Rectangular Winding Research Articles

Determination of Hotspot Temperature Margin for Rectangular Wire Windings Considering Insulation Thermal Degradation and Partial Discharge

Increasing current density is a common way to improve the power density of electrical machines (EMs) which also boosts the winding temperature. Higher winding temperature accelerates the thermal degradation of insulation and also increases the risk of partial discharge (PD). Commonly, the winding hotspot temperature constraint is decided based on an over-engineering approach (i.e., the winding hotspot temperature is 30°C below the wire thermal class) constraining the EM’s performance. In this paper, the margin of winding hotspot temperature is precisely determined focusing mainly on the insulation degradation issues through experimental investigation. The partial discharge inception voltage and partial discharge extinction voltage have been measured under different temperature conditions for samples with different thermal aging statuses. Rectangular wires which find application in automotive motors are selected as test samples. The results link the temperature with the PD risk and the thermal lifetime of the insulation, and the winding hotspot temperature margin is accordingly determined. An automotive case study is presented to prove the applicability of the investigation outcomes.

Study on AC Loss Suppression in Rectangular Winding Motors for Electric Vehicles

Study on AC Loss Suppression in Rectangular Winding Motors for Electric Vehicles

Analytical Double-2D Frequency-Dependent Leakage Inductance Model for Litz-Wired High-Frequency Transformer

Accurate and fast calculation of frequency-dependent leakage inductance is critical for the optimization of the high-frequency transformer with Litz wire winding. The analytical method is widely used due to its high computation speed. However, its computation accuracy is limited due to the following factors. i) One-dimensional (1D) or two-dimensional magnetic field model (2D) has unsatisfying accuracy for the transformer with a rotationally asymmetric structure. ii) The skin and proximity effect factors based on the multilayer foil winding are inaccurate for the Litz wire winding in the calculation of frequency-dependent magnetic energy. This paper proposes a double-2D frequency-dependent leakage inductance model for the transformer with Litz wire winding. It uses the image method to calculate the 2D leakage magnetic field inside and outside the core window, respectively, which considers the rotationally asymmetric structure in leakage inductance calculation. The round conductor model is proposed for the frequency-dependent magnetic energy calculation. The single strand in a Litz wire is taken as the basic modeling object of the round conductor model, which is more detailed than the multilayer foil winding model for the Litz wire winding. The comparison between the experiment, FEM, state-of-the-art models and the proposed model is conducted for eight transformers with E-core, U-core, round or rectangular Litz wire winding. The proposed model shows satisfying computation accuracy in the whole frequency band. And the computational speed of the proposed model is 100 times that of the FEM.

Extension of Simple and Accurate Inductance Estimation for Rectangular Planar Windings

This paper proposes a method to generalize the equations estimating the inductance of square-shape planar windings to rectangle shape. This is done by utilizing the optimal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$p$</tex-math></inline-formula> -norm of the Generalized Mean Value or Power Mean (PM). Three well-established equations with verified accuracy are examined, namely Wheeler's, Rosa's, and the Monomial, which by definition consider only regular polygons. One critical parameter of the original equations is the outer-side length of the winding, which for the rectangle case, can be substituted by the PM of the two outer-side lengths, without the need for any further modifications. A methodology to select the optimal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$p$</tex-math></inline-formula> -norm for the PM is presented in terms of achieving the best accuracy for this estimation. The selection of the optimal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$p$</tex-math></inline-formula> is based on results from datasets containing more than 2600 simulations of different rectangle-shaped windings. Finally, the estimation accuracy is verified by laboratory measurements for a selection of planar inductors.

Reduction in Eddy Current Loss of Special Rectangular Windings in High-Torque IPMSM Used for Wind Generator

A special rectangular winding structure, which has different cross-sectional shape but the same cross-sectional area for each turn, has been adopted in a high-torque IPMSM used for a wind generator to improve slot factor and heat dissipation. However, large eddy current loss occurs to the rectangular windings. According to this problem, this paper proposes three improvements to reduce the eddy current loss. Among them, removing a portion of windings and replacing a portion of windings with aluminum are discussed to realize a tradeoff between eddy current and copper losses. And adjusting the tooth-tip shape is discussed to suppress the magnetic flux passing through the windings by mitigating magnetic saturation around the tooth-tip. Additionally, manufacturing costs can also be reduced by adopting a portion of aluminum windings. Moreover, a 3-step-skewed rotor structure is discussed to reduce cogging torque and lower the start-up wind speed. And its influence on losses is also discussed. Furthermore, three models adopting round windings are made and discussed for comparison. The FEM (Finite Element Method) results show that compared with the three round windings models, the proposed model still has a better performance in the reduction of windings eddy current loss. Finally, a prototype machine is manufactured to verify the FEM results, and the experimental results show that the maximum efficiency of the prototype can exceed 97.5%.

