2D Analytical Model of Armature Reaction Magnetic Field Distribution in Slotless Permanent-Magnet Linear Tubular Machines

This paper presents a 2D analytical model for predicting the magnetic flux density distribution in slotless permanent-magnet (PM) linear tubular (PMLT) motors due to armature reaction effects based on the sub-domain method. According to this method, the machine cross-section is divided into the six sub-regions and Maxwell partial differential equations (PDEs) are formed in each sub-region. Solving these PDEs leads to defining the magnetic vector potential in each sub-region and applying curl on the calculated magnetic vector potential results in determining the magnetic flux density components. Eventually, the extracted results are compared with those of the finite-element method (FEM) to confirm the accuracy of the described analytical model. The results reveal that the presented analytical model is a suitable candidate for predicting the magnetic flux density components of the slotless PMLT motors in a shorter time

Flux switching machine design for high-speed geared drives

Electrical machines capable of high-speed operation are key technology used in many modern applications, such as gas turbine electrical systems, high-speed fly-wheels, turbochargers, and computer numerical control (CNC) machines. The use of geared high-speed machines to replace low-speed high torque drives has not been adequately researched to-date. The rationale of this thesis is to investigate a candidate high speed machine, namely flux switching machines to be used together with new types of core material with mechanical gearing to deliver high-torque and low speeds. Modern developments in advanced material technology have produced new magnetic materials capable of dealing with high resulting in very low losses in high speed machines. However, such metals typically have low mechanical strength, and they are found to be brittle. In order to manufacture electromechanical device with such new materials, it has to be reinforced with a mechanically strong structure. The use of multiple types of magnetic materials referred as a MMLC has been proposed in this thesis for high-speed machine design. In this research, a generic method using magnetic equivalent circuit to model flux switching machines (FSMs) is investigated. Moreover modeling, based on machine dimensions for multiphase FSMs having any pole and slot number has been introduced. The air-gap permeance modeling to simplify the magnetic circuit calculation of FSMs was also investigated in this thesis. It is shown that the permeability of magnetic material can be adjusted with the use of MMLC material. Using this feature, the FSM mathematical model is used to show the impact on electromagnetic performance using MMLCs and is shown to be beneficial. In order the evaluate the weight benefits of using geared high speed FSMs, the planetary gear systems are studies and their design constraints have been identified. An abstract form of weight estimation for given torque and speed requirements has been developed and validated using commercially available planetary gear specifications. FSMs together with gear boxes have been considered and it is shown that significant weight savings can be achieved at higher diameter and at high speeds

Design and performance investigation of flux-concentrated tubular linear generator for an external combustion free piston engine

PhD ThesisThe increasing global desire for highly fuel efficient power systems and the need for environmentally friendly energy sources is driving much present research in electrical power. A linear power system, where a linear machine is driven directly by a free piston engine, offers scalability and a wide range applicability. Standalone power units, hybridised power systems and range extenders in electrified vehicles are all potential applications for this technology. This thesis explores the application of a Linear Joule Engine driving a Permanent Magnet Linear Machine for electrical power generation. Whereas most Joule cycle engines have a rotary compressor and expander, at smaller scale this configuration suffers from leakage around the blades. The linear engine uses a double acting free piston configuration running on the external combustion Joule-cycle, overcoming the low efficiency inherent in small scale gas turbines. The key element for electrical power generation, and the main focus of this thesis, is the development of a linear machine operating as a generator, the design of which is heavily constrained by the geometrical and the operational characteristics of the engine. Using specific constraints for an 5kW engine and by using two dimensional finite element analysis, a novel design methodology of tubular PM linear machine with modular armature winding and feasible arrangements of magnets on the translator member is outlined. The effect of core material, pole number and power conversion system on the machine design are investigated, highlighting the effect of the interconnected design variables on the resulting performance and material use, all satisfying design objectives. A Flux – Concentrated PM configuration is selected for further development. vi In order to accomplish an overall system performance investigation tool, at first the development of a general novel linear machine model is introduced and tested in a feedforward manner with accounts for all machine interacting electromagnetic forces. Then, a novel dynamic model incorporating both the linear machine model driven by the linear Joule engine model, coupled together in a closed loop form, is realized. The coupled model bridges mechanical and electrical parts of the engine-generator, and provides a solid dynamic performance prediction of the system focusing on identifying the effect of cogging force on system performance and the resultant electrical power loss and electrical efficiency. Compared with the reported cogging force reduction techniques, a novel structural technique and a selection criteria are presented with two dimensional axisymmetric finite element analysis verification showing the effectiveness of the proposed technique. Finally, a machine prototype of the selected design model is manufactured and tested on a bespoke test rig to validate the design model findings. Manufacturing recommendations and future achievable steps are reported for future development of the existing work.The Iraqi Ministry of Higher Education and Scientific Research – University of Baghda

