To meet the fast-growing energy demand and, at the same time, tackle environmental concerns resulting from conventional energy sources, renewable energy sources are getting integrated in power networks to ensure reliable and affordable energy for the public and industrial sectors However, the integration of renewable energy in the ageing electrical grids can result in new risks/challenges, such as security of supply, base load energy capacity, seasonal effects, and so on Recent research and development in microgrids have proved that microgrids, which are fueled by renewable energy sources and managed by smart grids (use of smart sensors and smart energy management system), can offer higher reliability and more efficient energy systems in a cost-effective manner Further improvement in the reliability and efficiency of electrical grids can be achieved by utilizing dc distribution in microgrid systems DC microgrid is an attractive technology in the modern electrical grid system because of its natural interface with renewable energy sources, electric loads, and energy storage systems In the recent past, an increase in research work has been observed in the area of dc microgrid, which brings this technology closer to practical implementation This paper presents the state-of-the-art dc microgrid technology that covers ac interfaces, architectures, possible grounding schemes, power quality issues, and communication systems The advantages of dc grids can be harvested in many applications to improve their reliability and efficiency This paper also discusses benefits and challenges of using dc grid systems in several applications This paper highlights the urgent need of standardizations for dc microgrid technology and presents recent updates in this area

DC Microgrid Technology: System Architectures, AC Grid Interfaces, Grounding Schemes, Power Quality, Communication Networks, Applications, and Standardizations Aspects

The impending global energy crisis has opened up new opportunities for the automotive industry to meet the ever-increasing demand for cleaner and fuel-efficient vehicles. This has necessitated the development of drivetrains that are either fully or partially electrified in the form of electric and plug-in hybrid electric vehicles (EVs and HEVs), respectively, which are collectively addressed as plug-in EVs (PEVs). PEVs in general are equipped with larger on-board storage and power electronics for charging or discharging the battery, in comparison with HEVs. The extent to which PEVs are adopted significantly depends on the nature of the charging solution utilized. In this paper, a comprehensive topological survey of the currently available PEV charging solutions is presented. PEV chargers based on the nature of charging (conductive or inductive), stages of conversion (integrated single stage or two stages), power level (level 1, 2, or 3), and type of semiconductor devices utilized (silicon, silicon carbide, or gallium nitride) are thoroughly reviewed in this paper.

Comprehensive Topological Analysis of Conductive and Inductive Charging Solutions for Plug-In Electric Vehicles

Installation of many distributed generations (DGs) could be detrimental to the power quality of utility grids. Microgrids facilitate effortless installation of DGs in conventional power systems. In recent years, dc microgrids have gained popularity because dc output sources such as photovoltaic systems, fuel cells, and batteries can be interconnected without ac/dc conversion, which contributes to total system efficiency. Moreover, high-quality power can be supplied continuously when voltage sags or blackouts occur in utility grids. We had already proposed a “low-voltage bipolar-type dc microgrid” and described its configuration, operation, and control scheme, through experiments. In the experiments, we used one energy storage unit with a dc/dc converter to maintain the dc-bus voltage under intentional islanding operation. However, dc microgrids should have two or more energy storage units for system redundancy. Therefore, we modified the system by adding another energy storage unit to our experimental system. Several kinds of droop controls have been proposed for parallel operations, some of which were applied for ac or dc microgrids. If a gain-scheduling control scheme is adopted to share the storage unit outputs, the storage energy would become unbalanced. This paper therefore presents a new voltage control that combines fuzzy control with gain-scheduling techniques to accomplish both power sharing and energy management. The experimental results show that the dc distribution voltages were within 340 V ± 5%, and the ratios of the stored energy were approximately equal, which implies that dc voltage regulation and stored energy balancing control can be realized simultaneously.

Distribution Voltage Control for DC Microgrids Using Fuzzy Control and Gain-Scheduling Technique

Although conventional electromechanical circuit breakers have a proven record as effective and reliable devices for circuit protection, emerging power distribution technologies and architectures, such as dc microgrids, require improved interruption performance characteristics (eg, faster switching speed) The need for faster switching operation, in combination with the latest developments of advanced power semiconductor technologies, has spurred an increase in the research and development in the area of solid-state circuit breakers This article provides a comprehensive review of various solid-state circuit breaker technologies that have been reported in the literature during recent years First, we categorize solid-state circuit breakers based on key features and subsystems, including power semiconductor devices, main circuit topologies, voltage clamping methods, gate drivers, fault detection methods, and commutation methods for power semiconductor devices Second, we discuss the various challenges associated with the design of solid-state circuit breakers from the perspective of generic applications and provide a comparison of several solid-state breaker technologies based on key metrics Finally, we provide a useful framework and point of reference for future development of solid-state circuit breakers for many emerging power distribution applications

