Transformer Loss Analysis and Dynamic Performance of Isolated Dual Active Bridge DC-DC Converter under Triple Phase Shift Modulation

Abstract

Advances in power electronics over the last 30 years have enabled the re- alisation of highly efficient energy conversion systems. Such systems have

found use in applications such as electrical networks and renewable energy interfaces etc. A converter which has recently received much attention is the isolated Dual Active Bridge (DAB) dc-dc converter. This converter has the potential for bidirectional energy flow at high powers and efficiencies; the latter being a result of its soft switching capabilities. The ability of the converter to operate efficiently at high switching frequencies enables it to be effectively applied in systems requiring high bandwidth control. Recent publications have focused on the modulation strategy of the DAB converter and its effect on the efficiency of the power electronic switches. The Triple Phase Shift modulation method has been found to be highly effective to reduce reactive power and minimize the current stress. The shortcomings of these approaches are that the shape of the waveform applied to the isolation transformer not only affects the power losses of the power electronics but also the transformer losses and therefore the overall converter efficiency. This thesis presents two main contributions to knowledge in this area.

The first is to consider the effect of the modulation method on the effi- ciency of the transformer to maximise the efficiency of the overall converter

rather than just the power electronics. The second is to obtain high band- iv

width control and fast dynamic response by augmenting the Triple Phase Shift modulation method of the converter with a predictive control strategy. Analysis is supported by complete experimental results from an 1kW DAB lab demonstrator.