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Electro-thermal Design of a Solid-State MVDC Circuit Breaker
A. Giannakis,D. Peftitsis 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
This paper investigates the impact of several design parameters on the electro-thermal performance of a solid-state circuit breaker (CB) for medium voltage DC (MVDC) grids. The parameters studied are the cooling system design along with the ambient temperature under steady-state. The impact of the current limiting inductor and the threshold current that trips the breaker on the CB operation under short circuit condition was also investigated. The performance of the breaker is evaluated in terms of conduction power losses, dissipated power and junction temperature in the power electronic devices used. Four electrothermal models for heat flux and junction temperature estimation have been developed and presented. The simulations highlighted the superiority of the “RC” equivalent thermal network in terms of required computational time and accuracy. Finally, the importance of designing the breaker according to the electrical and thermal limitations of the power electronic devices used is also highlighted.
Digital-Carrier Multi-Band User Codes for Baseband UWB Multiple Access
Yang, Liuqing,Giannakis, Georgios-B. The Korea Institute of Information and Commucation 2003 Journal of communications and networks Vol.5 No.4
The growing interest towards ultra-wideband (UWB) communications stems from its unique features such as baseband operation, ample multipath diversity, and the potential of enhanced user capacity. But since UWB has to overlay existing narrowband systems, multiple access has to be achieved in the presence of narrowband interference (NBI). However, existing baseband spreading codes for UWB multiple access are not flexible in handling NBI. In this paper, we introduce two novel spreading codes that not only enable baseband UWB multiple access, but also facilitate flexible NBI cancellation. We construct our codes using a single carrier or multiple carriers (SC or MC), which can be implemented with standard discrete-cosine transform (DCT) circuits. With our SC/MC codes, NBI can be avoided by simply nulling undesired digital carriers. Being digital, these SC/MC codes give rise to multiband UWB systems, without invoking analog carriers. In addition, our SC/MC codes enable full multipath diversity, and maximum coding gains. Equally attractive is their capability to reduce the number of interfering users, with simple matched filter operations. Comprehensive simulations are also carried out to corroborate our analysis.
Designing Optimal Pulse-Shapers for Ultra-Wideband Radios
Luo, Xiliang,Yang , Liuqing,Giannakis, Georgios-B. The Korea Institute of Information and Commucation 2003 Journal of communications and networks Vol.5 No.4
Ultra-wideband (UWB) technology is gaining increasing interest for its potential application to short-range indoor wireless communications. Utilizing ultra-short pulses, UWB baseband transmissions enable rich multipath diversity, and can be demodulated with low complexity receivers. Compliance with the FCC spectral mask, and interference avoidance to, and from, co-existing narrow-band services, calls for judicious design of UWB pulse shapers. This paper introduces pulse shaper designs for UWB radios, which optimally utilize the bandwidth and power allowed by the FCC spectral mask. The resulting baseband UWB systems can be either single-band, or, multi-band. More important, the novel pulse shapers can support dynamic avoidance of narrow-band interference, as well as efficient implementation of fast frequency hopping, without invoking analog carriers.
Cooperative Synchronization and Channel Estimation in Wireless Sensor Networks
Oh Mi-Kyung,Ma Xiaoli,Giannakis Georgios B,Park Dong-Jo The Korea Institute of Information and Commucation 2005 Journal of communications and networks Vol.7 No.3
A critical issue in applications involving networks of wireless sensors is their ability to synchronize, and mitigate the fading propagation channel effects. Especially when distributed 'slave' sensors (nodes) reach-back to communicate with the 'master' sensor (gateway), low power cooperative schemes are well motivated. Viewing each node as an antenna element in a multi-input multi-output (MIMO) multi-antenna system, we design pilot patterns to estimate the multiple carrier frequency offsets (CFO), and the multiple channels corresponding to each node-gateway link. Our novel pilot scheme consists of non-zero pilot symbols along with zeros, which separate nodes in a time division multiple access (TDMA) fashion, and lead to low complexity schemes because CFO and channel estimators per node are decoupled. The resulting training algorithm is not only suitable for wireless sensor networks, but also for synchronization and channel estimation of single- and multi-carrier MIMO systems. We investigate the performance of our estimators analytically, and with simulations.