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

Left-hand side BBN model for process safety

This paper describes the blueprint of a model for calculating the left-hand side of the bow-tie for chemical plants is described. The model is based on Non-Parametric Bayesian Belief Nets so that uncertainties are automatically included. Also, the procedure for constructing the elements for the model is described. The aim is to calculate LoC frequencies for entire chemical plants in a single straightforward modeling approach in a single model. It is demonstrated that only four principle design rules are required to construct the blueprint for a model that is flexible and straightforward to work with. It was also found that design process for the components of the model is traceable and reproducible. A structured working procedure was designed to meet those requirements. A numerical validation process will follow in the future.Values and TechnologyTechnology, Policy and Managemen

Continuous/discrete non parametric Bayesian belief nets with UNICORN and UNINET

Hanea et al. (2006) presented a method for quantifying and computing continuous/discrete non parametric Bayesian Belief Nets (BBN). Influences are represented as conditional rank correlations, and the joint normal copula enables rapid sampling and conditionalization. Further mathematical background is in Kurowicka and Cooke (2007). This article sketches the current stage of development. The driving application currently involves 133 continuous and discrete probabilistic nodes, and 330 functional nodes. Boolean functions enable fault trees to be fully represented as functional nodes in a BBN. Repeated nodes are easily handled with the identity function. Current perspectives and challenges conclude the paper.Delft Institute of Applied MathematicsElectrical Engineering, Mathematics and Computer Scienc