Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics

Human Risk of Fire: Building a decision support tool using Bayesian networks

Safety Science GroupTechnology, Policy and Managemen

Modelling risk in high hazard operations: Integrating technical, organisational and cultural factors

Recent disasters in high hazard industries such as Oil and Gas Exploration (The Deepwater Horizon) and Petrochemical production (Texas City) have been found to have causes that range from direct technical failures through organizational shortcomings right up to weak regulation and inappropriate company cultures. Risk models have generally concentrated upon technical failures, which are easier to construct and for which there is more concrete data. The primary causes, as identified by the US Chemical Safety Board for Texas City and the Presidential Commission for the Deepwater Horizon, lie firmly rooted in the culture of the organization and determine the way in which individuals go about risky activities. Modelling human activities, especially collectively rather than individual human errors as is done in most human models, is a quite different proposition, in which complex interactions between different individuals and levels change over time as success and failure alter the pattern of payoffs. This paper examines the development of an integrated model for risk in a real-time environment for the hydrocarbon industry. It is based originally on the CATS model for commercial aviation safety, that first attempted to address some of these problems in a relatively simple way. Aviation is, however, a relatively simple activity, with large numbers of common components in a constrained environment. The Oil and Gas industry is significantly more diverse, covering the gamut from exploration, drilling, production, transport, refining and chemical production, each with its own potential for large scale disaster, but in the case of an integrated oil company all run by individuals within a common company culture. Other papers will cover the details of specific issues; this paper covers the integration of the model as a whole.Values and TechnologyTechnology, Policy and Managemen