Modelling and Control of Switched Reluctance Machines

Today, switched reluctance machines (SRMs) play an increasingly important role in various sectors due to advantages such as robustness, simplicity of construction, low cost, insensitivity to high temperatures, and high fault tolerance. They are frequently used in fields such as aeronautics, electric and hybrid vehicles, and wind power generation. This book is a comprehensive resource on the design, modeling, and control of SRMs with methods that demonstrate their good performance as motors and generators

Modelling and Control of Switched Reluctance Machines

Today, switched reluctance machines (SRMs) play an increasingly important role in various sectors due to advantages such as robustness, simplicity of construction, low cost, insensitivity to high temperatures, and high fault tolerance. They are frequently used in fields such as aeronautics, electric and hybrid vehicles, and wind power generation. This book is a comprehensive resource on the design, modeling, and control of SRMs with methods that demonstrate their good performance as motors and generators

High performance, direct drive machines for aerospace applications

For aerospace related electric systems, torque/force density, reliability and fault tolerance are of the utmost importance. A method by which high figures of reliability can be achieved is by eliminating any mechanical gearing or interconnection elements between the electrical machine and its mechanical load. This means that direct drive, electrical machines must be employed. However, to implement such solutions (without any mechanical advantages), electrical machines with excellent torque density (for rotational machines) and force density (for linear machines) performances are required. In this work, the main aim is to propose and investigate possible methods for extending and improving the torque/force density capabilities of high performance, state of the art, electrical machines (both rotational and linear). This is done in order to be able to meet the performance requirements while lacking the mechanical advantages synonymous with gearing and/or mechanical interconnections. Novel electro-magnetic and thermal management structures, detailed design and optimisation procedures for electrical machines are presented in this thesis. As vehicles to investigate these novel concepts, a tubular linear, permanent magnet motor and a rotational, synchronous permanent magnet motor are designed, built and experimentally tested. These machines which are both for aerospace related applications serve to show and validate the worthiness of the proposed, performance enhancement measures

Magnetic Material Modelling of Electrical Machines

The need for electromechanical energy conversion that takes place in electric motors, generators, and actuators is an important aspect associated with current development. The efficiency and effectiveness of the conversion process depends on both the design of the devices and the materials used in those devices. In this context, this book addresses important aspects of electrical machines, namely their materials, design, and optimization. It is essential for the design process of electrical machines to be carried out through extensive numerical field computations. Thus, the reprint also focuses on the accuracy of these computations, as well as the quality of the material models that are adopted. Another aspect of interest is the modeling of properties such as hysteresis, alternating and rotating losses and demagnetization. In addition, the characterization of materials and their dependence on mechanical quantities such as stresses and temperature are also considered. The reprint also addresses another aspect that needs to be considered for the development of the optimal global system in some applications, which is the case of drives that are associated with electrical machines

Design and optimisation of outer-rotor hybrid excitation flux switching motor

Permanent Magnet Flux Switching Motor (PMFSM) with outer-rotor configuration recently reported in the literature can potentially lead to a very compact in-wheel electric vehicle (EV) drive design and increased cabin space through the elimination of mechanical transmission gears. Nevertheless, the output torque is still insufficient to drive heavier EV especially at starting and climbing conditions. On the other hand, with the permanent magnets placed along the radial V-shaped segmented stator, the PMFSM is prone to excitation flux leakage and demagnetization, making optimisation of the rotor and stator dimensions a difficult objective to achieve, while keeping the PM volume constant. In this thesis, design and optimisation of high torque capability salient stator outer-rotor hybrid excitation flux switching motor (OR-HEFSMs) are investigated. With the additional DC field excitation coil (FEC) as a secondary flux source, the proposed motor offers advantage of flux control capability that is suitable for various operating conditions. The design restrictions and specifications of the proposed motor are kept similar as interior permanent magnet synchronous motor (IPMSM) employed in the existing hybrid electric vehicle (HEV) Toyota Lexus RX400h. The JMAG-Designer ver.14.1 was used as 2D-finite elements analysis (FEA) solver to verify the motor’s operating principle and output torque performance characteristics. The subsequent optimisation work carried out using deterministic optimisation approach (DOA) has produced a very promising 12S-14P OR-HEFSM configuration, where a maximum torque density of 12.4 Nm/kg and power density of 5.97 kW/kg have been obtained. These values are respectively 30% and 68% more than that produced by IPMSM of comparable dimensions. A reduced-scale prototype 12S-14P OR-HEFSM has also been fabricated to minimize the manufacturing cost and no-load laboratory measurements have been carried out to validate the simulation results. The results obtained show that they are in good agreement and has potential to be applied for in-wheel drive EV

