This paper presents a comprehensive state-of-the-art review of the modeling and analysis methods for the multidisciplinary design of electric motors for various applications including vehicular power and propulsion systems and electrified powertrains. It covers the important aspects of different engineering domains, such as dynamic modeling, loss calculations, demagnetization analysis, thermal modeling, acoustic noise and vibration analysis, and mechanical stress modeling. This paper intends to guide the electric motor designers through examples and results on how to apply different analysis techniques on electric motors.

/pdf/modeling-and-analysis-of-electric-motors-state-of-the-art-w5fev9dx90.pdf

Modeling and Analysis of Electric Motors: State-of-the-Art Review

In the design of electrical machines, the increase in power density has become one of the main research themes. With most of the power loss in high power density electrical machines often being generated in the stator winding assembly, it is necessary to reduce these losses. The effects of strands and bundle positions in the slot on the ac losses in the winding are often overlooked. Taking as a case-study an existing high-frequency machine, this article analyzes and provides an in-depth insight into such effects. Exploiting the rapid advancements in precision three-dimensional printing, it is found and experimentally verified that by controlling the position of the conductors within the top of the slot the ac losses can be markedly reduced.

/pdf/reduction-of-winding-ac-losses-by-accurate-conductor-bo3tlvx0r4.pdf

Reduction of Winding AC Losses by Accurate Conductor Placement in High Frequency Electrical Machines

The stator winding is known to be a key factor to enhance the performance of electrical machines in terms of efficiency, lifetime, volume and consequently the costs. Therefore, the selection of the suitable winding technology and a proper design are mandatory to fulfill the challenging requirements defined by transportation electrification. The paper deals with the comparison of stator winding technologies to be used for high speed electrical machines for propulsion applications. The most commonly used winding configurations in automotive applications such as stranded wire and hairpin are compared with an innovative winding solution featuring formed litz wires. The analysis is carried out by comparing the main figures of merit such as the phase resistance, the AC loss factor and the thermal behavior of the different winding configurations. The reference machine explicitly designed for the analysis is a 24 krpm Permanent Magnet assisted Synchronous Reluctance Machine featuring a peak power of 200 kW. The performance assessment, supported by analytical and numerical electromagnetic and thermal simulations, highlights the main features of each design solution.

Comparison of Stator Winding Technologies for High-Speed Motors in Electric Propulsion Systems

The purpose of this paper is to analyze ac copper losses of the ironless brushless dc machine (BLDCM) used in the flywheel energy storage system. The influence factors of the ac copper losses, such as the winding diameter, phase current, and machine speed, are analyzed. The research results show that the winding wire diameter has a huge effect on the ac losses in ironless BLDCM, and the shunt wound structure with multiple wires method can reduce winding ac losses effectively. However, due to induced voltage and impedance unbalance, additional circulating current losses are induced. For circulating current losses calculation, a winding circulating current equivalent calculation model is built. The circulating current losses are calculated by a simplified three-dimensional finite element method and the winding wires arrangement methods to reduce circulating current losses are explored. Three winding wires arrangements are compared and discussed. The results show that the ironless BLDCM using multiwires with suitable arrangements can reduce the copper losses.

AC Copper Losses Analysis of the Ironless Brushless DC Motor used in a Flywheel Energy Storage System

Analysis of ac effects, such as skin and proximity effect as well as the circulating currents and corresponding losses are usually done by finite-element analysis, while mostly only a single slot is considered, neglecting the influence of neighboring phases on the flux density of the stator iron and thus the resulting slot leakage flux. As the simulation of single stranded finite element (FE) models is computationally very demanding and time consuming, this paper compares different levels of detail of two-dimensional FE models and investigates the impact of the modeling depth on the resulting copper loss to find a computation time optimized modeling setup. It is shown that the use of single slot models is sufficient in case of distributed windings. Moreover, the potential increase of ac losses is assessed for two machines that are identical except for the stator winding, so that one and the same machine is investigated at two different voltage levels, namely 400 and 800 V. The reference machine is a 160 kW nominal power and 9000 r/min maximum speed permanent magnet synchronous machine. Since the magnetic circuit has to remain constant, both designs share the same overall winding scheme and total number of strands within a slot but differ in the number of parallel and serial connected strands. Due to the increased bundle cross section of the lower voltage winding, it is more susceptible to ac effects and thus tends to increased winding losses.

Influence of the Modeling Depth and Voltage Level on the AC Losses in Parallel Conductors of a Permanent Magnet Synchronous Machine

Due to high range and continious power requirements in electric and hybrid cars the efficiency of electrical machines is one key parameter. In this paper ac copper loss effects, mainly circulating currents, are investigated. A permanent magnet machine used for electric and hybrid cars showing 6 pole pairs, a maximum power of 80kW and a maximum speed of 12000 rpm is used for this analysis. In general parallel strands of small diameter are used to facilitate handling tasks and to minimize skin and proximity effects. But in the design process feasible circulating currents due to unsuitable strand distribution are often not considered. Furthermore the wire distribution is very often unkown due to automatic winding technology. So the main topic of this study is to analyze the impact of the parallel wires' placement based on the described machine and to propose a measurement technique which could be used later to judge automatically wound machines containing unknown strand placement. For this study a good and bad case machine is built up by hand winding to clarify the influence. To realize high quality measurements both machines use exactly the same rotor, about 60 thermocouples and a specific current measurement system in each parallel strand of one phase. It is shown that the measured losses differ for more than 3kW, meaning an additional loss amount of 65% at 11000 rpm. Looking at the measured currents the frequency dependency can be clearly seen. About three times higher current load in some strands is identified compared to ideal wire distribution. So overheating and possible cases of failure are possible. The measured data is used to validate a common analytical as well as a transient FEA model. While the FEA matches the measurement almost perfectly the analytical approach delivers some deviations, especially in bad case conditions. At the end an outlook regarding the temperature dependent loss scaling is given. Addicted to the ac loss amount different scaling behaviors occur.

Influence of parallel wire placement on the AC copper losses in electrical machines

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Influence of parallel wire placement on the AC copper losses in electrical machines