Back-iron extension thermal benefits for electrical machines with concentrated windings

This paper proposes a novel, low-cost, effective way to improve the thermal performance of electrical machines by extending a part of the back-iron into the slot. This modification helps in reducing the thermal resistance path from the center of the slot to the coolant, however its thermal benefits must be clearly evaluated in conjunction with the electromagnetic aspects, due to the higher iron losses and flux-leakage, and furthermore such an extension occupies space which would otherwise be allocated to the copper itself. Taking a case study involving an existing 75kW electric vehicle (EV) traction motor, the tradeoffs involving the losses, fluxleakage, output torque, torque-quality and the peak winding temperature with back-iron extension (BIE) and without are compared. Finally, experimental segments of the aforesaid motor are tested, verifying a significant 26.7% peak winding temperature reduction for the same output power with the proposed modification

Equivalent slot thermal conductivity and back-iron extension effects on machine cooling

Back-iron Extension (BIE) is an effective thermal management technique which reduces the winding temperatures by projecting part of the back iron into the center of slot, thereby shortening the heat transfer path between the coil and back iron. Based on an existing concentrated-wound traction motor, this paper investigates the effects of equivalent slot thermal conductivity of coil on the optimal back iron extension geometry and temperature reduction

Sensitivity analysis of machine components thermal properties effects on winding temperature

This paper investigates the sensitivity analysis of winding temperature to key parameters in electrical machine thermal design. With a validated 3D thermal model based on an existing 75kW traction machine for an electric vehicle, the methodology of the sensitivity analysis study is conducted and presented. Finally, further research and practical guidelines on reducing the peak temperature of electrical machines are proposed

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

Thermal Model Approach to Multisector Three-Phase Electrical Machines

© 1982-2012 IEEE. Multisector machines reveal a high fault-tolerant capability, since failure events can be isolated by de-energizing the faulty sector, while the healthy ones contribute in delivering the required power. This article is focused on the thermal analysis of multisector three-phase machines in healthy and faulty operations. First, a 3-D lumped parameter thermal network (LPTN) of a single sector is developed and finetuned against experimental data, through a genetic algorithm for identifying the uncertain parameters. According to the operating conditions, the varying housing surface temperature affects the heat exchanged to the ambient. Hence, an analytical formula is proposed to adjust the natural convection coefficient value depending on the operating condition. Then, the 3-D LPTN, modeling the whole machine, is built aiming at investigating the thermal behavior during faulty conditions. Finally, the complete 3-D LPTN is employed for predicting the machine thermal performance under several faulty conditions. Furthermore, the current overload experienced by the healthy sector (in order to keep the same torque level as during the pre-fault operation) is determined, in accordance with the magnet wire thermal class. The effectiveness of the 3-D LPTN in predicting the temperature is experimentally demonstrated

Electrical Machine Slot Thermal Condition Effects on Back Iron Extension Thermal Benefits

The slot thermal condition is critical for thermal management of high performance electrical machines, due to the high heat losses and poor heat transfer ability within the slot. With a part of the back-iron projected radially downwards into the slot, back-iron extension (BIE) shortens the heat dissipation path from the slot coil to the back-iron and was proven to be an effective thermal improvement technique. The relationship between BIE thermal benefits and various electrical machines’ parameters remains to be investigated. Based on an existing concentrated-wound machine, the relationship between the equivalent slot thermal conductivity (ESTC) and the back-iron extension effectiveness is researched in this paper. Utilizing a developed 3D thermal model, the equivalent slot thermal conductivity effects on the temperature reduction with BIE are indicated with simulation results and verified with experimental tests. BIE is reported to provide temperature reductions ranging from 48°C down to 18°C across the plausible range of ESTC values considered. Guidelines are given in the final part to suggest the situations under which BIE is more effective

Axial flux permanent magnet machines for direct drive applications

This thesis explores aspects of the design, analysis, and experimental test of permanent magnet axial flux machines for use in diesel engine generator sets, vertical axis wind turbines, and wheel motors for solar cars. The characteristic geometry of axial flux machines is naturally more suitable than that of conventional topologies in certain applications. However, convenient and accurate methods of electromagnetic design and analysis are less well established for such machines. The purpose of the research described herein is to benchmark a range of methods of analysis which can be extended to novel designs. There is a particular focus on the use of Finite Element Analysis to facilitate greater understanding of these machines through the illustration and quantification of the electromagnetic aspects of their operation, and the verification of a selection of analytical approaches. Prototype TORUS machines are first considered; the various analyses are then extended to iron-cored axial flux machines having slotted conductors and finally to a selection of novel machines having concentrated coils and an ironless stator. The analyses are successfully extended to a range of machines, and the particular suitability of axial flux permanent magnet machines in certain direct drive applications is demonstrated

Improved Thermal Modelling and Experimental Validation of Oil-Flooded High Performance Machines with Slot-Channel Cooling

Thermal management is often considered a bottleneck in the pursuit of the next generation electrical machines for electrified transportation with a step change in power density. Slot-channel cooling is considered to be an effective cooling technique, either as an independent method or as a secondary heat transfer path which compliments traditional cooling systems. The slot-channel specific geometry and position effects on the thermal benefits are not thoroughly investigated in literature, while previous work focuses on passing fluid through the un-used space left in between coils forming concentrated windings. In this paper, slot-channel cooling is implemented within an oil-flooded cooling system for a high power density motor used as a pump. A flexible and detailed lumped parameter thermal network (LPTN) is proposed for the cooling system, with the LPTN used to optimize the slot-channel dimensions and location for obtaining maximum thermal benefits. Finally, a surface-mount permanent magnet (SPM) machine with the optimized slot channel geometry is built and tested to validate the thermal model, experimentally achieving an armature continuous current density in excess of 30A/mm2

Computationally Efficient Optimization of a Five-Phase Flux-Switching PM Machine Under Different Operating Conditions

This paper investigates the comparative design optimizations of a five-phase outer-rotor flux-switching permanent magnet (FSPM) machine for in-wheel traction applications. To improve the comprehensive performance of the motor, two kinds of large-scale design optimizations under different operating conditions are performed and compared, including the traditional optimization performed at the rated operating point and the optimization targeting the whole driving cycles. Three driving cycles are taken into account, namely, the urban dynamometer driving schedule (UDDS), the highway fuel economy driving schedule (HWFET), and the combined UDDS/HWFET, representing the city, highway, and combined city/highway driving, respectively. Meanwhile, the computationally efficient finite-element analysis (CE-FEA) method, the cyclic representative operating points extraction technique, as well as the response surface methodology (in order to minimize the number of experiments when establishing the inverse machine model), are presented to reduce the computational effort and cost. From the results and discussion, it will be found that the optimization results against different operating conditions exhibit distinct characteristics in terms of geometry, efficiency, and energy loss distributions. For the traditional optimization performed at the rated operating point, the optimal design tends to reduce copper losses but suffer from high core losses; for UDDS, the optimal design tends to minimize both copper losses and PM eddy-current losses in the low-speed region; for HWFET, the optimal design tends to minimize core losses in the high-speed region; for the combined UDDS/HWFET, the optimal design tends to balance/compromise the loss components in both the low-speed and high-speed regions. Furthermore, the advantages of the adopted optimization methodologies versus the traditional procedure are highlighted

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