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High Step-Up Forward-Flyback Converter
with Parallel Output
Abstract:
A high efficiency, low profile and high step-up dc-dc converter is proposed
for low dc voltage renewable energy system. Generally, the power source
such as photovoltaic array and the fuel cell stack have low voltage output
because of that a high voltage step-up converter is required to boost the
voltage much higher than the voltage level for front-end application. The
efficiency and voltage gain of conventional dc-dc converter are limit due to
the parasitic components. In order to solve the above mentioned problem,
the proposed converter is based on active clamp technique and the
converter is the combination of a forward converter and a fly back
converter. Multiple secondary windings can be employed for low profile
design and help to reduce high transformer copper loss and high output
rectifiers conduction losses. The proposed converter is confirmed with
experiments on 250-W prototype and the maximum efficiency of ±94% was
measured at full load.
Existing system:
The power source such as photovoltaic array and the fuel cell stack have
low voltage output because of that a high voltage step-up converter is
required to boost the voltage much higher than the voltage level for frontend application. The efficiency and voltage gain of conventional dc-dc
converter are limit due to the parasitic components.
Proposed system:
The proposed topology combines the concept of the active-clamp forwardfly back converter and the LLC converter. It combines simplicity of PWM
converter with soft-switching characteristic of resonant converters. Active
clamp techniques are used achieve Zero Voltage Switching
(ZVS) for both switches, thereby reducing the switching loss without
increasing their voltage or current stresses, but the ZVS range is limited by
the output load. LLC techniques are used to achieve ZVS on switches and
achieve Zero Current Switching (ZCS) on the output diodes over the entire
load range, but the size reduction and filter design have some difficulties
because the wide variation of switching frequency.
Circuit diagram:
Reference:
[1] K.C. Tseng, and T.J. Liang, “Novel high-efficiency step-up converter,”
IEE Proceedings-Electric Power Applications, vol. 151, no. 2, pp. 182–
190, March 2004.
[2] Jee-Hoon Jung, Woo-Young Choi, and Shehab Ahmed, “High Step-Up
DC-DC Converter with Two Transformers for Low DC Renewable
Energy Systems,” in Proc. IPEC, 2010, pp.1471–1477.
[3] R. Watson, F. C. Lee, and G. C. Fua, “Utilization of an Active-clamp
Circuit to Achieve Soft Switching in Flyback Converters,” IEEE Trans.
Power Electronics, vol. 11, pp. 162- 169, 1996.
[4] B. Yang, F.C. Lee, A.J. Zhang, and G. Huang, “LLC Resonant
Converter for Front End DC/ DC Conversion,” IEEE APEC’02, vol.2,
pp.1108-1112, 2002.