirements of a high power density, low-cost and rare earth magnet-free machine. The designed motor structure with ferrite PMs replacing the rare earth PMs and the results of three-dimensional finite element analyses are introduced in detail in this paper. Moreover, a prototype with 600W nominal output power was produced and tested.

Modeling, simulation and design of a claw pole machine using soft magnetic composites

Using soft magnetic composites (SMC) allows the construction of motor geometries with reduced complexity and high power density. In the automotive industry, these properties become more and more important. Regarding the suitability of SMC for electric machines, the claw pole motor turns out to be highly promising. This paper deals with the analysis and optimization of such a claw pole geometry. The initial design dimensions are achieved with the help of an analytic design parameter model. Furthermore, the details of the magnetic circuit are optimized with 3D finite element (FE) simulations. A comparison between the analytic model, the FE calculation and the measurements on the real system proves good coherence.

Accurate and Easy-to-Obtain Iron Loss Model for Electric Machine Design

Iron loss modeling is crucial for electric machine design. However, current models feature severe drawbacks. They are 1) very complex, and thus, can hardly be applied, 2) require very high effort for measuring and computation, and/or 3) are not very accurate. In this paper, a new modeling technique is introduced for calculating the instantaneous power loss in ferromagnetic materials without taking the magnetization history into account. A standard measurement setup and specimen shape is used. The considered approach comprises the required measurements, the nonlinear loss modeling by itself, and an extensive verification for different flux density waveforms and frequencies. In addition, a detailed qualitative comparison to well-known iron loss models is given. The presented technique gives very accurate results, while obtaining the model is comparably easy. Moreover, as the calculation of the instantaneous losses is not based on the previous magnetization state of the material, a modeling error for a particular instant of time has no impact on the subsequently calculated characteristics. In the future, this model should ensure a more accurate iron loss calculation for electric machine designs.

Fundamental wave analysis of the switched permanent magnet reluctance machine

In this paper the driving principle of a special permanent magnet excited synchronous machine, in the following called the switched permanent magnet reluctance machine (SPM), is discussed. The SPM is a promising variant of the brushless DC (BLDC) machine concerning design and robustness. The mechanical construction is similar to the switched reluctance motor (SRM), whereas the driving characteristics relate to the BLDC machine. The linear relation between torque and current results from the fact that the SPM uses permanent magnetic (PM) energy and is leading to a strong affiliation to the BLDC. Due to the fact that the fundamental frequency of the SPMs inductances differs from that of the BLDCs a fundamental wave calculation of the torque has been achieved and was analyzed in this paper.

Design of a measurement system for investigating the magnetic characteristics of soft magnetic materials for non-sinusoidal periodic excitations

Abstract This article is about the design of a measurement system for measuring the iron losses in soft magnetic materials exerted by periodic flux density characteristics. The losses are due to hysteresis and eddy currents effects. The aim is to predict the iron losses which occur in electric machines. Common loss modeling techniques are derived by considering sinusoidal flux density characteristics. As nowadays highly-utilized machine designs with special winding topologies are employed, the periodic flux density characteristics in a big part of the ferromagnetic components are far off from being sinusoidal. Hence, the here presented measurement system and the associated control are especially developed for analyzing any periodic flux density characteristics. A further part of this article is dedicated to the comparison of state-of-the-art iron loss modeling techniques and measurement results. Several scenarios with different flux density harmonic magnitudes and frequencies are considered. It turns out that currently available loss modeling techniques show significant modeling errors for non-sinusoidal periodic flux density excitations. Thus, future work has to be on deriving more accurate models by considering their applicability for computer-aided engineering software.

Current feed optimization for the switched permanent magnet reluctance machine

In this paper the driving principle of a special permanent magnet excited synchronous machine, in the following called the switched permanent magnet reluctance machine (SPM), is discussed. The SPM is a promising variant of the brushless DC motor concerning design and robustness. The mechanical construction is similar to the switched reluctance motor (SRM), whereas the characteristics relate to the brushless DC motor. The linear relation between torque and current results from the fact that the SPM uses permanent magnetic (PM) energy and is leading to the comparison with the BLDC. Due to the fact that the resulting flux in one coil depends on all inductances (PM, mutual and self) the question for an effective current feed method came up. With the help of an electromechanical model an optimization process has been done and is presented. Furthermore with the help of the model the resulting torque of the SPM can be split into the different parts. Hence, the mutual dependencies of torque, power factor, efficiency and current can be explored.

Design of a rotational iron loss measurement system

Abstract This article is about the design of a measurement system for measuring iron losses in soft magnetic composites under controlled circular flux density patterns. With conventional measurement setups for iron loss determination, material samples are usually magnetized along a single spatial direction. However, in some parts of electrical machines magnetization loci over time substantially divert from the patterns used during conventional alternating loss measurements. Based on previous findings, iron losses strongly depend on the actual two dimensional magnetization locus over time. Therefore, the measurement with alternating magnetization cannot fully reflect the magnetizing conditions and iron losses present during machine operation. Available data especially for soft magnetic composites (SMC) regarding rotational losses is very limited. Hence, in this article a new measurement setup for the investigation of iron losses under controlled circular flux density loci was designed. It turns out, that iron losses show a significant deviation when comparing alternating and rotational losses with regard to the flux density magnitude and frequency.

Modeling, simulation and design of an axial flux machine using soft magnetic composite

Soft Magnetic Composites (SMC) allow the construction of electrical machines with three dimensional flux paths with maintainable effort, yielding high efficiency and outstanding power density. These are the typical requirements of automotive companies. The benefits of SMC-materials meet the demands of axial flux machines (AFM) very well, which offer a high power to weight ratio. This paper deals with the analysis and optimization of the AFM geometry. An analytical model defines the initial design parameters. Furthermore, the details of the magnetic circuit are optimized using 3D finite element (FE) simulations. Finally, the analytical model and the FE calculation are compared.