Tsarafidy Raminosoa

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.

Performance Evaluation of a Vector-Control Fault-Tolerant Flux-Switching Motor Drive

A novel fault-tolerant flux-switching permanent-magnet synchronous machine drive topology is presented, which is able to operate during open- and short-circuit winding and converter faults. The scheme is based on a dual winding motor supplied from two separate vector-controlled voltage-sourced inverter drives. The windings are arranged in a way so as to form two independent and isolated sets. Simulation and experimental work will detail the drives performance during both healthy and faulty scenarios including short-circuit faults and will show the drive robustness to operate in these conditions.

Reduced Rare-Earth Flux-Switching Machines for Traction Applications

There has been growing interest in electrical machines that reduce or eliminate rare-earth material content. Traction applications are among the key applications where reducing cost and, hence, reduction of rare-earth materials are key requirements. This paper will assess the potential of different variants of flux-switching machines (FSMs) that either reduce or eliminate rare-earth materials in the context of traction applications. Two designs use different grades of dysprosium-free permanent magnets (PMs), and the third design is a wound-field variant that does not include PMs at all. A detailed analysis of all three designs in comparison to the required set of specifications will be presented. The key opportunities and challenges will be highlighted. The impact of the high pole-count/frequency of the FSMs will also be evaluated. Experimental results for one of the designs with dysprosium-free PMs will also be presented.

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.

A High-Speed Permanent-Magnet Machine for Fault-Tolerant Drivetrains

This paper details the design considerations of a permanent-magnet three-phase synchronous machine for fault-tolerant operation. A multidisciplinary approach to the optimal design of the machine is adopted, targeted at minimizing the additional losses resulting from faulty operating conditions and accounting for the remedial control strategy implemented. The design of a closed-slot six-slot four-pole machine is presented. The machine is prototyped and tested to validate the analytical-computational performances predicted in the design and analysis stage under healthy and faulty conditions.

Time-Stepping Simulation of Synchronous Reluctance Motors Using a Nonlinear Reluctance Network Method

We present a nonlinear reluctance network approach for the computation of the electromotive force (EMF) waveforms of synchronous reluctance motors (SynRM) with a massive rotor or a flux barrier rotor. We model all ferromagnetic parts of the machine by nonlinear reluctances in order to take the saturation into account. The model of the motor consists of three reluctance networks: of the stator, of the rotor, and of the air gap. The originality of the work lies in the automatic computation of the topology and of the reluctance values of the reluctance network. The computation models the air gap for any relative position of the rotor and the stator; thus, the movement of the rotor can be taken into account. For any saturation level, a comparison with time-stepping finite-element results shows good agreement for the EMF fundamental, the mean torque, and the EMF and torque harmonics of order lower than the slotting ones. For a normal saturation level, the reluctance network models also accurately compute the slotting harmonics.

A combined electromagnetic and thermal optimisation of an aerospace electric motor

An innovative design strategy has been set up which is capable of optimising both the electromagnetic as well as the thermal design of permanent magnet synchronous machines (PMSM) for aerospace actuation systems. This has been achieved by linking up the electromagnetic design process and motor housing design process for an overall minimum mass. A validation process was initially performed on a PMSM to ensure the correct functionality of the thermal model. Tests were carried out to calibrate the model with experimental data. This paper further describes the adopted optimisation procedure of a 12.75Nm – 2000rpm, horizontally mounted, 12 slot 14 pole Aerospace Permanent Magnet Synchronous motor and highlights the significant weight and volume saving capabilities.

A comparative study of permanent magnet - synchronous and permanent magnet - flux switching machines for fault tolerant drive systems

Flux switching machines are quickly gaining popularity due their inherent advantages stemming from having both the current conductors and permanent magnets mounted on the stationary side of the electrical machine. Their power density has already been shown to be comparable to that of permanent magnet synchronous machines, however their fault tolerant capabilities are somewhat limited in their standard form. This paper looks at a novel design of a fault tolerant flux switching permanent magnet machine able to operate with both open circuit and short circuit winding faults and compares its healthy and faulty performance to a fault tolerant permanent magnet synchronous machine.

Robust non-permanent magnet motors for vehicle propulsion

There has been growing interest in electrical machines that reduce or eliminate rare-earth material content. Traction applications are among the key applications where reducing cost and hence reduction or elimination of rare-earth materials is a key requirement. This paper will assess the potential of three non-permanent magnet options in the context of vehicle propulsion applications: 1) a conventional Switched Reluctance Machine (SRM), 2) a DC-biased Reluctance Machine (DCRM) and, 3) a Wound Field Flux Switching Machine (WFFSM). The three machines were designed to achieve the hybrid vehicle traction requirements of 55kW peak and 30kW continuous over a speed range going from 2800rpm to 14000rpm. Their performance will be compared and the key opportunities and challenges will be highlighted. Preliminary experimental results for the DCRM will be presented.