Abstract

A novel control method for a fixed-pitch variable speed wind turbine is introduced and experimental results are presented. The measured absorbed power and rotational speed, together with a look-up table for the aerodynamic efficiency, are used to estimate the wind speed reaching the turbine as well as the tip speed ratio. Thereby, the control is independent on wind speed measurements and the wind turbine itself is used as an anemometer. Tip speed ratio control is implemented by comparing the estimated tip speed ratio to a reference value and adjusting the DC voltage level accordingly. Tip speed ratio control benefits from that the aerodynamic efficiency hardly varies with changing tip speed ratio when close to its optimum value. Experimental results from a 200 kW vertical axis wind turbine are presented. The voltage from the permanent magnet generator is passively rectified and the alternating DC voltage is then inverted, filtered, transformed, and grid connected. The estimated wind speed is compared with the measured wind speed. The absorbed power when tip speed ratio control has been implemented is shown. It is concluded that the presented control method works and some future improvements are discussed.

Abstract

Structural problems in modern societies, such as climate change and congestion problems, require 'transitions' towards a more susTWNnable fulfilment of social needs. Recent research shows that experimenting in niches is crucial for learning about social challenges and stimulating transitions. Through a series of 'transition experiments' in different niches, social innovations can be improved and eventually replace dominant practice. This article reviews the literature on transitions and strategic niche management and argues that it has a strong analytical core, but less effort has been made to develop a managerial perspective. The authors aim to contribute to such perspective by developing a 'competence kit': a learning module that provides practitioners (e.g., policy makers, companies, intermediary organisations and NGO's) that are involved in transition experiments with an analytical framework, guidelines and tools and recognisable examples. The results from the first workshop with practitioners to explore potential applications of the competence kit are promising. Copyright © 2010 Inderscience Enterprises Ltd.

Abstract

Twitter data are used as alternative metrics (altmetrics) to measure the impact or attention of research. Tweets are used to communicate about papers. However, Twitter data can only be used for research evaluation purposes, if biases do not influence tweet decisions on papers. The existence of biases can only be reasonably investigated using an experimental design with controlled (marginal) manipulations. In this comment, we propose to undertake an experimental approach to study the decision of scientists to ‘tweet’ on a paper. We describe the design of a study that might allow the experimental investigation of tweet decisions including randomized variations and theoretically derived mechanisms for explaining the empirical results. The described study design should be adaptable to other social media platforms (e.g., Facebook or ResearchGate). This comment is intended to be a plea for using an experimental design to investigate biases in tweet decisions. It is an advantage of tweets –in contrast to citations– that an experimental approach can be applied to investigate the decision of scientists to communicate on papers.