Robert J. Davy

Exploring the Power Flow Solution Space Boundary

A knowledge of the structure of the boundary of solutions of the power flow problem is important when analyzing the robustness of operating points. This paper proposes a predictor-corrector technique to assist in exploring that structure. Points on the solution boundary satisfy the power flow equations together with an equation that forces the power flow Jacobian to be singular. Curves of such points result from freeing two parameters of the system. The proposed technique follows those curves. A simple example is used to illustrate the complex nature of the power flow solution space.

Long-Term Wind Speed Trends over Australia

AbstractAccurate estimates of long-term linear trends of wind speed provide a useful indicator for circulation changes in the atmosphere and are invaluable for the planning and financing of sectors such as wind energy. Here a large number of wind observations over Australia and reanalysis products are analyzed to compute such trends. After a thorough quality control of the observations, it is found that the wind speed trends for 1975–2006 and 1989–2006 over Australia are sensitive to the height of the station: they are largely negative for the 2-m data but are predominantly positive for the 10-m data. The mean relative trend at 2 m is −0.10 ± 0.03% yr−1 (−0.36 ± 0.04% yr−1) for the 1975–2006 (1989–2006) period, whereas at 10 m it is 0.90 ± 0.03% yr−1 (0.69 ± 0.04% yr−1) for the 1975–2006 (1989–2006) period. Also, at 10 m light winds tend to increase more rapidly than the mean winds, whereas strong winds increase less rapidly than the mean winds; at 2 m the trends in both light and strong winds vary in lin...

A Simple Temporal and Spatial Analysis of Flow in Complex Terrain in the Context of Wind Energy Modelling

A simple temporal and spatial analysisis done on wind speed and direction data from a number ofmeteorological towers separated by distances between roughly 1 and 100 kilometres. The analysis is done in the context of expected model error in wind energy calculations. The study first uses single point statistics to show the evolution of mean values with time. It is shown that strong seasonal signals are present and that stable means are achieved only after averaging periods of a year or more. The study then uses discrete Fourier transforms to show that significant amounts of spectral energy reside in modes with periods of a few days to less than a day. Frequency dependent cross correlation values are then derived and used to show how correlation between towers diminishes with increasing frequency. The mechanism responsible for this diminished correlation is shown through the comparison of cross-correlation phase as a function of frequency and its relationship to distance between towers. Error in wind energy estimates are shown to be strongly related to correlation and therefore distance over which the prediction is made. In summary, much of the inaccuracy in modelling flow in the context of wind energy calculations is due to a lack of scale separation between the deterministic part of the flow, which is well modelled, and that part of the flow that is stochastic at the length and time scales modelled.

Methodology for High-Throughput Field Phenotyping of Canopy Temperature Using Airborne Thermography

Lower canopy temperature (CT), resulting from increased stomatal conductance, has been associated with increased yield in wheat. Historically, CT has been measured with hand-held infrared thermometers. Using the hand-held CT method on large field trials is problematic, mostly because measurements are confounded by temporal weather changes during the time required to measure all plots. The hand-held CT method is laborious and yet the resulting heritability low, thereby reducing confidence in selection in large scale breeding endeavors. We have developed a reliable and scalable crop phenotyping method for assessing CT in large field experiments. The method involves airborne thermography from a manned helicopter using a radiometrically-calibrated thermal camera. Thermal image data is acquired from large experiments in the order of seconds, thereby enabling simultaneous measurement of CT on potentially 1000s of plots. Effects of temporal weather variation when phenotyping large experiments using hand-held infrared thermometers are therefore reduced. The method is designed for cost-effective and large-scale use by the non-technical user and includes custom-developed software for data processing to obtain CT data on a single-plot basis for analysis. Broad-sense heritability was routinely >0.50, and as high as 0.79, for airborne thermography CT measured near anthesis on a wheat experiment comprising 768 plots of size 2 × 6 m. Image analysis based on the frequency distribution of temperature pixels to remove the possible influence of background soil did not improve broad-sense heritability. Total image acquisition and processing time was ca. 25 min and required only one person (excluding the helicopter pilot). The results indicate the potential to phenotype CT on large populations in genetics studies or for selection within a plant breeding program.

Simulation of Wind Power at Several Locations Using a Measured Time-Series of Wind Speed

The large-scale integration of wind power into electrical power systems is likely to require significant improvements to transmission infrastructure over coming years. Planning for these developments may involve modeling of power systems using estimates of the time-varying power output of proposed wind farms. Such estimates may be derived from wind measurements, although it is rarely the case that measurements are available simultaneously for all sites of interest. In the present work, a method is developed to produce synthetic time-series of wind power at several locations based on a measured time-series of wind speed from a reference site. The stochastic properties of the modeled time-series are shown to be comparable with those of measured data from south-eastern Australia. It is anticipated that with appropriate tuning for local conditions, the method could be applied in other geographical regions.

Lyapunov function analysis of power systems with dynamic loads

A Lyapunov (energy) function incorporates both generator and load dynamics. This paper reviews that energy function. Its use in the assessment of the stability of power systems where generator and load dynamics are active is presented. Further, generator/load interaction is explored. This new energy function allows for direct assessment of (dynamic) voltage collapse scenarios. It provides an analytical basis for establishing critical capacitor and load switching times. These issues are considered.