A Review of Solid-State Circuit Breakers

DC microgrids have attracted significant attention over the last decade in both academia and industry. DC microgrids have demonstrated superiority over AC microgrids with respect to reliability, efficiency, control simplicity, integration of renewable energy sources, and connection of dc loads. Despite these numerous advantages, designing and implementing an appropriate protection system for dc microgrids remains a significant challenge. The challenge stems from the rapid rise of dc fault current which must be extinguished in the absence of naturally occurring zero crossings, potentially leading to sustained arcs. In this paper, the challenges of DC microgrid protection are investigated from various aspects including, dc fault current characteristics, ground systems, fault detection methods, protective devices, and fault location methods. In each part, a comprehensive review has been carried out. Finally, future trends in the protection of DC microgrids are briefly discussed.

/pdf/dc-microgrid-protection-a-comprehensive-review-38dp561hfd.pdf

DC Microgrid Protection: A Comprehensive Review

400-V direct current (400-V dc) distribution systems are promising candidate of highly efficient and reliable distribution systems for data centers. To realize the 400-V dc distribution systems, development of methods for high-speed overcurrent protection is one of the important issues. In this paper, as a solution to this problem, a semiconductor dc circuit breaker using SiC static induction transistors (SiC-SIT's) is investigated. The SiC-SIT's has extremely low on-state resistance and very large safe operating area (SOA). These properties are attractive in the application of the circuit breakers for 400-V dc distribution systems. A novel control method of the gate voltage waveform to reduce the transient overvoltage and resonance during the interruption process is proposed. The effectiveness of the proposed method is confirmed by actual operation tests employing an experimental prototype of the dc distribution system. All of the result is confirmed by the fabricated SiC-SIT circuit breaker prototype.

SiC-SIT Circuit Breakers With Controllable Interruption Voltage for 400-V DC Distribution Systems

We outline the specifications and performance of a 400-Vdc distribution system and 400-Vdc output rectifier prototypes. In 2008, The NTT-group began developing a 400-Vdc distribution system for reducing power consumption and the usage of materials, such as copper in power cables. In conjunction with this project, NTT Facilities developed prototype rectifiers, a prototype voltage compensator used during interruption periods, and a prototype battery charger in 2008, and reported a portion of their verification test results. From their developments, we found some problems for installing and operating in telecommunication buildings and data centers. Therefore, we developed new prototypes for resolving these problems. They have almost equal efficiency and output regulation, saving installation space, and they are more maintainable and safer for operating than previously developed prototypes.

Development of 400-Vdc output rectifier for 400-Vdc power distribution system in telecom sites and data centers

In recent years, Higher Voltage Direct Current (HVDC) distribution systems have been proposed to reduce power consumption in telecommunication buildings and data centers. NTT FACILITIES and NTT Data conducted verification tests of a HVDC distribution system at a Tokyo data center from January 29 to October 30, 2009. This paper summarizes the results of studies on HVDC distribution systems obtained so far, describes verification tests based on those results, and examines the test results. The verification tests were conducted with the cooperation of domestic and international ICT equipment vendors. We measured the energy savings and stability of the power supply involved long-term powering of ICT equipments (servers and storages) with an HVDC system. The test results show the superiority of the HVDC distribution system over the existing AC system. These test results also validate the HVDC system specifications proposed by the NTT group for standardization. These results may develop the current vigorous discussion of international standardization for HVDC distribution systems.

Evaluation results of power supply to ICT equipment using HVDC distribution system

Provided is a connector wherein, when a plug is inserted in a socket, the plug is prevented from being erroneously inserted, and it is not necessary to rotate the plug to a great extent. A plug-in connector (1) is comprised of a pin plug (10) and a receptacle (20), and the pin plug (10) and the receptacle (20) are connected. A plurality of pin plug key protrusions (15) are spaced and arranged on a pin cover main body (14) of the pin plug (10) in the circumferential direction. A plurality of groups of a plurality of key grooves (28) spaced in the circumferential direction are arranged so as to be deviated from one another in the circumferential direction, in a socket cover (27) of the receptacle (20). A socket plug (30) may be used in place of the receptacle (20). As described above, there are a plurality of groups of grooves in the plug or the socket, and accordingly, the circumferential angle of the plug with respect to the socket can vary depending on the number of the groups of grooves. Therefore, the connector can reduce the twisting angle of a cable connected to the plug, and can reduce the load on the cable.

Connector and connector set

Recently, DC power supply systems have been widely viewed as an energy-saving solution. The protection of the system from over current is one of the most important factors in DC power supply system. This paper presents noise current characteristics of a semiconductor circuit breaker.

Noise current characteristics of semiconductor circuit breaker during break-off condition in DC power supply system

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