Jason D. Ede

Rotor resonances of high-speed permanent-magnet brushless machines

For high-speed machines, in particular, it is very important to accurately predict natural frequencies of the rotor at the design stage so as to minimize the likelihood of failure. Finite-element analysis and experimental measurements are used to establish the natural frequencies and modes of the rotor of a high-speed permanent-magnet brushless motor, and to assess the influence of leading design parameters, such as the active length, the shaft diameter and extension, the bearings, and the material properties.

Effect of optimal torque control on rotor loss of fault tolerant permanent magnet brushless machines

A faulted phase in a fault-tolerant permanent-magnet brushless machine can result in significant torque ripple. However, this can be minimized by using an appropriate optimal torque control strategy. Inevitably, however, this results in significant time harmonics in the phase current waveforms, which when combined with inherently large space harmonics, can result in a significant eddy-current loss in the permanent magnets on the rotor. This paper describes the optimal torque control strategy which has been adopted, and discusses its effect on the eddy-current loss in the permanent magnets of four-, five-, and six-phase fault-tolerant machines.

Optimal split ratio for high-speed permanent magnet brushless DC motors

The ratio of rotor to stator diameter, i.e. split ratio, is one of the most important design parameters for permanent magnet machines, as it can significantly influence their power density and efficiency. Previous work has shown that an optimal split ratio exists for minimum copper loss and can be obtained by using a simple formula. However, this expression neglects the stator iron loss which for high-speed and/or high pole permanent magnet machines can become the dominant motor loss. This paper investigates the influence of iron loss on the optimal split ratio for maximum efficiency, with particular emphasis on high-speed machines.

Design variants of modular permanent magnet brushless machine

The article describes an analytical technique for determining all possible slot-number and pole-number combinations, of modular permanent magnet brushless machines. It is shown that a large number of design variants exist. Furthermore, typical performance parameters, such as back-emf and cogging torque wave forms, for selected fault-tolerant designs are presented.

Experimental Testing of a 250 kW Fault-Tolerant Permanent Magnet Power Generation System for Large Civil Aero- Engines

This paper describes the experimental testing of a 250 kW fault-tolerant permanent magnet power generation system (machine and converter) for the low-pressure shaft of a large civil engine. The relative merits of this system as a reliable electrical power source for safety critical applications are discussed and its performances under both healthy and fault conditions are analyzed and experimentally tested. It has been shown that the power generation system has a high efficiency over a wide output power range under healthy conditions. However, a large torque ripple and potentially destabilizing output power swing will result under an open- or short- circuit fault condition. This problem can be eliminated by employing an optimal torque control strategy. The utility and effectiveness of the control technique have been experimentally validated.

Design Of A 250kW, Fault-tolerant PM Generator For The More-electric Aircraft

*† ‡ § ** †† This paper describes a fault-tolerant permanent magnet machine for use as a direct-drive low-pressure shaft generator for a large civil aircraft engine. The paper is concerned specifically with the design of a 250kW generator for a ‘more-electric’ engine which operates over a speed range of 1050rpm to 3100rpm. The paper describes the issues which must be considered in the selection of the preferred topology, phase number and pole/slot combinations, with particular reference to achieving the desired fault-tolerance and power density. Having established a candidate design using well established design guidelines, the performance of the generator in terms of electrical and thermal behavior is predicted using a range of detailed modeling tools. The importance of several design features such as stator core air cooling ducts and rotor magnet segmentation are illustrated within the context of this design study.

Testing of a 250-Kilowatt Fault-Tolerant Permanent Magnet Power Generation System for Large Civil Aeroengines

This paper describes the experimental testing of a 250-kW fault-tolerant permanent magnet power generation system (machine and converter) for the low-pressure shaft of a large civil engine. The relative merits of this system as a reliable electrical power source for safety critical applications are discussed, and its performances under both healthy and fault conditions are analyzed and experimentally tested. It has been shown that the power generation system has a high efficiency over a wide output power range under healthy conditions. However, a large torque ripple and potentially destabilizing shaft power swing will result under an open- or short-circuit fault condition. This problem can be eliminated by employing an optimal torque control strategy. The utility and effectiveness of the control technique have been experimentally validated.

An integrated starter -generator for a large civil aero -engine

*† ‡ § . This paper considers the feasibility of incorporating a switched reluctance starter generator within the high -pressure (HP) region of a large civil aero -engine, specifically in terms of achievable power densities, inverter rating, machine losses and the consequent cooling requirements. The high -pressure shaft of a typical large turbo -fan e ngine rotates at speeds of ~15000rpm on a typical flight duty cycle, and up to ~20000rpm in an over -speed condition, with ambient temperatures of the order of 300 to 400°C and the required powe r rating is in excess of 100kW. This harsh operating environmen t necessitates a multi -physics design approach, encompassing mechanical, thermal, electromagnetic and electrical disciplines, and serves to quantify the performance trade -offs that result from closely integrating an electrical machine into the harsh enviro nment of an aircraft engine. Nomenclature PFE = Iron loss density (W/kg) � = Electrical conductivity ( � -1 ) � = Mass density (kg/m 3 ) � = Period of flux waveform (s) d = Lamination thickness (m) B = Instantaneous flux density (T) ke = Excess loss coefficient kh,a,b = Hysteresis loss coefficients

Design of powder aligning systems for the compression molding of radially anisotropic permanent magnet rings

The article describes the design of powder aligning fixtures for the compression molding of radially anisotropic NdFeB magnet rings. The implications of the high fields required are discussed, with particular reference to the limitations imposed on the aspect ratio of the magnets that can be satisfactorily aligned. Features for enhancing the magnitude of the aligning field in the mold cavity, e.g., a magnetic shunt to shield the inner core and tapering of the upper plate are discussed. These issues are illustrated by means of a design study on a powder aligning fixture for a NdFeB magnet ring with an outer diameter of 26 mm and a wall thickness of 3 mm. Extensive finite element analysis is employed to investigate the role of various features, and to optimize the geometry. The findings of the design study are validated by comparison with measurements on a prototype fixture.

Effects of load conditions on rotor eddy current loss in modular permanent magnet machines

The paper describes an investigation into rotor magnet eddy current losses in modular machines within the context of a 250kW, 5-phase fault-tolerant permanent magnet generator for a “more-electric” aero engine. It is shown that the interaction of the rotor permanent magnets and stator slotting results in dominant space harmonics having the same pole-pairs and frequencies as those generated by the stator mmf, with their interactions resulting in on-load rotor eddy current being lower than no-load eddy current loss.