Distributed Generation Technologies Research Articles

Distributed Generation Islanding Effect on Distribution Networks and End User Loads Using the Master-Slave Islanding Method

This study aims to address the feasibility of planned islanding operation and to investigate the effect of unplanned islanding using the master-slave islanding method for controlling the distributed generation units during grid-connected and islanding operation. Neplan desktop power simulation tool was used for the modelling and simulation of a realistic MV network with four different distributed generation technologies (diesel, gas, hydro and wind) along with their excitation and governor control systems, while an exponential model was used to represent the loads in the network. The dynamic and steady state behavior of the four distributed generation technologies were investigated during grid-connected operation and two transition modes to the islanding situation, planned and unplanned. The obtained results that validated through various case studies have shown that a suitable planned islanding transition could provide support to critical loads at the event of electricity utility outages.

Analyzing Distributed Generation Impact on the Reliability of Electric Distribution Network

With proliferation of Distribution Generation (DG) and renewable energy technologies the power system is becoming more complex, with passage of time the development of distributed generation technologies is becoming diverse and broad. Power system reliability is one of most vital area in electric power system which deals with continuous supply of power and customer satisfaction. Distribution network in power system contributed up to 80% of reliability problems. This paper analyzes the impact of Wind Turbine Generator (WTG) as a distribution generation source on reliability of distribution system. Injecting single WTG and close to load point has positive impact on reliability, while injecting multiple WTGs at single place has adverse impact on distribution system reliability. These analyses are performed on bus 2 of Roy Billinton Test System (RBTS).

Optimal Configuration of DG in Distribution System: An Overview

Distributed generation (DG) has increased ever attention in the distribution system from last few years. The main reason for DG in distribution system is increasing electric demand, deregulated power system and congested transmission network, which eventually declines the system performance. There is also increasing pressure of greenhouse gas emissions. For proper utilization of DG, the optimal placement and sizing is of main concern. Because improper DG location and size will increase the losses and decrease the system performance than existing. On the contrary, proper placement will maintain voltage profile, reduce power loss, and increase voltage stability in the distribution system. This paper presents overview of DG, the advances in DG technology and different optimization methods used for optimal placement and sizing problem. The key issues and challenges offered in the development of DG is also presented in this paper.

Application of Dc-grid for Efficient use of solar PV System in Smart Grid

This paper is about efficient use of smart dc grid technology for photovoltaic distributed generation and utilizing it in smart way, to build infrastructure more reliable and to achieve the goal to cater the need for tomorrow. As there are many conversion losses from ac to dc, world is moving towards dc appliances as most of the electronic appliances at home accept dc power supply. Receiving dc power from Photovoltaic solar, it is clear there would be benefits in avoiding the conversion losses, especially when most of the devices used at home run on dc. This benefit is further enhanced if dc is directly used for lighting, electric vehicle charging, Digital equipment etc. PV solar energy produces dc power and if used directly then power loss will be minimized. Exact calculation of solar panels and proper battery sizing leads to a reliable distributed generation system. 240Vdc grid will also help to minimize the power transmission losses for up rise buildings, this will further enhance the system efficiency. Proper selection of wire minimizes the electric corrosion. Series and parallel combination of PV and battery cells will enhance the use of suitable power supply for each electronic device. Other side where ac supply is required 240Vdc directly converts to 240Vac for Ac machines such as conventional appliances in order to minimize transformer losses. This paper also presents an idea for smart load shedding techniques and its practical implementation in the form of smart dc Grid. Its various applications will enhance the functionality of a smart Dc grid on residential load.

Power electronics in smart grid distribution power systems: a review

Distributed generation (DG) in smart grid (SG) is being employed as a means of achieving increased reliability for electrical power systems as regarded by consumers. As the most of DG technologies utilise renewable sources, the power electronic interface plays a vital role to match the characteristics of a DG unit with the grid requirements. This paper presents the power electronics capabilities required for DG systems in SG to convert the generated power into useful power that can be directly interconnected with the utility grid and/or that can be used for consumer applications. Because of the enhancement and the different power ranges of power electronics devices, the development of advanced power electronic interface that is scalable to meet different power requirements, with modular design, lower cost, and improved reliability, will improve the overall performance and durability of smart grid distributed power systems.

