Slot Winding Research Articles

Oil Cooling Method for Internal Heat Sources in the Outer Rotor Hub Motor of ElectricVehicle and Thermal Characteristics Research

The heat dissipation of wheel hub motors is difficult due to the limited installation space and harsh working environment, which will lead to an increase in the operating temperature of the motor. Excessive motor temperature will limit the further increase in the power density and torque density of the motor. Taking the outer rotor hub motor as the research object, a heat dissipation structure is designed by passing oil through the stator core, slot wedge, and the motor end, mainly the cooling stator core, slot winding, and the end winding from inside of the motor. The internal heat is mainly carried away through lubricating oil by convective heat transfer and heat conduction. The heat distribution model of the motor based on the new cooling structure is established using the centralized parameter heat network method. The Motor-CAD software is used to build the motor 3d model and simulate the motor temperature field, and the temperature distribution in the motor under the rated working condition is analyzed. The temperature rising test of the motor prototype are performed on a bench built in the laboratory. The experimental results are consistent with the simulation results of the temperature field, which verify the rationality of the model.

Dual winding slot area allocation ratio effect on torque and suspension performance of BPMSMs

Dual winding slot area allocation ratio effect on torque and suspension performance of BPMSMs

Research on optimum design and control of permanent magnet synchronous motor for elevator

Abstract Due to the impact of the world energy crisis and environmental pollution problems, the combination of frequency converter and permanent magnet synchronous motor (PMSM) as the core of elevator drive has become a new direction for the development of the elevator industry. Compared with the traditional electric excitation synchronous motor, because the rotor of PMSM adopts permanent magnet excitation, no excitation winding, brush and slip ring are needed, the motor volume is greatly reduced. At the same time, for there is no excitation loss, the efficiency of PMSM) is higher than that of electric excitation synchronous motor. Therefore, the application of PMSM in elevator drive system has more obvious advantages. In this paper, PMSM for elevator is taken as the research object, and motor design software Motor-CAD is used to optimize the design of a kind of PMSM with power level. Then, the fine-tuned and optimized model is imported into the finite element analysis software, and the magnetic field analysis method is used to simulate the electromagnetic field of PMSM, so as to observe the magnetic field distribution of PMSM in the static field. At the same time, the three phase EMF and current waveform of PMSM is analysed to verify the design meets the requirements. Finally, the cogging torque of PMSM is studied in detail. Because the stator fractional slot winding design is adopted, the cogging torque of the prototype is greatly reduced.

Calculation of Equivalent Thermal Conductivity of Motor Winding Based on Conductor Distribution

Abstract To improve the calculation accuracy of motor thermal field, this paper proposes a method for calculating the equivalent thermal conductivity of winding based on conductor distribution, and a 24-slot 26-pole outer-rotor permanent magnet synchronous motor is taken as an example to verify the method. First, the equivalent thermal conductivity of winding is calculated by traditional equivalent methods, namely the equivalent insulation layer method and the area weighting method. Second, the equivalent thermal conductivity of the slot winding and end winding in the three-dimensional (3D) direction is derived using the conductor distribution method. Third, the 3D finite element models corresponding to three equivalent methods are established, and the temperature of the motor under different operating conditions is simulated and compared. Finally, an experimental platform is built to verify the accuracy of the proposed conductor distribution method.

Torque Pulsations in Machines with Fractional Slot Windings and Permanent Magnets

Torque Pulsations in Machines with Fractional Slot Windings and Permanent Magnets

Five-phase synchronous reluctance machines equipped with a novel type of fractional slot winding

Five-phase synchronous reluctance machines equipped with a novel type of fractional slot winding

Combined Electromagnetic and Mechanical Design Optimization of Interior Permanent Magnet Rotors for Electric Vehicle Drivetrains

