Design, simulation and evaluation of two different topologies for the 2.4 MW 4/6 kV DC-DC fullbridge converter

University essay from Chalmers tekniska högskola/Institutionen för energi och miljö

Abstract: In this thesis, a hard switched and zero-voltage switching fullbridge converter for high power applicationsare compared in terms of their losses. Important issues in designing these kind of converters are to achievehigh efficiency with low cost and low weight. Managing the converter parasitics and calculating the lossesfor the switches as well as for the high frequency transformer with square wave input are important issuesin designing such a high power density converter which are discussed in this thesis. The proposed fullbridgeconverters are designed to convert 4 kV input voltage to 6 kV with a rated power of 2.4MW. The comparisonis done for three different frequencies: 500 Hz, 1 kHz and 2 kHz. Also, the simulation result s and losscalculations are presented.Based on the design and analysis of both hard and soft switching schemes of the high power density DCDCfull bridge converter, it has been concluded that since for the lower frequencies the efficiency is almostthe same for the two topologies, hard switched is preferable due to the lower cost. However, for the higherfrequencies where the total losses are dominated by the switching losses, the soft switched topology issuperior. The core loss of the transformer which was exposed to the high frequency square wave excitationhas been calculated by using FEMsimulation and it shows that the transformer contribution of the total lossof the converter is about 30% at all three studied frequencies for the phase shift controlled converter.The total efficiency of the hard switched converter is 97.3%, 96.3% and 94.5%for 500Hz, 1 kHz and 2 kHzswitching frequencies respectively. For the zero voltage switching converter, the total efficiency changeslike 97.8%, 97.1% and 96% for 500Hz, 1 kHz and 2 kHz respectively. As it is seen, for the low switchingfrequencies, the two topologies have almost the same efficiency. However, by increase in the switchingfrequency, the efficiency of the hard switched converter has higher reduction in comparison with the zerovoltage switching converter. The less reduction of efficiency for the zero voltage switching topology is dueto elimination of the switching losses in this topology.