Design, simulation and evaluation of two different topologies for the 2.4 MW 4/6 kV DC-DC fullbridge converter
Examensarbete för masterexamen
In this thesis, a hard switched and zero-voltage switching fullbridge converter for high power applications are compared in terms of their losses. Important issues in designing these kind of converters are to achieve high efficiency with low cost and low weight. Managing the converter parasitics and calculating the losses for the switches as well as for the high frequency transformer with square wave input are important issues in designing such a high power density converter which are discussed in this thesis. The proposed fullbridge converters are designed to convert 4 kV input voltage to 6 kV with a rated power of 2.4MW. The comparison is done for three different frequencies: 500 Hz, 1 kHz and 2 kHz. Also, the simulation result s and loss calculations are presented. Based on the design and analysis of both hard and soft switching schemes of the high power density DCDC full bridge converter, it has been concluded that since for the lower frequencies the efficiency is almost the same for the two topologies, hard switched is preferable due to the lower cost. However, for the higher frequencies where the total losses are dominated by the switching losses, the soft switched topology is superior. The core loss of the transformer which was exposed to the high frequency square wave excitation has been calculated by using FEMsimulation and it shows that the transformer contribution of the total loss of 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 kHz switching frequencies respectively. For the zero voltage switching converter, the total efficiency changes like 97.8%, 97.1% and 96% for 500Hz, 1 kHz and 2 kHz respectively. As it is seen, for the low switching frequencies, the two topologies have almost the same efficiency. However, by increase in the switching frequency, the efficiency of the hard switched converter has higher reduction in comparison with the zero voltage switching converter. The less reduction of efficiency for the zero voltage switching topology is due to elimination of the switching losses in this topology.
Elkraftteknik , Electric power engineering