In many high-speed electrical machines, centrifugal forces within the rotor can be first-order constraints on electromagnetic optimization. This can be particularly acute in interior permanent magnet (IPM) machines in which magnets are usually retained entirely by the rotor core with no additional mechanical containment. This study investigates the nature of the trade-off between mechanical and electromagnetic requirements within the context of an eight-pole, 100 kW IPM machine with a base speed of 4000 rpm and an extended speed range up to 12,000 rpm. A series of mechanical and electromagnetic models are used to estimate the level of shaft interference, mechanical stress in critical regions of the rotor and the impact of various features and dimensions within the machine on electromagnetic torque. A systematic exploration of the design space is undertaken for rotor diameters from 120 mm to 180 mm, with optimal designs in terms of torque per unit length established at each diameter while meeting the constraints imposed on mechanical stress. The final preferred design has a rotor of 165 mm and an axial length of 103 mm long with a fractional slot winding in a 30-slot stator. The overall machine has an active mass of 42.3 kg, which corresponds to ~2.4 kW/kg. This paper describes the optimization study in detail and draws on the results to explore the nature of the design trade-offs in such rotors and the impact of core properties.

A Novel Brushless PM-Assisted DC Motor with Compound-Excited Circular Winding

A novel compound-excited brushless DC motor with polygonal circular winding is proposed in this paper. The key is that DC excitation is effectively coupled with PM excitation, significantly improving the torque density per PM volume and improving the machine flux weakening performance in the proposed design. This proposed design provides simplified control characteristics similar to a compound-excited DC motor. Further, the flux weakening of the proposed machine can be smoothly achieved using polygonal closed-loop circular winding and a lagging slot winding shifting method.

Lumped parameter thermal model for segmental translator linear switched reluctance motor

AbstractThe segmental translator linear switched reluctance motor (STLSRM) is a special type of linear switched reluctance motor (LSRM) that has more output power than its conventional type. Therefore, it can be a good choice for certain applications. Heat is one of the factors limiting the output in machines. Therefore, predicting the thermal distribution of machine is as important as the magnetic design. A comprehensive thermal model is presented based on the lumped parameter approach for STLSRM, which predicts temperature distribution in different parts of this motor, including slot winding, end‐winding, stator pole, stator yoke, and the moving part. Considering that the proposed thermal model depends on dimensions and materials used in machine, it can be used for other designs of the STLSRM. The presented thermal model is applied to a typical STLSRM and temperature is determined in its different parts. The simulation results are then compared with the results of 3‐D thermal modelling based on the finite element method (FEM) for validation.

Lumped model for the calculation of harmonic eddy current losses in permanent magnets for homogeneous flux distributions considering eddy current reaction flux

This is the first of a series of papers on novel methods for the calculation of eddy current losses in permanent magnets (PMs) and the shortcomings of previously conducted analyses. Eddy current losses in PMs and their mitigation are significant factors when designing inverter-fed electric drives. Especially with the need for drives with high power density, a trend toward increased rotational speeds and, therefore, higher fundamental frequencies and inverter switching frequencies are observable. Higher harmonic frequency components of concentrated windings and fractional slot windings are widely taken into account when designing rare sintered earth magnets for permanent magnet synchronous machines (PMSMs). However, inverter-related losses are rarely simulated in Finite Element Method (FEM) co-simulations and can contribute as a major factor to the power losses in PMSMs. In the worst case, this neglection can lead to the thermal demagnetization of the permanent magnets. Segmentation provides an effective measure to limit eddy current losses. However, not every kind of segmentation proves effective in a drive application. Depending on the frequency behavior of the magnetic flux in a permanent magnet, segmentation can increase eddy current losses within the magnet compared to a non-segmented magnet. This behavior is due to the reaction to the flux caused by the eddy currents within the magnet. The reaction of the eddy currents is often neglected [1, 2], and, in other cases, the vicinity of ferromagnetic material is neglected in analytical calculations [3] but proves crucial for the exact calculation of higher frequency losses [4, 5]. In this paper, an analytical solution to calculate harmonic eddy current losses in permanent magnets, including the reaction flux with homogeneous excitation, is given.

