High efficiency resonant dc/dc converter for solar power applications

Abstract

This thesis presents a new topology for a high efficiency dc/dc resonant power converter that utilizes a resistance compression network to provide simultaneous zero voltage switching and near zero current switching across a wide range of input voltage, output voltage and power level. The resistance compression network maintains desired current waveforms over a wide range of voltage operating conditions. The use of on/off control in conjunction with narrowband frequency control enables high efficiency to be maintained across a wide range of power levels. The converter implementation provides galvanic isolation and enables large (greater than 1:10) voltage conversion ratios, making the system suitable for large step-up conversion in applications such as distributed photovoltaic converters. Three 200 W prototypes were designed, built and tested. The first prototype was made as a proof of concept and operated at a switching frequency of 100 kHz. It had an efficiency of 93.5% (at 25 V input and 400 V output). The second prototype was operated at a switching frequency of 500 kHz and had an efficiency of 93% (at 25 V input and 400 V output). The high frequency losses caused by the ringing in voltage and current due to the resonating parasitics of the transformer were removed with the help of a matching network in the third prototype. This final prototype operated at a switching frequency of 500 kHz and showed that over 95% efficiency is maintained across an input voltage range of 25 V - 40 V (at 400 V output) and over 93.7 % efficiency across a wide output voltage range of 250 V - 400 V (at 25 V input). These experimental results demonstrated the effectiveness of the proposed design.