The large-scale deployments of dc appliances and renewable generation have increased industry and research interest in dc electrical distribution systems for homes, offices, and other small buildings. In these systems, it is necessary to provide an isolated active front-end (AFE) interface between an ac grid and a residential dc microgrid/nanogrid. These power devices are often referred to as isolated active front-end (i-AFE) or grid interface converters. Single-stage isolated ac-dc converters can be a promising solution for the concept of the i-AFE converters. Single-stage topologies have no intermediate dc bus and potentially lead to reduced system weight, volume, and cost, compared to traditional two-stage solutions (ac-dc/dc-dc). Despite the potential advantages, single-stage isolated ac-dc converters are still an emerging topic in power electronics, which has not yet gained wide industrial adoption. This paper provides an overview of single-stage isolated ac-dc topologies, for dc microgrids application.

Overview of Single-Stage Isolated AC-DC Topologies for Interfacing DC and AC Grids

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.

https://ieeexplore.ieee.org/ielx7/8782709/8932554/09931500.pdf

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

This paper proposes a new zero-current-switching (ZCS) pulsewidth modulation (PWM) switch cell that has no additional conduction loss of the main switch. In this cell, the main switch and the auxiliary switch turn on and turn off under zero-current condition. The diodes commutate softly and the reverse-recovery problems are alleviated. The conduction loss and the current stress of the main switch are minimized, since the resonating current for the soft switching does not flow through the main switch. Based on the proposed ZCS PWM switch cell, a new family of DC-to-DC PWM converters is derived. The new family of ZCS PWM converters is suitable for the high-power applications employing insulated gate bipolar transistors. Among the new family of DC-to-DC PWM converters, a boost converter was taken as an example and has been analyzed. Design guidelines with a design example are described and verified by experimental results from the 2.5 kW prototype boost converter operating at 40 kHz.

Novel Zero-Current-Switching (ZCS) PWM Switch Cell Minimizing Additional Conduction Loss

Neste trabalho e apresentado o conversor CC-CC ZVS isolado bidirecional Dual Active Bridge (DAB) monofasico, baseado na celula de comutacao de tres estados. A proposta e aplica-lo em sistemas fotovoltaicos com banco de baterias em redes inteligentes. Basicamente o controle do conversor consiste na razao ciclica (D) dos interruptores e o Phase Shift (φ) entre as componentes fundamentais das tensoes entre as pontes. A modelagem por gyrator do conversor e apresentada, destacando-se sua caracteristica natural de funcionamento como gyrator. Mostra-se a analise qualitativa e quantitativa do conversor, realizando o estudo completo das etapas de operacao da topologia e verificando todas as dezesseis regioes de operacao. Para obtencao das regioes de comutacao suave, e aplicado o modelo fundamental. O procedimento de projeto do conversor e apresentado, alem dos resultados de simulacoes. Um prototipo de 2 kW foi desenvolvido, visando a obtencao dos resultados experimentais e validando a analise teorica

/pdf/conversor-cc-cc-bidirecional-dab-monofasico-baseado-na-5e6eimhdl0.pdf

Conversor CC-CC bidirecional DAB monofásico baseado na célula de comutação de três estados

This work proposes an extensive investigation of a solid-state transformer (SST) with an integrated ac–dc bidirectional stage feasible to medium-voltage (MV) railway systems, based on an arrangement that uses an input-series-output-parallel (ISOP) configuration with identical power modules. Each module has a three-leg configuration: in the primary side, there are two interleaved legs using coupled windings connected to a medium-frequency transformer (MFT) and another leg operating at the grid frequency; and a conventional H-bridge is used in the secondary side. Qualitative and quantitative analyses are presented to demonstrate the aspects of the proposed topology and are validated by steady-state experimental results using an 8.33-kW prototype. Dynamics results are also presented, with a two-module structure with a low rated power to validate the control strategy and modularity. A comparative analysis considering real traction system parameters is carried out, demonstrating some well-defined trends of the proposed topology in this application, such as a reduction in conduction loss up to 32% and lower number of switches compared with another five topologies. The analyses and preliminary results show that the proposed structure could indeed be considered as a possible solution for SSTs in MV traction systems. 

