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

Rational design of a robust diesel particulate filter

Applied Science

Bankruptcy by catastrophes for major multi-nationals: Stock exchange sensitivity for three catastrophes

This paper investigates the effect of major catastrophes have on stock exchange values for the major multi-nationals. The paper demonstrates that the Sharpe analysis is more sensitive in identifying effects than just following the daily stock values for assessing market response. It was found that major multi-nationals are capable of absorbing incredible amounts of financial damage following from catastrophes before stock markets react. This is partly due to the complexity of modern financial market risks that can be sold or transferred easily from the operative entity to another entity. The findings suggest that Hudson’s (2007) HSE culture ladder requires a step below the pathological to reflect the reaction of the stock exchange market on major catastrophes: the indifferent level. If the financial risks of catastrophes are covered, market traders rarely assign further consequences for the loss of life to the company through the lowering stock prices. Despite that, there may be a threshold value for financial loss that could bring major multi-nationals to bankruptcy due to market capital loss.Values and TechnologyTechnology, Policy and Managemen

Human factors in layers of defense in airport security

Airport security systems are built up out of layers of defence based on the security-in-depth model (Talbot & Jakeman, 2008). The Transport Safety Authority (TSA) in the United States defined a staggering 20 layers of defence to control security risks. This means that not only security personnel is responsible for security at the airport but many others too. However, the perceptions vary between different users of airports so it is difficult to involve all airport users in the security process. This paper focuses on identifying these factors through surveys. Differences were found between the level of education, between employees and passengers, between job groups working in the airport for instance the perceived level of trust in technology used in airport security or the perceived level of safety in the airport.Values and TechnologyTechnology, Policy and Managemen

SURVEILLE Deliverable 3.8: Report combining results of all effectiveness research

Values, Technology and InnovationTechnology, 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

Artificial Force Fields for Multi-agent Simulations of Maritime Traffic: A Case Study of Chinese Waterway

Collisions are an important factor in probabilistic risk modeling of waterway infrastructures. Especially in the design of bridges and terminals, the probability of ship collision is important. Researchers are looking for simulations that mimic ship behavior and estimate accident probabilities rather than using probabilistic accident models. AIS (Automatic Identification System) data forms a valuable basis for development of such simulation models. The data is a valuable asset for the validation and calibration of accident simulation models. Hence, a detailed analysis of AIS data is being undertaken as part of current research on ship collision simulations. Based on AIS data analysis, we developed a primary application of multi-agent simulation for ship traffic in the Yangtze River, which provides a realistic representation of the shipping traffic. Visual comparisons between AIS data and simulation data show comparable ship movements. More importantly, many different simulations show that the output of the simulation reproduces the behavior of real ships according to AIS data. Further down the road, ship failures will also be simulated, which results in a probability of ship accidents. Rather than the existing mathematical methods to estimate the risks of maritime accidents, multi-agent simulations provide a realistic ship behavior and all the details of ship movement. The model provides detailed information on how ships go wrong, and forms a useful tool in the design of waterways, design of bridges, and in traffic management.Values and TechnologyTechnology, Policy and Managemen

Participant observation in risk problems

Participant observation is a method to collect information through active participation in the social world that is under study, in this case two different risk-related working areas where confidentiality and secrecy are paramount. In reality there is a difference between what people do and say they do. With participant observation this discrepancy can be found. New research areas can be explored with participant observation when there is limited or no data available. In participant observation a level of immersion can be chosen. What position the observer takes depends on the situation and the goal of the research. In both studies discussed in this paper the ‘observer as participant’ form is chosen. The objective of this paper is to investigate whether in behavior or in operation between a traditional ‘safety’ working area and a ‘security’ working area show any similarities. We work from the hypothesis that since both are risk areas similarities exist. The object of study is rule violation and compliance in regulations. In this paper two relatively new areas of research are described which have limited data available. The main focus of one study is observation of decision making airport employees dealing with security. The other focus of study is observation of Seveso inspections of chemical corporations. Justification for participant observation comes from the fact that little is known of the strengths and weaknesses of current processes and procedures. Advantages and limitations of this method will be discussed after the comparison of results from the different working areas, as well as ethical issues that emerged in relation to confidentiality and secrecy. Other differences between settings and the influence of these differences of participant observation and methods of recording and interactions with the observed will be described in this paper.Values and TechnologyTechnology, Policy and Managemen

AIS data anlaysis for realistic ship traffic simulations model

AIS (Automatic Identification System) data provide valuable input data for the development of simulation models to prevent shipping accidents. This paper reports on the detailed analysis of AIS data for that purpose. This analysis is focused on restricted waterways to support inland waterway simulations, comparing the differences between a narrow waterway in the Netherlands (narrow waterway in the Port of Rotterdam) and a wide one in China (wide waterway of Yangtze River). Statistical distributions can be used to characterize position, speed, heading and interval times for different types and sizes of ships. It was found that the distributions between narrow and wide waterways differ significantly.Values and TechnologyTechnology, Policy and Managemen

Nautical traffic simulation with multi-agent system

This paper describes a microscopic nautical traffic simulation model based on multi-agent system. The ship traffic is produced from the behavior of autonomous agents that represent ships. Especially, we look at the behaviors for collision avoidance in different encountering situations with different local environmental conditions. The behavior of the ships is simulated with a dynamic ship maneuvering model, taking into account the movements in different local circumstances. And we utilize AIS data for input in simulation, model validation, and model verification. Moreover, we use the ODD (Overview, Design concepts, Details) protocol as a framework for the detailed description of the model.Hydraulic EngineeringCivil Engineering and Geoscience