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

Control Strategies for Improving Reliability and Efficiency in Modular Power Converters

The significance of modular power converters has escalated drastically in various applications such as electrical energy distribution, industrial motor drives and More Electric Aircraft (MEA) owing to the benefits such as scalability, design flexibility, higher degree of fault tolerance and better maintenance. One of the main advantages of modular systems is the ability to replace the faulty converter cells during maintenance instead of the entire system. However, such maintenance cycles can result in a system of converter cells with different aging. A system with cells having different aging arises the threats of multiple maintenance, lower reliability and availability, and high maintenance costs. For controlling the thermal-stress based aging of modular power converters, power routing strategy was proposed. The thesis focuses on the different implementation strategies of power routing for modular converters. Power semiconductors are one of the most reliability critical components in power converters, and thermal-stress has been identified as the main cause of their failure. This thesis work concentrates on the power semiconductor reliability improvement algorithms. For improving system lifetime, virtual resistor based power routing algorithms for single stage and multi-stage modular architectures have been investigated through simulations and validated with experiment. A unified framework for routing the power in complex modular converter architectures is defined based on graph theory. Popular converter architectures for Smart Transformer (ST) and MEA applications are modeled as graphs to serve as the basis for developing power flow optimization. The effectiveness of graph theory for optimizing the power flow in modular systems is demonstrated with the help of proposed algorithms

A Comprehensive Review of DC-DC Converters for EV Applications

DC-DC converters in Electric vehicles (EVs) have the role of interfacing power sources to the DC-link and the DC-link to the required voltage levels for usage of different systems in EVs like DC drive, electric traction, entertainment, safety and etc. Improvement of gain and performance in these converters has a huge impact on the overall performance and future of EVs. So, different configurations have been suggested by many researches. In this paper, bidirectional DC-DC converters (BDCs) are divided into four categories as isolated-soft, isolated-hard, non-isolated-soft and non-isolated-hard depending on the isolation and type of switching. Moreover, the control strategies, comparative factors, selection for a specific application and recent trends are reviewed completely. As a matter of fact, over than 200 papers have been categorized and considered to help the researchers who work on BDCs for EV application

Grid Integration of DC Buildings: Standards, Requirements and Power Converter Topologies

Residential dc microgrids and nanogrids are the emerging technology that is aimed to promote the transition to energy-efficient buildings and provide simple, highly flexible integration of renewables, storages, and loads. At the same time, the mass acceptance of dc buildings is slowed down by the relative immaturity of the dc technology, lack of standardization and general awareness about its potential. Additional efforts from multiple directions are necessary to promote this technology and increase its market attractiveness. In the near-term, it is highly likely that the dc buildings will be connected to the conventional ac distribution grid by a front-end ac-dc converter that provides all the necessary protection and desired functionality. At the same time, the corresponding requirements for this converter have not been yet consolidated. To address this, present paper focuses on various aspects of the integration of dc buildings and includes analysis of related standards, directives, operational and compatibility requirements as well as classification of voltage levels. In addition, power converter configurations and modulation methods are analyzed and compared. A classification of topologies that can provide the required functionality for the application is proposed. Finally, future trends and remaining challenges pointed out to motivate new contributions to this topic

A Comprehensive Assessment of Multiwinding Transformer-Based DC-DC Converters

Multiwinding-Transfomer-based (MTB) DC-DC converter did emerge in the last 25 years as an interesting possibility to connect several energy systems and/or to offer higher power density because of the reduction of transformer core material and reduction of power converter stages. MTB DC-DC converters can be considered as an interesting compromise between non-modular and a modular DC-DC converter since they are themselves modular in the construction. This eventually leads to some fault-tolerant possibilities since the multiwinding transformer (MWT) connects multiples ports and if one of them is not working anymore and it can be isolated, the others might still continue operating. Unfortunately, it is exactly the MWT that creates most of the technical challenges of this class of DC-DC converters because of the cross-coupling effects among the cells which make especially the resonant-topology very challenging to be designed. This paper reviews the history of the MTB DC-DC and then provides a classification of them, comparing them with Figure of Merits (FOM) and focusing on which is the maximum possible number of windings and which are the most suited magnetic core types. The problems coming from cross-coupling and the possible fault-tolerant operation are analysed with the help of simulation and experimental results

