Keith Sunderland

Enhanced Network Voltage Management Techniques Under the Proliferation of Rooftop Solar PV Installation in Low-Voltage Distribution Network

The proliferation of rooftop solar PV distributed generator (PVDG) installation in a low-voltage distribution network (LVDN) imposes voltage fluctuation challenges that are a threat to distribution system operators. Reactive power control (RPC) methods are insufficient in isolation to combat the overvoltage fluctuations manifested in an LVDN with a significant number of grid-tied PVDG installations, whereas active power curtailment (APC) control can alleviate the voltage fluctuation in such situations and it is achieved at the cost of reduced active power injection. This paper explores how deficiencies in both RPC and APC as separate approaches can be mitigated by suitably combining RPC and APC algorithms. Strategies combining two RPCs and one RPC in conjunction with APC are proposed as two coordinating algorithms by means of an instantaneous measurement of node voltage and active power. These coordinating algorithms are embedded in all the rooftop PVDG grid-tied inverters (GTIs), where the GTI coordinates among them for voltage support without exceeding individual inverter volt-ampere rating. The result of the combined approach shows a significant improvement in managing and stabilizing the voltage and allows the penetration of PVDG to be increased from 35.65% to 66.7% of distribution transformer kilovolt-ampere rating.

4-Wire load flow analysis of a representative urban network incoprating SSEG

The effect of increased connections of micro generation technologies can only be truly analysed if accurate distribution network models are used. Such models must be 4-wire, capable of load unbalance consideration and cognisant of the effects associated with multiple grounding on the network. This paper describes such a model. Through a multi-phase load flow algorithm based on the backward/forward load flow technique, a 4-wire suburban distribution network in Dublin, Ireland which explicitly incorporates representation of the earth will be analysed. In conjunction with representative consumer load and commercially available micro wind generators, issues including voltage unbalance, voltage rise (associated with varying penetration of micro/small generation technologies) and neutral earth voltage (NEV) effects associated with such technologies are investigated.

Analysis of Wind Velocity and the Quantification of Wind Turbulence in Rural and Urban Environments Using the Levy Index and Fractal Dimension

This paper is concerned with a quantitative and comparative analysis of wind velocities in urban and rural environments. It is undertaken to provide a route to the classification of wind energy in a rural and urban setting. This is a common problem and the basis of a significant focus of research into wind energy. In this paper, we use a non-Gaussian statistical model to undertake this task, and, through a further modification of the data analysis algorithms used, extend the model to study the effect of wind turbulence, thereby introducing a new metric for this effect that is arguably superior to a more commonly used and qualitatively derived measure known as the Turbulence Intensity. Starting from Einstein’s evolution equation for an elastic scattering process, we consider a stochastic model for the wind velocity that is based on the Generalised Kolmogorov Feller Equation. For a specific ‘memory function’ the Mittag-Leffler function it is shown that, under specified conditions, this model is compatible with a non-Gaussian processes characterised by a Levy distribution that, although previously used in wind velocity analysis, has been introduced phenomenologically. By computing the Levy index for a range of wind velocities in both rural and urban environments using industry standard cup anemometers, wind vanes and compatible data collection conditions (in terms of height and sampling rates), we show that the intuitive notion that the ‘quality’ of wind velocity in an urban environment is poor compared to a rural environment is entirely quantifiable. This quantifies the notion that a rural wind resource is, on average, of higher yield when compared to that of the urban environment in the context of the model used. In this respect, results are provided that are based on five rural and urban locations in Ireland and the UK and illustrate the potential value of the model in the consideration of locating suitable sites for the development of wind farms (irrespective of the demarcation between an urban and rural environment). On this basis, the paper explores an approach whereby the same model is used for evaluating wind turbulence based on the Fractal Dimension using the ‘polar wind speed’ obtained from three-dimensional data sets collected in urban environments.

The role of micro wind generation in Ireland’s energy future

This paper defines the current position for micro-generation, with particular reference to the potential for micro-wind units, in the Irish electricity supply system. A network model is developed using the Distflow method of load flow analysis and is applied to consider the appropriate level of micro-generation penetration.

Application of a correction current injection power flow algorithm to an unbalanced 4-wire distribution network incorporating TN-C-S earthing

Power flow analysis of distribution networks incorporating Low Voltage (LV) consumer representations needs to be cognisant of both a highly unbalanced load structure as well as the provision of the grounding network between the consumer and grid operator (TN-C-S earthing). In this paper, the asymmetrical 3-phase (plus neutral) power flow problem is solved by a correction current injection method using a complex Y matrix approach in consideration of a representative Irish urban distribution network. This methodology offers a much improved and more robust alternative for ill-conditioned asymmetrical network scenarios compared to the standard power flow methodologies such as the Newton-Raphson methods or the forward-backward sweep approach (which encounters convergence issues as a consequence of the complex earthing arrangements). The model refers to a 4-wire representation of a suburban distribution network within Dublin city, Ireland, which incorporates consumer connections at single-phase (230V-N). Investigations relating to a range of network issues are presented. More specifically, network issues considered include voltage unbalance/rise and the network neutral earth voltage (NEV) for increasing levels of micro/small wind generation technologies with respect to a modeled urban wind resource.

