Michael Galea

Design Considerations for a Fault-Tolerant Flux-Switching Permanent-Magnet Machine

In safety critical aerospace applications, fault-tolerant drives can help reach the necessary system reliability levels without replicating the entire drive system and thus minimizing the overall system weight. Machine selection and design for fault tolerance has to be considered at an early stage to ensure optimal performance at a system level. This paper looks at the fault-tolerant properties of permanent-magnet flux-switching machines (PMFSMs) and proposes a new configuration able to fulfill the fault-tolerant requirements. PMFSMs have the distinct property of having a robust rotor construction with the permanent magnets embedded in the stator while having their operational characteristics similar to those of synchronous permanent-magnet machines. While these machines have numerous inherent advantages for achieving a high power density, in their basic form, they are not tolerant to short-circuit winding failures. This paper will look at a novel stator structure able to achieve a 1-p.u. winding inductance and will subsequently look at design iterations to maximize the torque density.

A Thermal Improvement Technique for the Phase Windings of Electrical Machines

In electrical machines, a higher torque/force density can usually be achieved by increasing the current density in the windings. However, the resulting increase in copper losses leads to higher temperatures in the coils, particularly in the center of the slots where the thermal resistance to the ambient/cooling surfaces is highest. In this paper, a novel, simple technique is presented in which a higher thermal conductivity path between the center of the slot and the cooling arrangement is created, thus increasing the heat flow away from the slot center. A lumped-parameter thermal model is presented and used along with finite-element analysis to investigate the effectiveness of the proposed technique. The lumped-parameter model is also used for optimizing the high conductivity path for maximum air-gap shear stress and to obtain a compromise between the reduced slot area and the improved temperature distribution. Experimental validation is then presented to compare the predicted results with the measured results on a purposely built instrumented setup.

Feasibility and electromagnetic design of direct drive wheel actuator for green taxiing

This paper considers the feasibility of equipping the main landing gears with electric motors for the aircraft traction during the taxi phase. Those electromechanical wheel actuators make possible a “Green Taxi” operation by considerably reducing the on-ground carbon emission. Moreover, this will enable important fuel saving for short distance flights with high frequency of landing and take-off. In this work, direct drive wheel actuator is considered for energy efficiency and mechanical reliability. Two possible locations of the actuator are examined and the weights of the corresponding electric machines are compared. The most weight efficient location is then selected. A high torque density permanent magnet machine is then designed to fit in this envelope and to satisfy peak torque, weight and flux weakening capability requirements. The design procedure as well as several technologies adopted to maximize the torque density are presented.

Demagnetization Analysis for Halbach Array Configurations in Electrical Machines

This paper proposes and investigates an analytical method for assessing the risk of potential irreversible demagnetization in the permanent magnets (PMs) of electrical machines equipped with n-stages, Halbach arrays. The higher risk of demagnetization, synonymous with Halbach arrays, imposes that the method be both load and temperature dependent. In fact, the proposed method studies the magnetic field distribution in the air gap and PM region, for various operating temperatures and expresses these fields as analytical expressions for the no-load and peak-load conditions. The model can cater for Halbach arrays with up to n stages, thus making it a versatile tool that can be utilized for various Halbach configurations. Finite-element analysis is used to validate the method. The analytical tool is then used for the design and analysis of a high torque density, outer rotor, traction motor. The motor is for an aerospace application and its operating duty cycle imposes very high, short-time, peak-load conditions at elevated temperatures, posing an elevated risk of irreversible PM demagnetization. The model is used to investigate various Halbach configurations for this application, in order to reduce the demagnetization risk and also to improve the general performance of the machine. The analytical method thus provides a computationally efficient tool that can be used to predict and prevent demagnetization in Halbach-equipped electrical machines operating in harsh environments such as the aerospace sector.

Design of a High-Force-Density Tubular Motor

This paper deals with the design, construction, and experimental verification of a high-force-density, tubular, linear, and permanent-magnet motor driven from a high-power-density matrix converter for an aerospace application. This paper also describes the implementation and experimental verification of a novel thermal management technique for the phase windings of electrical machines. The technique introduces a higher thermal conductivity path between the center of the slot and the cooling arrangement, thus increasing the heat flow away from the slot center. An introduction to the design of the motor is first given, after which an introduction to the technique is presented. A study of how the implementation of the technique affects motor performance is then presented. A detailed overview of the construction aspects is highlighted, and finally, experimental validation is used to illustrate the comparison between the predicted results and the measured results, obtained from an instrumented test rig.

Torque density improvements for high performance machines

In this paper, the main aim is to propose and investigate possible methods for extending and improving the torque density capabilities of high performance, electrical machines. This is achieved by combining performance enhancing strategies such as the use of an outer rotor, the use of cobalt iron laminations and the adoption of high performance winding arrangements into a structured methodology that details the potential improvements step by step. A main point of interest of this paper is the permanent magnet demagnetisation analysis, resulting in the adoption of an optimum arrangement of a five stage, full-Halbach array. The above is presented in terms of an electrical machine used as an in-wheel motor in an aircraft traction application.

Development of an aircraft wheel actuator for green taxiing

In this paper, the design and construction aspects of a wheel actuator to be used for aircraft taxiing on the ground and which will be located in the main landing gear are addressed. The main challenges with the application are the high torque density and fault tolerance requirements. This paper will look at all the different design aspects of the traction motor required for the actuator, including the electro-magnetic design and analysis, thermal management and mechanical analysis. The paper will then conclude with a brief overview of the construction aspects of the motor of the wheel actuator and experimental validation.

Design of a high force density tubular permanent magnet motor

This paper considers the design and analysis of a tubular linear permanent magnet machine for high force density applications, such as in the aerospace industry. Different machine topologies and slot-pole combinations are considered. Optimization with respect to machine geometry is addressed analytically and validated through finite element simulations. A technique to reduce heat build-up in the winding coils is introduced, allowing for higher current density and subsequently resulting in a higher output force for a given winding temperature rise.

Thermal design of a permanent magnetic motor for direct drive wheel actuator

A permanent magnet motor was designed for aircraft traction during the taxiing phase. In order to improve the reliability, the motor was attached to enable direct drive of the wheel without additional gearing. Due to the high torque needed for the aircraft traction, and the space and mass limitations of the wheel environment, the thermal management of the motor presents a big challenge. This paper describes the thermal management of the direct drive motor. Computational Fluid Dynamics (CFD) and lumped parameter thermal models were applied to predict and improve the thermal performance of the motor. Experimental testing provided thermal data, which was compared with the lumped thermal model and the CFD results.

Improved Damper Cage Design for Salient-Pole Synchronous Generators

The benefits of implementing a damper winding in salient-pole synchronous generators are widely known and well consolidated. It is also well known that such a winding incurs extra losses in the machine due to a number of reasons. In order to improve the overall efficiency and performance of classical salient-pole, wound field synchronous generators that employ the traditional damper cage, an improved amortisseur winding topology that reduces the inherent loss is proposed and investigated in this paper. This is essential in order to meet modern power quality requirements and to improve the overall performance of such “classical” machines. The new topology addresses the requirements for lower loss components without compromising the acceptable values of the output voltage total harmonic distortion and achieves this by having a modulated damper bar pitch. As vessel for studying the proposed concept, a 4-MVA salient-pole synchronous generator is considered. A finite element model of this machine is first built and then validated against experimental results. The validated model is then used to investigate the proposed concept with an optimal solution being achieved via the implementation of a genetic algorithm optimization tool. Finally, the performance of the optimized machine is compared to the original design both at a steady state and transient operating conditions.