1 Megawatt, 20 kHz, isolated, bidirectional 12kV to 1.2kV DC-DC converter for renewable energy applications

The design of a 1 MW, 20 kHz, isolated, bidirectional 12kV to 1.2kV DC-DC converter for renewable energy applications is presented. The main topics addressed are: High-Voltage (HV) side switch, topology & modulation and Medium Frequency (MF) transformer. A study of the possible HV side switches, considering 4.5kV IGBTs is performed, fixing the requirements from the topology and modulation side in order to reach a highly efficient system. The studied topologies are the Dual Active Bridge (DAB) with triangular modulation and the Series Resonant Converter (SRC) with constant frequency operation. Both topologies are able to achieve Zero Current Switching (ZCS) in the HV side switches, reducing the switching losses in these devices, which contribute to a large share to the system losses. Efficiency curves are presented for different semiconductor technologies for the Low-Voltage (LV) side switch in order to study the trade-offs between the selected topologies. Three MF transformer concepts, namely core-type, shell-type and matrix transformer, are presented and compared in respect of winding arrangement, isolation mechanisms and thermal management. Power losses and volume are calculated in each case and used to compare the different transformer concepts.