Stability boundary analysis of the dynamic voltage restorer in weak systems with dynamic loads

In this contribution, a stability analysis for a dynamic voltage restorer (DVR) connected to a weak ac system containing a dynamic load is presented using continuation techniques and bifurcation theory. The system dynamics are explored through the continuation of periodic solutions of the associated dynamic equations. The switching process in the DVR converter is taken into account to trace the stability regions through a suitable mathematical representation of the DVR converter. The stability regions in the Thevenin equivalent plane are computed. In addition, the stability regions in the control gains space, as well as the contour lines for different Floquet multipliers, are computed. Besides, the DVR converter model employed in this contribution avoids the necessity of developing very complicated iterative map approaches as in the conventional bifurcation analysis of converters. The continuation method and the DVR model can take into account dynamics and nonlinear loads and any network topology since the analysis is carried out directly from the state space equations. The bifurcation approach is shown to be both computationally efficient and robust, since it eliminates the need for numerically critical and long-lasting transient simulations.

'Which is the best Doctor Who story?' : a case study in value judgements outside the academy'

One of Cultural Studies' most important contributions to academic thinking about culture is the acceptance as axiomatic that we must not simply accept traditional value hierarchies in relation to cultural objects (see, for example, McGuigan, 1992: 157; Brunsdon, 1997: 5; Wark, 2001). Since Richard Hoggart and Raymond Williams took popular culture as a worthy object of study, Cultural Studies practitioners have accepted that the terms in which cultural debate had previously been conducted involved a category error. Opera is not 'better' than pop music, we believe in Cultural Studies - 'better for what?', we would ask. Similarly, Shakespeare is not 'better' than Mills and Boon, unless you can specify the purpose for which you want to use the texts. Shakespeare is indeed better than Mills and Boon for understanding seventeenth century ideas about social organisation; but Mills and Boon is unquestionably better than Shakespeare if you want slightly scandalous, but ultimately reassuring representations of sexual intercourse. The reason that we do not accept traditional hierarchies of cultural value is that we know that the culture that is commonly understood to be 'best' also happens to be that which is preferred by the most educated and most materially well-off people in any given culture (Bourdieu, 1984: 1- 2; Ross, 1989: 211). We can interpret this information in at least two ways. On the one hand, it can be read as proving that the poorer and less well-educated members of a society do indeed have tastes which are innately less worthwhile than those of the material and educational elite. On the other hand, this information can be interpreted as demonstrating that the cultural and material elite publicly represent their own tastes as being the only correct ones. In Cultural Studies, we tend to favour the latter interpretation. We reject the idea that cultural objects have innate value, in terms of beauty, truth, excellence, simply 'there' in the object. That is, we reject 'aesthetic' approaches to culture (Bourdieu, 1984: 6; 485; Hartley, 1994: 6)1. In this, Cultural Studies is similar to other postmodern institutions, where high and popular culture can be mixed in ways unfamiliar to modernist culture (Sim, 1992: 1; Jameson, 1998: 100). So far, so familiar.