Geraint Bevan

Bond-graph modeling

The bond-graph method is a graphical approach to modeling in which component energy ports are connected by bonds that specify the transfer of energy between system components. Power, the rate of energy transport between components, is the universal currency of physical systems. Bond graphs are inherently energy based and thus related to other energy-based methods, including dissipative systems and port-Hamiltonians. This article has presented an introduction to bond graphs for control engineers. Although the notation can initially appear daunting, the bond graph method is firmly grounded in the familiar concepts of energy and power. The essential element to be grasped is that bonds represent power transactions between components

Trajectory generation for road vehicle obstacle avoidance using convex optimization

Abstract This paper presents a method for trajectory generation using convex optimization to find a feasible, obstacle-free path for a road vehicle. Consideration of vehicle rotation is shown to be necessary if the trajectory is to avoid obstacles specified in a fixed Earth axis system. The paper establishes that, despite the presence of significant non-linearities, it is possible to articulate the obstacle avoidance problem in a tractable convex form using multiple optimization passes. Finally, it is shown by simulation that an optimal trajectory that accounts for the vehicles changing velocity throughout the manoeuvre is superior to a previous analytical method that assumes constant speed.

Automatic lateral emergency collision avoidance for a passenger car

Longitudinal collision avoidance controllers are of limited benefit for preventing head-on collisions between road vehicles travelling at high speed or for preventing rear end collisions when there is insufficient separation between the vehicles. In these circumstances, aggressive lateral vehicle manoeuvres are more appropriate. This paper develops a controller architecture to perform an emergency lateral collision avoidance manoeuvre. Simulation results indicate significant improvements in collision avoidance at vehicle speeds up to 100 [km/hr] using integrated automatic steering and braking.

Inspector interfaces to facilitate subjective reasoning about quantities in trends

Nuclear safeguards inspectors view historical trends on a regular basis to reassure themselves that a plant is operating as declared. Other types of inspector are likely to perform similar activities. Nuclear safeguards are founded on materials accountancy, and hence nuclear safeguards inspectors often want to relate what they see to laws of mass conservation. The interfaces discussed in this paper facilitate a synergy between qualitative reasoning regarding trends with quantitative reasoning about simple models that are driven by forcing functions, which describe materials flows through a plant. The focus in the paper is on the assessment of data trends that pertain to a standard 3-tank arrangement in a nuclear fuel reprocessing plant, and on how inspectors might wish to interact with evaluations performed.

Performance comparison of collision avoidance controller designs

A comparison is made between two vehicle control strategies for two different manoeuvres: a gentle and aggressive lane-change. Simulation results demonstrate that the choice of control objectives and selection of appropriate design approximations have a significant impact on the performance of the controller under these different manoeuvre conditions. A lateral control design trade-off between passenger comfort and collision avoidance capability is evident.

Review of Energy Storage Systems in electric grid and their potential in distribution networks

Concerns over changes to the global environment and the growing need for energy have increased the penetration of renewable energy (RE) generation into low voltage distribution networks. The introduction of Energy Storage Systems (ESS) into distribution networks has been proposed to improve the reliability and performance of power systems. Energy storage systems will also be important in helping to regulate the supply from intermittent RE sources that feed into variable load demand. The focus of this paper is to provide an overview of the state of the art of ESS, concentrating on the distinct characteristics and applications of the different types. The analysis includes comparison and evaluation of different storage preferences with regard to integration of these technologies with an electric grid at the distribution network level that may lead to benefits such as distribution upgrade deferral and improvements in power quality and reliability.

Failure prediction of power cables using failure history and operational conditions

This paper classifies the causes of cable failures according to two types: unpredictable random causes; and predictable ageing effects. A piecewise power-law non-homogeneous Poisson process and a stochastic electro-thermal model are proposed to predict total annual failures and failures due specifically to ageing, respectively. An amalgamation of the two models is then used to estimate the number of failures attributable to random causes or ageing. The proposed method is successfully applied to real data of vintage unjacketed XLPE cables. The results show that these cables have an expected lifespan of 39 years based on ageing effects alone; however, failure of these cables is dominated by random failure modes such as manufacturing defects, sudden shock, or water and electrical tree, which cause many of these cables to fail earlier in their life.

Cost effective replacement of power cables by stochastic dynamic programming approach

In this paper, we have presented a stochastic dynamic programming model to optimize the cost of proactive replacement of power cables. The proposed methodology can be implemented on cables with known failure distribution and insulation degradation level; the methodology to estimate both of the elements is based on previously developed Non-homogenous Poisson Process model (NHPP) and stochastic degradation model, respectively. The model gives the sequence of decisions for each year of the planning horizon such that it optimizes the overall cost and improves the reliability by lowering the frequency of unplanned outage. The model was tested on a XLPE cable.