Search Results (21)

The partial discharge (PD) measurement under pulse width modulation (PWM) voltage is a critical measurement of quality assessment for inverter-fed motors, as outlined in IEC 60034-18-41 and IEC 60034-18-42. One of the key parameters in PD measurement is the repetitive partial discharge inception voltage (RPDIV). This paper examines factors that influence the ageing process of hairpin windings in motors, with ageing tests designed using the Design of Experiment (DoE) method. The study focuses on the effects of electrical and thermal stresses on the ageing process. To achieve this, the failure rate, the RPDIV data, and the lifetime data are selected as the output responses. The findings highlights that RPDIV measurements alone cannot accurately predict the degree of ageing of hairpin windings. Specifically, RPDIV results are influenced not only by the quality of the hairpin windings under PWM voltage but also by other contributing factors. Furthermore, the change in RPDIV during the ageing process showed that the RPDIV measurement cannot predict the ageing degree of the hairpin winding. Experimental data on failure rates and lifetimes reveal that both electrical and thermal stresses significantly influence the ageing process, with a notable interaction between these factors. Among the three output responses, the failure rate provides a more accurate reflection of this interaction. To reliably estimate the lifetime of hairpin windings, more precise parameters are necessary. Further research is required to deepen the understanding of the underlying PD mechanisms under PWM voltage, which could enhance diagnostic and predictive capabilities for hairpin winding performance. Full article

The asymmetric design of hairpin windings is known as a method for reducing AC losses in electric motors, especially at high frequencies. However, the design of the asymmetric winding is very critical to obtaining the best benefit regarding the efficiency and the thermal performance of the motor. Compared to the state-of-the-art in this paper, deep investigations are carried out to obtain the optimum design of the asymmetric hairpin windings while still employing a conventional manufacturing method. An analytical model is developed to speed up the investigation process, and the results of the analytical model are validated with a finite element method (FEM) model. The conclusions from the analytical investigation are considered in the design of an electric vehicle (EV) motor. The performance of the motor is studied for two different driving profiles to validate the rules of the asymmetric windings design and check the degree of dependency of the design of asymmetric windings on the application. It is proved that using asymmetric design reduces motor losses and improves thermal performance. Full article

Modern electric motors developed for the automotive industry have an ever higher power density with a relatively compact size. Among the various existing solutions to improve torque and power density, a reduction in the dimensions of the end-windings has been explored, aiming to decrease volume, weight, and losses. However, more compact end-windings often lead to complex shapes of the conductors, especially when preformed hairpin windings are considered. The rectangular cross-section of hairpin conductors makes them prone to deviating out of the bending plane during the forming process. This phenomenon, known as torsional–flexural instability, is influenced by the specific aspect ratio of the cross-section dimensions and the bending direction. This study focuses on understanding this instability phenomenon, aiming to identify a potential threshold of the cross-section aspect ratio. The instability makes it difficult to predict the final geometry, potentially compromising the compliance with the geometric tolerances. A finite element model is developed to analyse a single planar bend in a hairpin conductor. Various cross-section dimensions with different aspect ratios are simulated identifying those that experience instability. Moreover, an experimental campaign is conducted to confirm the occurrence of instability by testing the same single planar bending. The experimental data obtained are used to validate the finite element model for the tested dimensions. The aim is to provide designers with a useful tool to select hairpin geometries that are more suitable for the folding process, contributing to successful assembly and improving the overall design process of preformed hairpin conductors. Full article

This paper presents the application of a numerical approach known as proper generalized decomposition (PGD) to calculate the per-unit length (PUL) ac resistance of rectangular conductors. PGD has been successfully used in areas such as fluid mechanics and biomedical applications. It solves a partial differential equation (PDE) by decomposing the answer into a set of unknown one-dimensional (1D) functions in an iterative approach until it reaches a predetermined convergence. In this paper, a frequency-dependent meshing scheme is employed in the PGD technique at each frequency to properly take skin and proximity effects into account. One of the main advantages of PGD over traditional numerical approaches such as finite element or finite difference methods is that it confines the answers within a set of one-dimensional functions, which require fewer computational resources. Different examples of single and multiple rectangular conductors are considered to study skin and proximity effects. The PGD results are compared with those obtained using a commercial finite element method (FEM) software to verify the accuracy of the model. This approach can be used in applications such as white box modeling of transformers, EMC analysis, hairpin winding design used in electric vehicles, and busbar simulation. Full article

In this paper, the cooling performance of oil-cooling PMSM with hairpin winding under various oil parameters is analyzed via a simulation and an experiment. The effects of oil jet positions, oil temperatures, and oil flow rates on the cooling performance are analyzed. It is found that increasing the oil temperature in the range of 20 °C to 60 °C, increasing the flow rate of oil jets whose position angle is from 15° to 45°, and increasing the flow rate in the range of 1 L/min to 2 L/min will significantly improve the cooling performance. The apertures of the oil spray ring are optimized using the Taguchi algorithm. The cooling performance is the best when the flow ratio is m(0°):m(15°):m(30°):m(45°):m(60°):m(75°) = 4%:19%:10%:10%:4%:4%. This study provides a guide for the design of the oil-cooling system for the hairpin winding of the PMSM. Full article