Analysis and Design of a Linear Tubular Electric Machine for Free-piston Stirling Micro-cogeneration Systems

The UE investments for the renewable source development, in order to achieve the set goals (Kyoto protocol and “20-20-20” targets), push to investigate in new technologies and to develop the existing. In this context, the cogeneration (CHP) plays a fundamental role, and in particular, the micro-CHP has wide development margins. Among the different cogeneration process, the systems driven by a free-piston Stirling engine are one of the most significant challenges in the research area. In such systems, the thermal energy, coming from primary energy source (for example renewable energy), is converted into mechanical energy through a Stirling engine, and then a linear generator converts the mechanical energy into electrical energy, finally, the generator is connected to the electric grid or to the load by means of an electric converter. The use of the linear generator, instead of the traditional systems of linear to alternating motion conversion (rod-crank system), allows achieving several advantages, including: improving the system reliability, noise and cost reduction. Finally, this kind of system, if well-designed, allows improving the system efficiency. In this thesis a linear generator, directly coupled to a free-piston Stirling engine in a CHP system, was developed and analysed. It was found, after a first phase of the study and literature review, that the most convenient choice, from the technical and economic point of view, is a single-phase tubular permanent magnet linear generator. In particular, the magnets are made of plasto-neodymium, while, for the realization of the stator magnetic circuit, due to the geometrical complexity, soft magnetic composites (SMC) materials have been considered. In order to determine the generator performance, an analysis method based on FEAs was developed. This simplified method (HFEA) allows the study and the comparison of different magnetization patterns and current supply strategies. The proposed methodology exploits the representation of the magnetization spatial harmonics through an analytical processing that allows taking into account different magnetization profile of the permanent magnets. Thus, it was possible to reconstruct the most important quantities, such as the flux density and the flux linkage, superposing the effect of each harmonic obtained through the Fourier analysis. Furthermore, a procedure, able to reproduce the effects of magnetic saturation of the mover, generally not negligible in such kind of machines, was developed. For this purpose, an appropriate surface current distribution on the yoke of the mover was introduced, in order to reproduce the demagnetizing effect due to the saturation. By means of the air gap flux density, the force provided by linear generator was calculated, while, by means of the flux density sampled on suitable points on the stator and mover yokes, the iron losses were estimated and then the machine efficiency. By means of the flux linkage the emf provided by linear generator was determined. The results show a very good agreement with corresponding FEAs. The proposed analysis method allows carrying out a parametric analysis with a lower computational effort. Thanks to this feature, different magnetization patterns, supply strategies and SMC materials can be compared in order to optimize the machine design. A prototype based on the design guidelines was built; then, a procedure based on experimental measurement was developed to characterize the electromagnetic parameters. To determine the magnetization profile of the magnets, the flux density on the mover surface was carried out by means of a Gaussmeter. As regards the SMC materials that compose the stator core, a calculation method was developed from suitable experimental elaborations, in order to determine the most important magnetic properties, such as the BH curve and core loss coefficients. From experimental results, it can be noted that the actual characteristics are poorer than those provided by the manufactured datasheets, likely due to the manufacturing processes and spurious air gaps between the SMC modules. The update electromagnetic parameters are used to determine the actual performance of the machine, particularly to estimate the efficiency, the emf and the force. Finally, a simplified model of the cogeneration system was developed in order to predict the dynamic behaviour and particularly, the actual values of the speed, output power and efficiency. This model allows developing the control strategy of the linear generator acting on the electric converter