Research on optimal schedule strategy for active distribution network using particle swarm optimization combined with bacterial foraging algorithm

Comparing with the traditional distribution network, a significant feature of the active distribution network (ADN) is that the performance of distributed generation (DG) units, energy storage units and micro-grid (MG) in the network is controllable for the distribution network operator. Considering the characteristics of the distributed power supply and micro-grid, and giving full play to the advantages of distributed generation technology in the economic, environmental and energy aspects, this paper highlights an environmental protection and energy saving optimal schedule model for ADN. The scheduling model focuses on the minimum network loss, minimum voltage deviation and minimum difference between peak and valley load. In addition, the two stage algorithm is presented to solve the proposed multi-objective scheduling model of ADN. First, a set of Pareto solutions are obtained by using the proposed particle swarm optimization combined with bacterial foraging algorithm (PSO-BFO) to solve multi-objective optimization problems, then the optimal schedule strategy of ADN is gained through evaluating the Pareto solutions with entropy weight decision-making method. To avoid the search falling into local optimal solution, the two-value crossover operator is introduced to exchange the information among subpopulations and update the position of related particles. Meanwhile, the adaptive adjusting inertia constant strategy is used to improve the algorithm convergence speed. Finally, the case study results demonstrate the rationality of the proposed optimal schedule model and the validity of its solution algorithm for ADN.

ANALISIS PENGARUH INTERKONEKSI DISTRIBUTED GENERATION (PLTSA SUWUNG) TERHADAP RUGI-RUGI DAYA DAN KEANDALAN PADA PENYULANG SERANGAN

The distributed generation technology or in this case abbreviated DG is a kind of power plants with small scale which prioritizes the utilization of renewable energy resources such as wind, water, solar, geothermal, ocean waves (Wave Energy), ocean currents (Ocean Current Energy), biomass, and biogass to produce the electrical energy with range of power generation between 1 kW-10 MW. One of the DG in Bali and still in operation is the garbage power plant which located in Suwung, South Denpasar. An analysis has been done using load flow analysis and reliability assessment to determine the effect of DG interconnection against the power losses and the level of reliability on the Serangan feeder. Based on the research that has been done, DG intercon-nection on the Serangan feeder decrease the power losses and increase the reliability and it can visible from the acquisition of SAIFI and SAIDI index which decreased. The best location of DG interconnection to get low of the power losses and the high level of reliability is at 97% from the total length of the feeder. At that location the power losses is decrease as big as 4.5 kW or 11.25% of the total power lossess without the DG interconnection and decrease of the SAIFI and SAIDI index respectively to 0.1 failure/customers/year and 1.4150 hour/ customer/year

Sensitivity analysis of smart grids reliability due to indirect cyber-power interdependencies under various DG technologies, DG penetrations, and operation times

The cyber failures such as failures in protection and monitoring systems will not stop the operation or change the behavior of the power system instantly but will adversely affect the performance of the power system against the potential failure. Such indirect cyber-power interdependencies (ICPIs) may either intensify the probability of future failures or postpone the repercussion to the present failure of the power elements. The much less effort has been devoted in literature to investigate the ICPIs impacts, particularly in stochastic simulating space. In this paper, a novel stochastic-based reliability evaluation method which considers the ICPIs impacts under various uncertain parameters is proposed. The consideration of uncertainty regarding the renewable distributed generation (DG) units, consumption patterns, power and cyber elements, and ICPIs is one of the most important contributions of the proposed method. Further, a novel stochastic-based state upgrading is introduced to concern the ICPIs of protection and monitoring systems. By using the proposed state upgrading methodology, it is possible to evaluate the reliability of smart grid based on ICPIs by using conventional reliability evaluation methods.The proposed risk assessment methodology is applied to an actual distribution grid. The several sensitivity studies are performed to gain insight into how the penetration level of DG units under various DG technology scenarios can affect the ICPIs impacts on the risk level of smart grid. The test results show that regardless of the DG technology scenario, the ICPIs impacts of protection system vulnerabilities gradually increase while the DG penetration increases. On the contrary, the ICPIs impacts which are corresponding to the monitoring system monotonically decrease as a function of DG penetrations, and it saturates when the penetration exceeds a certain level. The test result infers that the ICPIs impacts on the risk level of smart grid are more dramatically emphasized when the extended study duration is analyzed. In fact, the ICPIs impacts increase as a function of system age, because the failure in monitoring system may accelerate the aging failures, and particularly when the system is subject to wear out period, the ICPIs impacts on the system reliability should be more concerned.