Estimation of Stator Vibration in DFIM Under Various Types of Rotor Excitation

Variable speed power generation using Doubly Fed Induction Machine requires an adjustable frequency supply at the rotor terminals which can be achieved using power converters. Ideally, a variable frequency sinusoidal voltage should be applied, but it is not possible without the help of power converters. For a typical 250 MW DFIM with a speed variation of -10.73% to +8.33%, excitation power of 25 MW at 3.3kV and 11600 Amps is required. With this much high rotor current at low fundamental rotor frequency (3.75 Hz) electromagnetic forces in the air gap contain harmonic force components. Also, any time harmonic of radial force density in the rotor will be induced in the stator as a distinct time harmonic, modified by the influence of space harmonics in DFIM with regular three phase integral slot winding on both stator and rotor and vice versa. So, if the frequency and order of electromagnetic force components conflicts with mode shape and natural frequencies of the machine stator strong magnification in vibration will occur or more severely develops mechanical resonance. The stator vibration of electrical machine is generated by the electromagnetic forces acting on the surface of the stator tooths. This paper analyzes stator vibration for 250 MW DFIM in multiphysics simulation with its rotor winding excited through pure sinusoidal excitation at fundamental rotor frequency of 3.75 Hz and with two-Level voltage source converter at 3.75 Hz fundamental rotor frequency. Hardware results with supported multiphysics simulation on a laboratory prototype of 2.2 kW rating DFIM.

Employing the Peltier Effect to Control Motor Operating Temperatures

Electrical insulation failure is the most common failure mechanism in electrical machines (motors and generators). High temperatures and/or temperature gradients (HTTG) are the main drivers of insulation failure in electrical machines. HTTG combine with and augment other destructive effects from over-voltage, to voltage transients, overload and load variations, poor construction techniques, and thermal cycling. These operating conditions cause insulation damage that leads to electrical insulation failure. The insulation failure process is greatly accelerated by pollutants and moisture absorption. A simple and robust way to reduce HTTG and moisture adsorption is by maintaining constant internal temperatures. The current method to maintain elevated internal temperatures and reduce condensation issues is by internal electrical heating elements. This paper examines the effectiveness of applying thermoelectric coolers (TECs), solid-state heat pumps (Peltier devices), as heaters to raise a motor’s internal temperature by pumping heat into the motor core rather than heating the internal air. TEC technology is relatively new, and the application of TECs to heat a motor’s internal volume has not previously been explored. In this paper, we explore the hypothesis that TECs can pump heat into a motor when out of service, reducing the HTTG by maintaining high winding slot temperatures and eliminating condensation issues. This paper describes a test motor setup with simple resistive heating (traditional method), compared with the application of TECs with heat sinks, heat pipes, and a water circulation heat exchanger, to gauge the capability of TECs to heat the inner core or winding area. In this paper, we demonstrate the full integration of TECs into a motor. The results show that each of the systems incorporating the TECs would effectively pump heat into the core and keep the winding hot, eliminating condensation issues and water ingress due to thermal cycling.

Development and Discharge Characteristics of Surface Tracking on the Interface Between the PD Suppression Coatings Outside of Stator Winding Slots

During the operation of high voltage (HV) motors, the end-winding surface can be contaminated by oil or dust, resulting in a type of intense discharge: surface tracking, which gradually develops into phase-to-phase or phase-to-ground faults. To improve our understanding of the development process and characteristics of surface tracking on the end-winding, an accelerated aging test was performed on 10-kV stator coils to induce surface tracking under electrical and oil contamination stresses. To understand the evolution of surface tracking, the partial discharge (PD) was collected and the characteristics of the corresponding phase-resolved PD (PRPD) patterns and pulse sequence analysis (PSA) patterns were analyzed. Combined with finite element analysis (FEA) simulations, the development process of surface tracking was interpreted. It is established that the electrical field of a dry band with high resistivity on the contamination is much higher than other contaminated areas via FEA simulation, causing the electrical breakdown of the adjacent air and discharge. Such continuous and intense discharges finally leave on the end-winding surface a carbonized channel, forming a tree-like structure. This article presents the results of changes in PRPD patterns and PSA patterns during different stages, together with the surface potential distribution after tracking generation. The research of this article is devoted to providing a reference for PD monitoring and fault diagnosis of HV motors.

