Armature Windings Research Articles

A Static FEA Framework for Fast Analysis of HTS Armature Windings in AC Superconducting SMPM Machines

A Static FEA Framework for Fast Analysis of HTS Armature Windings in AC Superconducting SMPM Machines

Параметрическая модель синхронного реактивного двигателя с TLA-ротором в установившихся и переходных режимах

There is considerable practical and scientific interest in synchronous reaction motors (SynRM) with TLA rotor. The core of the TLA rotor has a transversal charge, internal slots, and highly saturated areas. The configuration of the rotor slots is complex and diverse. The task to develop a parametric model of the SynRM with a TLA-rotor designed for calculation of steady-state and transient modes of the motor is relevant. The classical parametric model of SynRM based on the theory of two reactions is used. The calculation method for the parameters of the SynRM model with TLA rotor is presented. The method uses the results of field calculation of two static states of the magnetic field. The steady-state conditions of SynRM are calculated according to the engineering formulas derived from the equation of equilibrium stresses in the stator phase. The Park-Gorev equations are used to calculate the transient modes of the SynRM. Field models of the SynRM under study at longitudinal and transverse rotor positions are presented. Main harmonics of magnetic field in the gap and their dependence on armature current are calculated. Formulas to calculate the inductive parameters of armature winding and performance characteristics of SynRM are given. Differential equations to calculate processes in SynRM are given. The parametric model is used to calculate performance characteristics of SynRM, frequency start process, electromechanical process of SynRM operation in case of asymmetric power supply. The calculation results are compared with the results of field simulation of SynRM with TLA rotor in the Ansys Maxwell environment. The classical parametric model of the synchronous machine based on the theory of two reactions allows fast and high-quality analysis of steady-state and transient modes of operation of a synchronous reactive motor with TLA-rotor under various conditions of power supply and mechanical load, including abnormal ones.

Electromagnetic design of ultra-high speed superconducting motors applied to electric pumps in liquid-propellant rockets

This paper provides an electromagnetic design for the 100 kW-class superconducting (SC) motor consisting of MgB2 armature windings and permanent magnet rotor; its stator part is made of non-magnetic and non-metallic materials. The SC motors, which are to be applied to future liquid-propellant rocket pump systems, are designed for the use at the ultra-high rotating speed: 50,000 rpm. The obtained results via the finite element method show that the output density of the designed SC motor reached 17.8 kW/kg, and that even at the ultra-high speed, total motor losses of the SC motor were so small as around 0.2 kW.

Performance Analysis of HTS Armature Axial Flux Magnetic Field Modulation Direct Drive Wind Generator

Axial flux electrical machine has higher power density than the radial flux electrical machine, showing a promising application in the field of offshore wind power generation. However, the conventional copper armature winding will suffer from severe joule loss when improving the electrical loading, resulting in that the further improvement of the power density of axial flux electrical machine is limited. In order to overcome the limitation of the electrical loading improvement of the copper armature winding, this paper uses the high-temperature superconducting (HTS) armature winding instead of the conventional copper armature winding, proposes an HTS armature axial flux magnetic field modulation direct-drive wind generator (HTSAAFFM-DDG). In this paper, the topology and operational principle of the proposed HTSAAFFM-DDG is clearly demonstrated. Meanwhile, the electromagnetic performances are carefully analyzed, including airgap magnetic field, basic electromagnetic characteristics, and AC loss analysis of the HTS armature winding. The research results show that the torque density of the proposed HTS armature axial flux machine can be 24% higher than that of the copper armature axial flux machine with the same size and topology. Besides, the superconducting (SC) shielding layer used in the proposed HTSAAFFM-DDG exhibits an excellent inhibition effect on the PM excited field, and can reduce the AC loss of the armature winding obviously.

A Double Rotor Flux Switching Machine With HTS Field Coils for All Electric Aircraft Applications

The increasing demand for high-power density motors in electric transport industries opens a new research opportunity to develop motor topologies with less weight and high efficiency. In particular, all-electric aircraft applications require very high power density motors. This paper shows the design of a new 1 MW 20-pole/15-slot double rotor flux switching machine with high-temperature superconducting field coils and thermal management system. The proposed motor features an air-core stator. Aluminum Litz wire is used for the armature conductors, and the YBCO- high-temperature superconducting material is used for the field coils. The armature winding and field coils operate at 95K and 65K, respectively. The active part power density including rotors, armature windings and field coils obtained with the proposed design is 29.3kW/kg. The specific power density of proposed motor considering mechanical, support structure and TMS is about 18.5 kW/kg. The efficiency can be higher than 98.7% which satisfies the requirement of electric aviation.

