Convection Heat Transfer and Flow Calculations Suitable for Electric Machines Thermal Models

This paper deals with the formulations used to predict convection cooling and flow in electric machines. Empirical dimensionless analysis formulations are used to calculate convection heat transfer. The particular formulation used is selected to match the geometry of the surface under consideration and the cooling type used. Flow network analysis, which is used to study the ventilation inside the machine, is also presented. In order to focus the discussion using examples, a commercial software package dedicated to motor cooling optimization (Motor-CAD) is considered. This paper provides guidelines for choosing suitable thermal and flow network formulations and setting any calibration parameters used. It may also be considered a reference paper that brings together useful heat transfer and flow formulations that can be successfully applied to thermal analysis of electrical machine

Evolution and Modern Approaches for Thermal Analysis of Electrical Machines

In this paper, the authors present an extended survey on the evolution and the modern approaches in the thermal analysis of electrical machines. The improvements and the new techniques proposed in the last decade are analyzed in depth and compared in order to highlight the qualities and defects of each. In particular, thermal analysis based on lumped-parameter thermal network, finite-element analysis, and computational fluid dynamics are considered in this paper. In addition, an overview of the problems linked to the thermal parameter determination and computation is proposed and discussed. Taking into account the aims of this paper, a detailed list of books and papers is reported in the references to help researchers interested in these topics

Lumped Parameter Thermal Network Modelling for Thermal Characterization and Protection of Traction Motors in Electric Vehicle Application

This thesis investigates thermal modelling of traction motors for thermal characterization and protection in electric vehicle application. The requirements for traction motor characteristics include high power density; high torque at low speed for starting and climbing; high power at high speed for cruising; wide speed range; a fast torque response; high efficiency over wide torque and speed ranges and high reliability. High torque and power density requirements in traction motors mean increasing current and consequently, higher temperature rise in the motor. When the temperature of the winding and magnet in traction motors exceed permissible thermal limit frequently due to lack of proper understanding and managing of the thermal conditions it will have a short-term and a long term impacts on the motor operation. In the short-term, it will never be able to produce required torque and power for standard driving conditions of electric vehicle. In the long-term, it will have the detrimental effects on the life of insulation material and consequently, it will cause permanent insulation breakdown and on the other hand, demagnetization due to higher temperature will cause a permanent damage to the motor. Hence, it is extremely important to predict temperature rise in the motor accurately and regulate liquid cooling accordingly so that the motor does not fail to produce required torque and power for any driving conditions. This research work proposes a higher order lumped parameter thermal network (LPTN) model to determine a comprehensive thermal characterization of the traction motors. Such characterization predicts the temperature of the winding, magnet and other parts of the motor. The proposed model is capable of taking inputs dynamically of motor operating parameters in electric vehicle and generate a motor loss model that feeds loss results into LPTN thermal model to predict motor temperature. The proposed model investigates cooling requirements to the motor so that the motor continues to produce the rated torque and power. The LPTN model results are validated through thermal tests on a copper rotor induction motor (CRIM) and an interior permanent magnet synchronous motor (IPMSM) in the laborator

Advanced design methodology for permanent magnet synchronous machines in power applications