Three-Leg Integrated Stage AC–DC Solid-State Transformer Feasible for MV Railway Applications

This paper shows the experimental validation of a basic module from a single-stage ac-dc bidirectional power converter, which is feasible for solid-state transformer applications. The proposed converter is based on the dual active bridge (DAB) using an interleave technique. The converter can be modularized and applied at high voltage in a three phase system operating as rectifier or inverter. The topology is briefly presented and experimental results from a small-scale prototype are discussed to validate its operation principles and control strategy. The results show that the control strategy is able to operate the converter properly maintaining all DC bus on reference value. The converter is also capable of operate with a high power factor and a low harmonic distortion. Simulation results are shown from a prototype that is under construction with a higher power and magnetic integration.

Experimental validation of a basic module based on a single-stage AC-DC converter, feasible to solid-state transformer applications

Resumo – Este artigo apresenta o estudo e a implementação de um novo conversor CA-CC trifásico bidirecional de único estágio com correção de fator de potência e isolado em alta frequência. O conversor proposto é concebido utilizando-se o conceito de interleaving, e no dual active bridge (DAB) com controle phase-shift. São desenvolvidas análises teóricas baseadas no uso do modelo fundamental e utilizando-se o conceito da modulação AM DSB (Amplitude Modulation with Double Side-Band), sendo validado por simulações numéricas. Resultados experimentais obtidos com um protótipo de 1,5 kW são apresentados a fim de validar o estudo da topologia proposta.

/pdf/three-phase-single-stage-bidirectional-rectifier-with-high-4ei7294etb.pdf

Three-phase Single-stage Bidirectional Rectifier With High Frequency Isolation And Pfc

This paper presents the study of the single-stage rectifier with high-frequency isolation, focusing on its soft switching analysis in the primary side. The converter uses the concepts of interleaving by coupled-windings and the dual active bridge (DAB) structure, so that it is possible to obtain a power flow control through the delay angle applied on the secondary side with a good distribution of the semiconductor efforts. The soft switching investigation was carried out by the qualitative and quantitative analysis of the converter. The validation of such analysis is elaborated by spreadsheets and simulation results considering a 1 kW load. Experimental partial results is presented to validate the proposed converter.

AC-DC Converter with High-Frequency Isolation Operating Under ZVS

This paper presents the study and development of a single stage three-port non-isolated DC-DC converter, suitable for PV integration to the grid or isolated systems. The proposed topology uses a boost Artigo submetido em 20/10/2016. Primeira revisão em 22/12/2016. Aceito para publicação em 05/03/2017 por recomendação do Editor Marcelo Cabral Cavalcanti. converter with high voltage gain based on bidirectional three state switching cell. It allows the connection of a battery bank, a set of photovoltaic panels and the dc link of a inverter in a single stage of processing. The bidirectional characteristic of the proposed topology allows photovoltaic panels charge the battery bank and supply the load depending on sunlight while providing a variable dc link to an inverter. Another important feature of this converter is the soft switching in ZVS mode for all switches. A 500W experimental prototype was developed in order to validate all the theoretical analysis. The developed converter was subjected to three operational conditions: the energy flowing from the battery to the load, from the PV to the load and from PV to the battery, reaching efficiency of 94.18%, 96.09% and 94.67% respectively for each operational point. Besides the efficiency, a complete theoretical study is also presented with the main waveforms for all operation modes. The high voltage gain and the performance of this topology, makes it a strong competitor when there is need to step up the voltage from batteries or PV panels (typically 12V, 24V or 48V) to 200V or 400V DC link.

Demercil Junior

Papers

Experimental validation of a basic module based on a single-stage AC-DC converter, feasible to solid-state transformer applications

Three-phase Single-stage Bidirectional Rectifier With High Frequency Isolation And Pfc

AC-DC Converter with High-Frequency Isolation Operating Under ZVS

Single Stage Three-port Dc-dc Converter With High Voltage Gain And Bidirectional Capability Feasible To Small Pv Systems