A Review of Active Management for Distribution Networks: Current Status and Future Development Trends

Driven by smart distribution technologies, by the widespread use of distributed generation sources, and by the injection of new loads, such as electric vehicles, distribution networks are evolving from passive to active. The integration of distributed generation, including renewable distributed generation changes the power flow of a distribution network from unidirectional to bi-directional. The adoption of electric vehicles makes the management of distribution networks even more challenging. As such, an active network management has to be fulfilled by taking advantage of the emerging techniques of control, monitoring, protection, and communication to assist distribution network operators in an optimal manner. This article presents a short review of recent advancements and identifies emerging technologies and future development trends to support active management of distribution networks

Solid state transformer technologies and applications: a bibliographical survey

This paper presents a bibliographical survey of the work carried out to date on the solid state transformer (SST). The paper provides a list of references that cover most work related to this device and a short discussion about several aspects. The sections of the paper are respectively dedicated to summarize configurations and control strategies for each SST stage, the work carried out for optimizing the design of high-frequency transformers that could adequately work in the isolation stage of a SST, the efficiency of this device, the various modelling approaches and simulation tools used to analyze the performance of a SST (working a component of a microgrid, a distribution system or just in a standalone scenario), and the potential applications that this device is offering as a component of a power grid, a smart house, or a traction system.Peer ReviewedPostprint (published version

A Novel Three-Level Isolated AC-DC PFC Power Converter Topology with Reduced Number of Switches

The three-level isolated AC-DC power factor corrected (PFC) converter provides safe and more efficient power conversion. In comparison with two-level, three-level PFC converter has the advantages of low total harmonic distortion, low device voltage rating, low di/dt, better output performance, high power factor, and low switching losses at higher switching frequencies. The high frequency transformer (HFT) grants galvanic isolation, steps up or down secondary voltage, and limits damage in case of a fault current. The existing three-level converter based on solid-state transformer (SST) topologies convert ac power from the electrical grid to a dc load while maintaining at least the minimum requirements set by the international standards (i.e., high power factor and low total harmonic distortion). The SST topologies with the capability of controlling intermediate dc-bus and output voltage simultaneously require two full bridges at the primary and secondary side of the HFT. As the power level increases, the number of cascaded bridges increases accordingly, and the price associated with these semiconductor devices becomes highly expensive. As result, the demand of converting high power level led to emphasis on high performance and cost-effective power conversion topology. The aim of this dissertation is to develop a new low-cost and high-performance three-level isolated AC-DC (PFC) converter topology. The proposed topology replaces the conventional three-level inverter in the secondary side of the HFT by only two switches and four diodes while still maintaining the basic functionality of a three-level converter (i.e., regulating the output voltage, controlling the dc-bus voltage to be within desired limits). The advantages of this new topology are: (1) low conduction losses; (2) low-cost; (3) no need to consider the issue of the power backflow; (4) zero-voltage switching (ZVS) and zero-current switching (ZCS) at turn ON are inherently guaranteed without any extra control effort. Two isolated three-level AC-DC power converter topologies are developed and investigated through the dissertation. First topology is based on the neutral point clamping (NPC) converter, and the second topology composed of the T-type converter. Two scale-down prototypes rated at 900-W and 1kW, 200 V are built to test the overall performance of the proposed topologies. The first and second topologies exhibit 94.5 % and 95.8 % efficiency scaled at a nominal power, respectively. The secondary bridge (novel circuit) in both topologies, which consists of two switches and four diodes, has 99.34 % practical efficiency

High-Frequency Transformer Design for Solid-State Transformers in Electric Power Distribution Systems

The objective of this thesis is to present a high- or medium-frequency transformer design methodology for Solid-State Transformer (SST) applications. SSTs have been proposed as a replacement of the traditional 50/60 Hz transformer in applications demanding high-power density. Moreover, due to the high penetration of distributed generation, DC grids, energy storage systems, and sensitive loads, SSTs have been considered as an enabling technology for envisioned future energy systems. These applications demand additional functionalities that may not be achieved with traditional transformers. For example, active power flow control, harmonic suppression, voltage regulation, voltage sag compensation, and reduced size and volume. In this thesis, SST topologies are evaluated in order to determine their impact upon the transformer design. In addition, design considerations for core and wire selections, isolation requirements, and different transformer structures are investigated. As a result, the proposed transformer design methodology accounts for leakage inductance requirements for optimal power transfer, high-frequency effects in the transformer core and windings, and a flux density optimization to maximize transformer’s efficiency. The design procedure has been implemented in MATLAB® as an interactive tool for designing high-frequency transformers

Management Of Plug-In Electric Vehicles And Renewable Energy Sources In Active Distribution Networks

Near 160 million customers in the U.S.A. are served via distribution networks (DNs). The increasing penetration level of renewable energy sources (RES) and plug-in electric vehicles (PEVs), the implementation of smart distribution technologies such as advanced metering/monitoring infrastructure, and the adoption of smart appliances, have changed distribution networks from passive to active. The next-generation of DNs should be efficient and optimized system-wide, highly reliable and robust, and capable of effectively managing highly-penetrated PEVs, RES and other controllable loads. To meet new challenges, the next-generation DNs need active distribution management (ADM). In this thesis, we study the management of PEVs and RES in active DNs. First, we propose a novel discrete-event modeling method to model PEVs and other loads in distribution networks. In addition, a new optimization algorithm to integrate as many PEVs as possible in DNs without causing voltage issues, including the violation of voltage security ranges and voltage stability, is studied. To further explore the active management of PEVs in the DNs, we develop a universal demonstration platform, consisting of software packages and hardware remote terminal units. The demonstration platform is designed with the capabilities of measurement, monitoring, control, automation, and communications. Furthermore, we have studied the reactive power management in microgrids, a special platform to integrate distributed generations and energy storage in DNs. To solve possible voltage security issues in a microgrid with high penetration of single-phase induction machines under the condition of fault-induced islanding, a voltage-sensitivity-based reactive power management algorithm is proposed