Power Interface Design and System Stability Analysis for 400 V DC-Powered Data Centers

The demands of high performance cloud computation and internet services have increased in recent decades. These demands have driven the expansion of existing data centers and the construction of new data centers. The high costs of data center downtime are pushing designers to provide high reliability power supplies. Thus, there are significant research questions and challenges to design efficient and environmentally friendly data centers with address increasing energy prices and distributed energy developments. This dissertation work aims to study and investigate the suitable technologies of power interface and system level configuration for high efficiency and reliable data centers. A 400 V DC-powered data center integrated with solar power and hybrid energy storage is proposed to reduce the power loss and cable cost in data centers. A cascaded totem-pole bridgeless PFC converter to convert grid ac voltage to the 400 V dc voltage is proposed in this work. Three main control strategies are developed for the power converters. First, a model predictive control is developed for the cascaded totem-pole bridgeless PFC converter. This control provides stable transient performance and high power efficiency. Second, a power loss model based dual-phase-shift control is applied for the efficiency improvement of dual-active bridge converter. Third, an optimized maximum power point tracking (MPPT) control for solar power and a hybrid energy storage unit (HESU) control are given in this research work. The HESU consists of battery and ultracapacitor packs. The ultracapacitor can improve the battery lifetime and reduce any transients affecting grid side operation. The large signal model of a typical solar power integrated datacenter is built to analyze the system stability with various conditions. The MATLAB/Simulink™-based simulations are used to identify the stable region of the data center power supply. This can help to analyze the sensitivity of the circuit parameters, which include the cable inductance, resistance, and dc bus capacitance. This work analyzes the system dynamic response under different operating conditions to determine the stability of the dc bus voltage. The system stability under different percentages of solar power and hybrid energy storage integrated in the data center are also investigated

Power Interface Design and System Stability Analysis for 400 V DC-Powered Data Centers

The demands of high performance cloud computation and internet services have increased in recent decades. These demands have driven the expansion of existing data centers and the construction of new data centers. The high costs of data center downtime are pushing designers to provide high reliability power supplies. Thus, there are significant research questions and challenges to design efficient and environmentally friendly data centers with address increasing energy prices and distributed energy developments. This dissertation work aims to study and investigate the suitable technologies of power interface and system level configuration for high efficiency and reliable data centers. A 400 V DC-powered data center integrated with solar power and hybrid energy storage is proposed to reduce the power loss and cable cost in data centers. A cascaded totem-pole bridgeless PFC converter to convert grid ac voltage to the 400 V dc voltage is proposed in this work. Three main control strategies are developed for the power converters. First, a model predictive control is developed for the cascaded totem-pole bridgeless PFC converter. This control provides stable transient performance and high power efficiency. Second, a power loss model based dual-phase-shift control is applied for the efficiency improvement of dual-active bridge converter. Third, an optimized maximum power point tracking (MPPT) control for solar power and a hybrid energy storage unit (HESU) control are given in this research work. The HESU consists of battery and ultracapacitor packs. The ultracapacitor can improve the battery lifetime and reduce any transients affecting grid side operation. The large signal model of a typical solar power integrated datacenter is built to analyze the system stability with various conditions. The MATLAB/Simulink™-based simulations are used to identify the stable region of the data center power supply. This can help to analyze the sensitivity of the circuit parameters, which include the cable inductance, resistance, and dc bus capacitance. This work analyzes the system dynamic response under different operating conditions to determine the stability of the dc bus voltage. The system stability under different percentages of solar power and hybrid energy storage integrated in the data center are also investigated