Jason Yon

Design study of a three-phase brushless exciter for aircraft starter/generator

This paper presents a design study of a 3-phase AC main exciter (ME) for an aircraft starter-generator. A computationally efficient methodology for optimizing the design of the ME is presented. The optimisation is carried out using coupled two-dimensional (2D) magnetostatic finite element solver and particle swarm optimisation procedure (PSO). The ME design is then analysed using 3D FE to account for the end-winding effects, and the results are fed into a lumped-parameter circuit model of the ME. The circuit model allows for the operating modes of the ME being analysed in a computationally efficient manner also accounting for non-linearities. The theoretical findings are experimentally validated on a prototype generator.

Design and Characterization of a Three-Phase Brushless Exciter for Aircraft Starter/Generator

This paper evaluates a three-phase ac main exciter (ME) for a wound-field synchronous aircraft starter-generator capable of operating in both starting and generating modes. The research has been based around a 225-kVA generator utilizing the existing single-phase ME hardware. Initially, a reconfiguration of the existing single-phase unit into a three-phase one has been carried out. Subsequently, an optimization of the ME stator has been performed. The hardware evaluations have been performed in parallel to the development of design methodologies suitable for future starter/generator design. The three-phase ac ME design needs to satisfy the required current output at both start and generate modes with minimum input voltampere rating of the inverter required to drive the ME. The MEs output capabilities have been predicted in all operating conditions using a computationally efficient combination of 3-D finite-element models together with a lumped-parameter circuit approach. The theoretical findings from the analyses have been validated on a prototype ME, confirming that the three-phase ac ME is capable of generating the required current output in both operating modes. The developed modeling system allowed for the identification of the MEs optimal operating points with regard to the minimum input apparent power (in voltamperes) at the required output power and a methodology for the accurate and computationally efficient evaluation of future starter/generator designs.

Analysis of Semipermeable Containment Sleeve Technology for High-Speed Permanent Magnet Machines

This paper presents an alternative permanent magnet rotor containment technology. The use of a semipermeable material in a laminated structure is shown to result in a significant improvement in magnetic loading for a given thickness of containment compared to the use of magnetically inert materials such as carbon fiber or Inconel, while minimizing eddy current losses in the containment layer. An analytical model is presented for determining the air-gap field delivered from a permanent magnet array with a semipermeable containment. The analysis is validated through finite element analysis. The fabrication of a prototype machine is detailed and the results presented show good agreement with the analysis. The validated modeling process is used to assess the potential of the new technology.

A comparison between maximum torque/ampere and maximum efficiency control strategies in IPM synchronous machines

This paper presents a comparison between maximum torque/ampere and maximum efficiency control strategies for interior permanent magnet synchronous machines (IPMSMs) in an electrical vehicle propulsion application. A mixed theoretical and experimental approach is adopted to demonstrate how an improvement in performance may be achieved when maximum efficiency control is utilised. The study is completed on three machines, a 36 slot 10 pole fractional slot per pole distributed winding, a 30 slot 10 pole integer slots per pole distributed winding design and a 12 slot 10 pole concentrated winding design. The findings are experimentally validated on the 36 slot 10 pole IPM motor. It is shown that the largest improved in efficiency is achieved with a concentrated winding design however for all three designs a significant efficiency gain is achieved in the most common operating regions of the standard international and US urban drive cycles, WLTP and UDDS.

Impact of slot shape on loss and thermal behaviour of open-slot modular stator windings

This paper presents results from an investigation into the optimal design of an open-slot, modular stator winding. The impact of the stator slot shape on the winding temperature rise is explored, taking account the distribution of loss that occurs in the open slot winding, including ac effects, and the heat transfer characteristics from the winding assembly into the stator core pack. The application focus is a single-layer, concentrated wound brushless PM machine, however the work is applicable to other machine formats. Alternative stator lamination profiles are compared; the commonly used parallel sided tooth with a trapezoidal slot, and a parallel sided slot with a trapezoidal tooth. The investigation includes the development of a reduced order thermal model representation of the stator. This model is employed to undertake coupled loss and thermal analyses to provide more accurate comparisons of the designs accounting for ac and temperature effects. The experimental and theoretical findings indicate the parallel sided slot design will result in a 37°C lower winding temperature or an 11% increase in torque at the intended machine operation point.