Performance Analysis of Distributed HTS Armature Winding Direct Drive Wind Generator With Active Magnetic Shielding Layer

High-temperature superconducting (HTS) electrical machine has higher torque density and higher efficiency than permanent magnet electrical machine, showing a great application prospect in the field of offshore wind power generation. However, if there is applied magnetic field acting on the wide plane of HTS tape perpendicularly, the current-carrying capacity of the HTS tape will be greatly reduced, resulting in the performance limitation of the HTS electrical machine. In order to reduce the negative effect of the applied magnetic field on the HTS tape, this paper proposes a new distributed HTS armature winding direct drive wind generator (DHTSAW-DDG) with active magnetic shielding layer. In this paper, the topology and working principle of the DHTSAW-DDG is clearly illustrated, meanwhile, the basic electromagnetic performances of the DHTSAW-DDG are carefully analyzed and compared with the counterpart with the copper armature winding. The results show that the active magnetic shielding layer made of HTS material can significantly weaken the negative effect of the applied magnetic field on the current-carrying capacity of the HTS tape. The electromagnetic performance of the HTS electrical machine can be significantly improved, if the distributed HTS armature winding and the active magnetic shielding layer are adopted. The torque density and the power factor of the proposed DHTSAW-DDG with active magnetic shielding layer can increase approximately 40% than the copper armature winding electrical machine with same topology.

Concentric-Coil Distributed Winding Design for Large Direct-Drive Fully Superconducting Machines

Fully superconducting generators (FSCGs) use superconducting wires for both the field and armature windings to reach a high torque density for wind turbine applications. The AC armature winding of an FSCG design mostly employed racetrack tooth-coils to form fractional-slot concentrated windings. This winding type has high leakage flux and excessive harmonics, especially when used in superconducting machines. Other attempts like applying full-pitch racetrack coils can only be with one slot per pole per phase which also has significant slotting harmonics. This paper proposes an innovative concept of double-layer concentric coils to enable distributed windings with a larger integral number of slots per pole per phase. The concept successfully breaks the limitation that racetrack coils cannot be built with such integral slots. This paper then assesses the performance of the proposed winding concept within a context 20 MW FSCG design. The assessment finds out that the proposed concept has balanced three phases but reduces inductance compared to single-layer windings. The force on each concentric coil can significantly be different, thereby complicating the mechanical design of these superconducting coils.

Control Method of HTS Permanent Magnet Synchronous Machine With a Nonlinear Disturbance Observer

The high temperature superconducting (HTS) permanent magnet synchronous machine (HTS-PMSM) uses the HTS armature winding instead of the copper armature winding, having higher torque density and higher efficiency and showing a great application prospect. Although the mathematical analysis model of the HTS-PMSM is similar as that of the conventional PMSM with the copper armature winding, as the load current increases, the stator core of the HTS-PMSM is more likely to be saturated, the inductance of quadrature-axis and direct-axis will be reduced. That leads that the power density and overload capacity of the HTS-PMSM will be affected, the control performance of the controller will be reduced as well. In order to solve the problem of the great change of the inductance values with the load variation, this paper proposes a nonlinear disturbance observer (NDOB) to estimate the disturbance of inductance parameter caused by the core saturation of the HTS-PMSM and builds a compensation strategy, combining with robust sliding mode control (SMC) to improve the stability of the speed and torque of the HTS-PMSM. The effectiveness of the proposed control method is verified by the combination method of the finite element analysis and Matlab/Simulink simulation.

Superconducting Synchronous Motor Development for Airplane Applications - Mechanical and Electrical Design of a Prototype 100 kW Motor

A 100 kW, 4500 RPM synchronous superconducting motor is being built at the Paihau-Robinson Research Institute, Victoria University of Wellington, New Zealand. The motor has superconducting excitation field coils on the rotor and a conventional stator winding. To minimize mass the motor is an air-core type, meaning no ferromagnetic materials are employed inside the motor. Some of the salient features of this motor include: 1) field winding coils employing REBCO CORC conductor; 2) field coils powered with a contactless superconducting dynamo exciter; 3) an EM shield on the rotor for protecting the field coils from high frequency magnetic fields due to stator harmonics and the switching of the drive electronics; 4) a unique single-layer winding design for the stator winding, where the stator coils are made with copper Litz wire and are liquid-cooled. This paper describes the electrical design and 3D simulation of the motor including the superconducting dynamo, and highlights stator and rotor coil developments that will be validated in the prototype. Sensitivity to critical design parameters has been assessed in simulation and initial sub-system prototypes manufactured for testing. Preliminary design is projecting this motor diameter and axial length as 360 mm and 550 mm respectively, with an efficiency of 96.4 % at the rated load. These numbers may be comparable with permanent magnet motors of similar rating, but this motor is being built to serve as a test-bed for evaluating different technologies for rotor and stator components. The ultimate goal for this program is a 3.0 MW machine with superconducting armature and field windings. In comparison with the permanent magnet motor in 2.5 - 3.0 MW range, the superconducting motors are expected to be 4 to 5 times smaller in size and mass with efficiency exceeding 99 %.