In a typical inverter-fed AC drive system, the stator windings carry a current with a large harmonics content, resulting in an increased AC loss. In this paper, the additional copper losses caused by non-sinusoidal currents are investigated for different magnet wire topologies, including the flat conductor, stranded, and litz wires. Also, a two-slot simplified model is introduced for accurate prediction of the AC losses at high frequency. It is found that one of the major issues of the conventional copper coil is that the losses are not uniformly distributed across the slot, and over 70% of the losses are concentrated near the slot opening. Moreover, using the transient finite element method, different winding topologies and arrangements are simulated at the stranded level to evaluate the losses and current density for each strand under highly distorted currents. Furthermore, different coil samples are prototyped for the same slot geometries to compare their performance under the same pulse-width modulation (PWM) waveforms for a wide range of frequencies. Finally, new hybrid coil topologies are proposed, which employ different magnet wires or materials within the same slot. The results demonstrate that utilizing a mixed wire configuration can effectively mitigate the adverse effects of eddy current losses. This approach can yield up to 16–41% lower losses while also achieving a weight savings of 36–70%. Full article

Laminar-to-turbulent transition in a swept flat-plate boundary layer is caused by the breakdown of the crossflow vortex via high-frequency secondary instability and is promoted by the wall-surface roughness and the freestream turbulence (FST). Although the FST is characterized by its intensity and wavelength, it is not clear how the wavelength affects turbulent transitions and interacts with the roughness-induced transition. The wavelength of the FST depends on the wind tunnel or in-flight conditions, and its arbitrary control is practically difficult in experiments. By means of direct numerical simulation, we performed a parametric study on the interaction between the roughness-induced disturbance and FST in the Falkner–Skan–Cooke boundary layer. One of our aims is to determine the critical roughness height and its dependence on the turbulent intensity and peak wavelength of FST. We found a suppression and promotion in the transition process as a result of the interaction. In particular, the immediate transition behind the roughness was delayed by the long-wavelength FST, where the presence of FST suppressed the high-frequency disturbance emanating from the roughness edge. Even below the criticality, the short-wavelength FST promoted a secondary instability in the form of the hairpin vortex and triggered an early transition before the crossflow-vortex breakdown with the finger vortex. Thresholds for the FST wavelengths that promote or suppress the early transition were also discussed to provide a practically important indicator in the prediction and control of turbulent transitions due to FST and/or roughness on the swept wing. Full article

The hairpin winding configuration has been attracting attention as a solution to increase the power density of electric vehicle motors by enhancing the slot-filling factor. However, this winding configuration brings high AC losses during high-speed operation and we require new approaches to tackle this challenge. This paper considers reducing AC losses by proposing two main methods: correct transposition of conductors in parallel paths, and enhancing the number of conductor layers in a slot. First, the proper connection of conductors in parallel paths is considered, and the essential rules for this purpose are described. Next, the paper uses a numerical approach to deal with the effect of incorrect conductor transposition in winding paths on generating additional AC losses due to circulating currents. Finally, the impact of the number of conductor layers in the mitigation of AC losses is also discussed in detail. According to the results, by increasing the number of layers, ohmic losses in the layer near the slot opening dramatically decrease. For instance, ohmic losses in the layer near the slot opening of the eight-layer setup were 82% less than the two-layer layout. Full article

Today, an extensive electrification is occurring in all industrial sectors, with a special interest seen in the automotive and aerospace industries. The electric motor, surely, is one of the main actors in this context, and an ever-increasing effort is spent with the aim of improving its efficiency and torque density. Hairpin windings are one of the recent technologies which are implemented onto the stator of the electric motor. Compared to conventional random windings, it inherently features lower DC resistance, higher fill factor, better thermal performance, improved reliability, and an automated manufacturing process. However, its bottleneck is the high ohmic losses at high-frequency operations due to skin and proximity effects (AC losses), resulting in a negative impact on the temperature map of the machine. Nevertheless, while it is well-known that DC losses increase linearly with the operating temperatures, the AC losses trend needs further insight. This paper demonstrates that operating the machine at higher temperatures could be beneficial for overall efficiency, especially at high-frequency operations. This suggests that a paradigm shift is required for the design of electric motors equipped with hair-pin windings, which should therefore focus on a temperature-oriented approach. In addition, the effect of the rotor topology on AC losses, which is often overlooked, is also considered in this paper. The combination of these effects is used to carry out observations and, eventually, to provide design recommendations. Finite element electromagnetic and thermal evaluations are performed to prove the findings of this research. Full article

