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.

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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.

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

A multiphysics simulation model that consists of electromagnetic field, mechanical field, and acoustic field was established to predict the electromagnetic vibration and noise of claw pole alternators. First, magnetic force exerted on the stator inner surface was calculated by three-dimensional (3-D) transient electromagnetic field analysis and the characteristic of magnetic force was analyzed. Second, finite-element modal analysis of alternator assembly was conducted while taking into account the anisotropy of the stator core and armature winding and the installation condition. Simulation result was validated by modal test. Afterward, magnetic force was transferred to the structural mesh using mesh mapping method and the vibration and noise were predicted by using mode superposition method and boundary-element method, respectively. Simulation results agree well with those measured by experiments. Finally, the mechanism of electromagnetic vibration and noise of the claw pole alternator was revealed with the help of 2-D Fourier transform of magnetic force and the mode participation factor of each mode. Results show that for three-phase 12-pole/36-slot claw pole alternator, electromagnetic vibration, and noise are mainly caused by the zeroth-order (circumferential spatial order) force harmonics whose frequencies are 36 kfr ( k = 1, 2, 3,…) and the sixth-order (circumferential spatial order) force harmonics whose frequencies are (36 k ± 6) fr ( k = 1, 2, 3,…).

Vibroacoustic Prediction and Mechanism Analysis of Claw Pole Alternators

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

This paper introduces two different structure types of claw pole machines, conventional claw pole motor (CCPM) with inner claw pole rotor and permanent magnetic claw pole motor (PMCMM) with outer PM rotor. Their magnetic loop and electric circuit model have been built respectively, and the calculation method of the electrical machine parameter is also put forward in detail. The operation characteristics of the CCMM and PMCPM have been studied comparatively. The simulation results show that the CCPM and PMCPM have similar power output ability but the PMCPM would have higher operation efficiency than the CCPM.

Comparative Study on Claw Pole Electrical Machine with Different Structure

This paper introduces the structure and operation principle of claw pole motor with permanent magnet outer rotor. The three dimensional magnetic field distribution at no-load condition has been analyzed by using the scalar magnetic potential. Moreover, the operation characteristic curves have been obtained at different speeds. The results of the paper are helpful to the computation of performance and optimal parameters.

Magnetic Field Analysis and Performance Calculation for New Type of Claw Pole Motor with Permanent Magnet Outer Rotor

This paper introduces a new type of permanent magnet claw pole generator (PMCPG) with outer rotor. The magnetic circuit and electrical circuit model of this kind of machine have been built, and the effect of armature current on magnetic field is also considered in the models. The operation characteristics are simulated by means of powerful simulation software on the basis of coupling between magnetic circuit and electric circuit. The computation results indicate that the PMCPG have good operation characteristics.

Electromagnetism Model and Characteristic Simulation of Novel Claw Pole Generator with Permanent Magnet Outer Rotor

This paper introduces a novel permanent magnet claw pole generator (PMCPG) with outside rotor. Its structure and operation principle are described. The magnetic field distribution and induction EMF of the PMCPG are calculated by ANSYS software. The calculation formula of inductance parameter has been also given in this paper. By means of two powerful simulation tools, the ANSYS and CASPOC software, the operation characteristic of the PMCPG with and without load is simulated on the basis of coupling of magnetic field and electric circuit. The simulation result shows that the PMCPG has well operation performance and is suitable to be used in vehicle.

Eugen Nolle

Papers

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

Comparative Study on Claw Pole Electrical Machine with Different Structure

Magnetic Field Analysis and Performance Calculation for New Type of Claw Pole Motor with Permanent Magnet Outer Rotor

Electromagnetism Model and Characteristic Simulation of Novel Claw Pole Generator with Permanent Magnet Outer Rotor

Study on Novel Claw Pole Automobile Generator with Outer PM Rotor