Structural Multi-Tooth Modification of Hybrid-Excited Doubly Salient Dual-PM Machine for Torque Production Improvement

A hybrid-excited doubly salient dual-PM machine (HE-DSDPM) was presented by using the structural multi-tooth modification for an improvement of torque production. The multi-tooth structure modification of HE-DSDPM was clearly described. The PM and stator arcs were further examined for structural optimization. The electromagnetic performance including magnetic flux distribution, flux linkage, back-electromotive force (back-EMF), total harmonic distortion (THD), cogging torque and electromagnetic torque, was investigated with various field current under the same structural constraint. The simulation based on 2-D finite element analysis was used to validate all electromagnetic performance. The results showed that the proposed multi-tooth HE-DSDPM provides the best stator/rotor combination, the appropriate PM characteristics and the enlarged winding slot area. This proposed structure produces better overall electromagnetic performance because of its improved symmetrical magnetic flux path and greater flux regulation quality. In particular, it can generate a larger average torque of 26.18% with the lower ripple torque of about 4% compared to the conventional structure at no field current since the good back-EMF profile and low cogging torque. The largest variance of the torque percentage is occurred when excited by different field currents for the proposed multi-tooth HE-DSDPM. Hence, modification of multi-tooth structure could be beneficial in the electrical machine design of other types of doubly salient structures.

A Novel Three-Layer Symmetry Winding Configuration for Five-Phase Motor

This paper presents a new three-layer, five-phase winding configuration theory of unconventional slot-pole combinations by each layer of winding for a phase vector correction, three layers of winding superimposed together to achieve the results of three-phase symmetry. Since the single-layer unconventional winding has to have an empty slot to meet its symmetry, based on the characteristics of single-layer winding, the unconventional winding design is carried out. Based on the simulation comparison between the single-layer unconventional winding and double-layer unconventional winding, a three-layer, nine-phase unconventional winding is proposed, which is based on the theory of single-layer unconventional winding, and three layers are staggered and stacked to realize nine-phase winding, which not only increases the utilization rate of the winding slot but also improves the fault tolerance performance. In addition, a 105-slot, 20-pole, three-layer, five-phase motor is proposed for a winding configuration and performance analysis to achieve both low torque pulsation and high fault tolerance.

Research on Dual 12-Phase 12-Slot Winding Permanent-Magnet Propulsion System Based on All-SiC Power Module

All-SiC power modules have lately received great attention for multiphase motor propulsion systems due to their low radiator temperature and high efficiency. However, the application of all-SiC power modules for dual 12-phase 12-slot winding permanent-magnet propulsion systems remains an ongoing challenge, owing to synchronous operation. In an effort to overcome this challenge, this article quantified and compared the all-SiC power module with Si-insulated gate bipolar transistor (IGBT) to underpin the all-SiC power module as the preferred choice for propulsion inverter application. The motor mathematical model and control strategy were illustrated in detail. Moreover, the crucial features of the propulsion inverter and synchronous control were elucidated by the theoretical and experimental analysis. The synchronous switching of the dual all-SiC power modules allowed the same slot windings to achieve excellent operation. The experimental results were given for the operation of propulsion systems based on all-SiC power modules. The motor operations under different speeds were investigated as well. Finally, the fault tolerance of the dual 12-phase 12-slot permanent magnet synchronous motor (PMSM) was validated under an open circuit.

