Microgrid Enabling Towards the Implementation of Smart Grids

Smart grids have emerged as dominant platforms for effectively accommodating high penetration of renewable-based distributed generation (DG) and electric vehicles (EVs). These smart paradigms play a pivotal role in the advancement of distribution systems and pave the way for active distribution networks (ADNs). However, the large number of smart meters deployed in the distribution system (e.g., 200 million smart meters will be installed in Europe by 2020) represents one of the main challenges facing the management and control of distribution networks and thus the enabling of smart grids. In addition to the data tsunami flooding central controllers, the concerns about privacy and system vulnerability are fast becoming a key restraint for the implementation of the smart grids. These concerns are prompting utilities to be more reluctant to adopt new techniques, leaving the distribution system mired in relatively old-fashioned routines. Microgrids provide an ideal paradigm to form smart grids, thanks to their limited size and ability to ‘island’ when supplying most of their loads during emergencies, which improves system reliability. However, preserving load-generation balance is comprehensively challenging, given that microgrids are dominated by renewable-based DGs, which are characterized by their probabilistic nature and intermittent power. Although microgrids are now well-established and have been extensively studied, there is still some debate over having microgrids that are solely ac or solely dc, with the consensus tending toward hybrid ac-dc microgrids. Furthermore, while some research has addressed using solely ac microgrids, the planning of hybrid ac-dc microgrids has not yet been investigated, despite the many benefits these types of microgrids offer. Additionally, developing steady-state analysis tools capable of handling grid-connected mode and islanded mode for the operation of ac microgrids and hybrid ac-dc microgrids still has uncertainties about their computational burden, complexity, and convergence. The high R/X ratio characterized distribution systems result in ill-condition that hinders the convergence of conventional Newton Raphson (NR) techniques. Moreover, calculating the inversion of the Jacobian matrix that is formed from the calculation of derivatives adds to the complexity of these techniques. Therefore, developing a simple, accurate, and fast steady-state analysis tool is crucial for enabling microgrids and hence smart grids. Driven by the aforementioned challenges, the broad goal of this thesis is to enable microgrids as building clusters to smooth and accelerate the realization of smart grids. Achieving this objective involves a number of stages, as follows: 1) The development of probabilistic models for loads and renewable DG-based output power. These models are then integrated with the load flow analysis techniques to form a probabilistic power flow (PPF) tool. 2) The proposal of a novel operational v philosophy that divides existing bulky grids into manageable clusters of self-adequate microgrids that adapt their boundaries to keep load-generation balance at different operating scenarios. 3) The proposal of planning a framework for the newly constructed grids as hybrid ac-dc microgrids with minimum levelized investment costs and consideration of the probabilistic nature of load and renewable generation. 4) The development of a branch-based power flow algorithm for steady-state analysis of ac microgrids and hybrid ac-dc microgrids

Microgrid Enabling Towards the Implementation of Active Distribution Systems: Planning, Operation, and Energy Trading

Recent years have perceived a substantial surge in interest in green technologies due to the growing awareness about the environmental concerns and the technologies’ development, which have resulted in considerable utilization of DC-based distributed generators (DGs) and loads such as photovoltaic (PV) panels and electric vehicles. This increased penetration has reformed the generation and utilization of electric, resulting in promoting the microgrids (μGs) as a promising candidate for future systems. Despite the well-establishment and the extensive studies of μGs, there is still some debate over having μGs that are purely AC, purely DC, or AC-DC hybrid. Purely AC and purely DC configurations cannot meet the challenges and the new technologies that are expected to emerge in the near future as they require many interfacing converters to accommodate the high penetration of DC DGs and loads. These interfacing converters increase the system costs, the conversion losses, and the system complexity. The aforementioned reasons have resulted in the consensus tending towards a new vision of combining the AC and DC to acquire the benefits of both systems, which calls for further investigation of the AC-DC system compositions. The growing electricity demand, aging of the power system infrastructure, and countries effort to utilize renewable-based DGs have stimulated the concept of isolated μGs.Isolated μGs could allow utilities and developers to defer the installation of new generation capacities, in addition to transmission and distribution capacities upgrades by connecting distributed energy resources. Despite the significant benefits provided by isolated μGs, preserving load-generation balance is comprehensively challenging, given that μGs are dominated by renewable-based DGs, which are characterized by their probabilistic nature and intermittent power. This challenge introduced the interconnection of μGs as a promising solution that enhance the system operation and increase the system reliability. The interconnection of a group ofμGs essentially leads to a (small scale) energy market of interconnected microgrids (IμGs) when these μGs exchange energy with each other. Therefore, it is vital to refine and enhance the way in which players from different μGs construct the interconnected μGs and manage electricity trading. Driven by the aforementioned challenges, the main objective of this thesis is to promote the concept of μG and optimally accommodate the expected increased penetration of DC DGs and DC loads in future systems, and ensure the continuity of power supplied to these future systems through their interconnection and managing the energy trading process. Achieving this target entailed the completion of the following parts: 1) Proposing the bilayer μGs configuration, in addition to its power flow model, at which each node is a universal node that can include two buses with different types of power (AC and DC) or a single bus (AC or DC). The inclusion of the two types of power reduces the number of interfacing converters and allows for the accommodation of the increased penetration of DC DGs and loads besides the existing conventional AC DGs and loads. 2) Proposing a stochastic planning framework for the network configuration of AC-DC bilayer μGs that is capable of minimizing the total system costs through the determination of the optimal BμGconfiguration. 3) Investigating the AC-DC bilayer μGs operation under fault conditions and introducing a multilevel converter with fault confining capability that can isolate the faulty layer, and hence ensures optimal and reliable operation of the healthy layer under fault conditions. 4) The proposal of a stochastic planning framework for the IμGs that minimizes the total system costs and minimizes the loads curtailment under DG failure, while considering the stochastic variations of the renewable-based DGs and loads. 5) Developing an energy trading mechanism that facilitates the power trading between the interconnected μGs, provides full utilization of the renewable output power, minimizes operation cost, and minimizes load curtailment