The isolation of graphene in 2004 from graphite was a defining moment for the “birth” of a field: two-dimensional (2D) materials In recent years, there has been a rapidly increasing number of papers focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because of the new properties and applications that emerge upon 2D confinement Here, we review significant recent advances and important new developments in 2D materials “beyond graphene” We provide insight into the theoretical modeling and understanding of the van der Waals (vdW) forces that hold together the 2D layers in bulk solids, as well as their excitonic properties and growth morphologies Additionally, we highlight recent breakthroughs in TMD synthesis and characterization and discuss the newest families of 2D materials, including monoelement 2D materials (ie, silicene, phosphorene, etc) and transition metal carbide- and carbon nitride-based MXenes We then discuss the doping and functionalization of 2

Recent Advances in Two-Dimensional Materials beyond Graphene

Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

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A review of single-phase improved power quality AC-DC converters

The solid-state transformer (SST), which has been regarded as one of the 10 most emerging technologies by Massachusetts Institute of Technology (MIT) Technology Review in 2010, has gained increasing importance in the future power distribution system. This paper presents a systematical technology review essential for the development and application of SST in the distribution system. The state-of-the-art technologies of four critical areas are reviewed, including high-voltage power devices, high-power and high-frequency transformers, ac/ac converter topologies, and applications of SST in the distribution system. In addition, future research directions are presented. It is concluded that the SST is an emerging technology for the future distribution system.

Review of Solid-State Transformer Technologies and Their Application in Power Distribution Systems

Three-phase multipulse AC-DC converters (MPC) are developed for improving power quality to reduce harmonics in AC mains and ripples in DC output. This paper deals with the multipulse AC-DC converter configurations, state of art, their performance, power quality aspects, components selection considerations, latest trends, future developments, and potential applications. It is targeted to provide broad perspective on multipulse converter technology to the researchers, engineers, and designers dealing with them. A classified list of more than 250 research publications on the subject is also given for quick reference.

Multipulse AC–DC Converters for Improving Power Quality: A Review

The solid-state transformer (SST) is one of the key elements in power electronic-based microgrid systems. The single-phase SST consists of a modular multilevel ac-dc rectifier, a modular dual active bridge (DAB) dc-dc converter with high-frequency transformers, and a dc-ac inverter stage. However, due to dc bus voltage and power unbalancing in each module, the modular SST often presents instability problems making its design difficult and causing unpredictable behavior. Moreover, the unbalanced dc-link voltages increase the stress of the semiconductor devices, and also cause high harmonic distortions of grid current, therefore, necessitating the use of a bigger ac filter. This paper presents a novel single-phase d-q vector-based common-duty-ratio control method for the multilevel rectifier, and a voltage feedforward and feedback based controller for the modular DAB converter. With the proposed control methods, the dc-link voltage and power in each module can be balanced. In addition, the low-distortion grid current, unity power factor, and bidirectional power flow can be achieved. Simulation and experimental results are presented to validate the proposed control methods.

Research on voltage and power balance control for cascaded modular solid-state transformer

A transformer performs many functions such as voltage transformation, isolation and noise decoupling, and it is an indispensable component in electric power distribution systems. However, at low frequencies (60/50 Hz), it is a bulky and expensive component. In this paper, the concept of electronic transformers is further extended and explored for its suitability in power distribution systems. It should be noted that from the input/output behavior, the electronic transformer and the conventional transformer are identical. Possible topologies employing static converters connected on the primary and secondary sides are explored to realize high-frequency operation of the magnetic core. To assist the commutation process, a four-step switching has been developed which does not require the use of snubbers. Reduced size, losses, higher efficiency, and better voltage regulation are some of the advantages of this approach. A 10 kVA design example along with experiment results are discussed. It is shown that a transformer designed with a conventional grain-oriented silicon-steel core can process three times the power at 1 kHz operating frequency as compared to 60 Hz. The proposed method is scalable in voltage/current with the currently available insulated gate bipolar transistor (IGBT) devices connected in series without special snubbers.

Analysis and design of electronic transformers for electric power distribution system

A power transformer performs many functions such as voltage transformation, isolation, noise decoupling and is an indispensable component in electricity distribution systems. However, at low frequencies (60/50 Hz) it is a bulky and expensive component. In this paper, the concept of electronic transformers is further discussed. Several possible topologies employing static power converters connected on the primary and secondary side in combination with magnetic circuits are explored to realize a high-frequency AC link. The focus of this paper is to realize an electronic transformer as a power delivery component in an electric distribution system. Reduced size, losses, higher efficiency and better voltage regulation are some of the advantages of this approach. A 10 kVA design example along with preliminary experiment results is discussed. It is shown that a transformer designed with a conventional grain-oriented silicon steel core can process three times the power at 1 kHz operating frequency compared to 60 Hz.

A lamp, lamp holder, and a power supply substrate that allow easy fabrication of a backlight assembly or a power supply module for a display device are presented. The lamp includes a lamp tube and an electrode that extends outside the lamp tube to form a lamp lead. The lamp holder includes a body for holding the lamp tube and a power supply member for providing voltage to the lamp lead. A power supply module includes a power supply substrate combined with a lamp holder holding the lamp. The lamp holders are fixed to fixing portions of the power supply substrate or to fixing holes of a connection plate. As the design allows easy separation of the lamp holders from the power supply substrate, building a backlight assembly or a display device is facilitated.

Lamp, lamp holder, power supply module, backlight assembly having the power supply module and display device having the power supply module

Disclosed is a liquid crystal display device having a lamp driving apparatus for preventing lamps from being damaged due to electric current variation among the lamps. A DC/DC converter converts an externally provided DC voltage input into a converted DC voltage signal having a predetermined voltage level. A DC/AC inverter inverts the converted DC voltage signal into an AC voltage signal to supply the inverted AC voltage signal to an input terminal of a lamp. A power controller detects electric current flowing the lamp at an output terminal of the lamp to control the level of the inverted AC voltage signal output from the DC/AC inverter and bypasses a part of electric current applied to the input terminal of the lamp when a level of the detected electric current is higher than a predetermined threshold value. Therefore, when the level of the electric current flowing through the lamp exceeds the predetermined threshold value, the power controller bypasses the part of the electric current supplied to the lamp to the ground, thereby decreasing the amount of the electric current supplied to the lamp and preventing the lamp from being damaged.

Apparatus and driving lamp and liquid crystal display device having the same

Disclosed are a power supplying apparatus and a LCD having the same that reduces manufacturing cost of a large-scale LCD module and enhances powpower efficiency by integrating an external dc power supply used in a large-scale LCD panel into a LCD panel. A first voltage converter converts an external ac voltage into a first dc voltage, and changes a voltage level of the first de voltage into a second dc voltage having a highr voltage level than that of the first de voltage. A second voltage converter converts the second dc voltage into an ac voltage, raises a voltage level of the converted ac voltage, and provides the raised ac voltage to a load. A current detector detects a current flowing through the load, and provides a current detection signal as a feedback signal to the first voltage converter so that the first voltage provide a constant direct current output voltage.

Moon-Shik Kang

Papers

Analysis and design of electronic transformers for electric power distribution system

Analysis and design of electronic transformers for electric power distribution system

Lamp, lamp holder, power supply module, backlight assembly having the power supply module and display device having the power supply module

Apparatus and driving lamp and liquid crystal display device having the same

Apparatus for supplying power and liquid crystal display having the same