Designing and Commissioning an Experimental Setup to Evaluate AC Losses in Superconductors Under Transverse Rotating Fields

The development of low AC loss MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> conductors and the increasing interest in a liquid hydrogen-based economy have reignited research into high power density fully superconducting (SC) electrical machines. In these machines, the armature winding experiences rotating fields that generate AC losses, making it essential to estimate these losses during machine design. While analytical and finite element analysis (FEA) models are available in the literature for estimating AC losses, these models for multi-filament MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconductors have yet to be experimentally validated for machine operating regions. This paper presents a high-precision AC-loss test setup to measure AC losses in SC MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> windings under rotating fields at the air-gap field, frequency, and operating temperature levels relevant to electrical machine applications. The experimentally measured AC losses are then compared with analytical and FEA models. Results demonstrate good agreement between measurements and predictions. The paper discusses the experimental setup, sample preparation, calibration, measurement method, and results. The study provides a significant contribution to the development of high power density fully SC electrical machines.

Current Distribution of Armature Coils Combining Two Different Sizes of REBCO Racetrack Double Pancakes

We are currently developing superconducting electric propulsion armature coils which utilize REBa2Cu3Oy (REBCO) strands. To implement the REBCO coils in aircraft, the voltage must be reduced for safety concerns by using high-current capacity. Parallel conductors can be used to expand the current capacity, but the current cannot flow equally through each strand owing to the slight difference in inductance. We have investigated transposed parallel conductors which can almost equalize the inductance of each conductor. Conversely, the distributed windings for the armature coils can improve the magnetic field waveform and transform it into a sine wave by reducing the distortion of the magnetic flux density about the rotating magnetic field. However, it is difficult to implement a distributed armature winding using the REBCO strands since it is tape-shaped and difficult to twist. Therefore, we propose a distributed armature winding which combines two types of racetrack double pancakes. Each double pancake comprises two-strand insulated REBCO superconducting parallel conductors transposed inside the pancake for current equalization. In this study, we perform an experimental demonstration of the current equalization based on the transposition of the distributed armature winding. We made coils with two-strand as a simplified, but the actual coils were needed more 10 strand parallel conductors. In future works, we will manufacture transposed parallel conductor coils using much more strands and measure the current distribution. Additionally, this study measured the current distribution with only the stater. Thus, we will combine the rotor and measure the magnetic field distribution of the rotating magnetic field in the armature.

Application of Acoustic Signals for Rectifier Fault Detection in Brushless Synchronous Generator

One of the most important issues that power companies face when trying to reduce time and cost maintenance is condition monitoring. In electricity market worldwide, a significant amount of electrical energy is produced by synchronous machines. One type of these machines is brushless synchronous generators in which the rectifier bridge is mounted on rotating shafts. Since bridge terminals are not accessible in this type of generators, it is difficult to detect the possible faults on the rectifier bridge. Therefore, in this paper, a method is proposed to facilitate the rectifier fault detection. The proposed method is then evaluated by applying two conventional kinds of faults on rectifier bridges including one diode open-circuit and two diode open-circuit (one phase open-circuit of the armature winding in the auxiliary generator in experimental set). To extract suitable features for fault detection, the wavelet transform has been used on recorded audio signals. For classifying faulty and healthy states, K-Nearest Neighbours (KNN) supervised classification method was used. The results show a good accuracy of the proposed method.