Development of an open access tool for design, simulated dispatch, and economic assessment of distributed generation technologies

The design and deployment of DG systems requires an integrated assessment of the building and generator dynamics including the time-variant energy costs and emission factors. Static design optimizations are unable to consider the physical generator operating constraints, seasonal variability and non-coincidence in electric, heating, and cooling demands. This paper introduces the Distributed Generation Build-out Economic Assessment Tool (DG-BEAT) which combines building, utilities, and emissions databases with a library of simplified generator and building models in a user-friendly interface. Five control strategies are presented for the dynamic dispatch of distributed generation technologies at commercial buildings. The control approaches stem from the physical limitations of different generator types. Methods are also outlined for the dispatch of complementary technologies (e.g. energy storage) and accommodation of on-site renewables (e.g. solar PV) which could further improve the economic or environmental benefits of distributed generation. This paper details the methodology of sizing and dispatching distributed generation components, outlines eight databases that are employed to capture regional variations in pricing and building dynamics, and discusses the myriad of customizations available to provide a tailored analysis for a single building or national impact studies.

A control approach for the operation of DG units under variations of interfacing impedance in grid-connected mode

Abstract Voltage source converter (VSC) can be considered as the heart of interfacing system for the integration of Distributed Generation (DG) sources into the power grid. Several control methods have been proposed for integration of DG sources into the power grid, and injection of high quality power. However, the converter-based DG interface is subjected to the unexpected uncertainties, which highly influence performance of control loop of DG unit and operation of interfaced converter. The interfacing impedance seen by interfaced VSC may considerably vary in power grid, and the stability of interfaced converter is highly sensitive to the impacts of this impedance changes; then, DG unit cannot inject appropriate currents. To deal with the instability problem, a control method based on fractional order active sliding mode is proposed in this paper, which is less sensitive to variations of interfacing impedance. A fractional sliding surface, which demonstrates the desired dynamics of system is developed and then, the controller is designed in two phases as sliding and reaching phases to keep the control loop stable. Stability issues of the control method are discussed in details and the conditions in which the proposed model works in a stable operating mode is defined. The proposed control method takes a role to provide high quality power injection and ensures precise references tracking and fast response despite such uncertainties. Theoretical analyses and simulation results are established to confirm the performance and feasibility of the proposed control method in DG technology.

Bidding strategies for virtual power plants considering CHPs and intermittent renewables

Energy efficiency and renewable-energy sources (RES) are fundamental parts of the European energy policy. For this reason, efficient distributed generation technologies such as combined heat and power coupled to district heating (CHP–DH) and RES based electricity are largely promoted. Additionally, the flexibility that CHP–DH offers to the power system is seen as an option to balance the intermittent output of RES-based generation. This could be done by aggregating RES based electricity generation and CHP DH in a virtual power plant (VPP).In this framework, the present work presents a methodology to evaluate the optimal bidding strategy of a VPP composed of a CHP–DH and RES based generators. The objective is to investigate the optimal bidding strategy for a VPP that uses CHP DH to compensate for the uncertainties regarding RES-based electricity generation and market prices. The VPP operator nominates its energy to the day ahead market the day before the actual delivery (D-1). In real time, any deviation from the day-ahead schedule is settled in the imbalance market. The uncertainties are modeled using a two stage stochastic programming approach.Three different bidding strategies are studied: ‘static’, ‘flexible DA’ and ‘flexible RT’. The major difference between the studied strategies lies in the dispatch decisions. The ‘static’ strategy does not adjust the scheduled output of the CHP. Whereas, the ‘flexible DA’ and ‘flexible RT’ strategies differ from each other in terms of the information available at the moment of performing the reschedule (second stage decision). The ‘flexible DA’ reschedules the CHP output for the whole day assuming full knowledge of the RES scenario, but under uncertainty regarding the imbalance price. The ‘flexible RT’ strategy allows the VPP to adjust its position at each time step depending on the RES generation and imbalance price scenarios.The results show that in comparison with the ‘static’ strategy, the ‘flexible DA’ operation results in a profit increase during summer (5900€/week), the intermediate season (2800€/week) and winter (2700€/week). This increase is moderate when compared against the total fuel cost in these seasons. Better results are obtained when the ‘flexible RT’ strategy is applied. Using this strategy larger profits are achieved for all seasons. For instance, during winter the difference between the ‘flexible RT’ operation and the ‘static’ case amounts to 22,600€/week, approximately 5% of the fuel cost.

