High-Voltage-Gain DC-DC Power Electronic Converters -- New Topologies and Classification

This dissertation proposes two new high-voltage-gain dc-dc converters for integration of renewable energy sources in 380/400V dc distribution systems. The first high-voltage-gain converter is based on a modified Dickson charge pump voltage multiplier circuit. The second high-voltage-gain converter is based on a non-inverting diode-capacitor voltage multiplier cell. Both the proposed converters offer continuous input current and low voltage stress on switches which make them appealing for applications like integration of renewable energy sources. The proposed converters are capable for drawing power from a single source or two sources while having continuous input current in both cases. Theoretical analysis of the operation of the proposed converters and the component stresses are discussed with supporting simulation and hardware results. This dissertation also proposes a family of high-voltage-gain dc-dc converters that are based on a generalized structure. The two stage general structure consists of a two-phase interleaved (TPI) boost stage and a voltage multiplier (VM) stage. The TPI boost stage results in a classification of the family of converters into non-isolated and isolated converters. A few possible VM stages are discussed. The voltage gain derivations of the TPI boost stages and VM stages are presented in detail. An example converter is discussed with supporting hardware results to verify the general structure. The proposed family of converters can be powered using single source or two sources while having continuous input current in both cases. These high voltage gain dc-dc converters are modular and scalable; making them ideal for harnessing energy from various renewable sources offering power at different levels --Abstract, page iv

Overview of Technical Challenges, Available Technologies and Ongoing Developments of AC/DC Microgrids

Gradual depletion of fossil fuel resources, poor energy efficiency of conventional power plants, and environmental pollution have led to a new grid architecture known as smart microgrid. The smart microgrid concept provides a promising solution that enables high penetration of distributed generation from renewable energy sources without requiring to redesign the distribution system, which results in stable operation during faults and disturbances. However, distributed generators/loads and interaction between all nodes within a microgrid will substantially increase the complexity of the power system operation, control, and communications. Many innovative techniques and technologies have been proposed to address the complexity and challenges of microgrids including power quality, power flow balancing, real‐time power management, voltage and frequency control, load sharing during islanding, protection, stability, reliability, efficiency, and economical operation. All key issues of the microgrids, different solutions, and available methods and technologies to address such issues are reviewed in this chapter. Pros and cons of each method are discussed. Furthermore, an extensive comprehensive review for researchers and scholars working on microgrid applications is provided in this chapter to help them identify the areas that need improvements and innovative solutions for increasing the efficiency of modern power distribution grid

Review on Control of DC Microgrids and Multiple Microgrid Clusters

This paper performs an extensive review on control schemes and architectures applied to dc microgrids (MGs). It covers multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms. Islanding detection, protection, and MG clusters control are also briefly summarized. All the mentioned issues are discussed with the goal of providing control design guidelines for dc MGs. The future research challenges, from the authors' point of view, are also provided in the final concluding part

Improving the Performance of a Line Regulating Converter in a Converter-Dominated DC Microgrid System

This paper describes the controller design procedure for a line-regulating converter in a converter-dominated dc microgrid system. The purpose of the controller is to mitigate the effects of the constant power loads on the stability and performance of the dc microgrid system. In this work, first, the overall structure, operation, and building blocks of the dc microgrid under analysis are introduced. Next, the dynamic model of the dc microgrid and the required transfer functions for the controller design are derived. Then, two proposed controller design methods are introduced and implemented on an virtual line-regulating converter in a dc microgrid system. Finally, the controller design methods are verified experimentally using the results from a built prototype dc microgrid system

Factors Affecting Efficiency of LVDC Distribution Network – Power Electronics Perspective

The power distribution network will be changed towards the future Smart Grid due to increased number of installed renewable power generation units to fulfill the tightened environmental regulation. The control of the future Smart Grid will be challenging due to increased number of renewable power generation units, which are variable in nature, and at the same time, the customers are highly dependent on uninterruptable, high quality power supply. The Smart Grid control is intensively studied. It can be concluded that the control might be simpler and the grid operation more reliable if the AC grid would be replaced by DC grid. However, the detailed energy efficiency analysis of the DC grid is not thoroughly studied. The efficiency and total lifetime costs are the key parameters when the network owners consider the future grid structure.This thesis addresses the factors, which affect the energy efficiency of the low voltage DC (LVDC) distribution network from power electronics perspective. The power loss models for the converters and their AC filters are developed and verified by measurements. The impact on the converter topology, used power semiconductor switches, AC filter design and inductor core material, DC network configuration, customer behavior, the need of DC voltage balancing in the bipolar DC network as well as the grounding issues to fulfill the electrical safety standards are treated. For facilitating the design of cost effective LVDC distribution networks, the total power losses of the network with different configurations are evaluated and compared.It is revealed that the used filter inductor core material has a significant impact on the power losses of the LVDC distribution network. The inductor core material having low high-frequency power loss characteristics, such as amorphous alloy, is recommended. The LVDC distribution network should be grounded to minimize the power losses whenever it is possible according to the local safety standardization and grounding conditions. The three-level NPC converters connected to 1500 VDC should be used to minimize the power losses. The grid-frequency isolation transformer is the main power loss source if the galvanic isolation is needed to isolate the ungrounded LVDC distribution network and the grounded customer electrical installations. In this case, the highest energy efficiency is achieved by using two- or three-level converters connected to 750 VDC if the DC cable length is less than 600 m. Otherwise, slightly higher energy efficiency is achieved by using three-level converters connected to 1500 VDC. Therefore, voltage transformation ratio of the isolation transformer must be 800V/400V instead of 400V/400V. Moreover, the efficiency of the power converters is increased by using SiC MOSFETs instead of conventional IGBTs as power semiconductor switches