Operation Of Distributed Generation Units Research Articles

Combined Firm and Renewable Distributed Generation and Reactive Power Planning

The benefits of integrating Distributed Generation (DG) into the distribution networks depend on the characteristics of different types of DG units, loads and Reactive Power Sources (RPS). These benefits can be optimized if the firm DG units such as biomass energy and renewable DG units such as photovoltaic (PV) and wind system are optimally sized, located and coordinated with reactive power sources. In this paper, by assuming that the Distribution System Operator (DSO) has got the ownership and operation of DG units and RPS, a new planning strategy is proposed for determining the optimal placement and rating of DG units and RPS. This strategy overcomes the challenge of intermittency of renewable production in order that this planning will assist the system operators in defining the better integration strategies of firm and intermittent energy systems and reactive power sources in distribution networks. The proposed planning is based on single objective optimization so that it optimizes one of the following objective functions every time: the system energy losses, voltage stability margin, self-adequacy of microgrids defined on the distribution system and exchange of active and reactive powers between the distribution system and upstream network. The proposed technique accounts for the uncertainties associated with solar irradiance, wind speed and demand through a probabilistic optimization. The formulation of each planning problem is presented and applied to the 69-bus distribution system. The results of different planning strategies are compared and analyzed. Furthermore, the impact of the planning with each objective function on other indices is evaluated.

Multi‐objective optimisation method for coordinating battery storage systems, photovoltaic inverters and tap changers

The many well-established advantages of distributed generation (DG) make their usage in active distribution networks prevalent. However, uncontrolled operation of DG units can negatively interfere with the performance of other equipment, such as tap-changers, in addition to resulting in sub-optimal usage of their potential. Thus, adequate scheduling/control of DG units is critical for operators of the distribution system to avoid those adverse effects. A linearised model of a multi-objective method for coordinating the operation of photovoltaics, battery storage systems, and tap-changers is proposed. Three objective functions are defined for simultaneously enhancing voltage profile, minimising power losses, and reducing peak load power. The formulated multi-objective problem is solved by means of the epsilon-constraint technique. A novel decision-making methodology is offered to find the Pareto optimality and select the preferred solution. To assess to proposed model's performance, it is tested using 33-bus IEEE test system. Consequently, tap-changers suffer lessened stress, the batteries state-of-charge is kept within adequate limits, and the DG units operation is at higher efficiency. The obtained results verify the effectiveness of this approach.

A Quasi-Oppositional-Chaotic Symbiotic Organisms Search algorithm for optimal allocation of DG in radial distribution networks

This paper aims to apply an improved meta-heuristic method to optimize the allocation of distributed generation (DG) units in radial distribution networks (RDNs). The proposed method, namely the Quasi-Oppositional Chaotic Symbiotic Organisms Search (QOCSOS) algorithm, is the improved version of the original SOS algorithm. QOCSOS incorporates the Quasi-Opposition-Based Learning (QOBL) and Chaotic Local Search (CLS) strategies into SOS to improve the global search capacity. In this study, the objective of the optimal DG allocation (OGDA) problem is to optimally reduce the real power loss, improve the voltage profile, and increase the voltage stability in RDNs. The proposed QOCSOS algorithm was applied to find the optimal locations and sizes of DG units with different DG power factors (unity and non-unity) in the RDNs including 33, 69, and 118-bus. It was found that the operation of DG units with optimal power factor significantly improved the performance of RDNs in terms of voltage deviation minimization, and voltage stability maximization, especially for power loss reduction. After the DG integration, for the case of DG units operating with unity power factor, the power loss reduction was reduced by 65.50%, 69.14%, and 60.23% for the 33, 69, and 118-bus RDNs, respectively. In addition, it should be emphasized that for the cases of DG units operating with optimal power factor, the power loss reduction was reduced up to 94.44%, 98.10%, and 90.28% for these RDNs, respectively. The obtained results from QOCSOS were evaluated by comparing to those from SOS and other optimization methods in the literature. The results showed that the proposed QOCSOS method performed greater than SOS, and offered better quality solutions than many other compared methods, suggesting the feasibility of QOCSOS in solving the ODGA problem, especially for a complex and large-scale system.

Loss minimization in distribution systems based on LMP calculation using honey bee mating optimization and point estimate method

Locational marginal price (LMP) calculation at distributed generation (DG) busses is an effective way for optimal operation of DG units. The aim of this study is presenting a new LMP formulation which includes distribution loss minimization. A Meta-heuristic modified honey bee mating optimization (MHBMO) algorithm is used to obtain optimal values of LMP and power factor of DG units so that the loss of network is minimized, and the benefit of DG units is maximized. Furthermore, a stochastic power flow based on the point estimate method (PEM) is located in MHBMO algorithm to capture uncertainty in the market price and load demand. The proposed policy is applied to a realistic distribution system for the various market prices at substation buses. The results of this study prove the accuracy and efficiency of the new method over the previous methods in terms of the DG units' benefit, loss minimization, and state estimation of the system.

