Dong-Myung Lee

A Voltage Sag Supporter Utilizing a PWM-Switched Autotransformer

This paper proposes a novel distribution-level voltage control scheme that can compensate voltage sag and swell conditions in three-phase power systems. Faults occurring in power distribution systems or facilities in plants generally cause the voltage sag or swell. Sensitivity to voltage sags and swells varies within different applications. For sensitive loads, even a voltage sag of short duration can cause serious problems. Normally, a voltage interruption triggers a protection device, which causes the shutdown of the entire load. In order to mitigate power interruptions, this paper proposes a scheme for voltage sag support based on a pulse width modulated autotransformer. The proposed scheme is able to quickly recognize the voltage sag or swell condition, and it can correct the voltage by either boosting the input voltage during voltage sag events or reducing the voltage during swell events. The key advantage in this voltage control topology is that it uses only one controlled switch per phase to control the output voltage, thereby resulting in minimum cost per kVA. The paper presents the new voltage control topology, as well as the voltage detection method, the snubber design, and the commutation logic for the thyristor bypass switch. Experiments have been carried out to verify the validity of the proposed scheme

CMOS image sensor with analog gamma correction using nonlinear single-slope ADC

A human eye has the logarithmic response over wide range of light intensity. Although the gain can be set high to identify details in darker area on the image, this results in saturation in brighter area. The gamma correction is essential to fit the human eye. However, the digital gamma correction degrades image quality especially for darker area on the image due to the limited ADC resolution and the dynamic range. This paper proposes a CMOS image sensor (CIS) with nonlinear analog-to-digital converter (ADC) which performs analog gamma correction. The CIS with the proposed nonlinear ADC conversion scheme was fabricated with a 0.35-mum CMOS process. The test results show the improved image quality than digital gamma correction

Provable Per-Link Delay-Optimal CSMA for General Wireless Network Topology

In the past few years, an exciting progress has been made on CSMA (Carrier Sense Multiple Access) algorithms that achieve throughput and utility optimality for wireless networks. However, most of these algorithms are known to exhibit poor delay performance making them impractical for implementation. Recently, several papers have addressed the delay issue of CSMA and yet, most of them are limited, in the sense that they focus merely on specific network scenarios with certain conditions rather than general network topology, achieve low delay at the cost of throughput reduction, or lack rigorous provable guarantees. In this paper, we focus on the recent idea of exploiting multiple channels (actually or virtually) for delay reduction in CSMA, and prove that it is per-link delay orderoptimal, i.e., O(1)-asymptotic-delay per link, if the number of virtual channels is logarithmic with respect to mixing time of the underlying CSMA Markov chain. The logarithmic number is typically small, i.e., at most linear with respect to the network size. In other words, our contribution provides not only a provable framework for the multiple-channel based CSMA, but also the required explicit number of virtual-multi-channels, which is of great importance for actual implementation. The key step of our analytic framework lies in using quadratic Lyapunov functions in conjunction with (recursively applying) Lindley equation and Azumas inequality for obtaining an exponential decaying property in certain queueing dynamics. We believe that our technique is of broad interest in analyzing the delay performances of other general queueing systems.

Resonant Plasma Display Panel Driver with Efficient Energy Recovery Function

A resonant plasma display panel (PDP) driver with energy recovery function has been proposed based on the boost converter operation. It utilizes three semiconductor devices, one resonant inductor, and one external capacitor for energy source in the X and Y side, respectively. The proposed driver is designed to use the reactive energies in both the capacitor and the inductor. The proposed driver has inherent protection function from possible surge voltage caused by parasitic inductance resonance, resulting in no additional protective devices. Thus, the overall PDP system using the proposed structure can be implemented with low-cost and simple structure, compared to conventional driver approaches. In addition, the proposed circuit can control external capacitor voltage and inductor current by adjusting time durations of driving operation. Furthermore, the driver utilizing boosting function provides immunity to inevitable parasitic components in circuit components and patterns

Novel Driver Structure Based on Low-Cost and Low-Rating Devices for Plasma Televisions

A simplified driver based on low-cost and low-rating devices is presented for plasma display panels (PDPs). Since the proposed driver has been designed by devices with half of voltage rating compared with the conventional Weber-type driver, it can take advantages of semiconductor devices with reduced conduction and switching losses as well as cheaper costs. In addition, a simpler structure of the proposed circuit with fewer devices can eliminate drawback of the prior approach with a series-connected Weber-type driver, which utilizes reduced voltage rating components. Moreover, the proposed driver is supplied from half of required sustain voltage level. The reduced supply voltage of the driver results in cost reduction and improved efficiency in the power supply blocks. Thus, the PDP driver presented in this paper can feature smaller size, lower cost, and high efficiency for both the sustain driver and the power supply circuit.

