Novel Unidirectional Hybrid Three-Phase Rectifier System Employing Boost Topology Ricardo Luiz Alves, Carlos Henrique Illa Font, IEEE Student Member and Ivo Barbi, IEEE Senior Member Power Electronics Institute – INEP Department of Electrical Engineering Federal University of Santa Catarina – UFSC P. O. Box 5119 – Fax +55-48-234-5422 88040-970 Florianópolis, SC – BRAZIL E-mail: alves@inep.ufsc.br, illa_font@ieee.org, ivobarbi@inep.ufsc.br Abstract — This paper presents a new hybrid rectifier composed by the parallel association of a single-switch three- phase Boost rectifier with a PWM three-phase unidirectional rectifier. According to this proposal, each rectifier processes about a half of the output rated power. Thus, it allows to improve the robustness and to provide a high efficiency to the system. The hybrid rectifier is capable of providing output voltage regulation and power factor correction. An overview of some high power rectifier topologies and the mathematical analysis, the control scheme and the simulation results of the proposed hybrid rectifier are also presented in this paper. I. INTRODUCTION Before the semiconductor invention, the use of rectifiers in industrial applications was made with the electromechanical contact converters (an AC motor coupled with a DC generator) and with the mercury converters [1]. A new stage started to high power converters when, in 1960, the first diode rectifier above 100kA was placed to the market, and, ten years later, the first thyristor plant of this rating was operational. The capability of to dissipate the internal losses is the restriction factor of semiconductor element usage. This way, to medium and high power converters, forced-cooled heatsinks are frequently used. However, depending on the application area and the required operational behavior some switches can not be applied. The concerns regarding restrictions in the harmonic content generated by the power converters, above all the framing in the standards IEEE 519 and IEC 61000-3-4, has been objective of many recently studies. Nevertheless, to obtain low THD (Total Harmonic Distortion) in high power converters can be quite a complex task. Some technological limitations restrict the use of certain topologies in pre-established power levels. The latest advances in high-power semiconductor devices have introduced newer solutions for high power conversion systems, however, the degree of acceptance of each technology vary in according with various industries and applications. The aim of this paper is to propose a new hybrid rectifier topology capable of providing sinusoidal input currents and output voltage regulation. The paper presents a brief overview of some high power rectifier topologies and the mathematical analysis, the control scheme and the simulation results of the proposed hybrid rectifier. II. OVERVIEW OF SOME HIGH POWER RECTIFIER TOPOLOGIES Power converters systems have a high variety of topologies with different complexity. The line commuted- rectifiers are very simple and robust due to be composed by non controlled and/or semi-controlled switches, as diodes and thyristors. However, these structures present the inherent characteristic of high harmonic distortion in input currents. In the other hand, the self-commuted rectifiers are composed by active switches (as power MOSFETs, IGBTs and GTOs) and are capable to produce reduced effects on the mains. However, the complexity and the cost are increased. A basic overview of some high power rectifiers are performed in the sequence. A. Diode Rectifiers Diode rectifiers are the simplest of all rectifier topologies. Robustness and low cost are main attractive characteristics that allow these structures to be applied in high power applications. However, due to not allow, by it self, to control the output voltage, these converters are rarely applied in industrial applications, only in the cases when the output voltage control is not required. Other important factor that reduce the acceptance of this converters is the high THD observed in input currents. To compensate the harmonic distortion generated by the standards diode rectifiers, passive linear filters or power factor correction structures can be employed. Multipulse techniques are frequently found in high power applications. In these cases, special winding connections are used in transformers and, for this reason, they become, as the linear filters, heavy and bulky, however are extremely robust. A significant reduction in the final weight and volume can be achieved replacing the transformers by autotransformers with differential connections. However, for the 12-pulse structure six secondary windings and four interphase reactors are required. For the 18-pulse structure, twelve secondary 487 0-7803-9033-4/05/$20.00 ©2005 IEEE.