Loss Reduction Optimization for Heat Capacity Improvement in Interior Permanent Magnet Synchronous Machine

When calculating the permanent magnet (PM) eddy current loss (ECL) in the interior permanent magnet synchronous machine (IPMSM) under pulse width modulation (PWM) voltage source inverter (VSI) supply, it is very important to take the high frequency harmonic voltages (HFHVs) in the input voltage into consideration because most of the PM ECL in IPMSM with distributed windings is caused by them [1–2]. However, common finite element analysis (FEA) with sinusoidal current source supply isn’t able to take the HTHVs into consideration and the coupled field-circuit time-stepping FEA under PWM VSI supply with fine time step is needed for the calculation, which is very time-consuming especially when conducting 3D FEA to take the end effect and axial segmentation into consideration. A hybrid method with the combination of 2D FEA and analytical method has been proposed in [3] for fast calculating the PM ECL considering axial segmentation. However, the 2D time-stepping FEA with fine time step, which takes several hours for one case study, is still needed for the PM ECL calculation under one load condition with the method proposed in [3]. In this paper, the analytical method in [3] is further developed and applied for the PM ECL calculation of an IPMSM applied in the HEV application [4]. Rather than calculating the PM ECL with the average flux density passing through the PM as input [3], the relationship between arbitrary HFHV and the corresponding PM ECL is established. Hence, the total PM ECLs can be calculated with the FFT results of the input line-line voltage directly without time-stepping FEA at a given load condition.

This paper investigates the accurate and fast permanent magnet (PM) eddy current loss calculation method for flux switching permanent magnet (FSPM) machine. First, the 3D finite element analysis (FEA) model is used and the distributions of the magnetic vector potential (MVP) and eddy current loop are presented, based on which a modified combining 2D FEA electromagnetic computation and analytical equations is proposed to calculate PM eddy current loss. Then the axial and radial segmentation of magnets are taken into consideration. The results obtained by the proposed method is proved to be extremely close to those obtained by 3D FEA.

This paper investigates and compares the eddy current loss induced in permanent magnet (PM) in both rotor-PM flux-switching (RPM-FS) machines and stator-PM flux-switching (SPM-FS) machines. Based on the field modulation principle, the harmonic components of both the PM field and armature reaction field are deduced, as well as the corresponding frequencies. Then, the PM loss production mechanisms due to eddy current are revealed for the RPM-FS and SPM-FS machines, respectively. Consequently, the similarities and differences between two FS machines are investigated from the perspectives of both electromagnetic torque and PM eddy current loss production mechanisms. The results indicate that the PM eddy current loss in SPM-FS machines influences efficiency dramatically. However, for the RPM-FS machine, the armature reaction field affects the PM loss more sensitively. In addition, a large PM eddy current loss is associated with high-power rating and large current density FS machines for electric vehicle application, and can be reduced by utilizing PM segmentation method.

A study on permanent magnet (PM) eddy current and core losses of dual-stator PM machines is investigated in this paper. The analyzed core losses include: the rotor core loss, stator core loss and the total core loss of the machines. Further, the effect of their different rotor pole number is also presented with quantitative comparison. Due to the relatively high electrical frequency of the analyzed 14-rotor pole machine, it gives the largest amount of PM eddy current loss. Similarly, the 13-pole machine exhibits the largest amount of total core loss amongst the compared machines. Although, the investigated machine having 4-rotor pole has a low core loss value, likely due to its low electrical frequency. However, it has the poorest efficiency amongst all, due to its very low output torque. Overall, largest torque density is obtained in the 13-pole machine at rated current condition. http://dx.doi.org/10.4314/njt.v36i4.21

The analysis of AC losses, including the core and permanent magnet (PM) eddy current losses, requires a long computational time because of the large number of analysis steps and elements for the overall consideration of current harmonics. Therefore, this paper proposes a cost-efficient analysis of the AC losses considering current harmonics. First, the permeability of all the elements at each step is obtained via a nonlinear static finite element analysis (FEA), using the fundamental component of the current. Then, the harmonics of AC losses are calculated using a linear static FEA and a two-dimensional time-harmonic T-Ω method, which are well-known for their fast computation. At each analysis step, the permeability of each element is interpolated from the obtained permeability map. The cost-efficiency of the proposed analysis is validated with a PM synchronous motor used for vehicle traction.