Optimal Allocation and Operating Point of DG Units in Radial Distribution Network Considering Load Pattern

Distributed generation (DG) is a new approach for solving some problems of older power networks. Due to the increasing power demand in recent power systems, the importance of power loss reduction and maintaining system voltages within an acceptable range has given rise to the wide use of DG units in power systems. On the other hand, unplanned and non-optimal application such as installation and operation of DG units might cause other technical problems. In addition, it is important to consider the load pattern in the network, and the best decision for DG unit's operation must be chosen accordingly. In this paper, a method is introduced in order to make the optimal placement and find an optimal operating point for the DG units, which means the power output of DG units, considering the load pattern of the network. This load pattern has an average load of 24 hr a day, four seasons a year. In the proposed method, optimization has two goals: first, is optimizing the DG unit's placement based on improvement of the voltage profile, and the second is operating DG units with optimum power factor, minimizing power loss, and improving voltage profile, with regard to the load pattern. In order to solve this problem, the gravitational search algorithm and genetic algorithm are used. The proposed method is applied on the IEEE 33-bus test system, and the result shows the effectiveness of the proposed method. In order to solve the optimization problem, MATLAB software is used.

PWM Harmonic Signature-Based Islanding Detection for a Single-Phase Inverter With PWM Frequency Hopping

Distributed generation (DG) has gained popularity in recent years due to the increasing requirement for renewable power sources. A problem that exists with DG systems is the islanding of DG units that creates safety issues for personnel as well as the potential for damage to utility infrastructure. Therefore, islanding detection methods are utilized to mitigate the risk of islanded operation of DG units. A new passive method of islanding detection based on the signature of the pulse width modulation voltage harmonics is proposed. The viability of the algorithm is investigated with the use of an analytical and time-domain model of the inverter and further validated with experimental results. Furthermore, an extension of the detection scheme is proposed for use in multi-inverter scenarios composed of adaptive frequency hopping to eliminate unwanted tripping.

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.

A Fuzzy-Multiagent Service Restoration Scheme for Distribution System With Distributed Generation

This paper proposes a new multiagent control system (MACS) for service restoration in distribution systems with integrated distributed generation (DG) units. First, the MACS detects and locates faults, then decides the optimal reconfiguration of the network for restoring de-energized loads, and finally regulates the nodes voltages. Unintentional islanding operation of DG units is avoided and different postfault response modes of DG unit are addressed in the MACS design. The MACS has a hybrid centralizeddecentralized structure where agents are arranged in two layers with different responsibilities and communication capabilities. Agents at load buses in the first layer can only communicate directly with its next neighbor load agents on the same feeder and to its feeder agent, whereas the higher level agents in the second layer can communicate directly with each other. This MACS structure reduces the possibilities of control system failures for a moderate communication network infrastructure. Full dynamic simulation model for evaluating the MACS is implemented.

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.

Investigating the Controller Interactions of Distribution Systems with Distributed Generation

This paper investigates the interactions among multiple controllers in distribution systems in the presence of distributed generation (DG). Two doubly fed induction generator (DFIG) type wind turbines are connected to a distribution system to investigate their influence in the system. Simulation results indicate that the parallel operation of DG units and their controllers in the same network in a relatively smaller geographical area have negative interactions giving rise to control mode oscillations. It is also investigated that the coupling of the load dynamics with DG-controllers reduces the damping of the system.

Distributed generation planning based on the distribution company's and the DG owner's profit maximization

Summary In recent years, Distributed Generation (DG) has been utilized in electric power networks increasingly. DG units can affect the system operational conditions in different ways such as voltage profile improvement, amending voltage stability, reliability enhancement, securing power market, etc. if they are managed properly. Otherwise, they may have undesirable impacts on technical issues of power grids. A lot of studies have been done on various aspects of control and operation of DG units to find the optimal placement, sizing and also the proper technology of them. This paper proposes a novel comprehensive economic method for planning DG units which considers both the Distribution Company's (DisCo) and the DG Owner's (DGO) profits simultaneously. Multi-objective particle swarm optimization technique is used to simulate many case studies on the IEEE 33-bus distribution test system and finally find the best solution for the placement, size and contract price of the generated power of DGs. The proposed methodology not only considers operational aspects such as power loss reduction, voltage profile and stability improvement and reliability enhancement, but also leads to an accurate analysis which satisfies both the DisCo's and the DGO's economic viewpoints. Finally, an encouragement to invest more on DG technologies is proposed based on the gained results. Copyright © 2013 John Wiley & Sons, Ltd.

Possibilistic Evaluation of Distributed Generations Impacts on Distribution Networks

In deregulated power systems, the distribution network operator (DNO) is not responsible for investment in distributed generation (DG) units, and they are just concerned about the best architecture ensuring a good service quality to their customers. The investment and operating decisions related to DG units are then taken by entities other than DNO which are exposed to uncertainty. The DNO should be able to evaluate the technical effects of these uncertain decisions. This paper proposes a fuzzy evaluation tool for analyzing the effect of investment and operation of DG units on active losses and the ability of distribution network in load supply at presence of uncertainties. The considered uncertainties are related to load values, installed capacity, and operating schedule of DG units. The proposed model is applied on a test system and also a real French urban network in order to demonstrate its functionality in evaluating the distribution expansion options.