Effect of placement of droop based generators in distribution network on small signal stability margin and network loss

For a utility-connected system, issues related to small signal stability with Distributed Generators (DGs) are insignificant due to the presence of a very strong grid. Optimally placed sources in utility connected microgrid system may not be optimal/stable in islanded condition. Among others issues, small signal stability margin is on the fore. The present research studied the effect of location of droop-controlled DGs on small signal stability margin and network loss on a modified IEEE 13 bus system, an IEEE 33-bus distribution system and a practical 22-bus radial distribution network. A complete dynamic model of an islanded microgrid was developed. From stability analysis, the study reports that both location of DGs and choice of droop coefficient have a significant effect on small signal stability, transient response of the system and network losses. The trade-off associated with the network loss and stability margin is further investigated by identifying the Pareto fronts for modified IEEE 13 bus, IEEE 33 and practical 22-bus radial distribution network with application of Reference point based Non-dominated Sorting Genetic Algorithm (R-NSGA). Results were validated by time domain simulations using MATLAB. (C) 2016 Elsevier Ltd. All rights reserved

Responsive End-User-Based Demand Side Management in Multimicrogrid Environment

This paper presents an agent-based demand side management framework (ADSMF) as an intelligent solution to shorten the supply-demand gap in microgrids by forming virtual market environments that allow neighboring microgrids to trade with each other. The framework does two essential tasks: 1) routing power from surplus locations to deficit locations by effectively coordinating with distributed energy resources (DERs); and 2) enabling customers' participation in electricity enterprise through demand response (DR). The low preference loads of the end-users are grouped into two categories, viz. shiftable and curtailable loads, according to the level of flexibility involved in their operation. Also, three smart DR options are identified to allow the customers to choose as per their requirement. The customer's participation is encouraged through a priority-based incentive mechanism. The proposed incentive mechanism uses frequency of participation of customers in DR and their contribution to benefit gained by the overall system to cater the incentives. The feasibility of the framework is demonstrated by applying on a case study network with two grid-tied microgrids simulated using Java Agent DEvelopment framework (JADE). The extensive simulation studies on the test network have proved the applicability and effectiveness of the proposed agent-based framework in mitigating the supply-demand gap in multimicrogrid environment

Demand Response in Smart Distribution System With Multiple Microgrids

In this paper, an agent based intelligent energy management system is proposed to facilitate power trading among microgrids and allow customers to participate in demand response. The proposed intelligence uses demand response, and diversity in electricity consumption patterns of the customers and availability of power from distributed generators as the vital means in managing power in the system. A new priority index is proposed for customers participating in the market based on frequency and size of load participating in demand response. In order to validate the proposed method, a case study with two interconnected microgrids is simulated. Based on extensive simulation results of the system developed using Java Agent DEvelopment framework (JADE), it has been found that multi-agent based demand response is successful in reducing the system peak in addition to cost benefit for the customers with high priority index

Diffusion of grid-connected pv in india: an analysis of variations in capacity factor

This paper analyses variations in capacity factor on diffusion of solar PV in the context of National Solar Mission announced by the Government of India. The capacity factor is evaluated by considering meteorological conditions and choice of technology. A mathematical model is developed to determine the capacity factor considering cell efficiency, solar irradiance and local temperature. The output of the model is used as input for determining cost of generated electricity. Simulation is performed for a 1MWp grid connected PV plant by considering daily average hourly solar irradiance and temperature variation. With a view to achieve a vision of PV diffusion in India, the present work includes system data for representative places located in different latitudes. Feed-in-Tariff (FiT) determined by various states for grid connected PV is compared with cost of electricity generated obtained from simulation. The cost of electricity generated from solar PV is found to vary between 26 phi/kWh and 33 phi/kWh based on the capacity factor. This comparison helps to bridge the gap between FiT and actual cost based on capacity factor by way of additional incentives for a fixed period. This analysis would be useful for utilities/states to assess the diffusion of PV power into the grid and determine tariff based on meteorological parameters. The reduction in CO(2) emission is computed for various locations considering the actual generation mix. Analysis is also carried out to determine the growth of cells and module manufacturing capacity in India for 2022. Simulation result indicate that the present high growth rate (> 30%) for both cells and modules is sufficient to achieve the target set by the National Solar Mission. This paper also discusses briefly about National Solar Mission and status of grid connected PV power in India

Multiagent-Based Distributed-Energy-Resource Management for Intelligent Microgrids

