Design considerations for the brushless doubly-fed (induction) machine

© The Institution of Engineering and Technology. A design procedure for the brushless doubly-fed machine is based on equations derived from a simplified equivalent circuit. The method allows the many variables in the design of this machine to be handled in a straightforward way. Relationships are given for the division of slot area between the two stator windings and for the design of the magnetic circuit. The design method is applied to a frame size 180 machine. In particular, calculated values for flux densities in the machine have been verified by time stepping finite element analysis for actual operating conditions. The approach outlined can also be used as part of a design optimisation routine

How Valid Are Measures of Children’s Self-Concept/ Self-Esteem? Factors and Content Validity in Three Widely Used Scales

Children’s self-esteem/self-concept, a core psychological construct, has been measured in an overwhelming number of studies, and the widespread use of such measures should indicate they have well-established content validity, internal consistency and factor structures. This study, sampling a demographically representative cohort in late childhood/early adolescence in Dublin, Ireland (total n = 651), examined three major self-esteem/self-concept scales designed for late childhood/early adolescence: Piers-Harris Self-Concept Scale for Children 2 (Piers et al. 2002), Self-Description Questionnaire I (Marsh 1992) and Self-Perception Profile for Children (Harter 1985). It also examined findings in light of the salient self factors identified by participants in a linked mixed-methods study. The factor structure of Piers-Harris Self-Concept Scale was not replicated. The Self-Description Questionnaire I and Self-Perception Profile for Children were replicated only in part although in similar ways. In all three scales, a global/ appearance self evaluation factor accounted for the largest variance in factor analyses. Sport/athletic ability, school ability, school enjoyment, maths and reading ability/enjoyment, behaviour, peer popularity, and parent factors were also identified but did not always reflect existing scale structures. Notably, the factors extracted, or items present in these scales, often did not reflect young people’s priorities, such as friendship over popularity, the importance of family and extended family members, and the significance of incremental personal mastery in activities rather than assessing oneself as comparatively good at preferred activities. The findings raise questions about how self-esteem/self-concept scales are used and interpreted in research with children and young people

Wireless energy harvesting for rotor instrumentation in electrical machines

In order to perform experiments on electrical machines, it is desirable to measure rotor parameters such as currents and temperatures. A Bluetooth module have been developed which sends data from the rotor, however this module is battery powered, and therefore the duration of the tests is limited. This paper presents a solution to this problem, by developing a rotor-mounted power supply system which can harvest energy from leakage magnetic flux inside the machine, by fixing an external loop to the rotor and making use of induced voltages in the loop. A full-bridge rectifier, boost converter and battery charging module was developed to supply sufficient power to the Bluetooth module

Design and performance analysis of a 6 MW medium-speed Brushless DFIG

The paper presents the design and performance analysis of a 6 MW medium-speed Brushless Doubly-Fed Induction Generation (Brushless DFIG) for a wind turbine drivetrain. Two machines with different frame sizes have been designed to show the flexibility of the design procedure. The mediumspeed Brushless DFIG in combination with a two stage gearbox offers a low-cost, low-maintenance and reliable drivetrain for wind turbine applications