• ETRI Journal
• /
• v.38 no.4
• /
• pp.746-756
• /
• 2016

Owing to the intermittent power generation of renewable energy sources (RESs), future wireless cellular networks are required to reliably aggregate power from retailers. In this paper, we propose a distributed power allocation (DPA) scheme for base stations (BSs) powered by retailers with heterogeneous RESs in order to deal with the unreliable power supply (UPS) problem. The goal of the proposed DPA scheme is to maximize our well-defined utility, which consists of power satisfaction and unit power costs including added costs as a non-subscriber, based on linear and quadratic cost models. To determine the optimal amount of DPA, we apply dual decomposition, which separates the master problem into sub-problems. Optimal power allocation from each retailer can be obtained by iteratively coordinating between the BSs and retailers. Finally, through a mathematical analysis, we show that the proposed DPA can overcome the UPS for BSs powered from heterogeneous RESs.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• v.4B no.3
• /
• pp.108-113
• /
• 2004

This paper presents methods to improve performance of the power supply system in a NASA deep space explorer. In the Stirling engine driven reciprocating Brushless DC (BLDC) generator, the accurate position information of the prime mover is important to diagnose the performance of the engine and prevent distortion of the output power. Since sensors to detect the position are fragile and unreliable, and conventional sensorless techniques have drawbacks in the low speed region, a novel sensorless position detection technique for the prime mover has been proposed and verified. Another major issue of the generator for the spacecraft is power density maximization. The mass of the power system is important to the mass of the satellite. Therefore, the components of the spacecraft should be lightweight. Conventional rectification methods cannot achieve the maximum power possible due to non-optimal current waveforms. The optimal current waveform for maximizing power density and minimizing machine size and weight in a nonsinusoidal power supply system has been derived, incorporated in a control system, and verified by simulation work.

• Journal of Power Electronics
• /
• v.12 no.2
• /
• pp.276-284
• /
• 2012

AC/AC power conversion is widely used to feed AC loads with a variable voltage and/or a variable frequency from a constant voltage constant frequency power grid or to connect critical loads to an unreliable power supply while delivering a very balanced and accurate sinusoidal voltage system of constant amplitude and frequency. The load specifications will clearly impose the requirements for the inverter stage of the power converter, while wider ranges of choices are available for the rectifier. This paper investigates the utilization of a buck-type current source rectifier as the active front-end stage of an AC/AC converter for applications that require an adjustable DC-link voltage as well as elimination of the low-frequency common mode voltage. The proposed solution is to utilize a combination of two or more zero current vectors in the Space Vector Modulation (SVM) technique for Current Sources Rectifiers (CSR).

• International Journal of Knowledge Content Development & Technology
• /
• v.12 no.1
• /
• pp.67-83
• /
• 2022

This study aims to evaluate some academic institutional repositories (IRs) in Ghana. Data were collected using observation and interview methods by examining the various websites of seven (7) selected academic institutional repositories in Ghana. The findings revealed that the University of Ghana, Legon, leads records count of the seven Institutional Repository (IRs) examined. Dspace was the prioritized software for managing and preserving the digital contents of these IRs. Theses, dissertations and research articles were the leading contents deposited on the IRs. The majority of the IRs have incorporated RSS (Rich Site Summary or Really Simple Syndication) feeds on their IRs with few using other Web 2.0 features. English was the only interface language used on all the IRs. From the interview, the findings revealed that most of the faculty members did not use the IR very often and 9(42.9) also indicated that, they have never deposited their materials on the IR. Faculty members again indicated that, inadequate ICT connectivity and infrastructure, unreliable power supply, Copyrights and intellectual rights, financial constrain, inadequate advocacy and training on the importance of IRs to faculty and users were the major challenges of academic libraries in operating IRs in Ghana.