Microgrid is a combination of distributed generators, storage systems, and controllable loads connected to low-voltage network that can operate either in grid-connected or in island mode. High penetration of power at distribution level creates such multiple microgrids. This paper proposes a two-level architecture for distributed-energy-resource management for multiple microgrids using multiagent systems. In order to match the buyers and sellers in the energy market, symmetrical assignment problem based on naive auction algorithm is used. The developed mechanism allows the pool members such as generation agents, load agents, auction agents, grid agents, and storage agents to participate in market. Three different scenarios are identified based on the supply-demand mismatch among the participating microgrids. At the end of this paper, two case studies are presented with two and four interconnected microgrids participating in the market. Simulation results clearly indicate that the agent-based management is effective in resource management among multiple microgrids economically and profitably

Real-Time Testing Approaches for Microgrids

Microgrids (MGs) are seen today as the solution to the challenge of meeting the ever-increasing demand of energy which is clean. A variety of challenges need to be overcome for these MGs to be successful varying from stability, power quality to protection, and management. Since the various control strategies are actively being researched and emerging challenges still being addressed, there has been a lot of interest related to the aspect of testing. The ever-increasing complexity of control mechanisms invokes the need for safer, faster yet reliable testing methods, which do not compromise on the degree of detail and at the same time are economical and require the minimum testing time. Off-line simulation, real-time (RT) simulation, hardware in the loop simulation, RT emulation, hardware test beds, pilot plants, and other integrated approaches are the major methods for testing in MGs. This paper gives an overview of the testing techniques and discusses the trends in the various technologies employed for testing MGs. First, the various methods are briefly discussed and a comparison is provided. Next, the various research efforts carried out on the aspect of MG testing are categorized and presented one-by-one. Furthermore, new methodologies and emerging approaches for the testing have also been highlighted, and the challenges and future research avenues have been presented

Improvement of Transient Response in Microgrids Using Virtual Inertia

Generation is shifting from a centralized power generating facility having large synchronous generators to distributed generation involving sources of smaller capacity. Most of these sources require inverters on the front end while being connected to the grid. Lower available kinetic energy, coupled with less short-circuit current ratio compared to large synchronous generators, compromises the transient stability of the microgrid when isolated from the main grid. Sources in the microgrid use droop control to share power according to their capacity without any form of communication. This paper proposes a novel controller for inverters to improve the frequency response of microgrid under disturbances involving large frequency deviations. It also discusses design of various parameters defined for the proposed control. The microgrid, which has two inverters and two synchronous generators, is simulated using Simulink/MATLAB software to test the proposed control strategy

Inertia Design Methods for Islanded Microgrids Having Static and Rotating Energy Sources

Dynamic frequency regulation and effect of penetration of static and inertial sources on system stability are important issues for islanded microgrid power quality and reliability. This paper presents a novel strategy of utilizing an inverter-based source as a voltage source inverter or virtual synchronous generator (VSG). Electromechanical and power modes are critical for small signal stability of an isolated microgrid having static and inertial sources. Interaction of these modes is analyzed through eigenvalue analysis of microgrid model and differential equations describing respective modes. Inertia is important for providing fault current, determining steady state and transient stability, and better system frequency profile. A novel technique is proposed to include inertia virtually to the inverter-based sources by adding swing equation. Furthermore, inverter-based sources with traditional and modified droop controls and VSGs are compared with respect to inertia, energy, and stability. The proposed control and stability comparison are verified through experimental microgrid setup having three inverter-based sources, which can be alternately operated as VSGs

Hopf bifurcation analysis in droop controlled islanded microgrids

The stability analysis of the microgrid has been carried out by several researchers. However, these studies have been limited to small signal (or linear) stability analysis. Such systems usually lose their stability via Hopf bifurcations. These bifurcations are either subcritical or supercritical. In case of subcritical bifurcations the stable region defined by small signal stability analysis may have unstable limit cycles. In other words, the region identified as stable for (infinitesimally) small signal may be unstable for slightly larger (finite) signal. Therefore, small signal analysis is not sufficient and it is imperative to identify type of Hopf bifurcation for a given system. In order to carryout stability analysis of the system, a generalised model is developed. This model is used for studying stability characteristics of a two bus system, modified IEEE 13 bus system and IEEE 33 bus system. Five different droop techniques from literature are compared with each other for relative stability. A non-dimensional index is proposed, which is used for comparing stability margin for each of these techniques using small signal stability analysis. (C) 2017 Elsevier Ltd. All rights reserved