This paper proposes a novel model for calculating eddy current losses (ECL) in permanent magnets (PMs) using the principle of magductance. The focus is on integrating magductance elements into the 2D electromagnetic field finite element method (FEM) analysis, thereby enabling simultaneous consideration of eddy current reactions, iron nonlinearity and saturation effects. The proposed method is based on the 2D distribution of eddy currents within the PMs, accounting for both axial and radial segmentations. Firstly, the analytical expression for the magductance corresponding to the PM eddy current reaction in a flux switched permanent magnet (FSPM) motor is derived based on the magductance principle. Secondly, the magductance is integrated into the 2D electromagnetic field FEM model with equivalent windings corresponding to the magductance added to the model. According to the magductance principle, the Joule losses of the magductance windings can be regarded as the PM ECL. Finally, the accuracy of the proposed method is validated through 3D electromagnetic field FEM analysis and experimental results.

Magnet eddy current loss is very important for any types of permanent magnet (PM) machines, especially for high-speed PM machine since it increases significantly with rotating speed and has a great effect on the temperature of a magnet and, hence, the electromagnetic performance, as well as irreversible demagnetization of the magnet. In this paper, a new method is proposed to reduce the rotor PM eddy current loss. The auxiliary slots with an optimized size and position are proposed. By this mean, the asynchronous spatial harmonics caused by the armature reaction and the conventional slots can be partially decreased by the harmonics produced by the introduced auxiliary slots. It is proved that the rated on-load magnet eddy current loss can be reduced as much as 81.5% by this method, whereas the rated on-load torque is only decreased by 4.8% in the 3-slot/2-pole machine. In addition, it also shows that the proposed method could offer a better performance in a machine with relatively larger air gap length and it is also effective for other slot/pole combinations.

This paper shows the characteristics of performance for interior permanent magnet machine (IPM) considering driving conditions such as maximum torque per ampere (MTPA) and flux-weakening control especially in terms of harmonic loss. In particular, based on finite element analysis (FEA), permanent magnet (PM) eddycurrent loss and the harmonic iron loss have been computed where the models have been intentionally designed to identify the effects of pole-slot combinations on the loss while maintaining the required power for electric vehicle. From the analysis results, it was shown that the rotor iron loss and PM eddy-current loss of machine employing fractional slot winding are extremely large at load condition. Furthermore, it was revealed that the harmonic iron loss at high-speed operation is mainly distributed over stator teeth and rotor surface, which may aggravate cooling system of the rotor structure in the vehicle.

This paper introduces a hybrid analytical model (HAM) for the evaluation of permanent-magnet (PM) eddy-current loss in dual-stator single-rotor axial flux permanent-magnet machine (AFPMM), accounting for stator saturation. The proposed model integrates the magnetic equivalent circuit (MEC) with an analytical model based on scalar magnetic potential, enabling simultaneous consideration of different rotor positions and stator slotting effects. The three-dimensional finite element method (3D-FEM) validates the no-load and armature reaction magnetic field calculated by HAM, as well as the PM eddy-current loss under both no-load and load conditions. Compared to 3D-FEM, the proposed model reduces the calculation time by more than 98% with an error of no more than 18%, demonstrating a significant advantage in terms of computational time. Based on the proposed model, the effects of air-gap length and slot opening width on PM eddy-current loss are analyzed; the results indicate that reducing the slot opening width can effectively mitigate PM eddy-current loss for AFPMM.

Eddy-current loss of NdFeB permanent magnets (PMs) is widely analyzed in PM motors. This paper proposes a coupled 2-D transient finite-element analysis (FEA) of the saturated core fault current limiter (SCFCL) and 3-D analytical model of PMs to evaluate eddy-current loss in SCFCL. The comparison between the result from coupled method and that from 3-D FEA verifies the applicability of the coupled method in analyzing eddy current loss of PMs in SCFCL. The 3-D analytical model of PM is applied to analyze the effect of segmentation on the reduction of PM's eddy-current loss. And the results show that segmentation along width has a better performance, which is also verified by 3-D FEA.

