Distributed Wind Generation Research Articles

RETRACTED: Priority Algorithm Based Coordinated Voltage Control for Distribution System with Distributed Wind Generators

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of scientific committee of SMART GRID Technologies 2015. The authors have plagiarized part of a paper that had already appeared in PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), 6 (2012) 304 - 312, http://pe.org.pl/abstract_pl.php?nid=6091. One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and has not appeared in a publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a severe abuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Two-stage Combinatory Planning Method for Efficient Wind Power Integration in Smart Distribution Systems Considering Uncertainties

—A crucial factor that may hinder the usage of renewable energies is the mismatch to load demand in the temporal dimension. In the smart-grid environment, demand response is regarded as a feasible solution to mitigate such a problem. In this study, a combinatory planning method is proposed for efficient integration of wind generation. The problem is formulated as a two-stage fuzzy chance-constrained programming model, which co-optimizes the installation of distributed wind generation along with network transformation and determination of optimal real-time prices to achieve the minimization of the total cost over planning horizons. The impact of both aleatory and epistemic uncertainties associated with wind generation, load growth, and responsive behaviors of customers has been considered. Results of the case study demonstrate the effectiveness of the proposed method and the necessity of considering different uncertainties in the planning.

Optimal mix of solar and wind distributed generations considering performance improvement of electrical distribution network

Renewable energy sources are gaining more and more interest because they are nonpolluting and sustainable. Recently, a notable number of renewable distributed generations (DGs) having intermittent generation patterns are being interconnected with the distribution network to meet growing load demand and nullify environmental threats. Appropriate integration of renewable DGs in distribution networks is crucial to guarantee the qualitative network operational benefits. In this paper a simple but efficient approach has been proposed for optimal placement and sizing of solar and wind DGs in distribution territory by considering electrical network power loss minimization, voltage stability and network security improvement. The stochastic nature of solar irradiance and wind speed are accounted using suitable probabilistic models. Weighted aggregation particle swarm optimization technique is employed to optimize the objective functions considering bus voltage limit, line loading capacity, discrete size limit and penetration constraints of DGs. Strategic weight selection technique has been adopted to assess the well trade-off solution by persuasion of multiple objectives regarding the performance of distribution network. The proposed method has been applied to a typical Indian rural distribution network, and the satisfactory results are obtained.

Coordinated planning model of BESS and controllable switches in distribution

Distributed wind generation (DWG) with increasing permeability has brought an adverse effect to grid security. The battery energy storage system (BESS) can solve this problem. However, the system reliability may be limited by the improper locations of switches. To make full use of BESS, a coordinated planning model of BESS and controllable switches (CSs) is developed for distribution networks. The objective is to minimise overall cost including investment cost, operation cost, network loss, insufficient power supply cost and energy price arbitrage, while satisfying security and BESS limitations. The simulation results show that the model proposed is effective.

Three-Phase Fault Direction Identification for Distribution Systems With DFIG-Based Wind DG

Distributed generation (DG) integration necessitates upgrading some distribution system overcurrent relays to directional ones to offer selective protection. The directional feature is conventionally achieved by phase angle comparison between phasors of the fault current and a polarizing quantity, normally a voltage signal. Doubly fed induction generator (DFIG)-based wind turbines constitute an appreciable portion of today’s DG power. This paper unveils that conventional directional elements malfunction during three-phase short-circuits when a distribution system incorporates DFIG-based wind DG. The maloperation is due to the exclusive fault behavior of DFIGs, which affects the existing relaying practices. The paper also proposes a fault current classification technique that replaces the conventional directional element during problematic conditions and provides accurate fault direction quickly based on waveshape properties of the current. An extensive performance evaluation using PSCAD/EMTDC simulation of the IEEE 34 bus system corroborates the effectiveness of the proposed method. Results are exceptionally encouraging in the case of resistive crowbar circuits for DFIGs, which is the typical scenario in practice.

