Description and Efficiency Comparison of Two 25 kVA DC/AC Isolation Modules

In the frame of the European project UNIFLEX-PM, two AC/AC converter topologies hove been studied and implemented. Both converters, rated for 25 kVA, are isolated by a medium-frequency power transformer. The first topology is based on a dual active bridge containing two additional voltage source inverters for the connection of both DC links to the interfaced grids. The second topology is based on a cycloconverter for the connection of the secondary side of the transformer to the grid without a DC link capacitor Both topologies hove an identical primary side so the efficiency study is focussed on the chain link from one DC link to a 25 kW output load. Experimental efficiencies are compared to theoretical expectations. Due to soft-switching operation hi the dual active-bridge, the cycloconverter based solution shows a lower efficiency than in the symmetrical topology.