Papers by Richard McMahon
2018 XIII International Conference on Electrical Machines (ICEM), Sep 1, 2018
In this paper, a new optimized rotor design for Brushless Doubly Fed Machines (BDFMs) is proposed... more In this paper, a new optimized rotor design for Brushless Doubly Fed Machines (BDFMs) is proposed. The BDFM is considered as an attractive generator particularly for offshore wind power generation and also as a replacement for doubly fed slip ring induction generators. This is due to its higher reliability and lower maintenance reported in the literature. It is shown in this paper from the study of the magnetic field distribution in the rotor core that the conventional design of the BDFM rotor iron core can be modified, leading to a lighter machine. The proposed design method is supported by an analytical study and its practicality is validated using 2-D Finite Element (FE) analysis. A 250 kW experimental BDFM with frame size D400 is considered as the prototype machine. Index Terms-Brushless doubly fed machine (BDFM), rotor back iron, finite element analysis (FEA), magnetic circuit, iron saturation, magnetic flux density.
Le Journal de Physique Colloques
... Ce rapport couvre l'ap-plicationdecette technique I la diffusion d'arsenic ... more ... Ce rapport couvre l'ap-plicationdecette technique I la diffusion d'arsenic contrBlee de tres pres, qui est adoptee pour les elements 1 ... 2 DJ Gbdfrey, AE Adams, RA McMahon and H Ahmed., 1st International Symposium on VLSI ECS 162nd Meeting, October 1982, Detroit ...
The Journal of Engineering
Journal of Vacuum Science and Technology
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Review of Scientific Instruments
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Artificial Organs
The IntraVAD is a miniature intra-aortic ventricular assist device (VAD) designed to work in seri... more The IntraVAD is a miniature intra-aortic ventricular assist device (VAD) designed to work in series with the compromised left ventricle. A reverse-rotation control (RRc) mode has been developed to increase myocardial perfusion and reduce ventricular volume. The RRc mode includes forward rotation in systole and reverse rotation in diastole, which requires the IntraVAD to periodically reverse its rotational direction in synchrony with the cardiac cycle. This periodic reversal leads to changes in pressure force over the impeller, which makes the entire system less stable. To eliminate the mechanical wear of a contact bearing and provide active control over the axial position of the rotor, a miniature magnetically levitated bearing (i.e., the PM-Coil module) composed of two concentric permanent magnetic (PM) rings and a pair of coils-one on each side-was proposed to provide passive radial and active axial rotor stabilization. In the early design stage, the numerical finite element method (FEM) was used to optimize the geometry of the brushless DC (BLDC) motor and the maglev module, but constructing a new model each time certain design parameters were adjusted required substantial computation time. Because the design criteria for the module had to be modified to account for the magnetic force produced by the motor and for the hemodynamic changes associated with pump operation, a simplified analytic expression was derived for the expected magnetic forces. Suitable bearings could then be designed capable of overcoming these forces without repeating the complicated FEM simulation for the motor. Using this method at the initial design stage can inform the design of the miniature maglev BLDC motor for the proposed pulsatile axial-flow VAD.
IEE Proceedings I Solid State and Electron Devices, 1982
Data are presented on the sheet resistance of ion-implanted silicon following isothermal electron... more Data are presented on the sheet resistance of ion-implanted silicon following isothermal electronbeam annealing by the multiple-scan method. Anneals were performed on implanted 5 mm square chips for times around 5 s, with anneal temperatures up to 1350°C. Implants of As, P, B, Sb and Ga were annealed, ranging in doses from 10 13 cm" 2 to 10 16 cm" 2 in both (100) and (111) orientation silicon, and the sheet resistance was measured with a four-point probe. The measurements are presented as a plot of sheet resistance against electron-beam power, for a given dopant and anneal time, and the corresponding temperatures are also shown. Above a threshold temperature region of 750°C to 950°C near-full electrical activation is obtained, except in cases where the doping level approaches the solid solubility limit, or for certain high-dose boron implants. Slightly lower sheet resistances are obtained for implants in (100) material than (111) material, and at temperatures exceeding 1100°C diffusion effects are expected to be significant. The activation of ion implants without significant redistribution of dopant during annealing can be used to improve the performance of ion-implanted devices.