Experience with smarter commercial arrangements for distributed wind generation

This study explores different practices for accelerating the integration of generating facilities to the electricity network using smart solutions. Case studies from Great Britain, Republic of Ireland and Northern Ireland, and the Unites States of America were selected. The paper assesses and compares the different Principles of Access that have been implemented in these countries, such as Last-in First-out (LIFO), Pro Rata and Market-Based. The social optimality of these approaches is also discussed. The paper also evaluates how the risk (regarding curtailment and investment) is allocated between parties (distribution network operators, generators and customers). Even though the cases are diverse, important findings and lessons have been identified which may assist distribution network operators to address the issue of increasing the connection of distributed generation while managing efficiently and economically energy exports from generators.

Fuzzy based prediction of wind distributed generation impact on distribution network: Case study—Banat region, Serbia

The paper proposes the methodology for the assessment of impact that wind distributed generation can have on distribution network. Effects of active power losses, voltage drops, and voltage total harmonic distortion are considered. The methodology uses fuzzy logic in order to address uncertainties in wind energy generation, as well as artificial neural networks for wind speed assessment. Measurement data of temperature, irradiation, and wind direction at different wind turbine hub heights are used. The predicted wind speed, active power loss variation, and elasticity of power quality constraints are presented in a form of fuzzy numbers. The proposed methodology is tested on realistic, 28-bus 35 kV voltage distribution system in the Banat region in Serbia. A steady-state voltage stability index is applied to select wind distribution generation locations. It is shown that wind distributed generation can improve voltage regulation and reduce active power losses. However, increase in voltage total harmonic distortion is possible. The proposed methodology enables analysis of the impact that wind speed has on possible effects of wind distributed generation.

Evaluating Future Power Distribution System Reliability Including Distributed Generation

This paper assesses the impact of conventional and renewable distributed generation (DG) on the reliability of future distribution systems, even when the connection may not be simply radial. The variability of the power output of renewable DGs, such as wind and solar is included. The stochastic nature of the renewable resources and their influence on the reliability of the system are modeled and studied by computing the adequacy transition rate. An integrated Markov model that incorporates the DG adequacy transition rate, DG mechanical failure, and starting and switching probability is proposed and utilized to give accurate results for the DG reliability assessment. The main focus in this paper is conventional generation, solar, and wind DG units. The technique used appears to be applicable to any renewable energy source.

Maximising revenue for non‐firm distributed wind generation with energy storage in an active management scheme

The connection of high penetrations of renewable generation such as wind to distribution networks requires new active management techniques. Curtailing distributed generation during periods of network congestion allows for a higher penetration of distributed wind to connect, however, it reduces the potential revenue from these wind turbines. Energy storage can be used to alleviate this and the store can also be used to carry out other tasks such as trading on an electricity spot market, a mode of operation known as arbitrage. The combination of available revenue streams is crucial in the financial viability of energy storage. This study presents a heuristic algorithm for the optimisation of revenue generated by an energy storage unit working with two revenue streams: generation-curtailment reduction and arbitrage. The algorithm is used to demonstrate the ability of storage to generate revenue and to reduce generation curtailment for two case study networks. Studies carried out include a single wind farm and multiple wind farms connected under a ‘last-in-first-out’ principle of access. The results clearly show that storage using both operating modes increases revenue over either mode individually. Moreover, energy storage is shown to be effective at reducing curtailment while increasing the utilisation of circuits linking the distribution and transmission networks. Finally, renewable subsidies are considered as a potential third revenue stream. It is interesting to note that under current market agreements such subsidies have the potential to perversely encourage the installation of inefficient storage technologies, because of increased losses facilitating greater “utilisation” of renewable generation.