Delay Optimal CSMA With Linear Virtual Channels Under a General Topology

In the past few years, an exciting progress has been made on CSMA (Carrier Sense Multiple Access) algorithms that achieve throughput and utility optimality for wireless networks. However, most of these algorithms are known to exhibit poor delay performance making them impractical for implementation. Recently, several papers have addressed the delay issue of CSMA and yet, most of them are limited, in the sense that they focus merely on specific network scenarios with certain conditions rather than general network topology, achieve low delay at the cost of throughput reduction, or lack rigorous provable guarantees. In this paper, we focus on the recent idea of exploiting multiple channels (actually or virtually) for delay reduction in CSMA, and prove that it is per-link delay order-optimal, i.e., O(1)-asymptotic-delay per link, if the number of virtual channels is logarithmic with respect to mixing time of the underlying CSMA Markov chain. The logarithmic number is typically small, i.e., at most linear with respect to the network size. In other words, our contribution provides not only a provable framework for the multiple-channel based CSMA, but also the required explicit number of virtual-multi-channels, which is of great importance for actual implementation. The key step of our analytic framework lies in using quadratic Lyapunov functions in conjunction with (recursively applying) Lindley equation and Azumas inequality for obtaining an exponential decaying property in certain queueing dynamics. We believe that our technique is of broader interest in analyzing the delay performance of queueing systems with multiple periodic schedulers.

On the economic impact of Telco CDNs and their alliance on the CDN market

The CDN (Content Delivery Network) market consists of content providers (CPs), Internet service providers (ISPs), and CDN providers and evolves based on their complex cooperation and competition. Recently, the rapid growth of content-oriented traffic has brought forth a new entity called Telco CDNs in the content delivery supply chain, where Telco CDNs are the ISP-operated CDN providers, vertically integrating content delivery service with traffic engineering, so as to provide better reliability and QoS to users and reduce infrastructure investments. Telco CDNs and traditional CDNs would compete for their market shares with their unique advantages: Telco CDNs are capable of jointly optimizing network costs and user-perceived QoS, but possibly with their geographical limitation in service areas, whereas traditional CDNs operate a network of servers worldwide, with the advantages of performing global, sophisticated analytics or providing better security solutions. Telco CDNs may form an alliance (e.g., cache server sharing) to compete with traditional CDNs, but with some alliance cost. With this CDN market evolution, this paper conducts a game-theoretic study of when and how traditional CDNs survive in the competition with Telco CDNs. In particular, our study answers the questions about the impact of Telco CDNs unique characteristics on the long-term competition against traditional CDNs, and the impact of Telco CDNs alliance. Our analysis provides useful implications on the economics of the future CDN market, e.g., what factors can be Achilles heel and thus what features should be more focused for Telco and traditional CDNs.

A New Driving Scheme for Plasma TVs Using Multi-Functional Gate Driver

This paper proposes a new cost-effective scheme that reduces the total number of switches in driving systems for plasma TVs. In conventional systems, power switches are involved in generating only one of the reset, scan, and sustain voltage waveforms. By contrast, the proposed scheme combines power switches by using a new gate driver that enables one switch to do multiple functions resulting in a low-cost driving system. A new gate driver is devised to turn on switches with either a fast transition or a slow switching process for generating reset voltage waveforms with sustain and scan switches. Short gate pulses are used instead of a continuous on signal during the reset period in order to minimize the size of an external capacitor involved in generating ramp-reset voltage. Experimental results implemented in a 42-inch TV demonstrate the validity of using a new gate driver.

Voltage distribution and design for lightning surge of A PWM-switched autotransformer-based sag supporter

This paper discusses the design of a voltage sag supporter (VSS) device for lightning surge protection. This novel distribution-level voltage control device can compensate voltage sag and swell conditions in three-phase power systems. It is based on a pulse width modulated (PWM) autotransformer. The proposed scheme is able to quickly recognize the voltage sag or swell condition, and it can correct the voltage by either boosting the input voltage during voltage sag events or reducing the voltage during swell events. There exist two possible configurations, series and shunt types. Since the majority of voltage sag events occur under severe weather conditions, the voltage distribution of the system under lightning surge must be investigated. The distribution of voltage across the switches during normal conditions as well as lightning surge conditions is evaluated for both the series and shunt type of VSS circuits. Based on these results, the shunt type VSS is preferred.