Investigations on High-Frequency Transformer Isolated CLL Resonant DC-DC Power Converter for Renewable Energy Applications

Abstract

Renewable energy sources have been the most promising substitute for conventional energy sources and are employed worldwide due to their cleanliness and sustainability. The power generated by using renewable energy sources is highly fluctuating as it depends on the environmental conditions and other operating conditions. A power conditioning unit comprising of DC-DC converter is required to convert this fluctuating power into a usable constant power. There is an increase in the demand of DC-DC power converters with compact size, higher power density and higher conversion efficiency for the applications involving wide variations in input voltage and load. These converters are also used in applications where electrical isolation is required. The intent of this research is in finding a suitable soft-switching DC-DC power converter topology and investigating on its performance for the applications in renewable energy generation. In this dissertation, literature review on various resonant power converter topologies and gating control scheme is carried out. The full bridge CLL resonant converter topology and fixed frequency gating scheme are chosen for the study. Three different converter topologies with suitable gating scheme were proposed and examined in detail. The first converter presented is a high-frequency transformer isolated CLL resonant DC-DC power converter operated with phase-shift gating scheme and modified PWM gating scheme. Modeling, analysis, design, simulation and experimental results of the converter are presented. Theoretical and experimental results are compared and performance of the converter when operated with both the gating schemes is analysed. A high-frequency isolated full bridge zero-voltage-transition (ZVT) CLL resonant DC-DC converter operated with a modified PWM gating scheme has been iv proposed. Various modes of operation of the converter are described using typical operating waveforms and equivalent circuit diagrams. Analysis, design, simulation and experimental results are presented and discussed. The proposed converter is able to provide ZVS for all the inverter switches for entire variations in input voltage and loading conditions. A three-phase interleaved full bridge CLL resonant DC-DC converter with fixed frequency modified PWM gating control has been proposed for medium to high power applications. Modeling and analysis of the converter is presented and the design procedure using a design example is explained. The designed converter is simulated using PSIM software to predict the performance of the converter for variations in input voltage and load conditions. The converter operates in ZVS for all the inverter switches with minimum input voltage and only one switch loses ZVS in each bridge/module for higher input voltages.