Novel synchronous reluctance motor with sinusoidal rotor lamination shape for less torque ripple contents

Abstract: This paper presents the analysis of a novel Synchronous Reluctance Motor (SynRM), which has an axially sinusoidal rotor lamination shape. The sinusoidal lamination shape is used to vary magnetic flux in the q-axis direction. Therefore, cancelling some torque harmonics produced by stator slotting effects and rotor anisotropy, while maintaining the average torque. The stator of a 5.5 kW, 4-pole, 50 Hz conventional three-phase squirrel cage induction motor, with distributed and chorded by one slot, double layer winding, is used for both standard and novel motors. The Finite Element Analysis (FEM) is used to study the electromagnetic parameters of interests. The FEA results are validated by means of practical measurements. The results obtained from both FEA and practical measurements evidenced that the novel SynRM dropped tremendously the torque ripple contents while still maintained the average torque. The drop in torque ripple contents is mainly due to mitigation of the most dominant torque harmonics caused by stator slotting and rotor anisotropy

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 Simulation and Experiments on Electrical Machines for Integrated Starter-Generator Applications

This thesis presents two different non-permanent magnet machine designs for belt-driven integrated starter-generator (B-ISG) applications. The goal of this project is to improve the machine performance over a benchmark classical switched reluctance machine (SRM) in terms of efficiency, control complexity, torque ripple level and power factor. The cost penalty due to the necessity of a specially designed H-bridge machine inverter is also taken into consideration by implementation of a conventional AC inverter. The first design changes the classical SRM winding configuration to utilise both self-inductance and mutual-inductance in torque production. This allows the use of AC sinusoidal current with lower cost and comparable or even increased torque density. Torque density can be further increased by using a bipolar square current drive with optimum conduction angle. A reduction in control difficulty is also achieved by adoption of standard AC machine control theory. Despite these merits, the inherently low power factor and poor field weakening capability makes these machines unfavourable in B-ISG applications. The second design is a wound rotor synchronous machine (WRSM). From FE analysis, a six pole geometry presents a lower loss level over four pole geometry. Torque ripple and iron loss are effectively reduced by the use of an eccentric rotor pole. To determine the minimum copper loss criteria, a novel algorithm is proposed over the conventional Lagrange method, where the deviation is lowered from ± 10% to ± 1%, and the simulation time is reduced from hours to minutes on standard desktop PC hardware. With the proposed design and control strategies, the WRSM delivers a comparable field weakening capability and a higher efficiency compared with the benchmark SRM under the New European Driving Cycle, where a reduction in machine losses of 40% is possible. Nevertheless, the wound rotor structure brings mechanical and thermal challenges. A speed limit of 11,000 rpm is imposed by centrifugal forces. A maximum continuous motoring power of 3.8 kW is imposed by rotor coil temperature performance, which is extended to 5 kW by a proposed temperature balancing method. A prototype machine is then constructed, where the minimum copper loss criteria is experimentally validated. A discrepancy of no more than 10% is shown in back-EMF, phase voltage, average torque and loss from FE simulation

Critical Aspects of Electric Motor Drive Controllers and Mitigation of Torque Ripple - Review

Electric vehicles (EVs) are playing a vital role in sustainable transportation. It is estimated that by 2030, Battery EVs will become mainstream for passenger car transportation. Even though EVs are gaining interest in sustainable transportation, the future of EV power transmission is facing vital concerns and open research challenges. Considering the case of torque ripple mitigation and improved reliability control techniques in motors, many motor drive control algorithms fail to provide efficient control. To efficiently address this issue, control techniques such as Field Orientation Control (FOC), Direct Torque Control (DTC), Model Predictive Control (MPC), Sliding Mode Control (SMC), and Intelligent Control (IC) techniques are used in the motor drive control algorithms. This literature survey exclusively compares the various advanced control techniques for conventionally used EV motors such as Permanent Magnet Synchronous Motor (PMSM), Brushless Direct Current Motor (BLDC), Switched Reluctance Motor (SRM), and Induction Motors (IM). Furthermore, this paper discusses the EV-motors history, types of EVmotors, EV-motor drives powertrain mathematical modelling, and design procedure of EV-motors. The hardware results have also been compared with different control techniques for BLDC and SRM hub motors. Future direction towards the design of EV by critical selection of motors and their control techniques to minimize the torque ripple and other research opportunities to enhance the performance of EVs are also presented.publishedVersio