Common-mode voltage reduction in three-level neutral-point-clamped converters with neutral point voltage balance

This paper investigates two conflictive issues of common-mode (CM) voltage reduction and neutral point (NP) voltage balancing in a three-level neutral-point-clamped (NPC) converter. The amplitude of NP voltage variation under CM voltage mitigation scheme has been derived analytically. Various factors affecting the NP voltage have been analyzed and the solutions to achieve these two objectives simultaneously have been proposed. Simulation and experimental results have been shown to validate the analysis and proposed control scheme.

Assessment of fluid drag loss in a flooded rotor electro-hydrostatic actuator motor

For a permanent magnet (PM) motor used in an electro-hydrostatic actuation system, fluid drag loss in the air gap can be as high as 60% of motor internal losses and affects the motor efficiency; especially at low temperatures where the viscosity of the hydraulic fluid increases significantly. A PM motor has been designed and built to assess electromagnetic, fluid drag loss and dynamic performance. The design process utilised a theoretical equation for the fluid drag loss estimation which assumes a laminar flow. Assumption of the laminar flow has been validated by computational fluid dynamic analysis. A dummy motor was built and the fluid drag losses were measured for various speeds and temperatures. The test results show reasonable agreement with the theoretical calculation although the self-heating effect of the fluid made measurements at constant temperatures difficult.

Electromagnetic and thermal coupling within a fault-tolerant aircraft propulsion motor

This paper describes the development of a fault-tolerant, high specific output motor for use in aircraft electrical propulsion. The program includes demonstration of a full scale propulsion motor to a specification representative of an electric tail rotor drive on a medium twin-engine helicopter. The safety critical nature of the application demands a redundant system architecture comprising four 3-phase motor channels integrated within a single air-cooled housing. A modular wound 24 slot, 28 pole brushless AC permanent motor design is selected for this purpose. In principle the topology should ensure minimal interaction between the phase coils. The degree of electrical and thermal coupling between the four independent motor channels is explored in this paper, during normal and faulted operation. The findings are accompanied with test results taken from the full-scale prototype machine.

Test characterization of a high performance fault tolerant permanenet magnet machine

It is well understood that an electric machines output performance is limited by its losses and thermal behavior. For novel prototype machines, hardware testing processes are an important part of quantifying these parameters. For some machines, effective characterization may be accomplished using a series of static and simple prime-mover tests. The resulting data permits calibration of loss- and thermal-models. These can then be used to predict on-load performance. Fault-tolerant machines based on single layer winding arrangements are designed to minimize interaction between windings or module-groups. This paper demonstrates that, for such a machine, the losses measured during simple DC and primer-mover tests may be used to infer performance during both ‘healthy’ and ‘faulted’ operating modes. Under faulted conditions the total machine loss is expected to be a combination of module-specific and common losses, which can be directly deduced from hardware tests. This paper discusses the accuracy of loss superposition when applied to a 180 kW multi-channel, fault-tolerant aerospace machine. From observations following faulted and healthy dynamometry tests, there exists close correlation between full-load performance and estimates made from the superposition of losses under discrete operating modes.

Investigation of equivalent stator-winding thermal resistance during insulation system ageing

High performance electrical machine operation is limited by the losses generated in the machine and how well the heat developed by these losses is extracted. For conductive heat transfer from the main winding body, the insulation materials provide the main heat transfer pathway. As a machine ages through its lifetime, these materials will change their properties, and therefore these heat transfer characteristics will also alter. This paper describes the methodology and measurements on a set of motorettes undergoing an insulation ageing process to identify the change in heat transfer characteristics. The motorettes are subjected to a combination of thermal, electrical, mechanical and humidity stresses, before their thermal performance is measured. It has been found that the equivalent thermal resistance of the motorettes over the nominal lifetime of the insulation increases by over 100%, with the current carrying capability of the machine reducing by over 30% across the machines lifetime. It is therefore recommended that this is taken into account during the initial thermal design of the machine to ensure it remains fit for purpose during its complete life.