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

Safety Management and Risk Modelling in Aviation: The challenge of quantifying management influences

Aviation accidents result from a combination of many different causal factors ( human errors, technical failures, environmental and organisational influences). Increasing interest over the past two decades in causal modelling of organisational factors has been motivated by the desire to understand these fundamental causes and their influences in risk. Although there is a need for system-wide accident models in air transport, such models are currently lacking. Causal Modelling of Air Transportation System (CATS) was one of the first projects to develop such a model in aviation. Based on the experience of CATS, this PhD research examines the place and role of the human and management models and their quantification in aviation. This study reveals several challenges in respect to safety management modelling, including availability of data, and techniques for the management quantification. New insights found in this research were taken on board to develop a generic hierarchical control model for aviation safety and a list of human and technical factors to be treated in risk modelling in aviation. A new way of quantifying safety management in risk model is also proposed. Several recommendations were made for an extension of risk modelling in CATS, or in the other research with similar research objectives.Ssafety Science GroupTechnology, Policy and Managemen

SURVEILLE Deliverable 3.4: Design a research methodology for assessing the effectiveness of selected surveillance systems in delivering improved security

Values, Technology and InnovationTechnology, Policy and Managemen

Modelling human and organizational behaviour in a high-risk operation

A core part of the risk modelling program for the Oil and Gas industry being carried out at Delft University of Technology is the influence of humans, within an organisation, as well as the technical factors. Specific attention is given to the incentive structure of operators, staff and managers, which in previous models had only been indicated more generally by motivation and conflict resolution. An incentive structure represents an empirical framework for an organisation which characterises the relationship between specific behaviours of employees and the probabilities of receiving various incentives. Most of the scientific literature on incentives is about the formal incentive structure that companies have in place. There are however, many more incentives so that a decision to choose one from several possible courses of action and decide to commit to safety above other personal and organizational goals is certainly influenced by personal safety attitudes, but there are also strong organizational aspects to these influences. Management influences and management actions are considered important in this respect because their actions influence personal safety attitudes to some degree. For instance, personal “need” and “incentives” are factors / motivations that can be coupled with a company’s goals influenced by management influences. Employees who feel they have access to good career development opportunities, or who are praised by managers for doing a good job, are more motivated and more likely to committed to their work. Lin (2008, 2011) studied quantifying the influences of management actions on human performance, expressed through the quality and operation of the management actions. Interviews with personnel serve to uncover which signals are sent by managers and colleagues and how they are received. This paper discusses the different incentive structures identified and describes methods used to uncover and quantify them in a wider risk model.Values and TechnologyTechnology, 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

A Risk Analysis for Asset Management Considering Climate Change

This paper presents an optimization framework for highway infrastructure elements that integrates risk profiles (for infrastructures) and economic aspects. One main goal is to assess the necessary additional effort to satisfy performance constraints under different scenarios of climate change. In order to be easily deployable by national road administrations (NRAs), this framework is built in such a way that it can be embedded into asset management systems that include an inventory of the asset, inspection strategies (to report element conditions and safety defects) and decision-making for funds allocation. Using the inventory of the asset and condition assessment as input, the method aims to determine some degradation profiles for bridge components, retaining walls and steep embankments. The method to determine the degradation process is detailed so that any infrastructure manager can determine their own deterioration processes based on the inventory and condition assessment of their stock. Combining degradation of highway infrastructures with a risk analysis, this paper presents an optimization framework to determine optimal management strategies.Safety and Security Scienc

Multi-criteria optimization framework for road infrastructures under different scenario of climate change

Values Technology and InnovationTechnology, Policy and Managemen

Causal Model for Air Transport Safety: Final report

Technology, Policy and Managemen

SURVEILLE Deliverable 2.6: Matrix of surveillance technologies

Values, Technology and InnovationTechnology, Policy and Managemen