Most of the world electrical energy is consumed by electric motors, and then, the improvement in their performance leads to essential savings in the global energy consumption, required to reduce the CO2 emissions. Actually, the policies of governments and institutions are becoming more demanding and the manufacturers are forced to offer more and more optimized products. Moreover, many applications are increasingly demanding high performance in terms of power density, reliability or dynamic response, as in the case of electric vehicle, wind power generation or railway traction. The high energetic content of neodymium magnets causes that the permanent magnet machines (PMSM) are the more attractive option with respect to power density. In addition, thanks to the almost complete elimination of the rotor losses they are the most energetically efficient machines. The PMSM design requires of a multiphysical approach since it comprises electric, magnetic and thermal aspects. In this work, a comprehensive review of the technical literature regarding these machines has been done, and some areas for improvement have been found. Firstly, it is common that the procedure starts from a quite defined machine and just an optimization of a specific part is realized. Moreover, excessive dependence on designer’s experience and knowhow is observed, without giving clear instructions for taking design decisions. Finally, excessive dependence on time consuming FEM models is found. Hence, the main objective of this thesis is to develop and propose an advanced design methodology for PMSM design, characterized by being clear and complete, considering whole the design process and giving criteria and tools for taking decisions which lead to an optimum choice of the final solution. A PMSM design methodology has been proposed that enables the evaluation of large amounts of configurations in an automatic manner, easing to the designer the process of taking the final design decision. To implement this methodology, several tools have been developed and explained in detail: electromagnetic models coupled to thermal models and lumped parameter electromagnetic models. Some important modifications were done in the thermal models taken as a reference in order to consider different cooling conditions. In addition, a basis permeance network model was adapted to the selected machine topology and it was used to demonstrate its suitability to be used in combination with Frozen Permeability technique. Following the proposed design methodology, a 75 kW PMSM prototype was designed and validated at the IK4‐IKERLAN medium voltage laboratory. The obtained results have validated both the proposed design methodology and the developed and employed tools.La mayor parte de la energía eléctrica mundial es consumida en motores eléctricos, por lo que la mejora de sus prestaciones conduce a ahorros en el consumo energético esenciales si se quieren reducir las emisiones de CO2. De hecho, las políticas de gobiernos y asociaciones cada vez son más exigentes, y los diseñadores se ven forzados a lanzar productos cada vez más optimizados. Además, cada vez hay más aplicaciones que son muy exigentes en términos de densidad de potencia, fiabilidad o prestaciones dinámicas, como son el vehículo eléctrico, la generación eólica o la tracción ferroviaria. El altísimo contenido energético de los imanes de neodimio provoca que las máquinas imanes permanentes (PMSM) sean las más atractivas en términos de densidad de potencia. Además, debido a la casi total eliminación de pérdidas en el rotor se convierten en las máquinas más eficientes energéticamente. El diseño de una PMSM requiere de un enfoque multidisciplinar, ya que engloba aspectos eléctricos, magnéticos y térmicos. En este trabajo, se ha realizado una revisión exhaustiva de la literatura técnica publicada hasta la fecha en relación con el diseño de estas máquinas, y se han encontrado ciertos puntos de mejora. En primer lugar, muchas veces se parte de un diseño bastante definido y se optimiza una parte concreta del mismo. Además, se aprecia excesiva dependencia de la experiencia y knowhow del diseñador, sin establecer pautas claras para la toma de decisiones de diseño. Finalmente, dependen excesivamente del temporalmente costoso FEM. Por lo tanto, el objetivo principal de esta tesis es desarrollar una metodología avanzada de diseño de PMSMs que sea clara y completa, abarcando todo el proceso de diseño y aportando criterios y herramientas para la toma de decisiones que conduzcan a una elección óptima de la solución final. Se ha propuesto una metodología de diseño que permite la evaluación de gran cantidad de configuraciones de PMSM de forma automática, facilitando la decisión de diseño final por parte del diseñador. Para la implementación de esta metodología, diversas herramientas han tenido que ser desarrolladas y son explicadas en detalle: modelos analíticos electromagnéticos acoplados con modelos térmicos, y modelos electromagnéticos de parámetros concentrados. Importantes modificaciones fueron realizadas sobre los modelos térmicos adoptados para considerar diferentes refrigeraciones. Además, el circuito electromagnético de parámetros concentrados fue adaptado a la topología seleccionada y demostró su validez para ser utilizado en combinación con la técnica de Frozen Permeability. Siguiendo la metodología propuesta, se ha diseñado y fabricado un prototipo de 75 kW y se ha realizado la validación experimental en el laboratorio de media tensión de IK4‐IKERLAN. Los resultados obtenidos han servido para validar tanto la metodología de diseño como las herramientas empleadas en la misma.Munduko energia elektrikoaren zatirik handiena motor elektrikoetan kontsumitzen da, eta, ondorioz, prestazioak hobetzeak lagundu egiten du kontsumo energetikoan funtsezko aurrezpenak egiten, CO2 igorpenak murriztu nahi badira. Berez, gobernuen eta elkarteen eskakizunak gero eta zorrotzagoak dira, eta diseinatzaileak produktu gero eta optimizatuak atera beharrean daude. Gainera, gero eta aplikazio gehiago daude zorroztasun handia eskatzen dutenak potentzi dentsitateari, fidagarritasunari edo prestazio dinamikoei dagokienez, esaterako, ibilgailu elektrikoan, sorkuntza eolikoan edo tren trakzioan. Neodimiozko imanen eduki energetiko itzelaren ondorioz, iman makina iraunkorrak (PMSM) dira erakargarrienak potentzi dentsitateari dagokionez. Gainera, errotorearen galerak ia guztiz deuseztatzen direnez, energetikoki makinarik eraginkorrenak dira. PMSM bat diseinatzeko diziplina askoko ikuspegia behar da, alderdi elektrikoak, magnetikoak eta termikoak hartzen baititu bere baitan. Lan honetan orain arte honelako makinen diseinuari buruz argitaratutako literatura teknikoaren azterketa zehatza egin da, eta hobetzeko hainbat puntu aurkitu dira. Lehenik eta behin, askotan, abiapuntua nahiko definituta dagoen diseinu bat izaten da, eta egiten dena da horren zati jakin bat optimizatu. Gainera, gehiegizko mendekotasuna egoten da diseinatzailearen esperientzia eta knowhow‐arekiko, diseinuaren inguruko erabakiak hartzeko jarraibide argiak ezarri gabe. Azkenik, mendekotasun handia dago FEMek behin‐behinean duen kostu handiarekiko. Horrenbestez, tesiaren helburu nagusia da PMSMak diseinatzeko metodologia aurreratu bat garatzea, argia eta osatua, diseinuaren prozesu osoa hartuko duena, eta erabakiak hartzeko irizpideak eta tresnak eskainiko dituena, amaierako soluziorik onena aukeratu ahal izateko. Diseinurako proposatu den metodologiarekin PMSMko konfigurazio kopuru handi bat ebaluatu daiteke automatikoki, diseinatzaileari amaierako diseinua erabakitzen laguntzeko. Metodologia inplementatzeko, hainbat tresna garatu behar izan dira, eta horiek zehatz esplikatzen dira: eredu analitiko elektromagnetikoak, eredu termikoekin uztartuta, eta parametro kontzentratuen bidezko eredu elektromagnetikoak. Hautatutako eredu termikoetan aldaketa garrantzitsuak egin behar izan ziren, hozkuntza desberdinak lantzeko. Horrez gain, parametro kontzentratuen zirkuitu elektromagnetikoa hautatutako topologiara egokitu zen, eta bere balioa frogatu zuen, Frozen Permeability teknikarekin konbinatuta erabiltzeko. Proposatutako metodologiari jarraituz, 75 kW‐eko prototipo bat diseinatu eta fabrikatu da, eta balioztapen esperimentala egin da IK4‐IKERLANeko tentsio ertaineko laborategian. Lortutako emaitzek diseinuaren metodologia zein bertan erabilitako tresnak balioztatzeko balio izan dute