A Non-Equilibrium Thermodynamic Approach for Analysis of Power Conversion Efficiency in the Wind Energy System

This article proposes an approach and develops an appropriate method of applying linear non-equilibrium thermodynamics to analyze energy processes, in particular using the example of the wind energy conversion system (WECS) with a directly connected vertical axis wind turbine (VAWT) and vector-controlled permanent magnet synchronous generator (PMSG). The main steps of the proposed approach are the description of the component subsystems as universal linear or linearized energy converters (ECs), which are characterized by several dimensionless parameters, the main one of which is the degree of coupling between their input and output. According to their value, as well as justified efficiency criteria, the optimal operating points of each ECs can be easily found. Such an approach makes it possible to abstract from physical laws of a different nature and equally assess the work of each of the subsystems. The next step is a connection of the received ECs. As shown in the paper, for the most common cascade connection of ECs, there are the best conditions for their connection, under which the newly formed equivalent EC can have maximum efficiency. This opens up an opportunity to analyze the influence of already real parameters of cascaded interconnected subsystems on the quality of their connection and justify specific solutions that would not have been seen without this approach. For example, in this study, from all parameters of the PMSG, only the selection of the optimal rated inductance of the armature winding made it possible to improve the quality of the connection of the PMSG with a specific VAWT and approximate the efficiency of the entire WECS to the maximum possible, especially in medium and high winds.

INCREASING THE MAXIMUM TORQUE OF SPECIAL DC MOTORS WITH PERMANENT MAGNETS

In the article proposes methods of increasing the maximum torque of built-in direct current torque motors by varying their design (the diameter of the armature winding wire; the dimensions of the armature in order to increase the number of conductors located on its outer surface; by changing the winding scheme) while maintaining the connection dimensions, which is an urgent task when designing or modernizing electric motors for autonomous transport devices. A number of calculations and experiments were carried out, the analysis of which showed that when the diameter of the winding wire increases, the resistance of the armature winding decreases and, as a result, the starting torque increases, the power consumption and losses in the armature winding also decrease. But at the same time, the starting current at a constant voltage increases by more than two times, which requires an increase in the installed capacity of the power source. Increasing the diameter of the armature allows you to increase the number of conductors and the cross-section of the armature copper while simultaneously reducing the width of the magnet and reducing the magnetic flux. As a result, the starting torque of the electric motor decreases. It is shown that changing the winding scheme can significantly complicate the technological process of manufacturing a simple loop winding and a complex multi-pass wave winding with a larger number of parallel branches and can create problems with the commutation of the armature winding. The work confirmed that increasing the diameter of the winding wire is the most effective and least expensive way to increase the maximum torque of built-in DC torque motors with excitation from permanent magnets and a slotless armature design, which have found their application in devices of autonomous objects (platforms). At the same time, changes are made only in the design of the anchor - the diameter of the anchor iron is reduced and the number of turns in the section is reduced. The magnetic system, brush-collector unit, bearing shields (if available) remain structurally unchanged.

Thermal Characteristic Analysis of Fully Superconducting Motors Employing Dilute Gas Rotor Cooling Structure

We have proposed a rotor cooling structure using dilute gas for a fully superconducting motor for aircraft application. Numerical analysis was performed to investigate the feasibility of the proposed cooling method and structure, which can make a fully superconducting motor lighter and more compact than a partially superconducting motor. The helium gas pressure in the gap, the rotor rotational speed, and the rotor loss are key parameters of the cooling, and thermal analysis was performed to clarify the dependence of the field winding temperature on these parameters. In the analysis, the motor model has the maximum output of 5.5 MW and the maximum speed of 5000 rpm. The superconducting armature windings are cooled down to 20 K by conduction cooling with liquid hydrogen, and the superconducting field winding is cooled down to about 50 K indirectly using helium gas in the gap. Numerical analysis results indicate that the helium gas pressure should be increased when the rotor loss is larger, but if the pressure is increased too much, the temperature of the field winding becomes higher due to wind loss. When the rotor loss is several hundred watts, the helium gas pressure should be in the range of 104 to 105 Pa.

Electromagnetic analysis of fully superconducting motors employing dilute gas rotor and liquid hydrogen stator cooling structure

This paper deals with fully superconducting motors (FSCMs) applied in the electric aircraft propulsion systems; the stator employs the MgB2-superconductor (SC) armature windings cooled at 20 K by using liquid hydrogen, while the rotor has the field windings made of REBCO SC wires cooled below 50 K via heat conduction and convective heat transfer by using dilute gas. The cooling structure of rotor can be simplified by adopting this type of design. The authors evaluated the optimal design for FSCM by using analytical equations and loss analysis via FEM. The FSCM characteristics were compared between ones using electromagnetic shield made of stainless steel (SUS) and ones using the shield made of copper (Cu); the results show that the output density using the SUS shield achieved 18.3 kW/kg, and that in terms of the loss estimation via FEM, both the motors had the efficiency over 98.5%.