On the Capacity Factor of Distributed Wind Generation in Droop-Regulated Microgrids

This paper presents the methodological basis for the computation of the capacity factor (CF) of the power delivered by an off-grid droop-regulated microgrid when the power is injected by distributed stochastic generation. More particularly, the paper is focused on wind generation and its modeling particularities. It shows how the availability of power can be efficiently sampled by a low variation Latin Hypercube Sampling (LHS) method, supplemented with a restricted pairing technique to account for correlation among generating units. The paper also presents a minimization problem that, combined with a Fischer-Burmeister-based formulation, permits obtaining the maximum deliverable power at each sample. This paper additionally shows a first numerical analysis of a 14-node microgrid supplied by five Enercon E40. The analysis includes an investigation into the best model that represents the CF of the microgrid, and highlights the effects of correlation and maximum loadability.

Reactive power management of distribution networks with wind generation for improving voltage stability

This paper proposes static and dynamic VAR planning based on the reactive power margin for enhancing dynamic voltage stability of distribution networks with distributed wind generation. Firstly, the impact of high wind penetration on the static voltage stability of the system is analysed and then the effect of composite loads on system dynamics is presented through an accurate time-domain analysis. A new index, reactive power loadability (Q-loadability), is used to measure the vulnerability of the network to voltage collapse. Compensating devices are located using Q-loadability to increase the system voltage stability limit. Finally, a cost-effective combination of shunt capacitor bank and distribution static compensator (D-STATCOM) is determined through static and dynamic analyses to ensure voltage stability of the system after a sudden disturbance for different wind penetration levels. This study takes into account the induction motor dynamic characteristics which influence the transient voltage recovery phenomenon. The results show that the proposed approach can reduce the required sizes of compensating devices which, in turn, reduces costs. It also reduces power losses and improves the voltage regulation of the system.

Planning for distributed wind generation under active management mode

In the smart grid (SG), the active management (AM) mode will be applied for the connection and operation of distributed generation (DG), which means real time control and management of DG units and distribution network devices based on real time measurements of primary system parameters. In this paper, a novel bi-level programming model for distributed wind generation (DWG) planning under AM mode is put forward. The model takes the maximum expectation of net benefit of DWG as the upper level program objective, and takes the minimum expectation of generation curtailment as the lower level program objective. The impact of active management algorithm on improvement of branch power flow and node voltage is taken into account. A hybrid algorithm combining the plant growth simulation algorithm (PGSA) with probabilistic optimal power flow (POPF) algorithm is presented to solve the optimal planning of DWG under AM mode. The case studies have been carried out on a 33-node distribution network, and the results verify the rationality of the planning model and the effectiveness of the proposed method.

An approach for placement and sizing of capacitor banks in distribution networks with distributed wind generation

In this paper, a modified simulated annealing technique is proposed for the simultaneous improvement of power quality and optimal placement and the sizing of fixed capacitor banks in a modern distribution network. The latter is supplying a mix of linear and nonlinear loads imposing voltage and current harmonics. Besides, the network includes integrated variable-speed wind turbines as distributed generation. The stochastic power output of the wind generation is considered by performing the Monte Carlo simulation of the distribution power flow. Operational and power quality constraints include the bounds of node voltage magnitude, the node voltage total harmonic distortion, and the number/size of installed capacitors. The net annual economic saving is defined as the associated objective function that accounts for the cost of the released power capacity because of the power losses reduction, the cost change of energy losses, and the extra cost of the searched capacitor banks. Solution results are discussed for a model-distorted distribution system under different conditions. Copyright © 2012 John Wiley & Sons, Ltd.

An Analytical Approach to the Economical Assessment of Wind Distributed Generators Penetration in Electric Power Systems with Centralized Thermal Generation

This paper presents an approach for economical assessment related to the penetration of wind power generators in electric power networks. The proposed method is based on analytical formulation that considers the uncertainties involved with wind speed and load demand. The results show that the methodology also permits the analysis of distributed wind generators insertion considering different technical and economical parameters.