This paper investigates the impact of the wire selection on the performance of induction motors for automotive applications. The section of wire and the material are evaluated at a high speed of 200 kW in an induction motor designed for premium vehicle applications. The proposed solutions have the same electromagnetic and thermal constraints, as well as the same final encumbrance. The various wire and winding types differ in terms of slot design, phase resistance, end-winding overhanging portion, skin and proximity effects, and equivalent slot thermal conductivity. Their impacts are analyzed in terms of the operating area motor efficiency and they are tested in an automotive drive cycle, highlighting the advantages and disadvantages of each configuration. Full article

In high-speed and high-frequency electric machines, one of the major issues that impacts the performance and capability of a machine is the high-frequency eddy current losses in the windings. This work deals with AC winding losses in flat rectangular conductors. Aiming for eddy current loss mitigation, two different materials are investigated and compared for the same winding design, namely copper and aluminum. Using the finite element method (FEM), the conductor loss and current density behavior are simulated at the strand level. Further, in order to verify the simulated losses, the AC losses are measured and compared over a wide range of frequencies. Finally, recommendations are provided based on the obtained measurements to identify the best winding topology that is most suitable for automotive applications. Full article

Permanent magnet synchronous motors (PMSMs) with rectangular coils in hairpin windings exhibit improved fill factor and reduced end turn of the coils, which in turn improve the efficiency and power density of PMSMs, making them ideal for e-mobility applications. Herein, the shape of a PMSM was optimized for torque ripple reduction using metamodels to improve the noise and vibrational performance of the motor. The objective function of the optimal design aimed to minimize the torque ripple, and the average torque and efficiency were set as constraints. The notch width and depth and barrier length were selected as the design variables to satisfy the objective function and constraints. Using the optimal Latin hypercube design technique, 27 experimental points were selected, and a finite element analysis (FEA) was performed for each point. Furthermore, a function approximation was performed using six metamodels, and the best metamodel was selected using the root mean square error test. Moreover, the optimization was performed by combining the best metamodels for each variable with a sequential two-point diagonal quadratic approximation optimization algorithm. The torque ripple was improved by approximately 1.63% compared with the initial model, whereas the constraint values remained constant. Finally, an FEA was performed on the optimal point, and the FEA results matched with those of the optimal method. Full article

A fully resolved (FR) NREL 5 MW turbine model is employed in two unsteady Reynolds-averaged Navier–Stokes (URANS) simulations (one with and one without the turbine tower) of a periodic atmospheric boundary layer (ABL) to study the performance of an infinitely large wind farm. The results show that the power reduction due to the tower drag is about 5% under the assumption that the driving force of the ABL is unchanged. Two additional simulations using an actuator disc (AD) model are also conducted. The AD and FR results show nearly identical tower-induced reductions of the wind speed above the wind farm, supporting the argument that the AD model is sufficient to predict the wind farm blockage effect. We also investigate the feasibility of performing delayed-detached-eddy simulations (DDES) using the same FR turbine model and periodic domain setup. The results show complex turbulent flow characteristics within the farm, such as the interaction of large-scale hairpin-like vortices with smaller-scale blade-tip vortices. The computational cost of the DDES required for a given number of rotor revolutions is found to be similar to the corresponding URANS simulation, but the sampling period required to obtain meaningful time-averaged results seems much longer due to the existence of long-timescale fluctuations. Full article

Nowadays, interest in electric propulsion is increasing due to the need to decarbonize society. Electric drives and their components play a key role in this electrification trend. The electrical machine, in particular, is seeing an ever-increasing development and extensive research is currently being dedicated to the improvement of its efficiency and torque/power density. Among the winding methods, hairpin technologies are gaining extensive attention due to their inherently high slot fill factor, good heat dissipation, strong rigidity, and short end-winding length. These features make hairpin windings a potential candidate for some traction applications which require high power and/or torque densities. However, they also have some drawbacks, such as high losses at high frequency operations due to skin and proximity effects. In this paper, a multi-objective design optimization is proposed aiming to provide a fast and useful tool to enhance the exploitation of the hairpin technology in electrical machines. Efficiency and volume power density are considered as main design objectives. Analytical and finite element evaluations are performed to support the proposed methodology. Full article

Interior permanent magnet (IPM) machines with hairpin windings have attracted significant attention in EV applications owing to their low DC resistance and excellent thermal capabilities. In this paper, we present a comprehensive investigation of AC winding losses in IPM machines for traction applications, including analytical modeling, the influence of design parameters, and finite element (FE) verification. The proposed analytical model can predict the trends in AC winding losses for any number of bar conductors and slot/pole combinations. The results of the parametric study, obtained via the analytical model, are presented to examine the effects of key design parameters, such as conductor width and height, phase arrangement, and slot-per-pole-per-phase (SPP). To incorporate more practical issues into the analysis of IPM machines with hairpin windings, extensive FE simulations were conducted. The results indicated that the AC winding losses decrease with an increasing number of conductor layers and phases inside the slot. Full article