Lumped Parameter Thermal Model of Permanent Magnet Synchronous Machines

This paper describes a thermal equivalent circuit of Liquid Cooling Totally Enclosed Permanent Magnet Synchronous Machines (LCTE-PMSMs). Conductive heat transfer in all directions is taken into account. Specific care has been taken to represent them by equivalent circuit. The conductive heat transfer in heterogeneous media like slots and the convective heat transfer in the airgap and the end-winding are studied

Thermal Management of E–Motors in Electric Vehicle Application Employing LPTN Model

The electric motor is at the center focus as an alternative to the internal combustion engine for automotive applications since it does not produce greenhouse gas emissions and can contribute significantly to the reduction of fossil fuel consumption globally. As extensive research works are being done on electric vehicles at present, thermal analysis of traction motor is increasingly becoming the key design factor to produce electric motors with high power and torque capabilities in order to satisfy electric vehicle driving requirements. Motor losses cause active heat generation in the motor components and excessive temperature rise affects the electromagnetic performance of the traction motor. High torque and power requirements based on the driving conditions under urban and highway drive conditions demand high capacity motor cooling system in order to keep the temperature within the safe limit. Hence, it is critical to develop and design a temperature prediction tool to dynamically estimate the winding and magnet temperature and regulate cooling to remove excessive heat from the motor. Conventional thermal modeling of motors includes analytical and numerical modeling. Analytical modeling is done by using Lumped Parameter Thermal Network (LPTN) which is analogous to electric circuit and a fast method for predicting temperature. It uses heat transfer equations involving thermal resistances and thermal capacitances to analytically determine temperature at different nodes. Numerical modeling is done in two ways–Finite Element Analysis and Computational Fluid Dynamics. Numerical modeling can produce more accurate results, but it requires more computational time. Since the temperature of motor components has to be predicted very quickly, i.e. during driving, LPTN is more effective because LPTN can quickly predict temperature based on the heat transfer equations. This thesis proposes an LPTN model that predicts motor temperature and regulates the required coolant flow rate simultaneously. Thus, it is able to dynamically predict the temperature. MATLAB Simulink has been used for simulation of the LPTN model for a laboratory PMSM prototype. The thermal resistances in the thermal network model have been obtained from the motor geometrical parameters. The electromagnetic loss data with respect to torque and speed were taken as input, and thus the temperature results of motor components have been found. The future work will be to implement this model into full scale prototype of the motor

