Hybrid micro-grids exploiting renewables sources, battery energy storages and bi-directional converters

publishedVersio

Optimization Techniques for the Developing Distribution System

The most rapidly changing part of today’s power grid is the distribution system. Many new technologies have emerged that revolutionize the way utilities provide, and now sometimes receive, power to and from their customers. To an extent, the push for de-regulation of utilities has also led to an increased focus on reliability and efficiency. These changes make design and operation of power systems more complex causing utilities to question if they are operating optimally. Operations Research (OR) is an area of mathematics where quantitative analysis is used to provide a basis for complex decision making. The changing landscape in electric distribution makes it a prime candidate for the application of OR techniques. This research seeks to develop optimization methods that can be applied to any distribution feeder or group of feeders that allows for optimal decisions to be made in a reasonable time frame. Two specific applications identified in this thesis are optimal reconfiguration during outage situations and optimal location of Battery Energy Storage Systems (BESS). Response to outages has traditionally relied on human-in-the-loop approaches where a dispatcher or a crew working the field decides what switching operations are needed to isolate affected parts of the system and restore power to healthy ones. This approach is time consuming and under-utilizes the benefits provided by widely-adopted, remotely-controlled switching technologies. Chapters Two and Three of this thesis develop a partitioning method for determining the switching operations required to optimize the amount of load that is restored during an event. Most people would agree that renewable forms of Distributed Generation (DG) provide great benefits to the power industry, especially through reduced impact on the environment. The variable nature of renewables, however, can cause many issues for operation and control of a utilities’ system, especially for distribution interconnections. Storage technologies are thought to be the primary solution to these issues with much research focused on sizing and control of BESSs. Equally important for integration, but often overlooked, is the location at which the device is connected. Chapter Four explores this idea by drawing conclusions about optimal BESS location based on well-studied ideas of optimal capacitor location

Microgrid cost optimization: a case study on Abu Dhabi

This paper presents a microgrid cost optimization study specifically focused on the United Arab Emirates (UAE) based on the Genetic and Ant-Bee Colony algorithms. The main objective of the paper is to identify size and amount of power supply sources in Microgrids that result in minimum cost. Specific parameters pertaining to the UAE were employed within the new objective function and constraints. Two different scenarios were tested, and their results have been discussed. During this study, it was evident that solar-PV systems were the second most cost-effective way to reduce cost of microgrids preceded by micro-turbines

Cooperation and Storage Tradeoffs in Power-Grids with Renewable Energy Resources

One of the most important challenges in smart grid systems is the integration of renewable energy resources into its design. In this work, two different techniques to mitigate the time varying and intermittent nature of renewable energy generation are considered. The first one is the use of storage, which smooths out the fluctuations in the renewable energy generation across time. The second technique is the concept of distributed generation combined with cooperation by exchanging energy among the distributed sources. This technique averages out the variation in energy production across space. This paper analyzes the trade-off between these two techniques. The problem is formulated as a stochastic optimization problem with the objective of minimizing the time average cost of energy exchange within the grid. First, an analytical model of the optimal cost is provided by investigating the steady state of the system for some specific scenarios. Then, an algorithm to solve the cost minimization problem using the technique of Lyapunov optimization is developed and results for the performance of the algorithm are provided. These results show that in the presence of limited storage devices, the grid can benefit greatly from cooperation, whereas in the presence of large storage capacity, cooperation does not yield much benefit. Further, it is observed that most of the gains from cooperation can be obtained by exchanging energy only among a few energy harvesting sources