published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Thesis (MScEng)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: This thesis deals with the design and evaluation of a 300 kW double stage axial-flux permanent magnet generator with an ironless stator. The magnetic and electrical design equations are derived for sinewave and quasi-squarewave axial-flux permanent magnet machines. The thermal design approach used is also described. The machine is optimised for maximum torque per current loading. A Matlab program code is developed to do the necessary calculations in the design optimisation and the calculation of the machine parameters. Mechanical finite element simulations are conducted to investigate the severity of the magnetic attraction force between the rotor discs. The results obtained from the simulations suggested an increase in the yoke thickness in order to withstand the attraction force. The construction of the prototype machine's rotor and stator is described. The flux density in the airgap is thoroughly investigated through measurements and analysis. Thermal measurements are also conducted to investigate the effect of eddy currents in the stator winding. Furthermore, no-load measurements conducted on the 300 kW machine showed that the machine has a serious problem of circulating currents in the parallel connected coils. Possible solutions for this are investigated and recommendations are given. Due to the circulating current problem and the relative high eddy current losses, it was not possible to do full-load tests on the machine. / AFRIKAANSE OPSOMMING: Hierdie tesis handeloor die ontwerp en evaluering van 'n multi-stadium Aksiale Vloed Permanente Magneet (AFPM) masjien met 'n ysterlose stator. Die magnetiese - en elektriese ontwerp-vergelykings is afgelei vir sinusgolf en quasi vierkantsgolf AFPM masjiene. Die termiese ontwerp word ook bespreek. Die masjien is geoptimeer vir maksimum draairnoment per stroombelasting. Daar is 'n program-kode in Matlab geskryf om die nodige berekeninge vir die optimering van die masjien uit te voer en vir die bepaling van die masjien-parameters. Meganiese eindige element berekenings is gedoen om die invloed van die magnetiese aantrekkingskrag tussen die rotorskywe te ondersoek. Die resultate het aangedui dat die rotorskyfdikte nie die magnetiese aantrekkingskrag van die magnete kan weerstaan nie en moes in dikte vedubbel word. Die konstruksie van die masjien se rotor en stator is behandel. Die vloeddigtheid in die luggaping is noukeurig ondersoek deur metings en analise. Termiese metings is ook gedoen om die invloed van die werwel strome in die statorwikkelings te ondersoek. Verder het die nullas-toetse wat gedoen is op die masjien, aangedui dat die masjien 'n ernstige probleem het met sirkuierende strome in die parallelle geleiers van die statorspoele. Moontlike oplossings is ondersoek en aanbevelings word gegee. Dit was nie moontlik om vollastoetse op die masjien te doen nie, as gevolg van die probleem met sirkuierende strome en die relatiefhoë werwelstoom-verliese in die statorwikkelings.

Many high performance drive applications require wide Constant Power Speed Range (CPSR) for efficient use of energy. The examples of such applications are the starter alternator system of automobiles proposed for the 42V PowerNet, traction in the hybrid/electric vehicle, wind power generator etc. The Permanent Magnet (PM) machine is the natural choice of such niche applications because of their higher efficiency and compact size. However, the Surface Permanent Magnet (SPM) machine with sine distributed winding and radially-laminated Interior Permanent Magnet (IPM) machine with conventional structure has very limited or zero flux-weakening capability. The flux-weakening capability of the SPM machine can be improved by using concentrated, fractional-slot stator but here well-known advantages of the sine distributed winding are needed to be compromised. In the IPM machine, fluxweakening was improved using axial lamination and more than two magnet layers per pole. However, the construction of such IPM machine is complicated and expensive. This thesis presents design and analysis of a new type of the Interior Permanent Magnet (IPM) machine that have a very wide Constant Power Speed Range (CPSR) without compromising simplicity of construction and advantages of the distribution winding. In the new IPM machine, the magnet poles were segmented in the radially direction and the iron bridges between magnet segments provide for additional paths of flux-canalization to give the rotor an inherent capability of fluxweakening. Consequently, a very wide constant power speed range can be achieved in such machines. The proposed IPM machine of this work was referred as the Segmented IPM machine. The thesis focuses on the optimization of the Segmented IPM machine in a 42V environment of the automobile. First, for the conceptual evaluation a 4 pole, 550W Segmented Magnet IPM machine was optimized using finite element analysis. The parameters were calculated for prediction of the steady-state and transient performances. The torque- and power-speed capability were estimated using time-step, circuit-coupled finite element analysis. The cogging torque and variation of iron loss with frequency were also investigated during the design process. A prototype machine was constructed on the basis of the optimized design. The steady-state and transient performances of the prototype machine were measured and compared with the predicted results for experimental verification. The measured performance analysis was found to match very well with the predicted results. The measured torque- and power-speed capability of the Segmented IPM machine was also compared to those of a conventional, non-segmented IPM machine of similar rating and size. The thesis also presents the optimized design of a 6kW, 12 pole Segmented Magnet IPM machine for application in the Integrated Starter Alternator (ISA) of the electric/hybrid vehicle. It can be concluded from the predicted steady-state analysis of the 6 kW, 12 pole Segmented Magnet IPM machine that it should be able to satisfy most of the required criteria of an ISA with appropriate design optimization.

This thesis presents a detailed comparison of the torque-speed characteristics of three permanent magnet synchronous machine designs based on how the magnets are mounted. The machines investigated are an interior permanent magnet machine, an interior-rotor surface-mounted machine and an exterior-rotor surface-mounted machine. They are designed for traction drives in hybrid electric vehicles. Two sets of comparisons based on the same machine volume and starting torque are performed. Important issues, such as machine mass and cost, cogging torque, and flux-weakening capability are addressed. Computer simulations were performed to estimate their performances and the results are presented. Design guidelines and tradeoffs of their performances are extracted from the simulation results. Relative strengths and limitations of different PM machine types are highlighted.

