Design Synthesis and Optimization of Permanent Magnet Synchronous Machines Based on Computationally-Efficient Finite Element Analysis

In this dissertation, a model-based multi-objective optimal design of permanent magnet ac machines, supplied by sine-wave current regulated drives, is developed and implemented. The design procedure uses an efficient electromagnetic finite element-based solver to accurately model nonlinear material properties and complex geometric shapes associated with magnetic circuit design. Application of an electromagnetic finite element-based solver allows for accurate computation in intricate performance parameters and characteristics. The first contribution of this dissertation is the development of a rapid computational method that allows accurate and efficient exploration of large multi-dimensional design spaces in search of optimum design(s). The computationally efficient finite element-based approach developed in this work provides a framework of tools that allow rapid analysis of synchronous electric machines operating under steady-state conditions. In the developed modeling approach, major steady-state performance parameters such as, winding flux linkages and voltages, average, cogging and ripple torques, stator core flux densities, core losses, efficiencies and saturated machine winding inductances, are calculated with minimum computational effort. In addition, the method includes means for rapid estimation of distributed stator forces and three-dimensional effects of stator and/or rotor skew on the performance of the machine. The second contribution of this dissertation is the development of the design synthesis and optimization method based on a differential evolution algorithm. The approach relies on the developed finite element-based modeling method for electromagnetic analysis and is able to tackle large-scale multi-objective design problems using modest computational resources. Overall, computational time savings of up to two orders of magnitude are achievable, when compared to current and prevalent state-of-the-art methods. These computational savings allow one to expand the optimization problem to achieve more complex and comprehensive design objectives. The method is used in the design process of several interior permanent magnet industrial motors. The presented case studies demonstrate that the developed finite element-based approach practically eliminates the need for using less accurate analytical and lumped parameter equivalent circuit models for electric machine design optimization. The design process and experimental validation of the case-study machines are detailed in the dissertation

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

Automated Design Optimization of Synchronous Machines: Development and Application of a Generic Fitness Evaluation Framework

A rotating synchronous electric machine design can be described to its entirety by a combination of 17 to 24 discrete and continuous parameters pertaining the geometry, material selection, and electrical loading. Determining the performance attributes of a design often involves numerical solutions to thermal and magnetic equations. Stochastic optimization methods have proven effective for solving specific design problems in literature. A major challenge to design automation, however, is whether the design tool is versatile enough to solve design problems with different types of objectives and requirements. This work proposes a black-box approach in an attempt to encompass a wide variety of synchronous machine design problems. This approach attempts to enlist all possible attributes of interest (AoIs) to the end-user so that the design optimization problem can be framed by combination of such attributes only. The number of ways the end-user can input requirements is now defined and limited. Design problems are classified based on which of the AoI’s are constraints, objectives or design parameters. It is observed that regardless of the optimization problem definition, the evaluation of any design is based on a common set of physical and analytical models and empirical data. Problem definitions are derived based on black-box approach and efficient fitness evaluation algorithms are tailored to meet requirements of each problem definition. The proposed framework is implemented in Matlab/C++ environment encompassing different aspects of motor design. The framework is employed for designing synchronous machines for three applications where designs based on conventional motor construction did not meet all design requirements. The first design problem is to develop a novel bar-conductor tooth-wound stator technology for 1.2 kW in-wheel direct drive motor for an electric/hybrid-electric two wheeler (including practical implementation). The second design problem deals with a novel outer-rotor buried ferrite magnet geometry for a 1.2 kW in-wheel geared motor drive used in an electric/hybrid-electric two wheeler (including practical implementation). The third application involves design of an ultra-cost-effective and ultra-light-weight 1 kW aluminum conductor motor. Thus, the efficacy of automated design is demonstrated by harnessing the framework and algorithms for exploring new technologies applicable for three distinct design problems originated from practical applications

Analysis and design optimisation of grid-connected wound-rotor synchronous and induction motors