The Small Wind Energy Estimation Tool (SWEET) –a practical application for a complicated resource

Of the forms of renewable energy available, wind energy is at the forefront of the European (and Irish) green initiative with wind farms supplying a significant proportion of electrical energy demand. Increasingly, this type of distributed generation (DG) represents a “paradigm shift” towards increased decentralisation of energy supply. However, because of the distances of most DG from urban areas where demand is greatest, there is a loss of efficiency. One possible solution, placing smaller wind energy systems in urban areas, faces significant challenges. However, if a renewable solution to increasing energy demand is to be achieved, energy conversion systems in cities, where populations are concentrated, must be considered. That said, assessing the feasibility of small/micro wind energy systems within the built environment is still a major challenge. These systems are aerodynamically rough and heterogeneous surfaces create complex flows that disrupt the steady-state conditions ideal for the operation of small wind turbines. In particular, a considerable amount of uncertainty is attributable to the lack of understanding concerning how turbulence within urban environments affects turbine productivity. This paper addresses some of these issues by providing an improved understanding of the complexities associated with wind energy prediction. This research used detailed wind observations to model its turbulence characteristics. The data was obtained using a sonic anemometer that measures wind speed along three orthogonal axes to resolve the wind vector at a temporal resolution of 10Hz. That modelling emphasises the need for practical solutions by optimising standard meteorological observations of mean speeds, and associated standard deviations, to facilitate an improved appreciation of turbulence. The results of the modelling research are incorporated into a practical tool developed in EXCEL, namely the Small Wind Energy Estimation Tool (SWEET). This tool is designed to assist engineers gain an intuitive appreciation of the limitations associated with this form of energy. It is only through an understanding of such limitations that informed decisions can be made which ultimately facilitate more intelligent installations

Levelised cost of energy analysis: A comparison of urban (micro) wind turbines and solar PV systems

The relatively high capital cost associated with micro wind energy systems and the resulting long payback periods, makes for a challenging argument for these technologies. However, as the global population becomes increasingly concentrated in urban areas, the potential for accessing any available renewable energy resource, including wind and solar PV, could become a necessity. This infers that the economics associated with small/micro energy systems need to be better appreciated. This paper presents a levelised cost of energy (LCOE) analysis for rural/urban small/micro wind energy systems that is contextualised by a solar PV system comparison. Further insight is offered through a design of experiments (DOE) consideration that affords an understanding of how system parameters, such as primary energy (rural/urban wind resource and solar insolation), capital cost and loan/finance interest rate individually and collectively affect the respective technologies. The results suggest that from an economic justification perspective, urban installations are difficult to justify and solar PV systems, with the associated lowering system costs, are challenging the viability of small/micro rural wind energy systems.

Comparative study between direct load control and fuzzy logic control based demand response

Demand response (DR), as part of Demand side management (DSM), is a method that modifies consumer side energy consumption. By actively controlling the time associated with electricity consumption, both energy and economic efficiencies are increased. There is however, depending on the algorithm employed, potential for consumer comfort levels to be adversely affected. Generally direct load (Boolean logic) control is employed, which solely considers demand reduction and not customer comfort. In comparison, fuzzy logic based programs can consider non-deterministic inputs such as consumer comfort level with ease and simplicity. This paper considers the evolution of DR through a comparison of the classical (direct load method) and modern (fuzzy method) methods, with particular attention on the advantages provided by the latter. The impact on consumer comfort in fuzzy DR implementation is further explored through the effect of temperature deviation. In this regard, the consequences for fuzzy DR are considered in respect to three temperature profiles. Finally, temporal availability and the consequences for DR are considered in the context of a household.

The impact of urban atmospheric turbulence on the generation capability of a micro-wind generator

The purpose of this study is to analyse the implications of atmospheric turbulence within the urban environment on the generation capability of a micro-wind turbine. In the interests of determining an empirical relationship regarding the influence of ambient turbulence on the generation of a micro-wind turbine, wind resource data from a number of sites has been considered in accordance with corresponding measured power data for a micro-wind generator. The results of this study illustrate that atmospheric turbulence has a considerable impact on the power generation of a micro-wind turbine, but that this effect differs depending on the region of the power curve considered. However, as turbulence has been found to only considerably affect power generation at wind speeds that are doubtful to occur in the urban environment due to its high roughness, it could be interpreted, that with specific regard to urban wind energy, the level of turbulence at a particular site might not be such a critical factor in potential energy generation after all.