Mathematical Approaches to Modeling, Optimally Designing, and Controlling Electric Machine

Optimal performance of the electric machine/drive system is mandatory to improve the energy consumption and reliability. To achieve this goal, mathematical models of the electric machine/drive system are necessary. Hence, this motivated the editors to instigate the Special Issue “Mathematical Approaches to Modeling, Optimally Designing, and Controlling Electric Machine”, aiming to collect novel publications that push the state-of-the art towards optimal performance for the electric machine/drive system. Seventeen papers have been published in this Special Issue. The published papers focus on several aspects of the electric machine/drive system with respect to the mathematical modelling. Novel optimization methods, control approaches, and comparative analysis for electric drive system based on various electric machines were discussed in the published papers

Analysis, design optimisation and experimental performance of synchronous reluctance and permanent magnet assisted synchronous reluctance machines

The research studies, in detail, the synchronous reluctance machine (SynRM) and permanent magnet assisted synchronous reluctance machine (PMSynRM) to improve the machine performances. In this study, the SynRM analytical models are revisited, and functional characteristics are mathematically developed to improve the machine performance. The performance parameters such as torque density, power factor, and efficiency are investigated along with torque ripples. SynRM is known for its high torque density in a compact size. Its improvement is analytically studied further by optimising rotor properties. The power factor of these machines is rather low compared with its equivalent AC machines. Although the machine’s power factor can be improved using control techniques, it is still not high enough. The machine has gone through significant development over the years since J.K Kostko published the first paper on reluctance machines back in 1923. The researchers have tested various types of anisotropies, such as axially laminated and transversally laminated. The machine torque and power factor depend on its saliency ratio. Although the axially laminated structure offers high saliency ratio due to the naturally distributed flux barrier structure, it has mechanical constraints. The axial rotor segments are fixed together by specially designed bolts that are conductive material in nature. This mechanical arrangement increases quadrature axis inductance, consequently reduces the saliency ratio of the machine. On the other hand, the transversally laminated structure is more mechanically feasible and offers comparatively high performance. One of the primary focus of this study is to improve the power factor. It has been comprehensively investigated. The SynRM machine is also known for high torque ripples. The non-linear structure and its reluctance path along the air-gap make the machine highly susceptible to torque pulsation. The cross induction due to the D and Q axis along the air-gap increases the machine’s ripples. Besides, poor stator winding (both sinusoidal and step excitation) also increases the machine torque ripples. The existing ripple reduction practices are revisited in this study to further understand the torque ripples of this machine. The rotor of SynRM is redesigned and optimised to reduce the ripples effect. The causes of ripples are also analytically studied in detail, and mathematical models are developed and presented for understanding the phenomena. Two different ways of analysing the ripple effects are considered, and the pros and cons of both methods are discussed. The SynRM is simulated using an advanced finite element analysis (FEM) software to verify the analytical models as well as optimise the machine performance. Firstly, primitive rotor structures are developed so that they can be automatically varied during parameterisation and optimisation. Four flux barrier shapes are analysed to determine the optimum shape for high performance by investigating flux’s natural path. From the results, a multi-barrier arrangement is studied with an advanced algorithm for three and four-layer designs, and an optimum rotor is proposed based on the simulations. Using a single-objective and multi-objective optimisation techniques, the SynRM is optimised from the simulated design. An advanced topology is developed for automated optimisation that can offer flexibility in varying optimisation variables as part of this research. The optimised design’s performance is analysed in detail and compared with analytical models. The torque ripples are discussed in detail, and an advanced torque ripple minimisation topology is developed. Then the design is optimised for two types of barrier shapes. A number of designs are prototyped for experimental verification. Finally, the current trend in rare-earth magnets is investigated with its cost per volume ratio. The rare-earth neodymium magnets are focused on this study for improved performance with optimum volume. The analytical model of PM assisted design is studied in detail, and its performance parameters are compared with SynRM. A PMSynRM with a linear-barrier is simulated for a detailed analysis of the machine that discusses different PM volumes and the impact on machine performance due to the volume of PM and location. The performance parameters, discussed in the analytical model, are compared with the simulation results. The improvement in power factor and torque density is investigated using various designs. The optimisation is performed in two ways. The first one is adding PMs to the optimised SynRM. Single-objective and multi-objective optimisation are performed using an advanced optimisation algorithm. Secondly, the topology of SynRM is modified for PMSynRM in such a way the entire machine can be automated during optimisation by adding the PM’s variables to the existing one. The performances of the two optimised designs have been compared. PMSynRM prototypes are developed to verify the simulation results. The eight SynRM designs are prototyped to report the practical results. Six of them are to verify various performance parameters of SynRM and two of them to test the ripples effect. Moreover, two PMSynRM prototypes are fabricated to verify the simulation results. The saliency of each SynRM is measured and compared with simulated results. Then, each design is tested experimentally in all possible scenarios and compared. Extensive testing is performed on all prototypes under various operating conditions and reported