Thesis (DEng)--Stellenbosch University, 2019.ENGLISH ABSTRACT: The dissertation presents new approaches in the analysis, design and optimisation of three-phase cylindrical wound-rotor synchronous (WRSM) and induction (WRIM) motor types. The new approaches are based on the analysis of the steady-state finite element method (FEM) in which the parameters and performances of the motor types are predicted. Absolute optimum designed WRSM and WRIM motor types can at best be obtained by the use of improved parameters and performance calculation methods in the design optimisation process. This dissertation proposes simple, fast and accurate parameter and performance calculation modern approaches for grid-connected WRSM and WRIM motor types using two-axes electromagnetic models. The modern approaches are based on non-classical models in which iterative processes are utilised using static FEM in conjunction with the motor types phasor diagrams. During the iterative processes, the electric circuit and magnetic field equations are coupled to access important parameters of the motor types. The access of parameters using iterative processes solves the excitation currents at different operating points of the motor. The parameters are accurately calculated using a FEM based method of freezing the motor core permeance. The dissertation investigates and expands the use of these parameters as an effective and powerful tool for explaining the motor behaviour under different operating points. A great deal of attention is also given to the design optimisation of the motor types during which a relatively efficient optimisation procedure is shown. In this study, the proposed model approaches are verified by employing a commercial FEM ANSYS-Maxwell and experimental tests in the laboratory. The study also gives the model approach and the design optimisation procedure of a 6 MW slip-ring motor used for milling purposes. In the analysis of this, the skin effects are perfectly fitted in the proposed model approaches The study presents a successful application of the proposed model approaches to the parameters and performance prediction and the design optimisation of the grid-connected WRSM and WRIM motor types. The proposed model approaches demonstrate accuracy, simplicity and fastness which are some of the key aspects in the electrical machine design.AFRIKAANSE OPSOMMING: Die verhandeling stel nuwe benaderings vir die analise, ontwerp en optimering van drie-fase bewikkelderotor sinchroonmotor (WRSM) en induksiemotor (WRIM) tipes voor. Die nuwe benaderings is gebaseer op die analise van die bestendige toestand eindige element metodes (EEM) waarmee die vermo¨e van die motor tipes voorspel word. Die optimum ontwerpte WRSM en WRIM motors kan verkry word deur die gebruik van verbeterde parameter en vermo¨e berekeningmetodes in die ontwerp optimeringsproses. Hierdie verhandeling stel ‘n eenvoudige, vinnige en akkurate parameter en vermo¨e berekening vir netwerk-gekoppelde WRSM en WRIM voor deur gebruik te maak van twee-as elektromagnetiese modelle. Die moderne benaderings is gebaseer op nie-klassieke modelle waarin iteratiewe EEM in samewerking met die motor fasor diagramme gebruik word. Tydens die iteratiewe proses, word die elektriese stroombaan en magnetiese veld vergelykings gekoppel om belangrike motor parameters te kry. Die magnetiese veld vergelykings los die opweksstrome op by verskillende werkspunte van die motor. Die parameters word akkuraat bereken deur die gebruik van EEM gebaseer op die metode van die vries van die motor kern permeansies. Hierdie parameters word as ‘n effektiewe hulpmiddel gebruik om die motorgedrag by verskillende werkspunte te verduidelik. Aandag word gegee aan die motorontwerp optimering, waartydens ‘n effektiewe optimeringsproses gewys word. In die studie word die voorgestelde benaderingsmodelle deur ‘n kommersi¨ ele EEM pakket (ANSYS-Maxwell) en toetse in die laboratorium geverifieer. ‘n Benaderingsmodel en die ontwerp optimering van ‘n 6 MW sleep-ring motor vir wals toepassings word ook gegee, waar die benaderingsmodel aangepas word om huid effekte in ag te neem. Die studie wys ‘n suksesvolle toepassing van die voorgestelde benaderingsmodel vir parameter en vermo¨e voorspelling en ontwerp optimering van netwerk-gekoppelde WRSM en WRIM motor tipes. Die voorgestelde benaderingsmodel is akkuraat, vinnig en eenvoudig, wat van die sleutelaspekte in elektriese masjien ontwerp is.Doctora

Improved transistor-controlled and commutated brushless DC motors for electric vehicle propulsion

The development, design, construction, and testing processes of two electronically (transistor) controlled and commutated permanent magnet brushless dc machine systems, for propulsion of electric vehicles are detailed. One machine system was designed and constructed using samarium cobalt for permanent magnets, which supply the rotor (field) excitation. Meanwhile, the other machine system was designed and constructed with strontium ferrite permanent magnets as the source of rotor (field) excitation. These machine systems were designed for continuous rated power output of 15 hp (11.2 kw), and a peak one minute rated power output of 35 hp (26.1 kw). Both power ratings are for a rated voltage of 115 volts dc, assuming a voltage drop in the source (battery) of about 5 volts. That is, an internal source voltage of 120 volts dc. Machine-power conditioner system computer-aided simulations were used extensively in the design process. These simulations relied heavily on the magnetic field analysis in these machines using the method of finite elements, as well as methods of modeling of the machine power conditioner system dynamic interaction. These simulation processes are detailed. Testing revealed that typical machine system efficiencies at 15 hp (11.2 kw) were about 88% and 84% for the samarium cobalt and strontium ferrite based machine systems, respectively. Both systems met the peak one minute rating of 35 hp

Theoretical and Experimental Investigations of a Permanent Magnet Excited Transverse Flux Machine with a Segmented Stator for In-Wheel Motor Applications