This paper proposes two novel hybrid rotors permanent magnet (PM) machines for the high torque density in short duration condition operation. In order to enhance the torque performance, the flux concentrated structure of spoke-type PM is employed to increase the air-gap flux density. Meanwhile, the non-magnetic connector of the rotor is employed to eliminate the magnetic flux leakage. The rotors of the conventional machines and the proposed machines are optimized by the finite element analysis (FEA). Furthermore, based on the comparisons of electromagnetic performances for the optimized machines, including the open-circuit flux density, torque, PM eddy current loss, overload capability, the characteristics of the proposed machines are analyzed. The results indicate that the proposed machine can improve the torque at rated and overload operation with growth rate 14.3% and 13.1%, respectively. Finally, a 12-slots/10-pole PM machine is prototyped and FEA is to be validated.

In high speed permanent magnet (HSPM) machines, the computation of magnet eddy current loss is essential as these losses significantly affect the temperature of the permanent magnet (PM) and electromagnetic performance and can result in irreversible demagnetization of the PM. Several techniques have been adopted to minimize the eddy current loss of the PM; however, superior performance has not been achieved yet. In this paper, the design characteristics of the HSPM machine are analyzed. The PM is covered by a titanium sleeve to retain the PM on the rotor and to further reduce the eddy current loss of the magnet. The undesirable harmonics of the airgap flux density are minimized, which reduces the eddy current loss in the solid PM and rotor. Two existing models, with and without auxiliary slots, are examined and compared with the proposed design having a titanium-based retaining sleeve. The analysis reveals that the eddy-current loss, cogging torque, and iron losses of the PM are reduced by 82%, 73%, and 44.7%, respectively, in the proposed model; however, a marginal increase is observed in the average rated torque profile and open circuit flux linkage.

In today's highly automated world, permanent magnet synchronous machines (PMSMs), commonly used in the industrial automation of traction, robotics or aerospace, require higher power density and efficiency. When developing such PMSMs, the eddy current loss (i.e. permanent magnet loss) in the permanent magnets (PMs), especially with respect to temperature and frequency influence, must be considered. The increase in the temperature of PMs above the allowed maximum temperature leads to a tendency towards irreversible demagnetization and changes in the electrical conductivity of the material. Similarly, higher harmonics with different frequencies influence the eddy current loss of the PMs. The accurate analytical analysis and measurement methods of PM loss can help PMSM designers to create robust PMSMs with high tolerances and higher energy efficiency at low manufacturing costs. In this paper, measurement methods and a finite element method (FEM) simulation for the PM loss of PMSMs are presented and compared. In addition, we consider the eddy current loss (i.e. PM loss) in PMs, which are under external magnetic fields generated with a sinusoidal or non-sinusoidal pulse width modulation (PWM) signal under higher frequency effects.

The impact of granular microstructure in permanent magnets on eddy current losses are investigated. A numerical homogenization procedure for electrical conductivity is defined. Then, an approximated simple analytical model for the homogenized conductivity able to capture the main features of the geometrical and material dependences is derived. Finally eddy current losses analytical calculations are given, and the two asymptotic expressions for losses in the stationary conduction limit and advanced skin effect limit are derived and discussed.

The aim of the paper is the numerical calculation and analyze of eddy currents in permanent magnets (PM) of brush-less direct current (BLDC) machines. The main source of these induced eddy currents is in reluctance variation due to stator geometry. The study is carried out on outer rotor BLDC machine. The 3-D time-stepping finite-element analyze is used to clarify this phenomenon. The induced eddy-current distribution in the PM and the resulting power losses are calculated. Also, the study of this parasitic effect is curried out by 2D time-stepping finite-element analyze. The induced eddy current losses in PM due to different stator geometries are calculated and analyzed.