Advances in Rotating Electric Machines

It is difficult to imagine a modern society without rotating electric machines. Their use has been increasing not only in the traditional fields of application but also in more contemporary fields, including renewable energy conversion systems, electric aircraft, aerospace, electric vehicles, unmanned propulsion systems, robotics, etc. This has contributed to advances in the materials, design methodologies, modeling tools, and manufacturing processes of current electric machines, which are characterized by high compactness, low weight, high power density, high torque density, and high reliability. On the other hand, the growing use of electric machines and drives in more critical applications has pushed forward the research in the area of condition monitoring and fault tolerance, leading to the development of more reliable diagnostic techniques and more fault-tolerant machines. This book presents and disseminates the most recent advances related to the theory, design, modeling, application, control, and condition monitoring of all types of rotating electric machines

Investigation of performance improvement of doubly salient synchronous reluctance machine with current harmonic injection

This thesis investigates some novel current harmonic injection methods to improve the electromagnetic performance of doubly salient synchronous reluctance machines (DS-SRMs). These machines will have different winding configurations, slot/pole number combinations and phase numbers. The theoretical analyses (both static and dynamic) are carried out based on Fourier Series analysis, and validated by 2-dimensional finite element method and also experiments using several prototype machines. Based on the analytical torque model in abc-axis frame, a powerful insight into the mechanism of torque generation of the DS-SRMs with pure sinewave current supply can be achieved. The electromagnetic torque (both magnitude and phase angle) produced by each order of inductance harmonic can be predicted, which allows us to obtain the dominant torque ripple components for such machines. Therefore, the appropriate current harmonic (3rd, 5th and 7th) can be injected to generate torque ripple components in order to compensate that produced by the fundamental current, and hence to achieve an overall reduced torque ripple. On the other hand, the average torque of the DS-SRMs can also be improved by properly selecting the current harmonics in terms of harmonic order, amplitude and phase angle. However, it is found that the current harmonics, although can improve torque performance, will often cause extra losses (both copper and iron losses) and undesirable distortion in the phase voltages, which could lead to negative impact on the machine efficiency and dynamic performance. Therefore, in order to fully evaluate the potential of the proposed harmonic current injection method, comprehensive studies about losses, efficiency and dynamic performances such as torque-speed curves of 3-phase and multi-phase DS-SRMs have been carried out. In order to simplify the investigation of dynamic performance analyses such as the torque speed curves and efficiency maps, novel analytical torque model in dq0-axis frame has also been proposed. The findings in this thesis can provide some useful guidelines for torque performance improvement of DS-SRMs using harmonic current injections

Synchronous reluctance motors with fractional slot-concentrated windings

PhD ThesisToday, high efficiency and high torque density electrical machines are a growing research interest and machines that contain no permanent magnet material are increasingly sought. Despite the lack of interest over the last twenty years, the permanent magnet-free synchronous reluctance machine is undergoing a revival and has become a research focus due to its magnet-free construction, high efficiency and robustness. They are now considered a potential future technology for future industrial variable speed drive applications and even electric vehicles. This thesis presents for the first time a synchronous reluctance motor with fractional slot-concentrated windings, utilizing non-overlapping single tooth wound coils, for high efficiency and high torque density permanent magnet-free electric drives. It presents all stages of the design and validation process from the initial concept stage through the design of such a machine, to the test and validation of a constructed prototype motor. The prototype machine utilizes a segmented stator core back iron arrangement for ease of winding and facilitating high slot fill factors. The conventional synchronous reluctance motor topology utilizes distributed winding systems with a large number of stator slots, presenting some limitations and challenges when considering high efficiency, high torque density electrical machines with low cost. This thesis aims to present an advancement in synchronous reluctance technology by identifying limitations and improving the design of synchronous reluctance motors through development of a novel machine topology. With the presented novel fractional slot concentrated winding machine design, additional challenges such as high torque ripple and low power factor arise, they are explored and analysed - the design modified to minimise any unwanted parasitic effects. The electrical and electromagnetic characteristics of the developed machine are also explored and compared with that of a conventional machine. A novel FEA post-processing technique is developed to analyse individual air-gap field harmonic torque contributions and the machines dq theory also modified in order to account for additional effects. The developed machine is found to be lower cost, lower mass and higher efficiency than an equivalent induction or conventional synchronous reluctance motor, but does suffer higher torque ripples and lower power factor. The prototype is validated using static and dynamic testing with the results showing a good match with finite element predictions. The work contained within this thesis can be considered as a first step to developing commercial technology based on the concept for variable speed drive applications.Financial assistance was provided by was provided by the UK Engineering and Physical Sciences Research Council (EPSRC) in the form of a Doctoral Training Award and additional financial assistance was kindly provided by Cummins Generator Technologies, Stamford, UK, through industrial sponsorship of this wor