Eddy current loss estimation for direct drive wind turbine generators with superconducting excitation winding by numerical and analytical models

AbstractDirect drive wind turbine generators with superconducting excitation winding are studied with focus on the electromagnetic damper design. A semi‐analytical eddy current model is built for parametric design studies based on a vector potential approach. The considered generators employ open stator slots and exhibit strong saturation effects, so that an analytical expression for the source terms is not adequate. Whilst the field equations are solved analytically, an equivalent current loading, accounting for slotting effects and saturation, is obtained by magnetostatic models applying the 2D finite element method (FEM). The proposed framework for the extraction of the current loading is universal and may also be applied to other machine types (e.g., permanent magnet synchronous machines, [PMSM]). In relation to transient FEM models, a considerable time‐saving can be achieved, which is particularly beneficial in case of large models, for example, in case of fractional slot windings or intermittent feeding schemes. The eddy current loss in warm and cold rotor parts in a direct drive generator in the 7 MW power class are computed with the semi‐analytical and transient 2D FEM models under variation of the damper geometry and the stator winding configuration. Minimum damper dimensions as well as constraints regarding applicable stator windings are derived.

Comparative Analysis between Slotless Axial Flux Permanent Magnet Motor with Equidirectional Toroidal Winding and Integral‐Slot Winding

Fractional slot concentrated winding (FSCW) is a kind of winding structure with few‐slots/coils multi‐poles. FSCW has the potential value of high torque density due to its short end‐winding and high slot fill ratio and is widely used in low‐speed direct‐drive application situations. However, compared with integral slot winding (ISW), the back EMF coefficient of FSCW is smaller, which leads to smaller output torque under the same condition. To improve the back EMF coefficient of FSCW, equidirectional toroidal winding (ETW) is proposed and applied to the dual rotor slotless axial flux permanent magnet motor (AFPM), in which the unit structure is three slots/coils two poles, and the ideal back EMF coefficient is the same as that of ISW. In this paper, firstly, the structure of ETW is introduced and its operating principle is analyzed. Then, compared with the AFPM with ISW, the open circuit and load characteristics of the AFPM with ETW under two conditions of the same wire gauge and the same coil width are analyzed respectively. The back EMF coefficient and output torque of ETW‐AFPM are similar to that of ISW‐AFPM under the same coil width. The back EMF coefficient and output torque of ETW‐AFPM are a little lower than that of ISW‐AFPM under the same wire gauge. Finally, the experimental results also validate the feasibility of AFPM with ETW and the correctness of the analysis results. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Five-Phase Hybrid Single-/Double-Layer Fractional Slot-Winding PMSM for Torque Improvement Under Third Harmonic Current Injection Condition

A 60-slot/22-pole five-phase machine with hybrid single-/double-layer fractional slot winding is proposed to improve torque under third harmonic current injection condition. Design process of the proposed machine includes two steps of first combining two sets of 20-slot/22-pole machine windings and then shortening coil-pitch. Due to the special structure of the proposed machine, torque-contributing space harmonics in magnetomotive force (MMF) are improved, and redundant space harmonic in MMF which causes high eddy current loss in permanent magnets is suppressed. The proposed machine is evaluated under two modes of third harmonic current injection, namely constant rms and peak harmonic injection. Compared with 20-slot/22-pole machine, the proposed machine achieves higher torque and lower losses under both third harmonic current injection conditions. Besides, the performance of the proposed machine when injecting only the first or third harmonic current is also analyzed.

Experimental investigation on end winding thermal management with oil spray in electric vehicles

To achieve a carbon-neutral sustainable future, the transportation sector is experiencing quick electrification, as more and more vehicles are driven by electric motors. Electric motors are designing more and more powerful and thus pose a great increasing challenge for thermal management. In this paper, an innovative experimental study on oil spray for end winding thermal management were presented. The experimental results indicated that the oil spray cooling significantly decrease the temperature of the winding. With higher oil temperature and flow rate, better cooling performance and better temperature uniformity were achieved both for teeth and slot winding. Meanwhile, a heat transfer performance prediction model based on a fully connected artificial neural network (ANN) was developed to correlate oil spray. The model used Reynolds number and Prandtl number as inputs, and the number of neurons in hidden layer was optimized to 8. The model accurately predicts the heat transfer performance of oil spray with a correlation coefficient of 0.93. The paper is expected to be a good reference for the oil spray engineering application in e-motor cooling.