Analysis of a thrust magnetic bearing with rectangular wire winding

Active magnetic bearings generally use the coils made of enameled round wires, which have a low filling factor and waste plenty of slot space, resulting in large volume and weight of the machine. This paper introduces the rectangular wires to apply in magnetic bearings. The rectangular wires can be wound compactly without gaps and increase the wire filling factor, thereby reducing the size of the magnetic bearing stators, as well as the associated rotor part. These structural improvements are greatly beneficial to the high-speed rotating machinery in the aspects of windage losses, natural frequency, and material strength of the rotor, which are quantitatively analyzed. By utilizing the rectangular wire, a coil for a thrust magnetic bearing prototype is fabricated and tested, demonstrating the practical feasibility of the rectangular wires to apply in magnetic bearings.

Modified Halbach design for torque profile improvement in a permanent magnet synchronous motor dedicated to an electric city bus

In this work, a permanent magnet synchronous motor is designed for an electric city bus. The unit winding factor is considered for torque capability enhancement and completely open slots are adopted for low-cost rectangular wire winding implementation. Accordingly, extremely large pulsating torques that are predictable should be mitigated through the rotor design possibilities. In this regard, a modified Halbach pole configuration, named axially segmented Halbach, that is capable of producing considerably smooth torque as well as retaining the large mean torque is proposed. First, an optimised conventional Halbach array is calculated as the initial design. Then, following a detailed introduction to the new design concept, the modified Halbach pole parameters are obtained through the proposed 2D model-based optimisation algorithm. A rotor step skewing scheme is also evaluated to make the final comparisons, which are carried out via 3D FE models. The results demonstrate the admirable performance of the proposed Halbach configuration as an effective solution for torque profile improvement.

Evaluation and loss estimation of a high-speed permanent magnet synchronous machine with hairpin windings for high-volume fuel cell applications

High-speed machines offer several advantages, such as small sizes, avoidance of mechanical gears, and low maintenance, which has led to considerable research dedicated to them in the past decade. In recent times, rectangular wire windings with a hairpin structure have gained prominence in traction motors in the electromobility sector due to their high slot fill factor, simple production, and good thermal properties. Taking these advantages into consideration, this paper analyzes the possibility of using a high-speed permanent magnet synchronous machine (PMSM) with hairpin windings as an electric turbo compressor in fuel cell applications and outlines the critical design aspects.

Influence of Driving Mode on Loss Characteristics of Doubly Salient Brushless Motor With Rectangular Wire Armature Winding

The loss of a doubly salient brushless motor (DSBLM) with rectangular wire armature winding mainly includes ac copper loss, iron loss, and converter loss. The driving mode has a certain influence on motor loss. Therefore, the loss characteristics of a DSBLM with rectangular wire armature winding driven by brushless dc (BLDC) and brushless ac (BLAC) are comparatively studied in this article. First, the magnetic flux density waveforms of armature winding and stator under ideal currents drive are compared, and the waveform changes of ac copper loss and iron loss are analyzed. Second, the effect of pulsewidth modulation (PWM) on motor loss for actual operation in two driving modes is studied. Third, the converter loss of different driving modes is also considered. Finally, the theoretical analysis and simulation results are verified by the experimental results of a DSBLM. In the BLAC driving mode, a DSBLM with rectangular wire armature winding has better loss characteristics.