Residential- and commercial-scale distributed wind energy in North Dakota, USA

We use one year of hourly wind speed measurements at 14 sites across North Dakota to evaluate how both residential- and commercial-scale (utility-scale) wind turbines can help to meet electricity needs within the state. Data are available from April 2004 through March 2005, a period with slightly lower mean wind speeds as compared to a long-term climatology; thus our calculations represent a conservative estimate of wind power for these sites. We assume the wind patterns at each site are representative of the county as a whole and, using capacity factors of 20% (residential) and 35% (commercial), we estimate the amount of electricity that can be generated for the county and compare it to county-based estimates of electricity usage. Our results show that a residential-scale turbine could provide between 90% and 165% of annual net per-person electricity usage in these 14 counties, depending on the wind speed. In addition, for the counties with the smallest populations, only six commercial-scale turbines are needed to meet the net annual county electricity usage; the most populous county would require up to 69 turbines. An evaluation of month-to-month electricity supply and demand showed that between 9% and 20% (13% and 29%) of monthly electricity needs for a county with low (high) average wind speeds could be met if 30% of the county's households had a residential-scale turbine. Our results show that residential-scale turbines have the potential to contribute meaningfully to a distributed-generation wind energy landscape.

Wind energy generators sitting and sizing based on uncertain generation pricing

This paper proposes a methodology for sitting and sizing wind distributed generators (WDGs). These generators are characterised by an uncertain active power production due to the random behaviour of the wind speed. The uncertain generation directly impacts the network total generation cost and also the solution for the placement and sizing problem. So, this work takes into account this uncertain generation and presents a model (bus-based) to deal with uncertainties in active power production. Based on this model, the proposed methodology allows uncertain generation pricing and yields, after successive executions of an optimal power flow, a solution for the sitting and sizing problem of WDGs, considering economic dispatch conditions. Tests were carried out using the IEEE-14 buses system and the obtained results show the impacts of uncertainties in the placement, penetration and energy costs of WDGs.

The Impact of Connecting Distributed Generation to the Distribution System

This paper deals with the general problem of utilizing of renewable energy sources to generate electric energy. Recent advances in renewable energy power generation technologies, e.g., wind and photovoltaic (PV) technologies, have led to increased interest in the application of these generation devices as distributed generation (DG) units. This paper presents the results of an investigation into possible improvements in the system voltage profile and reduction of system losses when adding wind power DG (wind-DG) to a distribution system. Simulation results are given for a case study, and these show that properly sized wind DGs, placed at carefully selected sites near key distribution substations, could be very effective in improving the distribution system voltage profile and reducing power losses, and hence could improve the effective capacity of the system.

Influence of distributed wind generation and load composition on voltage sags

The envisaged increased penetration of distributed generation (DG) in electrical power networks poses challenging technical and contractual issues to both utilities and industry. Technical issues related to power quality, in particular to voltage-sag propagation and characteristics in networks with a large penetration of fixed speed wind DG are addressed. A comprehensive analysis of voltage-sag propagation in a realistic distribution network is performed. The influence of network topology, location and percentage of connected wind generation, network loading and load composition is investigated in detail. It is shown that the influence of DG on voltage-sag characteristics and propagation is strongly dependent on its location and on load composition.

Quantitative Techniques for Analysis of Large Data Sets in Renewable Distributed Generation

Distributed generation (DG) reduces losses and eliminates some of the transmission and distribution costs. It may also reduce fossil fuel emissions, defer capital costs, and improve the distribution feeder voltage conditions. The calculation of the effects of small residential photovoltaic and wind DG systems on various feeder operating variables is complicated by both the probabilistic nature of their output and the variety of their possible spatial allocations. A method based on a combination of clustering techniques and a convex hull algorithm is proposed that may reduce the computational burden by an order of magnitude, while still allowing accurate estimation of DG-enhanced feeder operation.

Voltage Regulation for Distributed Wind Generators

An existing group of wind generators, connected to a weak rural distribution network, has been retro-fitted with an active voltage control system. Detailed measurements have been made of the operation of the voltage controller, and the results used to optimise the target-voltage and bandwidth setting of the tap changer.