Design and Control of Electrical Motor Drives

Dear Colleagues, I am very happy to have this Special Issue of the journal Energies on the topic of Design and Control of Electrical Motor Drives published. Electrical motor drives are widely used in the industry, automation, transportation, and home appliances. Indeed, rolling mills, machine tools, high-speed trains, subway systems, elevators, electric vehicles, air conditioners, all depend on electrical motor drives.However, the production of effective and practical motors and drives requires flexibility in the regulation of current, torque, flux, acceleration, position, and speed. Without proper modeling, drive, and control, these motor drive systems cannot function effectively.To address these issues, we need to focus on the design, modeling, drive, and control of different types of motors, such as induction motors, permanent magnet synchronous motors, brushless DC motors, DC motors, synchronous reluctance motors, switched reluctance motors, flux-switching motors, linear motors, and step motors.Therefore, relevant research topics in this field of study include modeling electrical motor drives, both in transient and in steady-state, and designing control methods based on novel control strategies (e.g., PI controllers, fuzzy logic controllers, neural network controllers, predictive controllers, adaptive controllers, nonlinear controllers, etc.), with particular attention to transient responses, load disturbances, fault tolerance, and multi-motor drive techniques. This Special Issue include original contributions regarding recent developments and ideas in motor design, motor drive, and motor control. The topics include motor design, field-oriented control, torque control, reliability improvement, advanced controllers for motor drive systems, DSP-based sensorless motor drive systems, high-performance motor drive systems, high-efficiency motor drive systems, and practical applications of motor drive systems. I want to sincerely thank authors, reviewers, and staff members for their time and efforts. Prof. Dr. Tian-Hua Liu Guest Edito

Investigation of novel multi-layer spoke-type ferrite interior permanent magnet machines

The permanent magnet synchronous machines have been attracting more and more attention due to the advantages of high torque density, outstanding efficiency and maturing technologies. Under the urges of mandatory energy efficiency requirements, they are considered as the most potential candidates to replace the comparatively low-efficient induction machines which dominate the industrial market. However, most of the high performance permanent magnet machines are based on high cost rare-earth materials. Thus, there will be huge demands for low-cost high-performance permanent magnet machines. Ferrite magnet is inexpensive and abundant in supply, and is considered as the most promising alternative to achieve the goal of low cost and high performance. In consideration of the low magnetic energy, this thesis explored the recent developments and possible ideas of ferrite machines, and proposed a novel multi-layer spoke-type interior permanent magnet configuration combining the advantages of flux focusing technique and multi-layer structure. With comparable material cost to induction machines, the proposed ferrite magnet design could deliver 27% higher power with 2-4% higher efficiency with exactly the same frame size. Based on the data base of International Energy Agency (IEA), electricity consumed by electric machines reached 7.1PWh in 2006 [1]. Considering that induction machines take up 90% of the overall industrial installation, the potential energy savings is enormous. This thesis contributes in five key aspects towards the investigation and design of low-cost high-performance ferrite permanent magnet machines. Firstly, accurate analytical models for the multi-layer configurations were developed with the consideration of spatial harmonics, and provided effective yet simple way for preliminary design. Secondly, the influence of key design parameters on performance of the multi-layer ferrite machines were comprehensively investigated, and optimal design could be carried out based on the insightful knowledge revealed. Thirdly, systematic investigation of the demagnetization mechanism was carried out, focusing on the three key factors: armature MMF, intrinsic coercivity and working temperature. Anti-demagnetization designs were presented accordingly to reduce the risk of performance degradation and guarantee the safe operation under various loading conditions. Then, comparative study was carried out with a commercial induction machine for verification of the superior performance of the proposed ferrite machine. Without loss of generality, the two machines had identical stator cores, same rotor diameter and stacking length. Under the operating condition of same stator copper loss, the results confirmed the superior performance of the ferrite machine in terms of torque density, power factor and efficiency. Lastly, mechanical design was discussed to reduce the cost of mass production, and the experimental effort on the prototype machine validates the advantageous performance as well as the analytical and FEA predictions

Design of Synchronous Reluctance Machines for Automotive Applications

This dissertation reports an appropriate design methodology for synchronous reluctance machines, their important technical issues, and possible solutions for traction applications. The synchronous reluctance machines are used in industries owing to their unique merits such as high efficiency, fast dynamic response, and lower cost. Considering these superior properties, recently, this smart synchronous topology became more attractive for electrified powertrain applications in automotive industries. However, compared to the major requirements of the traction motors such as high torque and power density, low torque ripple, wide speed range, and proper size, this machine is still under investigations. The goals of this research work are first; to identify electrical, magnetic, and geometrical parameters which are dominant in the machine’s performance, and second; to verify appropriate design methodology for achieving a higher performance for automotive applications. Hence, analytical and computer aided analysis followed by experimental examinations on prototypes are carried out to support proposed methods and address possible solutions to the machine’s technical issues for these particular applications. Accordingly, the synchronous reluctance machine’s fundamental operations, electrical, magnetic, and geometrical parameters are investigated. Analytical approach and a sizing methodology corresponding to the desired specifications are presented through the machine’s mathematical model. Design of transversal laminated anisotropic rotor structure with different geometries is studied to identify the geometrical parameters effects on the machine’s performance in particular the output torque and torque ripple. An appropriate geometrical method along with an innovative rotor lamination assembly are proposed for improving the machine’s output functions such as torque, power, and saliency ratio. Finally, the future perspective of the research work is discussed for further investigations