Comparison of interior permanent magnet synchronous machines for a high-speed application

Permanent Magnet machines have been increasingly used in high-speed applications due to the advantages they offer such as higher efficiency, output torque and, output power. This dissertation discusses the electrical and magnetic design of permanent magnet machines and the design and analysis of two 10 kW, 30000 rpm Interior Permanent Magnet (IPM) machines. This dissertation consists of two parts: the first part discusses high-speed machine topologies, and in particular the permanent magnet machine. Trends, advantages, disadvantages, recent developments, etc. are discussed and conclusions are made. The second part presents the design, analysis and testing of interior permanent magnet machines for a high-speed application. The machines are designed from first principles and are simulated using Ansys Maxwell software to understand the finite element analysis. In order to obtain a fair comparison between the machines, the required output criteria was used as the judging criteria (10kW, 30000 rpm). As a result, the rotor diameter, stator diameter, airgap length, and stack length were kept the same for both machines. The winding configuration was set as distributed windings, however the number of turns and other details were kept flexible in order to be able to obtain the best design for each machine. Similarly, the magnet volume was kept flexible as this could be used as a comparison criteria relating to the cost of the machines. The two IPM topologies are compared with respect to their torque, magnetic field, airgap flux, core loss, efficiency, and cost. The radial IPM produces a smoother torque output, with lower torque ripple, and has lower losses compared to the circumferential IPM which produces a higher torque and power output. Furthermore, the circumferential IPM also experiences much higher torque ripple and core losses, both of which are highly undesirable characteristics for high-speed machines. In addition, the circumferential IPM has a much more complex manufacturing process compared to the radial IPM which would significantly increase the cost of prototyping the machine, thus the radial IPM was selected for prototyping and brief experimental analysis. The radial IPM has been experimentally tested under no-load conditions. These results were successfully compared to the simulated and analytical results to show correlation between the design and experimental process. Potential areas of further work may include conducting detailed loss analysis to understand the effects that changing various design parameters has on the core loss and overall performance. Detailed thermal and mechanical analysis of the machines may also result in interesting conclusions that would alter the design of the machine to make it more efficient

Aspects of magnetisation and iron loss characteristics in switched-reluctance and permanent-magnet machines

In the first section, the magnetisation characteristics of the switched-reluctance motor are examined. Measurements have been carried out using both static and dynamic test methods. The test data has been compared with simulation results from analytical design programs and finite element models. The effects of mutual coupling on the magnetisation characteristics are investigated through measurement and simulation. Results show that the degree of mutual coupling is strongly dependent on the winding arrangement of the machine. In the next section, the difficulties in measuring the properties of permanent-magnet machines are discussed in detail, and solutions to common problems proposed. The measurement and analysis methods used for the switched-reluctance motor are further developed for analysis of permanent magnet machines. Techniques for determining the variation in synchronous reactances and permanent magnet flux are presented. Finite element simulations are used to show the variation of magnet flux under loading, a condition ignored in classical analysis methods. The final section discusses the analysis of magnetisation characteristics of electrical sheet steels. Comparison is made between measurements carried out on single sheet tester and Epstein square test rigs. The iron losses of a typical non-grain-orientated steel are measured under both sinusoidal and nonsinusoidal flux density conditions. The iron losses are shown to increase significantly when higher harmonic components are introduced to the flux density waveform. The difficulties in modelling the nonlinear iron loss characteristics of electrical steels are considered

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

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

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