Active Torque Damping for an ICE-Based Domestic CHP System With an SPM Machine Drive

A domestic combined heat and power (CHP) system is an effective residential distributed energy generation technology. Nano-CHP is a growing technology that simultaneously provides heat and electricity to households. An electric machine (EM) connected to an internal combustion engine (ICE) is used to produce the electricity, whereas an ICE delivers heat. Any conventional ICE exhibits pulsating torque that causes vibration and noise in the system and reduces the powertrain lifetime. An additional task for the electric drive of smoothing the speed oscillations by controlling the EM as an active torque damping system, which applies an inverse torque sequence to the crankshaft, is here proposed. In this paper, different torque damping techniques have been explored with the aim of finding out the best solution; the investigated techniques have been taken from research in the field of hybrid electric vehicles. In order to model the torque engine oscillation phenomenon, an effective but simple ICE model has been developed. It allowed the comparison of the different techniques by simulations; some of them have been later validated by experimental tests carried out on a dedicated laboratory test bench composed of a real ICE connected to an EM.

Socio-Technical Lock-in and the Alignment Framework: The Case of Distributed Generation Technologies

Whereas a centralized energy supply system is still dominant today, the energy sector is currently witnessing the development of small-scale and more geographically dispersed generation units, so-called distributed generation technologies. The alignment framework proposes a very useful approach to look at this evolution. Yet, we argue in this paper that this framework does not fully take into account the inertia associated with past technological and institutional choices that may hinder future changes. Relying on the concept of socio-technical lock-in, we illustrate this point with the case of the diffusion of distributed generation technologies. Based on this analysis, we propose an adaptation of the alignment framework in order to integrate these elements.

Reliability evaluation of distribution transformers with high penetration of distributed generation

Abstract In this paper, a novel methodology is presented to evaluate the micro-grids reliability concerning the dynamic thermal aging failure of transformers. The widespread presence of distributed generation (DG) units reduces the loading passing through the distribution transformers and consequently improves the dynamic thermal failures. The system reliability is investigated for various penetrations of different scenarios from the view of DG technologies. The introduced method is applied to a realistic distribution system comprising different distribution transformers in Iran. The sensitivity analysis corresponding to adequacy indices such as expected energy not-supplied (EENS) based on DG penetrations is performed. By the use of the novel methodology proposed, it is possible to recognize how different DG technologies and penetrations can impact on the system reliability. The results demonstrate that the diesel generators and hybrid systems including diesel generators, photovoltaic units, and wind turbines are the most promising DG technologies to improve the transformer failures and the reliability of micro-grids compared with renewable DG units.

An energy integrated, multi-microgrid, MILP (mixed-integer linear programming) approach for residential distributed energy system planning – A South Australian case-study

The integration of distributed generation units and microgrids in the current grid infrastructure requires an efficient and cost effective local energy system design. A mixed-integer linear programming model is presented to identify such optimal design. The electricity as well as the space heating and cooling demands of a small residential neighbourhood are satisfied through the consideration and combined use of distributed generation technologies, thermal units and energy storage with an optional interconnection with the central grid. Moreover, energy integration is allowed in the form of both optimised pipeline networks and microgrid operation. The objective is to minimise the total annualised cost of the system to meet its yearly energy demand. The model integrates the operational characteristics and constraints of the different technologies for several scenarios in a South Australian setting and is implemented in GAMS. The impact of energy integration is analysed, leading to the identification of key components for residential energy systems. Additionally, a multi-microgrid concept is introduced to allow for local clustering of households within neighbourhoods. The robustness of the model is shown through sensitivity analysis, up-scaling and an effort to address the variability of solar irradiation.