2009 International Conference on Power Electronics and Drive Systems (PEDS), 2009
The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise as replacement for ... more The Brushless Doubly-Fed Induction Generator (BDFIG) shows commercial promise as replacement for doubly-fed slip-ring generators for wind power applications by offering reduced capital and operational costs due to its brushless operation. In order to facilitate its commercial deployment, the capabilities of the BDFIG system to comply with grid code requirements have to be assessed. This paper, for the first time,
Conference Record of the 2006 IEEE Industry Applications Conference Forty-First IAS Annual Meeting, 2006
The brushless doubly-fed machine (BDFM) shows commercial promise as a variable speed drive or gen... more The brushless doubly-fed machine (BDFM) shows commercial promise as a variable speed drive or generator. However, for this promise to be realised, the design of the machine must be improved. Accurate machine modelling is therefore required for design optimisation. The measurement of rotor bar currents is of considerable benefit in the process of developing an accurate machine model. The authors
2005 IEEE Instrumentationand Measurement Technology Conference Proceedings, 2000
Rogowski transducers have become an increasingly popular method of measuring current within proto... more Rogowski transducers have become an increasingly popular method of measuring current within prototyping applications and power electronics equipment due to their significant advantages compared to an equivalent current transformer. This paper presents a simple and practical construction technique of high-performance, low-cost Rogowski transducers and accompanying circuitry. Experimental tests were carried out to show the validity of the proposed construction technique
Proceedings of the 41st International Universities Power Engineering Conference, 2006
... to break an existing circuit to insert a measuring device, ... The circuit diagram microcontr... more ... to break an existing circuit to insert a measuring device, ... The circuit diagram microcontroller has the distinct advantage that no external LCD drive chip was required, hence reducing power consumption and overall cost. ... This gives a value of 10.6 for 4.uIQO .u O the scale factor. ...
Iee Conference Publication, Apr 1, 2006
... Performance Analysis in High Frequency Electronic Ballasts Mohsin Ayaz Shafi and RA McMahon E... more ... Performance Analysis in High Frequency Electronic Ballasts Mohsin Ayaz Shafi and RA McMahon Engineering Department, University of Cambridge, Trumpington Street, Cambridge, CB21PZ, UK Phone: +44 (0)1223 332768, Email: mas97@eng.cam.ac.uk ...
Iecon 2014 40th Annual Conference of the Ieee Industrial Electronics Society, Oct 1, 2014
Conference Record of the 2006 IEEE Industry Applications Conference Forty-First IAS Annual Meeting, 2006
Compact fluorescent lamps (CFL) incorporating electronic ballasts are widely used in lighting. In... more Compact fluorescent lamps (CFL) incorporating electronic ballasts are widely used in lighting. In many cases the ability to dim the lamp is a requirement. Dimming can be achieved by varying the voltage supplied to the inverter or by changing the switching frequency of the inverter. The effect of dimming by both approaches on the power losses in the inverter is
Artificial organs, Jan 30, 2016
The intra-aortic ventricular assist device (IntraVAD) is a miniature intra-aortic axial-flow vent... more The intra-aortic ventricular assist device (IntraVAD) is a miniature intra-aortic axial-flow ventricular assist device (VAD) that works in series with the left ventricle (LV) to assist the compromised heart. Previous in vitro results have shown that the IntraVAD can successfully increase coronary perfusion and offload ventricular volume by operating in reverse-rotation control (RRc) mode. The RRc mode includes forward rotation in systole and reverse rotation (RR) in diastole. It is necessary to derive a new diffuser design that can be used for the bi-directional rotation of the IntraVAD. In this work, a dual-diffuser set (DDS) was proposed to replace the conventional inducer and diffuser upstream and downstream of the pump. The DDS comprised two diffusers, located on both sides of the impeller, omitting the conventional inducer and diffuser. Different configurations of the DDS were designed and manufactured with various combinations of curved and straight blades. All configurations ...
2013 European Control Conference, Jul 17, 2013
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Papers by Richard McMahon