Topologies and Design Considerations for Distributed Power System Applications FRED C. LEE, FELLOW, IEEE, PETER BARBOSA, STUDENT MEMBER, IEEE, PENG XU, STUDENT MEMBER, IEEE, JINDONG ZHANG, STUDENT MEMBER, IEEE, BO YANG, AND FRANCISCO CANALES This paper describes current developments in the technology of converters primarily intended for server-type distributed power system (DPS) applications. The paper first addresses the single-phase two-stage DPS, discussing the available options for simple power factor correction and high-performance dc–dc converters. Next, the concept is extended to three-phase high-power front-end converters, which also use a two-stage approach. Finally, the paper presents the recent developments in load converters, with emphasis on low-, medium-, and high-voltage regulator modules used to supply high-performance microprocessors. The discussion throughout the paper is supported by an extensive list of references and experimental results. Keywords—DC–DC converters, distributed power systems, load converters, power factor correction. I. INTRODUCTION To power the next generation of information technology, the distributed power system (DPS) architecture has been widely adopted as an industry practice. The driving force comes from several key emerging applications. The latest generation of computer equipment has adopted an open-ar- chitecture, modular approach to signal and data processing. Network system routers and hubs now require modular dis- tributed power supplies. The DPS can also better address in- creasing concerns regarding fault tolerance, improved relia- bility and redundancy without adding significant cost. The widespread use of the DPS has given the power supply in- dustry the opportunity to develop a standardized modular approach to power processing. This approach will enable significant improvements in the design and manufacturing process and enhance system performance and reliability. As can be seen in Fig. 1, most of the existing front-end converters used in DPS applications adopt a two-stage ap- Manuscript received October 2, 2000; revised December 22, 2000. This work was supported in part by the ERC Program of the National Science Foundation under Award Number EEC-9731677. The authors are with the Center for Power Electronics Systems—CPES, The Bradley Department of Electrical and Computer Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0179 USA. Publisher Item Identifier S 0018-9219(01)04109-3. Fig. 1. Basic configuration of a distributed power system. proach. The first stage of the front-end converter provides the power factor correction (PFC), and the second stage pro- vides isolation and tight regulation of the dc output voltage. The interface between the front-end converter and the load is accomplished by several load converters. As a result, the per- formance of the entire system strongly depends on the choice and design of individual stages. This paper summarizes recent developments of the indi- vidual stages toward realizing a DPS. Section II gives partic- ular attention to the single-phase front-end PFC and dc–dc converter developed for applications with power levels of up to 1 kW. Section III discusses the three-phase two-stage front-end converter developed for 6-kW DPS purposes. Fi- nally, Section IV describes the main achievements in the de- velopment of load converters for high-performance micro- processors. The low-, medium-, and high-voltage regulator modules are discussed. II. SINGLE-PHASE FRONT-END DPS CONVERTER A. Single-Phase PFC for Front-End DPS Converters In the DPS structure for server applications, the front-end module needs to convert the single-phase ac-line voltage into a low dc output voltage, such as 48 V. Power quality is a major concern and stringent international requirements, such as the IEC 61000-3-2 [1], will soon be enforced to limit the harmonic currents drawn by the off-line equipment. As a 0018–9219/01$10.00 ©2001 IEEE PROCEEDINGS OF THE IEEE, VOL. 89, NO. 6, JUNE 2001 939