An Accurate Analytical Method for Leakage Inductance Calculation of Shell-Type Transformers With Rectangular Windings

This paper presents an accurate analytical method for calculating the leakage inductance of shell-type E-core transformers with rectangular windings. For this purpose, first, an expression for calculating the leakage inductance per unit length inside the core window considering the core walls as the flux-normal boundary condition is derived. Then, a new accurate method for determining the Mean Length of Turns (MLT) based on the total stored energy is presented. The MLT is needed for the leakage inductance calculation using 2-D methods. By dividing the MLT into three partial lengths and calculating the corresponding leakage inductances using three different core window arrangements, the effect of core structure on the total leakage inductance is considered. The method is verified by 3-D FEM simulations as well as the leakage inductance measurements on two different fabricated transformer prototypes. The superiority of the method is also confirmed by comparisons with the previous analytical approaches. The proposed method enables the leakage inductance calculation with an error less than 1%, compared to the 3-D FEM results. Using the presented method, the leakage inductance calculations can be performed rapidly and accurately in the design stage without the need for time-consuming 3-D FEM simulations.

Examination on Magnetic Tape Wrapped Rectangular Aluminum Winding for Weight and Copper Loss Reductions of High-frequency Transformer for Railway

Examination on Magnetic Tape Wrapped Rectangular Aluminum Winding for Weight and Copper Loss Reductions of High-frequency Transformer for Railway

Overview of the rectangular wire windings AC electrical machine

The rectangular wire winding AC electrical machine has drawn extensive attention due to their high slot fill factor, good heat dissipation, strong rigidity and short end-windings, which can be potential candidates for some traction application so as to enhance torque density, improve efficiency, decrease vibration and weaken noise, etc. In this paper, based on the complex process craft and the electromagnetic performance, a comprehensive and systematical overview on the rectangular wire windings AC electrical machine is introduced. According to the process craft, the different type of the rectangular wire windings, the different inserting direction of the rectangular wire windings and the insulation structure have been compared and analyzed. Furthermore, the detailed rectangular wire windings connection is researched and the general design guideline has been concluded. Especially, the performance of rectangular wire windings AC machine has been presented, with emphasis on the measure of improving the bigger AC copper losses at the high speed condition due to the distinguished proximity and skin effects. Finally, the future trend of the rectangular wire windings AC electrical machine is prospected.

Influence of surface rectangular defect winding layer on burst pressure of CNG-II composite cylinder

To study the influence of composite materials’ surface defect on the burst pressure of CNG-II composite cylinder, the surface defect was simplified as a rectangular slot of certain size on the basis of actually investigating the shape of cylinder’s surface defect. A CNG-II composite cylinder with a rectangular slot defect (2mm in depth) was used for burst test, and the numerical simulation software ANSYS was used to calculate its burst pressure. Through comparison between the burst pressure in the test and the numerical analysis result, the correctness of the numerical analysis method was verified. On this basis, the numerical analysis method was conducted for composite cylinders with surface defect in other depth. The result showed that surface defect in the form of rectangular slot had no significant effect on the liner stress of composite cylinder. Instead, it had a great influence on the stress of fiber-wrapped layer. The burst pressure of the composite cylinder decreased as the defect depth increasing. The hoop stress at the bottom of the defect in the shape of rectangular slot exceeded the maximum of the composite materials’ tensile strength, which could result in the burst pressure of composite cylinders decreasing.

Round and rectangular winding loss analysis and optimisation for a 22,000 rpm 150 kW switched reluctance machine

Round and rectangular winding loss analysis and optimisation for a 22,000 rpm 150 kW switched reluctance machine

Round and rectangular winding loss analysis and optimisation for a 22,000 rpm 150 kW switched reluctance machine

Under research is a switched reluctance machine for the powertrain of an electric vehicle. The research focuses on accurate estimation and optimisation of winding losses in switched reluctance machines. These losses result from both AC and DC resistance. An FEA-based procedure is described which computes both components of loss. Round and rectangular conductors are both analysed for a number of cases. Ultimately, rectangular conductors are chosen for more thorough analysis. Here, a number of winding geometries are simulated. Plotting conductor geometry versus conductor loss confirms a loss trend with a global minimum. For the motor design under consideration, this represents up to 4 kW reduction in loss over the initially simulated round conductors.