A three-phase transverse flux permanent magnet (PM) motor with flux concentrating (FC-) topology that has a segmented stator is studied in this dissertation. The phases of the stator have been placed around the rotational axis of the machine instead of placing them in a classical way over each other along the axial direction. Through this phase arrangement, the electrical and mechanical shifts between the phases are considered to ensure proper operation of the transverse flux machine (TFM) without the need of extra components such as a start-up capacitor or a special designed power supply. The segmented stator construction has required that the conventional ring coils to be replaced by a type of concentric winding that take a saddle shape enabling parallel magnetic circuits to take place. This has initiated studying the effect of the distances located between the phases on all over the performances of the machine. In order to select an initial construction for the stator, a preliminary assessment study of some conventional PM-TFMs having ring coils are carried out, through which they are re-designed as outer rotor motors and compared based on the level of electromagnetic torque and the inductance profile. As the main application of the design is to achieve a compact construction for an outer rotor, low noise and speed too for possible future in-wheel applications, the most interesting issue in this study is how to bring all the phases of the machine around the shaft in one layer without losing the torque productivity as when the phases are placed under each other in the conventional way. Therefore, the designed machine is set in further theoretical evaluation studies via finite element method (FEM) with the conventional layered TFM, and it shows that the TFM with segmented windings has a better torque density as its correspondence in the conventional layered structure. This result is in favor to the segmented structure, in particular, about 31% of the PMs number in the segmented structure (i.e., total number of PMs located between the phases) will not have an active role in the torque production. A detailed mathematical theory has been analytically developed and investigated to show the validity and limitation of the design. The study has incorporated how the segmentation of each phase and placement of the two parts opposite to each other can improve the mechanical balance of the TFM and hence quite rotation. The approach has been shown for two- and three-phase PM-TFMs. Moreover, illustration for applying the same principle of segmented stator to surface PM topology of TFMs is analytical verified and shown via FEM. Possible constructions with segmented stators are developed in a periodical table format to give the machine designer a shortcut for a possible construction with the selected number of magnets, number of segments per phase and the desired space between the phases. Since the noise is a well-known problem of TFMs, due to the ripple in the electromagnetic torque waveform and the natural magnetic normal forces, the normal and axial forces in PM-TFM with segmented stator have been investigated too, where introducing more segments per phase will reduce their effects. In order to validate the theoretical investigation, a low-scaled test machine is designed, constructed and a complete test bench has been built to experimentally test the machine. The experimental investigations have included generator and motor operation modes as well as measuring the ratings, performances of the machine and the starting methods. The test machine has reached via the conducted tests an average torque of about 2.1 Nm with an efficiency of 53% and it has a great development potential to be improved via shaping of stator poles, the room available for the windings, fill factor and more optimization possibilities. Based on the theoretical and experimental investigations, the operation of the segmented winding design of PM-TFM proves itself to work and to have a future for compact motors in industrial operation, or as in-wheel outer rotor motor for mobile platforms. For higher power applications, a machine with such type of stator should be designed with big diameters that will allow the utility of more PMs as well as more segments per phase, where both are involved in the torque production, i.e., more torque density for the segmented TFM

Design and control of a direct drive slotless permanent magnet alternating current generator for low speed Bristol cylinder wave device

Global demand for renewable energy is at an all-time high. Renewable energy can be extracted from naturally available resources such solar, wind, tides, geothermal heat, sea waves and the others. The percentage of renewable energy in the energy resources is increasing at an ever increasing rate. While much renewable energy is large scale, it is also suitable for rural and remote areas. The challenges facing today’s renewable energy supply industry are many, especially in the wave energy field which is still underdeveloped. The number of commercialised wave energy devices is very limited and the concepts implemented for harnessing wave energy are very different between the different devices and often struggle to be effective or survive ocean-going conditions. Thus, major research is required to find new and effective methods for harnessing wave energy which are able to supply power to the grid with high conversion rate and good reliability. The proposed Bristol cylinder device, in theory, should be able to harness sea wave energy and to convert it into useful electricity, and this device is studied in detail here. This device is still new in terms of practical application in ocean conditions. It needs power electronics and effective controllers for high-efficiency power extraction and to be successfully integrated into the power grid. When the device was first investigated in the 1970s, power electronics and variable-speed brushless permanent-magnet machinery was simply not developed to the level it is today, hence the revisiting of this device several decades later. A successful Bristol cylinder wave device which can extract renewable energy may well impact on the renewable energy sector. The wave characteristics were studied and simulated using Airy Linear Wave Theory and Stoke’s Second Order Theory. The dynamic characteristics of the Bristol cylinder are investigated when interacting with waves, together with the control necessary to make it a functioning device. A lab scale wave tank suitable to test the Bristol cylinder is designed. A surface magnet permanent magnet synchronous generator (PMSG) design is considered in this research project. This generator configuration shows its suitability in producing high conversion-rate power when working in a low speed environment. The sizing exercise is performed to determine the size of the lab scale PMSG. Analytical analysis and finite element analysis is performed to study the performance of the designed PMSG. A study of the effect of the armature length with the corresponding incident wave is done. Field oriented control (FOC) is applied to control the speed of the generator. FOC is shown to be suitable for stable control of the generator speed. Simulations using MATLAB are utilized and Simulink is used to construct the model and evaluate the potential performance of the control system design. In this thesis, theoretical analyses and simulations of the generator performances are carried out for several generator topologies and sizes. The grid side converter controller technique is also simulated in MATLAB/Simulink and the performance evaluated

Critical Evaluation of Slip Synchronous Wind Generator Technology

Electrical and Electronic Engineerin