Coil Winding Circuit Configurations for Permanent Magnet Synchronous Machines

The article outlines a procedure for drawing up the electric circuits of coil-type armature windings for salient-pole PM electric machines proceeding from the required number of pole pairs (the synchronous rotation frequency) and the number of phases. The procedure implementation algorithm is based on determining the stator teeth number as the one nearest to the number of rotor poles (2p) multiple to the number of phases. In this way, sufficient levels of coil pitch coefficient and winding coefficient are ensured. In accordance with the developed procedure, the coils in the phases can occupy one, two, or four phase zones from the adjacent coils connected into coil groups in a series opposition manner. The algorithm was tested on a few examples of drawing up the connection circuits of synchronous machine windings known from the electrical machinery construction theory and practice, including serially produced ones with the inner stator and for a pilot design of a high-capacity motor. For the latter one, its versions with three- and nine-phase windings for a 32-pole rotor (2p = 32) are compared. Numerical studies of the motor torque for both winding circuit versions carried out using the finite element method have shown that the version with the nine-phase winding produces a 20% higher torque. For one version of a serially produced motor, the winding electric circuit design validity was checked by calculating the torque-angle curves for different current densities. In all examples, formal compliance with the items of the outlined procedure has yielded correct circuit solutions. A criterion for evaluating the PM machine manufacturing complexity has been proposed, which depends on the winding type (distributed or coil-type) and on the number of PMs per magnetic system pole.

Novel Memory Motor Drive with Integrated Winding Concept for Traction Applications

This article presents a novel memory motor drive with integrated winding concept for traction applications. The key feature of the proposed idea is to integrate the excitation winding with armature winding, and hence eliminating additional magnetization winding to achieve online magnetization-state regulations. Hence, the spatial confliction of conventional memory motors can be solved. Upon implantation of the proposed design, the winding utilization, torque/power density and fault tolerant capability are significantly improved. Based on the field modulation theory, the air-gap flux densities under different magnetization states are derived quantitatively to provide design guideline in initial stage. The integrated memory motor drive is presented systematically to consolidate the field and armature windings. To illustrate the effectiveness of the proposed design, two other conventional memory motors are included for comparisons. It is revealed the presented memory motor with integrated winding concept exhibits 28% higher winding utilization, 43% higher torque/power density and 218% higher flux regulation capability than its counterpart with conventional separate windings. In addition, fault tolerant capability can be significantly improved by eliminating mutual coupling between two winding sets. Finally, a prototype is fabricated, and the experimental measurements are carried out to verify the presented concepts.

Topology Development and Performance Analysis of a Dual-Stator Permanent Magnet Arc Motor

In this paper, a dual-stator permanent magnet (PM) arc motor (DS-PMAM) with improved torque density is investigated for some specific direct-drive applications. The proposed DS-PMAM can be considered as the combination of the PM arc motor and the stator-PM motor. Benefiting from two different stator structure, two sets of armature windings are employed to improve the inner space utilization ratio and torque densities. The motor structure and working principle of the DS-PMAM are firstly introduced. The simplified analytical model is derived to provide a solid theoretical guidance for optimization design parameters selection. Then, the design considerations including the slot/rotor pole combination, the armature winding design, and the key structural parameters analysis are carried out to obtain the optimal motor performances of the DS-PMAM. After that, the electromagnetic characteristics of the DS-PMAM are evaluated together with the comparison with the inner-rotor PMAM, the outer-rotor PMAM, the surface-mounted PM PMAM, and the DS flux reversal PMAM. Finally, a prototype is manufactured and fully tested. Relevant experimental results verify the correctness of the FE analysis and the feasibility of this proposed design.

Investigation of Brushless Doubly-Fed Dual-Stator Machines for Traction Applications

Two brushless doubly-fed dual-stator machines with different inner-stator field windings, namely AC and DC field windings, are proposed and investigated. It is shown the proposed machine with AC field windings exhibits advantages of higher torque density and wider flux-regulation range compared with its DC field winding counterpart. Unlike conventional doubly-fed hybrid-excited machines, the proposed machine consists of AC field windings and hence resulting in more flexible field current control. Its armature and field windings are separately placed in two stators, which can alleviate the space competition between the field and armature slots, as well as significantly enhance the space utilization. Consequently, both flux-regulation capability and torque density can be effectively improved. The topology, operating principle, and mathematical model of the proposed machines are introduced. Then, a sectored flux-weakening control method is proposed and elaborated. Based on finite element method (FEM), the main electromagnetic performances of the proposed machines are comprehensively evaluated. The FEM results manifest the proposed machine with AC field windings shows greatly improved flux-regulation range, higher torque and output power under the proposed sectored flux-weakening method over the whole speed range. Finally, prototype machine of the proposed machine is fabricated, and experimental verifications are performed to validate the feasibility of the proposed machines.