INDUCTOR SYSTEM WITH ATTRACTING SCREEN AND RECTANGULAR SOLENOID

A theoretical investigation of electromagnetic processes in the working zone of the inductor system with the attracting screen and rectangular solenoid is carried out. The calculated ratios for eddy currents excited by oppositely directed currents of the rectangular solenoid winding in the screen and sheet metal are obtained. Expressions to specify the distributed force of attraction of a dent in sheet metal with the rigidly fixed screen as well as forces of magnetic pressure on the sample are determined.

A novel method to check the axial tilt instability of the rectangular winding of the amorphous alloy transformer

The paper proposes a three‐dimensional buckling finite element method (FEM) to calculate the tilt limit force of the rectangular winding of an amorphous alloy transformer. The short‐circuit leakage magnetic FEM is used to calculate the axially distributed force of the transformer. The maximum axial compression force is obtained by integrating the short‐circuit distributed force along the axial height of the winding. The model is used to characterize the axial stability of the transformer by means of the maximum compression force and the size of the tilt limit force, and thus to formulate the evaluation criterion of the axial instability of the amorphous alloy transformer. The proposed method is verified by the calculation results of the tilt limit force and by checking the axial stability of the rectangular winding of an actual amorphous alloy transformer. The analysis results show that reducing the size difference of the rectangular winding between the long side and the short side and increasing the width of the wire will improve the tilt limit force. Experimental results of the short‐circuit test on several amorphous alloy transformers verify the effectiveness of the proposed method. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Comprehensive Evaluation of Rectangular and Double-D Coil Geometry for 50 kW/85 kHz IPT System

In this paper, the influence of the inductive power transfer (IPT) coil geometry on the performance factors efficiency, power density, and stray field is studied for a public transport electric vehicle battery charging system. IPT coil geometries with rectangular winding and with double-D winding are compared based on the Pareto fronts obtained from a multi-objective optimization. In order to study the effect of the winding layout experimentally, two full-scale 50 kW/85 kHz hardware prototypes with the same outer coil dimensions ( $410\times 760\times 60$ mm3) and ferrite core structure are constructed. For both the prototypes, the measured dc–dc efficiency is approximately 95.5% at 50 kW with a 160 mm air gap and ideally positioned coils, which confirms the calculations. The positioning tolerance of the double-D prototype is inferior, because with coil misalignment the efficiency decays faster than for the rectangular winding prototype. Flux density measurements show that both the prototypes fulfill the ICNIRP 2010 standard at 800 mm lateral distance from the coil center. However, the measured magnetic stray field is a factor of two lower for the double-D prototype, which is a key advantage in high-power applications.

Motor Stator With Thick Rectangular Wire Lap Winding for HEVs

A stator structure with a rectangular wire distributed winding that exhibited high levels of productivity and extremely flexible design was designed for hybrid electric vehicle motors. We devised a method of forming thick rectangular wire diamond coils and determined the best conditions for forming high-density coils. A structure for terminal connections was also devised to achieve a short coil end. The slot-fill rate of a prototype stator was 80.5%, and its total coil end was 42 mm, which is roughly the same motor performance of a stator with segmented coil wave winding. The key advantage here is that the proposed stator had fewer coils and welding points than a stator with segmented coil wave winding and that the possible number of conductors per slot was higher than four, which is the limit for the stator with segmented coil wave winding.

Wireless-Power-Transfer Planar Spiral Winding Design Applying Track Width Ratio

With the increase of wireless power transfer (WPT) systems for home and industrial electronic applications, planar spiral winding design techniques are gaining attention due to their low profile, reproducibility, and manufacturability. The major design goal for windings in WPT systems is a high quality factor (Q) for a given inductance. This paper establishes a new method to improve and analyze Q by using a nonunity track-width-ratio geometrical arrangement. The results are applicable for a variety of planar spiral winding families and make full use of the ability to change the width of the traces to improve Q for wireless powered applications. In order to simplify the analysis and provide generality, a unified dimensional system framework is also proposed, covering the racetrack geometry and its derivatives-circular, rectangular, generalized octagonal, and traditional racetrack windings. The resulting dimensional system provides an accurate geometrical description of the windings to obtain high Q and a simple set of manufacturing specifications. Details and derivations of this new method to calculate inductance, dc resistance, and ac resistance estimation to obtain improved Q are presented. A comprehensive set of experimental measurements confirms the validity of the dimensional system and the improvements in Q for wireless powered applications.