An Evaluation of Customer-Optimized Distributed Generation in New England Utility and Real-Time Markets

The full worth of distributed generation systems must be measured not only by the impact on the customer, but also by DG's impact on the grid and surrounding market participants. A case study comparing customer incentives created by utility rates with the real-time prices market in New England provides a new model to quantify the value of customer peak shaving with distributed generation technologies.

Investigation of common-mode voltage and ground leakage current of grid-connected transformerless PV inverter topology

The problems of increasing electricity demand by the unabated population and economy growth can be solved by employing sustainable distributed generation technologies. Convectional primary energy sources such as coal, liquid hydrocarbons’ and natural gasses create environmental degradation and energy security problems. Even though the cost of solar energy is zero, the same cannot be said of a solar energy system. The system cost especially the initial capital investment has been hindering the rapid deployment of solar energy systems. One way of reducing the system cost of a solar energy system is to look into the constituent components and see where cost can be reduced without compromising the system efficiency and human safety. Eliminating the isolation transformer reduces the cost and increases the system overall efficiency. However, the galvanic connection between the PV array and the utility grid creates a safety problem for people and system equipment. We present a simplified model for the investigation of the common mode voltage and ground leakage current that can lead to electromagnetic interference. The leakage current level is used for the determination of the suitability of the investigated PV inverter topology for grid connection without isolation transformer.

A Multifunction Control Strategy for the Stable Operation of DG Units in Smart Grids

This paper describes the development of a multifunction control strategy for the stable operation of distributed generation (DG) units during the integration with the power grid. The proposed control model is based on direct Lyapunov control (DLC) theory and provides a stable region for the proper operation of DG units during the integration with the power grid. The compensation of instantaneous variations in the reference current components in ac-side and dc-voltage variations in the dc-side of the interfacing system are adequately considered in this control plan, which is the main contribution and novelty of this paper in comparison with previous control strategies. Utilization of the DLC technique in DG technology can confirm the continuous injection of maximum active power in fundamental frequency from the DG source to the power grid, compensating all the reactive power and harmonic current components of grid-connected loads through the integration of DG link into the grid. Application of this concept in smart grids system can guarantee to reduce the stress on the utility grid during the peak of energy demand. Simulation and experimental test results are presented to demonstrate the proficiency and performance of the proposed DLC technique in DG technology.

A Review of Distributed Generation Resource Types and Their Mathematical Models for Power Flow Analysis

The emergence of Distributed Generation (DG) in distribution network has changed the configuration of this century’s power system in terms of power flow. The reason for this is that DG affects the power flow and voltage conditions in the distribution system; contrary to its traditional unidirectional nature in radial configuration. It is worth mentioning that the change in the direction of power flow is not limited to the distribution network, but can as well extend to the transmission or sub-transmission systems, especially when DG penetration is high. This paper gives an overview of DG types and modeling techniques of the DG for power flow analysis during planning and operations. Various DG technologies are highlighted, different models of DGs are presented and some key challenges ahead with current drive towards smart grid networks is also discussed.

Optimal Location, Sizing, and Appropriate Technology Selection of Distributed Generators for Minimizing Power Loss Using Genetic Algorithm

Genetic algorithm (GA) is utilized to select most suitable Distributed Generator (DG) technology for optimal operation of power system as well as determine the optimal location and size of the DG to minimize power loss on the network. Three classes of DG technologies, synchronous generators, asynchronous generators, and induction generators, are considered and included as part of the variables for the optimization problem. IEEE 14-bus network is used to test the applicability of the algorithm. The result reveals that the developed algorithm is able to successfully select the most suitable DG technology and optimally size and place the DGs to minimize power loss in the network. Furthermore, optimum multiple placement of DG is considered to see the possible impact on power loss in the network. The result reveals that multiple placements can further reduce the power loss in the network.