Development of high efficiency high speed permanent magnet generator

Renewable energy technology is steadily gaining importance in the energy market because of the limited nature of fossil fuels, as well as the political pressures to reduce carbon emissions. To ensure sustainable development, adequate and affordable energy should be made available to satisfy the demand of electric energy. The High Speed Permanent Magnet (HSPM) generator is designed and developed and is expected to deliver 10 kW output power as well as to achieve a speed of 30000 RPM, however, to achieve a compact and efficient design with lower excitation losses, magnetizing currents and rotor losses requires the HSPM generator to be operated at high rated speeds of approximately 30000 RPM. However, at high speeds these machines produce a substantial amount of heat. This makes the thermal management of these machines difficult and complicated, which leads to demagnetization and the reduction of the output power and shortens the lifetime of the critical components such as the bearings. This thesis presents the design and development of the HSPM generator. It also identifies the heat generated by means of electromagnetic, mechanical and core losses. The development of an adequate cooling system (cooling jacket) is presented to avoid hot spots in the generator and thermal damage to the magnets, resulting in demagnetization. The use of pressurized oil air particles as a lubrication method for the bearings of the generator is also considered to avoid: thermal damage and starvation at the rolling element and to address the predominant concern of effectively cooling the HSPM generator ball bearings at elevated speeds. The HSPM generator is designed and developed to operate at a maximum speed of 30000 RPM to deliver 10 kW output power and is subjected to 80~92°C temperature rise with an idle power consumption of ~2kW, enough to cause hot spots on the generator, demagnetization of the magnets and severe impact to the rolling elements of the bearings. The developed cooling jacket and the newly developed oil air mist lubrication arrangement enables the control of the temperature rise of the generator and the temperature rise at the rolling element, respectively. A steady state analysis was also carried out at motor maximum power output to determine its safe operation with the objective of finding an optimal operating condition by performing a parametric study on the effect of cooling. A 3D steady state model of a 10-kW electric permanent magnet machine was generated and investigated with one cooling jacket layout. The end windings and bearings were not considered to simplify the motor model. Numerical analysis is performed with two different coolant flow rates, no flow and maximum flow (3.5 m3 /h) with special emphasis on the maximum motor temperature. The analytical calculations for the role of coolant flowrate on heat transfer characteristics for a high speed generator, showed that the convection heat transfer coefficient increases with an increase in flowrate (0.3 – 3.5 m3 /hr), while the numerical simulations showed that the maximum coolant flowrate conditions achieved lower temperature generation (27.9°C at the front bearing) throughout the generator compared to no coolant flowrate (43.7°C at the front bearing). The detailed understanding of the effects of these parameters on the generator’s temperature field will help in validating the performance of the generator with actual results

Design and Performance Analysis of Double Stator Axial Flux PM Generator for Rim Driven Marine Current Turbines

This paper deals with the design and performance analysis of double stator axial flux permanent magnet generators for rim-driven marine current turbines (MCT). Indeed for submarine applications, drive train reliability is a key feature to reduce maintenance requirements. Rim-driven direct-drive multi-stator generators can therefore be a very interesting solution to improve this reliability. In this context, the presented work focus on the design of a double-stator axial flux permanent magnets (PM) generator as a rim-driven direct-drive multi-stator generator. The paper details the models, specifications and an optimization procedure that allow to preliminary design these kind of generators for rim-driven marine turbines. Thereafter, validations with finite elements computations and performance analysis considering particular design of rimdriven generators are presented. The obtained results highlight some designs issues of PM generators for rim driven marine turbines. In order to assess the effectiveness of the double stator axial flux PM generator, a comparison with a designed surface mounted radial flux PM generator for rim marine turbines is carried out.. The comparison highlights that the double stator axial flux generator presents a better cooling and a reduced active parts cost and mass than the radial flux PM generator.International audienceThis paper deals with the design and performance analysis of double stator axial flux permanent magnet generators for rim-driven marine current turbines (MCT). Indeed for submarine applications, drive train reliability is a key feature to reduce maintenance requirements. Rim-driven direct-drive multi-stator generators can therefore be a very interesting solution to improve this reliability. In this context, the presented work focus on the design of a double-stator axial flux permanent magnets (PM) generator as a rim-driven direct-drive multi-stator generator. The paper details the models, specifications and an optimization procedure that allow to preliminary design these kind of generators for rim-driven marine turbines. Thereafter, validations with finite elements computations and performance analysis considering particular design of rimdriven generators are presented. The obtained results highlight some designs issues of PM generators for rim driven marine turbines. In order to assess the effectiveness of the double stator axial flux PM generator, a comparison with a designed surface mounted radial flux PM generator for rim marine turbines is carried out.. The comparison highlights that the double stator axial flux generator presents a better cooling and a reduced active parts cost and mass than the radial flux PM generator