Many high performance drive applications require wide Constant Power Speed Range (CPSR) for efficient use of energy. The examples of such applications are the starter alternator system of automobiles proposed for the 42V PowerNet, traction in the hybrid/electric vehicle, wind power generator etc. The Permanent Magnet (PM) machine is the natural choice of such niche applications because of their higher efficiency and compact size. However, the Surface Permanent Magnet (SPM) machine with sine distributed winding and radially-laminated Interior Permanent Magnet (IPM) machine with conventional structure has very limited or zero flux-weakening capability. The flux-weakening capability of the SPM machine can be improved by using concentrated, fractional-slot stator but here well-known advantages of the sine distributed winding are needed to be compromised. In the IPM machine, fluxweakening was improved using axial lamination and more than two magnet layers per pole. However, the construction of such IPM machine is complicated and expensive. This thesis presents design and analysis of a new type of the Interior Permanent Magnet (IPM) machine that have a very wide Constant Power Speed Range (CPSR) without compromising simplicity of construction and advantages of the distribution winding. In the new IPM machine, the magnet poles were segmented in the radially direction and the iron bridges between magnet segments provide for additional paths of flux-canalization to give the rotor an inherent capability of fluxweakening. Consequently, a very wide constant power speed range can be achieved in such machines. The proposed IPM machine of this work was referred as the Segmented IPM machine. The thesis focuses on the optimization of the Segmented IPM machine in a 42V environment of the automobile. First, for the conceptual evaluation a 4 pole, 550W Segmented Magnet IPM machine was optimized using finite element analysis. The parameters were calculated for prediction of the steady-state and transient performances. The torque- and power-speed capability were estimated using time-step, circuit-coupled finite element analysis. The cogging torque and variation of iron loss with frequency were also investigated during the design process. A prototype machine was constructed on the basis of the optimized design. The steady-state and transient performances of the prototype machine were measured and compared with the predicted results for experimental verification. The measured performance analysis was found to match very well with the predicted results. The measured torque- and power-speed capability of the Segmented IPM machine was also compared to those of a conventional, non-segmented IPM machine of similar rating and size. The thesis also presents the optimized design of a 6kW, 12 pole Segmented Magnet IPM machine for application in the Integrated Starter Alternator (ISA) of the electric/hybrid vehicle. It can be concluded from the predicted steady-state analysis of the 6 kW, 12 pole Segmented Magnet IPM machine that it should be able to satisfy most of the required criteria of an ISA with appropriate design optimization.

No description available.

This dissertation presents an investigation of miniaturized magnetic induction and permanent magnet (PM) machines, intended for use in a microengine. Similar to a macroscale turbogenerator, a microengine comprises a small, gas-fueled turbine engine for converting chemical fuel energy into mechanical power and an integrated electrical generator for converting mechanical power to electrical power. The microengine system is proposed as a revolutionary, high power-density source for portable electronics. In this research, miniaturized magnetic induction machines and PM machines were designed, fabricated, and characterized. Both types of machines used axially directed magnetic fields and were nominally 10 mm in diameter and 1.5-2.3 mm in thickness. Innovative microfabrication techniques were developed to demonstrate the feasibility of integrating magnetic machines within a bulk-micromachined, silicon-based microengine system. Two-phase, eight-pole induction machines were constructed within silicon substrates using Cu coils in a laminated, slotted ferromagnetic NiFe or CoFeNi stator core. Silicon etching, wafer bonding, and electrodeposition were used to form all of the magnetic machine components. The induction machines were characterized in motoring mode using tethered rotors and demonstrated motoring torques of up to 2.5 uN-m. Also, three-phase, eight-pole, surface wound PM machines were built using a hybrid microfabrication/assembly approach. The stators were fabricated by electroplating Cu coils on ferromagnetic NiFeMo (Moly Permalloy) substrates. The rotors were formed by assembling a magnetically patterned SmCo PM with a FeCoV (Hiperco 50) back iron. The PM machines were tested as generators with free-spinning rotors, powered by an air-driven spindle, and demonstrated 2.6 W of mechanical-to-electrical power conversion with continuous DC power generation of 1.1 W at 120 krpm rotor speed. The primary contributions of this work are (1) the demonstration of microfabricated magnetic machines integrated within bulk-micromachined silicon and (2) the demonstration of multi-watt power conversion from a microfabricated PM generator. These achievements represent progress in the ongoing development of silicon-based microengines, but in addition, the fabrication technologies and device structures may find application in other microsystems.

In recent years, due to growing environmental awareness regarding global warming, green cars, such as hybrid electric vehicles, have gained a lot of importance. With the decreasing cost of rare earth magnets, brushless permanent magnet motors, such as the Interior Permanent Magnet Motor, have found usage as part of the traction drive system in these types of vehicles. As a design issue, building a motor with a performance curve that suits both city and highway driving has been treated in this thesis as a multi-objective problem; matching specific points of the torque-speed curve to the desired performance output. Conventionally, this has been treated as separate problems or as a combination of several individual problems, but doing so gives little information about the trade-offs involved. As a means of identifying the compromising solutions, we have developed a stochastic optimizer for tackling electromagnetic device optimization and have also demonstrated a new innovative way of studying how different design parameters affect performance.

No description available.