Knut A. Kasper

Calculation of the Acoustic Noise Spectrum of SRM Using Modal Superposition

This paper presents a method to calculate the harmonic content of stator vibrations and acoustic noise resulting from radial force excitations in switched reluctance machines (SRM). The method is based on a thin cylinder approximation of the stator. The eigen modes are represented by their transmission impedance. The spectral composition of the vibrations can be calculated using superposition of the eigen modes and vibrations caused by all phases of the SRM.

Temperature Rise Analysis of Switched Reluctance Motors Due to Electromagnetic Losses

We present a finite-element analysis of the temperature rise of switched reluctance motors (SRM) due to electromagnetic losses. We estimate the various components of electromagnetic losses, including core loss in the lamination as well as copper and eddy-current losses in windings, and then predict the temperature rise within the motor due to these losses. We present simulation results for an 8/6 SRM and discuss various aspects of thermal design of SRMs. To validate the procedure for the estimation of electromagnetic losses, we compare predicted and measured losses.

Vibration Synthesis for Electrical Machines Based on Force Response Superposition

A universal and modular approach for synthesizing electromagnetically excited vibrations in electrical machines is presented. The synthesis process uses force responses, i.e., the normalized structural vibration responses for a machines generic set of force excitation shapes. The responses are superposed after scaling by the operating point dependent force excitation amplitudes. This leads to a computationally efficient process. It allows to use detailed structural 3-D models and to synthesize the vibrations in the entire operating range of the machine. For validation, measured and synthesized vibration spectrograms of a run-up test of an interior permanent magnet traction motor are presented.

Noise Reduction Control Strategies for Switched Reluctance Drives

The usage of switched reluctance machines (SRMs) in acoustically critical applications like vehicles requires low noise emissions. This paper gives a brief introduction to noise development in SRMs with a special focus on the influence of the radial force. Based on this analysis in the time and the frequency domain, several noise reduction control strategies are presented and investigated for their effectiveness using simulation techniques and measurements. One of them is a new approach for partial load operation applying a single current pulse close to the unaligned position

Acoustic noise in switched reluctance drives: an aerodynamic problem?

In this paper, it is shown that under certain conditions aerodynamic sources dominate the acoustic noise emission of switched reluctance drives. It is indicated how the noise sources can be easily identified experimentally. Additionally, simple measures to reduce aerodynamic noise are presented

High-speed switched reluctance drives: A promising alternative to power electric vehicles

Since electric vehicles are becoming increasingly popular, there will be a large market for electric machines to power them. The typically applied rotating field machines, however, are not cost-efficient. Thus, the aim of this paper is to present an inexpensive alternative to power future electric cars using high-speed switched reluctance drives. Hereby, a conventional medium-speed and a high-speed switched reluctance machine were both designed to study the influence of high speed on power density, efficiency and acoustics. It was found that the proposed high-speed drive enhances power density and acoustics. Moreover, the simulated efficiencies of the FTP72 drive cycle of both the medium-speed and high-speed drive were comparable. In conclusion, the power density of high-speed switched reluctance drives is comparable to that of conventional drives. Importantly the decrease in drive-cycle efficiency of highspeed switched reluctance drives is negligible. Consequently, these new drives offer a promising alternative to power future electric cars.

Psychoacoustic quantities and their relevance for sound-quality optimization of switched reluctance machines

This paper gives a brief introduction to noise development in switched reluctance machines (SRMs) and presents psychoacoustic quantities that allow an objective evaluation of their sound quality by taking into account the characteristics of the human hearing system. The relevance of these quantities is determined by listening tests and statistical analyses. The goal of this work is to demonstrate that a successful acoustic optimization of a SRM should be performed based on both technical and psychoacoustic know-how

Noise Radiation of Switched Reluctance Drives

To simulate noise emissions of switched reluctance machines (SRMs), the entire signal transmission chain has to be modeled, starting with the radial force and ending with the radiated sound. Especially the last element of this transmission chain, the radiation characteristic of an SRM, is very rarely addressed in literature. This paper gives a brief introduction to noise development in SRMs and then presents the first phase- exact measurement of the radiation characteristic of an SRM that is known to the authors. Furthermore, methods to simulate the sound radiation are introduced.

Design and analysis of a pancake switched reluctance machine for use in household applications

The design process of a switched reluctance drive for household applications is described. The machine requirements for modern household applications are summarized and the design process of a 150 W three-phase switched reluctance drive is described. During the process special attention was paid to the stators mechanical resonance frequencies to assess influences of the acoustic noise. Also drive efficiency was optimized by shaping the current waveforms for the most occurring operating point. Due to application requirements, the designed machine has a very short stack length, which also leads to a considerable influence of end-effects on the machine inductance. Two-dimensional (2D) and 3D FEM simulation results are presented to show this influence. Furthermore, the influence of different control strategies on the machine vibration is reviewed. Finally, the acoustic performance of the switched reluctance drive was measured on an eddy current brake test bench and in the application itself. The results of these measurements are shown and analyzed.

Effectiveness of Noise Reducing Measures in Switched Reluctance Drives

Acoustic noise reduction in electrical drives can be achieved by either machine design or control measures. The corresponding strategies affect different parts of the acoustic noise transfer path and they can therefore be divided into different categories such as: reduction of the excitation, increase of transfer path impedance, decrease of radiation efficiency or reduction of the annoyance of the sound. In contrast to the first three strategies, the last does not necessarily result in a reduction of the resulting sound pressure level. Annoyance is a subjective impression but may be characterized well by psycho-acoustic quantities such as loudness, sharpness and tonality (Kasper et al., 2005). This paper begins with a detailed study of the acoustic noise transfer path. The derived theory is validated by numerical simulation and experiments. Finally, the effectiveness of the different noise reducing strategies as well as trade-offs are discussed