Coupled electromagnetic and thermal analysis of electric machines

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáThe actual trend of the design process of electric machines is oriented to specific requirements of the application and is no longer based in a standard structure. From this point of view, the design procedure of electric machines became a multidisciplinary process, involving electromagnetic, thermal, and mechanical modelling in a highly iterative process between the different physics fields. This dissertation deals with the design process of electric machines, proposing a coupling methodology for the electromagnetic and thermal models which are interrelated. The electromagnetic model establishes the main losses in electric machines: iron and resistive losses. These losses are, in turn, the main heat sources, responsible for heating and temperature distribution, i.e., the object of the thermal analysis, which affects recursively the losses, due to parameter’ dependency on temperature. Also, the machine temperature is crucial to maintain the lifetime of the machine. So, the coupled analysis is mandatory to achieve the nowadays requirements of higher energy efficiency and power density and cost reduction. Also, the coupled analysis enables optimization without the need to build several prototypes, making this process more time and cost-efficiency. Despite the temperature importance in electric machines, the thermal model was overlooked over the years. However, it has been receiving more attention in the past years. In this work, the thermal modelling process is handled analytically and numerically through finite element analysis (FEA), which is also used to obtain the electromagnetic model. The modelling processes detailed during this work are applied into a case study of a single-phase transformer with the rated power of 1 kW. The numerical models were developed in the Ansys software suite, being the electromagnetic model developed in Ansys Maxwell while the thermal model has developed in Ansys Mechanical. At last, the coupling between the electromagnetic and thermal models was accomplished in Ansys Workbench. The results obtained from the models are compared and validated with the experimental measurements of the losses and temperatures.A tendência atual do processo de projeto de máquinas elétricas é orientada para requisitos específicos de sua aplicação e não é mais baseada em uma estrutura padrão. Deste ponto de vista, o procedimento de projeto de máquinas elétricas tornou-se um processo multidisciplinar, envolvendo modelagem eletromagnética, térmica e mecânica em um processo altamente iterativo entre os diferentes campos da física. Esta dissertação trata do processo de projeto de máquinas elétricas, propondo uma metodologia de acoplamento dos modelos eletromagnético e térmico que se inter-relacionam. O modelo eletromagnético estabelece as principais perdas em máquinas elétricas: perdas de ferro e resistivas. Essas perdas são, por sua vez, as principais fontes de calor, responsáveis pelo aquecimento e distribuição de temperatura, ou seja, o objeto da análise térmica, que afeta recursivamente as perdas, pois os parâmetros são dependentes da temperatura. Além disso, a temperatura da máquina é crucial para manter a vida útil da máquina. Assim, a análise acoplada é obrigatória para atender aos requisitos atuais de maior eficiência energética e densidade de potência e redução de custos.Além disso, a análise acoplada possibilita a otimização sem a necessidade de construção de vários protótipos, tornando este processo mais eficiente em termos de tempo e custos. Apesar da importância da temperatura nas máquinas elétricas, o modelo térmico foi negligenciado ao longo dos anos. No entanto, tem recebido mais atenção nos últimos anos. Neste trabalho, o processo de modelagem térmica é tratado analiticamente e numericamente por meio da análise de elementos finitos (FEA), que também é utilizada para obter o modelo eletromagnético. Os processos de modelagem detalhados durante este trabalho são aplicados em um estudo de caso de um transformador monofásico com potência nominal de 1 kW. Os modelos numéricos foram desenvolvidos no pacote de software Ansys, sendo o modelo eletromagnético desenvolvido no Ansys Maxwell enquanto o modelo térmico foi desenvolvido no Ansys Mechanical. Por fim, o acoplamento entre os modelos eletromagnético e térmico foi realizado no Ansys Workbench. Os resultados obtidos com os modelos são comparados e validados com as medições experimentais das perdas e temperaturas

Measurement of stator heat transfer in air-cooled axial flux permanent magnet machines

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