Dewi Ieuan Jones

Visual control of an unmanned aerial vehicle for power line inspection

Using a robotic vehicle to inspect overhead power lines has many attractions. The concept of a small, rotorcraft which draws its power from the lines is introduced here. Some of its advantages compared with a free-flying aircraft are discussed. Achieving the required degree of autonomy and reliable power pick-up needs good control of the position and attitude of the vehicle relative to the overhead line. The paper considers an artificial-vision system, based on the Hough transform, for this purpose. A laboratory test rig is described which incorporates a dynamic model for a small, ducted-fan rotorcraft so that the response of the vehicle to wind gusts can be emulated. Measurements show that the closed-loop vision system is capable of counteracting the effect of such disturbances and maintaining the vehicles position relative to the line

Camera sightline pointing requirements for aerial inspection of overhead power lines

Abstract This paper considers the image quality requirements for video inspection of overhead power distribution lines from a helicopter. The use of video surveillance techniques for routine inspection of overhead lines is seen as a means of automating the process as well as improving the depth and coverage by provision of permanent visual records. One of the principal difficulties of remote video surveillance from a helicopter is the degradation of the image due to the motion of the camera sightline. The work reported here introduces simulated motion blur onto sharp images to show that the tolerable motion is of the order of 1–2% of the field of view for static images. An expression is obtained for the maximum allowable amplitude of (sinusoidal) sightline perturbation for a given value of image blur. The results of an experimental assessment of the quality of images subject to sightline motion are presented and it is shown that the tolerable motion for dynamic viewing is similar to that for static images. It is concluded that optical stabilisation of the order of 100 μr is necessary for satisfactory inspection detail.

Reproducing oscillatory behaviour of a hydroelectric power station by computer simulation

Abstract This paper describes a complex simulation of a pumped-storage hydroelectric power station. Dinorwig power stations fast response is essential for controlling the electricity supply frequency on the national grid in Great Britain. The paper describes the stations key physical features and it is shown that the plant is nonlinear, multivariable and time-varying. The details of a Simulink® model, which is valid over a wide range of operating conditions, are presented. The improved understanding of the stations dynamic characteristics is illustrated by using the simulation to investigate an incident of oscillatory behaviour in its power output.

Corner detection and matching for visual tracking during power line inspection

Abstract Power line inspection from a helicopter using video surveillance techniques demands that the camera be automatically pointed at the object of interest, in order to compensate for the helicopters movement. The possibility of using corner detection and matching to maintain the fixation point in the image is investigated here. An attractive feature of corner-based methods is that they are invariant to camera focal length, which can vary widely during inspection. The paper considers the selection, parameter determination and testing of a customised method for detecting corners present in images of pole-tops. The method selected uses gradient computation and dissimilarity measures evaluated along the gradient to find clusters of corners, which are then aggregated to individual representative points. Results are presented for its detection and error rates. The stability of the corner detector in conjunction with a basic corner matcher is evaluated on image sequences produced on a laboratory test rig. Examples of its response to background clutter and change of illumination are given. Overall the results support the use of corners as robust, stable beacons suitable for use in this application.

Predictive feedforward control for a hydroelectric plant

In this brief, it is shown that predictive feedforward control can be used to help a hydroelectric plant achieve its target for delivered power while operating in grid (power system) frequency control mode. Due to the fundamental limitation on how fast the water in the supply tunnel can be accelerated by gravity, a hydraulic turbine is always subject to some delay between opening or closing its guide vane and the consequent change in power. Here, it is proposed that the effect of this delay can be alleviated by predicting 3-4 s ahead what power will be required, based on grid frequency measurements, and using this as a feedforward signal to supplement the normal PID feedback controller. Results are presented to show the improved accuracy of power delivery achieved with this approach.

A standard method for specifying the response of hydroelectric plant in frequency-control mode

Abstract The paper proposes a specification for the transient and steady-state responses of a hydroelectric power station operating in frequency-control mode. It can be used during design, testing and commissioning as well as forming the basis for contractual agreement on performance during normal operation. The specification gives a generic definition of how the electrical power should respond to step, ramp and random changes in frequency. The rationale for the proposed specification is discussed. A prototype transfer function is proposed as an aid to formulating a step response specification. The length of record required during random testing is discussed. The use of the specification is illustrated by considering the response of the Dinorwig pumped-storage hydroelectric station.

A rapid method for planning paths in three dimensions for a small aerial robot

This paper describes a path planning method for a small autonomous aerial vehicle to be used for inspecting overhead electricity power lines. A computational algorithm is described which converts a standard three dimensional array representation of one or more obstacles in the vehicles environment into an octree and a connectivity graph. This achieves a significant reduction in computer memory usage and an increase in execution speed when the graph is searched. Path planning is based on a three-dimensional extension of the distance transform. Test results demonstrate rapid and effective operation of the planner within different workspaces.

Using a fuzzy inference system to control a pumped storage hydro plant

The paper discusses the development of a fuzzy inference system (FIS) based governor control for a pumped storage hydroelectric plant. The First Hydro Companys plant at Dinorwig in North Wales is the largest of its kind in Europe and is mainly used for frequency control of the UK electrical grid. In previous investigations, a detailed model of the plant was developed using MATLAB/sup (R)//SIMULINK/sup (R)/ and this is now being used to compare FIS governor operation with the proportional-integral-derivative (PID) controller currently used. The paper describes the development of an FIS governor, and shows that its response to a step increase in load is superior to the PID under certain conditions of load. The paper proceeds to discuss the implications of these results in view of the possible practical application of an FIS governor at the Dinorwig plant.

Outlook and Conclusions

This chapter looks at projected electricity markets and what part hydroelectricity is likely to play in future energy provision. The current trend for large hydro projects to be concentrated in non-OECD countries is likely to continue. There is likely to be increased emphasis on the use of pumped hydro plant to control power networks. This leads to a requirement for accurate, fast and flexible delivery of electricity in order to mitigate the effect of intermittent renewable sources. However, hydropower is not the only technology competing for this role and it is foreseen that continuous development will be needed in order to secure a healthy future.

Dinorwig Simulation Models

This chapter resumes the various mathematical models used to represent the dynamic characteristics of the Dinorwig Hydroelectric Pumped Storage Plant. As described earlier, the models were developed systematically with increasing complexity, each model suitable for a particular system dynamic study. For instance, linear models can be applied to represent the effects of low frequency and guidance in speed control and nonlinear models are required when large changes of speed and power are considered, such as in islanding, load rejection and systems restoration studies. As Dinorwig has six units, the approaches considered both single input single output (SISO) and multivariable (multiple inputs multiple outputs, MIMO) models. The model of the system can be separated into subsystems. Figure A.1 shows a schematic of the Dinorwig power plant model. The full hydroelectric station model is constructed combining the four subsystems: guide vane dynamics, hydraulic subsystem, turbine/generator and sensor filters.