Tese
Proposta, análise e implementação de técnicas de comutação sob tensão nula aplicadas a fontes cc-cc isoladas para telecomunicações
Fecha
2003-08-13Autor
Baggio, José Eduardo
Institución
Resumen
Dc-dc isolated converters with Zero-Voltage-Switching are proposed and studied in this
thesis. Special attention is focused on converters with series switches connections, which
allow the use of switches designed for half of dc bus voltage. A new modulation entitled as
interleaved-Phase-Shift-Modulation is proposed, which is applied to two half-bridges
converter connected in series. The main characteristics of the proposed modulation in relation
to the pulse-width-Modulation are the input capacitors voltage equalization and the switches
currents symmetrical sharing. This way, low frequency voltage oscillations are eliminated,
making possible the implementation of faster control law, and better switches utilization can
be obtained, producing higher efficiency. It is proposed an optimization process to design
auxiliary circuits of low cost which perform Zero-Voltage-Switching in entire load range. The
utilized circuit is composed of inductors connected in series and in parallel with the
transformer(s). The optimization method is applied to half-bridge converters connected in
series with soft commutation in entire load range with different modulations, and to the fullbridge
isolated converter. By the use of the optimization process, it is obtained the set of series
and parallel inductances values, which maximize the converters efficiency. Theoretical and
experimental results obtained from the converters with output of 60V/25A demonstrate that
converters with optimized designs can present efficiency even 2% higher than converters with
non-optimized designs. Moreover, it is demonstrated that by utilizing an optimization process,
converters with soft commutation in entire load range can present efficiency higher than
converter with soft commutation in only a load range, despite the inclusion of auxiliary shunt
inductors. An alternative for the use of phase-shift-modulation in half-bridge converter
connected in series is presented. The proposed converter utilizes a three-level boost rectifier,
which performs the input current power factor correction and maintains the dc bus voltage
equally shared. The series converter, with phase-shift modulation is connected on the rectifier
output. The main advantages of the phase-shift modulation utilization in relation to the pulsewidth-
modulation are the symmetrical current share through the switches and the smaller
current peaks on auxiliary circuits, resulting in smaller reactive energy in the converter and
higher efficiency. A comparative study among the full-bridge converter and converters with
series arrangement of half-bridges with different modulations is performed, considering the
efficiency and the cost of the converters as parameters. As a result it can be observed the best
performance and smaller cost of the full-bridge converter for 400V applications, while for
800V applications, the series converters present higher efficiency and smaller cost,
considering the actual technology.