| With the development of information technology, power management for telecom and computer applications become a large market for power supply industries. To meet the performance and reliability requirement, distributed power system (DPS) is widely adopted for telecom and computer systems, because of its modularity, maintainability and high reliability.; Due to limited space and increasing power consumption, power supplies for telecom and server systems are required to deliver more power with smaller volume. As the key component of DPS system, front-end AC/DC converter is under the pressure of continuously increasing power density. For conventional industry practices, some limitations prevents front-end converter meeting the power density requirement. In this dissertation, different techniques have been investigated to improve power density of front-end AC/DC converters.; For PFC stage, at low switching frequency, PFC inductor size is large and limits the power density. Although increasing switching frequency can dramatically reduce PFC inductor size, EMI filter size might be larger at higher switching frequency because of the change of noise spectrum. Since the relationship between EMI filter size and PFC switching frequency is unclear for industry, PFC circuits always operate with switching frequency lower than 150 kHz. Based on the EMI filter design method, together with a simple EMI noise prediction model, relationship between EMI filter corner frequency and PFC switching frequency was revealed. The analysis shows that switching frequency of PFC circuit should be higher than 400 kHz, so that both PFC inductor and EMI filter size can be reduced.; Although theoretical analysis and experimental results verify the benefits of high switching frequency PFC, it is essential to find a suitable topology that allows high switching frequency operation while maintains high efficiency. Three PFC topologies, single switch PFC, three-level PFC with range switch and dual Boost PFC, were evaluated with analysis and experiments. By using advanced semiconductor devices, together with proposed control methods, these topologies could achieve high efficiency at high switching frequency. Thus, the benefits of high frequency PFC can be realized. (Abstract shortened by UMI.)... |
